Browsing by Author "Zhou, Kequan Kevin"
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- Grape Extracts for Type 2 Diabetes Treatment Through Specific Inhibition of α-Glucosidase and Antioxidant ProtectionHogan, Shelly Patricia (Virginia Tech, 2009-04-02)Research was conducted to investigate the effect of phenolic compounds derived from inherently rich antioxidant grape extracts (GE) on α-glucosidase inhibitory activity in vitro and in vivo blood glucose control, oxidative stress, and inflammation associated with obesity-induced type 2 diabetes. Because intestinal α-glucosidase plays a key role in the digestion and absorption of complex carbohydrates, the inhibition of this enzyme is a metabolic target for managing diabetes by improving post-prandial blood glucose control. Initially, red Norton wine grape (Vitis aestivalis) and pomace extracts were evaluated and determined to have notable phenolic content and antioxidant properties. Next, grape skin (GSE) and pomace extract (GPE) were tested and both had in vitro yeast and mammalian α-glucosidase inhibitory activity. The GSE was 32-times more potent at inhibiting yeast α-glucosidase than acarbose, a commercial oral hypoglycemic agent. From HPLC and LC-MS analysis, three phenolics from the GSE (resveratrol, ellagic acid, and catechin) were identified as active inhibitory compounds. The acute administration of GPE (400 mg/kg bw) to mice reduced postprandial blood glucose level by 35% following an oral glucose tolerance test compared to the control. The daily supplementation (250 mg/kg bw) of GSE and GPE for 12-weeks to mice affected fasting blood glucose levels, oxidative stress, and inflammatory biomarkers associated with obesity and type 2 diabetes. At the end of the study, the GSE group gained significantly (P < 0.05) more weight (24.6 g) than the control, high fat, or GPE groups (11.2, 20.2, 19.6 g, respectively). Both GSE and GPE groups had lower fasting blood glucose levels (119.3 and 134.2 mg/dL, respectively) compared to the high fat group (144.6 mg/dL). The 12-week supplementation of GSE was associated with a higher plasma oxygen radical absorbance capacity (ORAC), lower liver lipid peroxidation as measure by TBARS, and lower levels of inflammation as measured by plasma C-reactive protein compared to the high fat group. In conclusion, our collective observations from these studies provide insight into the potential effects of antioxidant rich grape extracts on diabetes-related biomarkers through a dual mechanism of antioxidant protection and specific inhibition of intestinal α-glucosidases.
- Physicochemical and Sensory Properties of Resistant Starch-Based Cereal Products and Effects on Glycemic and Oxidative Stress Responses in Hispanic WomenAigster, Annelisse (Virginia Tech, 2009-09-01)The incidence of type 2 diabetes is considered an epidemic in Western countries, and its prevalence is more common in the Hispanic population than in non-Hispanic whites. Postprandial hyperglycemia has been associated with oxidative stress (OS), thus; reducing postprandial glycemia and/or OS through dietary consumption of resistant starch (RS) may be one approach to help modulate glucose and insulin responses. The purpose of this study was twofold: 1) to evaluate the physicochemical and sensory properties of cereal food products supplemented with RS. 2) to compare the effects of a single ingestion of granola bars with high (~18 grams of RS) and low (~0 grams of RS) RS compositions on the postprandial glucose and insulin responses (n=14) and oxidative stress parameters (cellular glutathione peroxidase, F2- isoprostanes, and oxygen radical absorbance capacity) in Hispanic women (n=9). Granola bars and cereals were developed to provide 2 levels (10% and 15%) of RS; isocaloric (0% RS) control samples were prepared with readily digestible (high amylopectin) starch. Samples were stored for up to 4 weeks at 20 °C. Mean composition of the high RS granola bars was 6% protein, 15% moisture, and 18% lipid. RS levels slightly increased from 14 to 16 g/serving after 4 weeks of storage, supporting published research that RS increases with storage due to retrogradation and crystallization of amylose chains. Color became lighter as the level of RS increased (p<0.001). Granola bars containing RS were less brittle (p=0.0043) than control granola bars. Sensory results indicated granola bars/cereals were acceptable. RS-supplemented granola bars were then used for the evaluation of RS ingestion in humans. There was no difference in postprandial glucose and insulin responses after a single ingestion of a RS-supplemented (18 g) granola bar. No differences were found in the oxidative stress parameters measured. In a subgroup of subjects (n=9), a lower glucose response 30 minutes after RS consumption was found (p=0.0496). Thus, RS consumption may lower fluctuations in blood glucose, which may help manage glucose levels in individuals at risk of type 2 diabetes. Further studies of short term RS consumption are warranted to elucidate its benefits in glucose management.
- Phytochemicals from Graviola fruit selectively inhibit breast cancer cells growth involving EGFR signaling pathwayDai, Yumin (Virginia Tech, 2010-03-30)There is a growing interest in using naturally-occurring compounds as cancer chemopreventive or chemotherapeutic agents. This study investigated the anticancer potential of the graviola fruit extract (GFE) on specific human breast cancer (BC) cells. GFE was found in our preliminary screening to selectively inhibit the growth of certain human BC cells (MDA-MB-468) but did not affect non-transformed breast epithelial MCF-10A cells. GFE treatment was very effective against the growth of MDA-MB-468 BC cells with an IC50 of 4.8 µg/ml. In vitro, effects of GFE treatment on MDA-MB-468 BC cells were further examined for apoptosis and cell proliferation. Apoptosis, determined qualitatively and quantitatively, was enhanced and accompanied by caspase-3 activation. GFE treatment also induced cell cycle arrest at the G1 cell cycle phase and significantly reduced the percentage of MDA-MB-468 cells in S-phase following 24h of exposure. Moreover, the results from analysis of the mRNA expression of epidermal growth factor receptor (EGFR), which plays an important role in regulating cell development and death, by qRT-PCR, suggested that GFE-induced selective growth inhibition of MDA-MB-468 BC cells is associated with a significant inhibition of EGFR gene expression in the cells. In vivo, dietary treatment with GFE significantly inhibited MDA-MB-468 tumor growth implanted in mice by reducing tumor wet weight and significantly reduced EGFR and p-ERK protein expression in tumors. Overall, GFE attenuated cell proliferation, induced apoptosis, modulated cell cycle regulation and downregulated EGFR gene expression both in vitro and in vivo. These discoveries support the further studies to fully elucidate the antitumor potential of GFE and its components as a dietary agent for BC.
- Rheological Properties of Peanut Paste and Characterization of Fat Bloom Formation in Peanut-Chocolate ConfectioneryBuck, Vinodini (Virginia Tech, 2010-04-12)Fat bloom in chocolates is the gray-white discoloration and dullness that can occur on the surface of the confectionery. Fat bloom is a common quality defect that can result from temperature fluctuations during storage. Chocolates candies with peanuts or other nut fillings are more prone to fat bloom compared to plain chocolates, due to a release of incompatible nut oils into the chocolate matrix. The overall goal of this study was to determine if differences in triacylglycerol (TAG) composition and rheological properties of high, medium, and normal oleic peanuts influence fat bloom formation. All three peanut varieties showed high concentrations of triolein. Normal oleic peanuts had a slightly higher trilinolein than high and medium oleic peanuts, which contained trilinolein in trace amounts. Peanut pastes from the three peanut varieties all had a minimum apparent yield stress, and all pastes showed varying degrees of shear thinning. The apparent yield stress of high and normal oleic pastes was higher than the apparent yield stress of medium oleic paste. The absolute value of the flow index behavior was 1 for the high oleic peanut paste, suggesting friction in the experimental apparatus, even with use of Teflon plates. The peanut chocolate candies took around 45 days for significant dulling of the chocolates with temperature cycling between 26-29 °C approximately every 26 hours. Optical microscopy scans showed differences in glossiness and surface textural attributes of the unbloomed and bloomed peanut chocolate confectionery. Consumer evaluation showed some differences in the glossiness and significant differences in surface texture of unbloomed and bloomed chocolates. A majority (62%) of the survey respondents had seen whitish discoloration in chocolates and 40% of the respondents thought this is because the chocolate had grown old.