Comparison Of Flour And Starch Characteristics And Related Gene Sequences Between Sweet And Grain Sorghum Varieties

Grain sorghum(Sorghum bicolor L.Moench)is important for the economy of semi-arid regions since it thrives and produces both grain and forage under conditions that cause other crops to fail.The worldwide interest about sweet sorghumgoes towards stem sugar,but little has been focused on its grain.In present study,four grain genotypes and eight sweet genotypes were subjected to chemical composition and physicochemical characterization of flour and starch from grains using different chemical composition and physicochemical parameters like protein content,starch content,amylase content and others.Besides,the sequence diversity of several key genes involving in starch and protein biosynthesis was analyzed and compared.The main results are as followings.1.Comparison of physicochemical characterization of grain flour.The flour was firstly prepared from clean seeds by dry milling and sieving.The results showed that amylose content(AC)for some sweet varieties had high value(YT,27.01%)as well as that of grain varieties(GL-1,27.19%).Total phenolic of some sweet varieties was high(GL-4 and T-1,0.3%)and others was low(GL-6,0.18%).On the other hand,grain varieties exhibited moderate values.Most of grain varieties showed thick gel and high protein content compared with sweet varieties.Total starch varying among all varieties ranged from 40.40%for TAT(a grain variety)to 82.6%for GL-13(a sweet variety).For pasting properties,all of the grain varieties located lower and clotted together in the RVA curve viscogram.Peak viscosity(PKV)showed a range from 569.0 cP for a grain variety GL-1 to 2143.0 cP(centipoises)for sweet variety GL-13.Sweet varieties exhibited higher values than grain varieties.Breakdown viscosity(BDV)for sweet varieties was noticed higher(23.0 to 227.0)from grain ones(307.0 to 837.0).The lowest value for Peak temperature(PT)among grain varieties(83.7℃ for ARG)ranked higher than seven of eight of sweet varieties.Peak time(Pt)for all varieties showed range from 4.1 min to 5.8min for a sweet variety GL-6 and a grain variety GL-1,respectively.The Pt means of sweet varieties(5.13min)slightly lower than that of grain varieties(5.53min).The range for setback viscosity(SBV)was from 405.0 cP to 1475.0 cP for GL-4 and ST,respectively.SB for grain varieties showed range from 638.0 cP to 904.0 cP.On the other hand three of eight of sweet varieties showed SB values higher than the highest value of grain varieties(904.0 cP for WAH).The range for final viscosity(FV)was from 1207.0 cP to 2963.0 cP and clearly significant difference was noticed between sweet and grain types.For thermal properties parameters:To,Tp and Tc(Onset,peak and conclusion temperatures,respectively)grain varieties showed higher degrees than that of sweet varieties.In general,the sweet varieties studied in general showed a low grain quality which renders their uses as food.Taking togather,among the parameter studies,we prove that the protein content,pasting properties and thermal properties are clearly differentiated between grain and sweet varieties.2.Comparison of physicochemical characterization of grain starch.Starch was isolated from polished grain by an alkaline protease method from sweet and grain sorghum varieties,and their physical,chemical and morphological properties were carefully pursued.The results showed that amylose content from sweet varieties(average 23.52%)was found significantly(p<0.05)lower than that of grain ones(average 35.61%).The vast range of AC observed in the current study will make sorghum of interest for starch industries.For thermal properties of starch there had been significant difference(p<0.05)among all varieties for DSC parameters studied.The highest degrees for enthalpy of gelatinization(△H)appeared from starch isolated from sweet varieties indicate existence of high level of the starch chain intra-molecular bond.For water solubility index(WSI)starch trom sweet varieties ranked top,whereas grain varieties ranked top for swelling power(SP).WSI for all varieties showed range from 10.0-95.0%,and SP showed range from 3.0-20.0g/g.Differences shown in WSI and SP probably attributed to the amylose to amylopectin ratio together with differences shown for morphological structure of starch granules.The starches from both sweet and grain varieties exhibited A-type crystalline pattern,further the relative crystallinity(RC)showed range from 15.340%to 25.14/%.Sweet varieties studied exhibited RC significantly(p<0.05)higher than grain varieties.The data from 13CNMR reflected little pattern differences for C1(contains information about both crystalline and non crystallinenon-crystalline nature)and C4 resonance between sweet and grain varieties for appearance of peaks and shoulders.Gel Permeation Chromatography(GPC)was used for investigation of chains-length distribution(CLD)of debranched starch from both sweet and grain varieties.A tri-modal of peaks for CLD was observed(fourth peak was not shown from some varieties)and designated as peakl,peak2 and peak3,respectively.Peakl and peak2 refer to amylopectin(AP)fraction representing the short branch-chains(A and short B chains)and long branch-chains(long B chains),respectively while peak3 refers to amylose(AM)fraction.Peakl showed that short chains are the major group and exhibited range from 36.81 to 76.02%,while Peak2 showed range from 11.96 to27.22%.The branching degree(BD)of AP(peakl/peak2)was from 2.00 to 3.96%and showed significant(P<0.05)differences between sweet and grain varieties.Scanning Electron Microscope(SEM)investigation for starch granules from sweet and grain varieties showed polygonal or spherical in shape without clear differences between them.The starch granules surface of sweet sorghum was smooth with some dents,while that for grain was smooth without appears of dents.The granules diameters of both sweet and grain varieties starch showed range from 13.35-15.67um.Starch granule size of sweet varieties was found significantly(p<0.05)larger than grain varieties.Sweet varieties GL-6 and GL-4 ranked top among all varieties(15.67 and 15.49um,respectively)in spite of they showed the lowest AC%(6.71%and 5.39%,respectively).Starch isolated from grains was free of protein and fat,therefore amylose content determinate from starch sample showed values higher than that from flour sample.3.Preliminary analysis of sequence diversity of key genes involving in starch and protein biosynthesis.Starch and protein are well known as important food components in cereals,including sorghum.Several genes previously reported to play a key role in the biosynthesis of these two components in sorghum were adopted for current study.A little differences of the tested genes were detected between sweet and grain varieties.Wx allele with very low amylose content was not detected,but some varieties like ARG and ZS include Wx gene in heterozygous status.Different SNPs and InDels were detected especially for genes Sh2,Bt2 and 02.Association between different S:NPs and Lamda-kafrin gene had been noticed from some varieties like TAT,YT and T-1,respectively.