Development of Starter Culture for Fermentation of Millet into Fura and Preservation of Fura by Gamma Radiation

ABSTRACT

Lactic Acid Bacteria (LAB) are the most widespread of organisms responsible for food fermentation and have been applied as commercial starter cultures in many food industries. A study was conducted to develop a starter culture for the fermentation of millet into Fura and to extend the shelf life of Fura by gamma radiation. The isolation, characterization and identification of the LAB and yeasts responsible for Fura fermentation was carried out using physiological methods. A brief survey was carried out in Dome and Nima in Accra to observe and confirm the processing operations documented in literature and also obtain samples for laboratory analysis. The enumeration of aerobic mesophiles, lactic acid bacteria (LAB) and yeasts populations were carried out on Plate Count Agar, de Man Rogosa Sharpe Agar and Oxytetracycline Glucose Yeast Extract Agar respectively. The LAB species were characterized using Gram Reaction, Catalase Reaction, Oxidase Test, Salt Tolerance Test, Growth at Different Temperatures and Growth at Different pH. The LAB and yeasts Isolates were tentatively identified by determining their pattern of carbohydrate fermentation using the API 50 CH and ID 32 C galleries respectively. The LAB were also screened for their technological properties on rate of acidification, production of exopolysaccharides (EPS), amylase and protease activity including their antimicrobial activity against some common enteric pathogens using the Agar Well Diffusion Assay. Starter culture trials were carried out using dominant strains of lactic acid bacteria and yeasts in singles and in combinations. Challenge testing with Escherichia coli (RM EC. 0157; 11Q-1411), Vibrio cholerae, Staphylococcus aureus (RM SA 1L-1304), and Salmonella typhimurium(RM ST 20B-1410), in a sterile millet dough was also carried out. The lactic acid bacteria identified were Lactobacillus fermentum (33.33%), Weissella confusa (20%), Lactobacillus brevis (16.67), Pediococcus acidilactici (13.33%), Lactococcus lactis ssp lactis 1 (10%) and Lactococcus rafinolactis (6.67%) whereas the yeasts were characterized and identified as Saccharomyces xii cerevisiae (43.75%); Candida krusei (25%) Candida albicans (18.75%) and Candida membranifascians (12.5%); Mean pH values decreased from 6.47-6.38 to 4 .02-3.83 with corresponding increase in titratable acidity from 0.18-0.19 to 0.51-0.62 during all the fermentation trials. The population of LAB increased from 107 to1010 cfu/g whilst the population of yeasts increased from 105 to108 cfu/g during all the dough fermentation trials. Three LAB isolates (Lactobacillus fermentum, Lactobacillus brevis and Weissella confusa) exhibited the fastest rates of acidification with the least pH values and corresponding high percentage titratable acidity values and therefore have the potential to be used as starter cultures for Fura production. All the lactic acid bacteria isolates exhibited antimicrobial activity against all the pathogens tested in the present work (Salmonella typhimurium, E. coli, Vibrio cholerae and Staphylococcus aureus), with L. fermentum exhibiting the strongest inhibition against Staphylococcus aureus and Vibrio cholerae. In the challenge test, the microbial numbers of most of the pathogens reduced significantly in the course of the fermentation and were not detected after 12 hours in many of the mixed culture combinations. Fermented and unfermented Fura samples were given different treatments involving vacuum packaging and irradiation and stored at ambient temperature. Fermentation did not have an effect on shelf life because the unfermented samples also fermented during storage. The combination of irradiation and vacuum packaging had the most significant effect on Fura and samples were wholesome after six (6) weeks. Samples which were irradiated but not vacuum packaged were also wholesome but had higher microbial counts. Samples which were vacuum packed but not irradiated had shelf life of four (4) weeks. Samples which were packed in polyethylene bags and given no further treatment had a shelf life of two weeks