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‘Namdokmai Sithong’ mangoes, grown in carbon paper bags, are harvested at commercial maturity. As chlorophyll is virtually absent, they have a yellow skin colour changing only slightly during fruit ripening. This special characteristic, i.e., the absence of chlorophyll, conceals the variation within the batch in maturity stage and as well as in quality. Quality variables were assessed during storage by destructive (traditional penetration test Fpff, flesh colour L*a*b*, total soluble solids TSS and titratable acidity TA) or non-destructive techniques (limited distance compression Fcomp, skin colour L*a*b*). Three batches of mango in export quality grown at different cultivation locations were stored at four constant temperatures (kinetic experiment) and at 13 °C for 14 d then at 25–28 °C (dynamic experiment). Huge variation was observed in all quality variables in both systems mainly due to differences in maturity of individual fruit. Kinetic models are presented to describe behaviour of quality variables including the biological variation expressed as biological shift factor. A logistic model (logis) was used for all variables, except flesh colour b* value and TSS in the dynamic experiment, where a first order production model (FOP) was applied to analyse the data. Destructively measured data were first grouped based on rank at every measuring time (probelation). Rank number and fruit number were used as an index in non-linear regression. High explained parts (R2adj above 90%) were obtained for firmness and skin colour (a* and b*) for all temperatures of the kinetic experiment separately as well as combined. The (lower) asymptote values for limited compression firmness (Fcomp) were somewhat different at different temperatures, which is again an indication of large difference in maturity. In absence of chlorophyll, a strong relation was found between the biological shift factors of Fcomp and all colour values. During first storage period at 13 °C of the dynamic experiment, most obtained explained part (R2adj) but not all were well over 90%. When both temperature schemes (13 °C and ambient temperature) were analysed together, the rate constant after the temperature switch for firmness and colour was higher indicating a faster fruit ripening. The two cultivation locations generated a substantial difference in colouration, but not so much in terms of firmness. A strong correlation between Fcomp, TSS and TA was revealed. All these results indicate that observed variation in any of the quality variables are all linked directly to variation in maturity. In fruit industry, the biological variation is ignored completely which results in a heterogeneity in the final product at the consumers. Modelling techniques have studied can take care of this variation and could help to improve quality management in the production line in order to assure a constant level of the fruit quality.

Sliced tomatoes soften rapidly as well as becoming translucent. To develop a physiologically-based mechanism to describe softening the firmness of two cultivars, as a function of time, storage temperature, type of compression (repeated on the same spot or single measurements on consecutive spots on the equator of the pericarp) and initial maturity was measured using tomato slices. The proposed mechanism assumes that the softening of slices is radically different from that of whole tomatoes and depends on the stage of ripening at slicing. The mechanism is also based on the assumption that the pericarp solubility will quickly increase because of exposure to, amongst others, vacuolar contents with a low pH. This exposure will have a more serious effect on the firmness behaviour of ripe tomatoes because the pericarp tissue will have been exposed longer to a lower pH environment that will affect pectin solubility. A kinetic model that describes the individual firmness behaviour over time was developed. This model described trends well despite the high variability of the raw data. It was found that firmness loss induced by wounding occurs within 12 h. The effect of the initial maturity on the final firmness of the slices was large. The model indicates that consumer acceptance of sliced tomatoes is greatly affected by selection of cultivars with sufficient final (structural) firmness combined with a thorough assessment of the maturity at the time of slice preparation.

Translucency is one of the major problems in fresh-cut fruit. This phenomenon affects the use of tomato fruit by the fresh-cut industries. Techniques for measuring translucency are not readily available. As a consequence, the processes that are important in the development of translucency are little understood, let alone described in detail. The colour of produce depends only on the absorption of light by colouring compounds. Translucency does not change the amount of colouring agents in the product, but it does change its appearance by changing the scattering properties. As a consequence the appearance, which is the result of light absorption and scattering combined, is affected by both translucency and colour development. Consumers do buy or reject products based on total appearance. In the short life time of cut fruits, the development of colouring compounds apart from possible oxidation effects will not be very large. Understanding the development of translucency is therefore of major importance for the fresh-cut industry. The development of translucency was visually assessed in tomato slices, obtained from tomatoes at three stages of maturity (mature green, breaker stage and full red) and stored at 5°C. In a second experiment, tomato slices were stored at three temperatures (5, 9 and 13°C) to assess the effects of temperature. In both experiments, non-cut tomatoes were also assessed. The data of both experiments were analysed using a very simple exponential model based on a massive approximation of the mechanism involved. The more precursor is present, the higher the obtainable translucency will be. A model was developed based on this simplified mechanism, and used to analyse all data. The stage of development (maturity) was found to have a major effect on translucency development regulated by the amount of precursor. The rate constant, however, was the same. The temperature only had a minor effect on the rate constant with the same amount of precursor. Explained parts (R2adj) obtained for mean data were well over 97%, for the individual data the explained part was somewhat less.

Apples are long-term stored in quite similar CA conditions, expecting the behaviour during that storage to be the similar for all apples, only affected by cultivar and picking time. The aim of this study, within the Monalisa project, is the effect of growing conditions on the firmness behaviour of apples during postharvest CA storage and shelf-life. Apples of two cultivars (‘Braeburn’, ‘Kanzi’) were harvested from four orchards (different altitudes and different crop loads) and stored in commercial CA storage for nine months. Samples of 30 apples were taken from CA storage every one or two months and subjected to storage at room temperature. Apples were assessed on firmness shelf-life. Firmness measurements were carried out using the (destructive) puncture test and the (non-destructive) Aweta firmness meter. The first and overwhelming outcome of this study is the huge variation in firmness and the almost absence of firmness decrease of ‘Kanzi’ apples both during CA and shelf-life. The huge variation was tackled by novel statistical analysis techniques (probelation, quantile regression) and assuming a logistic behaviour. Data sets were analysed including the biological variation between individual fruit with explained variation (R2 adj) often over 90%. Only minor effects of the CA duration on the rate of firmness loss during shelf life could be indicated. Altitude has a major effect on the level of firmness while crop load has less effect. Likely, higher altitudes result in lower growing temperatures and therefore in a lower rate of cell division during the early growth phase, which results in smaller and firmer apples. Crop load likely affects the amount of available photo assimilates per fruit. Higher crop load results therefore in smaller and firmer apples. These results clearly show that, up to now, the huge biological variation in the orchard prohibited progress in orchard dependant storage management.

The majority of experimental data are obtained by destructive measuring techniques. Inevitably, in all these data variation is present, sometimes small and negligible, sometimes large, preventing proper analysis and extraction of meaningful information by traditional statistical techniques altogether. In this paper, three systems are presented to analyse destructive (cross-sectional) data, including biological as well as technical variation. The first system involves ranking the data per measuring point in time which provides a pseudo fruit number that can be used in non-linear indexed regression analysis similar as for non-destructive (longitudinal) data. The rationale behind this is that the individual with the highest value at some point in time will resemble the most another individual with the highest value at previous or future times, and the second highest the second highest at previous times, and so on. The second system also relies on this ranking number, but is now converted into a probability, which is used in non-linear regression analysis with quantile functions. The third system is based on optimising the log likelihood of the density function derived from the applied model (i.e., the expected distribution) over the measured data. Simulated data are used to elucidate the power of the three systems. A dataset on mango colour is used to validate the systems on a real-world data set. Although all three systems perform satisfactorily with percentages variability accounted for (R2 adj) well over 90%, a clear preference cannot be given since the choice of the proper analysis system depends on the experimental conditions (number of data, individuals and sampling points in time). Non-linear indexed and non-linear regression with quantile functions delivered the most reliable estimates. The three systems open up the possibility to analyse and reanalyse destructively measured data providing a sufficient large number of individuals and a clear indication of the kinetic model is available.

Mango 'Nam Dok Mai See Thong' recently became the number-one exported mango of Thailand. It has an attractive appearance, with a golden-yellow peel colour at harvest and slight colour development during ripening. Its peel colour could possibly be used as an indicator for ripeness. Assessing the behaviour of peel colour during storage is the main objective of this research. Mangoes were kept at cool temperature (13°C) for 2 weeks prior moving to ambient temperature in Thailand (28°C). The data set was separated into two groups for non-destructive and destructive tests. In the non-destructive set, peel colour of 108 fruits was measured repeatedly until the quality became unacceptable. In the destructive set, 60 fruits were sampled at random to measure the peel colour and other quality attributes, each time on different fruit. Mangoes from two growing locations were compared. The results showed that peel colour (L∗, a∗, b∗ and Hue) developed gradually during cool storage, but changed drastically after relocation to higher temperatures. The L∗ a∗ and b∗ values and hue angle behaved according to a logistic function. a∗ and b∗ showed an increase, L∗ and hue a decrease. The variation is clearly high at the beginning and decreased gradually during the storage period. Fruit from both the non-destructive and destructive sets showed similar behaviour during storage. The obtained results allow prediction of the behaviour of peel colour during cool storage.

This study deals with quantifying sugar and acids levels important for the perceived taste of tomatoes (Solanum lycopersicum). Sugar and acids levels were measured repeatedly on the same tomato using tissue samples obtained with a biopsy needle in combination with HPLC protocols. Biopsies of pericarp and locular gel tissue from tomatoes differing in position in the truss, from mature green to ripe red, were taken from a beef- (‘Licorossa’), a cocktail- (‘Lucino’) and a cherry type (‘Petit Sweet’) cultivar. Tomatoes were stored up to three weeks at three temperatures (12, 19 and 24.5 °C) and biopsy samples were taken every few days. A model regarding the most important processes that interconvert sugars and acids (glycolysis, TCA cycle and gluconeogenesis (GNG)) is proposed. Results of the model calibration showed more breakdown of hexoses in red tomatoes and more conversion of malate into hexoses in green tomatoes. More hexose turnover was found in locular gel than in pericarp tissue. GNG was more important in the cherry type cultivar due to faster hexose and malate breakdown. In the round type cultivar malate levels were higher due to faster citrate breakdown and slower malate breakdown. Starch and sucrose levels did not significantly affect postharvest sugar and acid development. Molecular markers that quantify the kinetic parameters of the model might be important to develop genotypes with better taste performance.

Size is an important property of all fruit as it determines, together with crop load, fruit yield. The aim of this study is to model the increase in fruit size during cell expansion based on diameter or length and to predict fruit size and volume, including the variation in size and volume, at harvest. The size of individual fruit during growth of fruit (four apple, two tomato and six pepper cultivars) was measured from early fruit set until harvest at several seasons. Size data were evaluated as diameter and length using the von Bertalanffy growth model, adapted to include the variation in size between individuals and the effect of growing temperature. The adapted von Bertalanffy model describes the increase in diameter and length and their variation. For any fruit type, size increased along the same generic growth model. A single stochastic variable, the biological shift factor, was sufficient to describe the variation in development time, initial size and maximum size. For all batches the percentage variation explained for were well over 93% with growth rate constants similar per species and only a minor effect of growing temperature. Prediction of the maximum size distribution based on measurements half way the cell expansion period is explored and discussed. Size and its distribution can be predicted based on a single measuring point in time but with two or three points in time the prediction system becomes more robust.

Size increase (expressed as diameter) of four apple cultivars in five seasons during about 130 days before harvest, was analysed with a simple first order production mechanism. All variation in diameter among individual fruit could be attributed to the same origin (development stage or biological age), with explained parts (R2 adj) of more than 98%. The same general behaviour of diameter development was observed in two tomato cultivars whose fruits where grown at two different temperatures. These data were also analysed using the same model with explained parts (R2 adj) of about 90%. Converting diameter into volume (assuming a perfect sphere), the usually observed asymmetrical sigmoidal behaviour was obtained, frequently described in growth modelling with the Richard's curve. A similar sigmoidal behaviour was also observed in the accumulation of dry matter (DM), as measured with NIR technology in growing mangoes. The cubic root of these data on DM could be analysed using the same model formulation, including the variation between individual fruit, with R2 adj well over 90%. Accumulation of DM ends at harvest, so the mechanism of DM production can very well define the final level of DM obtained in harvested fruit. Since sugars and DM are strongly related (e.g., conversion of starch into sugars, Brix values), a very similar mechanism could govern the accumulation of sugars. Destructively measured data on sugars were collected in nectarines, showing indeed a very similar overall behaviour and variation. This indicates that growth (diameter, mass) and quality increase (DM, sugars) could be described by a very similar mechanism, providing the first tools in the quest to harvest quality.

A guide to include variation in statistical analysis of non-destructive data.Biological and technical variation are split up and estimated separately.Huge increase in reliability of the estimated parameters.Principles explained with simulated data on exponential decay.Applicability demonstrated on several examples from practise. More and more, the omnipresent variation between individual items in a batch is taken into account by using special analysing techniques like mixed effects and indexed regression. In this paper the assumptions upon which these techniques are based, are explained, based on a simulated data set. The most important issue is the separation of biological variation and the technical variation (or measuring error). The techniques are further elucidated with some examples from practise (skin colour apples in storage, softening of melons in storage and water loss in plums, melons and mandarins), to show the increased reliability of the analyses. Since variation is always present in any measured data set, the techniques are applicable in all fields working with living material.

Mango fruit maturity can be difficult to determine from external attributes. Assessment of parameters of fruit on tree (dry matter, internal flesh colour) relevant to estimation of fruit maturity was undertaken with a handheld (near infrared spectroscopic) system. Measurement error on dry matter was low (typical RMSEP 0.6% DM). Repeated measurements on the same individual fruit from 78 different blocks across two farms demonstrated that each piece of fruit was on a similar, but individual, maturation trajectory, with a time offset. The offset was presumably related to date of pollination or environmental conditions around the fruit (e.g., inner or outer canopy). A non-linear indexed regression model, coupled with the use of a ‘biological shift factor’, was used to describe the time series data. Estimated biological shift factors were larger for dry matter than flesh colour, indicative of an earlier change in dry matter, albeit at a lower rate. Differences between blocks within a farm and between two farms were small, indicating the maturation processes were independent of local conditions. This technique could be used to trace the source of variation within a block (e.g., to location in canopy or plant water status), towards the goal of reducing this variation, leading to crops of greater uniformity.

Traditionally, crop load and fruit yield from previous seasons are used as indicators for prediction of fruit size. Disregarding the inevitable biological variation between fruit, von Bertalanffy (1938) described the growth, expressed as length, of virtually any living organism. The model is here extended to include the variation between individuals in a batch. Using this extended model, fruit size and its variation can be predicted, using measurements of a large number of fruit at a single point during early development. The diameter of 200 tomatoes was measured 15 days after full bloom (DAFB). Using the density function derived from the extended von Bertalanffy model, and applying prior knowledge of some of the model parameters, the variation in size at harvest could be predicted. Validation of the results was obtained by comparing the predicted sizes with the diameters of the same tomatoes at harvest.

In this study, important quality properties such as firmness, sugar and acid levels were measured and analysed in tomatoes harvested from three greenhouses during a five month period and stored at 16 degrees C for over 20 days. Tomatoes were harvested from three identical, neighbouring, greenhouses which were either conventionally ventilated (open greenhouse) or mechanically cooled (semi-closed greenhouses). Sugar and acids levels were hardly affected by greenhouse type. Compared to the open greenhouse, semi-closed greenhouses produced heavier and less mature (firmer) fruit at the commercial harvesting stage based on colour. Fruit maturity differences could be linked to the vertical temperature gradient and to CO2 levels in the different greenhouses. This indicates that CO2 levels and temperature affect the synchronisation between colour and firmness maturity at harvest. The acceptance period, i.e., the time period both tomato colour and firmness are considered acceptable by consumers, will likely be positively affected when growers switch from conventionally ventilated to semi-closed production systems. Additional to greenhouse effects also effects of the harvest month were observed. The sugar to acid ratio was highest and glucose to fructose ratio was lowest in July, the month with the highest irradiance, irrespective of greenhouse type. The estimated value for the maximum firmness (F-max) varied from 17.9 N in August to 31.2 N in June. This monthly variation in F-max explains an important part of the variation found in the postharvest behaviour of tomatoes. Interestingly, the monthly variation in F-max showed the same trend as found for the monthly initial sugar levels. It might be hypothesised that the monthly variation in glucose and fructose levels causes variation in that part of firmness that is generated by cell turgor. The monthly variation in F-max, sugar and acid levels could not be linked to climate conditions and remains to be elucidated. (C) 2013 Elsevier B.V. All rights reserved.

Colour and taste are important attributes of apple fruit quality and have therefore been widely studied. Nevertheless, because of the destructive sampling methods commonly used to obtain the data, and of the subsequent traditional analyses, ignoring the effects of biological variation, the knowledge on the kinetic mechanisms of synthesis and degradation of individual quality components during fruit development and growth is still lacking. Spatio-temporal changes of taste components (sugars: fructose, sucrose, glucose, organic acids: malic, citric, shikimic and fumaric acid) and colour aspects (a) in individual apple fruits were monitored to assess the dynamics and mechanisms of change during development and ripening with respect to location within fruit as a factor and the variation between individual apples. Data were analysed with non-linear indexed regression based on either a logistic or an exponential process oriented model assessing the technical variation simultaneously. The rate constants for colour or taste component were roughly similar between cultivars, suggesting a similar mechanism of development and confirming the generic nature of the model. There was a very large biological variation in individual quality components observed in the raw data (the biological variation), which can be almost exclusively explained by the difference in the maturity stage between individual fruit. The explained parts (R2 adj) were, with one exception, higher than 0.90. The major contribution of this study is the fact that all the herein monitored taste defining components can be analysed and described with the same process-oriented model.

The aim of this study was to describe the physiology of fruit colour in tomato as affected by salinity and ripening on and off the plant. Chlorophyll and lycopene levels were repeatedly measured in ninety Raf tomatoes over a period of eight days using remittance spectroscopy. Fruits were subjected to three salinity levels and were measured either on or off the plant. The physiology of tomato colour was described by a kinetic model centred on the role of STAY-GREEN proteins (SGR) that was calibrated simultaneously on chlorophyll and lycopene data with a percentage variance explained for of 91%. Lycopene precursor and transcript SGR levels were estimated considerably higher for on-plant than for off-plant ripened fruits which indicates ongoing expression while attached to the plant. There is less inhibition of the lycopene precursor by SGR in on plant ripened tomatoes which results in higher maximum lycopene levels and less chlorophyll breakdown causing residual chlorophyll levels. Effects of salinity treatments on chlorophyll breakdown and lycopene synthesis are small, but higher salinity levels strongly diminish fresh weight. Ripening on and off the plant strongly affects colour physiology of tomato fruit and is described well by the proposed model.

The quantity and quality of food needed for reproduction differs from nutritional needs for health and longevity. The choice of food type and amount is driven by our genetic need for growth and reproduction, not for long term health. So, fast digestible food, rich in energy is searched for. We humans share that drive with almost all animals. The energy carrying nutrients in processed food are more accessible than in the same unprocessed food. That leads to an ever increasing level of processing, and an ever decreasing consumption of raw fruits/vegetables and home cooked meals. In the past, with alternating conditions of food shortage and food abundance, overeating in times of prosperity was a reproductive advantage. However, high energy food becomes a severe nuisance in the age of permanent food abundance. Obesity and heart diseases spread through the developed world. That behaviour is rooted in our genetic instincts. Cultural based sensorial preferences, induced mostly in childhood by an epigenetic mechanism, present a variation around the instinctive rooted preferences. Food choice based on reflective decisions appears of minor importance. Nevertheless, all government campaigns against over-eating appeal to reason, not to instinct. We are faced with a permanent dichotomy between what is good for reproduction and what is good for health. This occurs not only in what and how we eat, but also in all neighbouring areas on the edges of food science, biology, social science, medicine and ethics.

In developed countries, where the majority of the population has enough income to afford healthy diets, a large number of the inhabitants nevertheless choose unhealthy nutrition. WHO and FAO strategies to overcome this problem are mostly based on educational means. Implicitly, this approach is based on the presumption that the main causes of the problem are ignorance and culturally acquired bad habits. It has already been shown that wild animals, evidently acting solely on instinct without cultural effects, display tendencies that may damage their longevity: they tend to avoid healthy types of caloric restriction, prefer processed to raw food, and have an excessive intake of food stimulants and proteins when available (Ostan et al., 2009). This paper presents evidence for such nutritional patterns in humans as well and broadens the discourse to include proteins and fats and describes some human biological traits that present important differences between humans and other primates; among them are the human tendency for overeating and the inadequacy of a totally raw diet for human consumption (despite having some advantages for the human immune system). From an evolutionary perspective these strategies offer a biological advantage by enhancing the reproductive capability of the organisms, according to Dawkins' theory of the Selfish Gene. Genomic-based pleasure of such nutrition seems to be the main cause of instinctive nutritional drives. Further research on the process of food acceptance is needed to determine the role and importance of genomic-based pleasure compared to epigenetic or culture-based pleasure. Both, however, seem to be important and very stable factors in human nutritional choice and seem to prevail over conscious factors in food acceptance.

Respiration rate (RO2) of prickly pear cactus stems (Opuntia spp.) was measured as a function of 4 temperature (T) and 6 relative humidity (RH) combinations for O2 partial pressures between 15 and 0.8 kPa, which were considered to support aerobic respiration. The rate of respiration (RO2) was determined based on O2 depletion of the atmosphere in sealed containers containing 1 kg of stems. The O2 partial pressure declined linearly over time and the slopes of the fitted lines were used to calculate the rate of O2 uptake. The rate of O2 uptake increased with increasing temperature and decreased with increasing RH. The respiratory rate at 25°C was approximately 30 to 40 times higher than at 5°C. The respiratory rate at 65% RH was between 30 and 90% greater than at 90% RH, depending on the temperature. Data for ln(RO2) for each RH level were regressed against the inverse of the T (K-1) to determine Arrhenius constants and calculate the apparent Ea of respiration for the six RH conditions. The Ea was similar for each RH level, varying between a low of 113 to a high of 131 kJ•mol-1. An equation having an R2 of 0.95 was developed describing respiration as a function of RH and T (°C) using only four constants

Absorption and scattering of laser light pulse passing through the fruit determine among others, the optical properties of the product. Efforts have been made in the recent past to utilize innovative techniques such as time-resolved reflectance spectroscopy (TRS) to study the quality aspects of different fruit such as nectarines. These optical properties have been well related to firmness, sugars, acids and other quality attributes. TRS measurements were performed on 'Jubileum' plums at two different wavelengths: 670 nm and 758 nm. The fruit were harvested in Norway and brought to Italy under protected conditions. After sorting the fruit by size, TRS measurements were made and the fruit were randomized for different examinations of quality aspects. It was observed that the absorption coefficient μ a ) increased for both wavelengths as ripening progressed towards the melting stage of the fruit. The μ a values at 670 nm were higher than those at 758 nm. The higher rate in the μ a was distinguishable from the third day onwards as the fruit ripened. Similarly, it was interesting to note that the internal colour measured after destructing the fruit related well with the TRS absorption coefficient (μ a ), i.e., a decrease in the CIE L * (towards darker region) and b * (towards blue) value along with an increase in a * (towards red) from third day of storage.

BACKGROUND: The yellow aspect of colour is usually not considered for produce with a green-to-red or a green-to-yellow transition upon ripening. The magnitude of change is simply too small and, additionally, masked by a large variation. The colour of Granny Smith apples, harvested from three orchards at two stages of maturity, was measured individually using the CIE L*a*b* system during storage in a regular atmosphere at three temperatures: 1, 4 and 10 °C. A model was developed based on a simplified mechanism, consisting of two consecutive reactions, to describe the development of the apple colour expressed as b* and L* values during storage. RESULTS: Monitoring individual apples made it possible to include and describe the biological variance of colour in batches of apples and to extract information on chilling injury, as a process active at 1 °C. All variations could be attributed to a single source related to the amount of yellowing compounds at the moment of harvest, indicating differences in state of maturity between individual apples. The obtained explained part (R2adj), using nonlinear mixed effects regression analysis was well over 90% for all data combined over more than 3000 observations. CONCLUSION: Orchard location had a slight effect on the mean initial colour value, indicating differences in development stage, most probably due to differences in assessing the harvest date. The magnitude of the variation in these colour values was, however, the same for all three orchards. The behaviour of the green colour aspect (a* value) has been reported separately, as this represents the major change in perceived colour. The changes in b* and L* values are rather small, while the biological variation between the individual fruit is at least of the same magnitude. The model presented here is, as far as known, the first model on b* and L* values for green-coloured products. Analysing b* and L* data using this model provides additional information with respect to the stage of maturity at harvest in a batch or for an orchard of Granny Smith apples. All the variation in the yellow colour aspects could be attributed exclusively to the initial level of yellow compounds

No clear criterion exists to determine the optimum time to harvest mango. Some empirical relations are used to assess maturity, such as shoulder development. Moreover, as a result of the typical growing conditions in tropical climates, a huge variation in maturity and ripeness exists, seriously hampering the export of fruit in the global chain. The consequence for consumers in western countries is that sometimes mangoes are overripe at the retailer, or have to be kept for several days, even weeks, to reach the edible state, provided they do not rot in the meantime. To ensure an edible quality, the chlorophyll content in the fruit flesh, measured at harvest by Time-resolved Reflectance Spectroscopy (TRS), could be used as a maturity criterion for mango fruit. Commercially grown fruit were harvested in Brazil and transported to Italy by plane. Fruits were measured using TRS at 630 nm for absorption coefficient (µa) and skin colour. The development of µa was followed on 60 fruits during 15 days of storage at 20°C. The remainders of fruit were used to measure firmness destructively. Absorption coefficient decreased during shelf life according to a logistic pattern, as expected for colour development. Taking the variation between the individual fruit into account, 72% of the variation was accounted for. Nevertheless, µa assessed at harvest could be converted into a biological shift factor (BSF), as an expression of the maturity at harvest of each individual fruit. This biological shift factor explained about 70% of the variation in firmness development in individual fruit. These preliminary results indicate that TRS methodology coupled with BSF theory could be useful in assessing maturity at harvest and assuring acceptable eating quality of mango.

In ethology, the science of animal behaviour, the so-called “central theorem” states that organisms are expected to behave in a way that benefits their own “inclusive fitness.” Critics of this theorem claim that there is a dichotomy or even a contradiction in each organism, involving the tendency of genes for successful multiplication and the tendency of the body for healthy longevity, and that organisms prefer to satisfy the needs of genes for multiplication even to the point of damaging their health and longevity. This paper presents a reflection within the framework of the central theorem and its critics by focusing on three nutritional patterns in animals: the tendency for satiety, the tendency for fast/easy food, and the tendency for food stimulants. All of these patterns have greater beneficial effects for reproduction than for health and longevity. These and other instinctive nutritional patterns of behaviour may be important for a better understanding of human nutritional ethology.

The colour of ‘Granny Smith’ apples, harvested from three orchards at two stages of maturity, was measured individually using the CIE L*a*b* system during storage in regular atmosphere at three temperatures: 1, 4 and 10 °C. A model was developed based on a simplified mechanism to describe the development of the apple colour during storage as affected by senescence (aging) and chilling injury. Monitoring of individual apples made it possible to include and to describe the biological variance of colour in batches of apples and to correct the colour of each apple individually for its own biological shift factor (biological age; random effect). The biological shift factor is related to the initial condition and range of colour change. The rate of the colour development was estimated in common (fixed effects) for all batches using non-linear mixed effects regression analysis. The variance accounted for by the developed model, including effects of temperature, harvest maturity and orchard location, was more than 95% on 3211 observations. The overall reaction rate constant of decolouration, combining the effects of senescence and chilling injury, was found to depend on temperature. The temperature that showed the lowest overall reaction rate of decolouration is 8 °C, which is in contrast with the currently recommended storage temperature for ‘Granny Smith’ apples.

Broccoli combines high levels of vitamins, fibres and glucosinolates (GLS) with a low calorie count. GLS are precursors for the characteristic broccoli flavour and have anti-carcinogenic properties. This study describes the effect of controlled atmo¬sphere (CA) and temperature on GLS concentrations in broccoli. Data on GLS behaviour and gas exchange were gathered for broccoli heads that were stored at three temperatures and subjected to four levels of O2 and three levels of CO2. The GLS behaviour of three GLS (raphanin, GB and neo-GB) was examined that showed exponential decrease over time, possibly representing the GLS interaction with myrosinase. The most striking feature is the large variation in GLS concentrations at harvest. The propagation of the variation in GLS over time is clearly affected by CA and temperature. Variation in GLS concentrations over time at the same gas condi¬tions and temperature was interpreted with the moment of harvest as main cause of random variation. Assuming that this random variation is normally distributed, the exponential function over time can be transformed into a batch model that describes the changes of variation over time (Schouten et al., 2004, Hertog et al. 2004). The effect of the CA was modelled using the standard gas exchange model. This calibrated gas exchange model was then linked via the reaction rate constant to the batch model to create an integrated batch model. This integrated batch model was subsequently calibrated to describe the variation of the GLS as function of O2, CO2, time, tempera¬ture and the batch parameters (average biological age and standard deviation). The percentage variance accounted for was on average 85%. Considering that this modelling effort is based on destructive GLS measurements, this is a rather high value. All GLS species were retained by suitable (low O2, high CO2) gas conditions, but remarkably, raphanin was found to be less affected by temperature, indicating that CA storage and low temperature would both retain this GLS species to the same extent, while low temperature storage is a better option for e.g. neo-GB

The storage behaviour of apples is simulated with a model based on the changes in green ground colour of three apple cultivars (`Elstar?, `Topaz? and `Pinova?) during ripening on the tree in the same orchard in three consecutive seasons, and also the effects of at-harvest maturity criteria. Taking the variation over the seasons into account (mainly found in the potential greenness), using a fixed fraction of ground colour at the moment of harvest as a harvest criterion was found to exhibit a better performance than using a harvest criterion of a fixed colour. The second part of the paper deals with theoretical relations between the product properties at the moment of harvest. These relations constitute the calibration curve per season for harvest indices like the Streif index. Variations in properties due to different seasonal conditions can affect the range of colour, as indicated in previous examples, and the synchronisation in the biological shift factor for different properties (here colour and firmness). The first effect (colour range) generates a change in slope between the two variables (colour and firmness), the second one a parallel shift. These findings can be used to improve the general performance of harvest indices over the seasons and orchards.

Summary Brussels sprouts were stored at –18°C, –9°C and –4°C. During this storage, the colour of whole Brussels sprouts and Brussels sprouts slurry, measured as the greenness (Hunter –a value), decreased, probably can be described as a first order decay. The reflection at 680 nm of Brussels sprout slurry measures possibly the constant sum of chlorophyll and pheophytin. This can be a useful indication of the initial colour of the product. Also the ascorbic acid content can be a useful quality index, provided the initial level is known. Although not a very sensitive one, the shear force seems to be the most reliable textural parameter. From microbiological point of view, a storage temperature of –18°C as well as –9°C, is quite acceptable.

The maturity at harvest of nectarines can be assessed with the novel technique of time-resolved reflectance spectroscopy (TRS) measuring the light absorption at 670 nm in the fruit flesh. A kinetic model was developed that links this absorption coefficient (mu(a)), expressed as the biological shift factor, to firmness decrease during ripening. The model thus includes the variations in maturity at harvest of the individual fruit. In non-linear regression analyses of data from four different seasons, the explained part ranged from 81 to 92% for cv 'Spring Bright'. The kinetic parameters values obtained were highly similar in different seasons. The results suggest that in nectarines the degreening of fruit flesh, expressed as TRS absorption at 670 run, is synchronised with the softening. The distribution of mu(a) was skewed, but that of the biological shift factor, derived from mu(a), was normal. By measuring the colour of fruit flesh with the non-destructive and very rapid TRS technique, and applying the model parameters, individual fruit can be graded at harvest into classes of usability, selecting fruit with different ripening stages for different market segments and predicting their softening time, thereby guaranteeing sufficient firmness to transport the fruit and sufficient ripening potential to reach good eating quality upon arrival in the receiving regions or countries. Consumers therefore will be more satisfied, encouraging them to repeated purchase. Retailers and wholesalers will be more satisfied since fruit unfit for sale not longer needs to be transported. (c) 2007 Elsevier B.V. All rights reserved.

Biological variation is omnipresent in nature. It contains useful information that is neglected by the usually applied statistical procedures. To extract this information special procedures have to be applied. Biological variation is seen in properties (e.g. size, colour, firmness), but the underlying issue is almost always to the variation in development or maturity in a batch of individuals generated by small scale environmental differences. The principles of assessing biological variation in batches of individuals are explained without putting emphasis on mathematical details. Obtained explained parts increase from about 60 to 80 % for the usual approach to 95 when the biological variation is taken into account. When technical variation or measuring error is small even 99 % can be achieved. The benefit of the presented technology is highlighted based on a number of already published studies covering the colour of apples during growth and storage and the firmness of cut tomatoes during storage

Firmness and colour of Thai mango (‘Nam Dok Mai Si-Thong’) were assessed (firmness at two opposite sides) at regular intervals during storage at 13°C for 14 days, followed by storage at 28°C for another 8 days. The mangoes were individually labelled and the obtained data were analysed using a logistic decay for firmness and all colour attributes (L*, a*, and b*), including the biological variation within in a batch. The variation in maturity was expressed as biological shift factor. Explained parts of around 90% were obtained for all variables. The biological shift factors are normally distributed. No major difference was found for firmness between both sides of the mangoes. Hardly any relation was found between the biological shift factors of the colour attributes with that of firmness. That confirms that (skin) colour cannot be used to assess the maturity status of firmness in this cultivar. As expected, a pronounced effect of temperature was found, but only on the rate constant of the softening and colour decay process. At 28°C, softening was almost 1.65 times faster and colour development 5 times faster for a* and b* colour aspects than at 13°C. The other model parameters and the model structure were, however, not affected by temperature. That means that in the supply chain, the same model can be used to assess and predict the behaviour of colour and firmness in the entire chain.

Thai mango ‘Nam Dok Mai Si-Thong’ has an attractive golden yellow skin colour even in immature fruit, not ready for consumption. Firmness becomes an important quality attribute to assess the ripening stage of the fruit during storage. In this study, the possibility of a non-destructive method using a texture analyser for assessing the firmness behaviour during storage was investigated in three different experiments for (1) probe selection, (2) distance selection using the selected probe and (3) evaluation of the selected probe and distance on mango quality. The results revealed that an aluminium flat probe with 35 mm diameter is a suitable probe for measurement. Limited distance compression at 1 mm was selected since that combination did not leave any compression marks on the fully ripened mangoes. Evaluation of mango quality attributes obtained by this technique could be used to assess non-destructively the firmness behaviour of the mango fruit during storage. The technique can be used to monitor the firmness of mango fruit on an individual basis, using the same fruit in successive assessments. Non-linear indexed regression can be applied to extract information on the behaviour and variation of firmness of individual mangoes. Obtained explained parts (R2adj) frequently are well over 90%.

The aim of this research was to develop practical applicable models capable to describe and to predict the temperature dependent firmness and moisture loss of tomatoes during storage. To gather the required information to develop these models batches of 20 tomatoes (cv. Tradiro), each harvested at two maturity stages, were stored at four different temperatures (3, 12, 20 and 25 °C) up to four weeks. One temperature (3 °C) is known to cause chilling injury to the product. During storage at these temperatures firmness loss, moisture loss and near infrared spectra were measured on individual tomatoes at regular intervals. The decrease in firmness was measured non-destructively by flat-plate compression, moisture loss was measured by weight loss. The information on firmness and moisture loss was used to develop two types of models. The first type of model was based on fundamental laws of chemical kinetics, assuming plausible chemical reaction mechanisms. These reaction mechanisms describe the processes underlying either firmness, or moisture loss. From these reaction mechanisms a set of differential equations was derived and solved at constant temperature. For these kinetic models, both for firmness, and moisture loss, two independent processes were assumed. One process is mainly expressed at low (

To investigate the changes in total antioxidant activity of fresh-cut tomato during storage, tomato fruits harvested at three different stages of maturity were cut into 7-mm thick slices and stored at 5 °C. Intact fruits were stored in the same conditions as a control. The antioxidant activity was evaluated as the capacity to scavenge the radical ABTS+ in both hydrophilic (HAA) and lipophilic (LAA) extracts. Cutting resulted in a decrease in the HAA compared to the control fruits and did not influence significantly the LAA. Changes in LAA during storage were described by a simple exponential model developing towards an asymptotic end value. The HAA also decreased exponentially in the beginning of the storage time but increased again afterwards. For both hydrophilic and lipophilic antioxidant activity the riper the fruit the higher was the antioxidant activity. Since no relevant interaction was found between time of storage and stage of maturity, the major factor determining the level of antioxidants in tomatoes seems to be the initial level of antioxidant activity at the moment of harvest. The levels of HAA did not differ significantly due to ripening during storage, while the LAA increased with ripening. These results indicate a potential effect of processing to decrease the antioxidant activity in vivo. This would represent a decrease in the value of cut tomatoes as a source of hydrophilic antioxidants in the diet compared with the fruit stored intact. In another experiment, realized at the same conditions, the total antioxidant activity was evaluated using a lipid peroxidation inhibition assay. Antioxidant activity could be measured in methanol extracts, but not in THF extracts. Aqueous extracts showed pro-oxidant activity. No effect of cutting or storage time was observed

Data generated in postharvest research is characterised by its large sources of biological variance. This variance generally obscures the behaviour of interest, complicating both the statistical and conceptual interpretation of the data. To be able to manage the postharvest chain, clear inside is required in the propagation of biological variance during postharvest. Recently, biological variance has gained interest within the postharvest community. To analyse experimental data taking into account biological variance several (statistical) modelling techniques have been applied by different authors. These vary from models that can be solved analytically to analyse the effect of experimental design parameters (e.g., mixed effects models), via hybrid techniques which combine analytical and numerical techniques, to pure numerical models for dynamic simulations based on differential equations (like the variance propagation algorithm). Each of these techniques has its own possibilities and limitations in terms of the type of variance that can be accounted for, their technical complexity, and their applicability to practical situations. The different techniques are suitable to different degrees to answer specific questions in specific settings. Using tomato colour as an example, the different techniques are applied and compared to highlight their strong and weak points in interpreting biological variance. The added value of these techniques are discussed within the framework of managing biological variance in the postharvest chain.

Tomatoes (cv. Tradiro), harvested at two maturity stages, were stored at four different temperatures during up to four weeks. The lowest storage temperature was known to cause chilling injury, the three other temperatures were regarded save. During storage Near Infrared spectra of intact tomatoes were recorded and samples were taken at regular time intervals to determine the activities of the pectolytic enzymes polygalacturonase, pectin methyl esterase and β-galactosidase. The maturity stage of the tomatoes at harvest, followed by storage at the four different temperatures affects the activities of these enzymes. To describe the change in activity of these enzymes kinetic models were built based on fundamental laws of chemical kinetics using assumed, but plausible reaction mechanisms. For the models developed, a fixed and a variable enzyme activity were observed for these three enzymes. For polygalacturonase, this fixed amount of enzyme activity was dependent on maturity stage at harvest. For pectin methyl esterase and β-galactosidase the maturity at harvest had almost no effect on this fixed amount of enzyme activity. The variable part of the enzyme activity could either increase in time (polygalacturonase), followed by denaturation (β-galactosidase), or only decay in time (pectin methyl esterase). For the activity of polygalacturonase, a self-initiated, autocatalytic production of this enzyme was assumed. β-Galactosidase was formed, but inactivated in time. Pectin methyl esterase activity decayed exponentially in time. The models for polygalacturonase and β-galactosidase were integrated into the previously developed model for the firmness loss of tomatoes during storage [Van Dijk, C., Boeriu, C., Peter, F., Stolle-Smits, T., & Tijskens, L. M. M. (2005). The firmness of stored tomatoes (cv. Tradiro). 1. Kinetic and Near Infrared models to describe firmness and moisture loss. Journal of Food Engineering, in press]. It was concluded that any cell wall degrading enzyme, which activity remains within a certain bandwidth, can be integrated into the firmness model to explain the observed firmness decay. Based on Near Infrared spectroscopy, a statistical significant relation was only observed between the polygalacturonase activity and the Near Infrared spectra of intact tomatoes. It is argued that the consequences of the performed polygalacturonase activity are reflected in this relation rather than the amount of this enzyme. Since mutual statistical significant relations exist between Near Infrared spectra, polygalacturonase activity and the tomato firmness it seems reasonable to ascribe a significant role of this enzyme to the firmness decay.

A model was developed assuming that the occurrence and the development of physiological disorders are effects of a balance between processes of disorder formation and scavenging of initiating compounds. Based on this (simplified) mechanism and applying the fundamental rules of chemical kinetics, the differential equations can be derived. The observed effects depend on initial levels of some nutrients (N), free radicals (Ra) and scavenging activity (SS). All three types of compounds do depend on the growing conditions prior to harvest, and hence on season, weather and climate. Postharvest development of disorders (PD) depends also on conditions during storage, e.g. temperature and CO2 level. Thus their influence was incorporated into a model based on fundamental knowledge in that sphere. The benefit of the developed model is that it allows simulating very different ranges in type of development of disorder. From very fast and reaching high level of occurrence, very fast but stabilised at low level of occurrence, to slow but reaching high level of occurrence, and slow and stabilised at low level of occurrence. And of course simulating of cases where the disorder occurrence is not observed at all. The model was checked against measured data on pears, indicating that the approach seems to be realistic and powerful enough to pursue. Existing data are however gathered in a manner not suitable for this approach. Therefore further studies on dynamics of physiological disorders require improvement of experimental methods.

Tomato fruit (cultivar Belissimo) were harvested at three different stages of ripening, sliced and stored at at 2, 5, 8, 12 and 16 °C. Firmness was measured as the force necessary to cause a deformation of 3 mm, in the outer and the radial pericarp, daily or every two days, depending on the combination of stage of ripening and temperature. For constructing a model, firmness was considered to be built up by a variable part (e.g. pectin based firmness) that changes according to a first order reaction mechanism and a fixed part (e.g. cellulose or structure based firmness) that is invariable under the circumstances under study. The firmness of the tomato slices decreased exponentially during storage, with a reference rate constant of 0.0975 ± 0.0183 J/mol/K for the outer pericarp and 0.0712 ± 0.0328 J/mol/K for the radial pericarp and energy of activation of 87.5 and 94.8 kJ/mol, respectively for outer and radial pericarp. The parameters of the model were estimated using multiple variate non-linear regression analysis with time, temperature and stage of ripening of the fruit at harvest simultaneously as explanatory variables. To combine the information on firmness behaviour during the preharvest and the postharvest period at different temperatures, it was assumed that the process of firmness loss during ripening was the same whether the fruit ripened on the plant or off-vine. So, the initial firmness at the postharvest period depends on the time the tomatoes were allowed to ripen on the plant (stage of ripening). The statistical analysis of the mean values of firmness provided a percentage variance which accounted for 92% and 72% for outer and radial pericarp, respectively. Using a fundamental approach to build the reported model and using all available data and information made it possible to describe and simulate the firmness behaviour of tomato slices as a function of the stage of ripening and the applied storage temperature.

The food that we eat is uniform neither in shape or appearance nor in internal composition or content. Since technology became increasingly important, the presence of biological variance in our food became more and more of a nuisance. Techniques and procedures (statistical, technical) were developed. The most widely used are sorting or grading on large-scale operations. Statistical rules were developed on the sampling size to obtain a reliable mean value. Experimental design strategies were developed for efficient research. All the techniques used are rather empirical and only loosely connected to the theoretical and fundamental knowledge we do have. An effort is made to approach biological variance from a new perspective. The nature of biological variance is traced back to its origin in the processes of production and conversion, primarily driven by the "random" differences in climate and soil. By modelling the dynamics on the level of the individual units that constitutes a batch, rather then modelling the mean value for the batch itself, more fundamental models can be developed. These more fundamental models are generic in nature and describe changes in product properties for all kinds of circumstances like growing area, seasonal effects, harvest maturity and storage temperature.

A novel control structure for a potato storage facility is presented that is directly geared at the optimal preservation of product quality. The quality of the stored potatoes is defined as frying colour that depends on sugar concentration. The optimal storage conditions are estimated using models of both product behaviour and storage process to optimise quality and costs. The control structure is implemented in an industrial storage facility. Results show an improved product quality and lower energy cost. An important extension to the nominal product model is the consideration of product quality with its variation

Some hundred years ago, wise men decided that preharvest research and applications had to be regarded separated from the postharvest handling and behaviour. Over the years, both areas developed completely separated. Control over both areas was obtained by different companies and advisory boards, with mostly not too good means of communication between them. This decision hampered seriously the consistent and integral development of knowledge on food production and usage. Bridging the gap between all the knowledge and expertise available in the preharvest area of growing food and the postharvest area of storing and processing food, has become and is still becoming more and more important over the last couple of years. In this paper, based on theoretical considerations, on plausible (but unproven) mechanisms and applying the fundamental rules of chemical kinetics, a pathway to deduce general and generic models is developed towards a possible approach to integrate all available knowledge. Still the validity of this approach is not proven. However, a number of examples from both the applied as well as the fundamental point of view are elaborated to indicate such an interaction exists, and to indicate how to tackle the modelling problem. The examples range from physiological disorders like core brown, internal brown, chilling injury and the biological age of individual tomatoes in truss tomatoes as related to the maturity at harvest

The keeping quality for a cucumber, defined as the time the colour remains acceptable to the consumer, depends on the state of the chlorophyll metabolism. By building a physiological model of the chlorophyll metabolism for cucumbers and using colour data from cucumbers stored at 12, 20 and 28 °C, the parameters of the model were estimated with time and temperature simultaneously as explaining variables. Colour data were expressed as ratios of the separate intensities of the red, green and blue (RGB) values from a 3CCD digital camera, namely blue/red (B/R) and blue/green (B/G). The explained variance obtained was more than 93%. The model structure is generic in nature and describes the postharvest colour behaviour in time and temperature for cucumbers, irrespective of growing conditions and cultivar. For six batches, from three cultvars over two growing seasons, the batch keeping quality, i.e. the time that 95% of all cucumbers in a batch had an acceptable colour, was obtained at 20 °C. A batch was defined as all cucumbers from one grower, one cultivar and one harvest. It is shown that, for batches grown in the spring season, high (colour) keeping quality related to high resistance against bacterial spoilage. Model parameters were estimated using either B/R or B/G colour data. Comparing the model parameters, it was deduced that the average initial colour measurement, expressed as the ratio of the red and green intensities (R/G), would be indicative for the batch keeping quality. It was possible to predict batch keeping quality, on the basis of initial colour measurements only, with a percentage variance accounted for R2adj of 94%. As the basis of the batch keeping quality predictions is a generic model, it might be possible to predict batch keeping quality for many other products which have green colour as the limiting quality attribute.

The activity of lipase and peroxidase in Turkish hazelnuts was measured experimentally as a function of temperature at a constant pH of 4.5, and as a function of pH at a constant temperature of 25 degreesC. Lipase revealed an iso-enzyme system with two clearly distinguishable peaks in activity with pH, whereas peroxidase only showed one large peak of activity. The activity data obtained were analysed by non-linear regression using an existing model for enzyme activity as a function of pH and temperature simultaneously. The existing model was adapted to account for the iso-enzyme system found to be present in hazelnut lipase activity. The percentage variances accounted for (R-adj(2)) obtained for peroxidase were 85.6% and 96.2% for temperature and pH dependence, respectively. For lipase the percentages Were found to be 72.1% and 89.6%, respectively. These results corroborate significantly the previously developed fundamental model. (C) 2002 Elsevier Science Ltd. All rights reserved.

This chapter discusses different quality attribute models including models for batches, models for growth, and models for globalization. Dealing with general patterns and variation in measured properties or attributes is, in its basic premises the technical goal of batch modeling. This type of model describes the variation resulting from slightly different conditions during growth for all individuals with a common growth history. The modeling of quality attributes and quality related product properties during growth are not well developed. In general, quality attributes important for postharvest handling of fruit and vegetables play a minor role in the production phase, except in floriculture. The globalization of the fruit and vegetable supply chain has been occurring for quite some time. Globalization offers major advantages, but also considerable disadvantages. However, the need to understand how different regions and different seasons across the world affect quality and quality behavior has been neglected. Understanding and integration requires a fundamental approach that incorporates the relevant behavior of the product, both in the preharvest and in the postharvest realm. Quality differences induced by different cultivars, growing sites, soil types, climate, and weather have to be merged and combined into a single description, because traditional modeling approaches are unsuitable to accommodate this integration of knowledge.

The aim of this study was to increase the understanding of chlorophyll breakdown and lycopene synthesis at a quantitative level in Solanum lycopersicum fruit. To accomplish this, a kinetic model is proposed describing the transition from chloro- to chromoplast. Remittance VIS spectroscopy was used to assess chlorophyll and lycopene levels non-destructively in cocktail and round type tomatoes. Tomatoes were stored at constant temperatures between 4 and 24 °C, or at a stepwise changing temperature between 4 and 16 °C. Chlorophyll and lycopene levels were measured repeatedly over time and used to calibrate a kinetic model that describes how an autocatalytic enzyme system links chlorophyll breakdown to lycopene synthesis, including breakdown of lycopene precursor and lycopene itself. Increasing storage temperatures increased the reaction constant for lycopene synthesis more than that of chlorophyll breakdown for both tomato types. The reaction constants describing chlorophyll breakdown and lycopene synthesis were considerably larger, and the estimated enzyme levels lower for the round type. This allows round tomatoes to quickly resume lycopene synthesis after a cold storage period when enzyme levels are low. Lycopene breakdown was established for the round type while the cocktail type showed lycopene precursor breakdown. Chlorophyll breakdown and lycopene synthesis, as affected by storage temperature and tomato type, is covered well by the model for both tomato types. We hypothesise that the postulated enzyme system, responsible for the direct link between chlorophyll breakdown and lycopene synthesis, is due to STAY-GREEN proteins. Remittance VIS spectroscopy is, in combination with a parameter estimation tool, suited to screen tomato genotypes for intended colour transformation performance, or as tool in chloroplast to chromoplast transition studies.

Based on fundamental chemical relations, well-established in chemical engineering and chemical technology over almost a century, the effects of pH in food and agricultural products will be deduced for different situations and processes. Based on simple equilibria and dissociation of water, salts, acids and bases, and considering the reaction of hydrogen ions in these food-related systems, simple and reliable formulations are developed capable of describing surprisingly well the discoloration of blanched vegetables and the activity of enzymes in different buffered and unbuffered systems. The line of reasoning is generic and can be applied repeatedly to different problems, situations and processes.

The effects of pH observed in the activity of a number of enzymes from different origins and the degradation of green colour in blanched vegetables, was modelled based on fundamental kinetic principles by considering hydrogen ions as an integral part of the reaction mechanism. Parameters were estimated by non-linear regression analysis with explained parts (R2adj) was in all cases except for the enzyme lipase, well over 95°and frequently well over 98&Eth;Applying fundamental models in integral data analysis made it possible to pinpoint aberrations at high and low pH ranges in the discoloration of vegetables, which remained unnoticed using classical analysis procedures. The model on enzyme activity was successfully applied to analyse and to describe a double optimal pH region when iso-enzymes are present in the total pool of active enzymes.

The activity of pectin methyl esterase (PE) in peaches during blanching treatments was modelled and analyzed. It was postulated that the enzyme exists in two configurations, one bound and one soluble. The bound configuration can be converted into the soluble configuration. These two configurations have a different susceptibility to temperature. All rate constants of reaction were modelled as dependent on temperature according to the Arrhenius law. Despite the daily measuring variance, the variance accounted for by the model in multivariate nonlinear regression analysis was more than 90%. The obtained parameter values were highly comparable for two consecutive seasons. An analysis of the data of the two seasons combined was feasible with the kinetic parameters estimated in common, without losing information with a tremendous increase in predictive power.

A generic model is developed that describes rates of respiration and fermentation, in response to temperature and environmental gas conditions (oxygen and carbon dioxide). The mathematics of the model are based on Michaelis–Menten kinetics. Respiration is simplified as the effect of one enzymic reaction, inhibited by its own product, carbon dioxide. Both competitive, and uncompetitive inhibition are incorporated. Fermentation is modelled including the competitive inhibition of fermentation by both oxygen and carbon dioxide. Temperature dependence is introduced using Arrhenius equations for the maximum rates of oxygen consumption and carbon dioxide production. The model is generic in nature: it is applicable to different types of products (apple, chicory and tomato) at different conditions (in terms of O2, CO2 and temperature) and for different types of inhibition. This fitness is an indirect validation of the assumptions on which the model is based.

Peroxidase (POD) activity was measured in peaches, carrots and potatoes after blanching treatments at different constant temperatures. Two isoenzymes exist, one bound and one soluble. The bound form can be converted into the soluble form by a temperature-dependent conversion reaction. Both forms are susceptible to heat denaturation. However, the conversion precedes the denaturation of the bound form. Heat denaturation of the enzymes could be described using an exponential decay (first order reaction). The temperature dependence of all reaction rates could be described by Arrhenius' law. The simultaneous analysis of bound and soluble POD in peaches explained 96.4% of the observed variance. The analysis for carrots and potatoes on bound POD alone, yielded a ‘percentage variance accounted for’ of 94.5 and 70%, respectively.