Dielectric Pretreatment of Rapeseed 1: Influence on the Drying Characteristics of the Seeds and Physico-chemical Properties of Cold-Pressed Oil
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The aim of this study was to explore the effect of dielectric pretreatments on the drying characteristics of rapeseeds and physico-chemical attributes of cold-pressed rapeseed oil. Rapeseeds were adjusted to moisture contents of 15% and underwent dielectric pretreatments prior to oil extraction by cold pressing at frequencies of 27, 915, and 2450 MHz for 45, 30, and 22 min, respectively. Results showed that 2450 MHz dielectric heating had the highest temperature rising rate but the most nonuniform temperature distribution. Compared to the control samples, oil extraction yields were increased by 12.28, 17.25, and 22.08% for 27, 915, and 2450 MHz dielectric pretreatments, respectively. The SEM analysis indicated that the cell structures of pretreated rapeseed samples were severely damaged, thereby improving the extraction efficiency. Additionally, dielectric pretreatments significantly increased the total tocopherol content and improved the oxidative stability of cold-pressed oil (p < 0.05). The oil extracted from the 27-MHz pretreated rapeseeds exhibited lower acid and peroxide values and less color change, indicating better quality is achieved. Regarding fatty acid (FA) composition of the oils, oleic acid slightly increased and docosenoic acid decreased, but the total FA composition was not altered significantly by dielectric pretreatments (p > 0.05). These results suggested that dielectric pretreatment, a promising and environment-friendly technique, could be useful in the food industry for oil extraction.
KeywordsDielectric Radio frequency Microwave Oxidative stability Tocopherol
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