Title : Effect of extraction conditions on the antioxidant and antimicrobial activity of grape seeds
Abstract:
The need for bioactive compounds from natural sources has led to the valorization of agro-industrial by-products as sustainable sources of bioactive compounds. Grape seeds from Vitis vinifera L., which are one of the main by-products from the wine industry, are a rich source of bioactive compounds that have antioxidant and antimicrobial properties. However, extraction efficiency and bioactivities are largely dependent on processing conditions. Thus, this study aimed to optimize the extraction of bioactive compounds from grape seeds and evaluate their antioxidant and antimicrobial potential. A two-level fractional factorial design was employed to study the effect of five extraction conditions: ethanol concentration (20–80% v/v), extraction time (10–30 min), solid-liquid ratio (20–40 g/L), temperature (25–85 °C), and power input (250–350 W).
A total of eight experimental design points were included in this study and were used as a screening tool to identify the most important extraction conditions. TPC was determined by the Folin-Ciocalteu assay, and antioxidant potential was expressed as EC50 by the DPPH assay. Antimicrobial potential was expressed as MIC against four Gram-negative and three Gram-positive bacterial strains: Enterobacter cloacae, Escherichia coli, Pseudomonas aeruginosa, and Salmonella enterocolitica from Gram-negative group and Bacillus cereus, Listeria monocytogenes, and Staphylococcus aureus from Gram-positive group.
To compare antimicrobial potential against different microorganisms, MIC values were converted to a normalized activity score for both Gram-positive and Gram-negative bacterial groups by using a logarithmic scale. The results obtained showed that extraction conditions have a significant impact on both yield and bioactivity of extracts. The highest content of total phenolic compounds (110.83 mg GAE/g dw) and antioxidant activity (EC50 = 150.46 mg extract/mL) were recorded under conditions with high ethanol concentration (80%), high temperature (85 °C), long extraction time (30 min), and high power (350 W).
These results confirm that ethanol concentration and temperature have a positive effect on extraction and antioxidant activity. However, it was noted that the highest antimicrobial activity was recorded under conditions with low ethanol concentration (20%), high S/L ratio (40 g/L), low temperature (25 °C), and high power (350 W). It is important to note that this condition exhibited enhanced antimicrobial activity, especially against Gram-negative bacteria. Gram-positive bacteria were more susceptible to extracts than Gram-negative bacteria, as shown by lower MIC values. No direct linear relationship was observed between total phenolic content and antimicrobial activity, suggesting that specific phenolic compounds or other co-extracted constituents may play a more decisive role in microbial inhibition than the overall phenolic concentration. These findings further indicate that extraction conditions selectively modulate the chemical profile of the extracts, thereby enhancing distinct functional properties. In this context, grape seeds stand out as a valuable source of bioactive compounds, with their functional performance being highly dependent on the extraction parameters applied.
