Effect of drying method and extraction solvent on the total phenolics and antioxidant activity of cauliflower (Brassica oleracea L.) extracts

Plants, being a rich source of medicinally important compounds such as antioxidants, have chemo-preventive role against the risk of oxidative stress-related diseases. There has been much interest in fruits and vegetable rich diets as a natural source of antioxidants and functional ingredients. As well as targeting plants high in antioxidant activity it is also important to optimize extraction parameters. Four extracting solvents, methanol, ethanol, aqueous methanol (80% v/v) and aqueous ethanol (80% v/v) were evaluated for their efficacy to extract antioxidants from cauliflower that had undergone different drying processes namely air-drying, sun-drying and oven-drying. There was a significant difference (P 0.05) in the extracting ability of each of the solvents. The aqueous solvents were superior in their ability to extract the antioxidants and aqueous methanol was significantly more efficient than aqueous ethanol. This result was consistent across a number of parameters including extraction yield, total phenolic content and antioxidant activity. Furthermore, the samples drying process prior to extraction, also significantly influenced (P 0.05) the extraction yield. Oven dried (40 °C) cauliflower had the highest yield of extractable antioxidants while air dried (ambient, approx 25 °C) had the lowest. Again, there was excellent correlation between extraction yield, antioxidant activity and total phenolic content.