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Antioxidant and antimicrobial activities of muscadine grape extracts

The objective of this research was to investigate the antioxidant and antimicrobial activities of muscadine grape extracts. Three different cultivars of muscadine grapes including Higgings, Jumbo, and Noble were selected. The skin/pulp and seed parts of three selected muscadine grape cultivars were used for extraction. The total phenolic contents of muscadine grape extracts were expressed as gallic acid equivalents (GAE). The antioxidant activity of muscadine grape extracts were determined by scavenging activity of diphenylpicrylhydrazyl (DPPH) radical and expressed as effective concentration (EC50), which represented the concentration of the extract exhibiting 50% DPPH radical scavenging. The antimicrobial activity against E. coli K12 was determined and expressed as the minimum inhibition concentration (MIC). The seed extracts exhibited greater total phenolic contents than the skin/pulp extracts, ranging from 231.24 to 294.81 mg/mL GAE. The seed extracts exhibited greater antioxidant activities than the skin/pulp extracts (EC50 of Higgins seed extract=0.026 mg/mL). However, the skin/pulp extracts exhibited greater antimicrobial activities than the seed extracts, exhibiting the minimum inhibition concentration (MIC) in Higgins skin/pulp extract (MIC=4.0 mg/mL). This research indicated that the seed part and skin/pulp parts of the muscadine grapes possessed antioxidant activity and antimicrobial activity, respectively. Therefore, it was concluded that muscadine grapes possess the potential to be utilized as functional foods or nutraceuticals.

. Naturally occurring antimicrobial agents in foods may be desirable alternatives to replace synthetic preservatives food products.
Muscadine grapes (V itis rotundifolia) are one type of grape varieties grown in the south and southeastern areas of the United States (3). Due to the unique tastes and flavors, muscadine grapes are more often consumed as fresh table fruits, rather than as grape juice or muscadine wines (4).
The production and utilization of muscadine grapes are limited to the cotton-belt areas of the southeastern United States, primarily due to the necessity of a moderate climate condition.
In addition, since muscadine grapes have a relatively shorter storage periods compared to grapes, muscadine grapes were sold locally. Thus, the nutritional information and health benefits of muscadine grapes have not been publicized (4).
The major antioxidant compounds in muscadine grapes include monomeric procyanidin compounds such as (+)-catechines, However, compared to the extensive research on antimicrobial activity of other grapes, the antimicrobial activities of muscadine grapes are not well investigated. The information on the antimicrobial activities of muscadine grapes as well as the antioxidant activities will benefit the growers and consumers, and increase the production and consumption of the muscadine grapes. Therefore, the main objective of this research was to determine the antioxidant and antimicrobial activities of selected muscadine grape cultivars.

Materials
Three cultivars of muscadine grapes were selected, including Extraction of muscadine grape A portion of 1,500 g of each fresh muscadine grape cultivar was weighed and freeze-dried. The seeds were separated from the dried pulp and skin after freeze-drying. The dried skin/pulp and seed parts were ground and powdered using a blender. The muscadine extraction was performed following the protocols for the grape seed extraction developed by

Results and Discussion
The total phenolic contents in muscadine seed extracts exhibited approximately four-fold greater contents than the total phenolic contents in skin/pulp extracts (Table 1) Gallic acid, catechin, and epicatechin are believed to be the major phenolic compounds in muscadine grape seeds (16).
Yilmaz and Toledo (8) detected greater amounts of gallic acid in muscadine grape seeds than the amounts in other grape seeds. Different letters (a, b, and c) reflect significant differences at p<0.05.
The muscadine seed extracts from the tested cultivars exhibited significant greater free radical scavenging activities than the muscadine skin/pulp extracts (p<0.05), resulting in approximately two-fold greater percentages of scavenging activities than the skin/pulp extracts ( Table 2). A similar trend in antioxidant activity among selected parts was observed in effective concentration (EC 50 ). Jayaprakasha et al. (12) reported that the scavenging activities of grape seed extracts Greater scavenging activities in seed extracts than in skin/pulp extracts were expected based on greater total phenolic contents in seed extracts than in skin/pulp extract.
Extensive studies also reported greater antioxidant activities in grape seed parts than in other selected parts such as skin, pulp, or leaves (4,8,10,14).   Different letters (a, b, c, and d) reflect significant differences at p<0.05.
The antimicrobial effects of muscadine seed extracts against E. coli K12 are presented in Fig. 1. As the concentrations of muscadine seed extracts increased, the growth of E. coli K12 was gradually reduced, however the growth did not reach the levels of complete growth inhibition except for Higgins seed extract. As presented in Table 3,   activities. Our results also demonstrated greater phenolic compounds in muscadine seed extracts than in muscadine skin/pulp extracts (Table 1).
According to Jayaprakasha et al. (12), the antimicrobial activities of grape seed extracts might be the result of phenolic