Abstract

Effects of pulsed electric fields (PEF) on volatile constituents 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 volatile constituents of soymilk were extracted with the method of solid phase microextraction and analysed with gas chromatography-mass spectrometry (GC-MS). The result shows that contents of hexanal decreased from 47.00 to 35.88 percent and hexanol from 29.00 to 18.52 percent with the increase of PFE time from 0 to1036 μs, indicating PEF treatment affected volatile constituents of soymilk.

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 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). Traditionally thermal treatment can inactivate microorganisms and enzymes of soymilk. However, it induces dissociation, denaturation and aggregation of soybean protein, so makes soymilk aggregate, which negatively affects the overall quality of soymilk (5).
The off-flavours of soymilk have been attributed to soybean lipoxygenases. Lipoxygenases are non-heme and nonsulfur iron enzyme naturally presenting in soybean, which mediates the conversion of polyunsaturated fatty acids to hydroperoxides, which subsequent degradation products are responsible for the off-flavours generated (6). The primary off-flavour precursors in soybean are C18:2 linoleate, which produces hexanal, and ...