Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2000
Publication Date: N/A
Interpretive Summary: Oats are a nutritionally excellent, but underutilized, food. One reason they are not more widely consumed is because many oat food products are not very appealing or tasty. One way to make oats more acceptable for human consumption is to improve their food characteristics by malting them. Malting adds color, taste and sweetness to oat products. To optimize the benefits of the malting process, however, we need to better understand the chemical characteristics of germinating (malting) oats and how these can be manipulated. This study was carried out to define how one important set of oat components, the proteinase enzymes, behave during malting. In this study we prepared malt from oats and used two very different methods to measure the types of proteinases that formed during malting and when they developed in the grain. One method measured the individual proteinase forms while the other measured the total enzymatic activity. The activities were analyzed at three different pH values; 3.8, 6.2 (the normal pH inside an oat grain) and 8.0, so that the different classes of proteinases could all be detected. Few proteinases were present in unmalted oats but they formed rapidly during the first three days of the malting process and then remained constant. This knowledge will make it possible for food processors to scientifically tailor their oat malting procedures to prepare oat malts that are optimally suited for their various food uses.
Technical Abstract: During the germination of oats the major seed storage proteins, globulins, are hydrolyzed by endoproteinases. We have used two methods to characterize these endoproteinases. A qualitative PAGE method that used oat globulins as gel-incorporated substrates was used to determine which enzymes hydrolyzed the globulins. The proteolytic hydrolysis products were studied by hydrolyzing the globulins in vitro with the endoproteinases and analyzing the products by SDS-PAGE. Class-specific proteinase inhibitors were used to show that the globulin hydrolyzing enzymes were cysteine-class proteinases. The proteinases were active at pH 3.8. Using the gel analysis method, a little activity was present at the beginning of seed germination, but the major activity only appeared on the sixth day of germination. Extracts from 4-day germinated oats contained cysteine proteinases that hydrolyzed the globulins in vitro to form a polypeptide of 'intermediate' (app. MW 34,500) size. Cysteine proteases from the 8-day germinated sample totally hydrolyzed the globulins in less than 1 hr. Very little hydrolysis occurred at pH 6.2, the pH of germinated oats endosperm tissue. The fact that hydrolysis occurred quickly at pH 3.8 implies that there is probably pH compartmentalization within the endosperm, with some areas of the seed having a low pH value so that the globulins can be degraded.