Vitamin C and E contents and antioxidant, antibacterial, and antiproliferative activities of Citrus suhuiensis peel

Citrus suhuiensis is a citrus fruit with greenish yellow peel. It is consumed fresh but the peels are discarded as waste whereas they might also contain biological potentials. This study aimed to determine the vitamin C and E contents as well as the antioxidant, antibacterial, and antiproliferative properties of Citrus suhuiensis peel crude extract. Vitamin C and E contents were measured following the AOAC method. The total phenolic content was evaluated using Folin-Ciocalteau assay. Capability of the extract to scavenge free radical was elucidated using DPPH assay. Agar disk diffusion method was used to evaluate its antibacterial effect against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The antiproliferative effects of Citrus suhuiensis crude extract on MCF-7 (estrogen-dependent breast cancer), MDA-MB-231 (non-estrogen-dependent breast cancer), T84 (colon cancer) and MCF10a (normal fibroblast) cell lines were assessed via MTS assay. Vitamin C (19.18±0.14 mg/100 g) in C. suhuiensis peel was significantly higher than vitamin E (0.018±0.00 mg/100 g) (p<0.001). The total phenolic content was 108.00±1.00 mg GAEs/g sample. However, Citrus suhuiensis crude extract was unable to scavenge 50% of DPPH free radicals. The extract did not have antimicrobial effect against the bacterial strains tested. It inhibited 50% MCF-7 estrogen-dependent breast cancer and T84 colon cancer cell growth at 90.03±0.18 and 50.11±1.46 µg/ml, respectively. No inhibition was observed on MDA-MB-231 non-estrogen-dependent breast cancer and MCF10a normal fibroblast cell growth. In conclusion, although C. suhuiensis peel has very limited antibacterial and DPPH radical scavenging activities, it exhibited antiproliferative effect against estrogen-dependent breast cancer and colon cancer cell growth, what could be due to its vitamin C and E and total phenolic contents. Nevertheless, further investigations are required to increase understanding on the underlying mechanisms.