Antonio J. Trujillo

Applications of high-hydrostatic pressure on milk and dairy products: a review

Abstract Interest in high-pressure (HP) applications on milk and dairy products has recently increased. Pressures between 300 and 600 MPa have shown to be an effective method to inactivate microorganisms including most infectious food-borne pathogens. In addition to microbial destruction, it has been reported that HP improves rennet or acid coagulation of milk without detrimental effects on important quality characteristics, such as taste, flavour, vitamins, and nutrients. These characteristics offer the dairy industry numerous practical applications to produce microbially safe, minimally processed dairy products with improved performances, and to develop novel dairy products of high nutritional and sensory quality, novel texture and increased shelf life.

Changes in textural, microstructural, and colour characteristics during ripening of cheeses made from raw, pasteurized or high-pressure-treated goats’ milk

Abstract Goats’ milk cheeses were made from raw (RA), pasteurized (PA; 72°C, 15xa0s) or pressure-treated (PR; 500xa0MPa, 15xa0min, 20°C) milk to compare textural, microstructural, and colour characteristics in relation to ripening time. Texture, microstructure and colour were evaluated by uniaxial compression and stress relaxation tests, confocal laser scanning microscopy and Hunter colorimetry, respectively. Raw and PR cheeses were firmer and less fracturable than PA cheese, but differences became less notable toward the end of ripening. PA and PR cheeses were less cohesive than RA cheese. Although cheeses exhibited a loss of elastic characteristics with ageing, PR cheese showed the most elastic behaviour initially. Confocal laser scanning micrographs displayed PR cheese with a regular and compact protein matrix, with small and uniform fat globules resembling the structure of RA cheese. Finally, colour evaluation demonstrated significant differences between cheeses due to milk treatments and ripening time.

Lipolysis in cheese made from raw, pasteurized or high-pressure-treated goats’ milk

Abstract Free fatty acid (FFA) profiles of cheeses made from raw (RA), pasteurized (PA; 72°C, 15xa0s) or pressure-treated (PR; 500xa0MPa, 15xa0min, 20°C) goats’ milk were determined to assess the effect of milk treatment on cheese lipolysis. Total FFA content increased during ripening of all cheeses analysed. The main FFAs present in the three types of cheese were palmitic, oleic, myristic, capric and stearic acids. Cheeses made from PR milk showed a similar ( P P

Effects of ultra-high-pressure homogenization treatment on the lipolysis and lipid oxidation of milk during refrigerated storage.

Free fatty acid (FFA) release and quantification and lipid oxidation extent of ultra-high-pressure homogenized (UHPH) milk samples were evaluated to assess the effect of UHPH on the susceptibility of milk lipids to lipolysis and oxidation. Milk was UHPH-treated at 200 and 300 MPa with inlet temperatures of 30 and 40 degrees C. UHPH-treated samples were compared to high-pasteurized milk (PA; 90 degrees C, 15 s). Results showed that all FFA increased significantly during storage only in 200 MPa samples. Lipid oxidation was measured as an accumulation of lipid hydroperoxides as the primary oxidation product and malondialdehyde and hexanal as the secondary oxidation products. Samples treated at 300 MPa presented higher malondialdehyde and hexanal content compared to 200 MPa treated-samples and to PA milk.

Ultra-high pressure homogenization-induced changes in skim milk: impact on acid coagulation properties.

The effects of ultra-high pressure homogenization (UHPH) on skim milk yogurt making properties were investigated. UHPH-treated milk was compared with conventionally homogenised (15 MPa) heat-treated skim milk (90 degrees C for 90 s), and to skim milk treated under the same thermal conditions but fortified with 3% skim milk powder. Results of the present study showed that UHPH is capable of reducing skim milk particle size which leads to the formation of finer dispersions than those obtained by conventional homogenisation combined with heat treatment. In addition, results involving coagulation properties and yogurt characteristics reflected that, when increasing UHPH pressure conditions some parameters such as density of the gel, aggregation rate and water retention are improved.

Proteolytic activities of some milk clotting enzymes on ovine casein.

Proteolytic activity of some milk clotting enzymes (calf and lamb rennets, bovine chymosin and pepsin, and proteases from Rhizomucor miehei and Cryphonectria parasitica) on ovine whole casein was determined by urea-PAGE and RP-HPLC. Microbial enzymes were more proteolytic than animal enzymes when acting on ovine whole casein. Lamb rennet and C. parasitica protease showed the lowest and the highest degree of proteolysis, respectively. Urea-PAGE results showed that all enzymes hydrolyzed ovine casein resulting in the formation of αs1-I and β-I as initial breakdown products of αs1-CN and β-CN. In addition to these products, C. parasitica protease produced a series of degradation products with lower mobilities than β-CN. Minor quantitative differences between coagulants from animal origin, but great quantitative and qualitative differences between microbial and animal coagulants (assessed throughout the study of the RP-HPLC peptide profiles), were observed.

Specific effect of high-pressure treatment of milk on cheese proteolysis.

The extent of primary and secondary proteolysis of cheeses made from raw (RA), pasteurized (PA, 72 degrees C, 15 s) or pressure-treated (PR, 500 MPa, 15 min, 20 degrees C) goats milk was assessed. Modifications in cheese-making technology were introduced to obtain cheeses with the same moisture content, and thus studied per se the effect of milk treatment on cheese proteolysis. The PR milk cheese samples were differentiated from RA and PA milk cheeses by their elevated beta-lg content, and by the faster degradation of alphas1-, alphas2- and beta-CN throughout ripening. Non-significant differences were found in either pH 4.6 soluble-nitrogen or trichloracetic acid soluble-nitrogen contents of cheeses. However, the pasteurization of milk decreased the free amino acid production in cheese. The RA milk cheeses had the highest amount of proline and the lowest concentrations of serine, tyrosine, arginine and alpha-aminobutyric acid, whereas PR milk cheese showed higher levels of arginine.

Effect of inulin addition on the sensorial properties of reduced‐fat fresh cheese

A reduced-fat fresh cows milk cheese with inulin (3%) was compared with both full-fat and reduced-fat cheeses without the prebiotic. The pH and microbiological quality of cheeses were not affected by the presence of inulin. Cheeses produced with inulin were less hard, springy, cohesive and chewy than reduced-fat cheeses, and more similar to cheeses made from whole milk. Cheeses produced with inulin had the lowest lightness and the highest yellowness values, although these colour differences were not detected by the panellists. The sensory panel described the reduced-fat cheese with inulin as more acceptable than its counterpart without inulin.

Evaluation of the importance of germinative cycles for destruction of bacillus cereus spores in miniature cheeses

Our objective was to determine the effect of high pressure on inactivation of spores of Bacillus cereus ATCC 9139 inoculated into cheese made of raw cows milk. Inoculated miniature cheeses were manufactured under controlled bacteriological conditions, vacuum packed and kept at 8 °C for 15 days after pressure treatment. Cheeses were submitted to pressures of 300, 400 or 500 MPa at 30 °C, during 15 min. Some of them were treated with a germination cycle of 60 MPa at 30 °C for 210 min. Lethality was calculated comparing surviving sample counts to control ones. Adding the germinative cycle resulted in higher efficiency, and when applied with 500 MPa, lethality reached 2.0 log cfu/mL. We saw that with both cycles initial counts of spores diminish, but all of them were not inactivated. However, considering that in raw milk mesophilic spore counts are 2.6-2.9 log cfu/mL, this treatment may be useful.

Proteolytic specificity of chymosin on caprine α s1 -caseins A and F

From hydrolysis experiments carried out on α s1 -caseins A and F at pH 5.2 in the presence of 30 g NaCl/l, i.e. the conditions encountered in many young goats cheeses, it was found that minima of 19 and 9 bonds were sensitive to chymosin in variants A and F respectively. Variant A was hydrolysed faster than variant F and the proteolytic pattern (reversed-phase HPLC and polyacrylamide agarose gel electrophoresis) differed between the variants. Hydrolysates from both variants had a number of cleavage sites in common (Leu 20 -Leu 21 , Phe 23 -Ala 24 and Phe 32 -Arg 33 in both variants, Leu 101 -Lys 102 and Leu 64 -Lys 65 , Leu 120 -His 121 and Leu 83 -His 84 , Leu 142 -Ala 143 and Leu 105 -Ala 106 , Leu 149 -Phe 150 and Leu 112 -Phe 113 , Leu 156 -Asp 157 and Leu 119 -Asp 120 , Trp 164 -Tyr 165 and Trp 127 -Tyr 128 in variants A and F respectively), while other bonds were split only in variant A (Leu 16 -Asn 17 , Glu 18 -Asn 18 , Phe 28 -Pro 29 , Ile 44 -Gly 45 , Tyr 80 -Ile 81 , Gln 82 -Lys 83 , Tyr 91 -Leu 92 , Tyr 94 -Leu 95 , Leu 109 -Glu 110 and Phe 179 -Ser 180 ). Major cleavage sites appeared to be at Phe 23 -Val 24 , Leu 142 -Ala 143 and Trp 164 -TP 165 for variant A, and Phe 23 -Val 24 and Leu 64 -Lys 85 for variant F. Cleavage site Phe 23 -Val 24 could be the origin of the first breakdown product from goat α s1 -caseins A and F visible in polyacrylamide agarose gel electrophoresis.