Estamaran date vinegar: chemical and microbial dynamics during fermentation

Abstract

Vinegar is a fermented food produced by alcoholic and then acetic acid microbial metabolism. Date palm fruit (Phoenix dactylifera L.) is a valuable source for the production of vinegar. Microbial identification has a major role in the improvement and bio-management of the fermentation process of vinegar. Estamaran and Kabkab two varieties of date palm fruit were selected to study the fermentation process. A culture-dependent approach was used to study bacterial dynamics. 16 S rRNA gene was amplified by Polymerase Chain Reaction (PCR), also restriction enzyme analysis with HinfI and TaqI, and sequencing was done. Assessment of microbial flora of date palm fruit during fermentation showed that Fructobacillus tropaeoli, Bacillus sp., Leuconostoc mesenteroides, Leuconostoc pseudomesenteroides, and Weissella paramesenteroides existed in the first phase of fermentation. With fermentation progress, microbial diversity decreased so only one species remained. Komagataeibacter xylinus as an acid acetic producer was present in the third phase of fermentation. Based on chemical analysis, the concentration of reducing sugars decreased during fermentation. With decreasing pH, a simultaneous increase in acidity and total phenolic compounds occurred. The trend of changes during Estamaran fermentation was more severe and a vinegar with desirable properties was produced. Therefore, this date variety is recommended for the production of date vinegar.

Keywords: Acetic acid bacteria; Date palm; Fermentation; Polymerase Chain Reaction; Vinegar.

Fig. 1

Trends of pH and titratable acidity changes during fermentation of Kabkab and Estamaran over three months (KpH: pH of Kabkab, EpH: pH of Estamaran, ETA: titratable acidity of Estamaran, and KTA: titratable acidity of Kabkab)

Fig. 2

The variation of reducing sugars in the fermenting broth of dates over a quarterly period

Fig. 3

Changes in total soluble solids in fermented date broth over a quarterly period

Fig. 4

Total phenolic compounds of fermenting date brine over a quarterly period

Fig. 5

Acid production screening by the dissolution of CaCO₃ and a clear zone appearance around the colonies

Fig. 6

Enzymatic digestion pattern of amplified 16 S rRNA gene obtained from isolates of fermented Estamaran (panel a-Up) and Kabkab (panel b-Down) dates

Fig. 7

Phylogenetic tree designed by UPGMA method based on 16S rRNA gene sequence of acetic acid bacteria studied in this project and some registered sequence in gene bank by MEGA5

Fig. 8

Phylogenetic tree designed by UPGMA method based on 16S rRNA gene sequence of lactic acid bacteria studied in this project and some registered sequence in gene bank by MEGA5