The In Vitro and In Vivo Synergistic Antimicrobial Activity Assessment of Vacuum Microwave Assisted Aqueous Extracts from Pomegranate and Avocado Fruit Peels and Avocado Seeds Based on a Mixtures Design Model

Konstantinos Petrotos,Ioannis Giavasis,Stefanos Leontopoulos,Prodromos Skenderidis,Chrysanthi Mitsagga

doi:10.3390/plants10091757

Abstract

The present study aimed to assess the antimicrobial properties of encapsulated lyophilized powdered extracts of pomegranate peels (PP), avocado peels (AP) and avocado seeds (AS) in vitro and in vivo. Minimum Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) methods, optical density measurement, and well diffusion assay were used to determine antimicrobial activity against food borne bacteria (Gram− Escherichia coli, Salmonella typhimurium, Campylobacter jejuni, Pseudomonas putida), (Gram+ Staphylococcus aureus, Listeria monocytogenes, Clostridium perfringens, Lactobacillus plantarum), and fungi (Penicillium expansum and Aspergillus niger) based on a mixture design model. Additionally, the most effective powder was studied in vivo in yogurt, cream cheese, and minced meat burger. The samples that contained high polyphenol content also exhibited higher antioxidant, antimicrobial, and antifungal activity. From the results of the well diffusion, the MIC/MBC, and the cell optical density assays, the antimicrobial activity of the extracts was found to be correlated to the total phenolic content (TPC) of the samples and the type of the microorganism. The pomegranate peels extract presented the higher TPC and antioxidant activity and constitute the highest percentage in the most active antimicrobial mixture. The powders that were tested in vitro showed microbial type-dependent effects in each food model. The results presented here can be further studied in the large-scale industrial production of natural food preservatives.

Highlights

There is currently a growing interest in developing alternatives to synthetic antimicrobial agents widely used in the food and pharmaceutical industries
From the analysis of the total phenolic content (TPC) and the antioxidant activity based on the estimation of the IC50 of the DPPH radical scavenging, it is clear that pomegranate peel (PP) have a significantly higher concentration of polyphenols and antioxidant ability than avocado wastes
In the cheese salad model, sample No6 presented the best antimicrobial effect against yeasts and fungus compared to the control

Summary

Introduction

There is currently a growing interest in developing alternatives to synthetic antimicrobial agents widely used in the food and pharmaceutical industries. This is due to consumer interest in the safety of materials containing synthetic chemicals and the health dangers associated with them [1]. Many fruit by-products like peels and seeds that contain a high concentration of bioactive organic compounds are generally disposed of as waste, resulting in an unsolvable environmental problem [2]. Based on the high concentrations of these bioactive substances, peels and seeds have been used in cosmetics, food, and the medical industry [15]. Seeds are reported to contain a natural, oil-soluble fungicide called persin (belonging to biologically active aliphatic acetogenin) which is harmless to humans but can be toxic to birds and some animals [16,17]

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