The Effect Of Storage Time On The Content Of Bioactive Compounds And Oxidative Stability Of Cold-pressed Plant Oils

Cold-pressed plant oil is produced with the mechanical of pressing or expelling oil from seeds,fruits,germs of plants usually at temperature below 60℃.Compared with the method of refined-oil or normal pressed oi,low temperature press can avoid contacting with acid,alkaline,solvents and other harmful substances,as well as destruction of bioactive compounds by high temperature,it preserves lipid-soluble nutrients in the oil to the uttermost.In recent decades,people’s pursuit of health is improved with the increase of consumption level,cold-pressed oil has become more and more popular because of its advantages of good color,nature of its natural scent and rich nutrient valueCompared with western world’s markets,the cold-pressed plant oil industry is still in early step in China.At present,there are a few studies on the active compounds(phytosterols,tocopherols,etc.)of various cold-pressed plant oils.The quality of cold-pressed plant oils is degraded,it changes undesirably because of oxidation and rancidity during storage period,which affects the shelf life and causes health problems after consumption.Therefore,the aim of this study was to determine the quality of cold-pressed plant oils available in the market and the shelf life,also to discuss the use of cold-pressed vegetable oils as functional foods.By Schaal oven test,sixteen cold-pressed plant oils were subjected to analysis immediately and after purchase and after six and twelve days of storage at 60 °C,the acid value,peroxide value,fatty acid composition,sterols and tocopherols content were measured in the fresh and stored oils.Oxidative stability was also measured in the fresh oils.All the data collected in the above experiments indicated the following results after analysis:(1)Among 16 cold-pressed plant oils,the oxidation stability varies greatly and the induction time varies from 0.2h to 14 h.The saturated fatty acid concentration ranged from 5.2% to 28.9%.The unsaturated fatty acid content ranged from 8.8% to 83.4%.The polyunsaturated fatty acid content is between 1.8% and 80.7%.The tocopherol content is between 155mg/100 g and 1.4mg/100 g.The sterol content is 8.6 mg/g-0.11 mg/g.(2)After storing at 60°C for 6 days and 12 days,the peroxide value increased significant except the black cumin cold-pressed seed oil.The acid value and fatty acids compounds of the sixteen cold-pressed plant oil samples didn’t show significant change.However,phytosterols and tocopherol content both decreased.(3)By comparative of cold-pressed wheat germ oil and cold-pressed avocado fruit oil,coldpressed avocado fruit oil has higher phytosterol content than cold-pressed wheat germ oil,but the nutrition indices are lower than cold-pressed wheat germ oil.From this analysis,it is concluded that the incidence of cardiovascular disease is independent of any single attribute of consumption of cold-pressed vegetable oils.(4)Principal component analysis(PCA)and cluster analysis(CA)of all factors showed that the oils could be divided into two groups.The first contained cold-pressed argan oil,cold-pressed pine oil,cold-pressed apricot kernel oil,cold-pressed avocado fruit oil,and cold-pressed macadamia nut oil,which had high levels of saturated and monounsaturated fatty acids and low amount of sterols and tocopherols.These plant oils are relatively stable during storage and have a shelf life of up to 12 months.The second group included the oils from cold-pressed dill seed oil,cold-pressed milk thistle seed oil,cold-pressed parsley seed oil,cold-pressed watermelon seed oil,cold-pressed safflower oil,cold-pressed poppy seed oil,cold-pressed black cumin seed oil,coldpressed hemp oil,cold-pressed blackcurrant seed oil,cold-pressed borage oil,and cold-pressed wheat germ oil.The highest content of tocopherols and phytosterols were observed in coldpressed wheat germ oil and cold-pressed blackcurrant seed oil,and the lowest in cold-pressed black cumin oil and cold-pressed dill seed oil.Cold-pressed black cumin seed oil had the greatest oxidative stability.The oxidative stability of the tested cold-pressed oils depended mostly on their fatty acid composition and tocopherol levels.