Zhang Genyi, Sofyan Maghaydah, Hamaker Bruce R
School of Food Science and Technology, Jiangnan University, Wuxi 214122, Jiangsu Province, People's Republic of China.
J Agric Food Chem. 2008 Jun 25;56(12):4695-702. doi: 10.1021/jf072823e. Epub 2008 May 31.
The mechanism underlying the previously reported parabolic relationship between amylopectin fine structure, represented by the weight ratio of linear short chains [degree of polymerization (DP < 13) to long chains (DP >/= 13], and slowly digestible starch (SDS) content was investigated from the viewpoint of starch retrogradation and substrate susceptibility to enzyme hydrolysis. A maize mutant sample, termed "highest long-chain starch" (HLCS) representing group I samples with a higher proportion of long chains, showed a bell-shaped SDS pattern with retrogradation time, whereas insignificant changes in SDS were found for the sample termed "highest short-chain starch" (HSCS) representing group II samples with a higher proportion of short chains. This corresponded to results from X-ray powder diffraction and differential scanning calorimetry that showed a rapid increase of crystallinity and enthalpy for HLCS during retrogradation, but negligible changes for sample HSCS. Therefore, retrogradation was associated with SDS content for group I samples, but not for group II samples. Analysis of amylopectin fine structure, SDS content, retrogradation enthalpy, SDS material debranching profile, and hydrolysis pattern demonstrated, for group I samples, that linear branched chains of DP 9-30 of amylopectin may act as anchor points to slow the digestion of branced-chain fractions of DP > 30, which constitute the major slowly digestible portion, whereas for group II samples, it is the inherent molecular structure of amylopectin with a higher amount of branches and shorter chains that is not favorable for rapid enzyme digestion. The concept of a slowly digestible starch state (SDS state) that could be a chemical or physical entity is proposed to better describe the mechanistic underpinning of the slow digestion property of starches.
从淀粉回生和底物对酶水解的敏感性角度，研究了此前报道的支链淀粉精细结构（以线性短链[聚合度（DP<13）与长链（DP≥13）的重量比表示]与慢消化淀粉（SDS）含量之间抛物线关系的潜在机制。一个玉米突变体样本，称为“高长链淀粉”（HLCS），代表长链比例较高的I组样本，其SDS模式随回生时间呈钟形，而对于代表短链比例较高的II组样本“高短链淀粉”（HSCS），SDS变化不显著。这与X射线粉末衍射和差示扫描量热法的结果一致，即HLCS在回生过程中结晶度和焓迅速增加，而HSCS样本变化可忽略不计。因此，回生与I组样本的SDS含量相关，而与II组样本无关。对支链淀粉精细结构、SDS含量、回生焓、SDS物质脱支谱和水解模式的分析表明，对于I组样本，支链淀粉聚合度为9 - 30的线性支链可能作为锚点，减缓聚合度>30的支链部分的消化，而这部分构成了主要的慢消化部分；而对于II组样本，是支链淀粉具有较多分支和较短链的固有分子结构不利于酶的快速消化。提出了慢消化淀粉状态（SDS状态）这一概念，它可能是一种化学或物理实体，以更好地描述淀粉慢消化特性的机制基础。
