Effects of Pre-Heating Between Controlled Temperature Microwave Heating and Hot Air Oven Heating in Protein Extraction Process of Soybeans

Abstract Heating is an important treatment before protein extraction process. Rapid heating of microwave heating (MW) was investigated to compare with hot air oven (HA) heating prior to protein extraction in soybeans. Heating temperature was controlled at 50°C, with the heating time of 15, 30, 45, 60 and 75 min. The control treatment was no heat treatment. The treated samples were analyzed i) the total protein using Kjeldahl method, ii) the protein soluble by Bradford method and iii) cells microscope investigated by scanning electron microscope (SEM). The results were found that the pretreatment of 75 min microwave (MW75) heating provided the highest protein with the amount of absorbance value and total protein of 3.0365 ± 0.004 mg mL-1 and 3.70 ± 0.01% respectively. The lowest protein extraction of 2.7707 ± 0.020 mg mL-1 and 3.38 ± 0.005% total protein value occurred in the condition of 15 mines hot air oven (HA15) heating. The investigation using scanning electron microscope (SEM) revealed that protein extraction correlated with the enlargement and breakage of cell wall and endosperm caused by microwave heating rather than hot air oven heating. The rapid heating of microwave and heating time influenced the amount of extracted protein. Keywords: Soybean, Protein, Microwave, Hot air, Heating