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This study uncovered the impacts of microwave (MW) treatments compared to conventional pasteurization (TP) on the quality of functional citrus–maqui beverages, with added sucrose or stevia. The influence of these thermal treatments on the microbiological burden and phytochemical composition was determined by processing under two MW power levels (600 W and 800 W) and TP at 85 °C for 15 s for 60 days at room temperature (20 °C). The results indicated that, beyond the microbiological quality achieved in the juices treated by both MW and TP technology, there were no differences among the treatments regarding the stability of vitamin C, anthocyanin, and flavanone concentrations. However, anthocyanins were more stable in those beverages with sucrose added, rendering a better red color. Besides, all treatments ensured microbiological stability throughout the entire storage time. In conclusion, MW treatment could be considered as an alternative to TP, which ensures microbial safety, protecting functional compounds associated with health effects.

Microbial cells respond to sub-lethal stresses with several physiological changes to increase their chance of survival. These changes are of high relevance when combined treatments (hurdle technology) are applied during food production, as the cells surviving the first hurdle may have greater resistance to subsequent treatments than untreated cells. In this study, we analyzed if Salmonella develops increased resistance to thermal treatments after the application of an acid shock. We compared the heat resistance of acid-shocked (pH 4.5 achieved with citric acid) Salmonella cells with that of cells maintained at pH 7 (control cells). Thermal treatments were performed between 57.5 and 65°C. We observed a differential response between the two strains studied. Acid-shocked cells of Salmonella Senftenberg exhibited reduced heat resistance, e.g., for a treatment at 60.0°C and pH 7.0 the time required to reduce the population by 3 log cycles was lowered from 10.75 to 1.98min with respect to control cells. Salmonella Enteritidis showed a different response, with acid-shocked cells having similar resistance than untreated cells (the time required to reduce 3 log cycles at 60.0°C and pH 7.0 was 0.30min for control and 0.31min for acid-shock cells). Based on results by differential plating (with or without adding the maximum non-inhibitory concentration of NaCl to the recovery medium), we hypothesize that the differential response between strains can be associated to sub-lethal damage to the cell membrane of S. Senftenberg caused by the acid shock. These results provide evidence that different strains of the same species can respond differently to an acid shock and highlight the relevance of cross-resistances for microbial risk assessment.

Broccoli (Brassica oleracea var. italica) stalks account for up to 35% of the broccoli harvest remains with the concomitant generation of unused waste that needs recovery to contribute to the sustainability of the system. However, due to its phytochemical composition, rich in bioactive (poly)phenols and glucosinolates, as well as other nutrients, the development of valorization alternatives as a source of functional ingredients must be considered. In this situation, the present work aims to develop/obtain a new ingredient rich in bioactive compounds from broccoli, stabilizing them and reducing their degradation to further guarantee a high bioaccessibility, which has also been studied. The phytochemical profile of lyophilized and thermally treated (low-temperature and descending gradient temperature treatments), together with the digested materials (simulated static in vitro digestion) were analysed by HPLC-PDA-ESI-MSn and UHPLC-3Q-MS/MS. Broccoli stalks and co-products were featured by containing phenolic compounds (mainly hydroxycinnamic acid derivatives and glycosylated flavonols) and glucosinolates. The highest content of organosulfur compounds corresponding to the cores of the broccoli stalks treated by applying a drying descendant temperature gradient (aliphatic 18.05 g/kg dw and indolic 1.61 g/kg dw, on average, while the breakdown products were more abundant in the bark ongoing low temperature drying 11.29 g/kg dw, on average). On the other hand, for phenolics, feruloylquinic, and sinapoylquinic acid derivatives of complete broccoli stalk and bark, were more abundant when applying low-temperature drying (14.48 and 28.22 g/kg dw, on average, respectively), while higher concentrations were found in the core treated with decreasing temperature gradients (9.99 and 26.26 g/kg dw, on average, respectively). When analysing the bioaccessibility of these compounds, it was found that low-temperature stabilization of the core samples provided the material with the highest content of bioactives including antioxidant phenolics (13.6 and 33.9 g/kg dw of feruloylquinic and sinapoylquinic acids, on average, respectively) and sulforaphane (4.1 g/kg dw, on average). These processing options enabled us to obtain a new product or ingredient rich in bioactive and bioaccessible compounds based on broccoli stalks with the potential for antioxidant and anti-inflammatory capacities of interest.

Cooking vegetables in microwave bags has become a popular cooking method. However, information about the effect of this cooking method on the phytochemical content and microbiological safety of vegetables is limited. The aim of this work was to study the effect of microwave-bag cooking vs. conventional microwaving, on the phytochemical content and microbiological quality of broccoli florets. The influence of cooking time on these quality parameters was also evaluated. Broccoli florets were placed into microwaveable bags and cooked in a microwave oven for 3 and 5 min. The product cooked under the same conditions, without using bag, was used as a control. Samples were taken before and after cooking. Glucosinolate (GSL) content and hydroxycinnamic acid (HCAs) content were analyzed by HPLC-DAD-ESI-MSn. To evaluate the microbiological quality, aerobic mesophilic bacteria, aerobic psychrotrophic bacteria and moulds and yeasts were analyzed. Microwaving broccoli for 3 min showed no significant losses of total GSL content, regardless of cooking method. For 5 min cooking, microwave-bag-cooked broccoli showed higher total GSL content (32.3 ± 2.6 μmol g−1) than conventional microwaved broccoli (26.4 ± 1.3 μmol g−1). HACs content declined by 40% compared to fresh broccoli, in all conditions (from 2.52 ± 0.08 μmol g−1 to 1.52 ± 0.31 μmol g−1). Microwave-bag cooking showed a greater reduction in mesophilic and psychrotrophic bacteria than conventional microwaving. The counts of moulds and yeasts were

The effects of high hydrostatic pressure (HHP) compared to thermal pasteurization (TP) were studied in healthy citrus-maqui beverages. The impact of the processing technologies on the microbiological and phytochemical profile was assessed by applying two HHP treatments at 450 and 600 MPa for 180 s and TP at 85 °C for 15 s. The shelf life under refrigeration (4 °C) and room temperature (20 °C) was monitored for 90 days. All treatments ensured microbiological stability at both storage temperatures. Aside from that, the physicochemical parameters were not significantly different after processing or throughout the storage period. Regarding color parameters, an increase in the reddish coloration was observed during storage for those beverages treated by HHP. In general, phenolic compounds were little affected by the processing technique, even when treatment under HHP was more stable than by TP during storage. On the other hand, vitamin C showed great degradation after processing under any condition. It can be concluded that HHP is an effective alternative to thermal treatments, achieving effective microbial inactivation and extending the shelf life of the juices by contributing to a better preservation of color and bioactive compounds.

Natural antimicrobials are an alternative to the use of chemically synthesized preservatives and other technological treatments. They have the advantage of not being rejected by consumers because of their natural origin. However, prior to their usage at a food factory scale, their precise effects on microorganisms have to be known. Nisin, a bacteriocin, and carvacrol and thymol, phenolic compounds present in the essential oil fraction of Oreganum and Thymus plants, have been shown to inhibit growth of different bacteria. This research was conducted to show the effect of a thermal treatment, applied previously, on the growth of B. megaterium cells in a culture medium with and without nisin, carvacrol and thymol. It has been shown that a thermal treatment able to kill 90 % of the spore population of B. megaterium had little effect on the growth of the survivors in nutrient broth at 30 °C. Nisin, in a concentration of 0.05 mM, did not affect greatly the growth of unheated B. megaterium. When the same concentration of nisin was applied to the survivors of the heat treatment, lag phase was further increased and growth rate decreased. Thymol, applied at a concentration of 0.6 mM, increased the lag phase duration almost three times, although it did not change the growth rate. Although carvacrol, at the same concentration (0.6 mM), did reduce the growth rate to half its original value, it did not increase the lag phase duration significantly (only twice), resulting in a quite similar growth curve. The combination of thymol and carvacrol at these high doses (0.6 mM) resulted in a further increase of the lag phase and significant decrease of the growth rate. When carvacrol and/or thymol were combined with a previous thermal treatment (able to kill 90 % of the population), the growth of the survivors was inhibited for at least seven days. Therefore a combination of moderate conditions could be effective to control spoilage by sporeforming bacteria.

Minimal processing implementation greatly depends on a detailed knowledge of the effects of preservation factors and their combinations on the spoilage and foodborne pathogenic microorganisms. The effectiveness of mild preservation conditions will become increasingly dependent on a more stochastic approach linking microbial physiological factors with product preservation factors. In this study, the validity of frequency distributions to efficiently describe the inactivation and growth of Bacillus cereus in the presence of natural antimicrobials (essential oils) has been studied. For this purpose, vegetative cells were exposed to 0.6 mM of thymol or cymene, obtaining survival curves that were best described by the distribution of Weibull, since a tailing effect was observed. B. cereus was also exposed in a growth medium to a low concentration (0.1 mM) of both antimicrobials, separately or combined, and the lag times obtained were fitted to a normal distribution, which allowed a description of dispersion of the start of growth. This allowed a more efficient evaluation of the experimental data to establish safe processing conditions according to accurate parameters and their implementation in risk assessment.

In this paper, a novel technique to achieve precise temperatures in food sterilization has been proposed. An accurate temperature profile is needed in order to reach a commitment between the total removal of pathogens inside the product and the preservation of nutritional and organoleptic characteristics. The minimal variation of the target temperature in the sample by means of a monitoring and control software platform, allowing temperature stabilization over 100 °C, is the main goal of this work. A cylindrical microwave oven, under pressure conditions and continuous control of the microwave supply power as function of the final temperature inside the sample, has been designed and developed with conditions of single-mode resonance. The uniform heating in the product is achieved by means of sample movement and the self-regulated power control using the measured temperature. Finally, for testing the sterilization of food with this technology, specific biological validation based on Bacillus cereus as a biosensor of heat inactivation has been incorporated as a distribution along the sample in the experimental process to measure the colony-forming units (CFUs) for different food samples (laboratory medium, soup, or fish-based animal by-products). The obtained results allow the validation of this new technology for food sterilization with precise control of the microwave system to ensure the uniform elimination of pathogens using high temperatures.

Salmonella Senftenberg is a pathogen agent causative of foodborne disease and it is considered the most heat-resistant serovar within this genus. Food industries use heat treatment and chemical antimicrobials in order to eliminate this microorganism in food, but consumers prefer natural antimicrobials as essential oils and their components. This study evaluates the combined effect of thermal treatments and different concentrations of D-limonene nanoemulsion on the inactivation of Salmonella (S.) Senftenberg. The results showed an important effect of the nanoemulsified D-limonene on the heat resistance of S. Senftenberg. The δ50 °C value was reduced by 85%, 96% and 98% when 0.1, 0.5 and 1 mM of nanoemulsified D-limonene was added to the heating medium. The effect was kept along all the heating temperatures researched and the shape of the survival curves did not change with the addition of the antimicrobial. The results obtained in this research could be very useful for food industries for optimizing or improving heat treatments applied to food.

Different inactivation kinetics data have been used to predict the number of survivors exposed to a heat treatment and, in consequence, to design thermal processes for the food industry. In this work, spores of an acidophilic strain of Bacillus subtilis were heated under isothermal and non-isothermal conditions. Experimental results obtained after isothermal treatments were analysed using the classical two-step linear regression procedure and a one-step non-linear regression method. Data obtained after non-isothermal treatments were analysed using a one-step, non-linear procedure. Kinetic parameters obtained from isothermal heating were close, either using the two-step linear regression ( D 100=6.5 min) or the one-step non-linear regression ( D 100=6.3 min), although the second method gave smaller 95% confidence intervals. The z values derived from non-isothermal heating were higher than those obtained in isothermal conditions ( z=9.3 °C for non-isothermal heating at 1 °C/min versus z=7.7 °C for isothermal heating one step non-linear regression). Results were validated with experimental data obtained after different heat treatments, consisting of a phase of temperature increase at a fixed rate, followed by a holding phase. Non-isothermal methods predicted accurately the number of survivors after the heating ramp, while isothermal methods were more accurate for the holding phase of the treatment. When a temperature profile of a typical heat treatment process applied in the food industry was simulated, all predictions were on the safe side. [ABSTRACT FROM AUTHOR]

A new microbiological predictive model was developed, relating pH, NaCl concentration and temperature (T) with the decimal reduction coefficient D as dependent variable, using data previously reported by [1]. The model was obtained by multiple linear regression using only three predictor variables (T2, pH2 and NaCl), easily computed from the basic variables pH, NaCl concentration and temperature (T). The fitted model is robust, stable and satisfies all the basic hypotheses of the regression models. It also provides simplicity when compared with previously published models based on multiple linear regression tools. [ABSTRACT FROM AUTHOR]

Heat resistance of microorganisms can be affected by different influencing factors. Although the effect of heating rates has been scarcely explored by the scientific community, recent researches have unraveled its important effect on the thermal resistance of different species of vegetative bacteria. Typically heating rates described in the literature ranged from 1 to 20ºC/min but the impact of much higher heating rates is unclear. The aim of this research was to explore the effect of different heating rates, such as those currently achieved in the heat exchangers used in the food industry, on the heat resistance of Escherichia coli. A pilot plant tubular heat exchanger and a thermoresistometer Mastia were used for this purpose. Results showed that fast heating rates had a deep impact on the thermal resistance of E. coli. Heating rates between 20 and 50ºC/min were achieved in the heat exchanger, which were much slower than those around 20ºC/s achieved in the thermoresistometer. In all cases, these high heating rates led to higher inactivation than expected: in the heat exchanger, for all the experiments performed, when the observed inactivation had reached about seven log cycles, the predictions estimates about 1 log cycle of inactivation; in the thermoresistometer these differences between observed and predicted values were even more than ten times higher, from 4.07 log cycles observed to 0.34 predicted at a flow rate of 70 mL/min and a maximum heating rate of 14.7ºC/s. A quantification of the impact of the heating rates on the level of inactivation achieved was established. These results point out the important effect that the heating rate has on the thermal resistance of E. coli, with high heating rates resulting in an additional sensitization to heat and therefore an effective food safety strategy in terms of food processing.