超高压处理对脱脂乳感官特性的影响

以新鲜脱脂乳为原料,研究高压处理对脱脂乳感官特性的影响。脱脂乳在室温下经不同压力（0.1～700 MPa）和时间（10～30 min）处理后测定其透光率和平均粒径的变化,利用电子眼、电子鼻、电子舌分别检测色泽、气味以及滋味的变化。结果表明：当压力超过200 MPa时脱脂乳透光率增加,而平均粒径不同程度减小;高压处理导致脱脂乳感官特性的改变,在0.1～700 MPa范围内分别处理10～30 min,脱脂乳的主要色号（3002和3018）随着压力的升高逐渐消失,同时出现一些新的色号（如2183和2200）;在处理10 min后脱脂乳中丙酮相对含量的变化不大,处理20～30 min时整体呈减小趋势;乙醛在700 MPa处理10 min、200 MPa处理20、30 min后消失,且出现2-甲基噻吩和乙醇等气味成分,但整体无明显差异（识别指数均小于80）;在处理20～30 min后脱脂乳酸味、咸味与鲜味整体减弱,甜味和苦味增强。因此,超高压处理对脱脂乳气味的影响不大,但会引起色泽、滋味、透光率与粒径产生变化。     

超高压处理对紫甘薯中多酚氧化酶活力的影响

以济薯18号为原料,研究超高压结合温度处理对紫薯多酚氧化酶(PPO)活力的影响。实验压力范围100～600MPa,温度20～60℃。结果表明:在温度30℃、保压时间10min的条件下,压力在100～600MPa范围内,500MPa时紫薯多酚氧化酶的活力最高,并且高于自然酶活力;在600MPa压力下,当温度小于30℃时,酶活力随温度上升而升高,大于30℃时,随温度升高酶活力下降。另外,酶活力随保压时间的延长而减小;但在300MPa时,前20min酶活力随保压时间延长而降低,20～50min内随时间延长而升高。因此,紫薯多酚氧化酶具有较好的耐压性。对紫薯进行温度、压力、保压时间的L9(34)正交试验结果表明:在600MPa、65℃条件下处理35min后,PPO活性最弱,抑制效果最佳。     

超高压处理诸因素对辣根过氧化物酶活力的影响

目的:研究超高压处理对辣根过氧化物酶活力的影响。方法:实验压力为0.1～500MPa,温度为20～60℃,保压时间为5～30min,酶溶液pH7.0。结果:①在常压常温条件下,在酶溶液为pH7.0时酶活力最大,为其最适酸碱度。②在处理温度为40℃、保压时间为10min和酶溶液pH7.0的条件下,压力对酶活力有显著影响;在100MPa附近的低压处理时,酶活力会反常升高;大于400MPa处理时,酶活力下降趋势缓慢。③在处理压力为500MPa、保压时间为10min、酶溶液pH7.0条件下,在40℃以下的温度范围内,酶的活力下降趋势缓慢;40℃以后,酶活力随温度升高下降迅速。④在500MPa、40℃、pH值为7.0的条件下,保压25min辣根过氧化物酶的残留活力接近最低水平,进一步延长保压时间对酶的活力影响甚微;保压时间不是影响酶活力的主要因素。结论:超高压处理对辣根过氧化物酶活力影响显著;压力、温度和保压时间对酶活力均产生较大影响。     

马哈鱼鱼皮明胶提取温度和甘油质量浓度对其成膜特性的影响

明胶提取温度和甘油质量浓度是影响明胶膜性质的基本因素。本研究以马哈鱼（Oncorhynchus keta） 鱼皮为原料,采用不同温度（40、50、60、70、80、90 ℃）提取明胶,考察不同甘油质量浓度（1.1、1.2、 1.5 g/100 mL）下明胶膜的厚度、机械性能、光学性质、微观结构和红外特性。研究发现,40、50、60 ℃明胶 膜的厚度高于70、80、90 ℃明胶膜的厚度（P＜0.05）。50、60 ℃膜的拉伸强度（tensile strength,TS）高于 70、80、90 ℃膜的（P＜0.05）;添加1.5 g/100 mL甘油,膜的断裂伸长率随提取温度升高而上升（P＜0.05）; 50、70、80 ℃膜的TS随甘油质量浓度升高而下降（P＜0.05）。色差分析表明,膜的a*值随提取温度升高而上升 （P＜0.05）。水蒸气透过率随提取温度和甘油质量浓度的升高而升高（P＜0.05）。明胶膜于200、280 nm波长处 的透光率为0.00%,350～800 nm范围内的透光率为46.53%～74.57%,60 ℃膜的透光率低于40、50 ℃膜的透光率 （P＜0.05）。衰减全反射傅里叶变换红外光谱分析表明膜的图谱呈现典型酰胺A、B、Ⅰ、Ⅱ、Ⅲ带,酰胺A带随 提取温度的升高向低波数移动,且振幅随甘油质量浓度升高而增加。扫描电子显微镜结果显示,膜的截面和表面未 呈现明显断裂或空隙。以上结果表明,温度对马哈鱼鱼皮明胶膜的机械性能、透水性、颜色、透光率影响显著,甘 油质量浓度仅对前二者影响显著,可通过优化提取温度与甘油质量浓度改善马哈鱼鱼皮明胶膜性质。     

高压对从苹果渣中提取酚类物质的影响

考察高压对乙醇溶液提取苹果渣中酚类物质的影响。结果表明：乙醇浓度70％（V：V）比较适宜。随着处理压力的增大，酚类物质的得率逐渐升高（400MPa除外），且在500MPa以前得率提高的幅度较大，压力达到600MPa以上后得率增幅不大。随着提取时间的延长，酚类得率先升后降，提取时间以10min为宜。酚类物质的得率先随温度升高而增大，到50℃达到最高，随后又下降。高压对乙醇溶液提取苹果渣中酚类物质有显著的促进作用。     

高压对从桃渣中提取酚类物质影响的研究

考察高压对乙醇溶液提取桃渣中酚类物质的影响。结果表明,乙醇体积浓度70％比较适宜。随着处理压力的增大,酚类物质的得率逐渐升高（400MPa除外）,且在500MPa以前得率提高的幅度较大,压力到达600MPa以上后得率增幅不大。随着提取时间的延长,酚类得率先升后降,提取时间以10min为宜。酚类物质的得率先随温度升高而增大,到50℃达到最高,随后又下降。高压对乙醇溶液提取桃渣中酚类物质有显著的促进作用。     

高压结合热处理对猪肉中过氧化氢酶活性的影响

为研究不同压力(200~600 MPa)结合不同热处理温度(30~50℃)和处理时间(10~30 min)后对猪肉中过氧化氢酶(CAT)活性的影响,以猪背最长肌为实验原料,在单因素实验的基础上采用响应面法分析。实验结果表明:压力和温度是影响CAT活性的最显著因素,压力和温度及压力和保压时间对CAT活性的影响均有极显著交互作用(p<0.01),且影响CAT活性的临界温度随压力的升高呈线性下降趋势,影响CAT活性的临界保压时间随压力的升高呈线性上升趋势。CAT活性最高的处理条件是600 MPa、30℃、10 min,其活性为1.679 U/mg prot。      

高压结合热处理对猪肉中硫胺素含量的影响

为研究不同处理压力（200⁶00 MPa）、温度（20⁶0℃）和时间（10²0 min）对猪肉中硫胺素含量的影响,选择猪背最长肌为原料,在单因素实验基础上,根据Box-Behnken实验设计原理,采用三因素三水平的响应面法分析。结果表明:在压力、温度、时间三种因素中,压力和温度对硫胺素含量的影响极显著（p<0.01）,而时间对其影响显著（p<0.05）,压力和温度的交互作用对硫胺素含量也有极显著影响（p<0.01）。当处理温度在20⁴7℃左右时,硫胺素含量随压力的升高逐渐降低;温度高于48℃后,硫胺素含量随压力的升高先增加后减少,存在压力临界值;当压力一定时,硫胺素含量随温度的升高先增大后减小,存在温度临界值,且临界温度随压力的升高呈线性上升。在高压处理过程中,中温结合中压处理比单独的高压低温或低压高温处理更有利于硫胺素的保留。      

低温和中温协同超高压对鲜榨荔枝汁灭酶处理和色泽影响的研究

为探讨超高压处对鲜榨荔枝汁中过氧化物酶(POD)、多酚氧化酶(PPO)活性的影响,对鲜榨荔枝汁进行了单独超高压处理（300~450 MPa,10~40 min）及低温（10 ℃）、中温（40~70 ℃）协同超高压(450 MPa,20 min)处理,通过对荔枝汁品质指标测定,探讨了温度协同超高压对荔枝汁品质的影响。试验结果表明：在室温、保压时间为20 min的条件下,300~450 MPa压力范围内荔枝汁中POD酶被激活,在300 MPa时活性最高;PPO酶在此压力范围内则随着压力的升高而降低;POD比PPO酶更耐压;450 MPa压力条件下,随着保压时间的延长,POD、PPO酶的活性减小;低温和中温协同超高压处理对荔枝汁中POD、PPO酶的钝化存在一定的协同效应,且中温范围内（40~70 ℃）温度越高,协同抑制效应越明显;中温协同超高压处理后的荔枝汁的L*值显著升高,果汁的亮度增加,但是随着协同温度的升高,总色差ΔE*逐渐增大,果汁的色泽变化增大。     

高压对从梨渣中提取酚类物质影响的研究

考察高压对乙醇溶液提取梨渣中酚类物质的影响。结果表明,乙醇浓度70%(V/V)比较适宜。随着处理压力的增大,酚类物质的得率逐渐升高(400MPa除外),且在500MPa以前得率提高的幅度较大,压力到达600MPa以上后得率增幅不大。随着提取时间的延长,酚类得率先升后降,提取时间以10min为宜。酚类物质的得率先随温度升高而增大,到50℃达到最高,随后又下降。高压对乙醇溶液提取梨渣中酚类物质有显著的促进作用。     

Optimization of pressure-induced germination of Bacillus sporothermodurans spores in water and milk

Bacillus sporothermodurans produces highly resistant endospores that can survive ultra-high-temperature treatment in milk. The induction of endospore germination before a heat treatment could be an efficient method to inactivate these bacteria and ensure milk sterility. In this work, the rate of spore germination of B. sporothermodurans LTIS27 was measured in distilled water after high-pressure treatments with varying pressure (50–600 MPa), treatment temperature (20–50 °C), pressure-holding time (5–30 min) and post-pressurization incubation time (30–120 min) at 37 °C or 4 °C. The results showed that pressure-induced germination was maximal (62%) after a treatment at 200 MPa and 20 °C and increased with pressure-holding time and post-pressurization incubation time. Treatment temperature had no significant effect on germination. A central composite experimental design with three factors (pressure, pressure-holding time, and post-pressurization incubation time) using response surface methodology was used to optimize the germination rate in distilled water and in skim milk. No factor interaction was observed. Germination was induced at lower pressure and was faster in milk than in distilled water, but complete germination was not reached. The optimum germination obtained with experimental data was 5.0 log cfu/mL in distilled water and 5.2 log cfu/mL in milk from 5.7 log cfu/mL of spores initially present in the suspension. This study shows the potential of using high hydrostatic pressure to induce the germination of B. sporothermodurans spores in milk before a heat treatment.     

Inactivation of Escherichia coli in milk by high-hydrostatic-pressure treatment in combination with antimicrobial peptides

We studied the inactivation in milk of four Escherichia coli strains (MG1655 and three pressure-resistant mutants isolated from MG1655) by high hydrostatic pressure, alone or in combination with the natural antimicrobial peptides lysozyme and nisin and at different temperatures (10 to 50 degrees C). Compared with that of phosphate buffer, the complex physicochemical environment of milk exerted a strong protective effect on E. coli MG1655 against high-hydrostatic-pressure inactivation, reducing inactivation from 7 logs at 400 MPa to only 3 logs at 700 MPa in 15 min at 20 degrees C. An increase in lethality was achieved by addition of high concentrations of lysozyme (400 microg/ml) and nisin (400 IU/ml) to the milk before pressure treatment. The additional reduction amounted maximally to 3 logs in skim milk at 550 MPa but was strain dependent and significantly reduced in 1.55% fat and whole milk. An increase of the process temperature to 50 degrees C also enhanced inactivation, particularly for the parental strain, but even in the presence of lysozyme and nisin, a 15-min treatment at 550 MPa and 50 degrees C in skim milk allowed decimal reductions of only 4.5 to 6.9 for the pressure-resistant mutants. A substantial improvement of inactivation efficiency at ambient temperature was achieved by application of consecutive, short pressure treatments interrupted by brief decompressions. Interestingly, this pulsed-pressure treatment enhanced the sensitivity of the cells not only to high pressure but also to the action of lysozyme and nisin.     

超高压协同中温处理对番茄汁中番茄红素和总VC 含量的影响

探讨超高压协同中温加工对番茄汁中番茄红素和总VC 含量的影响。番茄汁在温度为33.5℃,压力为469.2MPa,时间为14.0min 的条件下处理,番茄红素含量显著增加,但番茄红素顺反异构体变化不明显;VC 含量变化不显著。     

High pressure treatment of bovine milk: effects on casein micelles and whey proteins

Effects of high pressure (HP) on average casein micelle size and denaturation of alpha-lactalbumin (alpha-la) and beta-lactoglobulin (beta-lg) in raw skim bovine milk were studied over a range of conditions. Micelle size was not influenced by treatment at pressures <200 MPa, but treatment at 250 MPa increased micelle size by approximately 25%, while treatment at > or = 300 MPa irreversibly reduced it to approximately 50% of that in untreated milk. The increase in micelle size after treatment at 250 MPa was greater with increasing treatment time and temperature and milk pH. Treatment times > or = 2 min at 400 MPa resulted in similar levels of micelle disruption, but increasing milk pH to 7.0 partially stabilised micelles against HP-induced disruption. Denaturation of alpha-la did not occur < or = 400 MPa, whereas beta-lg was denatured at pressures >100 MPa. Denaturation of alpha-la and beta-lg increased with increasing pressure, treatment time and temperature and milk pH. The majority of denatured beta-lg was apparently associated with casein micelles. These effects of HP on casein micelles and whey proteins in milk may have significant implications for properties of products made from HP-treated milk.     

Skim milk protein distribution as a result of very high hydrostatic pressure

This work studies the micellar size and the distribution of caseins, major and minor whey proteins in different fractions of skim milk treated up to 900 MPa for 5 min. Transmission electron microscopy showed that the smallest casein micelles were formed around 450 MPa with no variations at higher pressures. The changes found in micellar size correlated with the concentration of soluble casein, because treatments at 250 MPa significantly enhanced the level of non-sedimentable casein while, between 700 and 900 MPa, there were no further increases with respect to lower pressures. There was a severe β-lactoglobulin (β-Lg) denaturation at pressures ≥ 700 MPa, which reached 77–87%. α-Lactalbumin (α-La) was stable up to 550 MPa, but it denatured at higher pressures. The content of soluble lactoferrin (Lf) decreased with pressure, particularly from 550 to 800 MPa, while that of secretory IgA (sIgA) progressively decreased from 250 up to 700 MPa. Our results indicated that treatment of milk at very high pressures, from 700 to 900 MPa, did not reduce micellar size nor released more soluble casein with respect to treatments at lower pressures (250–550 MPa). However, these treatments led to a severe denaturation of the whey proteins, in particular of β-Lg and the minor proteins Lf and sIgA. The possibility of using high hydrostatic pressure to obtain a soluble milk fraction with a casein and whey protein composition similar to that of human milk is discussed.     

High pressure effects on the colloidal calcium phosphate and the structural integrity of micellar casein in milk. Part 1. High pressure dissolution of colloidal calcium phosphate in heated milk systems

Results of this study confirm that high temperature (118°C/15 min) and high pressure (400 MPa/5 min) processing of skim milk, skim milk ultrafiltration and ultracentrifugation fractions, and model milk salt solutions cause dramatic shifts in their colloidal and soluble Ca phospate equilibrium that affect their pH, dissolved Ca content, turbidity, and casein micelle microstructure. The relations between high temperature and high pressure processing-induced changes in the colloidal and soluble Ca phosphate equilibrium were evaluated in raw, pasteurized, and high temperature treated skim milk, ultrafiltration retentate and permeate of pasteurized skim milk, clear ultracentrifugation infranatant of pasteurized skim milk, and synthetic milk ultrafiltrates with and without lactose or Ca. The magnitude of the pH and dissolved Ca shifts caused by high temperature and high pressure processing was a function of casein micelle concentration. Ultrafiltration permeate exhibited the most drastic shifts in pH and dissolved Ca contents due to high temperature and high pressure processing. Although high temperature processing reduced the pH of ultrafiltration permeate from 6.59 to 6.03 and the dissolved Ca from 100% to 58%, high pressure processing reversed both of these changes. These changes in high temperature and high pressure processed milk, milk fractions, and model milk salt solutions were related to microstructural changes in the casein micelles as revealed by electron microscopy.     

Initial study on high pressure jet processing using a modified waterjet on physicochemical and rennet coagulation properties of pasteurized skim milk

Developments in material science and engineering have enabled high pressure jet (HPJ) processing at >500 MPa. The objective of this study was to characterize the physicochemical properties of pasteurized skim milk processed at pressures from 0 to 500 MPa using waterjet technology, to explore novel uses of this technology for milk. The apparent particle size of casein micelles increased from approximately 180–220 nm in milk processed from 0 to 200 MPa to approximately 280 nm in milk treated at 500 MPa. All milk samples were shelf-stable up to 14 days at 4 °C. The viscosity of skim milk processed at 400 and 500 MPa almost doubled (4.2 mPa s) when compared with control unprocessed milk (2.2 mPa s). Increasing HPJ processing pressure changed the structure–function properties of the casein micelles and no rennet-induced coagulation was observed for milk processed at 500 MPa.     

Effect of pressure and fat content on particle sizes in microfluidized milk

Average diameters and particle size distributions in fluid milks with different fat contents and subjected to various homogenization pressures with a "microfluidizer" were evaluated. Skim, 2%, and whole milks were microfluidized at 50, 100, 150, and 200 MPa. Cream containing 41% milk fat was microfluidized at 50, 100, and 150 MPa. Particle sizes were determined by laser light scattering. As microfluidization pressure was increased from 50 to 100 MPa, particle sizes in skim, 2%, and whole milks decreased. Microfluidization at pressures greater than 100 MPa had little additional effect on reducing the particle sizes in skim and 2% milks compared with microfluidization at 100 MPa, but the particle sizes in whole milk increased as the microfluidization pressure was increased from 100 to 200 MPa due to formation of homogenization clusters. The particle sizes in cream increased as the microfluidization pressure was increased from 50 to 150 MPa. When the microfluidization pressure was held constant, the particle sizes increased as the milk fat concentration was increased. The coefficients of variations of the volume-weighted particle size distributions for cream were higher than for skim, 2%, and whole milks. Larger "big" particles and smaller "small" particles were formed in whole milk after microfluidization at 200 MPa than at 100 MPa. Although microfluidization can be used to produce small particles in skim, 2%, and whole milks, a higher than optimum pressure (above 100 MPa) applied to whole milk will not lead to the minimum d(43) (volume-weighted average diameter) due to formation of clusters.     

The effect of high hydrostatic pressure on the flow behaviour of skim milk–gelatin mixtures

The flow behaviour of aqueous solutions of gelatin, and skim milk–gelatin mixtures treated by high-pressure processing (HPP) were investigated. HPP was carried out at 5 °C for 15 min, at 150 MPa, 300 MPa, 450 MPa and 600 MPa, and the gelatin concentrations were varied from 0 to 1 wt.%. Viscosity measurements showed that the HPP treatment did not affect the flow behaviour of gelatin alone, nor that of the skim milk–gelatin mixtures made with < 0.4 wt.% gelatin. However, at gelatin concentration > 0.4 wt.%, the mixtures treated with 300 and 450 MPa exhibited a peculiar flow behaviour, where at intermediate shear rates the viscosity was higher than that of the non-treated mixture or the mixtures treated at 150 MPa and 600 MPa. Particle size measurements showed that for gelled mixtures (> 0.4 wt.% gelatin) 300 MPa HPP treatment resulted in an increase in the particle size, while at all other pressure treatments (> 150 MPa), a shift in particle size distribution to lower sizes was observed. Confocal microscopy showed that these skim milk–gelatin mixtures were phase-separated with a gelatin continuous phase, this was confirmed by dynamic rheological measurements which showed that qualitatively the viscoelastic properties of the mixtures were the same. A mechanism of the effect of high-pressure treatment on the casein micelle in skim milk–gelatin mixtures is proposed.Industrial relevanceThis fundamental work, dealing with the effect of high pressure on the physicochemical properties skim milk–gelatin mixtures could be relevant to the industry in several ways. Firstly, skim milk–gelatin mixtures are widely used in the dairy industry, particularly in yoghurt manufacture, where gelatine is used as a stabiliser. In addition the application of High Hydrostatic Pressure to such a system is also relevant, as this technology could be used as a substitute to the conventional heat treatment processes. Secondly, an important finding of this study is that under certain conditions of high pressure and gelatine concentration, an increase in viscosity is observed at intermediate shear-rate (between 10 and 100 s^?1). This is highly relevant to Industry if the system requires subsequent pumping. Thirdly, from a sensory view point, this range of shear rates (10 and 100 s^?1) is comparable to that experienced by a food bolus during swallowing. Thus, this effect of high pressure on the viscosity can influence sensory attribute of the skim milk–gelatin food system.