Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2000
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 avenin proteins, are degraded. Two similar avenins occur in oats, called alpha-avenins and beta-avenins. The two avenin types were degraded at different stages of the malting process and neither was hydrolyzed at the general pH of the germinating oat kernel, indicating that there are probably places inside the grain where the pH is quite different from that of the majority of the kernel. One set of avenin-degrading enzymes was active during the first 4 days of germination, and a second set formed thereafter. All of these enzymes were 'cysteine class' proteases. 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 and will help researchers who are studying how compounds are recycled by plants during seed germination.
Technical Abstract: During oat seed germination, the insoluble storage proteins must be solubilized and transported to the embryo for use of the developing plantlet. We showed earlier that pH 6.2-active serine and metalloproteinases were the predominant gelatin-hydrolyzing enzymes of oats, while the oat globulins were degraded by pH 3.8-active cysteine proteases. The pH of the endosperms of germinating oats is 6.2. We have continued our characterization of the germinated oat proteinases by determining which hydrolyze avenins, the oat storage prolamins. Avenins of resting seeds were purified and hydrolyzed with proteinases extracted from oat seeds that were germinated for various periods. The peptides released were analyzed using SDS-PAGE. The alpha-avenins were hydrolyzed at pH 3.8 by cysteine proteinases from 4-day germinated seeds and the beta-avenins were hydrolyzed by similar enzymes from 8-day germinated seeds. At pH 6.2 or pH 5.0 the avenins were not degraded by any of the germinated oats endoproteinases. It is probable that some kind of pH compartmentalization occurs within germinating oat seed. After four days of germination either new proteinases form or some preexisting proteinases are activated. The cysteine proteinases are apparently responsible for the majority of the storage protein hydrolysis that occurs during oat germination.