Structure-activity Relationship Between Protein Structure Changes And Product Quality Properties During Drying Process Of Chinese Dried Noodles

Chinese dried noodles(CDN)is one of the most popular noodle types all over the world due to its convenience,variety,long shelf life and nutritional values,the processing level of which has reached a high degree of industrialization and automation.Over 8 million tons of CDN can be yielded per year in China,which consumes about 35% of the total flour consumption in mainland China.Drying is a crucial step in CDN processing.The process design and parameter control largely determine the quality of product,production efficiency,and energy consumption.Temperature(T)and relative humidity(RH)in drying chamber are the two main parameters during drying process.A reasonable drying temperature can promote the evaporation of moisture in noodles,improve the quality of noodles,shorten drying time,and reduce production costs.The quantity and quality of wheat protein,especially gluten protein,are closely related to processing parameters and product quality.During drying,a series of depolymerization or polymerization between gluten proteins could occur,which affected the quality of final product.However,the influence of drying parameters such as T,RH,and their interaction on the quality of CDN and protein structure changes,structurefunction relationship between protein structure changes and product quality properties during drying process of CDN are still unclear or uncertain.In our study,Chinese dried noodles were produced under the drying processes utilizing combination of three temperatures(40 ?,60 ? and 80 ?)and three relative humidity(65%,75% and 85%)at small industrial scale in a “food moisture analysis technology platform”.Effects of drying parameters on quality properties of CDN were determined.Protein molecule and structure changes under different drying combinations were observed via different methods,including SDS-PAGE,SE-HPLC,TGA,FTIR,SEM,ATR-FTIR-M et al.The changes of protein molecules and gluten network structure during drying were also investigated.By using Pearson correlation analysis,stepwise regression analysis and path analysis,the key protein quality characteristics affecting CDN quality were identified,and the influence of protein structure and physicochemical properties on product quality were discussed.The main conclusions were as follow:(1)The quality characteristics of CDN were significantly or extreme significantly affected by drying temperature,relative humidity,and their interactions.Temperature had the greatest influence on moisture content and cooking quality of CDN,while relative humidity mainly affected the color,density and bending resistance of CDN.The quality of CDN had significant difference between different combinations.(2)When noodles were dried under 60 ?/75%,the color and bending resistance of CDN were better than that using the normal drying method(40 ?/75%),the optimal cooking time and cooking loss rate were significantly decreased,the hardness,springiness,cohesiveness and resilience of cooked CDN were at medium level.Above all,comparing with low temperature drying method,the quality of CDN could be improved under appropriately increased temperatures.(3)There was no significant effect on the protein content,subunit composition and relative content between different drying conditions.Temperature had the greatest influence on different molecular protein content,GMP content and free sulfhydryl content.The interaction between temperature and relative humidity has the greatest influence on the secondary structure and thermal transition temperature.The protein molecular composition,aggregation state and network structure had significant differences under different temperature and humidity combinations.(4)With the progress of drying,the extraction rate of LPP and LMP decreased,protein aggregation degree and GMP content increased,which indicated that protein had certain aggregation and denaturation.The aggregation rate and degree of protein were affected by temperature and relative humidity.During the initial 0~60 minutes,the aggregation rate of protein was the fastest,and the change rate became slowly during 60~300 minutes.During the drying process,the different secondary structure of CDN transformed each other,but the changes were not consistent under different drying conditions.As drying time being prolonged,the gluten network became more compact,and gradually formed a network with slice structure,in which the A-type and B-type starch granules were adhered or wrapped.No significant changes in starch grain size of A-type and B-type were observed during drying.(5)GMP content and the ratio of LPP/LMP were the key protein physicochemical indexes affecting the quality of CDN,which could comprehensively reflect protein crosslink degree after drying.(6)The changes of protein aggregation degree and protein spatial conformation structure after drying might be the internal reasons for the differences in CDN quality.The higher aggregation degree and lower spatial orderliness of gluten network determined darker color,more cooking loss,and bigger hardness of cooked CDN.The present study indicated that the quality of CDN products could be adjusted by controlling the drying parameters.But in the practical application process,the adjustment should be considered based on the performance of drying equipment,production targets,energy consumption requirements,and drying process parameters.