Development of a Ready to Drink Sorghum Beverage Through Optimization of Malting and Fermentation.

Abstract

There has been a growing trend in production and marketing of a range of beverages with poor nutritional quality in Kenya resulting in public health concerns such as diabetes, overweight and obesity especially among children and adolescents. As such, development of a commercially viable and nutritious beverage from underutilized cereal such as sorghum has been limiting. This study was therefore designed to develop an alternative sorghum-based beverage with high nutritional and sensory quality compared to commercially readily available beverages in the Kenyan market. Four beverage formulations containing sweetened sorghum malt extracts were developed through malting (3, 4 and 5 days respectively) and fermentation using kombucha culture at different temperatures (between 20 ºC – 35 ºC) and analyzed for chemical composition and nutritional characteristics (protein, ethanol, sugars, calories, total phenolics, tannins, vitamin C, iron and zinc) using standard analytical procedures. For the nutritional components, the values ranged between 2.01- 3.63 % for protein, ethanol was absent, 1.42-2.47% for sugars, 13.19- 23kcal/ml for calories, 0.13 - 1.66 GAE/100ml for phenolics, 1.29 - 40.08mg/100ml for tannins, 4.35 - 6.13 mg/100ml for vitamin C, 1.25- 29.56g/l for iron and 0.7-2.11g/l for zinc. Iron was used in the process optimization to select the beverage with high nutritional and sensory quality. The best formulation based on the process optimization was obtained from an optimum of four days malting and fermentation temperature of 25 ºC (4D). The developed beverages were tested for their antimicrobial properties using food borne pathogens E. coli and S. aureus. Halo diameters were measured with significant differences (p<0.05) in diameters being noted for E. coli between the different samples, with the beverage formulation 3D forming the smallest halo zone compared to the rest. The minimum inhibitory concentration for the formulated beverages to be effective antimicrobials was found to be 8%. Microbial enumeration results showed dominance of lactic acid bacteria and yeasts compared to acetic acid bacteria. The microbial counts overall increased with increasing malting days and temperatures of fermentation. Total viable counts were highest in 5D2 with the least being in 4D and 5D1. Sensory analysis was conducted on the developed beverages and compared to a control commercial beverage under the brand name ‘Malto’ purchased from the local supermarket by a semi trained panel of 15 people composed of university staff and students to determine their ranking in terms of color, aroma, taste and overall

acceptability. The best beverage was 3D in terms of taste (4.9), color (4.40), aroma (4.90) and overall acceptability (4.87). Shelf-life analysis was also conducted on this best beverage to find out its shelf life at 4 ºC and 30 ºC. The shelf life was calculated according to Q10 factor that was found to be 1.89 leading to shelf-life values of 103 days and 17 days at 4 ºC and 30 ºC respectively. The study concluded that a nutritious and shelf stable sorghum based kombucha beverage is a viable alternative to current product variants in the market. The study however shows a need for further research on the effects of the kombucha culture on the functional and nutritional properties on sorghum and ways to optimize the beverage. The study nevertheless indicates the potentiality of sorghum as a viable alternative in food product development.