Antimicrobial activity of seed coat extracts of Tamarind cultivars and topical preparation

Abstract

Tamarindus indica L. has long been used as traditional medicine. Tamarind seed-coats have been found to contain flavonoid compounds. Bioactivities of flavonoids as antioxidant and antimicrobial have also been reported. This study was designed to evaluate antibacterial potential of seed-coat extracts from 8 Thai tamarind cultivars including the sour and sweet types. Tamarind seed-coats were extracted with 70% ethanol and shaken the extracts with chloroform (1:1) to extract lipids, the aqueous-ethanol extract was separated and dried. Antimicrobial activity of tamarind seed-coat extracts (TSCEs) was evaluated by agar-well diffusion and broth microdilution susceptibility tests, as well as the time-kill analysis. The results showed that all of TSCEs extracted from 8 Thai tamarind cultivars inhibited the growth of five tested bacterial strains including three of gram-positive bacteria, Staphylococcus aureus ATCC 6538P, S. epidermidis ATCC 12228, and Propionibacterium acnes (clinical isolate); two of gram-negative bacteria, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853. However, one of tested fungus, Candida albicans ATCC 10230, was not inhibited by TSCEs. The gram-positive bacteria were more susceptible to TSCEs inhibition than the gram-negative bacteria. Time-kill analysis demonstrated that at 0.39, 0.78 and 3.13 mg/ml of TSCEs, respectively, killed S. epidermidis, S. aureus and P. acnes in 10, 14 and 30 h, respectively. TSCEs exhibited 99% reduction of viable count of S. epidermidis and S. aureus within 4 h and P. acnes within 24 h, respectively. The TSCE from Tamarindus indica “Priao-yak” (TI-PY/P) was used as antibacterial agent for the preparation of TSCE gel for topical use. The appearances and physical properties of the finish product including color, air-bubble, viscosity, pH and antibacterial efficacy of TSCE gel were examined after freshly prepared and after stability tested. Good appearances as well as stability of the TSCE gel product were obtained. Antibacterial activity of TSCE gel was also observed against bacteria causing skin infection including S. aureus, S. epidermidis and P. acnes, as evaluated by agar-well diffusion and broth microdilution methods. The HPLC chromatogram of TSCE from the seed coats of T. indica “Priao yak” showed the chemical fingerprint of peaks that identical with the standard flavonoids including (+)-catechin, (-)-epicatechin and procyanidin B2.