The effect of roasting on the oxidation stability of vegetable oils

Wednesday, April 20, 2016

Authors: László Somogyi, Anita Soós, Orsolya Visy, Orsolya Volent

1. Summary

In our work, we were looking to answer the question whether the oxidation stability of apricot kernel oil and walnut oil obtained by pressing changes due to roasting. It is well known that the organoleptic properties of vegetable oils can be favorably influenced by the roasting of the seeds before pressing. Our results support the fact that the oxidation status of the oil obtained changes due to processes that take place during roasting. Our results also showed that the extent of the changes due to roasting depended very much on the starting material, in fact, in certain cases, opposite effects were observed. For example, the oxidation stability of apricot kernel oil, which is more resistant to oxidation to begin with and is rich in oleic acid, was increased by roasting, while the oxidation stability of walnut oil, rich in polyunsaturated fatty acids, was adversely affected by roasting.
As a result of the measurements it can be stated that the oxidation stability of vegetable oils is fundamentally determined by their fatty acid compositions, and roasting can increase the resistance to oxidation of those oils that are already stable to begin with.

2. Introduction

One of the important factors of vegetable oil quality is their tendency to become rancid. Resistance to oxidation is based on the combined effect of several factors. The oxidation tendency of oils is fundamentally influenced by the fatty acid composition and, in addition, the presence of substances with antioxidant effects is also important. It is so, because they can positively affect resistance to oxidation. Some of the antioxidant substances are natural components of vegetable oils, such as tocopherols, certain phenolic compounds, including oleuropein, hydroxytyrosol in olive oil, gamma-oryzanol in rice bran oil and sesamin in sesame oil. In addition, antioxidant compounds can also form during processing, for example, due to the preliminary roasting of oilseeds.
It was determined by Durmaz and his research group [1] that the extraction yield of naturally occurring antioxidants is generally improved by roasting processes, and according to Mohos [2], roasting is a heat transfer process, during which plant seeds are heated, with agitation, to temperatures over 100 °C. The purpose of roasting, on the one hand, is to improve the organoleptic properties of the seeds by producing flavor and aroma substances, and also to remove the possibly present volatile acids with unpleasant sensory effects.

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