Effect of high hydrostatic pressure on physicochemical and biochemical properties of milk

Interest in high hydrostatic pressure (HHP) applications on milk and dairy products has recently increased as HHP offers a new technology for food preservation to the food industry. Although HHP-induced microbial destruction, rennet or acid coagulation of milk and increase in cheese yield has been reported, the actual effect of HHP application on milk constituents still remains to be unexplained. Therefore, we have analyzed the effect of HHP on physicochemical and biochemical properties such as turbidity, pH and especially protein micelle surface hydrophobicity of milk proteins. To serve for this purpose, milk samples with different fat contents were pressurized from 110 to 440 MPa at 25 °C for 10 and 20 min. Turbidity decreased with pressure increase and there was a slight change in pH. In order to measure the extent of exposure of hydrophobic groups of proteins to HHP, the method described by Bonomi et al. [1], based on use of a fluorescent probe, was utilized. In the light of the results obtained, it can be concluded that HHP has an effect on non-covalent interactions and especially hydrophobic bonds in milk. As the pressure is increased from 110 to 440 MPa, the micelles possibly decompose into sub-micelles and the embedded hydrophobic areas inside these micelles re-position in such a way that they can readily interfere with the fluorescent marker, ANS. These results may lead to practical applications of HHP treatment in the dairy industry to produce microbiologically safe, minimally processed products with high nutritional and sensory quality and novel texture.     

Effect of high hydrostatic pressure processing on the rennet coagulation kinetics and physicochemical properties of sheep milk rennet-induced gels

The effects of high hydrostatic pressure on the constituents and coagulation ability and their effect on cheese production of sheep milk have not been studied in detail. The objective of this work was to evaluate the effect of high hydrostatic pressure processing on the coagulation kinetics and physicochemical properties of sheep milk and to explore how such treatment could improve the cheesemaking process. Five batches of milk were tested: 1 untreated control batch and 4 batches each subjected to a different pressure (150, 300, 450, or 600 MPa) for 5 min at 10°C. As treatment pressure increased, values of electrical conductivity and oxidation-reduction potential were found to decrease. However, no significant reduction in pH was recorded. Treatment pressures >300 MPa produced milk with lower lightness (luminosity) and a more yellow and green hue. Pressures >150 MPa resulted in micellar fragmentation, as well as significant increases in particle size, viscosity, and water-holding capacity as a consequence of the denaturing of soluble proteins. High-pressure treatments increased the solubility of colloidal calcium phosphate, leading to a considerable increase in the concentration of minerals in the serum phase. The highest concentrations of calcium and phosphorus in the rennet whey of milk were reached at 300 MPa. Curd coagulation time was reduced by 28% at pressures >300 MPa, and an increase in the curd firming rate was observed. As treatment pressure increased to 450 MPa, the firmness, elasticity, and the percentage creep recovery of gels increased, whereas values of compliance and fracture strain were reduced. Thus, we can conclude that 300 MPa is the optimum treatment pressure for milk intended for cheesemaking by enzymatic coagulation. This pressure produced milk with optimal coagulation kinetics and water-holding properties with the least loss of fat and protein to the whey.     

Effects of high‐pressure homogenisation on physicochemical characteristics of partially skimmed milk

The changes in partially skimmed milk (0.5% fat) physicochemical properties and proteins after high‐pressure homogenisation (HPH) at 100, 200 and 300 MPa were investigated. Processing parameters and changes in pH, ethanol precipitation stability, lightness, whey protein denaturation, hydrophobicity and viscosity were evaluated. No significant differences were found between milk pH and nonprotein nitrogen content before and after HPH. Ethanol stability, lightness and hydrophobicity increased when pressure was increased from 100 MPa to 300 MPa. Whey protein denaturation, evaluated through noncasein nitrogen, occurred only at 200 to 300 MPa, and viscosity increased just at 300 MPa. Therefore, HPH changed some milk physicochemical characteristics, mainly those related to protein content. These results highlight that HPH processing is a promising technology to improve partially skimmed milk mouth feel being suitable for dairy products manufacturing.     

Effects of high hydrostatic pressure on the physicochemical and emulsifying properties of sweet potato protein

The influence of high hydrostatic pressure (HHP) treatment on the physicochemical and emulsifying properties of sweet potato protein (SPP) at various concentrations, e.g. 2%, 4% and 6% (w/v, SPP‐2, SPP‐4 and SPP‐6), was investigated. Significant differences in hydrophobicity, enthalpy of denaturation and solubility were observed (P < 0.05). Emulsifying activity indexes (EAI) of SPP‐2 and SPP‐6 increased at 400 MPa, whereas EAI of all SPP significantly decreased at 600 MPa (P < 0.05). Emulsion stability (ESI) was significantly decreased for SPP‐2 and SPP‐6, while increase in ESI was observed for SPP‐4 above 200 MPa (P < 0.05). SPP‐2 emulsions showed sharp decrease in apparent viscosity with pressure increase, while pseudo plastic flow behaviour was not changed for all of emulsions. Sporamins A and B were well‐adsorbed in pressurised emulsion without displacement. These results suggest that HHP treatment could be used to modify the physicochemical and emulsifying properties of SPP.     

Survival and growth of Yersinia enterocolitica strains inoculated in skimmed milk treated with high hydrostatic pressure

Four human pathogenic strains of Yersinia enterocolitica (serotypes O:1, O:3, O:8, and O:9) were inoculated (7-8 log CFU/ml) in UHT skimmed milk and treated at 300, 400, and 500 MPa for 10 min at 20 degrees C, and then kept at 8 degrees C to assess their evolution for 15 days. Treatments at 400 and 500 MPa caused the highest lethality, generally reaching counts below detection level (1 CFU/ml) in the culture media. At 300 MPa, the most baroresistant serotypes were O:3 and O:8. After 15 days of storage at 8 degrees C, Y. enterocolitica showed growth over 8 log (CFU/ml) in all treatments. Kinetic study of microbial inactivation in skimmed milk was performed with serotype O:8 at 300 MPa, showing a tailing after 35 min of pressure treatment.     

Inactivation of pathogenic Escherichia coli in skimmed milk using hhigh hydrostatic pressure

The pressure resistance of a range of pathogenic Escherichia coli strains was determined in skimmed milk. Pressure resistances varied widely among the 12 strains tested, with the two most resistant being an enterotoxigenic E. coli (NCTC 11601) and an enteroinvasive E. coli (NCTC 9706). A pressure treatment of 500 MPa for 40 min gave only a 4-log reduction of these two most resistant strains, but after a treatment of 600 MPa for 30 min, no survivors of either strain could be detected (>7 log reduction). The effect of the length of time in the stationary phase on the pressure resistances of these two strains was determined. Pressure resistance (600 MPa for 10 min at 20°C) was determined after 12 h incubation at 37°C in tryptone soya broth with 0.6% yeast extract added (TSBYE) (early stationary phase) and at 24-h intervals after this. The pressure resistances of these strains did not change significantly for the first 5 days after the onset of the stationary phase, after which time their resistances decreased. When cells were pressure-treated 7 days after they went into stationary phase, no survivors could be detected.     

Effect of skimmed milk and its fractions on the inactivation of Escherichia coli K12 by high hydrostatic pressure treatment

We investigated the effects of skimmed milk and its protein fractions (casein, whey, globulin, and albumin) on the injury and inactivation of Escherichia coli K-12 by high hydrostatic pressure (HHP) treatment. The protective effect of skimmed milk on HHP-mediated inactivation and injury of E. coli increased with increases in the skimmed milk concentration. However, protein fractions derived from skimmed milk did not exhibit this protective effect. Microscopy analysis by DAPI/PI staining indicated that some cells were localized in the solid portion of skimmed milk, and some of these cells were alive. The coagulated fraction derived from the autoclaved whey fraction also showed a significant protective effect. We speculate that the solid portion in skimmed milk could provide the protective effect to bacterial cells.     

Effect of high hydrostatic pressure pretreatment on flavour and physicochemical properties of freeze-dried carambola slices

Ripe carambolas are hard to store and transport, while freeze-dried ones are easy to store. However, its long production time leads to higher costs. This study shows that high hydrostatic pressure (HHP) treatment could shorten the freeze-drying time of carambola slices. After HHP treatment (25–250 MPa), the drying time of the fresh sample can be shortened by 33.3–44.4% and the distribution of water and pigment in tissues is much uniform. With the increment of the pressure, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radical scavenging rate are increased. At 250 MPa, the total phenolic content (TPC) increased from 11.34 to 13.36 mg GAE g⁻¹, and the total flavonoid content (TFC) of the control sample was increased from 10.77 to 12.73 mg RE g⁻¹. Compared with the untreated sample, HHP treatment can enhance the flavour and shorten the freeze-drying time. This work guides the application of HHP technology for drying food processing.     

Effects of high hydrostatic pressure on physicochemical and functional properties of walnut (Juglans regia L.) protein isolate

BACKGROUND: Walnut (Juglans regia L.) is a good source of protein that has potential application in new product formation and fortification. The main objectives of this study were to investigate the effects of high hydrostatic pressure (HHP) treatment (300–600 MPa 20 min) on physicochemical and functional properties of walnut protein isolate (WPI) using various analytical techniques at room temperature. RESULTS: The results showed significant modification of solubility, free sulfhydryl content and surface hydrophobicity with increased levels of HHP treatment, indicating partial denaturation and aggregation of proteins. Differential scanning calorimetry and fluorescence spectrum analyses demonstrated that HHP treatment resulted in gradual unfolding of protein structure. Emulsifying activity index was significantly (P < 0.05) increased after HHP treatment at 400 MPa, but significantly decreased (P < 0.05) relative to the untreated WPI with further increase in pressure. HHP treatment at 300–600 MPa significantly decreased emulsion stability index. Additionally, HHP‐treated walnut proteins showed better foaming properties and in vitro digestibility. CONCLUSION: These results suggest that HHP treatment could be applied to modify the properties of walnut proteins by appropriate of pressure levels, which will help in using walnut protein as a potential food ingredient. © 2012 Society of Chemical Industry     

Food processing by high hydrostatic pressure

The use of high hydrostatic pressures (HHP) for food processing is finding increased application within the food industry. One of the advantages of this technology is that because it does not use heat, sensory, and nutritional attributes of the product remain virtually unaffected, thus yielding products with better quality than those processed traditional methods. HHP have the ability to inactivate microorganisms as well as enzymes responsible for shortening the life of a product. In addition to lengthening the shelf-life of food products, HHP can modify functional properties of components such as proteins, which in turn can lead to the development of new products. Equipment for large-scale production of HHP processed products are commercially available nowadays. Guacamole, sliced ham, oysters, and fruit juices are some of the products currently available on the market. HHP technology is one of the most promising nonthermal processes.     

Inactivation of Salmonella typhimurium DT 104 in UHT whole milk by high hydrostatic pressure

Cell suspensions of Salmonella typhimurium DT 104 in ultra-high temperature (UHT) whole milk were exposed to high hydrostatic pressure at 350, 400, 450, 500, 550, and 600 MPa at ambient temperature (ca. 21 degrees C). Tailing was observed in all survival curves, and sigmoidal survival curves were observed at relatively high pressure (500-600 MPa). Four modeling methods (linear and nonlinear including Weibull, modified Gompertz, and log-logistic models) were fitted to these data at 500, 550, and 600 MPa. Performances of the modeling methods were compared using mean square error (MSE). The linear regression model at these three pressure levels had a mean square error (MSE) of 1.260-2.263. Nonlinear regressions using Weibull, modified Gompertz, and log-logistic models had MSE values in the range of 0.334-0.764, 0.601-1.479, and 0.359-0.523, respectively. Modeling results indicated that first-order kinetics could not accurately describe pressure inactivation of S. typhimurium DT 104 in UHT milk; the log-logistic model produced the best fit to data.     

A preliminary study about the influence of high hydrostatic pressure processing on the physicochemical and sensorial properties of a cloudy wheat beer

High hydrostatic pressure (HHP) (400 MPa/15 min, 500 MPa/10 min, 600 MPa/5 min at 20 °C) and heat (60 °C/15 min) processing of wheat beers were evaluated by examining their impacts on microorganisms, colloidal haze, flavour, foam stability and shelf‐life prediction during 84 days of storage at 20 °C. The results obtained showed that the microbiological stability of HHP beers was comparable with heat‐treated samples, and the development of both aerobic bacteria and lactic acid bacteria was inhibited for 84 days of storage. The main parameters of the wheat beer, such as ethanol content, original extract, pH, bitterness and viscosity, were scarcely affected by either treatment compared with the control samples; however, heat pasteurization increased the colour value. Heat‐pasteurized beer resulted in an increase in the phenethyl alcohol concentration and a decrease in isoamyl acetate and ethyl acetate levels compared with the HHP samples. These treatments did not affect the amount of 4‐vinylguaiacol and 4‐vinylphenol in the beer. The HHP‐treated beers had higher colloidal haze and foam stability values than the heat‐pasteurized beers. Dynamic light scattering analysis showed that HHP treatments at 500 MPa/10 min resulted in smaller and more uniform particle sizes, which had a positive effect on beer haze stability during storage. Copyright © 2016 The Institute of Brewing & Distilling     

全脂乳粉和脱脂乳粉在1kHz～10MHz下的介电特征研究

分别研究了各4种不同品种的全脂乳粉和脱脂乳粉在1kHz～10MHz波段的介电特性。结果发现:随着频率的增加,全脂乳粉和脱脂乳粉的ξ’和ξ″值呈单调递减趋势;全脂乳粉的ξ’和ξ″值都高于脱脂乳粉,相同类型乳粉各品种间的ξ’和ξ″差异不大;全脂乳粉的ξ″值在103～105Hz频率段减小趋势明显,且ξ″值的对数与频率的对数成线性反比关系,而脱脂乳粉无此规律;全脂乳粉和脱脂乳粉的穿透深度Dp随频率的提高而减小,两类乳粉的介电特性差异可能与它们各自的脂肪和乳糖含量有关。     

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.     

Effects of high hydrostatic pressure on nutritional composition and cooking quality of whole grains and legumes

Whole grains and legumes are important sources of nutrients and have essential influences in the human diet. However, the consumption of whole grains and legumes faces many challenges, such as their poor edible and cooking qualities. Antinutritional factors and allergens also affect consumption of whole grains and legumes. High hydrostatic pressure (HHP) treatment is a recent non-thermal processing technology, which can improve the edible quality of whole grains and legumes. HHP also preserves the natural nutrition and freshness of food by lowering the concentration of antinutritional elements and sensitizing allergens while minimally altering the color and scent of the food components. This review summarized the principle of HHP treatment technology, the effects of HHP treatment on the nutritional components, antinutritional factors, and cooking qualities of whole grains and legumes. This review also described the potential effects of HHP-treated whole grains and legumes on some diseases. This review is expected to provide references for the application of HHP treatment in whole grains and legumes.     

Effect of combined treatments of ultrasound and high hydrostatic pressure processing on the physicochemical properties,microbial quality and shelf-life of cold brew tea

Effects of ultrasound combined with high hydrostatic pressure (HHP) on physicochemical properties,microorganisms and storage attributes of cold brew tea were investigated. HHP at 400 MPa/5 min/25 °C inactivated the total aerobic bacteria, yeast and mould in cold brewed tea prepared by static brewing (SB-tea) at 13 h/4 °C, ultrasonic bath (UB-tea) at 150 W/120 min/0 °C and ultrasonic pulveriser (UP-tea) at 600 W/40 min/0 °C, ensuring their microbiological safety. The results showed that there was no significant difference in the concentration of tea polyphenols between hot brewed tea prepared by 7 min/100 °C and cold brewed tea under different preparation conditions, while the caffeine in cold brewed tea was significantly lower (P < 0.05) than that in hot brewed tea. During the storage period of 8 days, compared with the untreated group, the cold brewed tea after HHP treatment had better microbiological safety. In addition, HHP treatment constantly maintained the tea polyphenols, pH, colour, antioxidant capacity and turbidity in cold brewed tea. The untreated and HHP-treated cold brew tea were evaluated by 20 trained volunteers. Results showed that UB-tea was more close to SB-tea than UP-tea in sensory profile, while HHP seem to maintain a good sensory profile as well. Therefore, this particular combined technology of ultrasonic bath and HHP displayed considerable potential for application in the cold brew tea manufacturing industry.     

Correlation between the dielectric properties and the physicochemical characteristics and proximate composition of whole,semi-skimmed and skimmed sheep milk using chemometric tools

The influence of temperature, frequency, composition and physicochemical characteristics of sheep milk on its dielectric properties was evaluated as well as the performance of different chemometric methods to predict the dielectric properties and classify the type of sheep milk (whole, semi-skimmed and skimmed). Of the chemometric methods evaluated, artificial neural network exhibited the best performance for prediction of the dielectric properties, while sensitivity analysis showed temperature, electrical conductivity, and fat and calcium content as variables with the most impact. All pattern recognition techniques showed 100% for recognition and prediction ability to classify correctly the type of milk. Although the approach used in this study is limited to the specific operating conditions and sheep milk studied, chemometric methods have proven to be promising tools because of accuracy and suitability for both prediction of the dielectric properties of sheep milk and monitoring quality control parameters of milk and dairy products.     

A comparative assess of high hydrostatic pressure and superfine grinding on physicochemical and antioxidant properties of grape pomace

In this study, we evaluate the effects of high hydrostatic pressure (HHP) and superfine grinding (SFG) treatment on grape pomace. The results showed that the HHP treatment improved physicochemical and antioxidant properties of grape pomace than the SFG treatment did. Moreover, the results of SEM indicated that the HHP‐treated grape pomace turned to have more lamellar structure, resulting in more hydrophilic groups exposed to improve WRC, WSC and SDF content. The results of FT‐IR spectra indicated that the main components and chemical structure of grape pomace after processing did not significantly change. Therefore, the HHP treatment had better effect in improving the functionality of grape pomace than that of the SFG treatment. The grape pomace treated by the appropriate processing methods could be used as functional foods.