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Influence of PDO Ragusano cheese biofilm microbiota on flavour compounds formation

Stefania Carpino a, Cinzia L. Randazzo b, *, Alessandra Pino b, Nunziatina Russo a, Teresa Rapisarda a, Gianni Belvedere a, Cinzia Caggia b

a- CoRFiLaC, Regione Siciliana, 97100 Ragusa, Italy
b- Department of Agricultural, Food and Environment, University of Catania, via Santa Sofia 98, 95124 Catania, Italy

Abstract

The objectives of the present study were to characterize the biofilm microbiota of 11 different farms (from A to K), producing PDO Ragusano cheese, and to investigate on its ability to generate volatile organic compounds (VOCs) in milk samples inoculated with biofilm and incubated under Ragusano cheese making conditions. The biofilms were subjected to plate counting and PCR/T/DGGE analysis and the VOCs generated in incubated milk samples were evaluated through SmartNose, GC/O, and GC/MS. Streptococcus thermophilus was the dominant species both in biofilms and in incubated milks. Lactobacillus, Lactococcus, Enterococcus and Leuconostoc were also identified. Low levels of  seudomonas spp. and yeasts counts were detected, whereas coliforms, Listeria monocytogenes and Salmonella spp., were never found. SmartNose and GC/O analyses were able to differentiate incubated milk samples on the basis of the odour compounds, highlighting that samples E and F overlapped and sample C was clearly separated from the others. These results complied with those acquired by GC/MS analysis, that detected in total 20 VOCs. Principal component analysis showed positive correlations (r > 0.6; P < 0.05) between some lactic acid bacteria (LAB) and VOCs: such as Enterococcus hirae with alcohols, Lactococcus lactis, Lactobacillus plantarum, Lactobacillus casei and Lactobacillus delbrueckii with aldehydes, and Lactobacillus fermentum, Lactobacillus helveticus and Lactobacillus hilgardii with ketones. This work demonstrates that biofilm represents an excellent source of LAB biodiversity, which contribute to generate VOCs during the production
of PDO Ragusano cheese.

Keywords: Traditional cheese, Tina biofilm, LAB, SmartNose, GC/MS, PCR/DGGE

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Cinzia L. Randazzo

Prof. Associato Microbiologia-Dipartimento di Agricoltura, Alimentazione e Ambiente (Di3A), Università degli Studi di Catania