Adsorption, Thermodynamic Properties and Shelf Life of Cocoyam, Red Kidney Bean and Mango-based Complementary Foods as Influenced by Fermentation and Malting

Abstract

This study examined the effects of fermentation and malting on the moisture adsorption behaviour, thermodynamic characteristics and predicted shelf life of complementary foods formulated from cocoyam, red kidney beans and mango. Flours derived from cocoyam, red kidney beans and mango were prepared using standard processing techniques and subsequently combined into four formulations: fermented cocoyam/malted red kidney bean/mango, fermented cocoyam/non-malted red kidney bean/mango, non-fermented cocoyam/malted red kidney bean/mango and non-fermented cocoyam/non-malted red kidney bean/mango. The samples were standardised to achieve a protein content of 16% using material balance calculations. Equilibrium moisture content (EMC) data were generated using the static gravimetric method and modelled using the Guggenheim–Anderson–de Boer (GAB) equation through polynomial regression analysis and the Brunauer–Emmett–Teller (BET) equation through linear regression analysis. The moisture adsorption isotherms of all formulations exhibited a characteristic Type II sigmoidal pattern. Across all samples, EMC increased with increasing water activity, whereas higher temperatures resulted in lower EMC values. Moreover, fermentation and malting significantly increased EMC, indicating an enhanced capacity of the formulations to adsorb and retain moisture. The monolayer moisture content (Mo) decreased with increasing storage temperature and increased with fermentation and malting. Both fermentation and malting enhanced the surface area of sorption, although this surface area diminished with increasing temperature. The isosteric heat of adsorption (kJ/mol) decreased from 27.77–4.22 (NFNMM), 25.05–1.27 (FNMM), 23.21–1.01 (NFMM) and 20.54–0.94 (FMM). The isosteric heat of adsorption decreased with increasing moisture content and was further reduced by fermentation and malting, suggesting a reduction in the energy required for moisture adsorption. The entropy of adsorption (kJ/mol K) decreased from 1.05–0.36 (FMM), 0.94–0.09 (NFMM), 0.87–0.06 (FNMM) and 0.66–0.02 (NFNMM) with decreasing equilibrium moisture content. Similarly, the entropy of sorption increased with moisture content and was further elevated by fermentation and malting, indicating greater molecular disorder during sorption. The shelf life of complementary foods packaged in aluminium pouches ranged from 317 to 689 days, whereas that of complementary foods packaged in LDPE ranged from 211 to 360 days. The shelf life of the food products decreased with increasing temperature and also decreased with fermentation and malting. These findings provide critical insights into the shelf life of complementary foods under varying processing and packaging conditions.