Electrochemical Determination of Antioxidant Capacity of Traditional Homemade Fruit Vinegars Produced with Double Spontaneous Fermentation.

Maja Chochevska,Galaba Naumova-Leţia,Tuba Esatbeyoglu,Elizabeta Jančovska Seniceva,Sanja Kostadinović Veličkovska,João Miguel F Rocha,Valentin Mirčeski

doi:10.3390/microorganisms9091946

Abstract

In the current study, the antioxidant activity of traditional homemade fruit vinegars (HMV) was estimated by measuring the rate of homogeneous redox reaction with 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical cation (ABTS•+) using cyclic voltammetry. The antioxidant capacity of six HMV produced using traditional methods and the physicochemical characterization were measured in different vinegar production steps throughout a double spontaneous fermentation process, i.e., without any addition of yeasts or acetic acid bacteria. Their antioxidant capacity was compared with seven fruit commercial vinegars (ComV). Furthermore, the antioxidant capacity was independently measured with the TEAC (Trolox equivalent antioxidant capacity) assay, aiming at correlating with the electrochemical experimental data. Obtained results from both methods, the electrochemical and TEAC assays, interestingly indicated that all HMV have at least 10 times higher antioxidant activity than ComV. Furthermore, the large range of values for antioxidant capacity in samples of commercial vinegars from apples attested the importance of the raw material quality and technological procedures. The positive correlation between total phenolic content and antioxidant capacity measured by the two type of assays indicated that rose hip homemade vinegar (HMV5) has the highest antioxidant capacity. In contrast, the lowest levels of phenolic compounds and antioxidant capacity were found in apple and persimmon homemade vinegars (HMV1 and HMV6, respectively) which indicated that the type of fruit is crucial towards the production of high-quality vinegars. In this way, the use of traditional processes for the production of fruit vinegars proved to be very promising in terms of producing differentiated vinegars and, concomitantly, reaching high levels of health-promoting antioxidant capacities.

Highlights

Vinegar is a 5–20% (v/v) acetic acid aqueous solution, containing a large number of organic substances such as carbohydrates, alcohols, organic acids, volatile compounds and amino acids
As a consequence of the loss of metabolic activity by yeasts as ethanol concentration in the fermentative medium increases, the subsequent time period was characterized by the consumption of ethanol and concomitant production of acetic acid by the autochthonous acetic acid bacteria (AAB) present therein (Equation (2))—and which typically became dominant as the spontaneous fermentation proceeds and at the expense of the disappearance of viable yeasts over the fermentation time
This study aimed to compare the production of fruit vinegars by spontaneous fermentation, with the possibility to examine the effect of the fruit matrix on the chemical characteristics of the final vinegars as well as in the antioxidant capacity determined by two different analytical methodologies: cyclic voltammetry and Trolox Equivalent Antioxidant Capacity (TEAC) assay

Summary

Introduction

Vinegar is a 5–20% (v/v) acetic acid (or ethanoic acid, CH3 COOH) aqueous solution, containing a large number of organic substances such as carbohydrates, alcohols, organic acids, volatile compounds and amino acids. Fruit vinegars contain high concentrations of polyphenolic compounds and their final quality depends mainly on the raw material used as a substrate, acidification process, fermentation and ageing procedures employed during manufacturing [1,2,3,4,5]. One of the most traditional procedures used for vinegar production is the conventional Orleans method, performed commonly at home by using a larger amount of fruits, resulting in high-quality vinegars [9,10,11,12]. Numerous studies have been focused on the antioxidant capacity of traditional and commercial vinegars—such as the most globally consumed apple cider, fruit and balsamic, wine and grape vinegars [13,14,15,16,17,18,19]. Cyclic voltammetry (CV), based on a redox mechanism, is a highly suitable technique for the quantification of antioxidant capacity of a variety of plant extracts and products, wines, fruits, vegetables and herbs, etc. [20,21,22,23,24,25]

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