CHARACTERIZATION AND SCREENING OF MICROFLORA OF TWO FERMENTED SOY-BEAN PRODUCTS AND PRELIMINARY APPLICATION AS STARTER CULTURES

Abstract

Naturally fermented soy-cheese (fermentation time: 12 h at 37oC) and soy-milk (fermentation time: 6 h at 42oC) were produced and their microflora were enumerated, isolated and identified. The dominating fermenting microorganisms were lactic acid bacteria of which 7 species were identified. The isolates were screened for possible use as starter cultures based on acidification profile and physico-chemical properties of the two soy products produced. The results showed that the total viable counts of the soy-cheese and naturally fermented soy-milk were 5.30 x 106cfu/g and 2.90 x 106cfu/ml respectively. The microflora of the naturally fermented soy-milk included Aeromonas hydrophila and Bacillus cereus while those of the soy-cheese included; Aerococcus viridians, Micrococcus kristinae, Micrococcus varians, Leuconostoc lactis, Lactobacillus fermentum, Lactococcus lactic spp cremoris, Lactobacillus pentosus, Lactobacillus delbrueckii spp bulgaricus, Lactobacillus brevis, Escherichia coli, Aeromonas hydrophila, Saccharomyces cerevisiae and Candida sake. The lactic acid bacteria isolates were used singly and in combination as starter cultures to produce soy-yoghurt while the lactic acid bacteria isolates were used singly to produce soy-cheese. The soy-yoghurt with starter culture had a pH ranging from 4.75 to 5.34, total titratable acidity ranging from 144.00 mg/ml to 177.00mg/ml and protein content ranging from 33.80% to 41.64%. The pH of the soy-cheese ranges from 5.41 to 5.74 and its protein content ranges from 27.34% to 51.85%. This study showed that the use of a mixed culture of Lactobacillus plantarum and Lactobacillus delbrueckii spp. bulgaricus in soy-yoghurt gave soy-yoghurt of higher protein content than the single cultures. Lactobacillus delbrueckii spp bulgaricus and Leuconostoc lactis spp cremoris which gave the highest protein contents in soy-cheese hold potential for use as starter cultures and the combination of soy-cheese isolates in mixed culture fermentation trials is recommended.