Author
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MIKOLA, MARKKU - UNIV OF HELSINKI, FINLAND |
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Jones, Berne |
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Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/29/1999 Publication Date: N/A Citation: 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 norma 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. The main proteinases formed were much more active in the presence of calcium and the amino acid cysteine than in their absence. 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 malting of oats, the insoluble seed storage proteins are hydrolyzed by endoproteinases and we are characterizing these germinated oat seed endoproteinases. A qualitative 2-D (IEF x PAGE) method using the gel-incorporated substrate gelatin was used to study the heterogeneity of the enzymes and a quantitative 'in solution' assay employing azogelatin was sutilized to measure the different proteinase classes present. Proteinase development during malting was monitored at pH 3.8, 6.2 (germinated oat endosperm pH) and 8.0. The numbers and intensities of the proteolytic activities increased during the first 3 days of germination, but not after that. Electrophoretic studies using class specific endoproteinase inhibitors indicated that the predominant enzymes were serine and metalloproteinases. No aspartic or cysteine proteinases were detected. The 'in solution' analyses gave somewhat different results. In the presence of the activators calcium and cysteine, a third of the 'in solution' activity was due to cysteine proteinases, the serine and metalloproteinases each contributed 15% of the activity and the other third of the activity was impervious to all of the inhibitors. These different 2-D and 'in solution' results may simply reflect the fact that the enzymes hydrolyze the dissolved ('in solution') substrate differently from the bound (2-D analysis) one. |
