Study On Quality Characteristics Analysis Of Olive Oil During Extraction And Storage

Olive oil is rich in oleic acid,squalene,and other nutrients,which have high nutritional value and health benefits.In recent years,China’s olive industry has been rapidly developing,the domestic production of olive oil has been increasing year by year.The quality and nutritional value of olive oil are closely related to the olive fruit quality,the extraction and storage of olive oil.At present,the effects of olive fruit short-term storage,oil extraction process,and the introduced pulsed electric field(PEF)technology on the micronutrients and volatile flavor compounds of olive oil are still unclear in China.Furthermore,there are few studies on the storage characteristics of crude olive oil obtained by centrifugation and the filtered oil obtained by filtration.In this paper,olive fruits obtained from Longnan,Gansu Province were taken as the research object,and the olive fruit storage,the extraction and storage of olive oil were studied,the changes of fatty acids,lipid concomitants,and volatile compounds were analyzed to identify the influence of raw materials,extraction and storage on the olive oil quality.The main conclusions are as follows:(1)The olive fruits were stored at room temperature(23±2℃),refrigerated(4℃)and frozen(-20℃)for 7 days before virgin olive oil(VOO)extraction.The fatty acids,minor components,and volatile compounds were determined to study the effects of olive fruit short-term storage on the VOO quality.The results showed that the oil yield of fruits stored at-20℃(about 10%)was lower than that stored at room temperature and 4℃(both>13%).The content of chlorophyll(3.15 ～ 3.16 mg/kg),carotenoid(3.35 ～ 3.47 mg/kg)and total phenols(345.20 ～ 347.38 mg GAE/kg)in the oil samples from the fruits stored at 4℃ were significantly higher than that of the other two treatments(p<0.05),while the loss of these substances was the most severe in the oil samples obtained from frozen fruits.There were obvious undesirable “fermented and musty” flavors detected from oil samples from fruits stored at room temperature.4℃ was the suitable temperature for the short-term storage of olive fruits,which retains the maximum amount of pigments,α-tocopherol,and total phenols of olive oil.(2)The changes in pigments,antioxidant capacity,and lipid concomitants of olive oils obtained from the traditional and PEF processing(crushing,malaxation,centrifugation,standing and filtration)were analyzed,and the the impact of PEF technology on the olive oil quality was also studied.The results showed that the pigments,total phenols,andα-tocopherol content increased significantly during the malaxation steps(p<0.05),which were then decreased during the subsequent centrifugation,standing,and filtration steps.The oil samples from the crushing and malaxation process had a high content of volatile alcohols and the samples from the centrifugation,standing and filtration process had a high content of aldehydes.The total phenols and antioxidant activity of samples increased significantly(p<0.05)after treatment with PEF technology,and the technology had little effect on fatty acids,phytosterols and squalene of oil samples.(3)The crude and filtered olive oils obtained by traditional and PEF processing were subjected to accelerated storage at 60℃.The changes of peroxide value,acid value,and fatty acids of samples during different oxidation times were studied,the storage characteristic of crude and filtered olive oils were studied.The results showed that the oxidation rate of filtered oils was higher than that of the crude oils.The saturated fatty acid(SFA)increased while the unsaturated fatty acids(UFA)decreased slightly in each oil sample.The degradation rate of total phenols in the crude oils(38.22% ～ 40.79%)was lower than that in the filtered oils(44.22% ～ 48.97%).The degradation rate of α-tocopherol was the fastest during the accelerated storage,while squalene and phytosterols decreased slightly,the contents of these minor components in crude and filtered oils had little difference.(4)The volatile oxidation products of crude and filtered oils obtained from traditional and PEF processing were determined by HS-SPME/GC-MS,and the volatile oxidation marker was identified to characterize the degree of olive oil oxidation.The results showed that a total of 30 volatile compounds were identified during accelerated oxidation,the flavor compounds hexanol,E-2-hexenal,E-2-hexen-1-ol,E-3-hexen-1-ol,1-penten-3-one and3-pentenone of each oil sample decreased gradually during oxidation,and the total loss rate in the filtered oils(23.98% ～ 42.45%)was higher than that in the crude oils(15.19% ～23.80%).With the exception of the above-mentioned substances,the content of other volatile oxidation products increased,with the total accumulation of aldehydes>carboxylic acids>ketones> alcohols >heterocycles,and the total accumulation of oxidation products in filtered oils was higher than that in crude oils.However,the accumulation of3-methyl-butan-1-ol,6-methyl-5-hepten-2-one,and octan-2-one in crude oils was relatively high,resulting in the “musty,muddy sediment” odor.E-2-pentenal,hexanal,nonanal and E-2-heptenal are compounds closely related to the olive oil oxidation.As E-2-heptenal was formed during oxidation,which could be used as a marker of olive oil oxidation.