RAFFINOSE METABOLISM AND UTILISATION BY L. PLANTARUM ISOLATED FROM INDIGENOUSLY FERMENTED CEREAL GRUELS FOR NUTRITIONAL IMPROVEMENT

Abstract

Most African foods used in weaning are usually cereal-based gruels fermented by Lactic Acid Bacteria (LAB). The food mainly supplies carbohydrate; excessive intake of which might cause malnutrition in growing children. Minimum dietary requirements of a child could be met through fortification with protein-rich supplements. Soybean is rich in dietary protein but contains some antinutritional factors and raffinose, an oligosaccharide responsible for gas formation, bloating and flatulence in weaning children. The use of microorganisms for hydrolysing raffinose has not been fully exploited in Nigeria. In this study, the use of LAB to hydrolyse raffinose, reduce antinutritional factors and improve nutritional composition of such food blends were investigated.

Commercially- hawked “Ogi” (CO) samples, Local Varieties (LV) of sorghum and maize were obtained from Bodija market, Ibadan and Typed Varieties (TV)-Samsorg 40, Samsorg 41 and Ex-Kano from the Institute of Agricultural Research and Training, Ibadan. The LAB were isolated from spontaneously-fermenting cereal gruels and identified using standard methods. Nine strains of Lactobacillus plantarum were selected based on the abundant production of -galactosidase, and characterized by PCR amplification of 16SrDNA genes. Plasmid presence was determined using agarose gel electrophoresis and the effect of plasmid curing was monitored. The growth of the organisms and metabolites production in different carbon sources were monitored at 200C to 800C and pH of 3.0 to 9.6. Soyabean was pre-treated by milling, cooking and roasting while the relationship of the isolates to raffinose metabolism during fermentation was monitored daily for 5 days. Reducing sugar, residual oligosaccharides, nutritional, antinutritional factors and alpha-galactosidase were determined using UV-spectrophotometer following Association of Official Analytical Chemist procedures. Data were analysed using ANOVA at p=0.05. One hundred and twenty LAB isolates were obtained and identified as L. plantarum (35.8 %), L. fermentum (12.5 %), L. pentosus (7.5 %), L. acidophilus (15.8 %), L. casei (5.8 %), L. brevis (6.7 %), L. cellobiosus (6.7 %), L. jensenii (5.0 %) and L. reuterii (4.2 %). Analyses of the nine L. plantarum isolates revealed high sequence identities (97.0 %). These isolates exhibited significant differences in utilization of raffinose at varying concentrations of 0.2 -1.0 mg/mL, while isolates obtained from LV performed better than those from TV and CO. Fermentation reduced the oligosaccharide content of the soyabean by 74.6 % while the reducing sugars increased by 65.0 %. Fortification of the gruel with soyabeans using uncured L. plantarum strains improved the nutritional quality (protein: 8.4 to 17.8 %, fat: 3.6 to 12.9 %, ash: 2.0 to 3.8 %, Fe: 6.4 to 10.7 mg/100g and Ca: 156.7 to 211.0 mg/100g), and a significant reduction in antinutritional factors (Tannin: 1.9 to 0.1 mg/g, Phytate: 1.2 to 0.1 mg/g and Trypsin Inhibitor : 1.2 to 0.0 mg/g) was observed after fermentation . Oligosaccharide content, reducing sugar, nutritional and antinutritional composition and organoleptic attributes of the end product were significantly affected by plasmid curing. Utilisation of raffinose by Lactobacillus plantarum from local food sources reduced antinutritional factors and oligosaccharides in soybeans. Nutritional quality of cereal gruels were improved by inclusion of Lactobacillus plantarum.