Abstract
Bacteriocinogenic cultures can represent a natural way to increase the safety of cheeses made from raw milk, in which a relevant role in ripening and flavor formation is exerted by the nonstarter lactic acid bacteria (NSLAB). Since the latter can be inhibited by bacteriocin producers, this study evaluated to which extent a nisinogenic culture inoculated at low initial levels can affect the growth rate and peptide degradation activity of the nisin-sensitive cheese isolate Lactobacillus plantarum LZ by comparison with its isogenic variant, L. plantarum LZNI, with increased immunity to nisin. A growth delay of the nisin sensitive strain was observed only when its initial number was 100-fold lower than the nisin producer and nisin was added as an inducer of its own production. In this case, the amount of free α-amino groups was significantly different between cultures of L. plantarum LZ and LZNI only at Day 1. Reverse Phase High Performance Liquid Chromatography (RP-HPLC) highlighted a few differences between the peptide profiles of co-cultures L. plantarum LZ and LZNI. However, results showed that the bacteriocin producer did not dramatically influence the behavior of the sensitive NSLAB and that the evaluation of the effects on microbial contaminants in cheese is worthwhile.
Highlights
Many Protected Designation of Origin (PDO) cheese productions follow manufacturing guidelines that prescribe use of raw milk
Data on the sensitivity to nisin of the nonstarter lactic acid bacteria (NSLAB) strains tested are reported in Table 1 in terms of diameter of the inhibition halo formed in the deferred agar spot test with L. lactis subsp. lactis DSM
L. paracasei isolated from cheese, for being one of the most sensitive to nisin and for the availability of a food-grade variant with increased immunity to nisin developed in a previous study [15]
Summary
Many Protected Designation of Origin (PDO) cheese productions follow manufacturing guidelines that prescribe use of raw milk. In this way, the diversity of the natural microbiota responsible for sensory distinctness, and, primarily, the starter lactic acid bacteria (SLAB) and nonstarter lactic acid bacteria (NSLAB), is preserved. Due in part to their peptide hydrolyzing activity, which increases the amount of short peptides and free amino acids after the proteolysis carried out by rennet and SLAB. L. plantarum influenced proteolysis and the amounts of individual amino acids in Canestrato Pugliese PDO cheese and predominated from 7–15 days until 90 days of ripening [4]. L. plantarum strains carry out transamination of amino acids with their conversion to flavor active compounds [5].
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