Evaluation of the efficacy of malted, gamma irradiated and enzymatically processed finger millet–soybean blends in supporting growth of a mixed culture of lactic acid bacteria

Abstract

Unprocessed, malted, gamma irradiated (2 kGy and 10 kGy) and enzymatically treated [α-amylase + glucoamylase (E1)/α-amylase + glucoamylase + alcalase (E2)] finger millet (ragi) – soybean blends (7:3) were assessed for their use as substrates for the growth of a mixed culture of lactic acid bacteria (LAB) [Lactobacillus rhamnosus MTCC 1423, Lactobacillus plantarum MTCC 2621 and Lactobacillus fermentum MTCC 903]. Results showed comparable growth profile in all the media to that of standard (MRS) media used for growth of these organisms achieving 3–4 log cycle increase in cell counts in 16 h. However, the blend of these grains could be used more efficiently, if subjected to malting, gamma irradiation or enzymatic processing. The attributes like lowering of pH, accumulation of organic acids and reduction in viscosity were better achieved with the use of processed commodities. Changes in the profile of sugars and free amino nitrogen (FAN) due to processing were in agreement with the rate of fermentation. Results suggest that radiation processing or enzymatic treatment could be used as faster alternatives to the malting process for improving the quality of cereals and legumes with regard to supporting the growth of a mixed culture LAB.