The global increase in demand for plant-derived products for therapeutic and nutraceutical purposes have stimulated the quest to identify the chemical compounds present in each plant and their various pharmacological activities. In addition, the need for researchers to search for safer antioxidants from natural sources over synthetic ones such as BHT, BHA, propyl gallate, and tertbutyl-hydro quinine which are known to be carcinogenic has increased over the years as well67. Thus, the consumption of natural products such as fruits and vegetables showing strong antioxidant activities in preventing heart diseases and several cancerous ailments becomes necessary68. The GCMS analysis showed that the pulp has potential novel compounds that could be isolated for therapeutic purposes and irrespective of the percentages of the identified compounds, scientific reports showed that each of the compounds possessed significant therapeutic potentials.
Although the pharmacological activities of the major and minor bioactive compounds of plants are rarely reported and pharmacological activities of plants are mostly attributed to the flavonoids, alkaloids and phenolic compounds, Shapla et al.69 indicated that 5-Hydroxymethylfurfural (HMF) is an organic compound that possesses several beneficial potentials including antioxidant, anti-allergic, antiproliferative, anti-sickling, anti-hypoxic and anti-hyperuricemic impacts while Rajkumari et al.49 documented its antibiofilm activity. Its mechanism of antimicrobial action was related to growth or proliferation inhibition. Similarly, these inhibitory activities of 5-Hydroxymethylfurfural were reported by Palchykov et al.70 as the major compound of Punica granatum peel extract with deleterious effect on bacteria, protists, and nematodes. This is in agreement with an earlier study by Ahmed and Ayoub71. Their studies affirmed 5-Hydroxymethylfurfural as one of the main compounds in Tamarindus indica pulp extract with over 30% of the extract component. While 3-O-Methyl-d-glucose (16.31%), identified also as a component of the Tamarindus indica pulp extract, have been implicated in preservative activities as well as antitumor and anti-inflammatory potentials57,58, other bioactive components of the extract with their various pharmacological activities have been reported in many studies as bactericidal, fungicidal, nematocidal and antioxidant agents48. Supaphon and Preedanon56 also reported on the anti-convulsant, antioxidant, antitumor, and the anti-bacterial potential of O-α-D-glucopyranosyl-(1.fwdarw.3)-β-D-fructofuranosylα-D-Glucopyranoside. That 2-ethyl-2-Butenal and 3-(hydroxymethyl)-6-2-Cyclohexen-1-one had no pharmacological activities reported from the literature search could mean that these are new compounds that may not have been previously identified in medicinal plants.
Furthermore, in this study, the test organisms could have been inhibited by this extract due to the presence of β-sitosterol, cis-Vaccenic acid and other compounds earlier reported to have antimicrobial potentials though their real mode of action on microorganisms is not clearly understood. The minimum inhibitory concentration of the extract against E. coli ATCC 8739 (1.75 mg/ml), Pseudomonas aeruginosa ATCC 19582 (0.88 mg/ml) and Plesiomonas shigelloides ATCC 15903 (0.22 mg/ml) showed the extract has stronger antimicrobial activities against the Gram-negative bacteria. This supports the findings of Abukakar et al.72, Adeola et al.73, and Bhadoriya et al.74 that showed that Tamarindus indica extract was capable of suppressing the growth of the test organisms. This implies that the extract would be an effective therapy for infections such as wounds, dysentery, diarrhea, and food poisoning in which the test organisms have been implicated75,77,77.
Since some metabolic and age-related ailments are intimately linked with oxidative activities, therefore the exploitation of herbs and spices as a natural origin of antioxidants to prevent oxidation deserves more awareness78. While Luengthanaphol et al.79 reported that ethanol extract of tamarind seed coat exhibited antioxidant activity, this study indicated that methanol extract of the pulp has strong antioxidant properties. Although a good correlation has been recognized between antioxidant capacity and ferric reducing potential of the extract, the radical scavenging and ferric reducing potentials were relatively low when compared with that of the standard. This is in agreement with Atawodi et al.80 and Reis et al.81 indicating that extracts of T. indica displayed high antioxidant activities and Ugwuona and Onweluzo82 reported that Tamarind pulp possesses high antioxidant activities at elevated extraction temperature. Many reports have shown strong interdependence between antioxidant activities, phenolic and flavonoid content of plant extracts83,84, a strong positive correlation was also noticed between the total phenolic (r=0.9912, p ˃ 0.05) and antioxidant activities evaluated by DPPH (r=0.8938, p ˂ 0.05) and FRAP (r=0.9808, p˂0.05) assays.