The molecular structural features controlling stickiness in cooked rice, a major palatability determinant

Abstract

The stickiness of cooked rice is important for eating quality and consumer acceptance. The first molecular understanding of stickiness is obtained from leaching and molecular structural characteristics during cooking. Starch is a highly branched glucose polymer. We find (i) the molecular size of leached amylopectin is 30 times smaller than that of native amylopectin while (ii) that of leached amylose is 5 times smaller than that of native amylose, (iii) the chain-length distribution (CLD: the number of monomer units in a chain on the branched polymer) of leached amylopectin is similar to native amylopectin while (iv) the CLD of leached amylose is much narrower than that of the native amylose, and (v) mainly amylopectin, not amylose, leaches out of the granule and rice kernel during cooking. Stickiness is found to increase with decreasing amylose content in the whole grain, and, in the leachate, with increasing total amount of amylopectin, the proportion of short amylopectin chains, and amylopectin molecular size. Molecular adhesion mechanisms are put forward to explain this result. This molecular structural mechanism provides a new tool for rice breeders to select cultivars with desirable palatability by quantifying the components and molecular structure of leached starch.

Comparison of textural properties and structure of gels prepared from cooked rice grain under different conditions

“…The estimation of relationship between solubilized starch content and gel hardness showed that solubilized starch and amylose contents were negatively correlated with the compressive force for rice gels on day 0 under most preparation conditions. On the other hand, the relationship between the molecular structure of solubilized starch and cooked rice texture has been reported elsewhere Li, Fitzgerald, Prakash, Nicholson, and Gilbert (2017). The leachedout starch, mainly amylose, plays a major role in forming a gel network with the swollen granules embedded in the matrix (Mei-Lin,Chin-Fung, & Cheng-Yi, 1997),and Orford, Ring, Carroll, Miles, and Morris (1987) reported that reducing the amount of solubilized amylose would lead to a softer gel.…”

Drought‐Proofing Barley (Hordeum vulgare): The Effects of Stay Green on Starch and Amylose Structure

“…Although the SEC results show that SG expression has a relatively small impact on starch structure, its effect on grain processing and product quality should be investigated in greater detail, because the CLDs of amylopectin and amylose are significant determinants of starch properties such as starch gelatinization, crystallinity, and so on, which in turn affect functional properties such as mouth-feel (Li et al 2016(Li et al , 2017, malt quality, germination, and brewing. Identifying what impact drought-stress tolerance expression has on grain quality is of interest.…”

“…Changes to the amylose/amylopectin ratios, such as increasing amylose content, can negatively impact on starch properties such as gelatinization temperature and fermentability. Although the SEC results show that SG expression has a relatively small impact on starch structure, its effect on grain processing and product quality should be investigated in greater detail, because the CLDs of amylopectin and amylose are significant determinants of starch properties such as starch gelatinization, crystallinity, and so on, which in turn affect functional properties such as mouth-feel (Li et al 2016(Li et al , 2017, malt quality, germination, and brewing. Maintaining consistent starch structure and functional properties under various stress conditions will result in optimal end-product quality.…”

Molecular structures and properties of starches of Australian wild rice

“…Both amylose content and the amylose and amylopectin fine structures influence this characteristic of cooked rice grains (Li et al, 2017;Li et al, 2016;Syahariza et al, 2013;Zhang, Venkatachalam & Hamaker, 2006). There is more rapid digestion in samples with more long amylose branches and a smaller relative amount of long (trans-lamellar) to short (single lamellar) amylopectin branches, as well as a smaller relative amount of long amylose branches to short amylopectin branches.…”

“…Gelatinization properties have been found to be controlled predominantly by the amylopectin chain length distribution (CLD: the number of chains as a function of their degree of polymerization, DP: the number of glucose monomer units in the chain), starch composition (such as amylose content, phosphorus, lipids, protein, and enzyme), granule architecture (crystalline to amorphous ratio), and crystalline polymorphism. Amylose content often has little impact on the gelatinization properties (Noda, Takahata, Sato, Suda, Morishita, Ishiguro & Yamakawa, 1998;Wang, Henry & Gilbert, 2014), but the amylose CLD influences some important functional properties such as digestion rate and sensory properties (mouth-feel) (Li, Fitzgerald, Prakash, Nicholson & Gilbert, 2017;Li, Prakesh, Nicholson, Fitzgerald & Gilbert, 2016;Syahariza, Sar, Tizzotti, Hasjim & Gilbert, 2013). Amylopectin structure also influences sensory properties such as hardness (Li et al, 2016).…”