| Sesame oil,as a traditional edible oil,is enjoyed by many Chinese for its rich nutrition and unique aroma.The aroma of sesame oil is an important index to measure its quality.At present,the research on the aroma quality of sesame oil mainly focuses on the identification of volatile components,and little is known about the key aroma-active compounds of sesame oil aroma.There is a lack of effective control over the factors affecting the aroma quality of sesame oil,and the lack of stability of sesame oil aroma is an issue to many manufactures.Therefore,using the concept and technologies of molecular sensory science,this study focused on the identification of the aroma-active compounds of sesame oil and revealed the molecular basis of sesame oil aroma.It explored important factors influencing the aroma quality of sesame oil,including the high-temperature seed roasting process,the moisture content of sesame seeds before roasting and the origins of sesame seed materials.Lastly,it investigated the changes in the aroma-active components and aroma quality of sesame oil during storage process.The main research foundings are as follows:(1)The key aroma-active components and sensory quality of roasted and cold-pressed sesame oils were compared.The numbers of aroma compounds identified with the flavor dilution(FD)factors between 1 and 2048 in the roasted and cold-pressed sesame oils were 57 and 16,respectively.A total of 28 aroma-active compounds were newly identified in sesame oils.Selected aroma compounds(FD?8)were quantified by the external standard method.The numbers of key aroma-active compounds(defined by OAVs?1)were 23 and 8,respectively,in the roasted and cold-pressed sesame oils.Phenols and pyrazines were the most important aroma-active compounds in the roasted sesame oil,contributing to the roasted,nutty,roasted sesame and smoked aroma.Whereas,aldehydes were the most important aroma-active compound in the cold-pressed sesame oil,contributing to the green,fruity and earthy aroma.(2)Before roasting,the moisture content of sesame seeds was adjusted to 6%,10%,15%,20% and 25%,and the differences in the aroma components and sensory quality of sesame oils prepared from these sesame seeds were compared.The results showed that with the increase of moisture content in sesame seeds,the acid value and red-color value(R)of sesame oil decreased gradually(p< 0.05).A total of 63 aroma-active compounds were detected in 5sesame oil samples.With the increase of moisture content in sesame seed,the relative concentrations of nitrogen-containing heterocyclic compounds,sulfur-containing compounds and furans decreased(p < 0.05),and the sensory intensity of roasted sesame,nutty,caramel,burnt flavor and bitter taste decreased(p < 0.05);whereas,the relative concentrations of 2-methoxy-4-vinylphenol and 2-methoxy-5-vinylphenol increased gradually(p < 0.05)and the smoked flavor was enhanced(p < 0.05).When the moisture content of sesame seed was 15%,the content of lignans in sesame oil was the highest,the amount of hydroperoxide was the lowest(lowest peroxide value),the relative concentrations of fatty acid oxidation products including n-hexanal,2-heptanone,3-pentanone and cyclopentanone were the lowest,and the concentration of Maillard reaction products including pyrazines was moderate.Consumers liked the sesame oil prepared from seeds with the 15% moisture content the most(liking rating= 7.2).(3)The aroma and sensory quality of sesame oils prepared by sesame seeds from 14 different cultivation areas were evaluated and compared.The results showed that sesame oils from Zhumadian(China),Myanmar and Pingyu(China)had a persistent and complexed aroma profile and soft monthfeel,which were the most liked by consumers.The crude fat contents of sesame seeds from Togo,Niger,Mali and Sudan were relatively high(49.06-52.03%),and their contents of ketones(17.27-26.13 ?g/m L),alcohols(12.35-14.72 ?g/m L)and pyridine(10.84-20.10 ?g/m L)were relatively high,contributing to stronger green,moldy,rancid and bitter taste compared to the sesame oils made by seeds from other origins.Correlation analysis were done between the basic components,aroma composition,sensory quality and liking ratings of sesame oils.The content of aroma-active pyrazines was positively correlated with the protein content(r = 0.553)and free amino acid content(r = 0.662)in sesame seeds.The pyrazine content was also positively correlated with roasted sesame flavor(r = 0.316).The liking ratings of sesame oils from consumers were positively correlated with the roasted sesame(r = 0.610)and roasted nutty(r =0 824)flavor.There was a significant positive correlation between the contents ketones and crude fat(r = 0.414).The content of soluble sugars in sesame seeds was positively correlated with the complexity of sesame oil aroma(r= 0.542),while the content of crude fiber was negatively correlated with the roasted nutty flavor of sesame oil(r =-0.549).The aroma-active sulfur compounds,pyrazines,furans and phenols contributed to the roasted sesame and roasted nutty aroma of sesame oil,and there was a significant positive correlation with the consumer acceptance.The aroma-active alcohols and ketones contributed to the green,raw sesame seeds,earthy and rancid aroma of sesame oil,and there was negatively correlated with the soft mouthfeel and aroma retention time of sesame oil.(4)The sesame oil(blank)and the sesame oil added with 0.02% TBHQ were sealed and stored in the oven at 63 ± 1 ? for 40 days.During storage,the acid value,peroxide value,anisidine value,conjugated diene and conjugated triene of sesame oils increased gradually(p< 0.05),indicating that the degree of lipid oxidation of sesame oil increased gradually.The oxidation degree of sesame oil added with TBHQ was lower than that of the blank sesame oil sample(p < 0.05).A total of 73 aroma-active compounds were detected.The relative concentrations of heterocyclic compounds and sulfur-containing compounds decreased gradually during storage(p < 0.05),while the concentrations of aldehydes,ketones,acids and esters increased gradually(p < 0.05).In addition,the total concentration of aroma-active substances in TBHQ group was generally lower than that in the blank group(p < 0.05).During storage,the roasted sesame,burnt,roasted nutty,caramel flavor and overall aroma intensity of sesame oils in both groups decreased(p < 0.05),while the rancid flavor gradually increased(p < 0.05).The sesame oil group added with TBHQ had higher roasted sesame,burnt,roasted nutty and caramel flavor than the blank sesame oil,and the former had a lower rancid flavor(p < 0.05).In conclusion,this study provides that roasting sesame seeds have a significant impact on the aroma and sensory quality of sesame oil.phenols and pyrazines were the most important aroma-active compounds in the roasted sesame oil,whereas,aldehydes were the most important aroma-active compound in the cold-pressed sesame oil.The moisture content of sesame seeds before roasting and the origins of sesame seed materials have great influence on the aroma and senseory quality of sesame oil.The addition of antioxidants can delay the deterioration of aroma and sensory quality of sesame oil during storage. |
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