Biochemical and microbiological characterization of artisan kid rennet extracts used for Cabrales cheese manufacture

Four samples of artisanal kid rennet extracts from four different Cabrales cheese producers were biochemically and microbiologically characterized. Most samples had a very acidic pH (around pH 4.0), which may condition their biochemical and microbial variables. The milk-clotting activity of the extracts was assessed using a Formagraph apparatus. The properties of these artisanal rennets were found to be comparable to a 1/10 dilution of 1:10,000 commercial calf rennet; their enzymatic potentials, measured with a semi-quantitative commercial system (API ZYM), showed only very slight differences. A large population of lactobacilli was found in all artisanal kid rennet samples, whereas coliforms, enterococci, staphylococci and leuconostocs were only occasionally encountered. Sixty-four representative colonies were classified by PCR amplification and the sequencing of a stretch of their 16S rDNA genes. Strains of Lactobacillus plantarum completely dominated one of the extracts. In all others samples, strains of this homofermentative species and of the heterofermentative Lactobacillus brevis were present in similar amounts.