A.J. Trujillo

Application of high pressure treatment for cheese production

Abstract High hydrostatic-pressure treatment offers the food industry a new technology for food preservation. Interest in high pressure application on milk has recently increased. Pressures between 300 and 600 MPa can inactivate microorganisms including most infectious food-borne pathogens. In addition to microbial destruction, it has been reported that high pressure improves rennet or acid coagulation of milk and increases cheese yield. A lot of work has been published on microorganism inactivation, denaturation of whey proteins, changes in the mineral distribution and coagulating properties on model or real milk systems. However, practical applications of high pressure treatment in the dairy industry have received little attention. This paper examines recent work in this area and summarizes parts of our ongoing work toward the development of high pressure applications for the cheese industry.

Influence of Pressurization on Goat Milk and Cheese Composition and Yield

Fresh goat cheese was made from pasteurized (72 °C, 15 s) or HP- treated milk (500 MPa, 15 min, 20 °C). Microbiological quality (i.e. mesophilic aerobic bacteria and enterobacteria) of pressurized milk was comparable to pasteurized milk. Pasteurized and HP-treated milks had different pHs and non-casein nitrogen. During the curd formation, the pH fell faster in pasteurized milk than in HP-treated milk and there was a slightly larger amount of milk fat separated from the curd whey in HP- treated milk. HP treatment reduced the level of whey expelled from the curd making the whey removal process more difficult, and so the time involved in the cheesemaking was increased. The cheese made from HP-treated milk had higher levels of moisture and salt, but a slightly lower fat content than pasteurized milk. Additional retention of whey protein and, especially, the greater moisture led to improvements in cheese yield from HP-treated milk.

Effects of High-Pressure Treatment on the Sensory Quality of White Grape Juice

The effects of high-pressure treatment on the colour (objective measurement) and sensory characteristics of white grape juice were studied during storage at 4 °C for 60 days. Grape juice was subjected to three different treatments: 400 or 500 MPa at 2 u °C, and 400 MPa at 40 °C during 10 min. Untreated juice was used as control. Colour parameters (CIE L * a * b *), hue angle (tan m 1 b */ a *), chroma {( a * 2 + b * 2 ) 1/2 }, luminosity Q *{(10 2 log( L *) + 100} and saturation S *( C */ L *) were measured. Juices were evaluated for sweetness, acidity, off-flavour and aroma. High-pressure treatments did not affect the colour parameters of juice, and similar sensory characteristics were observed in both control and treated samples on the first day. The colour and sensory characteristics of pressure-treated samples remained more stable than those of the control juice during 60 days of storage. The control juice was slightly fermented developing some changes in flavour and colour.

Ripening control of Manchego type cheese salted by brine vacuum impregnation

Abstract A new salting procedure was tested in Manchego type cheeses in order to shorten this processing step by decreasing the initial salt gradient in the cheese. This procedure was based on a fast mass transfer mechanism (the hydrodynamic mechanism) which acts when pressure differences are applied to porous products immersed in a liquid phase. The effective porosity of the studied cheese was 0.049 as established by the hydrodynamic mechanism. This value represents the introduction of 1.03 g NaCl 100 g −1 of cheese in the cheese pores, when a 19% ( w w ) brine was used, at 37mbar (absolute) of vacuum pressure. This quantity agreed with the salt content in this experiment. The duration of the new salting process step was 2 h. The hydrodynamic mechanism is based on the supposition that salt ions penetrate the internal part of the cheese through pores. Water loss during ripening was controlled by the external drying rate for the cheese. Vacuum-impregnated cheeses always had a higher water content as a consequence of lower drying rates during the brine immersion period. Nevertheless, the differences in water content neither affected the change in pH nor the ripening process during the maturation of the cheese.

Changes in microstructural, textural and colour characteristics during ripening of Manchego-type cheese salted by brine vacuum impregnation

A new salting procedure which was published in a previous paper on Manchego-type cheese is now studied in order to evaluate how it affects physical properties of cheeses during ripening. Textural characteristics were analysed within the ripening period in two cheese areas (internal and medium) by means of the uniaxial compression and the stress relaxation test. Cheese microstructure was assessed by confocal laser scanning microscopy. Colour values were also evaluated. Cheeses salted by brine vacuum impregnation were less fracturable and more elastic than conventional brine salted cheeses. This is a result of microstructural changes induced by the pressure gradients imposed on the system. Vacuum impregnated cheeses showed a compact and homogeneous protein matrix with small fat globules well dispersed. Conventional brine immersed cheeses showed a more irregular protein network, with larger pores and relatively large fat aggregates.

Proteolysis in goat cheese made from raw, pasteurized or pressure-treated milk☆

Primary and secondary proteolysis of goat cheese made from raw (RA), pasteurized (PA; 72 °C, 15 s) and pressure-treated milk (PR; 500 MPa, 15 min, 20 °C) were examined by capillary electrophoresis, nitrogen fractionation and HPLC peptide profiles. PA milk cheese showed a more important hydrolysis (P<0.05) of αs1-casein than RA milk cheese at the first stages of ripening (15 days), while PR milk cheese had a level between those seen in PA and RA milk cheeses. Degradation of β-casein was more important (P<0.05) in PA and PR than in RA milk cheeses at 15 days of ripening. However, from thereon β-casein in PR and RA milk cheeses was hydrolyzed at essentially similar rates, but at lower rates (P<0.05) than in PA milk cheeses. Pressure treatment could induce proteolysis of β-casein in a way, which is different from that produced by heat treatment. There was an increase in 4.6-soluble nitrogen (WSN) and in trichloroacetic acid (TCASN) throughout ripening in cheeses, but higher contents (P<0.05) in PA and PR milk cheeses at the end of ripening were observed. PR milk cheeses contained considerably higher content (P<0.05) of free amino acids than RA or PA milk cheeses. In general, heat and pressure treatments had no significant effect on the levels of hydrophobic and hydrophilic peptides.

Ultra-High Pressure Homogenization enhances physicochemical properties of soy protein isolate-stabilized emulsions

The effect of Ultra-High Pressure Homogenization (UHPH, 100-300MPa) on the physicochemical properties of oil-in-water emulsions prepared with 4.0% (w/v) of soy protein isolate (SPI) and soybean oil (10 and 20%, v/v) was studied and compared to emulsions treated by conventional homogenization (CH, 15MPa). CH emulsions were prepared with non-heated and heated (95°C for 15min) SPI dispersions. Emulsions were characterized by particle size determination with laser diffraction, rheological properties using a rotational rheometer by applying measurements of flow curve and by transmission electron microscopy. The variation on particle size and creaming was assessed by Turbiscan® analysis, and visual observation of the emulsions was also carried out. UHPH emulsions showed much smaller d3.2 values and greater physical stability than CH emulsions. The thermal treatment of SPI prior CH process did not improve physical stability properties. In addition, emulsions containing 20% of oil exhibited greater physical stability compared to emulsions containing 10% of oil. Particularly, UHPH emulsions treated at 100 and 200MPa with 20% of oil were the most stable due to low particle size values (d3.2 and Span), greater viscosity and partial protein denaturation. These results address the physical stability improvement of protein isolate-stabilized emulsions by using the emerging UHPH technology.

Proteolysis of goat casein by calf rennet

Abstract The proteolytic activity of calf rennet on goat casein (CN) was studied under various conditions which affect cheesemaking and ripening processes (pH, salt, calf rennet concentration and α s 1 -CN polymorphism). Electrophoretic studies showed that goat casein was hydrolysed to give characteristic breakdown products derived from individual caseins (β-I to β-V from β-CN, primary hydrolysis product from α s 1 -CN, para-κ-CN from κ-CN and other degradation products from α s 2 -CN). Both goat β-CN and α s 1 -CN were more sensitive to hydrolysis than their bovine counterparts under the same conditions. The pH did not influence the proteolytic specificity of rennet on β-CN, but rennet activity was highly dependent on the pH. However, in the case of α s 1 -CN, the rate of proteolysis and the nature of breakdown products were pH-dependent. NaCl affected only the rate of proteolysis. After prolonged incubation times, the electrophoretic patterns of hydrolysates produced from whole goat casein by rennet were similar to those produced from isolated β-CN, showing that β-CN and its degradation products are quite resistant to proteolysis compared with α s 1 -CN and its primary hydrolysis product. Rennet hydrolysates of goat casein, containing different α s 1 -CN genetic variants, showed slight differences in the electrophoretic profiles which tended to disappear as hydrolysis advanced.

Proteolysis of yogurts made from ultra-high-pressure homogenized milk during cold storage.

Proteolysis was investigated in yogurts made from milk that was ultra-high-pressure homogenized at 200 or 300 MPa and at 30 or 40 degrees C and compared with those produced from heat-treated milk containing 3% skim milk powder. To evaluate changes in the protein fraction, samples were analyzed at d 1, 7, 14, 21, and 28 of storage for residual caseins, peptides, and total free amino acids. Results showed that yogurts from heat-treated milk and 300 MPa-treated milk presented similar levels of residual caseins, as well as similar profiles of soluble peptides and total free amino acids. On the contrary, greater amounts of hydrophobic peptides were detected in yogurts made from 200 MPa-treated milk at both 30 and 40 degrees C, especially at the end of storage. In all treatments studied, caseins were hydrolyzed and hydrophobic peptides were increased during storage, as reflected by the increase in soluble nitrogen at the end of the storage.

Analysis of major ovine milk proteins by reversed-phase high-performance liquid chromatography and flow injection analysis with electrospray ionization mass spectrometry.

Ovine milk proteins were analyzed both by coupling HPLC and electrospray ionization mass spectrometry (ESI-MS) and by flow injection analysis and ESI-MS detection after separation and collection of fractions from gel permeation chromatography. These methods resolved the four ovine caseins and whey proteins and made it possible to study the complexity of these proteins associated with genetic polymorphism, post-translational changes (phosphorylation and glycosylation) and the presence of multiple forms of proteins. The experimental molecular masses of ewe milk proteins were: 19,373 for kappa-casein 3P; 25,616 for alpha(s2)-casein 10P; 23,411 for alpha(s1)-casein C-8P; 23,750 for beta-casein 5P; 18,170 and 18,148 for beta-lactoglobulins A and B; 14,152 for alpha-lactalbumin A and 66,322 for serum albumin.