Effect of moisture, microwave heating, and live steam treatment on phospholipase D activity in soybeans and soy flakes

Abstract

The impact of enzyme activity on the nonhydratable phospholipid content of crude soybean oil has been evaluated. A radiochemical method was used to assay phospholipase D activity in whole and flaked soybeans stored under a variety of storage and enzyme inactivating conditions. The crude enzyme was isolated and incubated with a mixture of 14C-labeled and unlabeled phosphatidylcholine. The amount of liberated radioactive choline was used as a measure of enzyme activity. Whole soybeans with moisture contents of 8-18% were stored at 40~ and sampled weekly for up to four weeks. Although the enzyme was active in all samples, the optimum moisture content for enzyme activity was about 14%. Flaking and flake thickness were shown to increase phospholipas D activity. At moisture levels above 10%, flakes at .012" showed about twice the activity of whole beans. As flake thickness was increased, enzyme activity decreased.Whole soybeans with moisture contents of 12-18% were treated by microwave heating under controlled conditions. During the early stages of heating, the enzyme was activated, and then was gradually destroyed by the time the temperature of the beans reached 11~120~ Approximately 8-10 min of microwave heating was required to completely destroy enzymatic activity. The inactivation of phospholipase D in soy flakes treated with live steam was also evaluated. The enzyme is rapidly destroyed at temperatures of about U0~ Evaluations of flakes subjected to live steam and whole beans treated by microwave heating to inactivate phospholipase D suggest that heat, moisture and enzyme activity are important factors contributing to the formation of nonhydratable phospholipid in extracted crude oils.

Soybean phospholipase D activity determination. A comparison of two methods

“…The phospholipase D was extracted from milled soybeans (List et al 1990(List et al ,1992 by a modification of the method proposed by Nakayama et al (1981). Methodological steps were established as follows:…”

“…Discrepancies in the values of PLD activity (PLDA) arise from comparing the results obtained by List et al (1990List et al ( , 1992 and by Tosi et al (1999). The PLDA found by Tosi et al was 150 times the PLDA found by List et al In their works, List et al (1990, 1992 applied the method of extracting the enzyme from the soybean original matrix according to a modification of the method proposed by Nakayama et al (1981) to extract the PLD from white cabbage.…”

“…Briefly, PLDA determination was based on the action of the phospholipase D, either extracted according to List et al (1990List et al ( ,1992, or not extracted but remaining in the original soybean matrix according to Tosi et al (1999), upon soybean lecithin releasing choline (Eq. 1).…”

Heat pretreatment of oilseeds: effect on oil quality

“…However, owing to its efficient heat transfer, which allows rapid heating, there is increasing interest in heating via electromagnetic radiation, such as microwave and infrared. Several authors studied the effect of microwave heating and found decreased phospholipase D activity in soy meal [2], decreased myrosinase activity in rapeseed [3], and inactivation of lipase and lipoxygenase [4,5]. We extensively studied the use of microwave heating for the heating of rape and sunflower seeds and evaluated its effect on the resulting oil quality.…”

Soybean drying in fluidized bed. effect on the hydratable and nonhydratable phosphatide concentration in crude and degummed crude oil

“…NHP content in CO increases at the same time as the extraction temperature (4). List et al (3,5) proved that moisture, cellular disruption, heat, and PLD activity are factors that promote NHP formation; PLD inactivation minimizes it. PLD was fully inactivated in whole soybeans by a 8-9 min microwave treatment at 115-120°C, and by a live steam treatment at about 110°C of soyflakes.…”