Smen/Dhan, beurre fermenté traditionnel

Abstract

In Algeria, a wide variety of fermented dairy products are traditionally prepared, these products are part of the Algerian heritage and represents a cultural, medicinal and economic importance. Among these products, Smen or Dhan is a naturally fermented butter made by traditional methods. A Better knowledge of this product in terms of technological, physicochemical and microbiological know-how represents a scientific interest in order to control its health and organoleptic qualities and also for its valorization. The first part of this study was to investigate the place and use of this product in the Algerian culture as well as to identify the traditional methods used for its preparation. A survey was conducted on 880 households in 7 regions of the South and East of Algeria. The results revealed that this product is known by the majority of the surveyed population and prepared at household level according to empirical methods. The production of Smen is mainly intended for home consumption or marketed informally. Two different preparation modes are used depending on the surveyed regions. Households from Batna, Khenchela and Setif proceed directly with butter salting, while in the Biskra, Jijel, El Oued and Ouargla regions, a different process is used which first involves a heat-treatment of the butter followed by the addition of one or more ingredients. After packing in a traditional ceramic container (Ezzir) and other containers, a maturation step is applied with a long duration varying from one month to several years. This product is consumed as an additive to enhance the taste and aroma of some traditional dishes (couscous/other) and is also used in traditional medicine. In the second part of this work, we studied the microbial diversity and its implication in the Smen maturation. To reach this goal, 15 Smen samples (final products) produced in households were collected from different regions in Algeria, while microbial dynamics were investigated for one Smen preparation. The culture-dependent approach allowed the evaluation of the hygienic and sanitary quality, and the molecular identification of lactic acid bacteria (rRNA16S) and yeasts (D1-D2-rRNA26S region). The culture-independent technique (metabarcoding) using illumina-Miseq sequencing, targeting the V3-V4 region of RNA16S (BL) and the ITS2 region of RNA26S (yeasts), was also carried out, in order to identify microbial species that leave their genetic fingerprints (DNA). Results showed that all hygiene and safety criteria were satisfactory for these Smen products. Molecular identification of LAB and yeasts isolates showed that the samples were highly diverse in microflora. Among the total isolates LAB (121), 82 strains were chosen for molecular identification, the results showed that they belong to 11 species and 4 genera. regarding yeast isolates (102), 48 strains were identified to belong to 15 species and 11 genera. Significant divergences were observed between the two techniques used, the independent culture revealed the most imposing species (Lactococcus lactis and Streptococcus salivarius subsp. thermophilus), these later were not isolated by dependent culture approach, which revealed that the species of lactobacilli and enterococci were the most represented in the collected Smen samples. Regarding fungal diversity, several key species involved in Smen manufacturing and maturation were identified by the two approaches, i.e., Geotrichum candidum, Wickerhamiella pararugosa, Kluyveromyces lactis, Yarrowia lipolytica, Kluyveromyces marxianus, Torulaspora delbrueckii, Clavispora lusitaniea et Rhodotorula mucilaginosa. In addition to these results, a new species of Moniliella sp., was isolated which sequence gene (D1/D2-rRNA26S) represents 95% of similarity with Moniliella dehoogii its closest phylogenetic. Finally, the third part of this work was the analysis of volatile compounds by GC-MS and their dynamic during Smen maturation, as well as to highlight the nature of correlations between the volatile compounds and microbial diversity. 81 volatile organic compounds belonging to different families have been identified: Esters (20), ketones (20), aldehydes (13), fatty acids (12), alcohols (7), furans (3), terpenes (2), styrene (1) and other compounds (3). Volatile compound diversity and their abundances were highly related to maturation time and lipolysis degree as well as to the nature of autochthonous microbiota for which several correlations were noted between volatile compounds and identified species. Smen/Dhan is a territory product with an ethnic name and know-how passed down through generations. It would therefore be very interesting to create cooperatives that could market this product in a formal way, with a specific property label. It could help local producers to improve the quality and safety of the product. The selection of some LAB and yeast strains for Smen on an industrial scale, would also be interesting for its quality attributes.