Date of Award

12-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Food Technology

Committee Member

Dr. Feng Chen, Committee Chair

Committee Member

Dr. Jun Luo

Committee Member

Dr. Anthony Pometto III

Committee Member

Dr. Nishanth Tharayil

Abstract

Muscadine grapes (Vitis rotundifolia) have attracted consumers because of their unique flavors and high concentrations of bioactive phytochemicals. The aim of this study was to investigate the effects of ripening stages (i.e., stage I, II, and III) of muscadine on physiochemical properties, volatile organic compounds (VOCs), and phenolic compounds in the grapes, and explore the enzymatic inhibitory effects of the muscadine extracts and some of its inherent phenolics on some important enzymes, such as angiotensin-I-converting enzyme (ACE), pancreatic lipase (PL), tyrosinase, collagenase and elastase, relevant to human chronic diseases. Physiochemical properties of the muscadine grapes were evaluated in order to understand the biological changes of the grapes during the ripening progress. Significance differences (p ≤ 0.05) were observed in regards of the size, weight, pH, total soluble solid, sugar content and titrable acidity of the muscadine grapes during their 3 ripening stages. The berry size, berry weight, and titrable acidity decreased after the stage II, whereas °Brix, pH, sugar content continuously increased through the whole ripening stages up to the stage III. Twenty eight VOCs were detected by headspace solid phase microextraction (HS-SPME) coupled to a gas chromatography-mass spectrometry (GC-MS). The grapes in the stages I and II had relatively similar flavor patterns, which were different from that in stage III. The principal component analysis (PCA) indicated that butyl-2-buetenoate, hexyl acetate, propyl acetate, ethyl trans-2-butenoate, hexyl-2-butenoate, ethyl acetate, butyl acetate, 1-octanol, ethyl hexanoate, and β-citral were present as distinct volatile chemicals in the stage III, which usually result in the fruity, floral, and pleasant aromas. Phenolic compounds (e.g., epicatechin, epicatechin gallate, resveratrol, and myricetin, etc) at three ripening stages were determined using a high-performance liquid chromatography coupled with diode array detector (HPLC-DAD). In addition, antioxidant activities of the muscadine extracts and identified major phenolics were determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-Azino-Bis-3-Ethylbenzothiazoline-6-Sulfonic Acid (ABTS). Total phenolic content (TPC) and total flavonoid content (TFC) decreased along with the ripening stages, while the antioxidant activities were enhanced through the ripening stages. With regard to the phenolic compounds, the concentrations of phenolic compounds were significantly different in three ripening stages. Most bioactive phenolic compounds, except myricetin and quercetin, consistently increased along with the ripening stages. The study of enzymatic inhibitory activities of ACE, pancreatic lipase, tyrosinase, collagenase and elastase demonstrated that the muscadine extracts, regardless of their ripening stages, and the selected phenolics (i.e., epicatechin, epicatechin gallate, resveratrol, and myricetin, etc) exerted their enzymatic inhibitions in a competitive inhibition model against all the aforementioned enzymes. The results indicated that the muscadine grapes possessed the strong anti-hypertension, anti-obesity and anti-skin disease activities. Furthermore, it was found that the extraction of anthocyanin was the most efficient at pH 3.0, which accompanied with a greater antioxidant activity. To quantify anthocyanidins in the muscadine grapes, the extracted anthocyanins were hydrolyzed under acidic conditions that were optimized at 100 °C for 60 minutes. The samples extracted from muscadine grapes at pH 3 and pH 5 showed similar anthocyanidin profiles with high concentrations of delphinidin and cyanidin, which are relatively unstable chemicals that are unfavorable for making muscadine juice or wine.

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