| Carya is an important tree nuts resources, there are 5 species distributed in China: Carya tonkinensis H. Lec., C. kweichowensis Kuang et AM Lu, C. hunanensis Cheng et RH Chang, C. dabieshanensis MC Lin et ZJ Li, C. cathayensis Sargent; C. illinoensis K. Koch. is the introduced cultivated species. The 5 kinds distributed in our country can be edible and extracted oil. The qualities of Zhejiang Hickory and pecan, which high economic valuable are especially good, and researches of pecan are more comprehensive both at home and abroad. Although Zhejiang Hickory is regarded as food in China for a long time, other aspect researches are still in initial stage. With growth of worldwide population, reduction of arable land, shorage of food and global oil, the research and utilization about pecan which is called "oil depots on tree" are urgent.In this study, We extracted Zhejiang Hickory oil by water substitution and heat squeeze from raw materials, optimized conditions of aqueous extraction, and examined economic traits of Zhejiang Hickory and conventional indexes of oil extracted by the two methods above. Analysised Volatile components of oil samples by SPME-GC and SPME-GC-MS, and studied the main components which impact the rich aroma of C. cathayensis Sarg. Oil. A preliminary study has been done on fatty acids by GC. Compared the physical and chemical indicators, aromatic components and fatty acids of two oil samples, and discussed the internal relations between oil extraction technology and quality.Experimental details and the basic conclusions of this paper are as follows:1. Under the basic conditions:baking temperature 150℃, baking time 20 min, ratio of solid to liquid 1:1, keep other conditions unchanging, process single factor experiments by changing the three basic conditions above respectively. Obtain the optimum aqueous extraction method conditions:baking temperature 150℃, baking time 25 min, ratio of water to liquid 1:1.2, and Zhejiang Hickory oil yield rate could reach 80%.2.Experimentize on 1000-grain weight, kernel rate, oil content, water content and other economic traits of Zhejiang hickory, compare the physical and chemical indexes of the oil extracted by water substitution and heat squeeze, contrast with national standard physical and chemical index of vegetable oil and find both extracted oil included in good quality oil system. And contrast physical and chemical index of nut oil, Zhejiang hickory oil is a high quality edible nut oil.3. With ethylacetate as internal standard, apply SPME and GC to the oil aroma components for rapid qualitative and quantitative analysis, and show the aroma components including ethylacetate, benzaldehyde,1-heptanol, octanal, nonanol, butylacetate,1-hexanol, butanol, octanol, nonanal. In addition, evaluat the reliability of the method and standard curves of 10 types standard substance showed good linearity, R2 in 0.981～0.999. The standard detection limit is 0.14 ng/g～225 ng/g, the recovery of standard addition is 85.5%～103.0%, average 97.09%. In seven consecutive experiments, the RSD range of measured 10 kinds standard is 1.04%～4.72%, and RSD<5.00%, so the method has good maneuverability. Analysis the two oil samples by GC and GC-MS, the ingredients are different except nonanal. The big difference results from the different batch hot pressed Carya which fruit maturity, quality and processed conditions are different. The oil is placed a short time at low temperature before detected by GC, and volatile oil components possibly change. Therefore the preliminarily determined aroma components of Zhejiang hickory oil are: Nonanal, Hexanal, Heptanal, (E)-2-Heptenal, (E, E)-2,4-Decadienal,2-Undecenal, 1-Octanol,β-Pinene, 1-ethyl-5-methylcyclopentene,4-methyl-2-Hexanone, N-octanol, Octanal, Ethylacetate, Butylacetate, etc.4. Detect fatty acid composition of oil samples by GC.10 and 12 kinds of fatty acids were detected from the two oil samples, and proportion of unsaturated fatty acid content is 92.54% and 92.46% respectively, more than world famous olive oil 86.68%. Most are oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3). Saturated fatty acids are 7.46% and 7.54% respectively, mainly palmitic acid (C16:0). Content of more than 20 carbon fatty acids are less. Consider content of linoleic acid and linolenic acid in Zhejiang Hickory Oil, the water substitution method is better than heat squeeze, but the oil extracted by both methods are very healthy edible oil.This study shows that Zhejiang Hickory is a good quality edible nuts, and water substitution method is better for oil extraction, because it is safe, low-carbon, environmental protection, and retains good aroma and nutritional value of nut oil. HS-SPME combined with GC/MS technology can be used to analyse Zhejiang Hickory oil aroma components. Characteristic aroma of hickory oil is a combination of some volatilematters, there are some connections among the volatile composition, oil quality, oil fatty acids and manufacturing process. |
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