Study On Composition And Oxidation Stability Of Bama Hemp Seed Oil

Hemp seed oil is a special longevity food in the famous hometown of longevity-Guangxi Bama Yao Autonomous County,and is dubbed "Longevity Oil".In this paper,the composition and oxidative stability of Bama hemp seed oil prepared by cold pressing,hot pressing,Soxhlet extraction and aqueous enzymatic method are studied.The results are as follows:The conditions for the extraction of polyphenols from hemp seed oil and the Folin method for total phenol determination are optimized: detection wavelength765 nm,0.1 M Folin-Ciocaileus reagent 3.5 m L,7.5% sodium carbonate reagent2.5 m L,reagent addition interval 10 min,The dark reaction time is 1h.The Bama hemp seed oil was extracted by cold pressing method,hot pressing method,Soxhlet extraction method and aqueous enzymatic method,and its physical and chemical indexes,fatty acid composition,lipid accompaniments and antioxidant activity were determined.The Schaal oven experiment was carried out to track the changes of various indicators in the accelerated oxidation process:(1)The order of the output rate of the four oil extraction methods is SE>HP>CP>EE,the acid value of hemp seed oil is between 1.60-2.04 mg/g,and the acid value of hot pressed hemp seed oil is(2.04 ±0.10 mg/g)is slightly higher;the peroxide value is generally low(0.028-0.08 g/100g),the peroxide value of hot-pressed hemp seed oil(0.080±0.001 g/100g)and Soxhlet extraction hemp seed oil The oxidation value(0.070±0.002 g/100g)is higher,and the peroxide value measured by cold-pressed hemp seed oil is the lowest,only0.028±0.005g/100 g.Hemp seed oil contains 67.13～67.38% of polyunsaturated fatty acids(PUFA),including linoleic acid(>50%),γ-linolenic acid,α-linolenic acid and stearidonic acid;containing 18.82%～ 20.61% of monounsaturated fatty acids(MUFA),including oleic acid(9-C18:1),palmitoleic acid(C16:1),13-octadecenoic acid(13-C18:1),arachidonic acid(C20:1);containing 10%saturated fatty acids(SFA),including palmitic acid(C16:0),stearic acid(C18:0),arachidic acid(C20:0)and behenic acid(C22:0).(2)The types of oil sterols in hemp seed oil produced by different extraction methods are the same,and the most phytosterols can be dissolved by the aqueous enzymatic method(194.96±6.09 mg/100g).The total sterol content in hemp seed oil follows EE-HSO>CP-HSO >HP-HSO>SE-HSO,the content of sterol types presents the rule of β-sitosterol>campesterol≥cycloartenol>stigmasterol.Soxhlet extract hemp seed oil has the highest squalene content(0.31±0.03 g/100g),heat treatment and petroleum ether help squalene dissolution.The total phenol content of hemp seed oil is in the order: HP-HSO>SE-HSO>CP-HSO>EE-HSO.Hotpressed hemp seed oil has the highest total phenol content(6659.60 μg GAE/m L),and enzyme-extracted hemp seed The total phenol content of oil is relatively low(4257.60±41.61 μg GAE/m L);the flavonoid content of hemp seed oil is in the order of: CP-HSO>EE-HSO>SE-HSO>HP-HSO,The treatment causes a greater loss of flavonoids.The total tocopherol content of hemp seed oil under different oil extraction methods showed the law of HP-HSO>SE-HSO>EE-HSO>CP-HSO,and the total tocopherol content of hemp seed oil was as high as 90.27±3.89 mg/kg,cold pressed hemp seed oil has the lowest tocopherol content(48.81±1.18mg/kg).The(β+γ)-tocopherol in hemp seed oil accounts for 62%～98% of the total tocopherols,while the content of δ-tocopherol in hot-pressed hemp seed oil is significantly higher than that in hemp seed oil obtained by other extraction methods.It was 34.07±1.79 mg/kg.(3)With the extension of the oxidation time,the acid value of hemp seed oil showed a gradual increase as a whole,and the peroxide value showed an exponential increase.On the 20 th day,the heat pressing,Soxhlet extraction,and aqueous enzymatic method The peroxide value of hemp seed oil has exceeded 12g/100 g,and the acid value and peroxide value of hot-pressed hemp seed oil change the most slowly;during the oxidation process,the content of polyunsaturated fatty acids in hot-pressed hemp seed oil slightly increases(67.38%to 75.07%),monounsaturated fatty acids decreased(20.45% to 13.67%);compared with fresh hemp seed oil,the content of saturated fatty acids after oxidation of hemp seed oil extracted by other methods increased,and polyunsaturated fatty acids And the content of monounsaturated fatty acids is reduced.(4)With the extension of oxidation time,hemp seed oil phenols are consumed in a large amount,and the total content of oil-like flavonoids shows a gradual decline.In the later stage of oxidation,the flavonoid content of hotpressed hemp seed oil is significantly lower than other extracted oils.The hemp seed oil obtained by the method was only 3.30±0.04 mg RE/kg;the tocopherol content showed a downward trend,and no tocopherol was detected at the 20 th day of accelerated oxidation;the cold pressed hemp seed oil had the fastest sterol loss The loss rate was 53.32%,and the total sterol loss rate of hemp seed oil extracted by enzyme was 30.48%,while the total sterol content of Soxhlet extracted hemp seed oil and hot pressed hemp seed oil did not change significantly.The loss of squalene in hemp seed oil is high,and the loss rate of squalene in cold pressed hemp seed oil is as high as 90.55%.(5)Comparing the infrared spectra of 0 d and 20 d of accelerated oxidation,on 0 d,the hydroperoxide peak of hemp seed oil under hot pressing and Soxhlet extraction is the highest(A=0.4),which is triggered by heating Primary oxidation of grease.Based on the changes in the spectrum peaks of the functional groups related to oxidation,the hemp seed oil obtained by the hot pressing method exhibits good oxidation stability during accelerated oxidation,followed by the Soxhlet extraction method followed by the hemp seed oil obtained by the cold pressing method.The hemp seed oil obtained by the enzymatic method showed poor oxidation stability during the accelerated oxidation process.(6)There is no significant difference in the scavenging ability of hemp seed oil samples DPPH free radicals under different oil extraction methods,about 0.12μmol Trolox/m L;the free radical scavenging ability of ABTS is between 0.19-0.42 μmol Trolox/m L,and the order of size is CP-HSO>SE-HSO>EE-HSO>HPHSO;FRAP reduction ability is between 0.33-0.43 μmol Trolox/m L,and the order of size is CP-HSO>EE-HSO>SE-HSO>HP-HSO.Partial least squares regression analysis was used to analyze the correlation between hemp seed oil concomitants and antioxidant activity in the accelerated oxidation process: the DPPH free radical scavenging ability of hemp seed oil and total flavonoids,total phenols,squalene,(Β+γ)-tocopherol and δ-tocopherol are significantly positively correlated(r>0.5);hemp seed oil ABTS free radical scavenging ability is correlated with total flavonoids,δ-tocopherol,squalene,(β+γ)-Tocopherols are all significantly positively correlated;Hemp seed oil FRAP reduction ability is significantly positively correlated with total flavonoids,(β+γ)-tocopherol and δ-tocopherol.(7)Through headspace solid-phase microextraction and GC-MS technology,4-methyl-2-pentanol was selected as the internal standard to qualitatively and semi-quantitate the volatile substances in hemp seed oil that accelerates the oxidation process.It is concluded that freshly prepared cold-pressed hemp seed oil contains the most esters,and the total content of esters is 447.97±10.62 μg/L,which can give cold-pressed hemp seed oil a unique fragrance.Hot-pressed hemp seed oil has a richer quantity and content of volatile substances,and is superior to other extraction methods in terms of flavor.Among them,pyrazines are the most abundant,with a content of 2540.46±305.46 μg/L,with roasted aroma,woody aroma and The nutty aroma gives the hot-pressed hemp seed oil a unique mellow aroma.Soxhlet extraction of hemp seed oil contains the most aromatic hydrocarbons and alkanes,which is not conducive to the formation of the fragrance of hemp seed oil.Enzyme-extracted hemp seed oil contains the most alcohols,with a total content of 2434.11±598.13 μg/L.Alcohols have a delicate,fruity and oily aroma,which can give enzyme-extracted hemp seed oil a unique fragrance.During the accelerated oxidation process,171 volatile components were detected in cold pressed hemp seed oil,175 volatile components were detected in hot pressed hemp seed oil,211 volatile components were detected in Soxhlet extraction hemp seed oil,and 161 volatile components were detected in enzymatic extraction hemp seed oil.With the extension of time,ketones,acids and aldehydes in the oil samples increased,while the contents of furans,aromatic hydrocarbons and olefins decreased gradually.