Comparative evaluation of soxhlet and ultrasonics on the structural morphology and extraction of bioactive compounds of lemon (Citrus limon l.) peel

Abstract

The relative recoveries of bioactive compounds and nutritional ingredients from lemon peel by ultrasound-assisted extraction (USAE/UAE) and traditional soxhlet extraction methods under different conditions of extraction were evaluated. The effect of these treatments on the morphological structure and tissue damage were assessed by scanning electron microscopy. The overall optimal conditions for maximum extraction of total phenolic content (TPC), total flavonoids content (TFC), vitamin C and anti-oxidant activity (AOA) using USAE (200 W output) was predicted using response surface methodology to be at the combined levels of 48 °C extraction temperature, 60 min extraction time and 80% duty cycle. Under these optimum conditions the corresponding predicted responses for TPC, TFC, vitamin C and AOA were 67.17 mg GAE/100 g, 4.52 mg CE/100 g, 26.46 mg/100 g and 61.68% respectively. USAE proved better as compared to soxhlet in the extraction of total phenolics, flavonoids, retention of vitamin C and showing antioxidant activity. In the case of USAE, the combination of factors for maximum extraction of total phenolics (88.06 mg GAE/100 g) was found to be at a temperature of 33 °C, 80% duty cycle and 40 min of treatment. With reference to maximum extraction of total flavonoids (13.92 mg CE/100 g) these conditions were 40 °C, 60% and 50 min and 40 °C, 100% duty cycle, 50 min of treatment for vitamin C (58.87 mg/100 g) contents respectively. The conditions which showed the maximum antioxidant activity (69.37%) was found to be 50 °C, 80% duty cycle and 40 min of extraction.