Study On Starch And Protein Changes And Nutritional Characteristics During Multi-bacterial Fermentation Of Porous Noodles

Yeast-fermented porous noodles are an emerging industrial noodle product,which has the advantages of easy cooking and unique flavor,but there are still problems such as single culture and low nutrient richness.At present,studies have proved that the compound fermentation of yeast and lactic acid bacteria is beneficial to improve the quality and flavor of steamed buns,bread and other products,but it is less used in noodle products and lacks scientific theoretical support.In view of the fact that the changes in the properties of starch and gluten protein,as well as the rheology of dough and the quality of porous noodles in the fermentation process of compound strains are insufficient,Meishan yeast（MY）and two lactic acid bacteria,respectively,were selected for compound fermentation,Lactobacillus plantarum and Lactobacillus casei（LPC）,Lactobacillus plantarum and Lactobacillus acidophilus（LPA）and Lactobacillus casei and Lactobacillus acidophilus（LCA）.The changes of dough physical and chemical properties and porous noodle quality under different fermentation times（0 min,15 mins,30 mins,45 mins,60 mins,75 mins,90 mins）of compound cultures were explored.Taking Meishan yeast as a reference,the mechanism of starch and protein characteristics change during fermentation was deeply explored,and the change law of nutritional characteristics of porous noodles was revealed.The research content of this paper mainly includes the following points:（1）The physical and chemical characteristics of multi-culture fermented dough and the quality change law of porous noodles were analyzed.The results showed that the porous noodles fermented by lactic acid bacteria,especially the mixed strains of Lactobacillus plantarum and Lactobacillus casei,could effectively improve the quality of porous noodles.During the fermentation process,the p H value of dough decreased and the gas yield increased,the weakly bound water was converted to free water and strongly bound water,and the expansion degree of porous noodles showed an upward trend.LPC has a faster acid production rate,a higher total acid yield,and excellent gas production and gas holding capacity.Moreover,LPC-60 has excellent hardness,fracture stress resistance,elasticity,taste,firmness,viscosity,surface state and hollowness,and the holes formed are uniform and dense.（2）The changes of starch properties and structure in the LPC fermentation process and four porous noodle samples were compared and analyzed.The results showed that multi-species fermentation would degrade starch and change the structure and properties of starch,thereby affecting the quality and nutritional characteristics of porous noodles.During LPC fermentation,pullulan degradation,A-starch is destroyed,particle size is reduced,and starch particles appear dented and cracked;The structure of starch changed:the absorbance ratio,FWHH value and relative crystallinity at1047 cm^-1and 1022 cm^-1increased.The properties of starch changed:the peak viscosity and regression value decreased first and then increased,and the elasticity,solubility and expansion increased.The absorbance ratio and FWHH value at 1047cm^-1to 1022 cm^-1of LPC-60 are larger and the solubility is high.（3）The changes of protein properties and structures in LPC fermentation process and four porous noodle samples were compared and analyzed.The results showed that multi-species fermentation would destroy the gluten network structure and change the properties of proteins,thereby affecting the quality and nutritional characteristics of porous noodles.During LPC fermentation,the gluten network becomes loose,the wet gluten content decreases,and the insoluble gluten polymer（GMP）degrades;The protein structure changed:β-fold showed a downward trend,andα-helix and irregular curling showed an upward trend;The hydrogen bond content increased and the hydrophobic interaction decreased.Free sulfhydryl content increases.The properties of the protein change:the water holding capacity increases,the oil absorption decreases.LPC-60 had lower total protein content andβ-folding,free sulfhydryl groups and irregular curl content.The protein molecules are arranged flat and dispersed,and the degree of aggregation and winding of the gluten network is low.（4）The changes of antioxidant and digestive properties in the LPC fermentation process and four porous noodle samples were analyzed.The results showed that multi-species fermentation could improve the antioxidant activity of porous noodles,the anti-digestion properties of starch and the digestion properties of proteins.With the extension of fermentation time,the antioxidant capacity gradually increases.LPC-60 had the strongest antioxidant capacity,the lowest hydrolysis parameters,and its RDS content decreased,and the digestibility of SDS,RS and protein increased significantly.