Optimization of Microwave-Assisted Extraction of Mucilage from Ocimum basilicum var. album (L.) Seed

Abstract

Microwave-assisted extraction (MAE) is an effective green extraction method of value-added and bioactive compounds. The impact of different extraction times (2-7 min), microwave power (360-760 W), and solvent-to-sample ratio (20 : 1-40 : 1 ml/g) on the extraction yield of Ocimum basilicum var. album L. using MAE was investigated. Maximum extraction yield ( $17.00\pm 0.14$ %) was obtained at optimal conditions for extraction using response surface methodology, including extraction time of 4.33 min, power of 570.32 W, and the solvent-to-sample ratio of 40 : 1 ml/g, which was very close to the model prediction (17.01%). The yield of the conventional extraction (CE) method (50°C, 100 rpm, 1 h extraction time, and solvent-to-sample ratio of 40 : 1 ml/g) was $14.53\pm 0.25$ %. Comparisons were made between the functional and structural characteristics of the mucilage extracted under optimal conditions and the CE method. Fourier transforms infrared (FTIR) spectroscopy was utilized to study the changes in functional groups, and scanning electron microscopy (SEM) was used to determine the morphological characteristics. Emulsion stability against heat, water absorption capacity, foaming capacity, and foaming stability of the extracted mucilage under optimal conditions were $80.73\pm 0.08$ %, $48.71\pm 0.32$  g/g, $24.55\pm 0.42$ %, and $91.6\pm 0.49$ %, respectively, which were higher than the CE method. SEM results showed a more porous structure in mucilage obtained by the MAE method, while no changes were observed by FTIR analysis between the functional groups of extracted mucilage obtained from the utilized extraction methods. Therefore, the application of the MAE method was superior to CE in terms of yield, structural and functional characteristics, and significantly shorter extraction time. The findings show the great potential of microwave processing in commercial and laboratory extraction of mucilage without deteriorative effects on the structural and functional properties of the extracted material.