ARS | Publication request: LIPASE ACTIVITY AND LIPID METABOLISM DURING OAT MALTING

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 16, 1998
Publication Date: N/A

Interpretive Summary: Malted oats may have useful properties as a food malt product, either similar or different from current uses of barley malt. Hulless oats or oat groats are easily malted, and have an advantage over normal barley in not having an unpalatable husk. However, oats have a high oil content and a high activity of lipase, an enzyme that degrades oil to free fatty acids, on the surface of the seed. Free fatty acids content needs to be minimized, because they can be oxidized, producing rancid flavors. Experiments were designed to determine if the high lipase activity of oats was related to the increased levels of free fatty acids that occurred with malting. We found no correlation between lipase activity levels and free fatty acid increase among a group of 12 varieties of oats. Chemical treatments that partially or completely inactivated lipase activity did not eliminate the free fatty acid buildup. We concluded that the surface lipase in oat, which is responsible for oil degradation in milled oats, was not the cause of the free fatty acid increase in malted oats. We suggest, but have not proven, that there may be another lipase present on or near the oil bodies in the cells of the oat seed that may be responsible. Further research is needed to substantiate or refute this hypothesis.

Technical Abstract: Experiments were conducted to determine the relationship, if any, between lipase activity and the metabolism of lipids during malting (germination) of oat seed. During the course of malting, concentration of the free fatty acid fraction increased markedly at the expense of the neutral lipid fraction (triacylglycerides), while the initial high lipase activity decreased by about 40%. The free fatty acid composition of total and neutral lipid fractions was stable during malting, but there were marked changes in the free fatty acid and phospholipid fractions. In a comparison among 12 genotypes, there was no significant correlations between lipase activities and the changes in lipid fractions. Brief treatments with chemicals or hot H2O that inhibited lipase activity had various effects on subsequent changes in lipid fractions, but these changes were not consistent with the inhibitions in lipase activity observed. It was concluded that the degradation in triacylglycerides and increase in free fatty acids observed during malting of oats was not controlled by the level of total lipase activity. Rather, it was suggested, that oat may have another lipase present in the cells where the oil bodies are located that hydrolyzes triacylglycerides from the oil bodies during germination. Further research is needed to substantiate or refute this hypothesis.