Physicochemical Changes of Grobogan Variety Soybean (Glycine max) during Pilot Plant Scale Steam Flash Explosion – A Reaction Kinetics Approach

A pilot plant scale of SFE (steam flash explosion) chamber has been developed in order to process raw grobogan soybean. The objectives of this research were to study the physicochemical changes of soybean in term of reaction kinetics approach and to determine the optimal variables to produce high quality soybean. We used 2.5 kg and 5 kg of soybean, representing 75% and 50%, respectively, of headspace volume of SFE chamber. After soaking in the water, these soybeans were then treated using SFE chamber operated at temperature of 115 °C (P=1 bar), 125 °C (P=2 bar), and 135 °C (P=3 bar) and time interval of 0, 5, 10, 15, 20, and 25 minutes, after which the steam was suddenly released from the chamber to provide explosion effect. The treated soybean samples were then analyzed for hardness, color characteristics, urease index (UI), protein dispersibility index (PDI), and protein solubility index (PSI). The result showed that the decrease of hardness and b-value (yellowness) of soybean during processing can be explained by 1st order kinetic model. As for hardness, SFE gave kT=115°C=0.0344 minutes-1, kT=125°C=0.0495 minutes-1, kT=135°C=0.0864 minutes-1, and Ea=60.350 Kj.mol-1 (for 2.5 kg capacity); and kT=115°C=0.0314 minutes-1, kT=125°C=0.0442 minutes-1, and kT=135°C=0.0858 minutes-1, and Ea=66.009 Kj.mol-1 (for 5 kg capacity). As for b-value, SFE gave kT=115°C=0.0225 minutes-1, kT=125°C=0.0378 minutes-1, kT=135°C=0.0558 minutes-1, and Ea=59.873 Kj.mol-1 (for 2.5 kg capacity); and kT=115°C=0.0258 minutes-1, kT=125°C=0.0393 minutes-1, kT=135°C=0.0553 minutes-1, and Ea=64.544 Kj.mol-1 (for 5 kg capacity). The Ea for 5 kg capacity is higher than Ea for 2.5 kg capacity. This research found no appropriate reaction kinetics model for urease index, PSI, dan PDI. Soybean treated under 115 °C (1 bar) within 5 minutes for both capacities satisfy the processed soybean quality requiement.