Pecorino d’Abruzzo raw ewes’ milk cheese: seasonal factors of biochemical and microbiological aspects

Quality of artisanal cheeses is closely associated with a given territory and its traditions. These products contribute to preserve food biodiversity. Such instances must cop the respect of quality and hygiene levels: the use of particular microbial starters is a key factor in this context. “Pecorino d’Abruzzo” cheese is a semi-hard cheese of Central Italy with raw ewe milk. This paper deals with the microbial, compositional and biochemical profiles during cheese ripening. Microbial isolates suitable as starter and adjuncts were characterized; their behaviour was investigated in response to variations of raw milk properties. Samples of traditional Pecorino to study microbial and biochemical characters were taken from three different batches worked out is usual in May (Spring) and November (Autumn). As much in 202 bacterial strains were isolated on M17 and MRS agar and identified by the combined use of physiological and biochemical assays, species-specific PCR and restriction analysis of the amplified 16S rRNA gene. The majority of the lactic acid bacteria isolates were Lactobacillus paracasei, Lactobacillus plantarum and Lactococcus lactis subsp. lactis. Enterococcus faecium and Enterococcus faecalis were also isolated, mostly from cheese samples (46% of the coccal isolates), together with a lower amount of Streptococcus thermophilus (3.4%). A substantial presence of enterococci already report by Di Cagno et al. (2003) in other Italian ewe cheeses was confirmed. Spring batches showed a more complex microbial population: Lactobacillus brevis, Lactobacillus curvatus, Lactobacillus paraplantarum, Lactobacillus pentosus, Lactobacillus plantarum, Lactobacillus paracasei, Lactobacillus delbrueckii subsp. lactis, Lactobacillus fermentum, Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, Pediococcus pentosaceus, Lactococcus lactis subsp. lactis, Lactococcus lactis cremoris, Leuconostoc mesenteroides were found, while in autumn batches only Lactobacillus pentosus, Lactobacillus plantarum, Lactobacillus paracasei, Lactobacillus zeae, Streptococcus thermophilus, Lactococcus lactis subsp. lactis were isolated. A decrease in moisture content, together with an increase in total proteins and fats was observed during ripening. In the first 20 days of ripening, pH values around 5.1 were measured followed by a slight increase up to 5.7 by the end of ripening. Urea-PAGE pH 4.6-insoluble fraction and RP-HPLC peptide profiles of the 70% (v/v) ethanol-soluble and ethanol-insoluble fractions of the cheeses demonstrated some proteolysis (O’Mahony et al., 2003). Urea- PAGE results showed extensive proteolysis of alfaS1-casein (CN). In autumn production alfaS1-CN was completely degraded in 20 days; while in spring cheeses it remained at low level and completely disappeared after 60 days. A slight hydrolysis of beta-CN with low level of gamma-CN was found; beta- CN was not completely hydrolyzed at the end of ripening for all cheeses. Formation of gamma-CNs from beta-CN was more evident in spring cheeses. RP-HPLC profiles 70% (v/v) ethanol-soluble and insoluble fractions showed several peaks, indicative of heterogeneous mixtures of proteolysis products evolving through ripening. Principal Component Analysis (PCA) of peak height data on covariance matrix was performed. PCA explained no more than 26.2% of cheeses variability as an effect of seasonality.