Study On Carya Cathayensis Sarg. Oil: Extraction And Its Oxidative Stability

Zhejiang hickory (Caiya cathayensis Sarg.) is a special and famous kind of nut and woody oil crop in China which is mainly located around the Tianmu mountain, at the junction of Zhejiang and Anhui province. This paper respectively adopted cold pressing technology, supercritical CO2 extraction technology and n-hexane solvent extraction technology to extract hickory oil from the kernal of Zhejiang hickory. Physical and chemical methods were applied to analyse the physicochemical indexes of hickory oil. GC method was used to determine the composition and relative content of fatty acids in hickory oil. Tocopherol components and content in hickory oil was analysed with HPLC method. Rancimat mehod was applied to analyse the oxidative stability of hickory oil and the antioxidative effect of TBHQ, AP, rosemary extract, dl-a-tocopherol and tea polyphenol on cold-pressed hickory oil. The results were as followed:(1) Acid values of cold-pressed hickory oil, supercritical CO2 extracted hickory oil and n-hexane extracted hickory oil were 1.96mgKOH/g,2.29mgKOH/g and 2.05mgKOH/g respectively, peroxide values were 2.24mmol/kg,1.12mmol/kg and 0.37mmol/kg respectively, and iodine values were 102.84gI2/100g,101.18gI2/100g and 100.21 gI2/100g respectively. Acid values and peroxide values both meeted the national standard. Because of the high content of moisture and volatile matter in supercritical CO2 extracted hickory oil and n-hexane extracted hickory oil, they required further refining. The moisture and volatile matter conent of cold-pressed hickory oil was 0.14% which was low enough to meet the standard of edible oil.(2) The main fatty acid components in hickory oil extracted by the three extraction methods were similar.They were mainly composed of unsaturated fatty acids, whose relative content was from 90.32% to 92.66%. The unsaturated fatty acids include oleic acid, linoleic acid and a-linolenic acid, the one of which with the highest relative content was oleic acid, followed by linoleic acid. The oil with the highest relative content of unsaturated fatty acid as well as oleic acid was supercritical CO2 extracted hickory oil, followed by cold-pressed hickory oil. As for the relative content of linoleic acid, cold-pressed hickory oil was slightly higher than supercritical CO2 extracted hickory oil. The saturated fatty acids in hickory oil extracted by the three extraction methods were mainly composed of palmitic acid and stearic acid.(3) The main tocopherol in hickory oil extracted by the three extraction methods wasα-tocopherol, followed byδ-tocopherol, andβ-tocopherol content was the lowest; the total content of tocopherol in the n-hexane extracted hickory oil> that in the cold-pressed hickory oil> that in the supercritical CO2 extracted hickory oil; n-hexane extracted hickory oil had the highest content of a-tocopherol, while supercritical CO2 extracted hickory oil had the lowest content.(4) The oxidative stability of hickory oil extracted by the three extraction methods was quite different, n-hexane extracted hickory oil> cold-pressed hickory oil> supercritical CO2 extracted hickory oil, which may be associated with the fact that different antioxidative substances were extracted by different methods.(5) Different antioxidants had different antioxidative effects on the oxidative stability of hickory oil. The antioxidant with the best antioxidative activity was TBHQ, followed by rosemary extract and tea polyphenol when added at the same amount.200mg/kg TBHQ had a significant antioxidative activity which could prolong the induction period of cold-pressed hickory oil at 120℃by 2.72 times compared with that without antioxidant. "100mg/kg TBHQ plus 200mg/kg rosemary extract" had a good synergistic effect as well as "100mg/kg AP plus 200mg/kg rosemary extract", whose synergistic percentage was 21.59% and 42.05% respectively. The combined antioxidant "100mg/kg TBHQ plus 200mg/kg rosemary extract" had a significant antioxidative activity which could prolong the induction period of cold-pressed hickory oil at 120℃by 2.88 times compared with that without antioxidant.