Changes in Physicochemical and Microbial Markers on the Storage of a Sweet Sorghum Beverage Treated with Preservatives

Abstract

A newly designed, functional beverage was manufactured from sweet sorghum, an underutilised crop, which constitutes a dietary source of bioactive phenolic compounds and minerals. Sweet sorghum syrup was diluted to ~ 8.0% soluble solids, pre-pasteurised (boiled for 5 min), carbonated, canned, and treated with various food-grade, chemical preservatives to extend its shelf life and aid its commercialisation. Three preservatives, potassium sorbate, sodium benzoate, and citric acid, were separately added to the carbonated beverage before canning and compared to an untreated control. The shelf lives of the canned beverages at room (~ 25 °C) and refrigeration (4 °C) temperatures were evaluated in real-time using physicochemical characterisation and microbial markers. The untreated sweet sorghum beverage was consistently shown to be susceptible to microbial deterioration, particularly by lactic acid bacteria, in transit and during storage and will require preservation technology. Citric acid performed worse than the control because it accelerated the acid degradation of sucrose and caused the explosion of cans. Optical density OD_{600 nm} based on light absorption and turbidity based on light scattering at a 90° angle of the beverage samples were both measures of opaqueness and microbial growth, but the turbidity values were more sensitive to significant (P < 0.05) changes during storage. The shelf life of the sweet sorghum beverage at 25 and 4 °C with potassium sorbate as a preservative will be 25 and < 109 days and with sodium benzoate will be 17 and > 109 days, respectively. Only potassium sorbate extended the shelf life at 25 °C by 8 days when compared to the control, and both potassium sorbate and sodium benzoate extended it at 4 °C by at least 84 days. The key nutrient of total phenolic acids was stable in storage.