Influence of chymosin type and curd scalding temperature on proteolysis of hard cooked cheeses.

In this work, we studied the influence of the type of coagulant enzyme and the curd scalding temperature on the proteolysis and residual coagulant and plasmin activities of a cooked cheese, Reggianito, in the interest of reducing ripening time. A two-factor experimental design was applied in two levels: type of coagulant enzyme, bovine chymosin or camel chymosin, and curd scalding temperature, 50 or 56 °C. The experimental treatments were applied in Reggianito cheese making experiments, and the samples were ripened for 90 d at 12 °C. Scalding temperature influenced residual coagulant activity; the cheeses cooked at 50 °C had significantly higher activity than those treated at 56 °C. In contrast, scalding temperature did not modify plasmin activity. Proteolysis was primarily affected by curd cooking temperature because chymosin-mediated hydrolysis of αs1 casein was slower in cheeses treated at 56 °C. Additionally, the nitrogen content in the cheese soluble fractions was consistently lower in the cheeses scalded at 56 °C than those cooked at 50 °C. A significant influence of the type of coagulant enzyme was observed, especially in the nitrogen fractions and peptide profiles, which demonstrated that camel chymosin was slightly less proteolytic; however, these differences were lower than those caused by the scalding temperature.

Leuconostoc citreum MB1 as biocontrol agent of Listeria monocytogenes in milk.

Cell-free supernatant from Leuconostoc citreum MB1 revealed specific antilisterial activity. Preliminary studies demonstrated the proteinaceous, heat-stable, bacteriocin-like trait of the antimicrobial components present in the supernatant. Determination of the genes encoding bacteriocins by PCR and DNA sequencing led to amplification products highly homologous with leucocin A (found in diverse Leuconostoc species) and UviB (found in Leuc. citreum KM20) sequences. Additionally, antimicrobial activity of cell-free supernatant from Leuc. citreum MB1 was revealed by an inhibition halo of the SDS-PAGE gel subjected to a direct detection using Listeria monocytogenes as indicator strain. Different assays were carried out to assess the capacity of Leuc.citreum MB1 to control List. monocytogenes growth: (i) inactivation kinetics of the pathogen by antilisterial compounds present in concentrated cell-free supernatant from Leuc. citreum MB1, (ii) evaluation of optimal Leuc. citreum MB1 initial concentration to obtain maximum List. monocytogenes ATCC 15313 inhibition, and (iii) biocontrol of List. monocytogenes ATCC 15313 with Leuc. citreum MB1 during growth in milk at refrigeration temperature. According to our results, it is unquestionable that at least one bacteriocin is active in Leuc. citreum MB1, since important antilisterial activity was verified either in its cell-free supernatant or in co-culture experiments. Co-culture tests showed that ∼107 CFU/ml Leuc. citreum MB1 was the optimal initial concentration to obtain maximum pathogen inhibition. Moreover, Leuc. citreum MB1 was able to delay List. monocytogenes growth at refrigerated temperature.

Characterisation of proteolysis profile of Argentinean sheep cheeses made by two different production methods.

BACKGROUND: In this work the proteolysis profiles of Argentinean sheep cheeses made by two different production methods were studied in order to develop products with typical and defined features. Cheeses with a starter of Streptococcus thermophilus, curd cut to corn grain size, washed and heated to 43 degrees C (S cheeses) and cheeses with a mixed starter of Streptococcus thermophilus, Lactobacillus helveticus and Lactobacillus bulgaricus, curd cut to rice grain size, unwashed and heated to 47 degrees C (L cheeses) were manufactured. The cheeses were ripened at 12 degrees C and 80% relative humidity for 180 days and samples were taken throughout this period. RESULTS: Gross composition and primary proteolysis were similar for both types of cheeses. Streptococci counts diminished from 10(9) to 10(7) colony-forming units g(-1) during ripening in both S and L cheeses. Lactobacilli counts in L cheeses decreased during ripening and disappeared at 180 days. L cheeses had significantly lower pH values and showed higher peptidolysis than S cheeses. Triangle sensory evaluation indicated important differences between the two types of cheeses. CONCLUSION: S cheeses had a low proteolysis level and a soft flavour, making them appropriate for consumption after a short ripening time. L cheeses had a higher proteolysis level and more intense sensory characteristics, making them appropriate for consumption after a longer ripening time.