Green tea (GT), cranberry (CR), and tart cherry extracts were evaluated for their ability to inhibit yeast alpha-glucosidase, relevant to glucose uptake. The total phenolic content (TPC), antioxidant activity, and in vitro inhibitory activity of yeast alpha-glucosidase were examined for the extracts in the present study. GT had higher TPC and antioxidant activity, but CR demonstrated a greater alpha-glucosidase inhibitory activity, on phenolic basis. CR was fractionated using LH-20 column chromatography into two fractions: 30% methanol (CME) and 70% acetone (CAE). TPC, antioxidant activity, and yeast alpha-glucosidase inhibitory activity were determined for the fractions. CAE had a greater TPC and antioxidant activity than CME, but the two fractions had a synergistic effect when inhibiting yeast alpha-glucosidase. Our findings suggest that CR has the greatest potential to possibly manage post-prandial blood glucose levels via the inhibition of alpha-glucosidase, and that the effect is through synergistic activity of the extract's phenolic compounds.

Dietary polyphenols are abundant antioxidants in the human diet and are associated with lower rates of diabetes and cardiovascular disease. This study aims to determine the effects of cooking white rice (WR) added with lingonberry (WRLB), cranberry (WRCB), and red grape (WRRG) on in vitro digestibility. There was significantly lower level of glucose release for WRRG compared with WR (p0.05). WRLB and WRCB showed no effect on glucose release compared with WR (p>0.05). Increasing concentrations of red grape polyphenol decreased digestibility of white rice (p0.05). A positive correlation between the red grape phenolic content and the resistant starch was observed (R=0.9854). Red grape polyphenol had the greatest impact on reducing in vitro digestibility of white rice. The addition of polyphenols in carbohydrate-rich foods may be a practical means to reduce the high glycemic response of rice eaten around the world.

Proanthocyanidins and ellagitannins, referred to as "tannins", exist in many plant sources. These compounds interact with proteins due to their numerous hydroxyl groups, which are suitable for hydrophobic associations. It was hypothesized that tannins could bind to the digestive enzymes -amylase and glucoamylase, thereby inhibiting starch hydrolysis. Slowed starch digestion can theoretically increase satiety by modulating glucose "spiking" and depletion that occurs after carbohydrate-rich meals. Tannins were isolated from extracts of pomegranate, cranberry, grape, and cocoa and these isolates tested for effectiveness to inhibit the activity of -amylase and glucoamylase in vitro. The compositions of the isolates were confirmed by NMR and LC/MS analysis, and tannin-protein interactions were investigated using relevant enzyme assays and differential scanning calorimetry (DSC). The results demonstrated inhibition of each enzyme by each tannin, but with variation in magnitude. In general, larger and more complex tannins, such as those in pomegranate and cranberry, more effectively inhibited the enzymes than did less polymerized cocoa tannins. Interaction of the tannins with the enzymes was confirmed through calorimetric measurements of changes in enzyme thermal stability.

Protein glycation caused by sugars and reactive carbonyls is a contributing factor to diabetic complications, aging, and other chronic diseases. The objective of this study was to investigate the inhibitory effects of cranberry phytochemicals on protein glycation. Cranberries, purified to yield sugar-free phytochemical powder, were fractionated into ethyl acetate and water fractions. Water fraction was further separated into water fraction I, II, and III on a Sephadex LH-20 column. Cranberry phytochemical powder and its fractions significantly inhibited the formation of glycated hemoglobin. The concentrations of cranberry phytochemicals required to inhibit 50% of albumin glycation (EC(50)) in albumin-glucose assay were lower than that of aminoguanidine except for water fraction I. Cranberry phytochemicals inhibited glycation of human serum albumin mediated by methylglyoxal, but the EC(50) were higher than that of aminoguanidine. Carbonyl scavenging assay showed that water fraction II scavenged 89.3% of methylglyoxal at 6 h of reaction. Fractions enriched with procyanidins showed higher antiglycation activities, suggesting procyanidins were the major active components. The hypothesis whether cranberry procyanidins scavenged reactive carbonyls by forming adducts was tested. Epicatechin was used as a model compound to react with methylglyoxal and glyoxal at pH 7.4. Five adducts were detected and their structures were tentatively identified using HPLC-ESI-MS/MS.

Aqueous solutions of two different cranberry powders (CP and CP-SAB) were evaluated for organic acids, sugars, total phenolics, antioxidant activity based on the 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay, and functionality such as in vitro inhibition of -amylase, -glucosidase, and angiotensin I-converting enzyme (ACE) relevant for potential management of hyperglycemia and hypertension linked to type 2 diabetes. The total phenolics content was 11 and 51 mg/g of sample dry weight for CP and CP-SAB, respectively. p-Coumaric acid and quercetin derivatives were the main phenolic compounds identified in the cranberry powders. CP-SAB had -glucosidase inhibitory activity that increased with increased dose (1-5 mg/mL) from 60% to 100% inhibition. There was limited amount of -amylase inhibitory activity that reached a maximum of 40% inhibition at 5 mg/mL treatment. Significant ACE inhibitory activity was detected for CP-SAB at 100 and 200 mg/mL sample concentrations. These in vitro results indicate the potential of cranberry powders as dietary supplement and food-based strategies for potential hyperglycemia management. This biochemical rationale provides the basis for further design of animal and clinical studies using standardized extracts.