Microwave-Assisted Extraction of Ocimum basilicum L. Seed, Trigonella foenum-graecum Seed, and Plantago ovata Forsk Seed Husk Hydrocolloids Compared with Conventional Heating Extraction at Optimum Extraction Conditions

The microwave-assisted extractions (MAE) of Ocimum basilicum L. (basil) seed, Trigonella foenum-graecum (fenugreek) seed, and Plantago ovata Forsk (psyllium) seed husk hydrocolloids (BSH, FSH, and PSH, respectively) were performed at their maximum desirability function (for BSH) or optimum (for FSH and PSH) conditions and compared with conventional heating extraction (CHE). The extraction conditions had been defined based on two responses (Yield % and viscosity, mPa s) after relevant post-screening or optimization experiments based on previous experiments. Higher (17.89, 12.33, 32.60, 30.19, 71.73%) average extraction yields were obtained for BSH extracted by MAE (MAE-BSH), BSH extracted by CHE (CHE-BSH), FSH extracted by MAE (MAE-FSH), FSH extracted by CHE (CHE-FSH), and PSH extracted by MAE (MAE-PSH) in respective order compared with the estimated values (15.03, 9.96, 32, 22, and 65.4). Molecular weight (Mw) measurements were executed and the average Mw was determined to be 3.93 x 10(6), 2.89 x 10(6), 6.81 x 10(6) Da in the heavier fractions of BSH, FSH, and PSH. The FT-IR spectroscopy was performed and the predominant absorbance bands were defined. Dielectric properties of the 2% BSH, FSH, and PSH solutions were found to be comparable with distilled water. The steady flow analysis showed shear-thinning behavior for BSH, FSH, and PSH. The apparent viscosity (eta, mPa s) of PSH was the highest followed by BSH and FSH. Dynamic flow measurements showed characteristics of a weak gel for BSH and PSH. Scanning electron microscopy showed morphological variations between the studied hydrocolloids. In addition, the study also indicated that microwave heating has lower destructive effects on the functional properties of the extract as compared to conventional thermal processing and could pave the way for future research. To conclude, MAE was found to be the efficient method for extraction of hydrocolloids with higher yield at a shorter extraction time.