Cultivar evaluation and effect of fermentation on antioxidant capacity and in vitro inhibition of α-amylase and α-glucosidase by highbush blueberry (Vaccinium corombosum)

Anthocyanins from fermented berry beverages inhibit inflammation-related adiposity response in vitro

Increased adiposity has been associated with macrophage infiltration into the adipose tissue which, in turn, leads to obesity comorbidities, including type 2 diabetes. The objective of this study was to evaluate the effect of anthocyanin (ANC)-enriched fractions from blackberry-blueberry beverages on inflammation and adipogenesis in an in vitro model of inflammation mimicking the pathologic interaction between adipocytes and macrophages. Blend ANCs inhibited secretion of nitric oxide (17.5%), tumor necrosis factor-alpha (TNF-α) (89.4%), and phosphorylated-p65 nuclear factor kappa-B (52.1%) in lipopolysaccharide (LPS)-induced RAW264.7 macrophages after 24 h. Blends reduced intracellular fat accumulation (28.2%) when applied during 3T3-L1 adipocyte differentiation and inhibited isoproterenol-induced lipolysis (18.6%) of mature 3T3-L1 cells. In addition, blend ANCs restored adiponectin-blunted gene expression induced by the TNF-α treatment (18.2%) and reduced the glycerol release (15.9%) induced by LPS-induced macrophage-conditioned media (CM) in adipocytes. Furthermore, blends slightly restored the insulin-induced glucose uptake of adipocytes, blunted by the CM treatment. In conclusion, ANCs from blueberry and blackberry dealcoholized fermented beverages are potential inhibitors of inflammation-related adiposity response and sensitizers of insulin signaling in adipocytes.

In vitro inhibitory effect on digestive enzymes and antioxidant potential of commonly consumed fruits

Dietary inhibitors of fats and carbohydrates degrading enzymes can reduce obesity and type 2 diabetes. In this study, we screened crude extracts from 30 commonly consumed fruits to test their in vitro inhibitory effect against key enzymes relevant for obesity (pancreatic lipase) and type 2 diabetes (α-glucosidase and α-amylase), total phenolic content (Folin-Ciocalteu method), and antioxidant capacity (ABTS and FRAP). The IC50 values of the fruits tested varied from 39.91 to >400 mg/mL, from 1.04 to >80 mg/mL, and from 0.72 to 135.07 mg/mL against α-glucosidase, α-amylase, and pancreatic lipase, respectively. Antioxidant capacity ranged from 0.66 to 124.66 μmol of TE/g of fruit and strongly correlated with phenolic content, while the enzyme inhibition was poorly correlated with total phenolic and antioxidant capacity. Among fruits tested, blue honeysuckle and red gooseberry exhibited the highest inhibitory activity with respect to the carbohydrate degrading enzymes, while lingonberry had the strongest anti-lipase activity.

Effect of fermentation on the antioxidant activity in plant-based foods

This study provides an overview of the factors that influence the effect of fermentation on the antioxidant activity and the mechanisms that augment antioxidative activities in fermented plant-based foods. The ability of fermentation to improve antioxidant activity is primarily due to an increase in the amount of phenolic compounds and flavonoids during fermentation, which is the result of a microbial hydrolysis reaction. Moreover, fermentation induces the structural breakdown of plant cell walls, leading to the liberation or synthesis of various antioxidant compounds. These antioxidant compounds can act as free radical terminators, metal chelators, singlet oxygen quenchers, or hydrogen donors to radicals. The production of protease, α-amylase and some other enzymes can be influenced by fermentation that may have metal ion chelation activity. Because the mechanisms that affect antioxidant activity during fermentation are extremely varied, further investigation is needed to establish the precise mechanisms for these processes.

Antioxidant and enzyme inhibitory activities of blueberry anthocyanins prepared using different solvents

We compared the biological activities of anthocyanins prepared from whole blueberries or pomace and extracted with acetone, ethanol, and methanol. Crude Amberlite extracts (CAE) and rehydrated powders of freeze-dried anthocyanins were used. Ethanolic CAE yielded the highest total monomeric anthocyanin content [TMAC] (160 ppm), ferric reducing antioxidant power [FRAP] (3.4 mM Fe(2+)), total phenolics content [TPC] (382 ppm gallic acid equivalents [GAE]), and α-amylase inhibitory activity (36.8%). The rehydrated powder from acetonic extract gave the greatest FRAP (5.19) and TPC (422.7). α-Amylase (26.1%) and α-glucosidase (91.5%) inhibitory activities were also sustained. Methanolic CAE yielded values intermediate between ethanolic and acetonic extracts. Comparison of mass spectra between Amberlite extracts and rehydrated preparations revealed putative degradation and dimerization products in the rehydrated powders, which could account for loss in biological activities for rehydrated methanolic and ethanolic powders. Results of this study provide useful information in optimizing anthocyanin preparation methods for improved biological activity.

Intake of Blueberry Fermented by Lactobacillus plantarum Affects the Gut Microbiota of L-NAME Treated Rats

Prebiotics, probiotics, or synbiotics can be used as means to regulate the microbiota to exert preventative or beneficial effects to the host. However, not much is known about the effect of the gut microbiota on hypertension which is a major risk factor of cardiovascular disease and also a symptom of the metabolic syndrome. The N^G-nitro-L-arginine methyl ester (L-NAME) induced hypertensive rats were used in order to test the effect of a synbiotic dietary supplement of Lactobacillus plantarum HEAL19 either together with fermented blueberry or with three phenolic compounds synthesized during fermentation. The experimental diets did not lower the blood pressure after 4 weeks. However, the fermented blueberries together with live L. plantarum showed protective effect on liver cells indicated by suppressed increase of serum alanine aminotransferase (ALAT) levels. The diversity of the caecal microbiota was neither affected by L-NAME nor the experimental diets. However, inhibition of the nitric oxide synthesis by L-NAME exerted a selection pressure that led to a shift in the bacterial composition. The mixture of fermented blueberries with the bacterial strain altered the caecal microbiota in different direction compared to L-NAME, while the three phenolic compounds together with the bacteria eliminated the selection pressure from the L-NAME.

Berries reduce postprandial insulin responses to wheat and rye breads in healthy women

Starch in white wheat bread (WB) induces high postprandial glucose and insulin responses. For rye bread (RB), the glucose response is similar, whereas the insulin response is lower. In vitro studies suggest that polyphenol-rich berries may reduce digestion and absorption of starch and thereby suppress postprandial glycemia, but the evidence in humans is limited. We investigated the effects of berries consumed with WB or RB on postprandial glucose and insulin responses. Healthy females (n = 13-20) participated in 3 randomized, controlled, crossover, 2-h meal studies. They consumed WB or RB, both equal to 50 g available starch, with 150 g whole-berry purée or the same amount of bread without berries as reference. In study 1, WB was served with strawberries, bilberries, or lingonberries and in study 2 with raspberries, cloudberries, or chokeberries. In study 3, WB or RB was served with a mixture of berries consisting of equal amounts of strawberries, bilberries, cranberries, and blackcurrants. Strawberries, bilberries, lingonberries, and chokeberries consumed with WB and the berry mixture consumed with WB or RB significantly reduced the postprandial insulin response. Only strawberries (36%) and the berry mixture (with WB, 38%; with RB, 19%) significantly improved the glycemic profile of the breads. These results suggest than when WB is consumed with berries, less insulin is needed for maintenance of normal or slightly improved postprandial glucose metabolism. The lower insulin response to RB compared with WB can also be further reduced by berries.

Antioxidant and α-glucosidase inhibitory phenolics isolated from highbush blueberry flowers

Blueberries have been extensively researched, but there are limited studies on other parts of the plant. Here we report the first phytochemical examination of highbush blueberry (Vaccinium corymbosum) flowers, which yielded 21 phenolics. The compounds were identified from extensive NMR and mass spectral analyses and included five caffeic acid (1-5), three coumaric acid (6-8), and two cinnamyl alcohol (9-10) derivatives, eight flavonol glycosides (11-18), and three phenylpropanoid-substituted catechins (19-21). The isolates were evaluated for antioxidant and α-glucosidase inhibitory activities. Overall, the flavonol glycosides and phenylpropanoid-substituted catechins showed superior antioxidant activities compared to the positive controls, vitamin C (IC(50)=63μM) and butylated hydroxytoluene (IC(50)=1548μM). Similarly, these phenolic sub-classes were more potent α-glucosidase inhibitors than the clinical drug, acarbose (IC(50)=200μM). Thus, non-consumed parts of food plants may be exploited as sources of bioactive compounds beyond their edible parts alone for nutraceutical and functional food applications.

Postprandial glucose, insulin, and free fatty acid responses to sucrose consumed with blackcurrants and lingonberries in healthy women

BACKGROUND

Sucrose induces high postprandial glucose and insulin responses. In vitro studies suggest that berries may reduce the digestion and absorption of sucrose and thereby suppress postprandial glycemia, but the evidence in humans is limited.

OBJECTIVE

We investigated the effects of sucrose ingested with blackcurrants (Ribes nigrum) and lingonberries (Vaccinium vitis-idaea) on postprandial glucose, insulin, and free fatty acid responses.

DESIGN

Twenty healthy women participated in a randomized, controlled, crossover meal study. They consumed whole blackcurrants or lingonberries (150 g served as purées) or blackcurrant or lingonberry nectars (300 mL), each with 35 g added sucrose. Sucrose alone (35 g in 300 mL water) was used as a reference. Blood samples were collected at 0, 15, 30, 45, 60, 90, and 120 min.

RESULTS

In comparison with sucrose alone, ingestion of sucrose with whole berries resulted in reduced glucose and insulin concentrations during the first 30 min and a slower decline during the second hour and a significantly improved glycemic profile. Berries prevented the sucrose-induced late postprandial hypoglycemic response and the compensatory free fatty acid rebound. Nearly similar effects were observed when sucrose was consumed with berry nectars. The improved responses were evident despite the higher content of available carbohydrate in the berry and nectar meals, because of the natural sugars present in berries.

CONCLUSIONS

Blackcurrants and lingonberries, as either whole berries or nectars, optimize the postprandial metabolic responses to sucrose. The responses are consistent with delayed digestion of sucrose and consequent slower absorption of glucose.

Strawberries, blueberries, and cranberries in the metabolic syndrome: clinical perspectives

Emerging science supports therapeutic roles of strawberries, blueberries, and cranberries in metabolic syndrome, a prediabetic state characterized by several cardiovascular risk factors. Interventional studies reported by our group and others have demonstrated the following effects: strawberries lowering total and LDL-cholesterol, but not triglycerides, and decreasing surrogate biomarkers of atherosclerosis (malondialdehyde and adhesion molecules); blueberries lowering systolic and diastolic blood pressure and lipid oxidation and improving insulin resistance; and low-calorie cranberry juice selectively decreasing biomarkers of lipid oxidation (oxidized LDL) and inflammation (adhesion molecules) in metabolic syndrome. Mechanistic studies further explain these observations as up-regulation of endothelial nitric oxide synthase activity, reduction in renal oxidative damage, and inhibition of the activity of carbohydrate digestive enzymes or angiotensin-converting enzyme by these berries. These findings need confirmation in future studies with a focus on the effects of strawberry, blueberry, or cranberry intervention in clinical biomarkers and molecular mechanisms underlying the metabolic syndrome.

Antidiabetic effects of natural plant extracts via inhibition of carbohydrate hydrolysis enzymes with emphasis on pancreatic alpha amylase

INTRODUCTION

The increasing prevalence of type 2 diabetes mellitus and the negative clinical outcomes observed with the commercially available anti-diabetic drugs have led to the investigation of new therapeutic approaches focused on controlling postprandrial glucose levels. The use of carbohydrate digestive enzyme inhibitors from natural resources could be a possible strategy to block dietary carbohydrate absorption with less adverse effects than synthetic drugs.

AREAS COVERED

This review covers the latest evidence regarding in vitro and in vivo studies in relation to pancreatic alpha-amylase inhibitors of plant origin, and presents bioactive compounds of phenolic nature that exhibit anti-amylase activity.

EXPERT OPINION

Pancreatic alpha-amylase inhibitors from traditional plant extracts are a promising tool for diabetes treatment. Many studies have confirmed the alpha-amylase inhibitory activity of plants and their bioactive compounds in vitro, but few studies corroborate these findings in rodents and very few in humans. Thus, despite some encouraging results, more research is required for developing a valuable anti-diabetic therapy using pancreatic alpha-amylase inhibitors of plant origin.