Screening of lactic starter from Tunisian fermented vegetables and application for the improvement of caper (Capparis spinosa) fermentation through an experimental factorial design

Samia Lakhal,Manel Ziadi,Mokhtar Hamdi,Xavier Dousset,Kaouther Zaafouri,Soumaya Massoudi,Taroub Bouzaiene

doi:10.1007/s13213-019-01519-x

Abstract

PurposeThis study aims at designing a lactic starter for caper fermentation isolated from Tunisian fermented vegetables to improve the process and produce consistent and high-quality product.MethodsIn this study, the lactic starter was isolated by exploring the lactic acid bacteria (LAB) of Tunisian artisanal fermented vegetables. Identification was carried out by partial 16S rRNA gene sequencing. Screening was based on salt tolerance and antagonistic activities against Escherichia coli ATCC 10536 and Enterococcus faecalis ATCC 10541. Caper fermentation was optimized through a full factorial experimental design (23), by exploring three factors: starter inoculum size, NaCl concentration, and acetate content. Differences in pH values, Total aerobic mesophilic bacteria and LAB counts between the beginning and end of fermentation are selected as responses and corresponding regression coefficients were calculated.ResultsThe lactic microbiota is mainly represented by Lactobacillus plantarum group. Based on salt tolerance and antimicrobial activity, the strain Lactobacillus plantarum F3 was selected as starter for caper fermentation. The effect of NaCl concentration, acetate content, and inoculum size on acidity, total aerobic mesophilic bacteria count, and LAB count after 1 week and 1 month of caper fermentation was studied. Depending on the fermentation time, either 1 week or 1 month, the initial conditions should comprise 0% acetate, 108 CFU/mL inoculum, and 5% NaCl for 1 week against 5% acetate, 107 CFU/mL inoculum, and 10% NaCl for 1 month lasting caper fermentation. A protocol for caper fermentation was set up ensuring hygienic quality and LAB viability.ConclusionLb. plantarum F3 was selected as lactic starter for caper fermentation, and initial fermentation conditions were optimized through a full factorial design. This work has shown loss in LAB viability after 1 week of fermentation. Based on results obtained, an optimized fermentation protocol was set up. This protocol ensures LAB survival and high hygienic quality of the product.

Highlights

In North African countries, traditional fermented fruits and vegetables are an important part of the diet
Spontaneous fermentation at the household level leads to variations in the sensory properties of the products and in poor hygienic quality (Benkerroum 2013)
The pH value of samples was determined at room temperature with an Inolab 740 pH-meter and combined glass electrode (Hanna Instruments, Germany) standardized with pH 4.01 and 7.01 standard buffer solutions (Scharlauchemie, Spain)

Summary

Introduction

In North African countries, traditional fermented fruits and vegetables are an important part of the diet. This importance is due to: (i) they provide variety in the flavors of existing staples, (ii) a cheap way of preservation, and (iii) improvement of the nutritional quality and digestibility of the raw food materials and made edible, some food that are barely edible (El Sheikha and Montet 2014). Spontaneous fermentation at the household level leads to variations in the sensory properties of the products and in poor hygienic quality (Benkerroum 2013). The use of starter cultures would be an appropriate approach for the control and optimization of the fermentation process resulting in alleviation of the problems of variations in organoleptic and hygienic quality (Callewaert et al 2000)

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Results