Résumé:
In Algeria, fermented durum wheat lemzeiet is used to produce couscous also named lemzeiet. Historically the fermentation was carried out in underground silos called matmor. Nowadays the wheat’s fermentation is made outside the matmor inside utensils of different shapes and sizes, by a new fast uncontrolled process. The fermentation of wheat in matmor has been progressively abandoned due to rural exodus and the expansion of modern wheat storage methods.
In order to master this new process and in an approach of making it valuable, we conducted a survey of wheat fermentation conditions applied outside the matmor. Following the obtained results, two types of fermentation (V and E), with and without initial addition of vinegar, were reproduced at laboratory scale in plastic jerrycans of 10 L.
The microbial communities present, in the two samples, were monitored and analysed by conventional microbiological farming methods. The results showed that the fermentation favours the disappearance of fungi flora since the first months with the settlement of a dominant lactic flora. This dominant flora, deriving from the two samples’ types, was defined and monitored by culture-independent (PCR-TTGE) and culture-dependent methods by coupling different molecular methods (ARNr 16S/pheS/rpoA gene sequencing and speciesspecific PCR). 69 isolates were identified as belonging to 16 species represented by 6 genera (Enterococcus, Lactobacillus, Leuconostoc, Pediococcus, Weissella, and Streptococcus).
TTGE revealed similar results us cultutre-dependent methods, with a chracteristic band assigned to Pediococcus.sp. The strain typing of Lactobacillus spp., Pediococcus spp., and Enterococcus spp., by RAPD and PFGE, showed a very important intrsapecies diversity.
To study the effect of LAB’s activity on the matrix changes, we analysed physico-chimical composition and characteristics of fermented wheat. The results showed that fermentation favours the increase of fat acidity, titratable acidity and a significant drop of pH The free amino-acids’ profiles and the volatile compounds were also evaluated using cation exchange chromatography and gas hromatography-mass spectrometry (CG-MS) respectively. 40 volatile aroma compounds and the 25 free amino acids showed a distinct effect of fermentation compared to non-fermented wheat (used as a control sample).Our results demonstrated an increase of proteogenic free amino acids and non-proteogenic ones (mainly ornithine and GABA).The hydrolytic activities of the isolated LAB species, belonging to 24 strains, were also highlighted using the API-ZYM kit.
This study enabled the exploration of a new fermentation process of wheat with the
determination of a large diversity of colonizing LAB and their interactions with the matrix of fermented wheat.
