Isolation, identification and selection of lactic acid bacteria cultures for production of food aroma & flavour compounds

Over the past few years, the increasing demand for natural products in the food industry has encouraged remarkable efforts towards the development of biotechnological processes for the production of flavour compounds. A total of 30 cultures were isolated from laban rayeb (natural sour milk), raw milk and soft & Ras cheeses obtained from different regions in Egypt. Lactic acid bacteria strains (LAB) were identified as Lactobacillus casei, Lactobacillus plantarum; Lecuconostoc mesentroides; Enterococcus faecium; Lactobacillus bulgaricus; Lactococcus lactis subsp lactis and Lactococcus lactis subsp diacetylactis. For flavour production, MRS and M17 media, sterilized milk with and without amino acid (methionine, leucine, phenylalanine) were used.The headspace volatiles of lactic acid bacteria (LAB) with media MRS or M17 and with sterilized milk with or without amino acids were collected and subjected to GC and GC-MS analysis. The major component was ethylacetate which comprises (83.791). in Lactobacillus casei; (81.99%) in Lactobacillus plantarum; (78.99%) in Lecuconostoc mesentroides; (74.30%) in Enterococcus faecium and (74.04%) in Lactobacillus bulgaricus; (59.50%) in Lactococcus lactyis subsp lactis, while acetadehyde was the most aboundant constituent (38.26%) in Lactococcus lactis subsp diacetylactis, also it comprised the highest concentration in 2,3-butanedione (18.15%). In case of fermented milk, the major component was ethyl butanoate. Which comprised 67.56%, 67.29% in Leuconostoc mesentroides and Lactobacillus plantarum and comprised 57.33%, 54.30% in Enterococcus faecium and Lactobacillus casei, also comprised 49.74%, 48.32% in Lactobacillus bulgaricus and Lactococcus diacetylactis compared to 24.35% in control milk sample. Also LAB cause a remarkable increase in ethylhexanoate. Addition of 0.25% phenylalanine causes increase in 2,3-butanedione percentage in most sample since comprised 33.89% in Lactobacillus plantarum, 25, 64% in Lactobacillus casei and 18.03% in Lactococcus diacetylactis compared to 15.08% in control sample. Strecker aldehydes 2/3- methylbutanal;phenylacetaldehyde and the two dicarbonyls 2,3-butanedione and 2,3-pentanedione were represented with remarkable concentration as the effect of leucine, phenylalanine and methionine addition which considered the main precursors of key aroma compounds.