| Sesame oil is a traditional Chinese specialty cooking oil,which is loved by consumers for its unique and rich flavor.Many scholars have analyzed the aroma composition of sesame oil,however,there is almost no research on the formation pathways of its key aroma substances,which cannot guide the sesame oil industry to achieve precise regulation of aroma quality.The existing aroma generation process using sesame meal protein hydrolysate and sugar based on the Maillard reaction has resulted in aroma that differs significantly from that of traditional fried sesame oil.This project proposes a new aroma formation pathway for sesame oil,the interaction between oil oxidation during frying and the Maillard reaction may have a synergistic aroma enhancement effect on the characteristic aroma of sesame oil.Therefore,this project firstly identified the aroma products and aroma of sesame oil by using molecular sensory science,and based on the results,we selected "glucose-lysine" as the key aroma substrate to establish a Maillard reaction simulation system,and investigated the interaction between sesame oil with different oxidation levels and the Maillard reaction simulation system and its effect on the formation of key aroma substances of sesame oil.The interaction between different oxidation levels of sesame oil and the simulated system and its effect on the formation of key aroma substances of sesame oil were investigated.The main contents and conclusions of the study are as follows:(1)The composition of aroma products and substrates of sesame oil was studied at different roasting temperatures.Sesame oil samples were obtained by roasting sesame seeds at four temperature gradients of 140℃,160℃,180℃ and 200℃ for 20 min and then pressed.88 aroma substances were identified in sesame oil using SAFE extraction combined with GC-O-MS.The total content of heterocyclic aroma substances in sesame oil increased from 7 μg/kg to 25,564 μg/kg with increasing roasting temperature,including 16pyrazines(roasted and nutty),10 pyrroles(sweet),6 pyridines(nutty),13 furans(caramel),9 thiazoles(garlic),and 5 thiophenes(meaty),which are typical of the Maillard reaction product;The total concentration of carbonyl group aroma substances in sesame oil increased from 50 μg/kg to 4,328 μg/kg,including 6 aldehydes(grassy flavor),10 ketones(sweet flavor)and 1 ester(pungent flavor),most of which were generated by lipid oxidation and a few of which were products of the Maillard reaction,The loss of lysine,serine,cysteine and arginine in sesame seeds was the highest,62.67%,42.67%,38.29%and 33.50%,respectively,which judged that they might be the key amino acid substrates involved in the aroma formation of sesame oil.Glucose was the most abundant reducing monosaccharide in sesame seeds(12.82 mg/g),and its consumption rate was 100% after roasting the seeds for 20 min at over 160 ℃,which may be the key monosaccharide involved in the Maillard reaction.(2)The interaction of sesame oil with the "lysine-glucose" Maillard reaction system at different oxidation levels and its effect on the aroma active substances of sesame oil were investigated.When cold-pressed sesame oil(acid value of 1.44 mg/g,peroxide value of5.59 mmol/kg)and oxidized sesame oil(acid value of 2.40 mg/g,peroxide value of 74.69mmol/kg)were added to the Maillard reaction system,the p H value of the Maillard reaction system(aqueous phase)decreased significantly(5.36 to 4.51)at 160 ℃ for 80 min,which may be due to the fact that The carbonyl products of lipid oxidation were involved in the Maillard reaction to generate more acids.The addition of oil and grease caused a significant increase in the absorbance of the Murad reaction solution at 294 nm(1.81 to1.93)and 420 nm(0.65 to 0.84),along with an enhanced scavenging ability of DPPH radicals(65.13% to 89.76%),indicating that the presence of oil and grease may have promoted the formation of intermediate and final products of the Maillard reaction solution,thus improving the the antioxidant capacity of the Maillard reaction solution.The content of 2,5-dimethylpyrazine,2-acetylpyrazine and pyrazine decreased and the content of other pyrazines increased in the reaction system with the addition of sesame oil or oxidized sesame oil in the Maillard reaction system.In addition,these substances decreased or increased to a greater extent in the reaction system with the addition of oxidized sesame oil than in the reaction system with the addition of cold-pressed sesame oil.The addition of oil and grease decreased the content of 2,5-diformylfuran,5-methyl-2-furanmethanol,and5-methyl-2-acetylfuran in the Maillard reaction solution,increased the content of2-methyltetrahydrofuran-3-one,furanone,furfuryl ketones,and methoxyacetic acid,and formed new substances,namely,2-methylpyrrole,2-valerylfuran,2-n-butylfuran2-acetylfuran and 3-octanone,which may be the products formed under the interaction pathway between the Maillard reaction and oil oxidation.The Maillard reaction also had a significant effect on the oxidation reaction of oil.The acid value of cold pressed sesame oil decreased from 2.70 mg/g to 2.60 mg/g and peroxide value decreased from 26.09 mmol/kg to 20.42 mmol/kg when "lysine-glucose" was added to sesame oil for 80 min;the acid value of oxidized sesame oil decreased from 3.41 mg/g to3.38 mg/g and peroxide value decreased from 112.08 mmol/kg to 107.20 mmol/kg.The acid value of oxidized sesame oil decreased from 3.41 mg/g to 3.38 mg/g and the peroxide value decreased from 112.08 mmol/kg to 107.20 mmol/kg,which indicated that the degree of oxidation of sesame oil was reduced by the Maillard reaction solution.The Maillard reaction reduced the loss of γ-tocopherol in cold pressed sesame oil(114.50 mg/kg to192.64 mg/kg)and oxidized sesame oil after thermal reaction(0 to 9.43 mg/kg);increased the content of sesamol in cold pressed sesame oil(0.69 mg/100 g to 10.44 mg/100g)and sesamol in oxidized sesame oil after thermal reaction content(0.91 mg/100 g to 19.58mg/100g)in oxidized sesame oil.This indicates that the Maillard reaction promoted the rate of conversion of sesamolin to sesamol.In addition,the Maillard reaction reduced the content of lipid oxidation products such as unsaturated aldehydes,ketones and alcohols,which are aroma active in oils,indicating that the Maillard reaction can affect the formation of aroma active substances in sesame oil by altering lipid oxidation.(3)The effect of the participation of key lipid oxidation products(hexanal,(E,E)-2,4decadienal and 2-heptanone)of sesame oil in the "lysine-glucose" Maillard reaction on the aroma formation of sesame oil was investigated.The addition of lipid oxidation products to the Maillard reaction system increased the absorbance of the Maillard reaction solution at294 nm(from 0.56 to 0.59)and 420 nm(from 0.49 to 0.60),improved its DPPH radical scavenging capacity(from 85.27 to 88.91 %),decreased the p H of the system(from 5.83 to5.51),and increased the total lysine consumption(from 48.14 to 54.57 %),suggesting that lipid oxidation products may compete with glucose for amino groups and participate in and influence the Maillard reaction.The lipid oxidation products were added to the Maillard reaction system,and the reaction products including 2-methylpyrazine(38,105μg/L to 58,037μg/L),2,3-dimethyl-pyrazine(251μg/L to 718μg/L)and 2,3,5-trimethylpyrazine(241μg/L to408μg/L)were elevated,and the remaining pyrazines(107,799μg/L降至70,037μg/L),pyrroles(3,019μg/L to 614μg/L),pyridines(118μg/L to 0μg/L)and nitrogenous aromatic substances decreased;the concentration of some furan aromatic substances increased(furanone,2,5-diformylfuran),and another part of furan substances(5-methylfuranal,5-methyl-2 furan methanol,furfuryl alcohol and 2-methyltetrahydrofuran-3-one)were reduced;the content of ketones(24,612μg/L to 35,434μg/L)and esters(550μg/L to43,478μg/L)was increased.In addition,the addition of lipid oxidation products to the Maillard reaction simulation system resulted in the formation of 8 new aroma active compounds,including 4 aldehydes,2 alkyl furans,1 ketones and methoxyacetic acid,which may be new products formed by the participation of lipid oxidation products in the Maillard reaction.Through[13C6]-glucose isotope tracing,it is found that the nitrogen containing heterocyclic compounds pyrazines and pyrroles are the products of Maillard reaction.The furan like substance 2-methyltetrahydrofuran-3-one may be the degradation product of glucose,while 2-n-butyl furan and 2-pentyl furan may be the degradation product of lipid oxidation product or the reaction product of lipid oxidation product and lysine.Other furans are products of Maillard reaction.5-ethyl-2-methyloctaneα-Phellandrene,Propionic anhydride,M-Xylene and methyl ethyl ketone are the products of Maillard reaction.Heptanal,n-octanal,and(E)-2-octenal are degradation products of lipid oxidation or may be products of lipid oxidation products reacting with lysine.Methoxy group acetic acid is the product of the reaction of aldehyde and ketone oxidation products of oils and fats with lysine.3-Hydroxy-2-butanone,2,3-pentanedione,and acetic acid may be products of glucose degradation.In conclusion,the oxidation of sesame oil interacts with Maillard reaction,which jointly affects the aroma formation of Sesame oil.The research results can provide Scientific theory guidance for the aroma fidelity and regulation of sesame oil. |
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