The study of properties and nutrient determination of hydrogel made of soybean meal (okara) using microwave-assisted heating

Abstract

Soybean meal (okara) poses one of significant disposal problems in several areas all over the world, as it is the residue left from ground soy beans after extraction of the water extractable fraction used to produce soy milk and tofu. However, it still contains high amounts of proteins and minerals with high contents of crude fiber. Therefore, dried and ground okara have a potential to be exploited as a starting material for hydrogel production. In this study, the biopolymer, okara based hydrogel, was fabricated to be exploited as water reservoir with high contents of nutrients for plant growth. Glutaraldehyde (GA) blended with a poly (vinyl alcohol) (PVA) was used for the PVA/GA/okara based hydrogel productions. By using microwave-assisted heating, the hydrogel was fabricated in the presence of a 100% of okara, but with conventional hotplate heating at least 50% starch needed for PVA/GA/okara based hydrogel productions. Water soluble fraction of nutrients including nitrogen, phosphorus, potassium, and calcium in the hydrogel was determined. The results showed that 1 g of the synthesized hydrogel contained approximately 0.05 mg of NO3-, 0.05 mg of P2O5, 4.50 mg of K2O, and 0.03 mg of Ca which were higher contents than those in a commercial hydrogel. © 2017 Elsevier Ltd. All rights reserved.