Effect Of Different Heat-treatment On The Anti-nutritional Factors And Quality Of Soybean

Soybean contains some anti-nutritional factors, such as urease, lipoxygenase and trypsin inhibitor, in addition to containing abundant nutrient substance. These anti-nutritional factors have bad influence on soybean nutritive value. There are already a lot of researches on the passivation of soybean anti-nutritional factors, but there is a few researchers studying the three anti-nutritional factors simultaneously. In this study, soybeans were heated by microwave, radio frequency and baking and the effect of different heating conditions on soybean urease, trypsin inhibitors, lipoxygenase, nitrogen solubility index, color and smell was investigated. Then soybeans were soaked with different amount of water and the effect of different moisture content on soybean anti-nutritional factors and quality was analyzed. The results are shown below:(1) The activity of soybean urease and trypsin inhibitor decreases from 10.19 U?g-1 and59.87 mg?g-1 to 0.11 U?g-1 and 11.65 mg?g-1, 0.25 U?g-1 and 7.76 mg?g-1, 0 U?g-1 and 22.53mg?g-1 respectively after microwave(385 W)heating for 3 min, RF heating 600 s, baking(150℃) for 45 min and the inhibition rate of trypsin inhibitor is respectively 80.54%, 87.03%,62.37%. It’s easy to passivate the lipoxygenase of soybean, and the activity of lipoxygenase is almost 0 after microwave heating for 2.5 min, baking for 30 min at 130℃, baking for 15 min at 140 ℃ or RF heating for 550 s. As the heating time and temperature increasing, the inhibition rate of anti-nutritional factors increases a lot.(2) The NSI value of raw soybean decrease from 80.05% to 10.65 %, 9.49 %, 5.44 %respectively after microwave heating for 3.0 min, RF heating 600 s, baking(150℃) 45 min.The L, a and b value of soybean become from 85.91,-0.93 and 20.71 to 81.42, 2.11 and 22.04;75.58, 5.38 and 24.23; 74.24, 5.98 and 24.48 respectively after microwave heating for 3 min,RF heating 600 s, baking(150℃) 45 min. The aroma components represented by No.2 and No. 7 sensor of electronic nose are the subject of soybean aroma components. The G/G0(relative resistivity values) of No. 2 and No. 7 sensors which represent main soybean aroma components increases from 2.16 and 3.36 to 2.84 and 5.27, 3.29 and 5.37, 6.38 and 9.45 after microwave heating for 3min, RF heating for 600 s, baking(150℃) for 45 min. As the heating temperature and time increasing, the NSI value decreases a lot, but the color of soybean darker gradually and the content of aroma components increases gradually.(3) When the moisture content comes to 7%, lipoxygenase has been completely inactivated. When the moisture content increases from 5.39% to 9.00%, the urease activity and trypsin inhibitor activity of soybean heated by microwave for 2.5min decreases respectively from 5.46 U·g-1 and 47.37 mg·g-1 to 0.35 U·g-1 and 10.39 mg·g-1; the NSI valuedecreases from 31.79% to 9.51%; and the L, a and b value of soybean become from 85.74,-0.76 and 20.52 to 84.78, 0.22 and 19.44. When the moisture content is 7%, the lipoxygenase is passivated completely. As moisture content increasing, the anti-nutritional factors activities and NSI value decrease gradually; the soybean color daker gradually. While the aroma components reduce first and then increase as the moisture content increasing, and reaches the minimum when the moisture content is 7 %.According to the results, we can conclude that microwave heating is more effective and faster on passivating anti-nutritional factors and there is less effect on soybean quality by microwave heating. So microwave heating is the best one among the three heating methods and the change of moisture content has significant effect on microwave heating.