Influence of impurities in raw material on sensory and physicochemical properties of cold-pressed rapeseedoil produced from conventionally and ecologically grown seeds.

BACKGROUND

The main problem of cold-pressed technology is its low yield and the varying quality of the end product, which is dependent on the quality of the raw material, technological process applied and also on conditions of packaging and storage. The effects of different contents of impurities in rapeseed on the sensory, physicochemical properties and oxidative stability of rapeseed oil produced by cold-pressing were investigated.

METHODS

Cold-pressed oil produced from conventionally grown rapeseeds (individual cultivars and industrial seeds) and certified ecological rapeseeds. Quantified quality parameters included the following: the content of impurities, acid value, peroxide value, spectrophotometric indices (K232, K268), oxidative stability determined by the Rancimat test, pheophytin a content, and sensory assessment.

RESULTS

The seeds which were homogenous in terms of cultivar contained the lowest level of impurities (up to 1.3%) and differed significantly in this regard from ecological and industrial seeds. It was found that the presence of impurities exerts an adverse effect on the sensory and physicochemical characteristics of the oil. Impurity content exceeding 5% resulted in the appearance of off -flavours, such as woody, strawy and fusty/musty. Furthermore, a positive correlation was found between impurity content and acid value (r = 0.781), peroxide value (r = 0.656), anisidine value (r = 0.645), K232 (r = 0.625), while in the case of oxidative stability, no such correlation was observed.

CONCLUSIONS

The type and percentage of seed impurities in the rape crop determines the sensory and physicochemical properties of the cold-pressed oil. It seems advisable, therefore, to minimize the amount of impurities, in order to obtain high-quality cold-pressed rapeseed oil.