Phytochemical Analysis and In vitro Antimicrobial Potential of Colocasia esculenta Tuber Peel Extract Against Pathogens Isolated from Water Yam (Dioscorea alata) Tubers

Abstract

The phytochemical analysis of the methanolic extract of Colocasia esculenta tuber peel and In Vitro antimicrobial sensitivity test was carried out against previously isolated and identified microorganisms from three water yam (Dioscorea alata) tuber varieties (Kor, Banada and Azawele) using standard methods. Phytochemical analysis of the extract revealed the presence of tannins, saponins, flavonoids, phenolics, alkaloids, steroids, and glycosides with varying contents. The highest phytochemical content was recorded of saponins (5.27 mg/100 g), followed by tannins (4.85 mg/100 g), alkaloids (3.46 mg/100 g), phenols (3.18 mg/100 g), flavanoids (2.50 mg/100 g), cardiac glycosides (2.16 mg/100 g), while steroids (2.01 mg/100 g) had the least content. The data obtained from the zone of inhibition (mm) was analyzed (descriptive statistics and inferential statistics to report the findings and to test hypothesis at 0.05 level of significance respectively) using statistical package for social science, SPSS Version 20. Results were reported as Mean ± SD. The statistical difference between more than 2 groups of data was evaluated using ANOVA with LSD post hoc test. Differences between means were considered significant at p < 0.05. The antimicrobial sensitivity test result against the fungi (Aspergillus niger, Aspergillus flavus, Botryodioplodia theobromae, Penicillium marneffei, and Myrothecium verrucaria as well as bacteria (Klebsiella oxytoca, Serratia marcescens and Pseudomonas aeruginosa) showed significant (p < 0.05) inhibitions in a dose-dependent manner when compared with standard commercial antifungal (Teraconazole) and antibacterial (Ciprofloxacin) as positive control agents at 100 mg/mL. The extract demonstrated the highest significant (p < 0.05) inhibition of 71.45 % and 69.10 % against Aspergillus niger and Pseudomonas aeruginosa respectively at 100 mg/mL. The lowest inhibition of 17.76 % and 17.40 % was obtained against Myrothecium verrucaria and Klebsiella oxytoca respectively at 25 mg/mL. Colossian esculenta tuber peel extract recorded MIC and Minimum Fungicidal Concentration (MFC) of 6.25 mg/mL against Aspergillus niger, Aspergilus flavus, Botryodioplodia theobromae, and Penecillium maeneffei; 3.13 mg/mL against Myrothecium verrucaria, Klebsiella oxytoca, Serratia marcesces, while Pseudomona aeruginisa recorded Minimum Inhibition Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of 3.13 mg/mL and 6.25 mg/mL respectively. The antimicrobial activities of the extract could be attributed to the high contents of saponins, tannins, phenols, and flavonoids. These research findings suggest that Colocasia esculenta tuber peel extract could be exploited in the control and prevention of postharvest water yam tuber rot and other tuber crops, which are the main staple foods in Nigeria and other tropical countries as it has the potentials to serve a natural antimicrobial agent. The research findings could also be of use to pharmaceutical companies in developing drugs that may help in combating drug resistance in pathogens.