Effect Of Fruit Fermentation Broth On The Properties Of Dough And The Quality Of Porous Dried Noodles

Porous dried noodles have a long edible history in our country.At present,with the development of food industrialization,it has already realized the industrialization of production.However,the porous dried noodles on the market now have deficiencies in taste,nutrition and flavor,and still need to improve the edible quality.Sourdough is used to ferment bread,Chinese steamed bread and other wheaten foods,which can produce unique flavor and effectively and improve quality.In this study,red grape and pear were used as the main culture substrate to prepare two kinds of fruit sourdoughs,and these two kinds of natural sourdoughs were added to the dough and made into porous dried noodles.Firstly,the microbial diversity of sourdough was comprehensively analyzed using high throughput sequencing technology.Secondly,the effects of sourdough fermentation on the physicochemical and rheological properties of dough were studied.Finally,the effects of sourdough fermentation on the quality of porous dried noodles were studied.The main research conclusions are as follows:（1）The average number of lactic acid bacteria in red grape sourdough noodle dough（GSD）and pear sourdough noodle dough（PSD）was 8.70 log CFU/g and 7.74 log CFU/g,while the average number of yeasts was 8.34 log CFU/g and 6.22 log CFU/g,respectively.Through microbial diversity analysis,it was found that at the phylum level,the bacterial communities in GSD and PSD were mainly distributed in Firmicutes and Proteobacteria;The fungal community was mainly distributed in Ascomycota.At the genus level,Lactobacillus and Saccharomyces were the first dominant bacterial and fungal genera of GSD and PSD,respectively.Other bacterial groups had less impact on fermentation.Principal coordinate analysis showed that the bacterial colony composition of GSD and PSD were relatively similar.The differences between the bacterial groups of GSD and PSD were shown in Acetobacter and Lactobacillus.The differences between fungal groups were mainly manifested in Saccharomycetes and Pleosporales.PICRUST function prediction found that the main functions of the bacterial flora in sourdough were carbohydrate transport and metabolism,amino acid transport and metabolism,and transcription.（2）Using wheat flour dough（WD）as blank control and commercial yeast fermented dough（CD）as positive control,the effects of sourdough fermentation on the physicochemical and rheological properties of dough were investigated.The results showed that compared with WD,the p H value and glutenin macropolymer（GMP）content of the dough after adding sourdough were significantly decreased（P<0.05）,while the total titrated acid（TTA）and free sulfhydryl content were significantly increased（P<0.05）.Fourier transform infrared spectroscopy results showed that sourdough fermentation resulted in the secondary structure of the protein was changed fromβ-sheet,random curling toα-helix andβ-turn and enhanced flexibility of protein chains.Sourdough fermentation was superior to commercial yeast in stabilizing the gluten network and could affect the elasticity and extensibility of the dough.The analysis of rheological fermentation characteristics showed that GSD and PSD had weaker gas production capacity than CD,and better gas holding capacity than CD.GSD and PSD were not prone to gas leakage during the fermentation process;Low-field nuclear magnetic resonance analysis showed that compared with WD,the relaxation time T₂₁,T₂₂,and T₂₃of GSD and PSD were significantly decreased（P<0.05）,the content of loosely bound water and free water significantly increased（P<0.05）,while the content of deep bound water significantly decreased（P<0.05）.The water distribution of dough changed,and some deep bound water migrated to loosely bound water and free water.（3）Using wheat flour noodles（WN）as blank control and commercial yeast porous dried noodles（CN）as positive control,the effect of sourdough fermentation on the quality of porous dried noodles was investigated.The results showed that compared with WN,the swelling index and porosity of grape sourdough porous dried noodles（GSN）and pear sourdough porous dried noodles（PSN）were significantly increased（P<0.05）,slightly lower than those of commercial yeast porous dried noodles（CN）.From the scanning electron microscope（SEM）observation of the microstructure of the cross section of the dried noodles,it could be seen that the central pores of GSN and PSN were smaller,the overall pore distribution was more uniform,and the internal structure is more compact.The results of cooking properties showed that compared to WN,sourdough fermentation had less the optimal cooking time of porous dried noodles and increased more water absorption.The results of texture characteristics showed that compared to WN,the flexural strength,flexibility,breaking force,and breaking distance of porous dried noodles fermented with sourdough increased,while the texture characteristics of porous dried noodles fermented with sourdough decreased.There was no significant difference in tensile properties between sourdough fermentation and commercial yeast fermentation.The sensory evaluation results showed that GSN had the highest score on taste and palatability among the three fermentation methods,and the two-sourdough fermentation had improved the taste of porous noodles.The volatile flavor compounds in dried noodles were analyzed using GC-MS technology.The results showed that sourdough fermentation can enhance the flavor of dried noodles.After sourdough fermentation,both the type and content of flavor substances in porous dried noodles have increased,mainly including alcohols and aldehydes.Due to the different internal microbial community structures of the fruit sourdough,GSN and PSN have different flavor compound characteristics.The unique flavor compounds in GSN include acetaldehyde,（E）-2-Butenal,and ethyl lactate;The unique flavor compounds in PSN include hexanoic acid,2,3-Butanediol,（E）-2-Octenal,Benzo[d]thiazole,and 2-Pentylfuran.According to odor activity value（OAV）,the key aroma components of GSN and PSN were citrus aroma,rose aroma,wax aroma,melon aroma,honey aroma,and apple aroma.（4）Finally,evaluate the nutritional characteristics of porous dried noodles.Compared with WN,the activities of tannin,phytic acid,and peroxidase（POD）in porous dried noodles fermented by sourdough decreased significantly.Total polyphenol content,β-glucosidase activity and antioxidant activity were significantly improved（P<0.05）,and PSN had the strongest antioxidant activity.Sourdough fermentation increased significantly the total amount of free amino acids and the content of essential amino acids in porous dried noodles,optimizing the amino acid composition pattern.The analysis of in vitro starch digestion showed commercial yeast fermentation improved the in vitro starch digestibility and glycemic index（GI）,while sourdough fermentation can effectively reduce the in vitro starch digestibility and GI.The GI values of the four types of dried noodles are in the order of PSN（58.89）<GSN（60.67）<WN（64.13）<CN（72.93）.