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Influence of primary starter on viability and biochemical activities of an adjunct culture of Lactobacillus plantarum I91 in an experimental model of hard cheese.
Simposio; III Simposio Internacional de Bacterias Lácticas; 2009
Adjunct cultures of mesophilic lactobacilli isolated from good quality cheeses have been proposed as a technological approach to improve control over cheese microbiota and biochemical activities during ripening. Although numerous strains of mesophilic lactobacilli have been obtained from hard cheeses, information about the application of adjunct cultures in hard cheeses manufacture is lacking.  In this work, we assessed the influence of the primary starter of Lactobacillus helveticus used in cheese-making, as well as the background level of proteolysis in the product, on the growth, survival and biochemical activities of an adjunct culture of L. plantarum. Reggianito cheeses made with L. helveticus SF138 or L. helveticus SF209, which showed different proteolytic and peptidolytic abilities, were employed to prepare an extract representative of the aqueous phase of cheese. Extracts were also obtained with cheeses of different ripening time (3, 90 and 180 days). The extracts were standardized for pH and salt content and sterilized by filtration. The so obtained sterile substrate was inoculated with L. plantarum I91 (104 UFC ml-1); non inoculated controls were also prepared. Substrates were incubated at 34ºC for 21 days and sampled during incubation (0, 1, 3, 7, 14 y 21 days) to record lactobacilli counts (MRS, 34ºC 48 h). In addition, pH and proteolysis by liquid chromatography of soluble peptides and free amino acids were determined. L. plantarum I91 reached a maximum of ca. 108 UFC ml-1 after 3 days in all the substrates assayed, then decreased 2 or more log orders according to the strain of L. helveticus and the age of the cheese. The pH decreased from 5.30 to final values ranged between 4.97 y 4.78; the lowest values were obtained for extracts of young cheeses, probably due to the occurrence of residual lactose. The contribution of L. plantarum I91 to proteolysis was mostly evidenced by soluble peptides profiles, and was clearly influenced by the primary starter employed to make the cheese. Principal components analysis showed that substrates derived from cheeses with L. helveticus SF209 formed two groups: one consisted of controls and the other of substrates inoculated with L. plantarum I91. For substrates prepared with cheeses made with L. helveticus SF138, a similar trend was observed, but it was mostly shown on principal components of lower significance. The impact of L. plantarum I91 on free amino acids production was mostly qualitative, as its inoculation in the substrate caused changes in free amino acids profiles, especially in the substrate prepared with the cheese containing L. helveticus SF138, but it did not increase the total content of free amino acids. L. plantarum I91 had a positive impact in peptidolysis acceleration in the experimental model proposed for Reggianito cheese, especially in combination with the primary starter L. helveticus SF209.