| As an important plateau cereal crop with high bioactive compounds and nutritional value,highland barley(HB)is suitable for making cookies due to its low content of gluten protein as well as high contents of dietary fiber and lysine.However,the presence of dietary fiber was also disadvantageous for the taste of whole HB products.Additionally,the different milling methods can influence the physicochemical properties and nutritional composition of HB flour(HBF),which will affect the quality of cookies.The physical modification technical means represented by extrusion modification can change the structure of food components and improve the quality of cereal products.Therefore,this study aims to investigate the effects of different milling methods on the physicochemical properties and nutritional characteristics of the HBF,and explore the correlation between the flour properties and sugar-free cookie qualities by evaluating the quality characteristics of sugar-free cookies.Aiming at the more drastic extrusion modification methods,the effects of various conditions(temperature,moisture)on the physicochemical properties and nutritional value of HBF as well as the multi-scale structure of starch were studied to investigate the relationship between starch structure and the its properties.This study aims to elucidate the correlation between the properties of HB products-flour-multi-scale structure by analyzing the quality of whole HB sugar-snap cookies made with added back,providing a theoretical foundation for improving the process of HBF production and developing in products.The main research results were summarized as follows:1.The four kinds of HBF were prepared via different milling methods(hammer mill,multi-purpose grinding,ultra-centrifugal grinding and superfine grinding,flour yield ranged from 89 to 99%.The effects of various milling methods on the physicochemical properties of HBF(such as microstructure,particle size,damaged starch,pasting and rheology)were studied.The results indicated that the ultra-centrifugal grinding sample had the highest content of damaged starch(35.07%)and β-glucan(5.65%),the brightness(87.89),water absorption(8.65 g/g)and swelling power(10.62 g/g)as well as the lowest whiteness index(15.89),water solubility index(18.60/100 g),pasting viscosity and gel strength.Meanwhile,the superfine grinding sample had the highest soluble dietary fiber(SDF,8.25%)and the lowest mean particle size.The multi-purpose grinding sample showed the largest mean particle size as well as the highest pasting viscosity and gel strength.The content of damaged starch(28.17%),β-glucan(4.70%),total(19.85%)and soluble dietary fiber(6.80%)in multi-purpose grinding sample was the lowest.The study indicated that different milling methods played a significant role on the physicochemical properties of HBF.The choice of milling method should be selected based on the quality requirements of the HB product.2.HB was subjected to dry-,semidry-,wet-milling methods and assessed for flour physicochemical properties and eating quality of corresponding sugar-free cookies.Results showed that there were significant differences between different milled flours in damaged starch content,particle size,hydration,pasting properties,and color.High a* values and poor hydration/pasting properties of wet-milled flours were associated with its smallest particle size and lowest content of damaged starch(25.3%),β-glucan(1.87%),and dietary fiber(10.87%),resulting in dark brown color,slightly high spread ratio,low hardness,and fast digestibility of the corresponding cookies.Conversely,the low digestibility of the cookies(predicted glycemic index58.85)prepared from dry-milled flours was attributed to the higher content of dietary fiber,β-glucan and V-type starch-lipid complex,which would affect enzyme accessibility.Dry-,semidry-,wet-milling have significant effects on the physicochemical properties of HBF and the edible quality of its corresponding cookies.Considering the production efficiency,convenience of operation and edible quality of cookies,the HBF prepared by dry milling is more suitable for processing into cookies.3.The effects of extrusion modification technology on physicochemical properties,nutritional properties and starch multi-scale structure of HBF under different temperature and water were studied.The results showed that the extrusion modification technology significantly changed the properties of HBF.The water absorption index(WAI),swelling power,gelatinization degree,a*,b*,whiteness value and initial viscosity were significantly increased,while the water solubility index and pasting parameters were significantly decreased,which indicated that extrusion enhanced the cold gel viscosity and retrogradation resistance properties of HBF.For 105℃ extrusion samples,the peak viscosity increased with the decrease of moisture(the highest increase was 86.21%).The nutritional value of the modified HBF(MHBF)were significantly increased by extrusion modification(soluble dietary fiber and β-glucan contents increased by 24.05% and 19.85%,respectively),and the starch granules and crystal structure were seriously damaged(the relative crystallinity decreased 57.28%).Moreover,with the increase of temperature and moisture,more the longer branch chains(B1 and B2 chains)in starch were sheared into shorter branch chains(A chains).In addition,extrusion treatment also promoted partial amylose leaching,forming more starch-lipid complex.4.Three MHBF(30-105/40-85/50-65/ moisture-temperature)were added back to prepare whole HB sugar-snap cookies.The quality and sensory evaluation of the cookies prepared by these flour with different additions(5/10/15%)were investgated.The results showed that the backfiling of different MHBF and its readdition amount had significant effects on the quality,structure and sensory evaluation of cookies.The WAI of 30-105 and 40-85 was higher,which resulted in the diameter and diffusion ratio of cookies decreasing,while the trend of 50-85 was opposite.The backfilling of MHBF further darkened the color of the cookies.The insoluble dietary fiber and gelatinized starch of 30-105 was higher,which increased the cookies hardness.The part of 40-85 and 50-65 insoluble dietary fiber was converted into soluble dietary fiber,reducing cookies hardness.Moreover,the isomaltolose in the formula competitively absorbed the water in the cookies with the starch,inhibiting the starch granules gelatinization and leaving A-type crystal structure partly preserved.Meanwhile,the butter in cookies also formed starch-lipid complexes with the starch.The cookies with 50-65 had the highest overall acceptability. |
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