Efeito do tipo de coagulante e acidificante no rendimento, proteolise e "shelf life" do queijo minas frescal / Effect of type of coagulant and acid in income, proteolysis and "shelf life" of fresh cheese mines

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

Three coagulating agents (bovine, microbial and one obtained by fermentation using a genetically modified E. col; K12) were evalueted for their use in the processing of Minas cheese. The objetive was to evaluate the shelf life of the cheeses using these coagulating agents together with mesophilic starter and 85%lactic acid. Cheeses were processed on three separate days using approximately 50kg milk for each batch and were denominated as follows: BOF (bovine coagulant plus mesophilic starter); MICA (microbial coagulant plus lactic acid); MICROF (microbial coagulant plus mesophilic starter); CHA (coagulant from fermentation plus lactic acid); CHF (coagulante from fermentation fermentation plus lactic acid). No signifcant differences were found in the percentagen recoveries of the protein, fat and total dry matter. No significant differences were observed in the yields from the treatments although the yield of cheese per kilo of milk was greater using the coagulant obtained by fermentation, suggesting a greater water retention in the final product. The levels of nitrogen soluble at pH 4.6 and in 12% TCA (NNP), increased significanly during the shelf life of the products (p=0,0001). The data suggest that the differences in salt content of the cheeses influenced the indices of proteolysis, which could be justified by the difference in the moisture content found between replicates. WIth respect to the electophoretic behaviour, the greatest protein degradation was shown by the microbial coagulant plus mesophilic starter (MICROF), followed by the microbial coagulant plus lactic acid (MICA), bovine coagulant plus mesophilic starter (BOF), coagulant obtained by fermentation plus mesophilic starter (CHF) and finally the coagulant obtained by fermentation plus lactic acid (CHA). Degradation of ?s1-casein occurred with all the treatments but was less intense in CHA. The ? casein also showed proteolysis with a perceptible decrease during the experiment, except for CHA, in which the ?-casein remained practically intact. There was apparently an accentuated synergistic effect between the microbial coagulant and the mesophilic starter , with the former providing substrates easily attacked by the enzymes of the latter. The cheese processed by the most commonly used combination in Brazil (BOF), showed an electrophoretic pattern in which the ?s1- casein was clearly proteoysed with time. The ? - casein was also proteolysed, showing a perceptible decrease during the experiment. The coagulant obtained by fermentation plus mesophilic starter (CHF) resulted in almost complete degradation of the ?s1-casein. These results are in accordance with the values for nitrogen soluble at pH 4.6 and 12% TCA. MICROF, BOF, and CHF lost their physical form during the first 15 days of storage. The instrumental evaluation of the texture of these eheeses was invalidated on aeeount of the heterogeneity of the products. The sensory evaluation determined the significant differences between the treatments with respect to time. The use of lactie aeid was shown to be a good alternative to inerease the shelf life of the products with respect to appearance and physical form, although it was the most liable to attack by contaminating mieroorganisms

ASSUNTO(S)

lactic acid queijo enzimas proteicas coagulants cheese acido latico coagulantes coalhos rennet protein enzymes

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