Analysis And Strengthening Method Of Characteristic Flavor Substances Of Scorched Rice In Electric Rice Cooker

Traditional scorched rice is favored by consumers,but currently,there is few relatively complete methods and standards for evaluating the scorched aroma of rice.Therefore,it is difficult to effectively design and optimize the procedure for cooking scorched rice in an electric rice cooker.In this study,the evaluation method for the characteristic flavor compounds of the scorched rice was established,and the intensification effect of the rice cooker soaking stage parameters on the characteristic flavors of the scorched rice was emphatically analyzed.On this basis,the relationship among the Maillard reaction intermediates,the formation of characteristic flavor substances and the generation of potential hazards of stewing rice was clarified.The aim was intended to provide guidance for the directional regulation of scroched rice flavor and the reasonable design of cooking procedures of the electric rice cooker.The two flavor enrichment methods of solid-phase microextraction and solvent-assisted flavor evaporation were compared,and the characteristic volatile flavors of the scorched rice were determined by the combination of gas chromatography-mass spectrometry-olfactometry and aroma activity value.The results showed that up to 48 kinds of volatile components were enriched by solid phase microextraction.Seven flavor compounds,including hexanal,nonanal,2-methylpyrazine,2-ethyl-6methylpyrazine,3-ethyl-2,5-dimethylpyrazine,4-methylthiazole,and p-vinylguaiacol were the characteristic flavor compounds of scorched rice.Based on the sensory scores and the partial least square regression analysis,the correlation between characteristic flavor substances and rice aroma,including grass and popcorn,was determined.Through flavor restructuring and deletion tests,it was found that 2-methylpyrazine,2-ethyl-6methylpyrazine,3-ethyl-2,5-dimethylpyrazine and 4-methylthiazoleall contributed to the scroched aroma of rice.Taking the content of characteristic flavor substances as the indicators,the effect of soaking temperature and time on the flavor of scorched rice were investigated,and the effect of amino acid and reducing sugar dissolved in the soaking solution on enhancing the flavor of scroched rice were analyzed.The results indicated that the content of the characteristic flavor substances of scorch aroma increased firstly and then decreased with the increase of soaking temperature and time,and the maximum content was obtained with soaking at 60°C for 20 min.Reasonable soaking temperature and time could promote the dissolution of reducing sugar mainly composed of glucose and maltose,and amino acids mainly composed of glutamic acid and aspartic acid,thereby enhancing the scorched flavor substances of the rice in the subsequent cooking and stewing process.By adding exogenous reducing sugar and amino acid,it was found that the presence of the two substances helped to produce more Maillard reaction intermediate products and end products in the rice,thus giving the rice a stronger scorched aroma.The addition of 0.05% glutamic acid and 0.1% glucose could increase the content of 2-methylpyrazine by nearly 5 times.The effects of temperature and time of stewing rice on characteristic flavor substances and content were analyzed,and the potential hazard factors and the generation of scorched aroma precursor substances were tracked by liquid-mass spectrometry.The results demonstrated that the content of scorched characteristic flavor substances increased with the increase of the temperature and time of stewing rice,and the formation of potential hazard factors tended to be consistent with their change.After stewing at 175°C for 20 min,the pyrazines in the rice tended to be stable,while the contents of the two potential hazards,5-hydroxymethylfurfural and acrylamide,were only 1.71 mg/kg and 0.08 mg/kg.The formation and accumulation of dicarbonyl compounds such as pyruvaldehyde promoted the production of characteristic flavor components of scroched aroma,however,Amadori compounds were more likely to be converted into harmful products at extreme high temperatures(above 200°C).