Antioxidant capacity, radical scavenger activity, lipid oxidation protection analysis and antimicrobial activity of red grape extracts from different varieties cultivated in Portugal

The aim of this study was to investigate the antioxidant capacity, radical scavenger activity, lipid oxidation protection and antimicrobial activity of grape extracts from 12 different red grape varieties cultivated in Portugal. The mean values of total phenolic content quantified in grape extracts varied from 833.7 to 2005.6 mg/L gallic acid. Antioxidant capacity results showed different values for each grape variety ranging from 3.96 to 32.96 mm/L Fe(II). The scavenger activity values ranged from 15.99% to 54.82% for the superoxide radical and from 11.79% to 29.67% for the hydroxyl radical. The grape extracts with the highest antioxidant capacity had a positive effect on the lipid oxidation protection and induced low peroxide values in butter samples. Finally, concerning antimicrobial activity, grape extracts from Touriga Nacional and Tinta Roriz grape varieties had significant antimicrobial activity, especially notable for total mesophilic aerobics.


Introduction
Grape (Vitis vinifera L.) has been appreciated for its rich content of phenolic compounds such as gallic acid, catechin, anthocyanins and resveratrol, and a wide variety of procyanidins (Jordão et al. 2001;Vincenzi et al. 2013).
In recent years, several authors have reported the phenolic composition and antioxidant capacity of several red and white grapes from different fractions, varieties and countries (Breksa et al. 2010;Xu et al. 2010). However, the biological properties and the potential lipid oxidation protection of grapes have not been extensively studied, and a lack of information about the antioxidant activities of the different red grape varieties cultivated in Portugal has been detected.
Thus, the purpose of this work was to investigate the antimicrobial activity, antioxidant capacity and lipid oxidation protection analysis of grape extracts obtained from 12 different red grape varieties cultivated in Portugal.

Results and discussion
The data in Table 1 show the total phenols, antioxidant capacity and scavenger activity quantified in the red grape extracts studied. Total phenolic compounds, expressed as equivalent of gallic acid, ranged from 833.7 to 2005.6 mg/L with an average of 1341.0 mg/L. The highest concentration of total phenols was detected in Touriga Nacional (1957.0 mg/L) and Tinta Roriz (2005.6 mg/L) grape extracts, while Mourisco Tinto (833.7 mg/L) and Cabernet Sauvignon (890.9 mg/L) grape extracts showed the lowest values.
In relation to hydroxyl radical scavenger activity (HRSA) and superoxide radical scavenger activity (SRSA), data revealed that the scavenger activity tendencies were similar to those obtained for the total antioxidant activity values. Thus, extracts from Touriga Franca, Syrah, Tinta Roriz and Touriga Fêmea samples had in general higher scavenger activity values than extracts from other grape varieties.
The lipid oxidation protection effect of the different grape extracts in butter samples at room temperature (208C) during 14 storage days is shown in Figure 1. Results showed that among the different red grape extracts studied, the extracts from Touriga Franca, Syrah, Alicante Bouschet and Touriga Fêmea caused significantly ( p , 0.05) higher oxidation protection in the two storage times considered than the control sample. For example, after 14 storage days, the control sample showed the highest peroxide value of 56.6 meq O 2 /kg, while the lowest value was obtained for Touriga Franca (38.1 meq O 2 /kg).
For the red grape varieties extracts with higher total phenolic content, Touriga Nacional and Tinta Roriz, an analysis of antimicrobial activity against total mesophilic aerobics and Staphyloccocus aureus was carried out. The results are shown in Figure 2. The extracts of these two red grape varieties exhibited significantly higher activity ( p , 0.05) against total mesophilic aerobics and S. aureus than extract of the control sample. These results were independent of the incubation time. However, it was clear that antimicrobial activity was less evident for S. aureus than for the total mesophilic aerobics group.

Conclusions
Our study demonstrates that grape extracts present important antioxidant, scavenging, antimicrobial and lipid oxidation protection activities, corroborating the notion of grapes as a healthy food and a potential source of antioxidant and antimicrobial drug substances.

Supplementary material
Experimental details relating to this article are available online.   Figure 1. Lipid oxidation protection of the different red grape extracts in butter samples. *Comparison of means was performed by the LSD method; means followed by the same letter for each storage day are not significantly different ( p , 0.05). Figure 2. Antimicrobial activity against total mesophilic aerobics and S. aureus of Touriga Nacional and Tinta Roriz grape extracts. *Comparison of means was performed by the LSD method; means followed by the same letter for each microorganism/incubation time are not significantly different ( p , 0.05); control (extract solvent, ethanol -water).