Composition Analysis Of The Aroma Volatile Compounds In Different Stabilized Rice Bran During Storage

Rice bran is one of the most nutritional by-products in the process of rice processing.As we all know,it has a "bran" taste that is unacceptable to consumers,so its application in food is restricted.However,research on the reason of its undesirable flavor is very rare.Therefore,this paper explored many reliable analytical methods to determine its unpleasant volatile compounds.By monitoring the dynamic changes of volatile compounds of rice bran during the storage,the key compounds related to the bad flavor of rice bran were determined;To prevent rice bran from being rancid,a variety of processing methods are used to improve its storage stability,so we had a further research on its volatile compounds after stabilization.Then a model of the relationship between key volatile compounds and odor attributes of rice bran was established,and the change trend of key flavor compounds during storage of different stabilized groups was compared to evaluate its effect on improving the undesirable flavor of rice bran.Finally,flavor is only one factor that affects the application of rice bran to the product,so the influence of stabilization methods on the physical and chemical properties of rice bran must be taken into account,which provided a scientific theoretical basis for the development and industrial application of rice bran products.The main research contents are as follows:Firstly,solid phase microextraction(SPME)-gas chromatography-mass spectrometry(GC/MS)was used to compare and analyze the volatile compounds of rice bran during accelerated storage,and 65 volatile compounds were identified.They were divided into 6categories.Combined with the electronic nose data,the samples were qualitatively analyzed through principal component analysis,and it was found that the flavor of rice bran gradually changed during the short-term accelerated storage,until the flavor characteristics became stable after 14 days.Through the analysis of quantitative data,it was found that the main volatile components of fresh rice bran were alkanes,and the relative concentrations of aldehydes,ketones,and alcohols increased with the time of storage.Among them,the content of hexanal was the highest,its concentration reached 1016.7μg/kg.The early oxidation of rice bran contributed to it.Through PLS-DA analysis,the contribution of key aroma compounds to the sensory attributes of the rice bran flavor model was studied,combined with the AOV value and a large number of references,14 key rice bran flavor compounds were determined.The correlation between storage time and key compounds was established through PCA.The untreated raw rice bran samples were related to octanoic acid,1-pentanol and 2-pentyl-furan,indicating that they can be used as markers of early rancidity of rice bran;1-octen-3-ol,1-octanol and vanillin were closely related to the samples at the later stage of storage.Secondly,the electronic nose,GC/MS and gas chromatography-olfactory method(GC-O)were combined to analyze the effect of stabilization methods on the odor of rice bran.Through principal component analysis,we found that the effect of different treatment on volatile substances was obviously different.It is worth noting that the acid volatile substances in the treated groups increased significantly after high-pressure steaming and oven-heating,increasing by 37% and 63% respectively,and some other compounds(furan,etc.)also increased2.7 and 4.6 times.The GC-O experiment verified that the processed samples gradually changed from the original grassy and oily flavors to vanilla,cheese and caramel flavors.Thirdly,the bitterness of the stored and stabilized samples was analyzed through the electronic tongue.The bitterness of the untreated rice bran increased during the storage,and the bitterness value reached 7.6 or more after 28 days of storage.The bitterness value of the rice bran after stabilizing increased,so it is speculated that the bitter substances were gradually released in the heating process.Furthermore,we studied the effect of stabilization treatment on the physical and chemical properties of rice bran.We found 30-minute steaming had the worst effect on enzyme inactivation.Extrusion,microwaving and high-pressure steaming had similar inactivation effects.In the study of the storage stability of rice bran,the acid value of the original rice bran increased rapidly in the accelerated storage experiment.After 4 weeks of storage,its fatty acid value was about 6 mg KOH/100 g.The acid value of the stabilized rice bran during the storage period increased slowly,it only increased to 1.7 mg KOH/100 g;the peroxide value of the raw rice bran showed a "N" shape,and the treated samples had a steady growth.Among them,suppression effect of the microwaving,extrusion and high-pressure steaming was better.The water holding rate,gelatinization degree and water solubility index were improved,which was related to the gelatinization of rice bran starch during heating.