Studies on Foaming of Mixed Edible Oil with Coconut Oil under Deep-fat Frying

1. 椰子油和棕榈仁油属于月桂油，具有重要的商业价值。这种油的缺点是与其他油炸油（如大豆油）混合在一起，在深度油炸时产生特有的泡沫。本文对月桂油与非月桂油混合油的发泡活性进行了详细的研究。随机酯化后，随着中间碳数三酰甘油的增加，混合油的发泡性能明显下降，而脂肪酸组成保持不变。在单酸三酰甘油混合物的模型系统中发现了类似的酯化作用。讨论了三酰甘油分子大小的差异，而不是脂肪酸组成的差异引起了泡沫的特征。以脂肪酸组成不同的大豆油、棕榈油和椰子油为原料，研究了在高温连续加热过程中，酯化反应对混合油热氧化稳定性的影响。每种油的热变质程度与不饱和程度成正比，混合油和它们的酯化油之间几乎没有差异。然而，酯化油的折射率比其他油增加得更快。推测其快速增长可能是由于易于聚合的三酰甘油分子种类增加所致。

1. Cococut and palm kernel oils belong to the lauric oil and are commercially important. The disadvantages of this type oil are that admixture of the oils with other frying oils, e.g., soybean oil, produces a characteristic foaming under deep fat frying. In the present study, the foaming activity of the mixed oil between lauric and nonlauric oils was investigated in detail.The foaming properties of the mixed oils decreased remarkably after random interesterification, when the intermediate carbon number triacylglycerols increased, while the fatty acid compositions of the oils were remained unchanged. Similar effects of interesterification were found in a model system of mixtures of monoacid triacylglycerols. It was discussed that the characteristic foaming arose from the disparity of triacylglycerol molecular size, but not from that of fatty acid composition.2. The influence of interesterification on the thermal oxidation stability of mixed oils during continuous heating at high temperature was investigated, using soybean, palm and coconut oils whose fatty acid compositions differ each other. The extent of thermal deterioration in each oil increased in proportion to the degree of unsaturation, and nearly no difference between the mixed oils and their interesterified oils. However, the refractive index of the interesterified oil increased more rapid than the others. It was supposed that the rapid increase might be caused by increasing of triacylglycerol molecular species which were easily polymerized.