| Potatoes,an important staple food in horticultural product,is mainly composed of starch.In recent years,colored potatoes are widely planted.But by now,the researches on colored potatoes focused on anthocyanins and other functional components.The effect of physicochemical properties and amylopectin fine structure of colored potato starch on food quanility haven’t been paid attention.Thus,it is important to study the physicochemical properties,the structure properties,and the relationship between structure and properties of potato starch for guiding the deep development of potato products.In this study,starches from red,purple and yellow-fleshed potatoes were selected as the research object.The physicochemical properties,structure features of starch and fine structure of amylopectin were studied,and the changes in the physicochemical properties and structures of acid modified potato starches were studied too.The main results are as follows:1.The phosphorus content of yellow,red and purple potato starch were 0.1301%,0.1519%and 0.1473%,respectively.The amylose content of yellow,red and purple potato starch were 25.23%,20.26%and 23.30%,respectively,and showed significant differences.The physicochemical properties of the three potato starches were significantly different.The apparent viscosity of red and purple potato starch were higher than yellow potato starch,because of the higher ratio of BI chains in red and purple potato amylopectin and the higher ratio of long B-chains in their φ,β-limit dextrins.The freeze-thaw stability of red and purple potato starch were superior to that of yellow potato starch,which was attributed to the red and purple potato amylopectin had higher ratio of B3 chains,and shorter average external chain length of their φ,β-limit dextrins.Moreover,the clarity of yellow potato starch was significantly lower than red and purple potato starch,because of the longer average external chain length of φ,β-limit dextrins in yellow potato amylopectin.2.The d(0.5)of yellow,red and purple potato starch granules were34.88,39.12 and 41.39μm,respectively.The granules of three potato starches had smooth surfaces,didn’t present difference in morphology,and exhibited obvious growth rings.Red and purple potato starch granules displayed more obvious birefringence.Three potato starches all belonged to B-type crystalline structure,and the crystallinity of yellow,red and purple potato starches were 20.33%,22.25%and 21.70%,respectively.The Mw and A/B ratio of yellow potato starch were 4.279×106 g/mol and 0.24,respectively;the Mw and A/B ratio of red potato starch were 8.806×106 g/mol and 0.23,respectively;and the Mw and A/B ratio of purple potato starch were 1.138×107 g/mol and 0.29,respectively.The difference in the ratio of long/short chains among the three saples was not obvious.3.The average DP of yellow,red and purple potato starches were 24.31,17.95 and 25.01,respectively,and the proportion of Afp chain were 12.01,5.21 and 9.73,respectively.The propotion of long chains in yellow and purple potato amylopectin was significantly higher than that of red potato amylopectin.4.The structure analysis of building blocks from φ,β-limit dextrins of cluster in amylopectin revealed that:The Mw of φ,β-limit dextrins of cluster from yellow,red and purple potato amylopectin were 3.06×1045 1.48×104 and 1.74×104 g/mol,respectively.The distribution pattern of Bfp chain in φ,β-limit dextrins from cluster in amylopectin was different,the ratio of Bfp chain in yellow,red and purple potato starches were 58.01%,63.60%and 60.78%,respectively.The ratio of B2 chains is relatively low,the ratio of B2 chain in yellow,red and purple potato starches were 0.61%,0.51%and 0.56%,respectively,and B3 chains decreased to 0.00%·The average external chain length of yellow and purple potato amylopectin were 21.63 and 22.29,respectively,which was larger than red potato amylopectin(15.01).The density of branches of yellow,red and purple amylopectin were 23.39,21.41 and 22.70,respectively,showed notable differences,and yellow potato amylopectin presented highest density of branches.The degree of polymerization of building blocks of φ,β-limit dextrins in cluster from yellow,red and purple potato amylopectin were 13.43,11.28 and 12.02,respectively,and the degree of branching were 16.75%,14.71%and 15.64%,respectively.5.The structure analysis of building blocks of φ,β-limit dextrins from amylopectin suggested that:the Mw of φ,β-limit dextrins from yellow,red and purple potao amylopectin were 4.32×104,3.24×104 and 5.65×104 g/mol,respectively,which was higher than the Mw of φ,β-limit dextrins from cluster in amylopectin.The molar percentage of Bfp chains in φ,β-limit dextrins from yellow,red and purple potato amylopectin were 53.02%,54.18%and 51.56%,respectively.The B3 chains of φ,β-limit dextrins from yellow poato amylopectin reduced to 0.00%,but the B3 chains of φ,β-limit dextrins from red and purple poato amylopectin were 5.74%and 8.07%,respectively.Compared to the φ,β-limit dextrins from cluster of amylopectin,the ratio of BL chains and the average internal chain length of φ,β-limit from amylopectin was higher.The density of branches and average external chain length of three potato amylopectin samples also presented significant differences,yellow potato amylopectin had highest density of branches and external chain length.The degree of polymerization of building blocks of φ,β-limit dextrins from yellow,red and purple potato amylopectin were 15.01,14.65 and 14.92,respectively,which was higher than that of building blocks of φ,β-limit dextrins from cluster in amylopectin.6.The structure analysis of building blocks in cluster suggested that:The degree of polymerization of building blocks in cluster from yellow,red and purple potato amylopectin were 16.03,16.18 and 15.25,respectively,which was higher than that of building blocks from φ,β-limit dextrins of cluster in amylopectin and building blocks of φ,β-limit dextrins from amylopectin.The number of chain of building blocks in cluster from yellow potato amylopectin was highest,up to 3.70,followed by red(3.68)and purple(3.62).The building blocks in cluster from purple potato amylopectin had the highest degree of polymerization,which wasl7.18.7.The results of fine structure analysis of three potato amylopectin with four methods showed that analysis of chain length distribution of amylopectin and analysis of structure ofφ,β-limit dextrins in amylopectin and its building blocks can better explain the differences of physicochemical properties among the three potato starch samples,and can summarize the influence rule of fine structure of amylopectin on the properties of starch.8.Three kinds of potato starch were treated with 2.2 N hydrochloric acid solution at 35℃.The three potato starches all presented two-phase hydrolysis patterns.Red potato starch presented the highest acid hydrolysis rate.It because that red potato amylopectin had higher ratio of short chain,resulting in its high sensibility to acid.The lintner granules were eroded and destroyed by acid hydrolysis,and the particle size of potato lintners was much smaller than the native starch.In addition,the birefringence disappeared from some granules.After acid treatment,sharp-edged cracks from the hilum towards the borders in the Iintners were observed,and the contrast between the amorphous and semicrystalline layers within the starch granules became subtle.The lintnerized starch samples retained the B-type crystal,but the relative crystallinity significantly increased compared to native starch.Moreover,the degree of short-range order of starch decreased after acid hydrolysisthe,and the molecular weight and Rz of lintnerized starches decreased.The branch-chain length distribution of the potato lintners before and after debranching was similar.Compared to native potato starches,the viscosity of potato lintners significantly decreased,the solubility and paste clarity of lintners got significantly improved.Therefore,compared with the native starch,lintners had different industrial application fields. |
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