RESUMEN
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.
Asunto(s)
Frío , Tecnología de Alimentos/métodos , Proteínas de la Leche/metabolismo , Presión , Yogur/análisis , Aminoácidos/análisis , Caseínas/análisis , Manipulación de Alimentos , Concentración de Iones de Hidrógeno , Nitrógeno/análisis , Péptidos/análisisRESUMEN
Ewe milk cheeses were submitted to 200, 300, 400, and 500 MPa (2P to 5P) at 2 stages of ripening (after 1 and 15 d of manufacturing; P1 and P15). The high-pressure-treated cheeses showed a more important hydrolysis of beta-casein than control and 2P1 cheeses. Degradation of alpha(s1)-casein was more important in 3P1, 4P1, and P15 cheeses than control and 2P1 cheeses. The 5P1 cheeses exhibited the lowest degradation of alpha(s)-caseins, probably as a consequence of the inactivation of residual chymosin. Treatment at 300 MPa applied on the first day of ripening increased the peptidolytic activity, accelerating the secondary proteolysis of cheeses. The 3P1 cheeses had extensive peptide degradation and the highest content of free amino acids. Treatments at 500 MPa, however, decelerated the proteolysis of cheeses due to a reduction of microbial population and inactivation of enzymes.
Asunto(s)
Queso/análisis , Proteínas en la Dieta/metabolismo , Manipulación de Alimentos/métodos , Leche , Péptido Hidrolasas/metabolismo , Presión , Aminoácidos/análisis , Animales , Caseínas/análisis , Caseínas/metabolismo , Queso/microbiología , Recuento de Colonia Microbiana , Enterobacteriaceae/aislamiento & purificación , Concentración de Iones de Hidrógeno , L-Lactato Deshidrogenasa/análisis , L-Lactato Deshidrogenasa/metabolismo , Nitrógeno/análisis , Ovinos , Factores de Tiempo , Agua/análisisRESUMEN
The effect of ultra-high pressure homogenization (UHPH) on microbial and physicochemical shelf life of milk during storage at 4 degrees C was studied and compared with a conventional heat preservation technology used in industry. Milk was standardized at 3.5% fat and was processed using a Stansted high-pressure homogenizer. High-pressure treatments applied were 100, 200, and 300 MPa (single stage) with a milk inlet temperature of 40 degrees C, and 200 and 300 MPa (single stage) with a milk inlet temperature of 30 degrees C. The UHPH-treated milks were compared with high-pasteurized milk (PA; 90 degrees C for 15 s). The microbiological quality was studied by enumerating total counts, psychrotropic bacteria, lactococci, lactobacilli, enterococci, coliforms, spores, and Pseudomonas. Physicochemical parameters assessed in milks were viscosity, color, pH, acidity, rate of creaming, particle size, and residual peroxidase and phosphatase activities. Immediately after treatment, UHPH was as efficient (99.99%) in reducing psychrotrophic, lactococci, and total bacteria as was the PA treatment, reaching reductions of 3.5 log cfu/mL. Coliforms, lactobacilli, and enterococci were eliminated. Microbial results of treated milks during storage at 4 degrees C showed that UHPH treatment produced milk with a microbial shelf life between 14 and 18 d, similar to that achieved for PA milk. The UHPH treatments reduced the L* value of treated milks and induced a reduction in viscosity values of milks treated at 200 MPa compared with PA milks; however, these differences would not be appreciated by consumers. In spite of the fat aggregates detected in milks treated at 300 MPa, no creaming was observed in any UHPH-treated milk. Hence, alternative methods such as UHPH may give new opportunities to develop fluid milk with an equivalent shelf life to that of PA milk in terms of microbial and physicochemical characteristics.
Asunto(s)
Bacterias/aislamiento & purificación , Manipulación de Alimentos/métodos , Presión Hidrostática , Leche/química , Leche/microbiología , Animales , Color/normas , Conservación de Alimentos/métodos , Glucolípidos/análisis , Glicoproteínas/análisis , Concentración de Iones de Hidrógeno , Gotas Lipídicas , Leche/enzimología , Leche/normas , Tamaño de la Partícula , Peroxidasa/metabolismo , Monoéster Fosfórico Hidrolasas/metabolismo , Temperatura , Factores de Tiempo , ViscosidadRESUMEN
The effects of single- or 2-stage ultra-high pressure homogenization (UHPH; 100 to 330 MPa) at an inlet temperature of 30 degrees C on the cheese-making properties of bovine milk were investigated. Effects were compared with those from raw, heat-pasteurized (72 degrees C for 15 s), and conventional homogenized-pasteurized (15 + 3 MPa, 72 degrees C for 15 s) treatments. Rennet coagulation time, rate of curd firming, curd firmness, wet yield, and moisture content of curds were assessed. Results of particle size and distribution of milk, whey composition, and gel microstructure observed by confocal laser scanning microscopy were analyzed to understand the effect of UHPH. Single-stage UHPH at 200 and 300 MPa enhanced rennet coagulation properties. However, these properties were negatively affected by the use of the UHPH secondary stage. Increasing the pressure led to higher yields and moisture content of curds. The improvement in the cheese-making properties of milk by UHPH could be explained by changes to the protein-fat structures due to the combined effect of heat and homogenization.
Asunto(s)
Queso , Manipulación de Alimentos/métodos , Leche/química , Presión , Animales , Quimosina/química , Concentración de Iones de Hidrógeno , Proteínas de la Leche/química , Nitrógeno/análisis , Tamaño de la Partícula , Temperatura , Factores de Tiempo , Agua/análisis , Proteína de Suero de LecheRESUMEN
The effect of high-pressure treatment on the volatile profile of ewe milk cheeses was investigated. Cheeses were submitted to 200, 300, 400 and 500 MPa at 2 stages of ripening (after 1 and 15 d of manufacturing) and volatile compounds were assayed at 15 and 60 d of ripening. High-pressure treatment altered the balance of volatile profile of cheeses, limiting the formation of acids, alcohols, ketones, aldehydes, and sulfur compounds and enhancing the formation of 2,3-butanedione. In general, cheeses pressurized at 15 d of ripening were more similar to untreated cheeses than those treated at 1 d. Cheeses treated at 300 MPa after 1 d of manufacturing were characterized by higher levels of free amino acids, ethanol, ethyl esters, and branched-chain aldehydes, whereas cheeses treated at 500 MPa after 1 d of manufacturing had lower microbial populations, showed the highest abundance of 2,3-butanedione, pyruvaldehyde, and methyl ketones, and the lowest abundance of alcohols.
Asunto(s)
Bacterias/aislamiento & purificación , Queso/análisis , Manipulación de Alimentos/métodos , Compuestos Orgánicos/análisis , Presión , Animales , Queso/microbiología , Recuento de Colonia Microbiana , Lactobacillus/aislamiento & purificación , Lactococcus/aislamiento & purificación , Leche , Análisis de Componente Principal , Ovinos , Factores de TiempoRESUMEN
A new salting procedure based on the brine vacuum impregnation of porous products was tested on Manchego-type cheese and compared with conventional brine immersion. Its effect on cheese proteolysis throughout a 90-d ripening period was determined. Three cheese regions were evaluated (the rind, the middle, and the internal regions). The parameters analyzed were total N, water-soluble N, soluble N in trichloroacetic acid and soluble N in phosphotungstic acid by using the Kjeldahl method, casein profile by urea-PAGE, and peptide profile of the water soluble nitrogen extract by reverse-phase HPLC. Free amino acid formation was monitored with a spectrophotometric method by using a Cd-ninhydrin reagent. Globally, proteolysis was significantly affected by ripening stage (increasing throughout all the maturation period studied) and cheese region (rind showed a proteolysis pattern different from the middle and internal regions). The salting procedure only affected cheese proteolysis in the rind, whereas conventional brine-salted cheeses showed lower proteolysis than vacuum-impregnated cheeses.
Asunto(s)
Queso/análisis , Endopeptidasas/metabolismo , Manipulación de Alimentos/métodos , Cloruro de Sodio , Aminoácidos/análisis , Animales , Caseínas/análisis , Cromatografía Líquida de Alta Presión , Electroforesis en Gel de Poliacrilamida , Nitrógeno/análisis , Ácido Fosfotúngstico , Ovinos , Solubilidad , Espectrofotometría , Ácido Tricloroacético , Urea , Vacio , AguaRESUMEN
High hydrostatic pressure inactivation of Escherichia coli, Pseudomonas fluorescens, Listeria innocua, Staphylococcus aureus, and Lactobacillus helveticus were studied. These microorganisms were inoculated at a concentration between 10(7) and 10(8) cfu/ml in Ringer solution and in ovine milk adjusted to 0, 6, and 50% fat content to evaluate the baroprotective effect of fat content on inactivation of microorganisms. Treatments of pressurization consisted of combinations of pressure (100 to 500 MPa) and temperature (4, 25, and 50 degrees C) for 15 min. Gram-negative microorganisms were more sensitive than were Gram-positive ones (more destruction P. fluorescens > E. coli > or = List. innocua > Lb. helveticus > S. aureus). Pressurizations at low temperature (4 degrees C) produced greater inactivation on P. fluorescens, List. innocua, and Lb. helveticus than at room temperature (25 degrees C), whereas for E. coli and S. aureus the results were opposite. Ovine milk per se (0% fat) showed a baroprotective effect on all microorganisms, but percentage of fat (6 and 50%) did not show a progressive baroprotective effect in all pressurization conditions or for all microorganisms.
Asunto(s)
Presión Hidrostática , Lípidos/análisis , Leche/química , Leche/microbiología , Ovinos , Animales , Escherichia coli/fisiología , Lactobacillus/fisiología , Listeria/fisiología , Pseudomonas fluorescens/fisiología , Staphylococcus aureus/fisiologíaRESUMEN
High isostatic pressures up to 600 MPa were applied to samples of skim milk before addition of rennet and preparation of cheese curds. Electron microscopy revealed the structure of rennet gels produced from pressure-treated milks. These contained dense networks of fine strands, which were continuous over much bigger distances than in gels produced from untreated milk, where the strands were coarser with large interstitial spaces. Alterations in gel network structure gave rise to differences in rheology with much higher values for the storage moduli in the pressure-treated milk gels. The rate of gel formation and the water retention within the gel matrix were also affected by the processing of the milk. Casein micelles were disrupted by pressure and disruption appeared to be complete at treatments of 400 MPa and above. Whey proteins, particularly beta-lactoglobulin, were progressively denatured as increasing pressure was applied, and the denatured beta-lactoglobulin was incorporated into the rennet gels. Pressure-treated micelles were coagulated rapidly by rennet, but the presence of denatured beta-lactoglobulin interfered with the secondary aggregation phase and reduced the overall rate of coagulation. Syneresis from the curds was significantly reduced following treatment of the milk at 600 MPa, probably owing to the effects of a finer gel network and increased inclusion of whey protein. Levels of syneresis were more similar to control samples when the milk was treated at 400 MPa or less.
Asunto(s)
Caseínas/ultraestructura , Quimosina/metabolismo , Micelas , Leche/química , Presión , Animales , Caseínas/química , Geles/química , Lactoglobulinas/química , Lactoglobulinas/ultraestructura , Microscopía Electrónica , Leche/enzimología , Proteínas de la Leche/química , Proteínas de la Leche/ultraestructura , Desnaturalización Proteica , Proteína de Suero de LecheRESUMEN
Ovine milk, standardized to 6% fat, was inoculated with Staphylococcus aureus CECT 534 and Lactobacillus helveticus CECT 414 at a concentration of 10(7) cfu/ml and treated by high hydrostatic pressure. Treatments consisted of combinations of pressure (200, 300, 400, 450, and 500 MPa), temperature (2, 10, 25, and 50 degrees C), and time (5, 10, and 15 min). Staphylococcus aureus was highly resistant to pressure; only pressurizations at 50 degrees C of 500 MPa for 15 min achieved reductions of > or = 7.3 log units. For L. helveticus, the number of surviving cells was reduced considerably at pressures of 400 MPa or more (up to 4.5 log units at 50 degrees C for 15 min), and pressure was more effective at low (2 and 10 degrees C) and moderately high (50 degrees C) temperatures than at room temperature (25 degrees C). Both species showed first-order kinetics of destruction in the range 0 to 60 min. The D values for S. aureus were 20 min (2 degrees C at 450 MPa) and 16.7 min (25 degrees C at 450 MPa), and D values for L. helveticus were 7.1 min (2 degrees C at 450 MPa) and 9.1 min (25 degrees C at 450 MPa). Lactobacillus helveticus showed higher rates of survival of pressure than those reported in previous studies for other Lactobacillus spp.
Asunto(s)
Presión Hidrostática , Lactobacillus/fisiología , Leche/microbiología , Ovinos , Staphylococcus aureus/fisiología , Animales , Femenino , Conservación de Alimentos/métodos , Cinética , Temperatura , Factores de TiempoRESUMEN
Ovine milk that had been standardized to 6% fat was inoculated with Escherichia coli 405 CECT and Pseudomonas fluorescens 378 CECT at a rate of 10(6) and 10(7) cfu/ml, respectively, and treated with high hydrostatic pressure. Treatments consisted of combinations of pressure (300, 400, 450, and 500 MPa), temperature (2, 10, 25, and 50 degrees C), and time (5, 10, and 15 min). Inactivation (> 6 log cfu/ml) of both strains was observed at 50 degrees C for all pressures and treatment times. A similar level of inactivation occurred at > or = 450 MPa and 25 degrees C for E. coli and at > or = 400 MPa and 10 degrees C for P. fluorescens. Destruction was lowest at 10 degrees C for E. coli and at 25 degrees C for P. fluorescens. The test strain of E. coli was more baroresistance than was the P. fluorescens strain.
Asunto(s)
Escherichia coli/crecimiento & desarrollo , Presión Hidrostática , Leche/microbiología , Pseudomonas fluorescens/crecimiento & desarrollo , Ovinos , Animales , Fenómenos Químicos , Química Física , Recuento de Colonia Microbiana , Cinética , Lípidos/análisis , Leche/química , TemperaturaRESUMEN
Ewe's milk standardized to 6% fat was inoculated with Listeria innocua 910 CECT at a concentration of 10(7)CFU/ml and treated by high hydrostatic pressure. Treatments consisted of combinations of pressure (200, 300, 350, 400, 450, and 500 MPa), temperature (2, 10, 25, and 50 degrees C), and time (5, 10, and 15 min). To determine numbers of L. innocua, listeria selective agar base with listeria selective supplement and plate count agar was used. Low-temperature (2 degrees C) pressurizations produced higher L. innocua inactivation than treatments at room temperatures (25 degrees C). Pressures between 450 and 500 MPa for 10 to 15 min were needed to achieve reductions of 7 to 8 log units. The kinetics of destruction of L. innocua were first order with D-values of 3.12 min at 2 degrees C and 400 MPa and 4 min at 25 degrees C and 400 MPa. A baroprotective effect of ewe's milk (6% fat) on L. innocua was observed in comparison with other studies using different media and similar pressurization conditions.