Guar gum enhances nutritional profile of hydrothermally treated rice by reducing glycaemic response

A recent study reveals that applying guar gum to hydrothermally treated rice optimises digestion and visual integrity, offering a promising avenue for healthier rice options with lower glycaemic impact.

Hydrocolloids can do more than alter rice texture; they can also change how quickly starch is digested. In this study, hydrothermally treated rice was compared with untreated grain to see how different gums affected kernel appearance, eating quality and estimated glycaemic impact. The results suggest that guar gum was the most useful compromise, reducing starch digestibility while preserving kernel integrity better than some alternatives, including xanthan gum, which produced a stickier but more damaged grain structure.

Hydrothermal treatment alone already improved the nutritional profile of the rice. Compared with native grain, the treated sample showed lower estimated glycaemic index, less rapidly digestible starch and more resistant starch. The treatment appears to have encouraged limited starch leaching during heating, followed by reorganisation during tempering and drying into a more enzyme-resistant surface layer. That is consistent with earlier research showing that hydrothermal processing can reduce starch digestibility in rice and related cereal products.

Adding hydrocolloids during the mild-heating stage changed the picture further, but not uniformly. Xanthan gum had the strongest thickening effect and produced the greatest surface coating, but it also damaged kernel integrity after cooking and raised hardness as well as adhesiveness. By contrast, guar gum and locust bean gum increased stickiness without making the cooked rice harder, although guar gum was clearly the more effective of the two at lowering digestibility. Carrageenan had the smallest effect overall. The pattern fits wider food-science findings that hydrocolloids can work by limiting water movement, coating grain surfaces and changing how readily enzymes reach starch.

Among the gums tested, guar gum stood out because it reduced the estimated glycaemic index more than the other non-xanthan options while keeping the rice visually more coherent after cooking. The report found that a 0.3% guar gum treatment gave the best balance: it lowered digestibility, raised resistant starch and increased adhesiveness without the firmer, more disruptive texture seen at higher levels. A 0.5% dose pushed adhesiveness further, but at the cost of clumping and a less appealing cooked appearance, with only a small extra gain in digestibility control.

The concentration study reinforced that point. As guar gum levels rose, the cooked kernels became progressively less transparent before cooking and more coated afterwards, suggesting stronger retention on the grain surface. That in turn was associated with lower starch hydrolysis. Yet the relationship was not linear. Once a surface layer had formed, higher concentrations delivered diminishing returns on glycaemic effect while worsening stickiness. In practical terms, the middle dose again appeared most promising.

The findings also sit comfortably with recent work on other hydrocolloids and starch systems. Studies on rice structured with gellan gum, emulsions and dry-heated starch have similarly shown that altering the food matrix can slow amylolysis and shift starch towards more slowly digestible or resistant fractions. The broader message is that hydrocolloids can be selected not only for texture, but also for how they shape starch behaviour during digestion. Even so, the present results remain instrumental rather than sensory, and the true acceptability of the treated rice would still need to be confirmed by tasting panels.