Cold-set gelation of high pressure-treated soybean proteins

The ability of soybean proteins to form cold-set gels, using high pressure (HP) processing as denaturing agent and calcium incorporation was evaluated. Different protein preparations were assayed: soybean protein isolate (SPI), a β-conglycinin enriched fraction (7SEF) and a glycinin enriched fraction (11SEF). 7SEF formed aggregated gels with low water holding capacity whereas 11SEF did not form self-standing gels. SPI formed the better gels: ordered and with high water holding capacity. SPI gels were relatively soft and their visual aspect, rheological and texture properties, and water holding capacity depended on HP level (400–600 MPa), CaCl₂ concentration (0.015–0.020 mol L⁻¹) and protein concentration (85–95 g L⁻¹), thus gels with different characteristics may be obtained. The gels comprised a three dimensional network stabilized by non-covalent interactions with spaces filled of proteins in aqueous solution. The results indicate that it is possible to use HP and subsequent calcium incorporation to form self-standing cold-set gels from soybean proteins. These gels may be of interest to incorporate heat-labile compounds or probiotics during the gelation step.     

Effect of combined high pressure and thermal treatment on kiwifruit peroxidase

The effects of high pressure and heat treatments on peroxidase (POD) activity in kiwifruit were investigated. Pressure levels ranging from 200 to 600 MPa and temperatures varying from 10 to 50 °C were applied for up to 30 min. Assays were carried out on crude peroxidase in kiwifruit juice and on partially purified peroxidase in a model system. Pressures higher than 400 MPa could be combined with mild heat (?50 °C) to accelerate enzyme inactivation. Prolongation of the exposure time had no great effect after the first 15 min. The slope of POD in kiwifruit juice at 30 °C was slightly decreased compared with that in a model system. Furthermore, the optimum pH for POD was 6.0–8.5. The presence of POD isoenzymes and their difference in resistance to pressure were thought to be responsible for the final residual activity observed in this study.     

Effects of high hydrostatic pressure treatment on allergenicity and structural properties of soybean protein isolate for infant formula

The objective of this study is to investigate the influences of HHP treatment on the allergenic properties of SPI for infant formula. The processing parameters, including HHP pressure and duration time, could significantly influence the allergenicity reducing efficiency. At 300 MPa and 15 min, the allergenicity decreased 48.6%, compared to the native SPI. In the ranges of 200-300 MPa and 5-15 min, the free SH content and hydrophobicity of SPI significantly increased. Meanwhile, at the levels above 300 MPa and 15 min, the two interactions progressively decreased. Whatever HHP pressure and time, the maximum emission wavelength indicated blueshifts. At 300 MPa and 15 min, there was an 11.5-fold increase in fluorescence intensity and the maximum emission wavelength shifted from 516 to 466 nm. After HHP treatment, the helix1 and turns content, significantly increased and the strand1 and unordered content considerably decreased; whereas the amount of the helix2 and strand2 did not indicate any obvious change. The average length of helices significantly increased, while the helices (per 100 residues) did not strikingly change after HHP modification. However, both the strand (per 100 residues) and the average length of strands clearly decreased. Some documents indicate that the epitopes of SPI allergens could be closely related to the secondary structure of α-helix and β-sheet. These interactions and secondary structure results can provide direct evidence, or explanation, for HHP-induced modification of soy proteins, which could alter the allergenicity of SPI and enhance the security of SPI for cow milk allergic babies.     

Assessment of the residual immunoreactivity of soybean whey hydrolysates obtained by combined enzymatic proteolysis and high pressure

Soybean (Glycine max) whey was hydrolyzed for 15 min using three food-grade proteases (Alcalase, Neutrase, Corolase PN-L) at atmospheric pressure (0.1 MPa) and under high pressure (HP) at 100, 200, and 300 MPa. All hydrolysates were analyzed by SDS-PAGE and their residual immunoreactivity was assessed by immunoblotting using the sera from children allergic to soybean. As shown in SDS-PAGE, Alcalase, Neutrase, and Corolase PN-L produced different patterns of hydrolysis. Each enzyme showed a similar proteolytic activity at atmospheric pressure and at 100 MPa, while an increased degree of hydrolysis was observed at 200 and 300 MPa. No residual antigenicity was observed in the hydrolysates obtained by Alcalase and Corolase PN-L in all considered conditions of hydrolysis. A positive reaction associated with a band having molecular weight of about 70 kDa was observed in the immunoblotting of the hydrolysates obtained with Neutrase at 0.1, 100, and 200 MPa, while no antigenicity was detected for those samples obtained under high pressure, at 300 MPa. These results suggest that high pressure combined with suitable enzymatic activity could be a useful tool for obtaining hydrolysates with low immunoreactivity to be used in special foods (hypoallergenic foods).     

Effect of NaCl on thermal aggregation of egg white proteins from duck egg

Thermal aggregation of duck egg white solution (1 mg protein/ml, pH 7) was monitored in the presence of different NaCl concentrations (0–6%, w/w) across the temperature range of 20–90 °C. Duck egg white solution exhibited higher turbidity with coincidental increases in surface hydrophobicity and decreases in sulfhydryl group content as temperatures increased from 70 to 90 °C (p < 0.05). As NaCl concentration increased, the negative charge decreased, with coincidental increases in particle size of aggregate after heating to 90 °C. As visualised by confocal laser scanning microscopy, larger clusters of protein aggregates were observed with increasing NaCl concentrations. Major duck egg white protein with molecular mass of 45 kDa disappeared in the presence of 2–6% NaCl after heating above 80 °C, regardless of concentrations. Therefore, NaCl, especially at high concentrations, could induce thermal aggregation of duck egg white protein, which could determine the characteristics of salted egg white after heating.     

High hydrostatic pressure effects on immunoreactivity and nutritional quality of soybean products

The aim of this research was to evaluate the protein pattern, immunoreactivity and amino acid composition of soybean seeds and commercial tofu after treating by high hydrostatic pressure (HHP) (300 MPa, 15 min, 40 °C), as well as of sprouts obtained from unpressurised and HHP-treated seeds. HHP did not affect the electrophoretic profile of soybean seeds or tofu protein extracts, but lower intensity of some protein bands were observed in HHP-treated products. A significant (P ? 0.05) reduced antigenicity was observed in the sprouts from HHP-treated seeds compared to the sprouts from untreated seeds, while higher antigenicity of the pressurised seeds compared with the untreated ones was found. HHP decreased the total essential amino acid content as well as two nutritional indexes, the Chemical Score (CS) and the Essential Amino Acid Index (EAAI), but only by 18%. The findings suggest that HHP applied to soybean seeds before germination could constitute a valuable technological approach for the industrial production of nutritive hypoallergenic soybean sprouts.     

Effect of salt addition on the thermal behavior of proteins of bovine meat from Argentina

Research was undertaken to investigate how the addition of sodium chloride (NaCl) and/or sodium tripolyphosphate (TPP) to sous vide cooked meat pieces produces an increase in water holding capacity (WHC). Semitendinosus muscles were injected to obtain tissue final concentrations of 0.70% NaCl, 0.25% TPP, 0.70% NaCl+0.25% TPP, and 1.20% NaCl+0.25% TPP. SDS-PAGE analysis showed increased protein solubilization in those treatments which included NaCl. Thermal analysis of whole muscles and isolated myofibrils showed the destabilizing effect of NaCl and a global stabilizing effect of TPP. Both salts together induced a destabilizing global effect, where TPP assisted NaCl in breaking the meat structure. It is suggested that the WHC increments are related to conformational changes in myofibrillar proteins and to the weakening of myofibrillar structure by the removal of myofibrillar proteins.     

氯化钠对玉米淀粉超高压改性的影响

分别用0．5％、1％和5％的NaCl溶液配成5％（W：V）的玉米淀粉悬浮液，在600MPa压力下处理5min，应用偏光显微镜和x．射线衍射仪进行分析测定。结果表明：随着NaCl溶液浓度的增加，玉米淀粉的结晶结构被破坏的程度降低．结晶度增大；5％的NaCl溶液能有效抑制玉米淀粉在超高压作用下的糊化作用。     

高压和热结合处理对牛肉蛋白质变性和脂肪氧化的影响

以不同压力(从200～800MPa)和温度(20、40和60℃)结合处理20min对牛肉蛋白质的变性和脂肪氧化的影响进行了研究。差示扫描量热仪(DSC)温度扫描图谱显示胶原蛋白对压力十分稳定,只有在60℃下压力处理才部分变性;而肌球蛋白对热和压力都不稳定,并且在压力变性的同时形成新的结构,这个新的结构对热表现出较低的稳定性。在较高温度(60℃)下,压力对温度引起的蛋白质变性起到部分抑制作用。压力和热以及两者结合处理都能加速脂肪的氧化过程,尤其是在400MPa及其以上压力。处理后的冷藏过程中,除20℃和40℃0.1MPa两个处理外,其它处理的TBA值均呈现快速增加。压力和热处理后蛋白质结构的破坏和变性,导致铁的释放在脂肪氧化过程中起着重要的作用,因铁离子是脂肪氧化的主要催化剂之一。差示扫描量热法(DSC)的扫描结果也显示,在400MPa及其以上压力时大部分蛋白质发生变性。      

Effect of high pressure treatment on thermal and rheological properties of lentil flour slurry

Thermal characteristics of high pressure (HP) treated lentil flour dispersions were studied as function of pressure level (350-650 MPa) and moisture content (14-58 g per 100 g of flour). Differential scanning calorimeteric (DSC) measurement of pressure treated lentil dispersions indicated incomplete denaturation of lentil proteins. The protein dentauration temperature (T_d) shifted with applied pressure and moisture content non-systematically. No starch gelatinization peak was detected during thermal scanning of lentil slurries (untreated or treated) irrespective of moisture content or heating rate. High pressure treatment of lentil dispersion significantly reduced the retrogradation behavior compared with that obtained from the thermally gelatinized sample. Dynamic rheological measurement indicated pressure treated lentil slurries exhibited a true viscoelastic fluid. Slurries gradually transformed from solid-like behavior to liquid-like behavior as function of moisture content and pressure level. Fourier transform infrared (FTIR) spectroscopy confirmed insignificant change in amide band of pressure treated slurry. This study has provided complementary information of pressure-induced structural changes on both the molecular and the sub-molecular level of lentil protein.     

High pressure microfluidization treatment of heat denatured whey proteins for improved functionality

Solutions (5% protein) of a whey protein concentrate (WPC) in fresh acid whey or in water, as well as the fresh whey alone, were adjusted to pH 5.8, 4.8 or 3.8, heat treated at 90 °C for 10 min and further exposed to high pressure (150 MPa) microfluidization treatment. The volumes of sediment after centrifugation were recorded as a measure of the degree of insolubility of the proteins. Microfluidization disrupted the heat-induced aggregates into non-sedimenting whey protein polymers so that in some cases, especially at pH 3.8, the products studied were almost completely resistant to sedimentation after the microfluidization treatments. Heat denatured/microfluidized whey proteins reaggregated upon subsequent heating, with the pH having a major impact on the amount of sediment produced. Microfluidization of aqueous WPC solutions heat-treated before spray- or freeze-drying substantially increased the solubility of the powders upon reconstitution. Heat-induced viscoelastic gels were produced from freeze-dried microfluidized samples processed at pH 3.8 and reconstituted to solutions containing 12% (w/w) protein.     

Effect of high pressure treatment on ovotransferrin

High pressure processing of ovotransferrin was carried out to study the structural and physiochemical changes of ovotransferrin under various pressure levels. At pH 8 and pressures higher than 200 MPa, a decrease in total sulfhydryl groups and an increase in surface hydrophobicity were observed along with a partial aggregation. A gradual shift of denaturation peak towards higher temperature was noticed up to 500 MPa, leading to a total loss of the enthalpy of denaturation at pressures of 600 and 700 MPa, where a significant decrease in intrinsic fluorescence was also observed. At pH 3, the ovotransferrin adopted a molten globule state, associated with a significant increase in surface hydrophobicity and reactive sulfhydryl content; structurally, no clear denaturation peaks in differential scanning calorimetry (DSC) were detected at any level of pressure treatment whereas a noticeable decrease in intrinsic fluorescence was evidenced up to 600 MPa and then increased at 700 MPa pressure treatment. Fourier transform infrared spectroscopy (FT-IR) revealed that the conformational structure were changed from helices, sheets, turns, and aggregated strand to mostly intermolecular β-sheets or aggregated strands at pH 8 at 200 MPa but switched back to original structure at higher pressures.     

Effects of high pressure/thermal treatment on lipid oxidation in beef and chicken muscle

Lipid oxidation was studied in beef and chicken muscle after high pressure treatment (0.1–800 MPa) at different temperatures (20–70 °C) for 20 min, prior to storage at 4 °C for 7 days. Pressure treatment of beef samples at room temperature led to increases in TBARS values after 7 days storage at 4 °C; however, the increases were more marked after treatment at pressures ?400 MPa (at least fivefold) than after treatment at lower pressures (less than threefold). Similar results were found in those samples treated at 40 °C, but at 60 °C and 70 °C pressure had little additional effect on the oxidative stability of the muscle. Pressure treatments of 600 MPa and 800 MPa, at all temperatures, induced increased rates of lipid oxidation in chicken muscle, but, in general, chicken muscle was more stable than beef to pressure, and the catalytic effect of pressure was still seen at the higher temperatures of 50 °C, 60 °C and 70 °C. The addition of 1% Na₂EDTA decreased TBARS values of the beef muscle during storage and inhibited the increased rates of lipid oxidation induced by pressure. The inhibition by vitamin E (0.05% w/w) and BHT (0.02% w/w), either alone or in combination, were less marked than seen with Na₂EDTA, suggesting that transition metal ions released from insoluble complexes are of major importance in catalysing lipid oxidation in pressure-treated muscle foods.     

Effect of high hydrostatic pressure (HHP) on structure and activity of phytoferritin

High hydrostatic pressure (HHP) has drawn considerable attention because of its potential application in food industry. Ferritin, an iron storage protein, is widely distributed in food made from legume seeds, which is highly stable due to its shell-like structure. Therefore, it is of special interest to know whether or not high HHP treatment has effect on this protein. In this study, the structure and activity of soybean seed ferritin (SSF) were examined by circular dichroism spectrum (CD), UV–VIS and fluorescence spectrophotometry in conjunction with stopped-flow light scattering upon treatment with HHP at 400 MPa for 10 min. Results revealed that such treatment has little effect on the primary and secondary structure of SSF, but pronouncedly altered its tertiary and quaternary structure. As a result, the protein aggregation property and iron release activity were dramatically changed, while its activity of iron oxidative deposition was kept unchanged.     

Combined thermal and high pressure inactivation kinetics of tomato lipoxygenase

The combined isothermal (10–60 °C) and isobaric (0.1–650 MPa) inactivation kinetics of lipoxygenase (LOX) extracted from tomatoes and reconstituted in a tomato purée were studied. Thermal inactivation of LOX at atmospheric pressure proceeded in the temperature range of 45–65 °C. LOX inactivation did not follow first order kinetics; the data could be fitted assuming that the two isoforms of LOX with different thermostability were present. Combined thermal and high pressure inactivation occurs at pressures in the range of 100–650 MPa combined with temperatures from 10–60 °C, and followed first-order kinetics. In the high-temperature/low-pressure range, (T≥50 °C and P≤300 MPa) an antagonistic effect is observed, therefore, the Arrhenius and Eyring equation cannot be used over the entire temperature and pressure range. Small temperature dependence is found in the low-temperature/high pressure range. A third degree polynomial model was successfully applied to describe the temperature–pressure dependence of the inactivation rate constants, which can be useful to predict inactivation rate constants of tomato LOX reconstituted in tomato purée in the temperature–pressure range studied.     

Effect of thermal and high hydrostatic pressure processing on antioxidant activity and colour of fruit smoothies

Fruit smoothie samples were thermally treated (P₇₀ ≥ 10 min) or high hydrostatic pressure (HHP) processed (450 MPa) with holding time of 1, 3 or 5 min and antioxidant activity, phenolic content and colour values (L*, a* and colour intensity) were determined. Significant reductions in antioxidant activity (p < 0.001) and phenolic content (p < 0.001) were observed at the applied pressure and a maximum treatment time of 5 min. Mean values for redness (a*) showed an increase (p < 0.001) in HHP processed smoothies compared to fresh. As expected, storage also had a significant effect on colour variables but the effect was more pronounced in high pressure treated samples stored for 30 days. Both colour and antioxidant activity were significantly affected by high pressure processing. Therefore, process optimisation of high pressure systems should be considered by processors prior to its adoption as a preservation technique in order to minimise the effect on the quality of fruit smoothie products.Industrial relevanceFruit smoothies have become popular with consumers and may significantly contribute to daily antioxidant intakes. Thermal processing has been shown to reduce the antioxidant activity of fruits, thus non-thermal methods of pasteurisation such as high hydrostatic pressure processing could help retain antioxidants in fruit smoothies offering a unique selling point for processors. The present study focussed on assessing the effect of thermal and high pressure processing on the antioxidant activity and phenolic content of fruit smoothies. Since decreases in levels of antioxidants were noted during long term storage it would appear that higher pressure treatments (> 450 MPa) might be required for better retention of antioxidant compounds in fruit smoothies.     

Effect of high pressure homogenisation on the capacity of Lactobacillus plantarum A6 to ferment rice/soybean slurries to prepare high energy density complementary food

New bioprocesses to prepare high energy density (HED) gruels for complementary young child feeding are being developed based on the ability of amylolytic lactic acid bacteria (ALAB) to modify the rheological characteristics of cereal-based slurries, provided appropriate pretreatment are applied. Gelatinisation is a common pre-treatment which could be implemented to enhance the action of amylases, and has been successfully used in a former study (Nguyen, T. T. T., Loiseau, G., Icard-Vernière, C., Rochette, I., Trèche, S., & Guyot, J.-P. (2007). Effect of fermentation by amylolytic lactic acid bacteria in process combinations on characteristics of rice/soybean slurries: a new method to prepare high energy density complementary foods for young children. Food Chemistry, 100, 623–631.) in combination with ALAB to prepare from a blend of rice/soybean flours semi-liquid fermented HED gruels with a high dry matter (DM) content (23–32%). In this study, it is shown that a mild pre-heating treatment which consists in suspending a rice/soybean flour blend in hot water (70 °C) combined with high pressure homogenisation (HPH) can substitute gelatinisation before fermentation by the ALAB Lactobacillus plantarum A6 to prepare HDE gruels after cooking of the fermented slurry. As an alternative, allowing better condition of handling and storage, spray drying can be applied to such pre-heated HPH treated fermented slurries to obtain fermented flours which can be used further to prepare HDE gruels.     

The effect of high hydrostatic pressure,sodium nitrite and salt concentration on the growth of Listeria monocytogenes on RTE ham and turkey

Growth of Listeria monocytogenes was evaluated for up to 182 days after inoculation on ready-to-eat (RTE) sliced ham and turkey breast formulated with sodium nitrite (0 or 200 ppm), sodium chloride (1.8% or 2.4%), and treated (no treatment or 600 MPa) with high hydrostatic pressure (HHP). HHP at 600 MPa for 3 min resulted in a 3.85–4.35 log CFU/g reduction in L. monocytogenes. With formulations at similar proximate analyses, one of the evaluation days (day 21) without HHP showed significantly greater growth of L. monocytogenes in ham than in turkey breast, but there were no significant differences on other evaluation days or with HHP. There were no differences in growth of L. monocytogenes due to sodium chloride level. Sodium nitrite provided a small, but significant inhibition of L. monocytogenes without HHP, but addition of sodium nitrite did not significantly affect growth of L. monocytogenes with use of HHP.     

Effects of potassium lactate and high pressure on transglutaminase restructured dry-cured hams with reduced salt content

Ten raw hams (from 5 carcasses) were boned and salted either with salt reduction (15 g/kg NaCl) or salt reduction with addition of potassium lactate (15 g/kg NaCl and 39.74 g/kg of a 60% K-lactate solution). Subsequently, the ham pieces were assembled together with transglutaminase, vacuum packed into water-permeable plastic bags and kept at 3 °C and 85% RH until reaching above 30% weight losses. The effects of K-lactate addition and the high-pressure (HP) treatment at 600 MPa on the physicochemical, instrumental colour and texture (Tensile test) and sensory characteristics of the biceps femoris (BF) muscle were evaluated. The addition of K-lactate did not have a negative effect on colour, flavour or texture of restructured dry-cured hams. The HP treatment increased significantly the pH, L^∗, a^∗ and b^∗ values and the breaking stress, and decreased the water-holding capacity and elasticity (apparent Young’s modulus) of BF muscle. The HP treatment also affected significantly the flavour (increasing saltiness, umami and sweetness) and the sensory texture attributes (increasing muscle binding, hardness, gumminess and fibrousness and decreasing adhesiveness and pastiness), as well as slice appearance (increasing brightness and iridescence and decreasing colour homogeneity).     

Plasmin activity, β-lactoglobulin denaturation and proteolysis in high pressure treated milk

The effects of high pressure (HP) on plasmin activity, β-lactoglobulin denaturation and proteolysis during subsequent storage of HP treated milk, were studied. Fresh raw milk samples were exposed to a range of pressures from 50 to 800 MPa, for times of 1, 10 or 30 min, at 20°C. Residual plasmin activity and whey protein denaturation were measured immediately post HP-treatment. Indices of proteolysis were measured during post-HP storage. Treatment at pressures >300 MPa resulted in extensive β-lactoglobulin denaturation. Plasmin activity decreased in milk treated at pressures 400 MPa; the loss of activity was not well correlated with β-lactoglobulin denaturation. Compared to raw milk, treatment at 50 MPa had little effect on proteolysis during storage of treated milk measured as increases in pH 4.6-soluble N and liberation of proteose peptones, but at pressures of 300–400 MPa, proteolysis was increased relative to raw milk. After pressurisation >500 MPa, proteolysis during storage of milk was less than that observed in raw milk. Overall, HP influenced proteolysis in milk in a way which is different from that produced by heat, in terms of subsequent susceptibility of casein to proteolysis during storage or incubation. In particular, HP treatment at pressures of 300–500 MPa can increase proteolysis in milk, possibly through changes in micelle structure facilitating increased availability of substrate bonds to plasmin, which has implications for products prepared from milk thus treated.