PHYSICAL, FUNCTIONAL, PASTING AND MICROBIAL PROPERTIES OF SORGHUM (Sorghum bicolor M.) OGI AS INFLUENCED BY FERMENTATION METHODS

Abstract

Ogi is a widely consumed food product but could possess low nutritional value when poorly processed. Fermentation had been found to improve its nutritional value, sensory properties and shelf life. However, information on fermentation of ogi using inocula from palm wine, burukutu and yoghurt is sparse. This study was designed to investigate the effect of processing and selected modified fermentation methods on quality attributes of sorghum ogi. Based on preliminary studies, ogi was processed from unmalted, malted (germinated for 72 hours, dried at 48oC for 24 hours) and milled sorghum using Spontaneous Fermentation (SF) method for between 24 and 72 hours. These samples were subjected to sensory evaluation using panelists. Ogi was also produced using sample with highest overall sensory score (control), and fermented with each of palm wine, burukutu and yoghurt inocula (0.08– 0.12 µL/500mL) as starter culture. Microorganism in SF samples, palm wine, burukutu, and yoghurt; Palm Wine Fermented Sorghum (PWFS), Burukutu Fermented Sorghum (BFS) and Yoghurt Fermented Sorghum (YFS) were cultured and isolated using ISO methods. Molecular characterisation of the isolates was done by polymerase chain reaction sequencing. Chemical, physical, functional and pasting properties, and in-vitro protein digestibility of samples were determined by AOAC methods. Sensory properties of the products were determined using panelists. Data were analysed using ANOVA at α0.05. Ogi from unmalted-whole sorghum spontaneously fermented for 72 hours had lowest overall acceptability of 5.51, while 48 hours spontaneous fermented malted-milled sorghum had highest score of 7.34. Lactobacillus plantarium, Bacillus subtilis, and Lactobacillus lactis were dominant in SF samples. Lactobacillus spp. were present in palm wine, burukutu, and yoghurt. Lactobacillus, Leuconostoc, Bacillus, Streptococcus and Saccharomyces spp.; Lactobacillus, Staphylococcus, Acetobacter, Weissella, Leuconostoc, Lactococcus, Bacillus and Saccharomyces spp.; and Streptococcus, Lactobacillus, Bacillus, Micrococcus and Pseudomonas spp. were the isolated organisms in PWFS, BFS and YFS, respectively. The concentrations of the inocula significantly affected starter culture activities, with 0.1 µL/500 mL being appropriate. Carbohydrate, protein, fibre and ash contents of the samples varied significantly. The SF sample had least protein content of 5.7%, while YFS had highest protein of 10.3%. Potassium was the dominant mineral in all the samples. The YFS sample had lowest tannin (0.08±0.01%), phytate (0.08±0.01%) and oxalate (0.99±0.01%) contents. The L*, a* and b* colour values of samples ranged from 51.27 to 65.66, 10.08 to13.27 and 11.35 to 18.79, respectively. The loose and packed bulk density was 0.44-0.62 and 0.58-1.82 g/mL, respectively. Total titratable acidity ranged from 0.20 to 1.83 g/L and pH from 3.50 to 5.72. Spontaneously fermented samples had lowest pH. The swelling power and solubility of samples was 3.11-7.20 and 0.03-2.04%, respectively. Fermenting using starter culture significantly reduced peak viscosity of sorghum ogi with SF samples being highest (126.83±2.59 RVU). Introduction of starter culture significantly increased protein digestibility of sorghum ogi. The PWFS had highest overall acceptability score of 7.28. Grain milling before fermentation and induced fermentation using palm wine, burukutu and yoghurt inocula improved the nutritional properties of sorghum ogi and were recommended for improving qualities of similar fermented food products.