Effects Of Polysaccharides On The Texture Of High Protein Nutrition Bar Systems During Early Storage

High protein nutrition bar(protein bar)has been used widely as military,aerospace and aid food as well as leisure food.However,the most severe problem of protein bar is the texture hardening occurred during the storage,especially the early stage(first 3 days).The protein bars made up of sodium caseinate or soy protein usually have higher hardness than others.Polysaccharides are normally efficient to modify the food properties as a kind of hydrocolloids.Therefore,three model systems consisting of sodium caseinate(Na-CN)/ soy protein isolate(SPI)/ whey protein isolate(WPI),water,glycerol and sorbitol were established respectively with different polysaccharides added to evaluate the influence of polysaccharides on the texture and microstructure of protein bar model system.As a consequence,this study developed a simple and effective method to improve the product properties and revealed the interaction mechanism,so as to provide a theoretical basis and application support for improving the quality of high protein nutrition bar.Firstly,Na-CN system added with 1% gum arabic(GA),carrageenan(CA)or xanthan gum(XG)was studied.In fact,protein bars made up of Na-CN had the most severe hardening problem during early storage.Texture analyzer,confocal laser scanning microscopy(CLSM),scanning electron microscopy(SEM)and low-field nuclear magnetic resonance(LF-NMR)were used to compare the effects of different polysaccharides on the texture,microstructure and molecular migration of the system.Results showed that the Na-CN particles swollen gradually and formatted a cross-network,which contributed to the firmness of the Na-CN system.GA hardly changed any properties of the system,whereas CA and XG decreased the Na-CN particle size and weakened the cross-network,making the system softer.In addition,XG had the most significant softening effect.whereafter,based on the study above,the Na-CN system added with different concentration of XG were further studied.Results showed that higher concentration of the XG induced lower swelling degree of the Na-CN particles.In the meantime,the original cross-network was destroyed gradually while a new soft network dominated by XG with Na-CN particles as infill was rebuilt,and finally the hardness of the system decreased.Secondly,SPI system containing different polysaccharides was studied by the same methods mentioned above.Results showed the phenomenon that swollen SPI particles aggregated and stacked with each other was the main reason for the firmness.GA and CA had little effect to change the hardness of the system.However,the hardness was dramatically decreased in the system added with XG,accompanied by the level of aggregation and the migration going down.Finally,WPI system containing different polysaccharides was studied.Rheometer,CLSM,SEM and LF-NMR were used to evaluate the effects of different polysaccharides on the texture,rheological behavior,microstructure and molecular migration of the system.Results showed the swollen WPI particles tended to collapse and dissolve in the liquid phase during hydration,which caused the hardening level was much lower than Na-CN and SPI system.GA showed no evident effect to the system.In contrast,CA and XG induced the system to form a protein-polysaccharide co-gelation structure due to the synergistic effect between polysaccharides and WPI,which increased the viscoelasticity and hardness.