Effects Of Drying On Physicochemical And Nutrition Properties Of The Steamed Highland Barley

Highland barley,distributed in high-altitude area in Western China,is traditionally used to make the daily staple food as Zanba for Tibetan people.At present,the processing method of highland barley is relatively simple,the edible area is limited,and the added value is relatively low.Therefore,this study used Tibetan white highland barley as experiment material to explore the effects of drying on the physicochemical properties and nutritional profiles of the steamed whole highland barley flour,with the aim to enrich the processing methods of highland barley.The effect of drying on the microstructure of steamed whole highland barley starch by scanning electron microscopy and microscopy.Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,differential scanning calorimetry（DSC）and rapid viscosity analysis（RVA）were used to study the effects of drying on the short-range molecular ordering,crystallization,thermal properties and gelatinization of steamed whole highland barley starch.Simulated in vitro system was used to study the effects of drying on digestion and fermentation characteristics of the steamed whole highland barley flour.The whole highland barley flour was reconstituted with the high gluten wheat flour to make highland barley noodles.The quality of noodle was evaluated by dough rheology,cooking characteristics,texture characteristics,and sensory evaluation.The main conclusions were as follows:（1）The surface of raw highland barley starch is smooth,with large round A-shaped and small oval B-shaped particles.Steaming and drying caused damage to the highland barley starch particles to a certain extent and the polarization cross gradually disappeared.The particle size distribution of raw highland barley starch showed two distribution peaks,the first particle size distribution peak disappeared after steaming and drying,and both D^[3,2]and D^[4,3]both increased significantly,while D^[3,2]decreased significantly with increasing drying temperature.The solubility and oil holding capacity of whole highland barley flour decreased and the swelling power and water holding capacity increased significantly.The relatively crystallinity was reduced by steaming and drying in highland barley.However,the relative crystallinity was decreased with the increased temperature of drying.The A-type diffraction pattern was changed into the V-type,indicating the formation of starch-lipid or starch-protein-lipid complexes after steaming and drying.The short-range molecular order structure of natural drying（ND）,hot air drying at 50℃（HD50℃）,hot air drying at 70℃（HD 70℃）,and hot air drying at 90℃（HD 90℃）highland barley starch decreased significantly.The peak viscosity,valley viscosity,and final viscosity decreased with the increased drying temperature.DSC showed that the raw highland barley starch had a gelatinization peak around 70℃,while no gelatinization peak was presented in samples after steaming and drying treatment.Steaming and drying significantly reduced the content of starch,protein,fat,soluble dietary fiber,solubleβ-glucan,and soluble pentosan content.In this study,the proportion of free polyphenols was significantly higher than that of bound polyphenols.After steaming,the drying condition and temperature has a significant effect on the content of free polyphenols.Compared with the raw whole highland barley flour,the content of free polyphenols in ND whole highland barley flour has no obvious change,while decreased slightly of HD50℃whole highland barley flour and HD 70℃whole highland barley flour,only decreased significantly of HD 90℃whole highland barley flour（2）Steaming and drying promotes the release of free amino acids and in vitro starch hydrolysis rate of the whole highland barley flour.During the pepsin digestion stage（0～120 min）,there was no difference in the released amount of free amino acids.In the trypsin digestion stage（120～240 min）,the release of free amino acids in the first 30 min increased more rapidly.At the end of digestion stage,the release of free amino acids was as follows:HD 50℃whole highland barley flour（5.18 g/100g Pro）>ND whole highland barley flour（4.38 g/100g Pro）>HD70℃whole highland barley flour（3.77 g/100g Pro）>HD 90℃whole highland barley flour（3.06 g/100g Pro）.Steaming and drying significantly increased the content of RDS（rapidly digestible starch）and SDS（slowly digestible starch）of whole highland barley flour,but significantly decreased the content of RS（resistant starch）.Compared with ND whole highland barley flour,the RDS of HD90℃whole highland barley flour increased by 14%,RS decreased by 54%.The trend of starch hydrolysis profiles was generally consistent between 0～180 min.When the starch was digested for 180 min,the starch hydrolysis rate of raw highland barley flour was only44.19%.The starch hydrolysis rate of steaming and drying whole highland barley flour was higher than that of raw highland barley,and it increases stepwise.The initial p H value of the fermentation system was 8.47～8.93.With the progress of fermentation,the p H value decreased gradually.At 12 h of fermentation,the p H value basically tended to equilibrium until the end of fermentation,which was closely related to the concentration of SCFAs（short chain fatty acids）produced by in vitro fermentation.Acetic acid was the most abundant SCFA,followed by propionic acid,and a small amount of valeric acid and butyric acid.The total SCFAs concentration of all fermentation systems increased with the progress of fermentation,and Raw-R is higher than ND-R,HD 5-R,HD 7-R,and HD9-R.This phenomenon existed in the whole fermentation period,and it is the most significant at 12 h of fermentation.Overall,the production of SCFAs will be reduced after heat treatment.（3）Dough and noodles properties were altered by reconstitution of the barley flour with wheat flour.In the frequency scanning process,the elastic modulus G’of all dough samples was greater than the viscous modulus G’’,and all increased with the frequency,was all less than 1.Both the G’and G″modulus of the highland barley dough was greater than that of the Control group,while the G’and G″modulus of the steaming and drying high barley flour dough was higher than those of the Raw-N dough.Highland barley noodles had a higher optimum cooking time,cooking loss and lower cooking yield than the Control group.The TPA test showed that the hardness of the noodles was not changed significantly.The shearing work and breaking force of the highland barley flour noodles did not change significantly,while the shearing force increased slightly,and the breaking distance decreased significantly.The microstructure of the cross section of the noodles showed that the gluten network structure could be formed evenly after addition of highland barley flour and the noodles had a compact structure.Therefore,the addition of30%whole highland barley flour not only had a minor influence on noodles quality but also can improve the dietary fiber content of noodles.