High pressure–treated sorghum flour as a functional ingredient in the production of sorghum bread

In this study, the application of high-pressure processing of sorghum batters was investigated in order to evaluate the potential of pressure-treated sorghum as a gluten replacement in the production of sorghum breads. For this purpose, sorghum batters were treated at pressures from 200 to 600 MPa at 20 °C, and the microstructure was investigated using scanning electron microscopy. Furthermore, the rheological properties of the control and pressure-treated batters were determined. The results revealed weakening of the batter structure at pressures ≤300 MPa. Addition of a blocker of free thiol groups indicated that protein depolymerization played a role in this strength decrease. At pressures >300 MPa, the batter consistency increased, mainly due to pressure-induced gelatinization of starch. Furthermore, freeze-dried sorghum batters treated at 200 MPa (weakest batter) and at 600 MPa (strongest batter) were added to a sorghum bread recipe, replacing 2 and 10% of untreated sorghum flour. The results showed a delayed staling for breads containing 2% of sorghum treated at 600 MPa. However, adding 10% resulted in a low specific volume and poor bread quality. The quality of breads containing different amounts of sorghum treated at 200 MPa was not significantly different from the control bread.     

Isomerisation kinetics and antioxidant activities of β-carotene in carrots undergoing different drying techniques and conditions

Carrots are known as a natural source of β-carotene. In order to preserve the latter, carrots must generally be processed, and drying is one of the most common methods for processing carrots. During drying β-carotene in carrots suffers degradation. β-Carotene degradation is generally due to thermal degradation and isomerisation. In this work, the drying kinetics as well as the isomerisation kinetics and antioxidant activities of β-carotene in carrots undergoing hot air drying, vacuum drying and low-pressure superheated steam drying (LPSSD) were determined within the temperature range of 60–80 °C and, in the case of vacuum drying and LPSSD, at a pressure of 7 kPa. A high performance liquid chromatography (HPLC) method was used to determine the β-carotene contents and its isomerisation kinetics, while the antioxidant activities of various combinations of all-trans- and cis-forms of β-carotene in carrots were evaluated using the Trolox equivalent antioxidant capacity (TEAC) assay.     

High pressure–low temperature processing of foods: impact on cell membranes,texture, color and visual appearance of potato tissue

To design and optimize high pressure processes at low temperatures, a quantification of the effects of different processing steps on the food structure is required. Beside pressure-shift freezing, the processes of freezing to ice III and ice V, as well as storage at −27 °C and 250 MPa up to 24 h (metastable liquid state of water) of potato samples were examined. Analyses of the structural changes of the plant tissue included impedance measurements, texture analysis, color measurements and the evaluation of the optical appearance. Storage at subzero temperatures without phase transitions resulted in low membrane damage; however, cell lysis was triggered. Freezing to ice III resulted in the lowest damaging effect on the tissue compared to the other phase transition processes investigated. Samples frozen to ice V and pressure-shift frozen were more deteriorated compared to those frozen to ice III. However, considerable improvements compared to conventional freezing were found. The direction of solid–solid phase transitions (phase transition of ice I to ice III or phase transition of ice III to ice I) influenced the result of high pressure–low temperature processing significantly.Industrial relevanceIt was previously shown that pressure supported phase transitions of ice I like pressure shift freezing are able to preserve the fragile stucture of biological samples like food better than conventional freezing. The present study extends the knowledge of pressure supported phase transitions to a higher pressure domain with the participation of other ice modifications. The authors demonstrate the influences of high pressure phase transitions of water on plant tissue material depending on the processing conditions. The study opens the way to new industrial processing concepts based on high pressure low temperature applications.     

The effect of pressure on the kinetics of polyphenolics degradation – Implications to hyperbaric storage using Epigallocatechin-gallate as a model

Understanding reaction kinetics at elevated pressures is of importance for the development of pressure-based technologies and especially for hyperbaric storage (HS), a potential alternative for the energy-consuming refrigeration. The effect of pressure on degradation kinetics of a polyphenol, Epigallocatechin-gallate (EGCG), was explored at pressures up to 200 MPa (HS levels) for several hours, with and without fructose. In a baroresistant buffer, pressure enhanced EGCG degradation, due to a negative activation volume, while in phosphate buffer the pH decreased (as is also expected to occur in many foods) resulting in a superposition of accelerating and protective effects. A previously undescribed protective, pressure-level dependent, effect of fructose was identified. Novel in situ spectroscopy and HPLC analysis revealed that in addition to the effect on EGCG degradation rate, pressure also modifies the ratios between the numerous degradation products, likely due to a varying effect on the different steps involved in the degradation pathway.Industrial relevanceThe effect of pressure on reaction kinetics in food systems can be of great importance in processing conditions combining thermal and high pressure, and critical for the emerging concept of hyperbaric storage, where the food is exposed to high pressures for long duration of time, allowing a plethora of reactions to take place, all varyingly affected by pressure. Yet the effects of pressure on kinetics are often overlooked. Polyphenolic compounds are a large group of molecules responsible for both sensorial and health-promoting functionality in plant-based foods. Those compounds are known to undergo degradation by several mechanisms during processing and storage and their successful conservation is often considered of significant industrial importance. The presented work provides fundamental information regarding the effects of pressure on the kinetics of EGCG (Epigallocatechin-gallate) degradation, as a model for relatively unstable, polyphenolic compound, (taking into account pressure-induced pH shifts, and the presence of co-solutes). EGCG is also of specific importance in many products where it naturally occurs (green tea drinks etc.) and where it is externally added as a valuable supplement.     

Valorization of olive oil solid waste using high pressure–high temperature reactor

The production of olive oil leads to considerable amounts of solid wastes rich in bioactive compounds with antioxidant properties, which have been partly used as inefficient polluting heating fuels for many years. This work was aimed to study the effect of extraction time and temperature on phenolics recovery from olive pomace. For this propose, different tests were performed, varying time from 15 to 120 min and temperature from 100 to 180 °C, using a high pressure–high temperature agitated reactor under a modified atmosphere. Total polyphenols, o-diphenols and total flavonoids were quantified. Maximum total polyphenols yield (45.2 mg_CAE/g_DP) was achieved at 180 °C and 90 min. HPLC analysis showed that oleuropein (2433 mg/100 g_DP) and tyrosol (485 mg/100 g_DP) were predominant phenolics in the extracts. Methanolic extracts, after additional purification processes, can be used in food, cosmetic and pharmaceutical industries. Solid residues, after phenolics extraction, are considered to have little environmental impact.     

High pressure–low temperature processing of beef: Effects on survival of internalized E. coli O157:H7 and quality characteristics

High pressure–low temperature (HPLT) processing was investigated to achieve Escherichia coli O157:H7 inactivation in non-intact, whole muscle beef while maintaining acceptable quality characteristics. Beef semitendinosus was internally inoculated with a four strain E. coli O157:H7 cocktail and frozen to − 35 °C, then subjected to 551 MPa for 4 min (HPLT). Compared to frozen, untreated control (F), HPLT reduced microbial population by 1.7 log colony forming units (CFU)/g on selective media and 1.4 log on non-selective media. High pressure without freezing (551 MPa/4 min/3 °C) increased pH and lightness while decreasing redness, cook yield, tenderness, and protein solubility. Aside from a 4% decrease in cook yield, HPLT, had no significant effects on quality parameters. It was demonstrated that HPLT treatment reduces internalized E. coli O157:H7 with minimal effect on quality factors, meaning it may have a potential role in reducing the risk associated with non-intact red meat.Industrial relevanceIn the current work, high pressure (551 MPa, 4 min) was applied to beef semitendinosus while it was at subfreezing temperatures (<− 30 °C). Most studies utilizing this high pressure–low temperature (HPLT) process employ subzero capable thermostatic high pressure equipment, which currently has no commercial equivalent. Successful HPLT runs were completed in this study using more conventional temperature control (1–3 °C) on pilot scale (20 L) high pressure processing equipment. The process yielded E. coli O157:H7 reductions of 1.4–1.7 log colony forming units (CFU)/g, which, while lower than conventional high pressure processing (HPP), may be sufficient to eliminate O157 populations typical of non-intact, whole muscle beef. Various quality factors, including color, purge losses and cooked tenderness, were unaffected by HPLT, while an equivalent HPP process at nonfreezing temperatures (551 MPa, 3 °C) induced color change (loss of redness), increased cook losses and decreased cooked tenderness compared to the control and HPLT beef. Producers of non-intact, whole muscle (blade tenderized or brine injected) meat, especially those that ship and sell frozen products, may look to HPLT processes to improve food safety.     

Growth kinetics of Salmonella in mixed cultures incubated in Rappaport–Vassiliadis medium

Reproducible numbers ofSalmonella enteritidis,Klebsiella pneumoniaeandStaphylococcus aureuswere mixed in various proportions and their growth in Rappaport–Vassiliadis enrichment broth quantified at 4 h intervals over a 24-h period. No limit in the ability of the RV medium to detectSalmonellain the presence of low or high numbers of competing organisms could be observed. After incubation salmonellae were found in all mixtures regardless of the composition of the mixtures.     

Relationship between the kinetics of β-carotene degradation and formation of norisoprenoids in the storage of dried sweet potato chips

The effects of storage temperature (10; 20; 30; 40 °C), water activity (0.13; 0.30; 0.51; 0.76) and oxygen level (0%; 2.5%; 10%; 21%) on the degradation of carotenoids and formation of volatile compounds during storage of dried sweet potato chips were evaluated. A kinetic model was developed for degradation of trans-β-carotene and it showed that breakdown followed first order kinetics with an activation energy of 64.2 kJ mol⁻¹. The difference between experimental data under laboratory or field conditions fitted and data predicted by the model was less than 10% for trans-β-carotene, or for total carotenoids. The formation of the volatile compounds, β-ionone; 5,6-epoxy-β-ionone; dihydroactinidiolide; β-cyclocitral, was measured by SPME-GC-MS and was clearly related to the degradation of trans-β-carotene. It is also suggested that carotenoid degradation in dried sweet potato was by autoxidation because of the trend in β-carotene degradation rate in relation to water activity or oxygen level.     

High pressure homogenization increases the in vitro bioaccessibility of α- and β-carotene in carrot emulsions but not of lycopene in tomato emulsions

Abstract: The correlation between food microstructure and in vitro bioaccessibility of carotenes was evaluated for tomato and carrot emulsions (5% olive oil) subjected to high pressure homogenization (HPH) at varying degrees of intensity. The aim was to investigate whether additional mechanical disruption of the food matrix could be utilized to further increase the carotene bioaccessibility of an already pre‐processed material. The carotene bioaccessibility of the samples was measured after simulated in vitro digestion, carotene release to the oil phase was estimated by Confocal Raman spectroscopy and, to measure active uptake of carotenes, Caco‐2 cells were incubated with the digesta of selected samples. HPH did not notably affect the retention of carotenes or ascorbic acid but significantly increased both the release and micellar incorporation of α‐ and β‐carotene in carrot emulsions 1.5‐ to 1.6‐fold. On the other hand, in vitro bioaccessibility of lycopene from tomato was not increased by HPH under any of the conditions investigated. Instead, the results suggested that lycopene bioaccessibility was limited by a combination of the low solubility of lycopene in dietary lipids and entrapment in the cellular network. Carotene uptake by Caco‐2 cells appeared to be mainly dependent upon the carotene concentration of the digesta, but cis‐trans isomerization had a significant impact on the micellarization efficiency of carotenes. We therefore conclude that HPH is an interesting option for increasing the bioaccessibility of carotenes from fruits and vegetables while maintaining a high nutrient content, but that the results will depend on both food source and type of carotene. Practical Application: A better understanding of the correlation between the processing of fruits and vegetables, microstructure and nutrient bioaccessibility can be directly applied in the production of food products with an increased nutritional value.     

Acrylamide and 5-hydroxymethylfurfural formation during baking of biscuits: NaCl and temperature–time profile effects and kinetics

The present study aimed to investigate the effect of recipe and temperature–time on the formation of acrylamide and 5-hydroxymethylfurfural (HMF) during biscuit baking. Baking experiments were performed with biscuits of two different recipes, with and without NaCl, at 180 °C, 190 °C and 200 °C. Acrylamide and HMF reached highest concentrations at 200 °C for both recipes. The presence of NaCl in the biscuit formulation lowered acrylamide concentrations at 180 °C and 190 °C but not at 200 °C, and led to higher concentrations of HMF at all the tested temperatures. Sucrose hydrolysis was a key step in acrylamide and HMF formation during biscuit baking, even though a significant amount of acrylamide already had formed before the onset of sucrose hydrolysis. A lag phase was observed before sucrose hydrolysis occurred, which might depend on the melting of crystalline sucrose occurring at approximately 180 °C.A mathematical model based on the chemical reaction pathways was developed for the recipe with NaCl baked at 200 °C. The model described the chemical evolution during the last part of biscuit baking, and accurately predicted acrylamide and HMF content at the end of baking. The model showed the significant contribution of the reducing sugars to the formation of both acrylamide and HMF. The model could not be extended to the entire baking period because it was not possible to incorporate the lag phase observed before sucrose hydrolysis. The results reported in this study confirm that the kinetics of acrylamide and HMF formation in real food and dry systems may depend on the physical state of their precursors.     

Batch drying of banana pieces — effect of stepwise change in drying air temperature on drying kinetics and product colour

Slices of banana were dried in a two-stage heat pump dryer capable of producing stepwise control of the inlet drying air temperature while keeping absolute humidity constant. Two stepwise air temperature profiles were tested. The incremental temperature step change in temperature of the drying air about the mean air temperature of 30°C was 5°C. The total drying time for each temperature-time profile was 240 min. The drying kinetics and temporal colour change of the products dried under these stepwise variation of the inlet air temperature were measured and compared with constant air temperature drying. The effects of the profile starting temperature and cycle time on both drying kinetics and product quality were also studied. It was observed that by employing stepwise-varying drying air temperature with appropriate starting temperature and cycle time, it was possible to reduce significantly the drying time to reach the desired moisture content with improved product colour.     

Characterization of high pressure jet–induced fat-protein complexation

High-pressure-jet (HPJ) processing of various dairy systems has been shown to disrupt fat droplets and casein micelles and cause a strong association between fat and casein proteins. The present work seeks to better describe this association between fat and casein using a model milk formulated from confectionary coating fat (3.6% wt/wt), micellar casein (3.4% wt/wt), and water (93% wt/wt), which was then pasteurized, homogenized, and then either HPJ-treated (400 MPa) or not (non-HPJ-treated, control). Upon ultracentrifugation, fat in the non-HPJ-treated model milk creamed due to its low density. In the HPJ-treated model milk, fat precipitated with protein into a thick bottom layer upon ultracentrifugation, reflecting a strong association between protein and fat. Differential scanning calorimetry (DSC) and time-domain nuclear magnetic resonance of the non-HPJ-treated model milk revealed fat in 2 physical states: (1) fat that is physically similar to the bulk fat and (2) fat that was in smaller droplets (i.e., homogenized) and crystallized at a lower temperature than the bulk fat. In contrast, DSC of HPJ-treated model milks supported the presence of fat in 3 states: (1) fat that is physically similar to the bulk fat, (2) fat in small droplets that required substantial supercooling beyond the non-HPJ-treated model milk to crystallize, and (3) fat in such small domains that it crystallizes in a less stable polymorphic form than the non-HPJ-treated model milk (or does not crystallize at all). The state of fat within the HPJ-treated model milk changed minimally with acidification, indicating that the association is not dependent on the charge on the casein. Cryogenic transmission electron microscopy (Cryo-TEM) of the non-HPJ-treated model milk revealed uniform casein micelles, which likely adsorbed to the surface of fat globules post-homogenization. In contrast, Cryo-TEM of the HPJ-treated model milk revealed a porous protein aggregate that likely had dispersed fat throughout. Together, these results suggest that HPJ treatment causes fat to be entrapped by casein proteins in very small domains.     

High pressure processing of fresh meat — Is it worth it?

When subjected to high pressures at ambient temperatures, the shelf life of fresh meat is increased; however the meat takes on a cooked appearance as the actomyosin denatures at about 200 MPa and the myoglobin denatures and/or co-precipitates with other proteins at about 400 MPa. In addition, at pressures of 400 MPa and above the unsaturated lipids in the meat become more susceptible to oxidation, probably due to the release of iron from complexes present in meat (haemosiderin and ferritin?) and/or changes in the lipid membrane. Thus, even if legislation allowed it, it is unlikely that many consumers would be prepared to buy such meat. However if pre-rigor meat is subjected to pressures of about 100–150 MPa, below those necessary to cause colour changes, it becomes significantly more tender than its untreated counterpart and this may now be a commercially viable process, given the decreasing cost of high pressure rigs. When treated at 100–200 MPa while the temperature is raised from ambient to around 60 °C post-rigor meat also yields a tender product and this may also be a commercially attractive process to parts of the food industry, for example those involved in catering.     

Effect of temperature and substrate on Pef inactivation of Lactobacillus plantarum in an orange juice–milk beverage

The inactivation kinetics of Lactobacillus plantarum in an orange juice–milk beverage treated by Pulsed Electric Fields (PEF) were studied. Experimental data were fitted to Bigelow and Hülsheger kinetic models and Weibull frequency distribution function. Results indicate that both Hülsheger model and Weibull function fit well the experimental data being Accuracy factor values (Af) closer to 1 and Mean Square Error (MSE) closer to 0. The parameter of the Weibull model can be considered as a kinetic indicator as it expresses the microorganism's resistance to treatment by electric pulses. An increase in temperature favoured the inactivation of L. plantarum by PEF as reflected by a decreased in value. Under the same conditions to those studied by other authors we reached less inactivation of L. plantarum in the beverage used in this study than in substrates with a simpler composition.     

Quality of shelf-stable low-acid vegetables processed using pressure–ohmic–thermal sterilization

Pressure ohmic thermal sterilization (POTS) involves ohmic heating of foods by applying an electric field under elevated pressure. Experiments were conducted using a custom made POTS apparatus using carrot as the model food. The samples were processed at a target temperature of 105 °C at 600 MPa and treated for 0, 1, 3, and 5 min by regulating the electric field (30 V/cm). POTS treated carrot sample quality attributes were compared against those processed using ohmic heating (0.12 MPa, 30 V/cm, 105 °C) and pressure-assisted thermal processing (PATP; 600 MPa, 0 V/cm, 105 °C). Within the experimental conditions of the study, the thermal come-up time of the POTS, Ohmic and PATP were 1.45 min, 3.58 min and 6.84 min respectively. PATP come-up time also included the pre-heating time (≈6 min). Results indicate the POTS samples had the least textural damage due to minimal thermal exposure. POTS samples had higher crunchiness index (CI) of 0.76 compared to PATP (CI = 0.57) and ohmic heated (CI = 0.62) carrots. All the technologies investigated had minimal impact on product color. This study demonstrates the potential to produce high quality shelf stable low-acid vegetable products using POTS.     

Effects of high pressure treatment (100–200 MPa) at low temperature on turbot (Scophthalmus maximus) muscle

Turbot fillets were subjected to high pressure treatments at 100, 140, 180 and 200 MPa for 15 and 30 min at 4°C. The influence of such treatments on the lipid and protein stability and on color was studied. It appeared that color, protein stability and lipid oxidation phenomena were influenced both by the pressure level and pressure holding time. The oxidative stability of lipids was particularly affected from 180 MPa as measured by the thiobarbituric acid number. Differential scanning calorimetry showed a full denaturation of myosin at 200 MPa and the appearance of a new structure from the treatment at 100 MPa for 30 min.     

Apparent voluminosity of casein micelles in the temperature range 35–70 °C

Casein micelles are basic units of dairy matrices that can be aggregated by reducing their electrostatic repulsion or by surface modifications. Studying casein micelles in terms of a colloidal suspension demands of a preferably complete physico-chemical characterisation. Process control in dairy technology as well as mechanistic models that explain the formation and structure of dairy products build on the specific hydration of the casein micelles. The effect of the temperature on the voluminosity of native casein micelles at pH 6.6–6.7 was investigated using rheometry covering a wide range of temperatures and mass fractions. Increasing temperature resulted in a constant decrease of the voluminosity up to 70 °C. A quadratic polynomial was tested to fit the temperature dependency the best. The apparent voluminosity of casein micelle suspensions was determined with 4.0 mL g⁻¹ at 35 °C, 3.6 mL g⁻¹ at 50 °C, and 3.5 mL g⁻¹ at 70 °C.     

Application of a biochemical time–temperature integrator to estimate pasteurisation values in continuous food processes

The microbiological safety of commercial fruit processes was evaluated using α-amylase time–temperature integrators (TTI) from either a Bacillus amyloliquefaciens or Bacillus licheniformis source. The TTIs were incorporated into silicone particles that were added to batches of fruit preparations to estimate the pasteurisation achieved during two different methods of continuous processing: a tubular heat exchanger and an ohmic column. Pasteurisation values (P-values) estimated with the TTIs represented the integrated thermal process at the core of 12-mm pear cubes for the tubular process of 12-mm strawberries, 12-mm pineapple and 10-mm blackcurrants for the ohmic process. The decimal reduction time at 85.0 °C (D₈₅) for the Bacillus amyloliquefaciens amylase was 6.8 min, with a kinetic factor (z-value) of 9.4±0.3 °C, and for the Bacillus licheniformis amylase the D₉₃ was 8.8 min with a z value of 9.1±0.3 °C. For the high-acid fruit products, the target P-value was equivalent to 5 min at 85 °C (T_ref=85 °C, z=10 °C). Amylase activity before and after processing was converted to P-values, with all of the processes showing a substantial safety margin, despite operating conditions that were deliberately set to represent the ‘worst case’ conditions. This method allowed P-value data to be collected under conditions that prevented the use of thermocouples.