Oat (Avena sativa) caryopses as a natural lipase bioreactor

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Abstract
The caryopses of oats, when moistened and immersed in oils, constitute a natural lipase bioreactor. Hydrolysis was monitored by titration of the free fatty acids in the oil phase and by thin‐layer chromatography. The optimum amount of additional water was about 20% of the weight of the caryopses, and the optimum temperature was about 40°C. The reaction was accelerated by gentle agitation, by reducing the viscosity of the oil phase by the addition of nonpolar solvents, and by increasing the amount of lipase on the caryopses. The reaction was inhibited by the accumulation of glycerol in the interior of the caryopses and free fatty acids in the oil phase. The lipase hydrolzyed all three positions of glycerol and there was little accumulation of mono‐ or diglyceride in the lipid phase. The time necessary to obtain 90% hydrolysis varied for a few days to several weeks. Greater degrees of hydrolysis could be obtained by replacing the caryopses when they became inhibited or by diluting the oil phase with hexane. The glycerol that was released could be recovered by extracting the caryopses with water. The moist oat bioreactor also was capable of catalyzing transesterification and interesterification reactions.