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Biogeneration of flavour compounds by L paracasei I90 and L. helveticus B02 in a hard cheese model
Simposio; IV International Symposium on Lactic Acid Bacteria: Food, Health and Applications; 2013
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Amino acid (AA) catabolism by lactic acid bacteria is one of the most important biochemical events that lead to bioformation of cheese flavour. The selection of adjunct strains of mesophilic lactobacilli possessing key enzymatic activities to AA catabolism and its combination with appropriate primary cultures represents an interesting strategy to accelerate or diversify the flavor development in cheeses. The aim of the present work was to evaluate the ability to produce volatile compounds derived from AA in a hard cheese model by a strain of mesophilic lactobacilli, Lb. paracasei I90, and a strain of thermophilic starter, L. helveticus B02, which were added individually and mixed. Hard cheese model consisted in a sterile extract standardized in salt content and pH, obtained from the aqueous phase of a Reggianito cheese manufactured with L. helveticus B02 and ripened for 3 months. From this model system were prepared: extracts inoculated with the same strain of L. helveticus (re‐inoculation) used in cheese - making, extracts inoculated with L. paracasei I90, extracts inoculated with both strains, and control extracts with not added lactobacilli. They were incubated at 37ºC for 14 days. The assays were performed in duplicate, by using two independent cultures of each strain for the inoculation. The production of volatile compounds was monitored by solid-phase microextraction (SPME) coupled to GC‐FID and GC‐MS. A total of 38 volatile compounds were identified in the chromatographic profiles of extracts. However, only 13 were related to AA catabolism: acetaldehyde, 2- and 3-methylbutanal, ethanol, diacetyl, acetoin, 3-methyl 1-butanol, benzaldehyde, acetophenone, acetic acid, 3‐methylbutanoic acid, phenylmethanol and phenol. The levels of acetaldehyde were statistically higher in the extracts inoculated with both strains in comparison to the rest of the extracts. diacetyl, 3-methyl 1-butanol and acetic acid had higher area values in all inoculated extracts in comparison to the controls. In particular, acetic acid was produced in higher levels in the extracts containing the mixed strains than in those with individual strains. A preferential production of isovaleric acid was observed in the extracts with L. paracasei I90 both alone as combined with L. helveticus B02. The cooperation effect between both strains was only detected for acetaldehyde and acetic acid. The benzaldehyde and phenylmethanol levels were always higher in the control extracts. Both strains did not significantly increase the amount of the remaining volatile compounds derived from AA. In the present study, L. helveticus B02 and L. paracasei I90 affected the production of some volatie compounds that play a key role in the aroma, therefore, theses trains could be used in cheese-making in order to improve flavor development.