| Cyperus esculentus is a small oilseed that has received a lot of attention in recent years,and its oil yield per unit area is about four times that of soybean.At the same time,the oleic acid content of tiger nut oil is similar to or even higher than that of high oleic peanut oil,making it a high-quality edible oil.The current research on tiger nut oil production is mostly direct pressing method or solvent leaching method,the aroma of the resulting tiger nut oil products is very light,can not reach the high value processing such as rich aroma peanut oil.The key technology for the production of strong aroma edible vegetable oil is to roast the oil first and then press the oil and refine the pressed oil by cooling and filtering,the suitable roasting treatment of the oil makes the oil produce strong aroma,while the moderate refining treatment reduces the loss of oil aroma as much as possible.In recent years,China’s production of rich aroma oil and grease continues to grow,has reached more than 10 % of edible vegetable oil.However,there is a lack of research on the production process conditions and the overall quality of fragrant tiger nut oil.In order to clarify the influence of the production technology of fragrant tiger nut oil,especially the roasting of tiger nuts and the oil refining process on the flavor and overall quality of the product,this paper roasted tiger nuts under different conditions and then pressed them to produce fragrant tiger nut oil,and used SDE-GC-MS technology to detect the volatile flavor components of fragrant tiger nut oil.In this paper,we analyzed the physical and chemical indexes,nutritional composition,risk components,and combined with sensory evaluation to determine the optimal roasting conditions of the concentrated tiger nut oil.In addition,the volatile flavor components and characteristic flavor components of fragrant tiger nut oil and fragrant peanut oil,which are both high in oleic acid,were examined and analyzed in comparison,and the material basis and generation mechanism of the flavor differences between the two oils were clarified in combination with the composition of sugars and amino acids in their raw materials and their changes during the oil preparation process,which provided support for the product development of fragrant tiger nut oil..(1)Study on the effect of roasting conditions on the flavor of concentrated tiger nut oil.Different roasting conditions(roasting temperature of 140,150,160,170 and 180 ℃,roasting time of 15,20,25,30 and 35 min,initial moisture content of 8 %,12 %,16 %,20 % and 24 %)were used to roast the tiger nuts,and then the oil was pressed to produce aroma tiger nut oil.The volatile components were analyzed and the effect of different roasting conditions on the flavor of tiger nut oil was clarified by combining sensory evaluation,odor activity value and PCA principal component analysis.The results showed that roasting temperatures at 150 ℃ and 160 ℃(25 min,moisture 12 %),roasting times at 25 min and 30 min(160 ℃,moisture 12 %),initial moisture at 8 % and 12 %(160 ℃,moisture 12 %),and initial moisture at 8 % and 12 %(160 ℃,moisture 12 %).The amount and concentration of volatile flavor substances were relatively higher at 160 °C and 170 °C(25 min,12 % moisture),25 min and 30 min(160 °C,12 % moisture),and 8 % and 12 % initial moisture(160 °C,25 min).The sensory evaluation scores were relatively high,and the tiger nut oil had a strong aroma and no offflavor under the conditions of 25 min and 30 min(160 ℃,moisture 12 %).The key flavor substances of tiger nut oil produced under different roasting conditions were not very different,and their key flavor substance contributions were all aldehydes,pyrazines and furans in order.According to the OAV,the characteristic flavor substances of fragrant tiger nut oil were 2-pentylfuran,3-ethyl-2,5-dimethylpyrazine,nonanal,2-undecenal,n-hexenal,and trans-2-decenal,and the results of PCA showed that the roasting temperature had the greatest influence on the flavor of fragrant tiger nut oil,followed by the influence of roasting time,and the flavor style of fragrant tiger nut oil produced under different initial moisture conditions The flavour styles of the oil produced under different initial moisture conditions varied greatly.(2)Study on the effect of roasting conditions on the overall quality of fragrant tiger nut oil.Tiger nuts were roasted under different conditions(roasting temperatures of 140,150,160,170 and 180 ℃,roasting times of 15,20,25,30 and 35 min,and initial moisture contents of 8 %,12 %,16 %,20 % and 24 %,respectively),and then pressed to produce fragrant tiger nut oil.The basic physicochemical parameters,nutrients,and risk components were examined to determine the effect of roasting conditions on the overall quality of tiger nut oil.The results showed that the acid value and peroxide value of the fragrant tiger nut oil produced under different roasting conditions met the limits in LS/T 3259-2018 "Tiger nut oil"(acid value ≤ 4 mg/g,peroxide value ≤ 9.85 mmol/kg).A total of eight VE components were detected in the tiger nut oil produced under different roasting conditions,with the highest content of α-tocopherol.The total VE content increased from 198.16 mg/kg to 207.14 mg/kg when the roasting temperature increased from 140 ℃ to 160 ℃,and decreased to 177.82 mg/kg when the roasting temperature continued to increase to 180 ℃.With the increase of initial moisture content,the total vitamin E content was lowest at 24 % moisture content.The changes in roasting temperature,roasting time and initial moisture content had little effect on the fatty acid composition and content of the tiger nut oil samples.With the increase of roasting temperature and roasting time,the overall trend of sterol content increased,and the highest was 230.01 mg/kg at 180 ℃ and 25 min,and the highest was 260.11 mg/kg at 160 ℃ and 35 min,and the overall trend of sterol content decreased with the increase of initial moisture content,and the lowest was 164.58 mg/kg at 160 ℃,25 min and 24 % moisture.Therefore,moderate roasting of tiger nuts could enrich the vitamin E and phytosterol content of tiger nut oil.With the increase of roasting temperature,the total TFA content increased from 0.02 % at 150 ℃,25 min to 0.05 % at 180 ℃,25 min,and with the increase of roasting time,the total TFA content increased from 0.02 % at 160 ℃,15 min to 0.04 % at 160 ℃,35 min,and with the increase of initial moisture content,the total TFA content first decreased and then increased to 0.05 % at 160 ℃,25 min.The total TFA content decreased and then increased with the increase of initial moisture content,and the lowest was 0.02 % at 160 ℃ and 25 min when the moisture content was 12 %;and no 3-chloropropanol ester was detected;the contents of Ba P,PAH4 and PAH16 increased continuously with the increase of baking temperature and time,and the contents of Ba P,PAH4 and PAH16 increased from 1.06 to 1.66 μg/kg and from 2.43 to 3.62 μg/kg,respectively,when the temperature increased from 140 ℃ to 180 ℃.The contents of Ba P,PAH4 and PAH16 increased from 0.89 to 1.62 μg/kg,from 2.21 to 4.10 μg/kg and from 60.13 to 82.41 μg/kg,respectively,when the time was increased from 15 min to 35 min.The contents of Ba P,PAH4 and PAH16 decreased and then increased with the increase of initial moisture content,and the lowest contents were 1.02,3.08 and 67.98 μg/kg at the initial moisture of 16 %,respectively.The changes in physicochemical properties,nutritional quality,risk indicators and flavor sensory of tiger nut oil under different roasting conditions were synthesized,and it was suggested that roasting,cooling,crushing and sieving,and pressing of tiger nut oil under roasting conditions of 160 ℃,25 min,and 12 % moisture could yield tiger nut oil with better overall quality.(3)A study on the comparative quality of fragrant tiger nut oil and fragrant peanut oil,both of which are high in oleic acid.The volatile flavor components in the two oils were analyzed and compared under the optimized process conditions established above,and the relative odor activity values and sensory evaluation were combined to determine the key flavor substances in the two strongly flavored oils and to clarify the material basis and generation mechanism of flavor differences between the two oils.The results showed that the oleic acid content of tiger nut oil and high oleic peanut oil were similar,but the sugar content of tiger nut was significantly higher and the protein content and fat content were significantly lower compared with high oleic peanut kernel,and thus the flavor of the two oils would also have significant differences,so the raw materials of peeled tiger nut and high oleic peanut kernel were roasted at 160 ℃,25 min,12 % moisture and then pressed to produce The total amino acid content of tiger nuts(4.27 g/100g)was significantly lower than that of peanut kernels(38.34 g/100g),but the glucose and fructose contents(1.80 and 1.24 g/100 g,respectively)were significantly higher than that of peanut kernels(0.52 and 0.46 g/100 g,respectively);after roasting,the total amino acid,aspartic acid and glutamic acid contents of tiger nut were significantly higher than that of peanut kernels.After roasting,the contents of lysine,aspartic acid and glutamic acid in tiger nut oil were significantly lower(0.04,0.03 and 0.02 g/100 g,respectively),and the contents of glutamic acid,aspartic acid,tyrosine and phenylalanine in peanut kernels were significantly lower(0.83,0.39,0.31 and 0.31 g/100 g,respectively),presumably the above amino acids and sugars were important precursors of the characteristic flavor The above amino acids and sugars are presumed to be important precursors for the characteristic flavors of the two oils.There were 20 characteristic flavor components with OAV ≥ 1 and the key volatile substances aldehydes > pyrazines in the fragrant tiger nut oil,while 14 characteristic flavor components with OAV ≥ 1 and the key volatile substances pyrazines > aldehydes in the peanut oil,in contrast.A total of 8 odor active substances were identified by GC-O combined with sensory evaluation analysis,and the flavor characteristics of sweet aroma,fruit aroma and nut aroma were more obvious in tiger nut oil,and peanut aroma and almond aroma were more obvious in peanut oil.Total vitamin E in tiger nut oil(219.05 mg/kg)was higher than that in high oleic peanut oil(191.61 mg/kg),phytosterol content(225.08 mg/100g)was higher than that in high oleic peanut oil(152.33 mg/100g),and the monounsaturated fatty acid content of tiger nut oil and high oleic peanut oil was high(72.69 %,85.72 %),respectively and its content was almost exclusively contributed by oleic acid(72.41 %,83.75 %).(4)Study on the effect of the refining process of concentrated aromatic tiger nut oil on flavor.The fragrant aromatic tiger nut oil was subjected to hydration degumming and lowtemperature filtration refining processes,respectively,with different degrees of loss in the number and concentration content of volatile components.The number and concentration contents of volatile components in the fragrant tiger nut oil were 118 and 22.42 mg/kg,including 13 types of flavor substances such as heterocyclic(pyrazines,furans,pyrroles),olefins,alkanes,esters,aldehydes,ketones,acids,alcohols,phenols,benzenes and others,and 89 flavor substances(15.96 mg/kg)were detected in the hydrated degummed oil.101 flavor substances(17.43 mg/kg)were detected in the cooled filtered oil,and none of the pyrrole substances were detected after the refining treatment.After different refining treatments,the content of volatile components decreased,but the highest percentage of them were all aldehydes,indicating that aldehydes existed stably in the tiger nut oil.Secondly,the transparency was improved after the refining treatment,and the heating experiments at 280 ℃ were all qualified,and the overall quality of tiger nut oil reached the standard of LS/T 3259-2018 "Tiger nut oil". |
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