Rice (Oryza sativa japonica) Albumin Suppresses the Elevation of Blood Glucose and Plasma Insulin Levels after Oral Glucose Loading

Abstract

The suppressive effect of rice albumin (RA) of 16 kDa on elevation of blood glucose level after oral loading of starch or glucose and its possible mechanism were examined. RA suppressed the increase in blood glucose levels in both the oral starch tolerance test and the oral glucose tolerance test. The blood glucose concentrations 15 min after the oral administration of starch were 144 ± 6 mg/dL for control group and 127 ± 4 mg/dL for RA 200 mg/kg BW group, while those after the oral administration of glucose were 157 ± 7 mg/dL for control group and 137 ± 4 mg/dL for RA 200 mg/kg BW group. However, in the intraperitoneal glucose tolerance test, no significant differences in blood glucose level were observed between RA and the control groups, indicating that RA suppresses the glucose absorption from the small intestine. However, RA did not inhibit the activity of mammalian α-amylase. RA was hydrolyzed to an indigestible high-molecular-weight peptide (HMP) of 14 kDa and low-molecular-weight peptides by pepsin and pancreatin. Furthermore, RA suppressed the glucose diffusion rate through a semipermeable membrane like dietary fibers in vitro. Therefore, the indigestible HMP may adsorb glucose and suppress its absorption from the small intestine.

Suppressive Effect of the α-Amylase Inhibitor Albumin from Buckwheat (Fagopyrum esculentum Moench) on Postprandial Hyperglycaemia

“…The oral starch tolerance test (OSTT) and oral glucose tolerance test (OGTT) were conducted according to the methods described by Ina et al [ 21 ] with some modifications. The OSTT and OGTT were carried out under non-anaesthesia conditions.…”

“…Wheat α-AI has already been used as a functional component to suppress the elevation of blood glucose level in Food for Specified Health Uses (FoSHU) in Japan [ 20 ]. On the other hand, rice α-AI has strong resistance to hydrolysis by digestive enzymes and inhibits α-amylase from insects, but does not inhibit that from mammals [ 21 ]. However, we have shown that rice α-AI suppresses blood glucose elevation even after glucose loading, indicating a starch-independent mechanism, such as adsorbing glucose in the small intestine [ 21 ].…”

“…On the other hand, rice α-AI has strong resistance to hydrolysis by digestive enzymes and inhibits α-amylase from insects, but does not inhibit that from mammals [ 21 ]. However, we have shown that rice α-AI suppresses blood glucose elevation even after glucose loading, indicating a starch-independent mechanism, such as adsorbing glucose in the small intestine [ 21 ]. Both wheat and rice α-AIs are water-soluble albumin proteins that are tasteless and odourless and can therefore be included in almost any kind of food.…”

Bioactive Ingredients in Rice (<i>Oryza sativa</i> L.) Function in the Prevention of Type 2 Diabetes

“…RA is a water-soluble protein derived from the endosperm of rice. RA inhibits the absorption of glucose by adsorbing glucose itself, thus suppressing postprandial blood glucose levels (37).…”

Alpha-Amylase Inhibitory Activity of Inhibitor Proteins in Different Types of Commercial Rice

“…The disturbance of these metabolisms is the result of defects in insulin secretion, insulin action or both [2]. This metabolic disorder of multiple aetiology is related to an increased risk of various complications; cardiovascular disease, retinopathy, and nephropathy [3].…”