Brewers spent grain drying: Drying kinetics, moisture sorption isotherms, bioactive compounds stability and Bacillus cereus lethality during thermal treatment.

Abstract

The most abundant by-product of the brewing industry is beer bagasse (BSG); its high moisture content requires a rapid drying process to stabilize the product. The objective of this work was to carry out the analysis and mathematical modeling of the drying process of thin layer bagasse at temperatures above 60 °C in order to establish adequate processing conditions that assure its safe use and storage as a functional ingredient. The moisture sorption isotherms of BSG were determined at 10, 20 and 40 °C. Considering the most unfavorable condition tested (40 °C), the maximum residual moisture content that avoids the growth of Bacillus cereus was 15% dry basis, that corresponds to aw = 0.93. The drying curves of thin layers of BSG were obtained experimentally and mathematically modeled using Fick's law; lethality to achieve at least a 2-log reduction in Bacillus cereus population was assessed in terms of thermal inactivation kinetic parameters. Drying conditions at temperatures above 75 °C with air velocity of 3.2 m/s, increased total phenol content levels enhancing antioxidant activity.