MAE of phenolic compounds from blueberry leaves and comparison with other extraction methods

Blueberry leaves are a prospective source of phenolic compounds which can be obtained by microwave assisted extraction leading to higher yield in shorter period of time and with lower solvent consumption when compared to solvent extraction. During this study, three experiments with microwave assisted extraction, were separately designed and conducted using highbush blueberry (variety Bluetta) leaves collected during the late fall season. The yields of different compounds obtained during these experiments with microwave extraction were compared with ultrasonic extraction for one hour and 24-h room temperature extraction. The first microwave assisted extraction experiment was conducted to streamline the combination of ethanol and citric acid concentration for further analysis of microwave as a potential extraction method for phenolic compounds and anthocyanins from blueberry leaves. During the second experiment the effect of microwave power level (10-20% absolute power level) and time of extraction (4-16 min) on total phenolics, total anthocyanins and chlorogenic acid was studied which was further used to design the third experiment consisting of a face-centred central composite design with varying factors namely power level and time, each at 3 levels. All the experimental combinations for the 2nd and 3rd experiments were conducted with 80 ml of solvent consisting of 30% ethanol and 1.5 M citric acid combination in ratio of 97:3 (v/v). The total anthocyanins and chlorogenic acid extracted during the study were between 2.321-2.636 mg malvidin 3-glucoside/g dry matter and 49.34-52.66 mg chlorogenic acid/g dry matter respectively, not showing a huge variation between highest and lowest yields, however both compounds with a noteworthy yield. For total phenolics extraction, both microwave power and time of microwave application were observed to be statistically significant factors and the yield of total phenolics was found to be much higher (in the range of 92.719-128.76 mg GAE/g dry weight) than for 24-h extraction at room temperature (average 89.164 mg GAE/g dry weight) and 1 h extraction by sonication (average 97.77 mg GAE/g dry weight) with the same solvent combination.