Microbiological Screening of a Starter Culture of Probiotic Status from Formulated Non-Dairy Yoghurt Analogue from Natural Fermentation of Soymilk-Achamilk Blends

Abstract

Non-dairy probiotic yoghurt analogue was formulated using cream variety of soybean (Glycine max L.) and white variety of acha (Digitaria exilis). One kilogram of cleaned soybean and 500grams of cleaned acha were used to produce soymilk and acha milk. Soymilk and acha milk were blended in different ratios (100:0; 90:10; 80:20: 70:30; 60:40; 50:50; 0:100),respectively. The various blends were pasteurized at 80°C for 30 minutes, cooled to 44±2°C fermented naturally for 8 hours until desired degree of acidity was achieved, cooled rapidly to 8±2°C, packaged in sealed plastic bottles and stored in the refrigerator. Microbiological analyses were done on the isolates obtained from incubation in an anaerobic jar at 37°C for48hours. The isolates were stored in sterile agar slants after purification by successive streaking on MRS and ST agar before being subjected to characterization. Microbiological screening (morphological, physiological and biochemical tests) was done to identify characterized a working isolate of probiotic status. Further assessment of performance of probiotic strains {acidifying activity and exopolysaccharide (EPS) production} were performed. Results show that the isolates were Gram positive, catalase negative, oxidase negative and non-sporing. A total of 7 isolates produced lactic acid. Among the 5 rods,3 were able to grow at 45°C ,produced acid and gas from glucose (characteristic of Lactobacillus spp.);2 isolates grew between 15 and 37°C,at 4%NaCl and pH of 9.6 (characteristic of Streptococcus spp) while 2 isolates grew between 15 and 42°C, produced acid from glucose and lactose, citrate positive (characteristic of Lactococcus spp). All the isolates showed tolerance to 5% bile and 3.0% NaCl (inhibitory substances) .There was no significant difference (p>0.05) in the acidifyingactivities of Lactobacillus, Lactococcus and Streptococcus species. After 6 hours of incubation, an increase in pH from 4.78 to 5.87(for Lactobacillus spp), 4.12 to 5.86(for Lactocccus spp) and 4.20 to 5.60(for Streptococcus spp) were observed. Lactococcus spp showed an acid value of 0.29g100m-1lactic acid after 6 hours and increased from 0.40 to 0.75g 100ml-1 after 12 and 24 hours respectively. These isolates were used for the formulation ofprobiotic yoghurt analogue.Keyword: Microbiological screening, Starter culture, Probiotic status, Non-dairy yoghurt analogue, Soymilk-achamilk blends