Effects Of Extrusion And Fermentation On The Properties Of Foxtail Millet Starch And Protein And The Quality Of Egg Rolls

Foxtail millet,originating in China,is easy to cultivate and has high nutritional and health value,with China ranking among the world’s top producers of foxtail millet.The limited gluten protein content in foxtail millet hampers its product development.Extrusion and fermentation are commonly used food modification techniques known for their green and efficient advantages.This study systematically investigated the effects of extrusion treatment,fermentation treatment,and their combined treatment on the starch,protein,and gelatinization characteristics of foxtail millet flour,as well as their application in the production of egg rolls,providing effective methods and theoretical basis for the deep processing and widespread application of foxtail millet.Initially,this study analyzed the starch content,amylose-to-amylopectin ratio,microstructure,crystalline characteristics,Fourier-transform infrared characteristics,gelatinization properties,thermodynamic properties,in vitro digestion characteristics,protein content,free sulfhydryl groups,and surface hydrophobicity of foxtail millet flour under different extrusion conditions.The research findings showed that:(1)Extrusion treatment reduced the starch and protein content of foxtail millet flour.The amylose content increased,influenced by temperature and material moisture content,with the starch content ranging from 70.99±0.68% to 80.61±0.42%.The protein content fluctuated around 10.5%,with no significant effect from temperature and material moisture.(2)Extrusion treatment altered the shape and structure of foxtail millet starch particles,resulting in an irregular chunk-like structure when mixed with proteins.(3)Extrusion treatment led to a decrease in the crystallinity of foxtail millet starch,from 40.18±0.36% to 16.07±0.57~25.68±0.30%,transitioning from A-type crystallinity to V-type crystallinity,with a decrease in the OD value.(4)Extrusion treatment changed the secondary structure content of foxtail millet proteins but did not induce the formation of α-helices.(5)Extrusion treatment affected the gelatinization properties,thermodynamic properties,and in vitro digestion characteristics of foxtail millet flour,reducing viscosity and resistant starch content while increasing rapidly digestible starch(RDS)and slowly digestible starch(SDS)contents.(6)The content of free sulfhydryl groups in foxtail millet proteins was related to the moisture content and temperature during extrusion.At low moisture content,extrusion increased the exposure of hydrophobic groups on proteins,resulting in increased surface hydrophobicity of foxtail millet proteins.Subsequently,this study selected two extruded flours with low content of rapidly digestible starch,high crystallinity,and peak viscosity for fermentation treatment,and analyzed their starch content,amylose-to-amylopectin ratio,microstructure,crystalline characteristics,Fourier-transform infrared characteristics,gelatinization properties,thermodynamic properties,in vitro digestion characteristics,protein content,and free sulfhydryl groups.The results revealed that:(1)With increasing fermentation time(0~24 hours),the starch content of raw foxtail millet flour gradually decreased from 80.60±0.09% to 72.53±7.77%,while the protein content increased.The starch content of extruded flour showed an initial increase followed by a decrease trend,with no significant change in protein content.Both extruded flour and raw flour exhibited an increasing trend in the amylose content.(2)Fermentation disrupted the binding of starch and protein in raw foxtail millet flour,resulting in a looser structure and did not change the particle binding morphology of extruded flour,but it made the particles smaller.(3)Fermentation disrupted the crystalline structure of foxtail millet starch,reducing its relative crystallinity,but did not alter the starch’s crystal type.Fermentation combined with extrusion increased the resistant starch content.(4)Fermentation affected the secondary structure content of foxtail millet proteins and induced the production of α-helices.(5)Fermentation treatment altered the gelatinization properties,thermodynamic properties,and in vitro digestion characteristics of foxtail millet starch,reducing the viscosity of raw flour and increasing the viscosity and enthalpy of gelatinization of extruded flour.(6)Fermentation significantly disrupted the disulfide bonds in raw foxtail millet protein,while its impact on the protein disulfide bonds of extruded flour was relatively minor.Finally,this study used extruded foxtail millet flour,fermented foxtail millet flour,and the combined treatment to produce foxtail millet egg rolls and analyzed their texture,digestibility,flavor,and sensory evaluation.The research findings showed that extrusion treatment improved the palatability,increased hardness and flavor of foxtail millet egg rolls,but had a negative impact on their brittleness while reducing the resistant starch content.Fermentation treatment improved the brittleness of raw foxtail millet flour egg rolls,increased the resistant starch content,and decreased the digestible starch content.The combined treatment of extrusion and fermentation significantly enhanced the crispiness,palatability,and flavor of foxtail millet egg rolls,resulting in higher sensory scores,while increasing the resistant starch content and reducing the digestible starch content.Among all the treatments,foxtail millet egg rolls made from extruded flour with 8 hours of fermentation at 165°C and 28% moisture content exhibited the best performance in all aspects,approaching the quality of commercially available egg rolls and demonstrating the potential for commercialization.This study provides theoretical support for the application of foxtail millet flour in egg roll products.