Biological Activity and Pectin Content in Orange, Lemon, Tangerine, Grapefruit and Kumquat Peels in Vietnam

Extracts of orange, lemon, tangerine, pomelos and kumquat peels were extracted by two methods viz. solvent extraction and ultrasound-assisted extraction. Extracts from peel were evaluated for their moisture, biological activity and antibacterial capacity. Raw material powder after preliminary processing tends to turn golden brown with moisture content below 10%. The antioxidant capacity of the extract from low to high (orange > tangerine > pomelos > lemon > kumquat) was found. The vitamin C equivalent of tangerine is the highest recorded at the value of 1.30 mg g−1 . In addition, the total polyphenol and flavonoid content of pomelos and tangerine was found to be higher than that of other extracts. The antibacterial ability was also evaluated based on four intestinal-specific strains including E. coli, B. subtilis, P. aeruginosa and S. aureus. The orange peel extract isolated from solvent extraction method has the highest resistant to bacterial strains, whereas, the other extracts have moderate antibacterial activity. The results on the pectin composition in the peels have also been specifically evaluated. All the types of pectin powders have a degree of esterification (DE) coefficient < 50% corresponding to pectin LM (low-methoxyl), especially pectin from lemon peel gives a DE coefficient > 50% corresponding to pectin HM (high-methoxyl).