Sustainable Management and Valorization of Spent Coffee Grounds Through the Optimization of Thin Layer Hot Air-Drying Process

Abstract

The spent coffee ground is a by-product of the coffee industry with high potential because of its beneficial properties for health, however, due to high water content, it is necessary to stabilize it without affecting bioactive capacities. The main objective of this work was to evaluate the effect of different convective drying conditions, on some technological and functional properties of the spent coffee ground and to determine the thermal degradation kinetics of chlorogenic acids. The methodology included the optimization of the drying process conditions of spent coffee ground: temperature (40–60 °C), air flow (1.0–2.0 m/s) and cake thickness (0.01–0.02 m). Effective diffusion coefficient, moisture, water activity, water and oil holding capacity, antioxidant capacity, caffeine, and seven chlorogenic acids were determined. The results showed that the best drying conditions were 60 °C, 2.0 m/s, 1.28 cm which allows retaining 84.24% of total polyphenols and 66.00% of the antioxidant capacity. Chlorogenic acids showed thermal degradation kinetics of first order under the optimal process conditions. In general, it is concluded that the convective drying process is a valid technique for processing of coffee grounds, as it allows the preservation of antioxidant compounds with a potentially beneficial effect on health, providing a stabilized low moisture content that can be used in food applications.