Two Lipoxygenases from Germinated Barley‐Heat and Kilning Stability

Abstract

Using ammonium sulfate precipitation followed by hydrophobic and ion exchange chromatography, two lipoxygenase isoenzymes, LOX 1 and LOX 2, were l&3-and 445fold purified from germinated barley, with 18 and 24% recovery of activity respectively. LOX 1 and LOX 2 were characterized by isoelectric points 4.9 and 6.4, and molecular weights of 90 kd and 110 kd, respectively. Apparent Km values for linoleic acid were 0.06 mM for LOX 1 and 0.18 mM for LOX 2. LOX 1 converted linoleic acid to 9 and 13 hydroperoxides at about 4:1, whereas the 13 hydroperoxide was the major product formed by LOX 2 (ratio 3:7). For both isoforms, thermal inactivation data indicated first order kinetics with activation energies influenced by ionic strength and pH. Isoenzymes composition was analyzed for three kilning schemes: the 1:3 ratio between LOX 1 and LOX 2 observed in germinated barley increased during the course of kilning.

High Pressure Treatments of Soybean and Soybean Products

“…The two activation energy values derived from the plots of the natural logarithm of inactivation rate constants, as a function of the reciprocal of the absolute temperature were larger, pointing to higher temperature sensitivity of the k values. Likewise, kinetic inactivation of lipoxygenase from many different sources, such as green peas, green beans, potatoes, asparagus, wheat germ, and germinated barley, have also been studied (Bhirud & Sosulski, 1993;Ganthavorn et al, 1991;Guenes & Bayindirli, 1993;Hugues et al, 1994;Indrawati et al, 1999;Park et al, 1988;Svensson & Eriksson, 1974). Indrawati et al (1999) reported that thermal inactivation of lipoxygenase in green bean juice could be described by a two-fraction first-order inactivation model, referring to the existence of two fractions (isozymes) with different thermal stability.…”

Characterization of Factors Involved in the Production of 2(E)-Nonenal during Mashing

“…Germinating seeds of barley have two isozymes of LOX, namely LOX-1 and LOX-2. 16,17) During the heat-drying process of germinating seeds, called kilning, LOX-2 is preferentially inactivated, 18) and as a result the residual LOX activity in malt mainly consists of LOX-1. 9-HPOD is mainly produced during mashing (9-W 13-HPOD ratio＝10:1; mashing at 529 C) by the action of malt LOX-1.…”

Preventive Production of Beer against Oxidation-Recent Advances in Brewing Technology.

“…LOXI mainly produces 9-LOOH (a precursor of trans-2-nonenal), while LOX2 catalyses 1 3-hydroxperoxide formation. If the activities of these enzymes could be successfully reduced or inhibited, the resulting beer would be resistant to the staling phenomel 71 non (Hugues et al, 1994).…”