Responses of Pseudomonas fluorescens to combined high pressure/temperature treatments

A Pseudomonas fluorescens strain isolated from pork meat and inoculated in culture broth was subjected to high pressure (200 and 400 MPa/10 min) at 5, 20 and 35 °C. Pressurization at 200 MPa/5 °C reduced the bacterial growth by 5 log cycles, and this effect decreased as the pressurization temperature increased. At 400 MPa, P. fluorescens growth was inactivated. The counts of P. fluorescens treated at 200 MPa after day 1 of incubation at 20 °C were higher than those obtained immediately after treatment; conversely, at 400 MPa, they were still below the detection threshold. After 8 and 16 days of incubation, counts of pressurized and non-pressurized bacteria were similar. Scanning electron microscopy showed that pressure-induced morphological changes were more pronounced at 400 MPa and that the effect of pressure was influenced by the treatment temperature.     

Dynamic high pressure-induced gelation in milk protein model systems

The structure-functional properties of milk proteins are relevant in food formulation. Recently, there has been growing interest in dynamic high-pressure homogenization effects on the rheological-structural properties of food macromolecules and proteins. The aim of this work was to evaluate the effects of different homogenization pressures on rheological properties of milk protein model systems. For this purpose, sodium caseinate (SC) and whey protein concentrate (WPC) were dispersed at different concentrations (1, 2, and 4%), pasteurized, and then homogenized at 0, 18 MPa (conventional pressure, CP), 100 MPa (high pressure, HP), and 150 MPa (HP+). Differences in viscosity were observed between WPC and casein dispersions according to concentration, heat treatment, and homogenization pressure. Mechanical spectra described the characteristic behavior of solutions except for the WPC 4% pasteurized sample, in which a network formed but was broken after homogenization. Dispersions with different ratios of WPC and SC were also made. In these systems, pasteurization alone did not determine network formation, whereas homogenization alone promoted cold gelation. A total concentration of at least 4% was required for homogenization-induced gelation in pasteurized and unpasteurized samples. Gels with higher elastic modulus (G′) were obtained in more concentrated samples, and a bell-shaped behavior with the maximum value at HP was observed. The HP treatment produced stronger gels than the CP treatment. Similar G′ values were obtained when different concentrations, pasteurization conditions, and homogenization pressures were combined. Therefore, by setting appropriate process conditions, systems or gels with tailored characteristics may be obtained from dispersions of milk proteins.     

花生蛋白的高静压联合酶法改性及其性质

为促进花生蛋白的深加工和更广泛的应用,采用高静压联合碱性蛋白酶酶法改性花生蛋白。通过单因素试验考察了静压力、pH、酶添加量、酶解时间和酶解温度对花生蛋白溶解度的影响,在此基础上,采用正交试验优化花生蛋白联合改性工艺条件,并测定了联合改性花生蛋白的起泡性和泡沫稳定性、巯基和二硫键含量以及总还原能力。结果表明：花生蛋白联合改性最佳工艺条件为静压力300 MPa、1 g/100 mL碱性蛋白酶（20万U/g）添加量3.0 mL（100 mL质量分数5%的花生蛋白溶液）、酶解时间60 min、pH 10、酶解温度50 ℃,在此条件下联合改性花生蛋白溶解度为（82.87±0.51）%;联合改性花生蛋白的起泡性、泡沫稳定性、巯基含量、总还原能力显著提高,二硫键含量显著下降。综上,高静压联合酶法改性改善了花生蛋白的理化性质及功能特性,有利于其深加工及更广泛的应用。     

应用高温高压镶嵌法的超疏水涤纶织物制备

为开发制备超疏水涤纶织物的短流程工艺,研究了高温高压下在涤纶表面镶嵌聚二甲基硅氧烷(PDMS)制备方法。结果表明：PDMS对涤纶表面的镶嵌作用能赋予涤纶超疏水性,水接触角能达到163.4o,滚动角最小可达7.0o,沾水等级达到5级,同时改性涤纶织物具有优异的耐洗性能。电镜观察表明,涤纶原有纤维棱角变模糊,表面粗糙度提高;红外光谱分析表明PDMS成功镶嵌到涤纶纤维结构中;X-衍射及DSC分析表明纤维主体结构基本不变;改性后涤纶织物断裂强力有所下降,折皱弹性有小幅度增加,抗弯刚度、白度基本无变化。该方法工艺流程短、成本低、效果好,具有良好的应用前景。     

Combination of high pressure and heat on the gelation of chicken myofibrillar proteins

The effects of combinations of high pressure and heat on chicken myofibrillar gels were investigated. High pressure was either applied simultaneously with heating (heating under pressure, HUP), before heating (PBH) or no high pressure with heat-only (HT). PBH treatment induced many similar properties in gels as did by HT treatment, except that PBH treatment promoted secondary structure transformation and formed more covalent bonds. HUP treatment resulted in less heat denaturation of the protein, induced fewer hydrophobic interactions and covalent bonds, hindered secondary and tertiary structural transformation, and formed a gel with a more porous microstructure. The gels induced by HUP treatment had softer texture and higher water holding capacity than gels induced by PBH or HT treatments. These findings suggest that high pressure with HUP treatment changes gel properties by resisting the heat-induced denaturation and gelation of myofibrillar proteins, while high pressure with PBH treatment alters gel properties by promoting denaturation of myofibrillar proteins.Industrial relevanceThe main constituents in meat are myofibrillar proteins, which are responsible for the functional properties of processed meat products. The gelation of myofibrillar proteins differs according to the sequence in which pressure/temperature combinations are applied. The pressure-modified protein interactions should be considered when adopting high pressure in meat product processing since the microstructure of the meat gel is affected by pressure, which would further affect water holding capacity and textural properties. HUP treatment showed its advantages in forming a fine microstructure and improving water-holding capacity.     

On the modelling of the inactivation kinetics of Saccharomyces cerevisiae by means of combined temperature and high pressure treatments

The inactivation kinetics of Saccharomyces cerevisiae with HP, thermal and combined HP-temperature treatments were studied to set up a complete kinetic model describing the dependence of yeast resistance on temperature and pressure. Fermi equation proposed by Appl. Microbiol. Biotechnol., 46. 303 to model the survival curves of yeasts treated with single inactivation processes is validated at different temperature and pressure levels and processing times whatever the growth phase of the micro-organisms. A combination of HP and thermal treatments is also studied to understand the possible synergetic effects of lethal agents. In combined processes, a characteristic value of the operating pressure does exist and can be determined in the hypothesis that the overlapping effects of the two treatments occurs. A model equation is proposed to describe the inactivation kinetics of microorganisms in combined treatments and the characteristic pressure is evaluated as a linear combination of the characteristic parameters T_C and P_C of single processes.     

Fermented minced pepper by high pressure processing,high pressure processing with mild temperature and thermal pasteurization

High pressure processing (HPP) and thermal pasteurization (TP) of fermented minced pepper (FMP) were comparatively evaluated by examining their impacts on microbial load, titratable acid (TA), pH, a_w, firmness, color, capsanthin, ascorbic acid (AA), and biogenic amines (BAs) after processing and during 12 weeks of storage at 25 and 37 °C. The total plate count (TPC) in FMP samples was reduced by 1.48, 0.12 and 1.58 log₁₀ CFU/g after TP (83 °C/15 min), HPP1 (500 MPa/20 °C/5 min) and HPP2 (500 MPa/50 °C/5 min), respectively. The population of spores was reduced by 1.21 log₁₀ CFU/g only after HPP2. During storage at 25 or 37 °C, the TPC in TP, HPP1, and HPP2 samples increased by 0.88/1.21, 0.41/0.62 and 0.60/0.86 log₁₀ CFU/g, respectively, while the spores decreased below the detection limit. The retention of firmness after TP, HPP1 and HPP2 was 36.91, 91.15 and 66.48% respectively, and HPP-treated samples exhibited more retention during the storage. Color of FMP samples was not changed by TP, but slightly changed by HPP1 and HPP2. The content of capsanthin retained 78.99, 93.71 and 88.19% after TP, HPP1 and HPP2, it showed a small decrease during storage. Levels of biogenic amines (BAs) in HPP2 samples were lower than that of TP and HPP1 ones. There were better sensory quality and lower microbial level in HPP-treated samples during storage, indicating that HPP is a better choice for the preservation of FMP.Industrial relevanceConsumption of fermented minced pepper (FMP), as a traditional Chinese food, is becoming increasingly popular. Considering that heat treatment may destroy some heat-sensitive quality of the products, this study evaluated the effects of high pressure processing (HPP) on quality of FMP. Findings of this study could help processors commercialize HPP to replace current thermal processing in industrial production.     

米糠蛋白的静高压联合酶法改性工艺优化及其特性研究

采用静高压联合碱性蛋白酶对米糠蛋白进行改性。考察静压力、保压时间对米糠蛋白溶解性的影响,优化静高压改性条件。以米糠蛋白溶解性、乳化性和乳化稳定性为指标,通过单因素试验和正交试验综合评分法优化了酶法改性工艺。结果表明,米糠蛋白最适改性条件为静压力200 MPa、保压时间15 min、碱性蛋白酶添加量1 500 U/g、pH 8、酶解温度50 ℃和酶解时间80 min,在此条件下米糠蛋白溶解性、乳化性、乳化稳定性、起泡性和泡沫稳定性分别增加了57%、88%、182%、185%、43%。     

Improvement of pea protein gelation at reduced temperature by atmospheric cold plasma and the gelling mechanism study

Pea protein as an alternative of soy protein has attracted growing interest in food industries. However, high temperature (> 95 °C) is required to enable heat-induced gelation and the formed gels are relatively weak. This research aimed to study the efficacy of atmospheric cold plasma (ACP) as a novel non-thermal technique to improve the gelling properties of pea protein. While native pea protein concentrate (PPC) (12 wt%) could not form gel under 90 °C, ACP-treated PPC showed good gelling properties when heated at 70–90 °C. The gels exhibited homogeneous three-dimensional network structure with interconnected macropores, and those prepared at 80 and 90 °C possessed good mechanical strength and viscoelasticity, as well as high water holding capacity. The gelling mechanism was studied by monitoring pea protein structural changes during ACP treatment and gel formation process via a transmission electron microscope, a Fourier transform infrared spectrometer, and a rheometer. These results revealed that ACP treatment contributed to the formation of protein fibrillar aggregates, and significantly reduced the PPC denaturation temperature, leading to protein unfolding at reduced temperature of 80–90 °C. ACP treatment also increased the protein surface hydrophobicity and exposed free sulfhydryl groups, which could facilitate the formation of hydrophobic interactions and disulfide bonds, leading to gels with improved mechanical properties. Moreover, hydrogen bonding could play an important role to stabilize the gel network during the gelling process. Owing to the short exposure time and energy efficiency, ACP is a promising technology to enable wide applications to pea protein as a gelling ingredient of plant protein-based food products, such as meat analogues and egg alternatives.     

Heat-induced gelation of whey protein at high pH studied by combined UV spectroscopy and refractive index measurement after size exclusion chromatography and by in-situ dynamic light scattering

Summary The interactions between β-lactoglobulin and α-lactalbumin involved in gelation at 67.5 °C at high pH and low salt concentration were studied by size exclusion chromatography, followed by UV and refractive index measurements, and by in-situ dynamic light scattering. This was achieved by choosing whey protein samples with different proportions of the two proteins. The ratio of absorbance at 280 nm to the refractive index was used to demonstrate that α-lactalbumin was incorporated in aggregates and gels and drastically changed the properties of the gel, making them much more turbid than the transparent gels formed by β-lactoglobulin alone at the same pH and ionic strength. At a ratio of 1:2 for α-lactalbumin relative to β-lactoglobulin in the samples, the gel consisted of a 1:1 mixture of the two proteins. The aggregates present after 10 min of heating at 67.5 °C had molar mass of about 6.10⁶ g/mol and a radius of gyration of about 40 nm. After gel formation the field autocorrelation function could be described as a power law over many decades of lag time for all samples, demonstrating selfsimilarity of the gel structure. The only exception to this was for the gel with high content of α-lactalbumin which showed an oscillatory behaviour of the autocorrelation function. Significant amounts of glycosylated caseino-macro-peptide were observed in many of the samples at the position of β-lactoglobulin. However it did not affect gelation as it remains in solution.     

纳米聚晶金刚石的高压高温合成

利用自行研制的二级大腔体静高压装置,通过高温超高压下石墨向金刚石的直接转变,合成出了纳米聚晶金刚石块体材料。合成压力约为17GPa,温度约为2300℃。微区X射线衍射分析表明,石墨转变成了立方相的金刚石。扫描电子显微镜及X射线全谱拟合分析显示,合成出来的金刚石晶粒尺寸约16nm。压痕法测得的样品维氏硬度为100GPa以上。     

超高压结合低温处理对牛肉组织结构及理化特性的影响

以牛肉为研究对象,通过均匀试验设计研究高压(100～600MPa,5～30min)结合低温(20～60℃)处理对牛肉的组织结构和理化性质的影响。结果表明,牛肉的弹性在一定压力(100～600 MPa)和温度(20～54.3℃)范围内增大。当温度低于41.6℃时,pH值因压力(100～600 MPa)的上升而增加,但压力与温度结合处理对pH值的影响无叠加作用。随着压力、保压时间以及温度的上升,肌肉的L值和煮制率均有不同程度的增加。同时,压力可导致肌肉的硬度增大,保压时间(5～30min)和温度(20～60℃)的上升则可引起硬度下降。     

Protein-based indicator system for detection of temperature differences in high pressure high temperature processing

Since the kinetics of change of target attributes in high pressure high temperature (HPHT) processing are not only pressure but also clearly temperature dependent, a control of temperature in space and time is indispensible. A tool that can easily detect temperature differences in prototype HPHT vessels during a HPHT process would aid the design of industrial HPHT equipments. In this work, the potential of ovomucoid as extrinsic, isolated, protein-based indicator to detect temperature differences inside a HPHT vessel was assessed. Ovomucoid fulfilled the selection criteria of a candidate indicator for HPHT. Solvent engineering was successfully used to shift the inactivation window of the candidate indicator into the HPHT processing window. Since, the dissociation equilibrium of buffer systems shifts under high pressure and/or under high temperature, a critical evaluation of the effect of a pH-shift of the selected phosphate buffer system in the context of protein-based indicator development was performed. The ovomucoid system inactivation kinetics were characterized under isobaric–isothermal conditions and modeled best by a first order inactivation model. A temperature dependent inactivation at constant pressure could be observed, which creates potential for the detection of temperature differences under HPHT conditions. These integrating properties were unaffected under dynamic, industrially relevant HPHT conditions.     

高温高压条件制备石榴皮鞣花酸的试验研究

目的:探索制备石榴皮鞣花酸新方法。方法:以高压蒸汽灭菌器为反应装置,分别研究了水解温度(压强)、水解时间和硫酸浓度(v/v)对鞣花酸得率的影响,并对工艺参数进行优化。结果:在最佳工艺条件:水解温度(压强)115℃(169 k Pa)、水解时间2 h、硫酸浓度6%(v/v)时,鞣花酸得率最高达3.09%,与常压相比得率提高了25.10%。结论:高温高压条件下水解石榴皮单宁制备鞣花酸效率较高,为生产工艺的改进提供了技术依据。      

Physicochemical and functional properties of cowpea protein isolates treated with temperature or high hydrostatic pressure

The effect of thermal (TT, 70 and 90 °C) and high hydrostatic pressure (HHPTs, 200, 400 and 600 MPa) treatments on physicochemical and functional properties of cowpea protein isolates (CPIs) extracted at pH 8.0 (A8) and pH 10.0 (A10) was analyzed. The pH of protein extraction affected some physicochemical properties (surface hydrophobicity (Ho) and denaturation temperature), without affecting the functional properties. Treatments led to the formation of soluble protein aggregates stabilized by disulfide bonds, especially with TT at 90 °C. TT and HHPTs shifted the wavelengths of maximum emission to red and to blue, respectively. All treatments induced unfolding and denaturation. HHPTs was more efficient than TT to enhance gelation and water holding capacities. Interestingly, treated and untreated CPIs exhibited high values of solubility (72–97%). TT and HHPT induced greater changes in physicochemical and functional properties of A8 than in those of A10. Remarkably, functional properties were improved from the less energetic treatments (70 °C, 200 MPa).Industrial relevanceThe comparison between treatments (one traditional and one corresponding to an emerging technology) gives information about the possibility of obtaining modified proteins for different functional purposes. The modified cowpea protein isolates may be used in beverages because of high solubility, in desserts because of gel formation capacity and/or as additives in other foodstuff because of improved water holding capacity. This knowledge would increase the added value of a local production currently marketed without processing.     

超高压与Alcalase协同作用制备牛乳清蛋白抗氧化肽

为探讨超高压与碱性蛋白酶Alcalase协同作用下乳清蛋白抗氧化肽的制备,以牛乳清分离蛋白(WPI)为原料,采用Alcalase分别对100～600MPa的超高压处理中和超高压处理后的WPI进行水解,并采用邻苯三酚自氧化法对其水解产物的超氧阴离子自由基清除能力进行测定。结果表明,超高压与Alcalase协同作用显著地促进了WPI的水解,其水解产物的抗氧化活性也显著提高;分子量小于3ku的组分具有最强的超氧阴离子自由基清除能力,其半抑制浓度IC50值最小,为411.62μg/mL。因此,超高压与Alcalase协同作用于乳清蛋白可用于开发新型天然抗氧化剂。     

Influence of protein concentration and coagulation temperature on rennet-induced gelation characteristics and curd microstructure

This study characterized the coagulation properties and defined the cutting window (CW; time between storage modulus values of 35 and 70 Pa) using rheometry for milk standardized to 4, 5, or 6% protein and set at 28, 32, or 36°C. Milks were standardized to a protein-to-fat ratio of approximately 1 by blending ultrafiltration retentate, skim milk, and whole milk. The internal curd microstructure for selected curd samples was analyzed with transmission electron microscopy and scanning electron microscopy. Lowering the coagulation temperature caused longer rennet coagulation time and time to reach storage modulus of 35 Pa, translating into a wider CW. It also led to a lower maximum curd-firming rate (MCFR) with lower firmness at 40 min at a given protein level. Increasing protein levels resulted in the opposite effect, although without an effect on rennet coagulation time at a given temperature. On coagulation at 28°C, milk with 5% protein resulted in a similar MCFR (～4 Pa/min) and CW (～8.25 min) compared with milk with 4% protein at 32°C, which reflects more standard conditions, whereas increasing milk to 6% protein resulted in more than doubling of the curd-firming rate (MCFR = 9.20 Pa/min) and a shorter CW (4.60 min). Gels set at 28°C had lower levels of rearrangement of protein network after 40 min compared with those set at 36°C. Protein levels, on the other hand, had no influence on the levels of protein network rearrangement, as indicated by loss tangent values. The internal structure of curd particles, as investigated by both scanning electron microscopy and transmission electron microscopy, appeared to have less cross-linking and smaller casein aggregates when coagulated at 28°C compared with 36°C, whereas varying protein levels did not show a marked effect on aggregate formation. Overall, this study showed a marked interactive effect between coagulation temperature and protein standardization of milk on coagulation properties, which subsequently requires adjustment of the CW during cheesemaking. Lowering of the coagulation temperature greatly altered the curd microstructure, with a tendency for less syneresis during cutting. Further research is required to quantify the changes in syneresis and in fat and protein losses to whey due to changes in the microstructure of curd particles arising from the different coagulation conditions applied to the protein-fortified milk.     

大麻纤维高温-酶联合脱胶技术

为克服单一化学法脱胶对环境污染严重和单一的生物酶脱胶率低的缺点,研究了大麻纤维高温-酶联合脱胶技术,讨论了高温脱胶后3种不同酶处理的大麻纤维化学成分与断裂强度的变化,用SEM、FTIR对大麻纤维高温酶脱胶前后的表面形态结构、化学成分进行表征。实验结果表明:果胶酶可作为高温脱胶后大麻纤维的脱胶酶使用;高温-果胶酶脱胶后大麻纤维中的果胶和半纤维素、木质素含量分别下降了83.3%和79.2%。     

Bacillus spore inactivation differences after combined mild temperature and high pressure processing using two pressurizing fluids

Spores of six species (28 strains) of dairy Bacillus isolates were added to sterile reconstituted skim milk and pressure processed (600 MPa for 60 s at 75 degrees C) using either a water-based pressurizing fluid or silicon oil. Processing temperatures peaked at 88 and 90 degrees C, respectively, for both fluids. For all strains, the log inactivation was consistently higher in the silicon oil than in the water-based fluid. This has potential implications for food safety assessment of combined pressure-temperature processes. High pressure processing causes mild heating during pressurization of both the target sample (i.e., spores) and the pressurizing fluid used for pressure delivery. Primarily, the adiabatic heat of compression of the fluids as well as other heat-transfer properties of the fluids and equipment determines the magnitude of this heating. Pressure cycles run with silicon oil were 7 to 15 degrees C higher in temperature during pressurization than pressure cycles run with the water-based pressurizing fluid, due to the greater adiabatic heat of compression of silicon oil. At and around the target pressure, however, the temperatures of both pressurizing fluids were similar, and they both dropped at the same rate during the holding time at the target pressure. We propose that the increased spore inactivation in the silicon oil system can be attributed to additional heating of the spore preparation when pressurized in oil. This could be explained by the temperature difference between the silicon oil and the aqueous spore preparation established during the pressurization phase of the pressure cycle. These spore-inactivation differences have practical implications because it is common practice to develop inactivation kinetic data on small, jacketed laboratory systems pressurized in oil, with extensive heat loss. However, commercial deployment is invariably on large industrial systems pressurized in water, with limited heat loss. Such effects should be considered in food safety assessments of combined pressure-temperature processes.