Moisture sorption models predicting sorption characteristics of malted and/or fermented Faro 44 rice plus soybean-based complementary foods

Abstract

The objectives of this study were to understand the responses of the formulated food products subjected to varying temperatures and relative humidity, to predict their storage stability, and to optimise and control their processing. Brunauer, Emmett and Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models, as well as a double-logarithmic polynomial equation, were used to model foods' sorption characteristics. FARO 44 rice and soybean were obtained from the National Cereal Research Institute and the Agric Seed Storehouse, respectively. Rice was processed into flours and formulated with processed soybean flour to provide 16% protein in each mixture. The ratio of rice to soybean was calculated using a material balance equation, and the experiment used a 2 × 2 completely randomised design. In this study, the equilibrium moisture contents of the formulated foods were determined gravimetrically at 20, 30, 40, and 50 °C, and the sorption models were fitted to the resulting data. The results of the study showed that the equilibrium moisture contents, GAB and BET monomolecular moisture contents, enthalpies of mono and multilayers, total surface area of solids of the formulated products ranged from 0.20 to 30.60 g H₂O/100 g solids, 2.24 to 7.68 (M_g) g H₂O/100 g solids, 2.28 to 4.61 (M_b) g H₂O/100 g solids, 40.95 to 64.75 kJ/mol, 31.42 to 42.25 kJ/mol, 80.24 to 162.02 m²/g solids, respectively. Interestingly, the sorption study agreed with the BET and GAB models. Isotherms were temperature-dependent and showed slight hysteresis. The monolayer moisture values varied, and the energy constants were temperature-dependent. The correlation coefficient and RMS values justified the sorption parameters. The non-fermented formulated rice-based products were more hygroscopic than the other samples. The malted-fermented rice-based product exhibited the highest thermostable and better-keeping qualities. Finally, the study has provided adequate information at every stage for stability, product-packaging optimisation and control.