| Rape is the oil crop with the largest planting area and the widest distribution in China.It is mainly divided into oil type,vegetable type and oil and vegetable dual-use type.Vegetable rape moss has tender stems and leaves,large quantity,high water content,short fresh eating time and difficult storage.Therefore,improving the processing and utilization rate is an important goal for the development of this industry.In this paper,fresh rape moss was used as raw material to study the effect of different fermentation conditions(raw material moisture content,salt addition,fermentation time,fermentation temperature)on the quality of fermented rape moss and its antioxidant capacity,in order to provide a theory for the development of fermented rape moss products.The main research contents and conclusions of this paper are as follows:1.Effects of different fermentation conditions on physical and chemical quality of rape mossThe Physicochemical Quality(protein,soluble sugar,nitrite,flavone,total phenol and fat)of fresh rape moss was determined under different fermentation conditions(raw material moisture content,salt addition,fermentation time and fermentation temperature).The results showed that: the variation range of protein content in rape moss was from 25.69 % to34.25 %.Compared with fresh rape moss,the protein content in fermented rape moss showed a downward trend.The fat content varied from 2.3 g/100 g to 3.93 g/100 g,which was significantly different from that of fresh rape moss.Compared with the influence of raw material moisture content and salt addition on nitrite content,the influence of fermentation time and fermentation temperature is more significant.The nitrite content is significantly reduced and lower than the national limit standard ≤ 20 mg/kg.The variation range of soluble sugar content was 0.87-1.44 g/100 g,and the variation trend was inconsistent.The flavonoid content showed significant differences under the fermentation conditions of different water content of raw materials.When the water content of raw materials was 70 %,the flavonoid content reached the peak of 19.79 mg/g,which was significantly higher than that of fresh rape moss by 18.40 mg/g.The total phenol content varies greatly,and the overall variation range is 2.46-4.7 mg/g,compared with fresh rape moss(2.45 mg/g),the total phenol content in fermented rape moss is increased in varying degrees.2.Effects of different fermentation conditions on flavor substances of rape mossThe volatile flavor components of rape moss under different fermentation conditions were determined by headspace solid-phase microextraction and gas chromatography-mass spectrometry(HS-SPME-GC-MS).The changes of volatile flavor components were studied.The main flavor components of fermentation were determined by relative odor activity value,and the characteristic flavor substances in fermented rape moss were analyzed.The results are as follows:The flavor substances of fermented rape moss were identified and analyzed by GC-MS.A total of 324 volatile flavor substances were detected,including 33 aldehydes,35 ketones,39 alcohols,74 esters,20 acids,39 alkanes,9 nitriles,44 heterocycles and 31 others.183,138,183 and 135 volatile flavor compounds were detected under different fermentation conditions(raw material moisture content,salt addition,fermentation time and fermentation temperature).Through the analysis of roav value of rape moss under different fermentation conditions,the results showed that: under the conditions of different raw material moisture,the main flavor substances were mainly extracted into three principal components,and the cumulative variance contribution rate was 92.393 %.Ethyl decanoate determines the size of the first principal component,lauric acid determines the size of the second principal component,and beta violone determines the size of the third principal component.The cumulative contribution of 894 principal components under different fermentation conditions was 90 %.Ethyl decanoate determines the size of the first principal component;The size of the second principal component is mainly determined by 1-octene-3-alcohol;2-vinylpyrazine determines the size of the third component.Under the conditions of different fermentation time,the main flavor substances were mainly extracted into three principal components,and the contribution rate of cumulative variance was 87.525 %.Dimethyl trisulfide,ethyl palmitate and leaf alcohol determine the size of the first,second and third principal components respectively.Under different fermentation temperatures,the main flavor substances were mainly extracted as two main components.The first principal component is mainly ethyl palmitate and ethyl linoleic acid,and the second principal component is mainly isovaleric acid.The cumulative variance contribution rate is 88.765 %.3.Effects of different fermentation conditions on antioxidant capacity of rape mossThe changes of antioxidant capacity of rape moss under different fermentation conditions were evaluated by DPPH radical scavenging capacity,ABTS radical scavenging capacity,hydroxyl radical scavenging capacity and total antioxidant capacity.The results showed that: fermented rape moss had strong antioxidant capacity and scavenging effect on free radicals.In the range of experimental concentration,with the increase of sample mass concentration,the free radical scavenging rate showed a rising trend,with an obvious doseresponse relationship.(1)When the water content of raw materials was different,the free radical scavenging capacity of fermented rape moss increased with the decrease of water content.Among the DPPH free radical scavenging capacity of fermented rape moss,the water content of raw materials is the strongest at 60%,and the highest scavenging rate is equivalent to the scavenging rate of 52.6 μg trolox.The free radical scavenging rate of ABTS increased with the increase of sample mass concentration.When the concentration was 10 mg/ml,the scavenging rates of samples reached 88.6 %,90.6 % and 89.13 % respectively,which was slightly higher than 88.44 % of fresh rape moss.The hydroxyl radical scavenging capacity increases with mass concentration,and the maximum water content of raw materials is 60%,which is equivalent to 262.79 μg Vc scavenging rate.The reduction ability of FRAP iron ions increases with the decrease of water content of raw materials,and the water content of raw materials is the strongest at 60 %.In conclusion,when the moisture content of fermentation raw materials is 60 %,the antioxidant effect of rape moss is the strongest.(2)With the increase of salt addition,the free radical scavenging ability of fermented rape moss increased first and then decreased.There was no significant difference in radical scavenging ability between DPPH and ABTS.The scavenging ability of hydroxyl radical increased with the increase of mass concentration.When the concentration is 60 mg/ml,the hydroxyl radical scavenging rates of fermented rape moss under different salt additions can reach 80.36 %(salt addition 6 %),85.94 %(salt addition 7 %)and 89.96 %(salt addition8 %)respectively,of which the scavenging rate of 8% salt addition is equivalent to 240.18μg Vc.There is also no linear relationship between FRAP iron ion reduction ability and salt addition.When the salt addition is 7 % and the concentration is 80 mg/ml,the reduction ability of FRAP iron ion is the same as that of fresh rape moss K.In conclusion,the antioxidant capacity of rape moss was the strongest when the amount of fermented salt was7 %.(3)When the fermentation time was different,the free radical scavenging ability of fermented rape moss first increased and then decreased with the extension of fermentation time.With the extension of time,the scavenging capacity of DPPH free radical first increased and then decreased.On the 7th day of fermentation,the free scavenging rate was close to that of fresh rape moss,which was equivalent to the scavenging rate of 50 μg Trolox.The scavenging rate of ABTS radical increased with the increase of mass concentration,which was equivalent to the scavenging rate of 4.89 μg Vc on the fifth day of fermentation.When the concentration was 10 mg/ml-42 mg/ml,the hydroxyl radical scavenging rate of fermented rape moss increased with the concentration;When the concentration is greater than 25 mg/ml,the growth rate of clearance rate is relatively gentle,and the maximum clearance rate on the 7th day of fermentation is 93.47 %,which is the same as that of fresh rape moss,equivalent to the clearance rate of 249.39 μg Vc.In conclusion,the antioxidant capacity of rape moss was the strongest on the 7th day of fermentation.(4)When the fermentation temperature was different,the antioxidant capacity of fermented rape moss decreased first and then increased with the increase of fermentation temperature.Compared with the fermentation temperature of 20 ℃ and 25 ℃,the DPPH radical scavenging ability was the strongest at 15 ℃;The free radical scavenging rate of ABTS reached 89.63 %,equivalent to the scavenging rate of 5.12 μg Vc;The scavenging rate of hydroxyl radical is 95.77 %,which is equivalent to the scavenging rate of 255.45 μg Vc.Among them,FRAP has the strongest iron ion reduction ability,which is significantly higher than that of fresh rape moss. |
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