Abstract

Effects of pulsed electric fields (PEF) on urease, soybean lipoxygenases (SLOX), and soybean trypsin inhibitors (STI) of soymilk were studied with different PEF parameters. Soymilk was exposed to treatment time from 0 to 1036 s at 400 Hz of pulse frequency, 2 2s of pulse width, and 30 kV/cm of electric strength. Then activities of urease, SLOX, and STI of soymilk were measured with ultra violet and visible spectrophotometry. The result shows that the relative activities of urease, SLOX, and STI decreased with the increase of PEF time from 0 to 1036 µs. Comparing with STI, urease and SLOX were more sensitive to PEF, while STI was resistent to PEF.

INTRODUCTION

Pulsed electric field (PEF) is a non-thermal food processing technology for an alternative to traditional thermal pasteurization (1). PEF has been successfully applied to a variety of liquid foods such as milk, soymilk, liquid egg, and juice (2, 3). Soymilk is especially regarded as a low-cost substitute for dairy milk for the poor in the developing countries and as a nutritive supplement for the lactose-intolerant population as soybeans do not contain lactose (4). Soymilk is rich in proteins and effective in lowering the serum cholesterol level of rats and humans (5, 6). Soybean isoflavones are reported to protect humans from atherosclerosis and cancer (7). However, a number of antinutritional factors are present in soybeans, such as soybean lipoxygenases (SLOX) and soybean trypsin inhibitors (STI). SLOX are responsible for the production of rancid off-flavours in soybean (8). SLOX activity is also related to the formation of bitter taste. STI affects protein digestibility and inhibit growth (9, 10). Traditionally thermal treatment can inactivate microorganisms and enzymes of soymilk. However, it induces dissociation, denaturation and aggre ...