Analysis Of The Effect Of Product Form On The Digestive Properties Of Starch In Highland Barley And Its Mechanism

Highland barley is a kind of cash crop with high nutritional value,and a further study on the starch digestive properties of highland barley will help the development and utilization of highland barley resources.At present,there are various forms of highland barley products,but the effects of structural state and gelatinization moisture on starch digestion of different forms of highland barley products are not well studied.Based on this,this study analyzed the composition and starch multi-layer structure of different varieties of highland barley with reference to unpolished rice and oat,and investigated the influence of composition and starch structure on the starch digestive properties of highland barley flour.This study also investigated the influence of different degrees of milling and cell wall structure changes on the starch gelatinization and digestion of highland barley kernels,and investigated the influencing mechanism of highland barley kernel structure on starch digestion.The gelatinization systems of high and low moisture were constructed to investigate the digestive properties of starch in highland barley flour under different gelatinization moisture conditions.The main research contents and results are as follows:The composition,starch structure and in vitro starch digestibilities of six varieties of white,blue and black highland barley flour from Qinghai and Tibet were comparatively analyzed.Theβ-glucan content（3.35 g/100 g～5.59 g/100 g）of highland barley was higher than that of oat,and the amylose content（18.34 g/100 g～21.55 g/100 g）and protein content（8.30 g/100 g～10.34g/100 g）of highland barley were higher than that of unpolished rice,the starch crystallinity（28.82%～35.17%）and R_1047/1022 value（0.59～0.73）of highland barley were lower than oat and unpolished rice.The six varieties of highland barley flour all had high starch digestibilities（88.17%～93.62%）,which were less different from unpolished rice flour and oat flour.The microstructure of gelatinized and digested samples was observed by scanning electron microscopy（SEM）,and it was found that gelatinized highland barley flour formed a denser network structure than unpolished rice flour and oat flour,probably due to the non-starch components such asβ-glucan and protein wrapping around starch during gelatinization.However,the structure was unstable and broken during digestion.Therefore,the differences in chemical composition and starch structure of highland barley flour had no significant effect on starch digestive properties.The digestive properties of starch in highland barley kernels were investigated.It was shown that the starch digestibilities of the chyme broken from cooked highland barley were54.95%～68.65%,which was significantly lower than unpolished rice（89.70%）and oat（75.29%）chyme.Different degrees of grinding promoted the water absorption of highland barley kernel during the cooking process and the starch digestion of highland barley chyme.Furthermore,the enthalpy changes of kernel slices were measured by differential scanning calorimetry（DSC）,which showed that the enthalpy change of highland barley kernel slice（1.13 J/g）was significantly lower than that of unpolished rice（1.89 J/g）and oat（2.54 J/g）,indicating that the disordered degree of the molecular chain of highland barley endosperm starch was lower.Combining fluorescence staining,confocal laser microscopy（CLSM）and SEM to analyze the kernel structure of highland barley and its changes during the cooking process.It was found that compared with unpolished rice and oat,the bran of highland barley kernel was thicker,the cell accumulation was denser,and the stability of the bran and endosperm cell walls was stronger.These effectively inhibited the deformation of the kernel and the expansion of starch particles during cooking.During the digestion process,the cell walls in highland barley chyme also had a stronger inhibitory effect on amylase.The digestive properties of starch in highland barley flour with different moisture gelatinization were investigated.The starch digestibilities of highland barley gelatinized with15%and 20%water contents（28.89%and 33.05%）were significantly lower than that of unpolished rice（76.83%and 83.72%）and oat flour（45.61%and 55.59%）gelatinized under the same conditions.The starch digestibility of highland barley flour gelatinized with 60%moisture was close to the unpolished rice flour and oat flour.The heavy average molecular weight of the hydrolysate fragments was determined by the gel chromatography,and it was found that the heavy average molecular weight of the small hydrolysate fragments of highland barley gelatinized with 20%moisture content was 44.88×10⁴ g/mol（digestion of 20 min）,which was much higher than that of unpolished rice（too small to be detected）and oat（0.17×10⁴ g/mol）.These results suggested that the low moisture gelatinized highland barley flour had a more significant advantage against enzymatic digestion.The analysis of starch ordered structure and surface characteristics of highland barley flour gelatinized with different moisture contents showed that compared with unpolished rice and oat,the starch crystallinity and helical structure contents of highland barley flour gelatinized with 15%and 20%moisture contents were lower.The SEM observation and polysaccharide probe（the size was close to amylase）penetration study revealed that the starch granule surface morphology of highland barley flour gelatinized with 15%and 20%moisture contents was more complete and difficult penetration of polysaccharide probe than unpolished rice and oat,suggesting that the slow digestion of highland barley flour gelatinized with low moisture was mainly due to the barrier of starch granule surface that effectively hindered the digestion of amylase.Thus,the product form had an important influence on the digestive properties of starch in highland barley,and this study provided a theoretical basis for the in-depth development of functional foods from highland barley.