FOOD. Science. Technology. Quality

Food. SCIENCE. Technology. Quality

Food. Science. TECHNOLOGY. Quality

Food. Science. Technology. QUALITY

Authors

AGNIESZKA RĘKAS, KATARZYNA WIŚNIEWSKA,MAŁGORZATA WRONIAK

Title

Effect of microwave heat treatment of rapeseeds on oil yield and quality of pressed oil

Abstract

The objective of the research study was to determine the effect of thermal pre-treatment of rapeseeds with the use of microwave radiation on the oil extraction yield, physical-chemical properties, and sensory characteristics of the virgin oil obtained. The ‘Kana’ and ‘Bakara’ winter rape cultivars were moisturised to a moisture content levels of 6.5 and 8.5 %; next, they were treated in a microwave oven (800 W, 2450 MHz) for 3 and 7 min.; then, the oil was pressed using a Farmer 10 screw press. The oils produced were assessed in terms of: degree of hydrolysis (LA), primary (PV) and secondary oxidation state (AnV), level of dienes and trienes, oxidative stability (Rancimat test) at a temperature of 130 °C, and contents of chlorophyll and carotenoid pigments. Also, the effect of microwave thermal treatment was analyzed on the flavour and aroma of the virgin oils obtained (profile method); moreover, the level of consumer acceptance of oils was assessed. It was shown that the microwave heat treatment of rapeseeds, after they were moisturized, contributed to the increase in the oil extraction yield compared to the control sample. The highest increase in the yield of pressed oil was found in oils produced from seeds with a moisture content level of 8.5 %, which were heated for a shorter time (3 min.). In the case of the seeds of ‘Bakara’ cultivar, the oil extraction yield was 19% higher and of the seeds of the ‘Kana’ cultivar: 16 % higher. Of the oils produced from the heated seeds, the above named oils were characterized by the highest level of consumer acceptance (‚Bakara’: 5.4 a.u., ‚Kana’: 5.5 a.u.). Furthermore, there were reported the decrease in the physical-chemical properties of those oils and the concurrent increase in the oxidative stability (Rancimat test) (as for ‘Bakara’: from 1.8 to 5.7 h; as for ‘Kana’: from 2.3 to 5.1 h). Heating the seeds with a lower moisture content (6.5 %) for a longer time (7 min.) most strongly contributed to the increase in the oil extraction yield, to the decrease in the level of consumer acceptance, and to the reduction in physical-chemical quality of oils.

Keywords

rapeseeds, microwave thermal pre-treatment, pressing, rapeseed oil, physical-chemical properties, sensory quality

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