Abstract

The extraction by means of sonication method, namely ultrasound-assisted extraction (UAE), is a very interesting technique to extract natural compounds from food matrices due to the cavitation effect, which enhances mass transport by disrupting the plant cell walls. Consequently, various factors can affect the extraction process and these have to be optimized in order to extract quantitatively the analytes of interest. In this research, the chemometric approach based on the advantages of the Central Composite Design (CCD) have been successfully applied in the optimization of anthocyanins from corn (Zea mays) grains using sonication.

In conjunction with Response Surface Methodology (RSM), CCD was applied based on six factors and three levels to evaluate the significances of studied factors prior to the optimization of extraction conditions. The effects of solvent composition (25−75% methanol in water), extraction temperature (10−50oC), solvent-solid ratio (2.5:1−5:1), solvent pH (2−7), amplitude (30−70%) and cycle (0.2−0.7 s-1) on the extraction yields were taken into account. Subsequently, extraction kinetic (5−30 min) was studied to confirm the full recovery of phenolic compounds extracted from the matrix. The levels of anthocyanins in the UAE extracts were quantified by High Performance Liquid Chromatography using a Dioda Array Detector (HPLC-DAD) in less than 10 min.

The optimized condition by RSM was then assed for a kinetic study to evaluate the extraction rate. The optimal UAE condition was as follows: extraction time 5 min, ultrasound amplitude 66%, cycle 0.2 s-1, extraction temperature 10oC, 75:25 methanol:water as the extraction solvent at pH 7 and solvent-solid ratio 2.5:1. Complete validation of the method was performed. High recovery and precision were found for the full analytical method. The suitability of the method was checked by application to corn grain cultivars and demonstrated this extraction method to be suitable for the extraction of anthocyanins from corn grain samples.