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Deep frying is one of the most used methods in the food processing industry. Though practically any food can be fried, French fries are probably the most well-known deep fried products. The popularity of French fries stems from their unique taste and texture, a crispy outside with a mealy soft interior, but also because of the ease and speed of preparation. However, despite being a practical and easy method, the fundamental phenomena that occur during frying are very complex. This thesis aimed at gaining a deeper understanding of the frying of French fries. This was done at the product level, with regards to heat transfer, moisture loss, oil uptake and crust formation, and at the process level, which encompasses the oil movement in a frying unit and the consequent oil-fry interactions. Firstly a numerical model was developed to describe the water evaporation during frying (Chapter 2). Though various models exist for describing moisture loss, they all use constant values for the heat transfer coefficient. However, the heat transfer coefficient actually varies greatly due to the varying degrees of turbulence, induced by the vapour bubbles escaping from the fry surface. Therefore, the model in this thesis incorporated an evaporation rate dependent heat transfer coefficient. Other than the varying heat transfer coefficient, the model was heat transfer dependent, with a sharp moving evaporation boundary and Darcy flow describing the flow of water vapour through the crust. The model was successfully validated against experimental results for moisture loss and temperature profiles in the fry. For oil uptake during frying, a pore inactivation model from membrane technology was adopted (Chapter 3). In membranes, pores will inactivate when the transmembrane pressure becomes too low. In fries, this can be translated as pores in the crust inactivating when the evaporation rate becomes too low. As pores stop expelling water vapour, oil can migrate into the fry. The model also took into account the lengthening of the pores with increasing crust thickness, allowing for more oil uptake in inactivated pores. The model fitted well with experimental data for oil uptake during frying. Also, the pore inactivation model better described oil uptake during the initial stages of frying, where the evaporation rate is still relatively high, compared to the linear relation between oil uptake and moisture content, which is usually assumed in literature. Both the influences of frying temperature and moisture content on crust structure and consequent textural properties were studied (Chapter 4). The crust structure was visualized and quantified using X-ray tomography (XRT), which uses multiple 2D X-ray pictures of a rotated sample to reconstruct a 3D density map. Textural properties, like hardness and crispness, were quantified using force deformation curves from a texture analyser. Moisture loss was shown to greatly increase porosity and pore size in fries. More crispy behaviour was also shown for higher moisture loss, though not significantly at moisture contents close to the initial moisture content. Though increased frying temperatures also showed an increased porosity and pore size, there was no significantly observed increase in crispness. This is most likely because the texture analysis was not sensitive enough to discern any increased crispness for porosities below a certain degree. Strikingly, for frying temperature around 195 °C, a decrease in crispness was observed. These samples visually also showed more plastic behavior. The most likely cause for this is degradation of sucrose, which happens around 186 °C, and consequent caramelization of glucose, thus increasing the glass transition temperature. At the process level, oil flow and fry quality distribution were investigated using a pilot scale cross-flow fryer (Chapter 5). Oil circulation velocities were varied to observe the initial fluidization behavior of the fry bed through an observation window. This fluidization behavior was well described by the Ergun equation, modified for non-spherical particles. The distribution in moisture content of the fries was used as an indicator for quality distribution. Though increased oil circulation initially increased the homogeneity of the moisture content, upon fluidization the homogeneity actually decreased. Image analysis of fries before and after frying showed local packing of fries around their fluidization point. This was due to the non-spherical shape of the fries, making them more sensitive to channelling. The results obtained in this thesis were finally discussed, together with the possibility to also model the process scale of the frying process (Chapter 6). The possibility of modelling the oil flow through a packed bed of fries, and the free-convective heat transfer during frying, using a CFD software package (STARCCM+) was shown. Additionally, the possibility of linking oil flows computed using CFD to the general models developed in this thesis was discussed. Modelling the momentum transfer of the expelled vapour bubbles to the oil, but also the movement of the fries themselves is still a faraway goal. However, a multiphase model that can describe both the entire frying setup as the consequent individual fry parameters would be invaluable.

Deep frying is one of the most used methods in the food processing industry. Though practically any food can be fried, French fries are probably the most well-known deep fried products. The popularity of French fries stems from their unique taste and texture, a crispy outside with a mealy soft interior, but also because of the ease and speed of preparation. However, despite being a practical and easy method, the fundamental phenomena that occur during frying are very complex. This thesis aimed at gaining a deeper understanding of the frying of French fries. This was done at the product level, with regards to heat transfer, moisture loss, oil uptake and crust formation, and at the process level, which encompasses the oil movement in a frying unit and the consequent oil-fry interactions. Firstly a numerical model was developed to describe the water evaporation during frying (Chapter 2). Though various models exist for describing moisture loss, they all use constant values for the heat transfer coefficient. However, the heat transfer coefficient actually varies greatly due to the varying degrees of turbulence, induced by the vapour bubbles escaping from the fry surface. Therefore, the model in this thesis incorporated an evaporation rate dependent heat transfer coefficient. Other than the varying heat transfer coefficient, the model was heat transfer dependent, with a sharp moving evaporation boundary and Darcy flow describing the flow of water vapour through the crust. The model was successfully validated against experimental results for moisture loss and temperature profiles in the fry. For oil uptake during frying, a pore inactivation model from membrane technology was adopted (Chapter 3). In membranes, pores will inactivate when the transmembrane pressure becomes too low. In fries, this can be translated as pores in the crust inactivating when the evaporation rate becomes too low. As pores stop expelling water vapour, oil can migrate into the fry. The model also took into account the lengthening of the pores with increasing crust thickness, allowing for more oil uptake in inactivated pores. The model fitted well with experimental data for oil uptake during frying. Also, the pore inactivation model better described oil uptake during the initial stages of frying, where the evaporation rate is still relatively high, compared to the linear relation between oil uptake and moisture content, which is usually assumed in literature. Both the influences of frying temperature and moisture content on crust structure and consequent textural properties were studied (Chapter 4). The crust structure was visualized and quantified using X-ray tomography (XRT), which uses multiple 2D X-ray pictures of a rotated sample to reconstruct a 3D density map. Textural properties, like hardness and crispness, were quantified using force deformation curves from a texture analyser. Moisture loss was shown to greatly increase porosity and pore size in fries. More crispy behaviour was also shown for higher moisture loss, though not significantly at moisture contents close to the initial moisture content. Though increased frying temperatures also showed an increased porosity and pore size, there was no significantly observed increase in crispness. This is most likely because the texture analysis was not sensitive enough to discern any increased crispness for porosities below a certain degree. Strikingly, for frying temperature around 195 °C, a decrease in crispness was observed. These samples visually also showed more plastic behavior. The most likely cause for this is degradation of sucrose, which happens around 186 °C, and consequent caramelization of glucose, thus increasing the glass transition temperature. At the process level, oil flow and fry quality distribution were investigated using a pilot scale cross-flow fryer (Chapter 5). Oil circulation velocities were varied to observe the initial fluidization behavior of the fry bed through an observation window. This fluidization behavior was well described by the Ergun equation, modified for non-spherical particles. The distribution in moisture content of the fries was used as an indicator for quality distribution. Though increased oil circulation initially increased the homogeneity of the moisture content, upon fluidization the homogeneity actually decreased. Image analysis of fries before and after frying showed local packing of fries around their fluidization point. This was due to the non-spherical shape of the fries, making them more sensitive to channelling. The results obtained in this thesis were finally discussed, together with the possibility to also model the process scale of the frying process (Chapter 6). The possibility of modelling the oil flow through a packed bed of fries, and the free-convective heat transfer during frying, using a CFD software package (STARCCM+) was shown. Additionally, the possibility of linking oil flows computed using CFD to the general models developed in this thesis was discussed. Modelling the momentum transfer of the expelled vapour bubbles to the oil, but also the movement of the fries themselves is still a faraway goal. However, a multiphase model that can describe both the entire frying setup as the consequent individual fry parameters would be invaluable.

Een nieuw productieproces voor het voorbakken van frites dat begon als een veelbelovende innovatieve procesroute biedt onvoldoende (economisch) perspectief. Wel heeft het project veel inzicht opgeleverd in de processen die op microschaal in frites optreden en in hoe de procesomstandigheden de productkwalteit beïnvloeden. Deze nieuwe kennis kan worden gebruikt bij het ontwikkelen van innovatieve producten met bijvoorbeeld verbeterde krokantheid

Biologische aardappeltelers hebben nog nauwelijks goede rassen voor chips en friet. In het project BioImpuls wordt gezocht naar een oplossing.

Biologische aardappeltelers hebben nog nauwelijks goede rassen voor chips en friet. In het project BioImpuls wordt gezocht naar een oplossing.

This thesis investigated how to develop an approach for the systematic and science based assessment of those points in food production systems that have a critical effect on quality; such points could be designated as critical quality points (CQPs). One of the fundamental objectives of quality control is to reduce variation in the final quality attributes, which makes it essential to understand causes of variation in these quality attributes. A so-called techno-managerial approach was applied as the research framework to study both technological and managerial aspects. French fries (FF) production chain was chosen as a case study, because of the many points in the French fries chain where variation in conditions can lead to substantial variation in the final quality. French fries production chain was analysed, a comprehensive literature analysis, to review causes of variation in the major quality attributes. It appeared not to be possible to firmly assign such control points, as a systematic approach appeared to be lacking to establish variation in the final quality attributes. Based on available quantitative data in literature, selection of suitable cultivar, time-temperature settings during bulk storage, blanching and final frying were indicated as potential sources of variation and can be considered critical to control final quality attributes. The conclusion of the study was that further quantitative insight was required in the contribution of variation in process and product factors to the actual variation in the profiles of major quality attributes of French fries. Consequently, a study was conducted to getquantitative assessment of variation in texture and colour profiles of French fries as a function of various fixed time-temperature (t-T) frying settings. The study indicated that increased frying temperature and time (from 170 to 190 oC, and from 4 to 6 min) resulted not only in higher mean ln (peak force) values as a measure for texture and colour index, but also in a larger variation in peak data force from (29 %) and colour index data from (41 %). These results were more obvious in the case of thin as compared to thick FF. Therefore, results suggested t-T settings during final frying can be considered as critical to control final quality attributes of French fries.However, t-T blanching settings were not considered as critical to control final quality attributes of French fries because of the minor effect on variation, but selection of an optimum t-T blanching setting is to be considered as an important design activity while making process and product specifications because of the large effect on the actual value of a quality parameter. The managerial part indicated that implementation of frying instructions, sharply reduced variation in ln (frying time) and ln (portion size). This reduction in variation ultimately resulted in significant reduction in variation (Cal Var) in the ln (Peak force) and colour index data of thin FF. Finally themain findings were discussed to put them in a general perspective.First, it was discussed that the well-known HACCP approach is not suitable for establishing CQPs because quality attributes are multidimensional and multifactorial as compared to hazards. Nevertheless, the HACCP approach was taken as the starting point and based on these insights, a systematic approach to assess CQPs is proposed. The proposed approach has provided a basic procedure consisting of six global steps for the assessment of critical quality points in a food production system, based on our research on the production chain of French fries. Each of these steps is discussed in detail with respect to the applicability to food chains. A general picture emerged but it is also clear that in some details further research is needed for specific food chains, Moreover, the TM (Techno-Managerial) approach applied in this thesis proved to be essential as well, as the case study clearly showed the interconnection between human and technological factors on variation in quality attributes. Whether or not this is also the case for other food chains remains to be established, but it is certainly a point to give attention to. This approach could be the base for further studies with different foods by investigating the production chain of other food products, to further evaluate and improve this approach as structured guidelines for the food industry to control and assure quality of the food products.

This thesis investigated how to develop an approach for the systematic and science based assessment of those points in food production systems that have a critical effect on quality; such points could be designated as critical quality points (CQPs). One of the fundamental objectives of quality control is to reduce variation in the final quality attributes, which makes it essential to understand causes of variation in these quality attributes. A so-called techno-managerial approach was applied as the research framework to study both technological and managerial aspects. French fries (FF) production chain was chosen as a case study, because of the many points in the French fries chain where variation in conditions can lead to substantial variation in the final quality. French fries production chain was analysed, a comprehensive literature analysis, to review causes of variation in the major quality attributes. It appeared not to be possible to firmly assign such control points, as a systematic approach appeared to be lacking to establish variation in the final quality attributes. Based on available quantitative data in literature, selection of suitable cultivar, time-temperature settings during bulk storage, blanching and final frying were indicated as potential sources of variation and can be considered critical to control final quality attributes. The conclusion of the study was that further quantitative insight was required in the contribution of variation in process and product factors to the actual variation in the profiles of major quality attributes of French fries. Consequently, a study was conducted to getquantitative assessment of variation in texture and colour profiles of French fries as a function of various fixed time-temperature (t-T) frying settings. The study indicated that increased frying temperature and time (from 170 to 190 oC, and from 4 to 6 min) resulted not only in higher mean ln (peak force) values as a measure for texture and colour index, but also in a larger variation in peak data force from (29 %) and colour index data from (41 %). These results were more obvious in the case of thin as compared to thick FF. Therefore, results suggested t-T settings during final frying can be considered as critical to control final quality attributes of French fries.However, t-T blanching settings were not considered as critical to control final quality attributes of French fries because of the minor effect on variation, but selection of an optimum t-T blanching setting is to be considered as an important design activity while making process and product specifications because of the large effect on the actual value of a quality parameter. The managerial part indicated that implementation of frying instructions, sharply reduced variation in ln (frying time) and ln (portion size). This reduction in variation ultimately resulted in significant reduction in variation (Cal Var) in the ln (Peak force) and colour index data of thin FF. Finally themain findings were discussed to put them in a general perspective.First, it was discussed that the well-known HACCP approach is not suitable for establishing CQPs because quality attributes are multidimensional and multifactorial as compared to hazards. Nevertheless, the HACCP approach was taken as the starting point and based on these insights, a systematic approach to assess CQPs is proposed. The proposed approach has provided a basic procedure consisting of six global steps for the assessment of critical quality points in a food production system, based on our research on the production chain of French fries. Each of these steps is discussed in detail with respect to the applicability to food chains. A general picture emerged but it is also clear that in some details further research is needed for specific food chains, Moreover, the TM (Techno-Managerial) approach applied in this thesis proved to be essential as well, as the case study clearly showed the interconnection between human and technological factors on variation in quality attributes. Whether or not this is also the case for other food chains remains to be established, but it is certainly a point to give attention to. This approach could be the base for further studies with different foods by investigating the production chain of other food products, to further evaluate and improve this approach as structured guidelines for the food industry to control and assure quality of the food products.

The aim of this thesis was first to identify the major technological and managerial factors and to investigate their contribution to variation in acrylamide concentrations. The second aim was to investigate the effect of technological and managerial control measures on the concentration and variation of acrylamide in the preparation of French fries in food service establishments (FSE). The variation ininitial concentration of reducing sugars, variable frying conditions and food handler’s inadequate control of these factors in their daily practice could lead to the large variation and high acrylamide concentrations. The least variation in acrylamide was found in French fries prepared in chain fast-food services (CFS) compared to institutional caterers(IC) and restaurants, although the mean concentration of acrylamide among the three FSE types was not significantly different. The variation in frying temperature contributed most to the variation in acrylamide, followed by the variation in frying time; no obvious effect of reducing sugars was found. The lack of standardised control of frying temperature and time (due to inadequate frying equipment) and variable frying practices of food handlers seem to contribute most to the large variation and high acrylamide concentrations in French fries prepared in restaurants. Lowering the concentration of reducing sugars in par-fried potato strips can be an effective control measure to reduce acrylamide concentrations in French fries, but only if prepared under standardised frying conditions in CFS and IC. Frying instructions were shown to support food handlers’ decisions to start frying when the oil temperature reached 175oC, although an inconsistent effect of the instructions on the food handlers’ decisions to end frying was observed. The mean concentration of acrylamide for the restaurants as a group was not significantly different, but data analysis for each restaurant showed that if the food handlers properly followed the instructions, the mean concentration of acrylamide was significantly lower compared to before instructions.

Uit bakproeven met biologische aardappelrassen blijkt dat een aantal rassen met een hoog niveau van Phytophthora-resistentie, perspectief biedt voor goede frites- en chipbereiding. Hoewel de bakkwaliteit van deze rassen standaard minder optimaal was dan van het ras Phytophthora-gevoelige hoofdras Agria, kan, door ‘reconditioneren’ en ‘blancheren’, met deze rassen toch een acceptabele frites- en chipskwaliteit verkregen worden. Gebruik van deze rassen als Bionica, Biogold en Sarpo Mira in de biologische teelt voor verwerking geeft extra productie voor de teler en meer leveringszekerheid voor de industrie in jaren met een vroege Phytophthora-aantasting.

Uit bakproeven met biologische aardappelrassen blijkt dat een aantal rassen met een hoog niveau van Phytophthora-resistentie, perspectief biedt voor goede frites- en chipbereiding. Hoewel de bakkwaliteit van deze rassen standaard minder optimaal was dan van het ras Phytophthora-gevoelige hoofdras Agria, kan, door ‘reconditioneren’ en ‘blancheren’, met deze rassen toch een acceptabele frites- en chipskwaliteit verkregen worden. Gebruik van deze rassen als Bionica, Biogold en Sarpo Mira in de biologische teelt voor verwerking geeft extra productie voor de teler en meer leveringszekerheid voor de industrie in jaren met een vroege Phytophthora-aantasting.

Monsters van partijen fritesaardappelen die bij de teler zijn genomen, wijken vaak af van de kwaliteitsbepaling op de fabriek. Daardoor kunnen partijen soms niet worden verwerkt. Hoe beter beide kwaliteitsbepalingen overeenkomen, hoe efficiënter de verwerking kan plaatsvinden. Binnen het AKK-project 'Pieper Profijt=gezamenlijk profijt' vindt onderzoek plaats hoe en wanneer de monsters bij de teler het best genomen kunnen worden om faalkosten binnen de fritesaardappelkolom te verlagen

The development and evaluation of a new production process for French fries is described. Superheated steam was used to replace pre-drying in hot air and par-frying in oil, and vacuum cooling was used for cooling and freezing. Finish-frying was still carried out in oil. In this way a substantial reduction of energy use and environmental costs was possible. However, problems with product quality were encountered. The main problem was skin formation, which resulted in a tough crust with a fatty appearance after finish-frying. The new process was modified, and this improved the product quality considerably. Unfortunately, the resulting energy reduction was too limited to justify the investment required for the new process.Furthermore, a new look into the quality aspects of French fries is presented using state-of-the-art equipment. A combination of sensory analysis, TextureAnalyser,andConfocalScanning Laser Microscopy was used to study crispness of French fries independent of moisture content and doneness. In this way a higher frying temperature was shown to increase crispness. Prolonged pre-drying in hot air caused blister formation, which was similar to the skin observed with superheated steam. Odour active compounds of French fries were identified using GC-MS and GC-Olfactometry. Subsequently, the release of some of these compounds was followed in real time with MS-Nose using assessors and a mouth model system. It was shown that increasing the frying time, adding salt, and also skin formation affect flavour release. Most of the identified flavour compounds originated either from theMaillardreaction or from lipid degradation.Acrylamideis formed in theMaillardreaction as well.Multiresponsemodelling ofacrylamideformation in a glucose-asparaginereaction system showed thatacrylamideis an intermediate rather than an end product. Early lipid oxidation was studied at frying conditions by following the decrease of the antiradical power. Frying French fries was found to slow down the decrease of antiradical power, suggesting that compounds withantioxidativeproperties migrate from the product to the oil.In conclusion, the work described in this thesis has contributed to insights into physicochemical processes that occur in French fries on micro-scale, and how process conditions influence the product quality.

Food processors face increasing demands to improve their raw material yield efficiency. To really understand the raw material yield efficiency of food processing, mass losses need to be divided in wanted (desired) and unwanted ones. The basic approach to increase the raw material yield efficiency is to mini mise unwanted mass losses at source. Wasting raw materials should be avoided, because the largest proportion of the overall business costs is associated with the purchase of raw materials. This wasting will therefore put the company's pro fit under pressure. From a sustainability point of view, it is also important to transform raw materials efficiently into final products. There is an increasing interest to find appropriate measures to track the yield efficiency of food processes in order to guide organisational actions to reduce unwanted mass losses. Many unwanted mass losses are hidden and need to be explored to make the management fully aware of these losses and the corresponding economic impact. Poor practice, poor maintenance, outdated equipment and technologies must first be visualised before they can be corrected.A new dimensionless number (called Yield Index) was developed to measure the true raw material yield efficiency of a transformation process. To measure the Yield Index, a food processor should measure the actual production yield and compare this with the maximum production yield. However, for many food processors the maximum production yield is unknown because of the lack of knowledge. With a systematic approach and considerable research effort it is possible to build a model that can predict the maximum production yield with respect to raw material parameters, additions and final product specifications. This model can then be used to pinpoint unwanted mass losses in the production process. The thesis describes in a comprehensive way the development of two models to estimate the maximum production yield of French-fries production and poultry-processing (transforming broilers chickens into meat parts). These models were used in practice, to pinpoint unwanted mass losses during processing and based on this knowledge, both processes were improved significantly. Based on these two practical case studies a general system approach was developed to implement production yield analysis (PY A) in other types of food processes.It was found that often a significant lack of knowledge in the true efficiency of the production processes exists. A PY A makes it possible to calculate the true yield efficiency of the process. This information is needed to convince management about the necessity to reduce unwanted losses. Not only to improve economics but also to improve aspects of modern sustainable food processing.

Een nieuw productieproces voor het voorbakken van frites dat begon als een veelbelovende innovatieve procesroute biedt onvoldoende (economisch) perspectief. Wel heeft het project veel inzicht opgeleverd in de processen die op microschaal in frites optreden en in hoe de procesomstandigheden de productkwalteit beïnvloeden. Deze nieuwe kennis kan worden gebruikt bij het ontwikkelen van innovatieve producten met bijvoorbeeld verbeterde krokantheid

Food processors face increasing demands to improve their raw material yield efficiency. To really understand the raw material yield efficiency of food processing, mass losses need to be divided in wanted (desired) and unwanted ones. The basic approach to increase the raw material yield efficiency is to mini mise unwanted mass losses at source. Wasting raw materials should be avoided, because the largest proportion of the overall business costs is associated with the purchase of raw materials. This wasting will therefore put the company's pro fit under pressure. From a sustainability point of view, it is also important to transform raw materials efficiently into final products. There is an increasing interest to find appropriate measures to track the yield efficiency of food processes in order to guide organisational actions to reduce unwanted mass losses. Many unwanted mass losses are hidden and need to be explored to make the management fully aware of these losses and the corresponding economic impact. Poor practice, poor maintenance, outdated equipment and technologies must first be visualised before they can be corrected.A new dimensionless number (called Yield Index) was developed to measure the true raw material yield efficiency of a transformation process. To measure the Yield Index, a food processor should measure the actual production yield and compare this with the maximum production yield. However, for many food processors the maximum production yield is unknown because of the lack of knowledge. With a systematic approach and considerable research effort it is possible to build a model that can predict the maximum production yield with respect to raw material parameters, additions and final product specifications. This model can then be used to pinpoint unwanted mass losses in the production process. The thesis describes in a comprehensive way the development of two models to estimate the maximum production yield of French-fries production and poultry-processing (transforming broilers chickens into meat parts). These models were used in practice, to pinpoint unwanted mass losses during processing and based on this knowledge, both processes were improved significantly. Based on these two practical case studies a general system approach was developed to implement production yield analysis (PY A) in other types of food processes.It was found that often a significant lack of knowledge in the true efficiency of the production processes exists. A PY A makes it possible to calculate the true yield efficiency of the process. This information is needed to convince management about the necessity to reduce unwanted losses. Not only to improve economics but also to improve aspects of modern sustainable food processing.

Resultaten van onderzoek naar optimale ruggen: 1. Grotere ruggen beperken de hoeveelheid groen en de netto opbrengst van de nieuwe (friet)rassen is er niet minder. 2. Rijenafstand van 90 cm biedt de beste mogelijkheid voor grote ruggen. 3. Bij rijenafstand van 75 cm hebben plateauruggen de voorkeur

Een netto ruggrootte van 600-700 vierkante centimeter dwarsdoorsnede geeft voor Bintje op 75 centimeter rijenafstand de beste groei, hoogste opbrengst en vrijwel geen groen