Exploring diversity and biotechnological potential of lactic acid bacteria from tocosh - traditional Peruvian fermented potatoes - by high throughput sequencing (HTS) and culturing

Highlights

• This is the first study on the tocosh LAB diversity.

• LAB populations were dominated by Lactobacillus at any stage in tocosh fermentation.

• Lb. sakei and Lc. mesenteroides were present in all tocosh samples.

• Out of twenty-four LAB species detected, six were recovered by culturing.

• Tocosh LAB isolates exhibited characteristics of biotechnological interest.

Abstract

Lactic acid bacteria (LAB) diversity associated with tocosh, Peruvian traditional fermented potatoes, was for the first time investigated by culturing and high throughput sequencing (HTS) approaches. They were applied on three samples i.e. freshly harvested potatoes, one-month and eight-months production. While by culture-dependent approach a few Lactobacillus (Lb) species (Lb. sakei, Lb. casei, Lb. farciminis, Lb. brevis, Lb. fermentum) and Leuconostoc (Ln) mesenteroides were identified, twenty-four OTUs belonging to six LAB genera were considered in tocosh samples by HTS, being Lactobacillus dominant in all three samples. LAB predominated on fresh potatoes, while Clostridium, Zymophilus and Prevotella were the most abundant genus in 1- and 8-months tocosh samples. When biotechnological features were investigated, amylase and phytate-degrading abilities as well as EPS and group B vitamin (riboflavin and folate) production were exhibited by several Lb. sakei and Ln. mesenteroides strains. Safety traits of major LAB species from tocosh showed antibacterial activities as well as biogenic amines production capacity. The molecular inventory achieved by HTS approach provided information on LAB population composition during fermentation of this ancestral potato fermented product while culturing allowed the selection of LAB strains suitable for novel functional cultures design for the production of fermented starchy products.

Introduction

Household fermentation of foods has a long and very important tradition in Latin American countries (Londoño-Zapata et al., 2017, Tamang et al., 2016). Andean communities have managed to preserve native crops as well as their production, harvesting and storage during centuries. Among them, potatoes, originated approximately 8000 years ago in the South American Andes, Perú lodging one of the most important reservoirs of varieties and wild relatives (Goldner et al., 2012, Mosso et al., 2016, Velásquez-Milla et al., 2011). Numerous ingenious ways of preserving potatoes in order to maintain adequate stocks for survival have been developed, such as sun-drying or natural freeze-drying to obtain white or black chuño and fermentation to obtain tocosh.

Potatoes tocosh is an ancestral fermented food product that is still prepared in small communities from the highlands of Central Peruvian Andes by local peasants (Horkheimer, 1973). The traditional preparation method consists of digging a well (0.70 × 1.50 m deep) in the ground near a water spring in which large amounts of potatoes (normally discarded potatoes) are placed between straw layers. Rocks are used to cover the pile in order to prevent the tubers to be washed away by the slight water current that passed through the ditch; the potatoes are then left to ferment in this running water up to 12 months. After this time, potatoes suffer an enzymatic browning (Zvitov-Ya'ari & Nussinovitch, 2014) and are laid in a dry shaded area to allow the water to drain. The obtained product is kept for consumption, sale or most commonly, as a sun-dried and ground fine flour-type product that is used to prepare different broths, stews and “mazamorra” which is a semi-liquid food with thick consistency (De Moreno de LeBlanc, Todorov, Vignolo, Savoy de Giori, & LeBlanc, 2014). From a microbiological point of view, only preliminary studies have been performed demonstrating that tocosh results from microbial fermentation, mainly by lactobacilli. Besides being an important staple food for local population, the compounds generated by these beneficial microorganisms are thought to be responsible for the large diversity of medicinal properties attributed to this product as such being known as the “natural antibiotic of the Incas”. Although no scientific articles supporting these claims were found, its probiotic potential was demonstrated using an experimental animal model and compared with a recognized probiotic Lactobacillus acidophilus LA-5^® strain (Prentice & Milka, 2005). Lactic acid bacteria (LAB) are usually involved in traditionally fermented food of vegetal origin and many LAB species have been described as vitamin producers or phytate degraders (Anastasio et al., 2010, Juarez del Valle et al., 2014, Ruiz-Rodríguez et al., 2016).

Recently environmental and food microbiology have benefited from the advances in molecular biology and adopted novel strategies to detect, identify, and monitor microbes. An in-depth study of the microbial diversity in food can now be achieved by using high-throughput sequencing (HTS) approaches after direct nucleic acid extraction from the sample to be studied; the current scenario of this metagenomic approach to study food microbiota was described by Ercolini (2013). Therefore, the aim of this study was to evaluate LAB populations present in tocosh and to disclose their biotechnological potential for future applications. Fresh potatoes and fermented samples from two wells corresponding to two storage times were analysed by combining both, culture-dependent and HTS approaches.