| Pecans(Carya cathayensis Sarg,CCS)have high nutritional value.The roasted pecans have a crisp taste and pleasant aroma,which are popular with consumers.T At present,relevant researches at home and abroad show that the application of variable temperature technology in food drying treatment can improve flavor quality,increase drying efficiency,and save energy.But there were few reports on its application in roasting technology.Therefore,this study introduced variable temperature technology into pecan roasting technology and sought the best process conditions by adjusting different parameters.Furthermore,the effects of variable temperature processing on the oxidation and anti-oxidation quality,in vitro digestion characteristics,and flavor components of pecans were explored,which provides a basic theoretical basis for the variable temperature roasting process.The main research contents and conclusions are as follows:1.Optimization of variable temperature roasting process.Based on sensory evaluation,three optimal parameters of the temperature,time and time ratio of variable temperature roasting were determined by single factor experiments.Then,response surface tests were carried out according to the Box-Behnken design principle to optimize the processing conditions of variable temperature roasting.The optimal temperature of process conditions was 140℃-155℃,the optimal time was 66 min and the optimal temperature change time ratio 1:2.2.Effect of variable temperature roasting technology on oxidation and antioxidation quality of pecan.The oxidation quality index(peroxide value,acid value,carbonyl value,malondialdehyde and iodine value)and antioxidant index(total phenol content,DPPH free radical scavenging ability,iron ion reduction(FRAP)ability)of unprocessed pecan(CCS-1),traditional constant temperature roasting pecan(CCS-2),optimal variable temperature roasting pecan(CCS-3),and high temperature and longtime variable temperature roasting pecan(CCS-4)were determined respectively.Then,through principle of principal component analysis,the comprehensive scores of the four groups of samples were calculated and ranked to judge the quality of them.The results showed that the CCS-2 score was 0.271,the CCS-3 score was 0.043,and the CCS-4 score was 0.728.In the end,CCS-3 has the best quality.3.Effect of variable temperature roasting on digestion characteristics of pecan in vitro.The matrix degradation index(MDI),the digestibility of fat,the release of free amino acids,the release of phenolic substances,and the scavenging ability of DPPH were determined by simulated digestion experiments in vitro.The results showed that compared with the unprocessed samples,the MDI and fat digestibility of roasted processed pecans were higher,but their protein digestibility levels were lower.There was no significant difference in antioxidant capacity between the two.In addition,the MDI,fat digestibility and protein digestibility of CCS-3 were higher than those of CCS-2 and CCS-4.4.Effect of variable temperature roasting on flavor components of pecan.Qualitative and quantitative analysis of the flavor components of the samples was carried out by SPME-GC-MS.Eight compounds were identified,which include alcohols,aldehydes,ketones,esters,pyrazines,furans,pyrroles and terpenes.The main flavor components of the samples were different in different roasting processes.CCS-1 was dominated by esters,CCS-2 was dominated by aldehydes and esters,CCS-3 was dominated by esters and pyrazines,and CCS-4 was dominated by aldehydes.The results of principal component analysis,cluster analysis and orthogonal partial least squares discriminant analysis showed that the cineole,1-undecanol and 2,5-diethylpyrazine were the different compounds in the roasted samples.In addition,the relative contents of pyrazines and aldehydes and the flavor of pecan were greatly affected by the roasting process at varying temperature,which can effectively improve the flavor of pecans. |
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