Carotenoids of indigenous citrus species from Aceh and its in vitro antioxidant, antidiabetic and antibacterial activities

Carotenoid contents of peel and pulp of local citrus fruits from Aceh were investigated using HPLC equipped with DAD detector and LC–MS. Most of the citrus samples investigated mainly contained lutein and zeaxanthin. Jeruk takengon (Citrus nobilis) had a more complex carotenoid profile and the highest carotenoid contents compared to other citrus fruits studied here, and peel contained higher carotenoid contents than pulp. (Z)-Violaxanthin and (all-E)-violaxanthin were the main carotenoids of the peel, while (all-E) β-cryptoxanthin and (Z)-violaxanthin were the main carotenoids of the pulp of jeruk takengon. Determination of the lipophilic antioxidant capacity (L-TEAC) of the carotenoid extracts of jeruk takengon showed promising antioxidant potential. The peel extract showed stronger antioxidant capacity than the pulp extract, and saponification further improved the antioxidant capacity. Investigating the inhibition of α-amylase activity resulted in a moderate α-amylase inhibition by jeruk takengon due to the carotenoid contents and the contribution of some flavonoids. Pulp extracts exhibited better inhibition activity than peel extracts, and saponification led to a reduction of the α-amylase inhibition activity. Antibacterial activity tests showed that jeruk takengon could inhibit the growth of K. pneumonia and S. aureus, and saponification enhanced the antibacterial activities. In general, the peel extracts showed biological potential due to the relatively strong in vitro antioxidant, antibacterial and α-amylase inhibitory activity. In addition, these by-products of food processing may serve as potential carotenoid sources.