Investigating glycemic potential of rice by unraveling compositional variations in mature grain and starch mobilization patterns during seed germination

Abstract

Rice lines with slower starch digestibility provide opportunities in mitigating the global rise in type II diabetes and related non-communicable diseases. However, screening for low glycemic index (GI) in rice breeding programs is not possible due to time and cost constraints. This study evaluated the feasibility of using in vitro cooked grain amylolysis, starch mobilization patterns during seed germination, and variation in starch structure and composition in the mature seed to differentiate patterns of starch digestibility. Mobilization patterns of total starch, resistant starch, amylose and amylopectin chains, and free sugars during seed germination revealed that the process is analogous to digestion in the human gastrointestinal tract. The combination of these biochemical markers can be used as an alternative measure to predict GI. Additionally, transcriptome analysis of stored mRNA transcripts in high and low GI lines detected differences in starch metabolism and confirmed the importance of seed storage pathways in influencing digestibility. Pathway analyses supported by metabolomics data revealed that resistant starch, cell wall non-starch polysaccharides and flavonoids potentially contribute to slower digestibility. These new insights can guide precision breeding programs to produce low GI rice with acceptable cooking quality to help mitigate the burden of diet-associated lifestyle diseases.

Integrating a genome‐wide association study with a large‐scale transcriptome analysis to predict genetic regions influencing the glycaemic index and texture in rice

“…It appears that the low GI rice varieties favoured the carbon sink for NSPs related to the cell wall residues in endosperm that can potentially reduce digestibility (Lafiandra et al ., ; Topping and Clifton, ). An intact cell wall with higher dietary fibre upon cooking is known to lower the in vitro digestion of legumes (Dhital et al ., ), and a similar mechanism might exist in rice (Butardo et al ., ; de Guzman et al ., ). NSP is well‐known contributor to dietary fibre (Tungland and Meyer, ) and is important in lowering the GI of food.…”

“…The consumption of such rice is associated with a sudden increase in blood glucose levels. Hence, alterations in the starch structure to lower digestibility can provide a slow and steady supply of energy while significantly lowering the GI (Butardo et al ., , ; de Guzman et al ., ). Generally, brown rice has an intermediate GI (Atkinson et al ., ) that increases when polished to white rice (Karupaiah et al ., ).…”

A Review of Rice Starch Digestibility: Effect of Composition and Heat‐Moisture Processing

“…Regardless of rice starch granule size and crystallinity, long chain amylopectin content is negatively correlated with in vitro starch digestibility and positively correlated with RS . Medium chain amylopectin content is not correlated with starch digestibility or negatively correlated with RDS content while short chain amylopectin content is positively correlated with starch digestibility . The degree of amylopectin branching is positively correlated with in vitro rice starch digestion rate .…”

“…The increased swelling of amorphous region results in side‐by‐side dissociation of amylopectin double helices followed by immediate unwinding of helix to coil structure . Coiled amylopectin long chains hold water and increase starch swelling while amylose leaches from the granules . Double helices may form between leached amylose in a cross‐linked network which may hinder the entry of water for further swelling .…”

“…Starch digestion is responsible for post‐prandial blood glucose concentration and an elevated post‐prandial glucose concentration for extended periods is linked with obesity, metabolic syndrome including insulin resistance and diabetes mellitus, and cardio‐vascular disorders . Rice starch digestibility is affected not only by the type of starch and its physicochemical properties and processing, but by non‐starch components . However, this effect depends on the interaction among the components, especially the interaction between starch and non‐starch components in a food matrix, which can be further altered by processing.…”