Optimization of the thin-Layer Drying of Brewers’ Spent Grain to obtain a safe and Functional Food Ingredient

Brewers’ Spent Grain (BSG) is the most abundant by-product of beer production; it is rich in fiber, protein, lignin, and bioactive substances. However, this product has environmental and health risks due to its high initial moisture content and susceptibility to microbial contamination.

The objective of the work was to design a thin-layer drying process of BSG that is coupled to the lethality evaluation of a pathogenic microorganism (Bacillus cereus spores) in order to optimize the industrial treatment.

Drying experiments were conducted using BSG with a high initial water content of 76.46 % (wet basis), varying the air temperatures (75–120 °C) and thin-layer thicknesses (0.75–1.3 cm). Mathematical modeling based on water vapor diffusion and Arrhenius kinetics enabled prediction of effective moisture diffusivity and drying times. The safety criterion was a minimum of a 2-log reduction of B. cereus spores, based on thermal death time (F) calculations using literature values for D- and z-parameters. Simultaneous measurement of thermal histories, at the interphase between the bottom of the product layer and the hot surface of the dryer, allowed precise estimation of microbial lethality.

The process ensured compliance with the Argentine Food Code requirement of ≤13% final moisture (wet basis) in the product and a maximum of 10³ CFU/g of B. cereus. Under optimal conditions (such as a treatment time of 5.9 h for a 1 cm layer thickness at 100 °C), both drying targets and microbial lethality were achieved. In terms of total phenolic content (TPC) and antioxidant activity (AC), the highest values were obtained at 120 °C: the TPC was 19.8 mg GAE/g dry matter, and the ACs using DPPH and ABTS were 20.9 and 17.6 mmol trolox/g dry matter, respectively.

The proposed method provides a scientifically validated drying process for BSG, promoting its use as a functional ingredient. It represents a sustainable approach aligned with circular economy goals.