共查询到20条相似文献,搜索用时 15 毫秒
1.
A secreted peptidase from Pseudomonas panacis was identified and purified. Genome sequencing of the producer strain allowed identification of the peptidase as AprA based on a comparison to peptide sequences of mass spectra obtained from the purified enzyme. The amino acid sequence of the 49.4 kDa peptidase was 98% similar to the metallopeptidase AprX from a Pseudomonas fluorescens strain. The peptidase showed maximum activity at pH 8 and 40 °C and withstood general ultra-high temperature (UHT) processing (138 °C for 18 s) in skim milk, with 88.0 ± 7.7% of the initial enzyme activity remaining after heating. The peptidase showed considerable enzyme activity under storage conditions of UHT milk. The potential for spoilage of milk might during storage was verified by adding very low enzyme activities to UHT-treated milk. The addition of 1 pkat mL−1 peptidase activity resulted in a destabilisation of the milk during four weeks storage. 相似文献
2.
《International Dairy Journal》2003,13(6):427-439
Whole raw milk was processed using a 15 L h−1 homogeniser with a high-pressure (HP) valve immediately followed by a cooling heat exchanger. The influence of homogenisation pressure (100–300 MPa) and milk inlet temperature Tin (4°C, 14°C or 24°C) on milk temperature T2 at the HP valve outlet, on fat globule size distribution and on the reduction of the endogenous flora were investigated. The Tin values of 4–24°C led to milk temperatures of 14–33°C before the HP valve, mainly because of compression heating. High Tin and/or homogenisation pressure decreased the fat globule size. At 200 MPa, the d4.3 diameter of fat globules decreased from 3.8±0.2 (control milk) to 0.80±0.08 μm, 0.65±0.10 or 0.37±0.07 μm at Tin=4, 14°C or 24°C, respectively. A second homogenisation pass at 200 MPa (Tin=4°C, 14°C or 24°C) further decreased d4.3 diameters to about 0.2 μm and narrowed the size distribution. At all Tin tested, an homogenisation pressure of 300 MPa induced clusters of fat globules, easily dissociated with SDS, and probably formed by sharing protein constituents adsorbed at the fat globule surface. The total endogenous flora of raw milk was reduced by more than 1 log cycle, provided homogenisation pressure was ⩾200 MPa at Tin=24°C (T2∼60°C), 250 MPa at Tin=14°C (T2∼62°C), or 300 MPa at Tin=4°C (T2∼65°C). At all Tin tested, a second pass through the HP valve (200 MPa) doubled the inactivation ratio of the total flora. Microbial patterns of raw milk were also affected; Gram-negative bacteria were less resistant than Gram-positive bacteria. 相似文献
3.
In this study, we compare the effects of single- and double-cycle HP treatments at 600 MPa on inactivation of the natural microflora and physicochemical properties of whole and skimmed milk of high bacterial load. The results show that two-cycled HP (2 × 2.5 min) was more effective (P < 0.05) on microbial inactivation, and caused similar or slightly less changes (P > 0.05) in physicochemical properties of milk in comparison to single cycled HP (1 × 5 min). In addition to the expected milk protein structure changes, HP at 600 MPa caused only slight effects on milk fat and lactose. Minor decreases in levels of short chain fatty acids were observed with the cycled treatments, and the volatiles in general decreased after HP treatment, depending mostly on the pressure time but also on cycling in skimmed milk. The study confirmed the superior effect of two-cycle HP on microbial inactivation, and shows a slightly better preservation of the physical-chemical milk quality.Industrial relevanceMulti-cycling HP has been shown to be advantageous for microbial inactivation, but limited information is available regarding the effect on milk components in whole milk or skimmed milk. The present study compares the psychochemical properties of whole and skimmed milk processed by multi-cycling in comparison to single cycle HP treatment. Double cycled HP presented a superior effect on microbial inactivation and slightly better preservation of milk quality than one continuous HP. 相似文献
4.
Punsandani Udabage Mary Ann Augustin Cornelis Versteeg Amirtha Puvanenthiran Jin Ah Yoo Narissara Allen Ian McKinnon Mary Smiddy Alan L. Kelly 《Innovative Food Science and Emerging Technologies》2010,11(1):32-38
Physical properties of stirred yoghurt made from reconstituted skim milk that was high-pressure (HP)-treated at 100, 250 or 400 MPa, at 25, 70 or 90 °C, for 10 min, prior to inoculation with yoghurt cultures, were studied; portions of milk HP-treated at 25 °C were also heat-treated at 90 °C for 10 min before or after pressure treatment. Control yoghurts were made from skim milk given a heat treatment at 90 °C for 10 min. Fermentation time was not affected by treatment applied to the milk. HP treatment of skim milk at 25 °C, before or after heat treatment, gave stirred yoghurts of similar viscosities to that made from conventionally heat-treated milk. Lower viscosities were obtained when stirred yoghurts were made with milk HP-treated at elevated temperatures. A model is proposed to correlate properties of yoghurt with HP/heat-induced changes in interactions and structures of protein in the milk samples.Industrial relevanceTo meet end user expectations, the dairy industry needs to diversify its product range by tailoring specific functionalities. To meet these expectations, new processing methods such as high-pressure processing are of interest for their potential to achieve specific and/or novel functionalities and/or improve efficiencies, including reduced chemical and water use. In this paper, an investigation of the use simultaneous pressurization and heating of milk before the manufacture of stirred yoghurt is presented. 相似文献
5.
The effects of high-pressure (HP) treatment (200–500 MPa for 25 min at 25 °C) combined with storage temperature (25 and 4 °C) on the physicochemical properties of raw caprine milk were studied. Storage of HP-treated and untreated milk samples at 25 °C considerably affected the changes in the conformation of milk proteins, which were reflected by changes in the protein sedimentation rate, gradual decreases in the soluble calcium and phosphorus contents, a slight decrease in pH, an insignificant decrease (P > 0.05) in viscosity, and a decrease in the casein hydration level of milk at the end of the storage time. In contrast, the HP-treated and untreated milk samples stored at 4 °C demonstrated different characteristics than the samples stored at 25 °C. These results could be due to calcium and phosphate association with caseins, which screen charges and reduce the repulsion of micelles during the storage time. 相似文献
6.
The potential of high pressure (HP) to control bioactive components using seedlings of Brussels sprouts as a simple non-chopped vegetable system was examined. Enzyme activity in situ compared to purified enzyme and residual enzyme substrate in situ are used as three complementary measures for the HP effect. Purified myrosinase and seedlings of Brussels sprouts were submitted to HP 200–800 MPa at 5 °C for 3 min. The myrosinase activity decreased for both myrosinase systems upon increasing pressure to 800 MPa. Applying first-order kinetic to determine activation volumes revealed a linear relationship from 400 to 600 (ΔV# = − 19.04 mL/mol) and 450–600 MPa (ΔV# = − 37.79 mL/mol) for seedlings and purified myrosinase, respectively, indicating a protective effect of the plant matrix against enzyme inactivation. Purified myrosinase was activated at 200 MPa but at 800 MPa the glucosinolate degradation due to pressure induced disruption of the plant matrix seems to be partly counter-acted by myrosinase inactivation.Industrial relevanceHigh Pressure (HP) processing is an effective non-thermal preservation treatment for liquid and solid food. Moreover, over the last years, the potential of this technology to improve health and safety attributes of foods has been demonstrated. In particular, the ability of HP to preserve bioactive compounds has been established. There are only few studies evaluating the impact of HP on the complex bioactive glucosinolates-myrosinase. Therefore, this study opens the doors through the application of HP to preserve the bioactive glucosinolates in cruciferous vegetables by creating new processing solutions through controlled enzyme inactivation. Thus, HP could be an effective tool to achieve more effective solutions to obtain the new generation of convenient food and meet the need for new bioactive food products. 相似文献
7.
Cristina Bilbao-Sáinz Frank L. Younce Barbara Rasco Stephanie Clark 《Innovative Food Science and Emerging Technologies》2009,10(3):314-320
At atmospheric pressure, inactivation of protease from B. subtilis in raw milk and pasteurized milk (with and without homogenization) was studied in a temperature range of 50–80 °C. Thermal inactivation followed a first order kinetic model in the temperature range tested. Temperature dependence of the first order inactivation rate constants could be accurately described by the Arrhenius equation, allowing Ea values to be calculated. Different milk systems did not show differences in enzyme thermo stability.The combined thermal (40, 50 and 60 °C)-high hydrostatic pressure (300–450 and 600 MPa) effect on protease activity was studied. Protease was very resistant to high pressures. Pressure stability was higher in raw milk than in pasteurized milk; homogenization appeared to have a protective effect on the enzyme. The separate effects of pressure and temperature on enzyme inactivation were related to changes in L?-values and milk appearance.A very pronounced antagonistic effect between high temperature and pressure was observed, i.e. at temperatures where thermal inactivation at atmospheric pressure occurs rapidly, application of pressure up to 600 MPa exerted a protective effect.Industrial relevanceHigh hydrostatic pressure (HHP) is an emerging technology that has been successfully applied as a minimal process for a variety of foods. Although the potential for the use of HHP treatment as an alternative method to heat treatment of milk was proposed almost a century ago, the suitability of this innovative technology to extend the shelf-life of milk hinges not only on its ability to inactivate pathogenic vegetative microorganisms but also on its effectiveness to inactivate indigenous and endogenous enzymes. This work examines the combined effects of temperature, pressure and homogenization on the protease (exogenous enzyme from B. subtilis) activity in milk. Inactivation of protease could extend the shelf life of milk. 相似文献
8.
Paneer, a product of India similar to cottage cheese, was prepared from cow's milk heat-treated (90 °C/5 min) (HTMP) or high-pressure (HP) treated (500 MPa/15 min) (HPPMP) for achieving pasteurization. HTMP and HPPMP paneer samples were HP treated (500 MPa for 15 min) again after vacuum packaging to get HTMP/HPP and HPPMP/HPP samples, respectively. The third set of samples were obtained by dipping HTMP and HPPMP paneer samples in 2% lactic acid solution and then subjecting them to the same HP treatment and stamped as HTMP/LA/HPP and HPPMP/LA/HPP, respectively. All six types of vacuum-packed paneer were studied for changes in moisture, acidity, pH, color, texture, and microbiological quality during storage at 5 ± 1 °C and 25 ± 1 °C. High-pressure treatment of milk increased the yield of paneer significantly (P < 0.05) from 13.9 ± 0.59% (HTMP) to 18.2 ± 0.32% (HPPMP). Paneer treated with lactic acid and high-pressure treatment (HTMP/LA/HPP and HPPMP/LA/HPP) had higher textural stability than HTMP, HTMP/HPP, HPPMP, and HPPMP/HPP for up to 28 days, but had a reduced moisture content, higher acidity, and lower whiteness index. High-pressure treatment of vacuum-packed paneer (HTMP/HPP and HPPMP/HPP) led to the formation of a more compact paneer matrix (higher hardness), higher moisture expulsion, and yellowness (b*). Thus, high-pressure processing of paneer could pave paths for extending paneer shelf-life without any additives and thermal treatment. 相似文献
9.
Clostridium sporogenes (ATCC 7955) spores inoculated in milk (2% fat) were subjected to high-pressure (HP) treatments (700–900 MPa) and at elevated
temperatures (80–100 °C) for selected times up to 32 min. Samples were sealed in 1-mL plastic vials and placed in a specially
constructed insulated chamber to prevent temperature drop during the treatment. Both pressure pulse (with no hold time) and
pressure hold techniques were employed for treatment. Pressure pulse resulted in a small, but consistent, destruction (up
to 0.5 log kill) of spores. During the pressure hold treatment, the destruction followed a first-order model (R
2 > 0.90). The kinetic data were compensated for the small variations in temperature during the treatment. As expected, higher
pressures and higher temperatures resulted in a faster rate of spore destruction. Temperature-corrected D values ranged from 13.6 to 2.4 min at 700 MPa and 7.0 to 1.3 min at 900 MPa, respectively, with process temperatures set
at 90 and 100 °C. In comparison, thermal treatments gave D values ranging from 156 min at 90 °C to 12.1 min at 100 °C. The temperature sensitivity Z
P values (16.5 to 20.3 °C) under high pressure (700–900 MPa) were higher than under conventional thermal processing (9.0 °C),
indicating the spore’s thermal resistance to increase at HP processing conditions. The pressure sensitivity Z
T values varied between 450 and 680 MPa under the elevated temperature (80–100 °C) processing conditions. Overall, C. sporogenes 7955 spores were relatively more sensitive to temperature than pressure. 相似文献
10.
Liao Hongmei Kui Zhong Xiaojun Liao Xiaosong Hu 《International Journal of Food Science & Technology》2014,49(3):696-702
This study assessed the inactivation of microorganisms naturally present in raw bovine milk by high‐pressure carbon dioxide (HPCD) at 10–30 MPa and 20–50 °C for 20–70 min. The log reduction of microorganisms increased as raw bovine milk was exposed to higher pressures and temperatures and longer treatment times. The maximum reduction of aerobic bacteria (AB) was 4.96‐log at 25 MPa and 50 °C for 70 min. At lower temperatures and treatment times, a complete inactivation of yeasts and moulds (Y&M) and coliform bacteria (CB) was obtained at 25 MPa. Changes in microorganisms naturally present in raw bovine milk during storage were also assessed. There were 1.83‐log survival of AB, 0.65‐log survival of Y&M and a complete inactivation of CB in raw bovine milk when subjected to HPCD at 25 MPa and 40 °C for 50 min. Moreover, the AB, Y&M and the CB in raw bovine milk exhibited insignificant alterations during storage at 4 °C for 15 days, indicating a potential capability of HPCD to extend the shelf life of milk. 相似文献
11.
Effect of perturbation factors on phase transition metastable positions of whole milk (4% fat content) and their influence on microbial destruction characteristics of non-pathogenic Escherichia coli inoculated in milk subjected to high pressure low temperature treatment were evaluated using a specially developed high pressure (HP) cooling system. Initially, the phase transition data of milk transitioning through the metastable phases were obtained and fitted successfully using Simon-like models as done in previous studies and polynomial formulas with R2 of 0.997 & 0.996 for ice I, and 0.989 & 0.989 for ice III, respectively. The phase transition position of milk was explored with 5% and 10% sodium chloride solution as perturbation sources, respectively. Results showed that the 5% sodium chloride solution can reduce the transition pressure of milk by 43 MPa and increase the transition temperature by 4.1 °C, so that the milk can achieve phase transition at lower pressure and higher temperature. Phase transition microbial destruction was characterized by discontinuity, mutation and segmentation when the phase transition pressure interval 250– 300 MPa was carefully refined. The inactivation amount of E. coli before the phase transition (250 MPa) was 1.11 log and the phase transition process itself brought an additional 1.26 log destruction of E. coli population in milk.Industrial relevanceHigh pressure low temperature (HPLT) phase change kinetics were employed to enhance microbial destruction. HPLT was established based on a self-cooling unit positioned inside conventional HP chamber offering opportunities for scale up and commercialization. The effectiveness of HPLT phase transition for Escherichia coli destruction was demonstrated. The related research in metastable state provides a reference point for commercial application of high-pressure-low-temperature technology for microbial destruction and quality enhancement. 相似文献
12.
《Innovative Food Science and Emerging Technologies》2008,9(2):217-223
The effects of pulsed electric field (PEF) treatments at field intensities of 25–37 kV cm− 1 and final PEF treatment temperatures of 15 °C and 60 °C on the inactivation of alkaline phosphatase (ALP), Total Plate Count (TPC), Pseudomonas and Enterobacteriaceae counts were determined in raw skim milk. At 15 °C, PEF treatments of 28 to 37 kV cm− 1 resulted in 24–42% inactivation in ALP activity and < 1 log reduction in TPC and Pseudomonas count, while the Enterobacteriaceae count was reduced by at least 2.1 log units to below the detection limit of 1 CFU mL− 1. PEF treatments of 25 to 35 kV cm− 1 at 60 °C resulted in 29–67% inactivation in ALP activity and up to 2.4 log reduction in TPC, while the Pseudomonas and Enterobacteriaceae counts were reduced by at least 5.9 and 2.1 logs, respectively, to below the detection limit of 1 CFU mL− 1. Kinetic studies suggested that the effect of field intensity on ALP inactivation at the final PEF treatment temperature of 60 °C was more than twice that at 15 °C. A combined effect was observed between the field intensity and temperature in the inactivation of both ALP enzyme and the natural microbial flora in raw skim milk.Industrial relevanceMilk has been pasteurised to ensure its safety and extend its shelf life. However, the need for retaining heat-sensitive nutrient and sensory properties of milk has resulted in interest in the application of alternative technologies. The results of the current study suggest that PEF as a non-thermal process can be employed for the treatment of raw milk in mild temperature to achieve adequate safety and shelf life while preserving the heat-sensitive enzymes, nutrients and bioactive compounds. 相似文献
13.
Inactivation of Escherichia coli ATCC 11775 and Pseudomonas fluorescens ATCC 948 in UHT whole (4% fat) milk during thermal processing at 56–62 °C and pulsed electric field (PEF) processing at 30 or 35 kV cm−1 at approximately 30, 40 or 50 °C was investigated. E. coli ATCC 11775 was more heat-resistant than P. fluorescens ATCC 948, but more susceptible to PEF processing. All inactivation kinetics showed strong deviations from log-linearity. Thus, a simplified logistic (log-decay) regression model was used to accurately predict thermal and PEF inactivation of E. coli ATCC 11775 and P. fluorescens ATCC 948 under various treatment conditions. This is a useful tool for identifying processing conditions to inactivate pathogenic and spoilage microorganisms in whole milk at sub-pasteurisation temperatures. 相似文献
14.
The advantage of using high pressure (HP) cycling treatment compared with continuous HP treatment was investigated for the inactivation of bacterial spores. The effects of parameters such as pulse number, pressure level, treatment temperature, compression and decompression rates, and time between pulses were evaluated. For this purpose, Bacillus subtilis and B. cereus spores (108 and 106 CFU/mL respectively) were suspended in 2-(N-morpholino) ethanesulfonic acid (MES) buffer solution, tryptone salt (TS) buffer solution, or infant milk and treated by HP cycling at 300–400 MPa, at 38–60 °C, for 1–5 pulses. Pressure cycling reduced the number of viable spores by 1.8 and 5.9 log respectively for B. subtilis and B. cereus species. Continuous HP treatments were performed at the same pressure and temperature for similar treatment durations. Our results showed that the spore inactivation ratio was correlated with the cumulative exposure time to pressure rather than to effects of the cycling process. Greater spore inactivation caused by HP cycling was observed only when faster compression and decompression rates were applied, probably due to adiabatic heating. A three-step kinetic model was developed, which seemed to support our hypothesis regarding the mechanisms of inactivation by pressure cycling and continuous HP treatments.Industrial relevanceThe resistance of bacterial spores to HP limits the industrial applications to refrigerated food products. In this study, we investigated the use of pressure cycling as a means to improve spore baroinactivation at moderate temperatures (T < 60 °C). We showed that cycling pressure does not significantly increase bacterial spore inactivation in comparable treatment duration, but certainly increases material fatigue in HP vessels. Thus, under moderate temperature, cycling pressure treatment is not industrially relevant. 相似文献
15.
The influence of high intensity ultrasound coupled with thermoprocessing on the inactivation of Geobacillus stearothermophilus vegetative cells and spores in skim milk powder was explored using response surface methodology and two polynomial models were developed. Optimization of cell reduction (4.8 log) was found to be at 19.75% total solids (TS), 45 °C, and 30 s, while optimization of spore reduction (0.45 log) was found to be at 31.5% TS, 67.5 °C, and 17.5 s. Model verification experiments were performed using common milk powder processing conditions. Results showed the inactivation of cells and spores to be most effective before (9.2% TS, 75 °C, and 10 s) and after (50% TS, 60 °C, and 10 s) the evaporator during milk powder processing and may produce an additive effect in microbial reduction when the two locations are combined, resulting in a 5.8 log reduction for vegetative cells and 0.51 log reduction for spores. 相似文献
16.
Fruit smoothie samples were thermally (P70 > 10 min) or high hydrostatic pressure (HHP) processed (450 MPa/20 °C/5 min or 600 MPa/20 °C/10 min) and the total antioxidant capacity (TAC), levels of antioxidant groups [total phenols (TP), anthocyanins and ascorbic acid], instrumental colour, polyphenol oxidase (PPO) enzyme activity and dissolved oxygen were examined over a storage period of 10 h at 4 °C. Thermal processing of smoothies reduced (p < 0.001) TAC and TP values, ascorbic acid and L and a colour attributes (lightness and redness respectively) compared to fresh and HHP-450 processed samples. Conversely, it did result in complete inactivation of PPO enzyme, with no activity detected. Of the HHP treatments, HHP-450 samples had higher (p < 0.001) levels of total antioxidant, phenols and anthocyanin content than HHP-600 samples. However, the latter was more effective in reducing (p < 0.001) the endogenous enzyme activity of the smoothies. .Ascorbic acid content degraded over the storage for all smoothies. HHP-600 samples had high initial values, which declined slowly over storage, while thermal samples had the lowest initial value (0.5 h) that fell below detectable limits by 10 h. Despite these data, less pronounced effects were observed for storage. No significant effects were observed for total anthocyanin and phenolic contents as well as L and colour change (ΔE) variables. Overall, HHP processing of smoothies at moderate temperatures may be a suitable alternative to traditional thermal processing. 相似文献
17.
《International Dairy Journal》2006,16(6):655-661
High pressure-induced inactivation of the indigenous milk enzymes alkaline phosphatase (ALP), γ-glutamyltransferase (GGT) and phosphohexoseisomerase (PHI) was studied in the pressure range 400–800 MPa at temperatures between 5 and 40 °C. With respect to pressure stability the following ranking was observed: ALP>GGT>PHI. PHI was inactivated after pressure treatment at 500 MPa and 20 °C for 10 min. In terms of reaction kinetics, inactivation of GGT followed first-order reaction kinetics in the range of 400–800 MPa whereas a reaction order of 1.5 was found for ALP. Reactivation of pressure-treated ALP was observed at low enzyme activity resulting from severe pressure treatment and 2 h storage at 35 °C. The influence of process temperature on the pressure-induced inactivation of GGT and ALP was limited in the range 5–40 °C. 相似文献
18.
Effect of thermal buffer zone was examined on the microbial inactivation through a pressure-assisted thawing. A plastic bag of bacterial suspension enclosed with a thermal buffer zone was frozen at − 50 °C, and treated for 20 min with a pressure-assisted thawing in water of 4 °C. A reduction of 8-log cycle was obtained at 200 MPa for the stationary growth phase cells of Escherichia coli that was suspended in 1% skim milk and enclosed with wheat flour/water paste and two polytetrafluoroethylene plates. When 100% ethanol was used as a thermal buffer and the samples were pressured at 194 MPa in 1% skim milk, levels of E. coli and Listeria monocytogenes were reduced by 6-log cycle and 7-log cycle, respectively. Staphylococcus aureus decreased by 4-log cycle.Industrial relevanceThis work will contribute to new developments in the pressure processing of foods, since the use of a thermal buffer zone in pressure-assisted thawing was very effective in enhancing the level of pressure-induced microbial inactivation. 相似文献
19.
J. M. Carreño M. C. Gurrea F. Sampedro J. V. Carbonell 《European Food Research and Technology》2011,232(2):265-274
The inactivation kinetics of Lactobacillus plantarum in a mandarin juice treated by thermal treatment (45–90 °C), high-pressure homogenisation (HPH) (30–120 MPa at 15 and 30 °C)
and high-pressure processing (HPP) (150–450 MPa at 15, 30 and 45 °C) were fitted to different Weibullian equations. A synergic
effect between pressure and temperature was observed in HPH and HPP treatments achieving 2.38 log cycles after 120 MPa at
30 °C for 10 s (final T of 45 °C) and 6.12 log cycles after 400 MPa at 45 °C for 1 min (final T of 60 °C), respectively. A combined treatment of 100 MPa at 15 °C for 10 s and 300 MPa at 15–30 °C for 1 min in HPH and HPP,
respectively, was needed to the first logarithm microbial population decline. Weibull model accurately predicted microorganism
inactivation kinetics after HPH and HPP processing when displaying single shoulder or tail in the survivor curves, whereas
when a more complex trend was observed after thermal treatment, the double-Weibull equation was found more appropriate to
explain such behaviour. Equivalent treatments that achieved the same degree of microbial inactivation (77 °C–10 s in thermal
processing, 120 MPa–10 s at 30 °C in HPH processing and 375 MPa–1 min at 30 °C in HPP) were selected to study the effects
on quality parameters. The application of dynamic pressure led to a decrease in sedimentable pulp, transmittance and juice
redness, thus stabilising the opaqueness and cloudiness of mandarin juice. Pectin methyl esterase (PME) was found to be highly
baroresistant to static and dynamic pressure. Carotenoid content remained unaffected by any treatment. This study shows the
potential of high-pressure homogenisation as an alternative for fruit-juice pasteurisation. 相似文献
20.
《International Dairy Journal》2005,15(6-9):655-662
The mechanism of high-pressure (HP)-induced changes in rennet coagulation properties of milk, particularly the role of whey protein-casein micelle associations, was studied. Treatment at 100 or 250 MPa reduced the rennet coagulation time (RCT) of raw skimmed bovine milk, compared with untreated milk. Treatment at 400 MPa had little effect, but at 600 MPa, RCT increased considerably. HP-induced increases in RCT did not occur in serum protein-free milk or milk treated with the sulphydryl-oxidising agent KIO3, which prevents association of denatured β-lactoglobulin with casein micelles. Treatment at 5 or 10 °C at 250–600 MPa resulted in shorter RCT than treatment at 20 °C. In milk without KIO3, coagulum strength was highest after treatment at 250 or 400 MPa, whereas in milk with KIO3 it was highest after treatment at 400 MPa. These results indicate the significance of HP-induced association of whey proteins with casein micelles for rennet coagulation properties of milk. 相似文献