Impact of food processing on postprandial glycaemic and appetite responses in normoglycaemic adults: a randomized, controlled trial

Chickpeas are among the lowest glycaemic index carbohydrate food eliciting protracted digestion and enhanced satiety responses. In vitro studies suggest that mechanical processing of chickpeas significantly increases starch digestion. However,...

Nutritional and Physiological Constraints Contributing to Limitations in Small Intestinal Starch Digestion and Glucose Absorption in Ruminants

Increased efficiency of nutrient utilization can potentially be gained with increased starch digestion in the small intestine in ruminants. However, ruminants have quantitative limits in the extent of starch disappearance in the small intestine. The objective is to explore the nutritional and physiological constraints that contribute to limitations of carbohydrate assimilation in the ruminant small intestine. Altered digesta composition and passage rate in the small intestine, insufficient pancreatic α-amylase and/or small intestinal carbohydrase activity, and reduced glucose absorption could all be potentially limiting factors of intestinal starch assimilation. The absence of intestinal sucrase activity in ruminants may be related to quantitative limits in small intestinal starch hydrolysis. Multiple sequence alignment of the sucrase-isomaltase complex gives insight into potential molecular mechanisms that may be associated with the absence of intestinal sucrase activity, reduced capacity for intestinal starch digestion, and limitations in the efficiency of feed utilization in cattle and sheep. Future research efforts in these areas will aid in our understanding of small intestinal starch digestion and glucose absorption to optimize feeding strategies for increased meat and milk production efficiency.

Purification and characterization of actinidin from Actinidia deliciosa and its utilization in inactivation of α-amylase

Background Actinidin is an anionic thiol-proteinase predominant and unique to Chinese gooseberry or kiwifruit, whose strong digestibility enables proteins or enzymes vulnerable to digestion. The arrangement of active cysteine–thiol residues (Cys22-Cys65, Cys56-Cys98, and Cys156-Cys206) stabilizes the catalytic unit, thus allowing an effective Inhibition of α-amylase protein on exposure to the highest concentrations of actinidin under optimum conditions. When starch-rich foods are consumed with kiwifruit, starch digestion may be slowed by the inactivation of α-amylase (digestive enzyme), specifically reducing the blood sugar levels by hindering starch digestion that is helpful in diabetes mellitus. Thus, the study aimed at actinidin purification, optimization for maximal activity, and its demonstration as a potential to degrade α-amylase. Results Protease showed a molecular mass of 27 kDa on SDS-PAGE analysis. One factor at a time method was applied for process optimization, increasing the actinidin yield up to 176.03 U/mg. The enzyme was stable at a wide pH range; however, it was most active and stable at pH 7.5. The enzyme possessed half‐life at 35 °C of 5.5 h, at 40 °C of 4.5 h, at 45 °C of 2.5 h, and at 50 °C of 1 h. Lineweaver–Burk plot showed Michaelis–Menten constant (Km: 3.14 mg/ml) and maximal velocity (Vmax: 1.428 mmol/ml/min) using casein. The actinidin activity was enhanced with Ca2+ while it was inhibited by Cd2+ and Hg2+ ions. The α-amylase protein was successfully inactivated upon incubation with actinidin for 30 min; around ~ 85% of the α-amylase activity diminished. IC50 for inhibition of α-amylase was 2.54 mg/ml for crude actinidin and 1.86 mg/ml for purified actinidin. Conclusions Purified Actinidin showed a 1.28-fold increase in proteolytic activity. The proteinase showed an active pH range of 3.5–8.5 under varied buffer conditions and thermostability up to 50 °C. The results revealed a significant potential utility of actinidin to retard amylase as it effectively degraded the amylolytic enzyme under in vitro conditions and could be beneficial for lowering glycemic response to ingested starch. However, further in vitro as well as in vivo studies need to be conducted under gastrointestinal conditions to establish the hypothesis.

Inhibitory Effect of Ascorbic Acid on in vitro Enzymatic Digestion of Raw and Cooked Starches

Ascorbic acid, also known as vitamin C, was previously reported to inhibit the activity of pancreatic α-amylase, the primary digestive enzyme for starch. A major implication of such inhibition is a slowed rate of starch digestion into glucose, which thereby reduces postprandial hyperglycemia. The aim of this study was to explore the inhibitory effects of ascorbic acid at various concentrations on the in vitro digestion of high amylose maize starch (HAMS) and potato starch (PS) in both raw and cooked conditions. Resistant starch (RS) content, defined as the starch that remained after 4 h of simulated in vitro enzymatic digestion, was measured for the starch samples. Upon the addition of ascorbic acid, the RS contents increased in both raw and cooked starches. Cooking significantly reduced the RS contents as compared to raw starches, and less increase in RS was observed with the addition of ascorbic acid. The inhibitory effect of ascorbic acid on the digestion of raw starches showed a dose-dependent trend until it reached the maximum extent of inhibition. At the concentrations of 12.5 and 18.75 mg/mL, ascorbic acid exhibited the most potent inhibitory effect on the in vitro starch digestion in raw and cooked conditions, respectively. Overall, our results strongly indicate that ascorbic acid may function as a glycemic modulatory agent beyond other important functions, and its effects persist upon cooking with certain concentrations applied.

Texture and Digestion Properties of Cooked Rice and Rice Noodles

Rice varieties high in amylose content have low glycemic and insulin responses. Rice noodles are processed by extrusion from high amylose content rice, which may also have low glycemic and insulin responses. In this study, cooked rice and rice noodles processed from two high amylose content cultivars, Guangluai4 (GL4) and Zhenguiai (ZGA), were chosen for in vitro starch digestion evaluation. Apparent amylose content of cultivars (i.e., GL4-28.4% and ZGA-26.8%) and pasting properties except final viscosity were significantly different between the cultivars. In vitro starch digestion results showed that the glucose production rate in rice noodles was significantly slower than that in cooked rice by 65.7% and 42.0% in GL4 and ZGA, respectively. The main reason for low glucose production in rice noodles was active digestion duration longer in rice noodles than in cooked rice, which reflects the slow release of glucose during starch digestion. The texture of rice noodles in the GL4 and ZGA cultivars is 3 and 2.3 times harder than that of cooked rice, respectively. Thus digestive enzymes can hardly enter the interior of rice noodles for amylolysis. As a result, the digestion time of rice noodles is longer, and the release of glucose during digestion is slower than that of cooked rice. The slower release of glucose during rice noodle digestion may be beneficial for prolonging satiety and reducing food intake. Consequently, eating rice noodles may help in improving or preventing diabetes and obesity over time.