Nutrition: The Changing Scene

THE GLYCAEMIC RESPONSE TO CARBOHYDRATE FOODS

Consumption of oligosaccharides which can evade host digestive enzymes but can be selectively taken-up by populations of bacteria native to the host colon in situ, improves the gut health of host through various mechanisms. However, their consumption from natural sources is constrained by adequacy, bioavailability and geography. Here in the present review, we detail the enzymatic production and applications of promising multifunctional dietary molecule “isomaltooligosaccharides (IMO)”. Although presently IMO are not considered as dietary fibers (vide FDA-2019-P-2239), these are proven as slowly digestible carbohydrates with multiple food applications and health benefits. Commercially IMO are synthesized using transglycosylating α-glucosidase (tAG) with pretreated starch as the substrate. Usually, the tAG obtained from Aspergillus spp. are widely used to produce IMO. The present review provides comprehensive information on tAG from different sources and their applications. Strategies to increase the transglycosylation to hydrolysis ratio by tAG is of both scientific and commercial interest. Some of the existing strategies to improve this ratio are detailed in this review. This review describes the use and application of IMO in food industry and its potential as functional oligosaccharides. Apart from production strategies, both food applications of IMO and their health benefits are discussed.

Starch digestibility strongly depends on the food composition and microstructure formed during food processing. Identifying the interplay among food ingredients is vital to design starch-based foods with low digestibility. In this work, the effects of native and enzymatic (pepsin and pancreatin) hydrolyzed rice proteins on structural features, enzyme activity and digestibility of cooked rice starch were systematically investigated. All protein and its hydrolysates showed potent abilities in mitigating starch digestion. Native and pepsin hydrolyzed proteins increased starch retrogradation extent and thus increased ordered and aggregated structures of cooked starch. Pepsin-pancreatin hydrolyzed proteins displayed anti-retrogradation activity and decreased starch ordered structures, however, increased V-type inclusion complexes and displayed a potent mixed-type (competitive and non-competitive) inhibitory activity against α-amylase. Based on these findings, it can be concluded that native and pepsin hydrolyzed proteins decreased starch digestibility via increasing ordered structures of cooked starch, while pepsin-pancreatin hydrolyzed proteins mitigated starch digestion by the synergistic effects of V-type structures enhancement and mixed-type suppression activity against α-amylase. The data is of significant to formulate low glycemic health-promoting food products via native or proteolytic proteins complexation.

Rice (Oryza sativa L.) is consumed by more than half of the world's population for whom it is the main source of nutrients and carbohydrates. Rice starch is hydrolyzed by enzymes in the digestive tract and converted into glucose which is the main energy source for metabolic functions. After meeting the energy requirement of the body, the extra calories from starch are stored as glycogen or fats for later use. Therefore, overeating rice with sedentary lifestyle potentially leads to some health problems, such as obesity, type-II diabetes, and colon diseases in long terms especially in Asian countries. Starch hydrolysis begins in the mouth with the action of salivary α-amylase and continues in the small intestine with involvement of other enzymes. However, the resistant starch (RS) which normally comprises < 3% of cooked rice escapes digestion and therefore, its calories are unavailable for use by cells. RSs are categorized into five types based on their mechanism of resistance to enzymatic digestion. Rice contains type 5 RS, wherein amylose forms complex with lipids making it more thermostable. The more the RS, the slower the digestion of rice and the lower is the glycemic index (GI), which is indicative of the ability of food to raise the blood sugar level. The GI of rice is known to be relatively high compared to other starchy foods. It was revealed that increased RS content in rice grain is mediated by soluble starch synthase (SSIIIa), which requires high level expression of granule bound starch synthase (gbssI). In this study, biochemical analysis was done to determine the GI, RS and amylose content (AC) in rice genotypes from different ecologies. Large variation in the value of GI (60.07–70.36), RS (0.35–2.57%) and AC (03.79–23.32%) was observed. Among the genotypes studied, Mahsuri showed lowest GI (60.07) and highest RS (2.57%). The highest value for GI (70.36) was found in Abhishek with relatively low RS (0.83%). O. brachyantha had the lowest RS content (0.35%) with relatively high GI (68.84). A significant negative correlation (R = −0.688) was also observed between GI and RS. Expression analysis of gbssI was carried out in developing grains of three rice genotypes (Mahsuri, Abhishek and Vandana) differing widely in GI, RS and AC. There was dramatic increase in the expression levels of the gene in the middle stage of grain development in all the three genotypes. Maximum expression of the gene was observed in Mahsuri at middle stage showing a positive correlation between RS content and gbssI expression in the rice cultivars studied. These findings emphasize upon the need to identify and develop rice genotypes with high RS, amylose and low GI which may be suitable for consumption by people suffering from diabetes, obesity and colon diseases.

Diabetes, a chronic hyperglycemic disorder, is a public health concern in India. High glycemic carbohydrate foods are linked to higher risk of diabetes. The chemical composition and in vivo glycemic potential of popular Indian rice varieties namely Jaya, Lalat, NDR-97, PR-113, Salivahana, Sasyasree, Savithri, Tellahamsa, Triguna, Varalu and one hybrid DRRH-3, having wide agronomical and grain morphological features were studied. Nutrient composition varied prominently among different varieties. Resistant starch (RS) content (2.03–2.91%) correlated negatively with the glycemic index (GI) (r = −0.674; p ≤ 0.05) and contributed for 45.5% of GI variability. Lalat, an aromatic traditional rice variety, with 2.91% RS and 27.9% amylose was the only one eliciting low GI of 50 and glycemic load (GL) of 13 while the rest exhibited GI ranging from 70 by Savitri to 80 by Salivahana. Identification of Lalat as a low GI variety is of significance in the dietary prevention and management of diabetes.

Diets that have been shown to reduce chronic disease risk focus on increasing intake of foods naturally high in fiber with minimal processing including fruits, vegetables, legumes, and whole grains. Despite evidence for reduced disease burden from both epidemiological and clinical trials, current intake levels of such foods are well below dietary recommendations. Consequently, low intakes of dietary fiber significantly reduce the amount of fermentable substrate available to the gut microbiota as a source of metabolic fuel and likely lead to a less than favorable gut microbial profile. Major end products of gut microbial fermentation of nondigestible and undigested carbohydrates are short chain fatty acids (SCFAs), which have been associated with decreasing the risk of gastrointestinal disorders, cardiovascular disease, and cancer. The ratio of the major SCFAs (acetate, propionate, and butyrate) produced is highly dependent on the chemical composition of the substrate source. A mismatch exists between our archaic genome and gut microbiota, which has evolved primarily on plant-based diets that are high in dietary fiber and fermentable substrate, and our modern diets that contain low intakes of plant-based foods. This deficiency may provide some explanation for the rise in chronic diseases in Western nations. Emerging evidence suggests that interindividual differences in the gut microbiota are influenced by diet (probiotics, prebiotics) or antibiotics and may be linked to variations in physiology, including lipid metabolism that may predispose an individual to risk of certain chronic diseases. Diet is one of the key modulators of gut microbial communities and may provide a tailored approach for optimizing human health.

In this paper, a three-step methodology is proposed for assigning foods with measured glycaemic index (GI) values to GI classes by using the fuzzy c-means classification technique, assigning foods with no measured GI values to GI classes by using the fuzzy pattern recognition technique, and estimating the glycaemic load (GL) values of foods with no measured GI values. In this methodology, the decision rules for menu planning are also defined, and a Linear Programming-based (LP-based) diet model is developed with the objective function of minimizing the total dietary glycaemic load and the constraints of the daily nutritional requirements. An application based on the real data of GI, GL, and nutritional values of the foods is also provided.