The Moroccan Pomegranate: An Underrated Source of Tannins Extracts and Natural Antimicrobials from Juice Processing Byproducts

Abstract

Purpose The pomegranate juice manufacturing industry produces vast quantities of non-edible portions of fruit as a by-product. The rind is a good source of many beneficial functional components, especially polyphenols and in particular tannins. This research was undertaken to expose the presence of active substances, including tannin compounds, in the crude extracts (aqueous (AE) and methanolic (ME)) and their fractions increasing in polarity, from Moroccan pomegranate rind samples. Methods To describe the molecular distribution of tannin content in crude extracts, steric exclusion chromatography (SEC) on Sephadex gel 50 was carried out. In addition, their antimicrobial properties were tested using agar diffusion, dispersion, and microdilution methods against the bacterial strains Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and the yeast strains Saccharomyces cerevisiae and Candida tropicalis. Results For both crude extracts, the SEC showed qualitative and quantitative differences in tannin polymerization. Diameters of inhibition zones (DIZ) obtained against bacterial species ranged from 20.6 to 30.3 mm for ME, from 10.8 to 15.3 mm for AE and from 0 to 16.6 mm for fractions. Among the selected fungal cultures, the highest antifungal activity was reported against S. cerevisiae; with an inhibition rate (I %) ranging up to 99.00% for AE. With I % reaching up to 93.35%, the C. tropicalis strain was more sensitive to ME, although the AE has no inhibitory effect on this yeast. For fractions, the I % ranged from 7.03 to 98.03% where a synergistic antifungal effect was observed between fractions. Conclusion Pomegranate processing by-product is a potential source which could be used as natural preservatives in food industry and non-toxic matrices replacing hazardous materials in surface treatment.