Study On Storage Stability And Oxidation Patterns Of Walnut Oil And Almond Oil Blends

The nutritional components of edible oil include fatty acids and micronutrients.Micronutrients include tocopherols,phytosterols and squalene.Blended oil is made from several refined vegetable oil in a specific ratio.It can provide a reasonable ratio of fatty acids and micronutrient content to meet consumer nutrition and quality needs.However,the oxidation of the blended oil not only reduces the amount of nutrients,but also produces harmful substances.At present,the understanding of blended oil is not deep enough,and the oxidation rules of fatty acids and micronutrients in blended oil are not fully understood.In this study,5%,10%,20%,and 30%almond oil were separately added to walnut oil to make the blended oil.The basic physicochemical indexes,micronutrient content and fatty acid composition of walnut oil,almond oil and blended oil with different proportions were determined.We used oven accelerated oxidation experiments to study the changes of fatty acids and micronutrients in blended oil at different storage times.And we used oven accelerated oxidation experiments to explore the correlation and change rules of micronutrients in blended oil with antioxidant capacity and oxidation products.This provides a scientific basis for comprehensive evaluation of the quality and oxidation law of the blended oil.The following is the research content and main conclusions of this thesis:(1)The blended oil was obtained by mixing walnut oil and almond oil in the ratios of 95:5,90:10,80:20 and 70:30.The peroxide value and acid value were measured to determine the freshness of the oil sample.The composition and content of fatty acids,tocopherols,phytosterols and squalene were measured by gas chromatography-mass spectrometry and high-performance liquid chromatography.The results showed that walnut oil,almond oil and blended oil all met national edible vegetable oil standards.The sample had a peroxide value of less than 10 meq/kg and an acid value of less than3 mg KOH/g.The fatty acid composition and content of walnut oil were 59.45±0.04%of linoleic acid,19.71±0.03%of oleic acid and 10.37±0.01%of linolenic acid.The fatty acids of almond oil with an oleic acid content of 60%the above.With the increase of almond oil content in the blended oil,the content of polyunsaturated fatty acids decreased,and the n-6/n-3 fatty acids were very close to the Chinese dietary nutrient intake standards.The total tocopherol content in the six oil samples ranged from 126.23 to 236.86 mg/kg.Among them,?-tocopherol and?-tocopherol accounted for a relatively high proportion.The phytosterol content in the oil samples were between 1795.27 and 3120.04 mg/kg.The phytosterol content in the almond oil was higher than that in walnut oil.The phytosterol content in the blended oil also increased with the increase in the proportion of almond oil.The content of squalene in the blended oil were relatively small,ranging from 12.27 to 15.69 mg/kg.(2)The walnut oil,almond oil and blended oil were placed in an oven at 60°C for accelerated oxidation experiments.The fatty acid and micronutrients contents(tocopherol,phytosterol and squalene)of the oil samples were measured every 4 days.The results showed that there were no significant difference in fatty acid composition and content of each sample.The content of saturated fatty acids,monounsaturated fatty acids and the ratio of n-6/n-3 fatty acids in oil samples increased slightly with the increase of oxidation time.The content of polyunsaturated fatty acids and the ratio of polyunsaturated fatty acids to saturated fatty acids decreased slightly with the extension of the oxidation time.During this period,each tocopherol content decreased.Different types of tocopherols had different degrees of loss,and their oxidation rates were in order:?-tocopherol>?-tocopherol>?-tocopherol.The phytosterol content in oil samples decreased with the increase of oxidation time.The order of sterols were:rapeseed sterol>stigmasterol>campesterol>?-sitosterol.During the storage,squalene slowed down first and then quickly,and the overall change were not obvious.(3)The walnut oil,almond oil and blended oil were placed in an oven at 60°C for accelerated oxidation experiments.The antioxidant capacity(DPPH free radical scavenging rate,ABTS~+free radical scavenging rate and oxygen absorption capacity)of the oil samples were measured every 4 days.The results showed that the oil samples had the lowest DPPH free radical scavenging ability,and theirs ABTS~+free radical scavenging ability were slightly higher than the DPPH free radical scavenging ability.In addition,the oil sample's oxygen absorption capacity could reach more than10 times the DPPH free radical scavenging capacity.During the 24-day accelerated oxidation process,the antioxidant capacity of the oil samples gradually weakened with the extension of the oxidation time,and the antioxidant capacity of the blended oil was higher than that of walnut oil.Pearson statistical results showed that there were a certain relationship between the micronutrients in oil samples and their antioxidant capacity.The correlations were:tocopherol>phytosterol>squalene.(4)The walnut oil,almond oil and blended oil were placed in an oven at 60°C for accelerated oxidation experiments.The physicochemical indexes(peroxide value,conjugated diene,acid value,anisidine value and thiobarbituric acid value)of the oil samples were measured every 4 days.The results showed that the oxidation products had an increasing tendency during the oxidation of oil samples,and the rate of primary oxidation products were greater than the rate of secondary oxidation products.Among them,the peroxide value and conjugated diene increased faster,and the acid value,anisidine value and thiobarbituric acid value increased from slow to fast,the acid value,thiobarbituric acid value change little,and the anisidine value changes obviously.Pearson statistical results showed that there were a certain degree of correlation between changes in micronutrients and oxidation products in oil during the accelerated oxidation process,and the correlation order were:tocopherol,phytosterol,squalene.These micronutrients played a significant role in the oxidative stability of the oil.