Optimization of fermentation conditions for the utilization of brewing waste to develop a nutraceutical rich liquid product

Utilization of brewers' spent grain (BSG), for the development of a fermented liquid product rich in value-added phenolic compounds was investigated. Changes in and liberation of phenolic compounds and antioxidant activity during fermentation of BSG was studied. The effect of various particle size (PS), solid liquid (SL) ratio, fermentation time and rotation speed was optimized using response surface methodology (RSM) for the purpose of improving bacterial growth and the enhancement in the release of polyphenolic compounds. Contour maps generated using the response surface equation showed that the experimental variables significantly affected the response. A production of 10.4. log. cfu/ml, 2.95. g/l lactic acid accompanied by a release of 268.6. mg Gallic Acid Equivalent (GAE)/ml of phenolic compounds, 135. mg Quercetin equivalent (QE)/ml of flavonoid compounds, 33.7. mg. TE/ml ferric reducing antioxidant power (FRAP) and 75.1% radical scavenging activity (RSA) was obtained with the optimized factors of 19. h fermentation time, 0.25. SL ratio, 85. rpm and 440 μm. PS. Shelf life was monitored over a period of 30 days and the product was shelf stable in terms of bioactive components for 15 days. The cell numbers, total phenol content and acidity (in terms of lactic acid) were maintained till 15 days storage period and a reduction was observed only after that.