Effect Of Sourdough On The Quality Of Raw Wet Whole Wheat Noodles Fermented With Exopolysaccharide Lactic Acid Bacteria

Whole wheat flour is abundant with dietary fiber,trace minerals and vitamins,which meets the consumers’pursuit of healthy and low-calorie meal.However,there is a low level of protein in whole wheat flour resulting in a poor structure of gluten network,and its high activity of polyphenol oxidase,hence resulting in poor textural quality,fast browning rate and short shelf life of raw wet whole wheat noodles（WWNs）,and restricting its industrial development.It is vital to improve the quality of WWNs and delay browning,in order to increase its popularity among consumers.In this study,the impact of exopolysaccharide-positive strain,Weissella cibaria fermented sourdough on the quality of WWNs and its improvement mechanisms were preliminarily studied,while the exopolysaccharide-negative Lactilactobacillus sakei was used as control strain.The main research and results were as follows:The characteristics of exopolysaccharide produced by W.cibaria were determined,including polysaccharide types,molecular weight,monosaccharides composition and the thermal stability.The results of Fourier transform infrared spectroscopy and composition of monosaccharides,showed the exopolysaccharide was a dextran withα-glycosidic linkages,and its relative molecular（Mw）weight was 3.96×10⁶ Da.And the result of thermogravimetric showed that it had well thermal stability and remained stable at 100°C,and could be used for noodles.Optimization of sourdough exopolysaccharide-producing fermentation conditions were determined.The basic parameters of whole wheat sourdough were measured,including total cell count and p H,the content of exopolysaccharide during fermentation,rheological properties of sourdough and changes of content of major monosaccharides and disaccharides.The results showed that the optimal fermentation conditions were found to be 30%sucrose content,fermented at 25°C for 12 h,which yielded the highest exopolysaccharide,28.06 g/kg,in the W.cibaria fermented sourdough with sucrose（DW+）.At the end of fermentation,the cell count reached 10^9.5 CFU/g,and the p H value decreased to below 4.55.The p H of sourdough with sucrose fermented by W.cibaria（DW+）was relatively higher（4.55）.The presence of sucrose was metabolized by W.cibaria to generate exopolysaccharide,thus slowing down the cell growth rate and the organic acids’accumulation.The contents of exopolysaccharide,monosaccharides and disaccharides in sourdough indicated W.cibaria had a strong ability to metabolize sucrose to produce large amounts of exopolysaccharide compared with L.sakei.At the end of fermentation,the DW+group had depleted sucrose and glucose,while the L.sakei fermentation of sucrose-containing sourdough group（DL+）had a higher content of sucrose and glucose.The result of rheological behavior of sourdough indicated that the exopolysaccharide-positive W.cibaria increased the viscoelasticity of dough significantly,compared with L.sakei.exopolysaccharide improved the qualities of whole wheat flour dough,enhancing the elasticity of fermented dough.The sourdough was subsequently applied in noodles making,to determine its effects on basic characteristics of WWNs,including sensory evaluation,textural properties,basic cooking properties,color profile,the changes of p H and moisture content during storage.The polyphenol oxidase activity,free phenolics content,molecular weight and secondary structure of proteins,microstructure,thermal property and crystalline structure of starch were preliminarily studied to investigate mechanisms of the improvement of WWNs.The result indicated:noodles made with sourdough were acceptable to the testers.The addition of DW+increased the hardness from 2184.99 to 2446.83 g,and the adhesiveness increased,i.e.,from72.01 to 86.13 g?s of the noodles（p<0.05）The sourdough increased water absorption of noodles significantly,but had a negative effect on their cooking loss.With the increased storage time,the sourdough diminished polyphenol oxidase activities,increased the free phenolic content,and delayed the browning of noodles.The sourdough promoted the aggregation of glutenin macropolymers（GMP）of noodles was increased.The content of GMP declined considerably from 74.01%（the noodles without sourdough,Control）to 63.77%（the noodles with sourdough fermented by L.sakei,L-）.And at the end of storage,the GMP content of WWNs with DW+was significantly higher（63.02%）,while that of WWNs with sourdough fermented by L.sakei（DL-）was the lowest（58.89%）.The W.cibaria fermented sourdough declined the evaporation of moisture of WWNs,which was owing to the water-binding capacity of exopolysaccharide.Exopolysaccharide mitigated the degree of acidification in sourdough,inhibited the excessive disaggregation of GMP.In addition,the microstructure of noodles containing exopolysaccharide sourdough also demonstrated the uniform distribution of gluten proteins.The starch granules were also tightly embedded in the gluten network,forming a more stable structure,which increases the hardness and reduces the cooking loss rate of the noodles.There were no significant changes in thermal properties,or crystalline structure of starch.