| As a grain rich in dietary fiber,unsaturated fatty acids and other nutrients,oatmeal has been widely concerned.However,the high fat content and the activity of endogenous enzymes lead to the oxidation rancidity and bad flavor in oat processing,which limits the commercial processing and application of oat.In traditional oat processing,the "three-ripening" process is usually used to improve the quality of oat products and enhance the flavor.Among them,the "stir-frying stage" and "steaming stage" have significant effects on the flavor due to the long-term high temperature,but the changing law of oat flavor and its influencing mechanism in the ripening process are not clear.From the perspective of flavor,this paper explores the rule of flavor change in oat ripening process(roasting,steaming),and probes into the mechanism of oat flavor formation in the ripening process from the perspective of fat oxidation and Maillard reaction.The main research results are as follows:(1)Headspace solid phase microextraction combined with gas chromatography-mass spectrometry(HS-SPME-GC-MS),electronic nose technology combined with relative odor activity value(ROAV),principal component analysis(PCA),cluster analysis and other methods were used to investigate the flavor changes of oat flour in the roasting process and oat nest in the steaming process.The results showed that a total of 70 flavor substances were identified in oat flour samples,among which the contents of hydrocarbons,aldehydes and alcohols increased first and then decreased with the increase of roasting time,while the contents of pyrazines increased significantly after roasting for 25 min.Cluster analysis showed that the oat flavor in early stage of roasting(≤15 min)and middle and late stage of roasting(≥25 min)was significantly different.Relative aroma activity value and principal component analysis showed that the characteristic flavor substances in the early stage of roasting were mainly aldehydes,including decaldehydes,(E)-2-nonenal,nonenal,benzaldehyde,etc.,showing fruit,sweet,floral and weak oil aroma.The characteristic flavor substances in the middle and late stage of roasting are mainly 2-ethyl-3,6-dimethylpyrazine,3,5-diethyl-2-methylpyrazine,capral,heptal,etc.,showing burnt flavor,nut flavor,fruit flavor.The results of electronic nose analysis showed that there were obvious differences in flavor profiles between the early and late frying samples.(2)A total of 72 flavor substances were identified in oat nest samples.The types of flavourings in oat hollow are obviously different from those in oat flour.Pyrazines are greatly reduced,and characteristic flavourings such as 2-amylfuran,benzoin and(E)-2-decenal are produced.Among them,when the steaming time was 7 min,the most volatile flavor substances were found in oat nest.Cluster analysis showed that the oat flavor in early stage(≤4 min)and late stage(> 10 min)was significantly different.The relative aroma activity value and principal component analysis showed that the characteristic flavor substances in the cooking stage were mainly aldehydes,including hexal,heptal,(E)-2-octenal,nonal,decalal,(E,E)-2,4-nonenal,(E,E)-2,4-decenal,1-octene-3-alcohol and2-amylfuran,etc.It has some contribution to the fruit,sweet,floral and oil fragrance of oat den.The results of electronic nose analysis showed that the flavor profiles of samples before and after steaming were significantly different and could be effectively distinguished.There were obvious differences in the relative content and types of characteristic flavor substances between roasted oat flour and steamed oat woollen,and the main flavor properties had great changes.(3)The influence of fat oxidation on oat flavor was explored through the change of fat oxidation in the process of roasting,and the influence of Maillard reaction pathway on oat flavor was explored by analyzing the degree of Rad reaction in the process of roasting.The results showed as follows: with the increase of roasting time,the content of unsaturated fatty acid(UFA)in oat was significantly decreased from 84.41% to 81.72% in the early stage(P<0.05),and there was no significant change in the middle and late stage of roasting.The aniside value(P-AV)of oat increased first and then decreased.Thiobarbituric acid(TBARS)increased at first and then remained unchanged.Acidity showed a decreasing trend;Fatty acid value(FFA)fluctuated.This indicates that free fatty acids are continuously involved in the reaction during the roasting process.With the increase of roasting time,the brightness L*value of oat flour decreased continuously,while the red and green values a* and yellow and blue values b* increased continuously.The Browning degree of oat flour showed an increasing trend,and the UV absorption intensity increased significantly after the roasting time was greater than 25 min.Reducing sugar content decreased from 0.89 mg/g to 0.37mg/g.During the roasting process,the contents of glutamic acid,serine,histidine and lysine decreased significantly after 25 min of roasting,indicating that these amino acids were heavily involved in the formation of special flavor substances of oat flour through Maillard reaction pathway in the middle and late roasting,and played an important role in the overall flavor of oat.(4)The influence of fat oxidation on oat woat flavor was explored through the change of fat oxidation in the process of steaming,and the influence of Maillard reaction pathway on oat Woat flavor was explored by analyzing the degree of Rad reaction in the process of steaming.The results showed that the contents of UFA and saturated fatty acid(SFA)had no significant change with the increase of steaming time.The P-AV value of oat nest increased first and then decreased,and reached the maximum value at 7 min of steaming.TBARS showed a fluctuating trend.The acidity decreased first and then remained unchanged.FFA value had no significant change after the decrease in the early stage of steaming.With the increase of the steaming time,the L* value of oat nest brightness decreased first and then remained unchanged,the a* value increased first and then decreased,and the b* value decreased sharply after the steaming time was greater than 7 min.The Browning degree of oat nest showed an upward trend and increased significantly after 7 min of steaming,but the UV absorption intensity did not change significantly during the whole steaming stage.The content of reducing sugar fluctuated with the cooking time,ranging from 0.77 to 1.27 mg/g.In the early stage of steaming,the contents of serine,glutamic acid,leucine and proline decreased with the increase of steaming time.However,the contents of alanine,isoleucine and lysine decreased at the later stage of steaming. |
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