Raw milk cheeses are known to have more intense and strong flavour and different texture due to natural microbiota and enzymes. Nevertheless, there are concerns about safety of these products. For microbial inactivation heat treatment of milk is used, but it can adversely affect the flavour, taste and texture of the product. Therefore, applying non-thermal technology such as high pressure processing is attracting alternative. The aim of this study was to examine the effects of high pressure treatment of cow`s milk at a wide range of pressures (400 -600 MPa) on milk rennet coagulation time, curd firmness and curd yield. Processed milk samples were subjected to enzymatic coagulation using commercial rennet to determine rennet coagulation time, yield of coagulum and curd firmness. High pressure processing insignificantly influences coagulation properties of whole milk. However, the magnitude of changes depended on applied pressure. Rennet coagulation time and curd yield were significantly different (p < 0.05) among the pressure treated milk samples. The higher firmness of the curd form pressurized milk than that of raw or pasteurized milk, evaluated positively. The main effects of high pressure treatment in milk appeared to involve dissociation of casein micelles from the colloidal to the soluble phase. This study suggests that high pressure treatments of milk at 500 MPa or 550 MPa for 15 min may be beneficial for improving the coagulation properties of milk. These positive effects indicated that high pressure processing may have potential for new cheese varieties development.

The acceptance and preference of milk and dairy products by consumers is determined by the products sensory characteristics. High pressure processing (HPP) can be applied as an alternative to thermal treatment to provide that sensory quality remains unaffected. The aim of this work was to evaluate the influence of high-pressure treatment on the acceptance of the sensory profile of milk, compared to untreated and thermally-treated milk. Milk was processed at 400 MPa or pasteurized at 78 °C for 15-20 seconds. Sensory evaluation of milk samples was carried out in two different groups -untrained panellists (at the international food industry fair 'Riga Food 2016') and trained panellists (finished basic course of sensory evaluation). Both groups evaluated the samples using a five point hedonic scale. The hedonic evaluation of liking of untreated, pasteurized and high-pressure treated milk samples' sensory properties showed that there were no significant differences (p>0.05) in aroma, but there were significant differences in the liking of milk samples colour, taste and aftertaste (p<0.05) depending on treatment type. The overall sensory properties of HP-treated milk were evaluated higher comparing to the traditionally pasteurized milk. The colour (which was measured in CIE L*a*b* colour system) difference was well visible in high-pressure treated milk in comparison to untreated and pasteurized milk.

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High pressure processing (HPP) is an alternative to traditional thermal treatment and can be used in the dairy industry for increasing the microbiological safety of milk and for preserving its biologically active substances. HPP effectiveness in providing microbiological quality of product is still under discussion; thus, the aim of the study was to evaluate the effect of HPP technology on microbiological quality of skimmed milk. Raw, pasteurised (78 °C, 15–20 s), HPP treated (250 MPa, 15 min; 400 MPa, 3 min; 400 MPa, 15 min; 550 MPa, 3 min) and skimmed milk, processed by combining pasteurisation and HPP were analysed and compared. The total plate count (LVS ISO 4833-1:2013) and presence of coliforms (LVS EN ISO 16654:2002) were determined in analysed skimmed milk samples. Significant decrease (p < 0.05) of colony forming units (CFU) was observed in samples processed by combining two treatment types: pasteurisation and HPP. The minimum treatment parameters for shelf-life extension of skimmed milk were determined: pressure not less than 400 MPa and holding time at least 15 minutes.

The aim of the study was to assess the ability of pathogens metabolic repair from injury within 10 days of refrigerated storage of milk after high pressure treatment. Two pathogenic strains-Listeria monocytogenes ATCC 7644 (LM) and Escherichia coli ATCC 25922 (EC) were inoculated in ultrahigh-temperature treated (UHT) milk at concentration of about 10 7 CFU mL-1 and treated at 400, 500, 550, and 600 MPa for 15 min with inlet temperatures 20 °C, and then stored at 4 ± 2 °C to evaluate survival and growth of pathogens. By increasing the applied pressure, an increased rate of the pathogens' inactivation was achieved. After 10 days of storage, milk treated at 400 MPa showed growth over 3.5 log CFU mL-1 of L. monocytogenes and 1.7 log CFU mL-1 of E. coli. In 550 MPa and 600 MPa treated milk samples after 8 and 10 days of storage colony formation occurred (3 CFU mL-1 (550 LM) and 2 CFU mL-1 (550 EC, 600 LM and 600 EC)). Although high pressure treatment is effective method for reducing of pathogenic bacteria, the metabolic repair from injury of bacterial cells in milk during storage should be considered.