Evolution of carrot pulps during spontaneous fermentation
Résumé
The spontaneous fermentation of carrot pulps was followed under different conditions during nine consecutive days. Trials were carried out to obtain interesting compounds: organic acids and volatile molecules. Factors were tested with a two-level full factorial design: temperature (24°C/37°C), grinding (with/without), addition of water (0%/50% w/w) and refreshment of the fermentation medium (without/after 3 or 7 days of incubation). During the course of the fermentations, different parameters were measured: microbial gross composition and diversity (REP-PCR), pH, lactic and acetic acids, ethanol, phenolic and volatiles compounds (SPME-GC-MS). Whatever the culture conditions tested, the pulp ecosystem remained quantitatively stable from the beginning to the end of the culture step. It was dominated by lactic acid bacteria (LAB), followed by Enterococci, yeasts, moulds and acetic acid bacteria (AAB); Enterobacteriaceae, Bacillus and Pseudomonas were found at low levels. However, the composition of each population changed. As a consequence, the LAB proved to be the most influencing population on the production of ethanol, acetic acid and lactic acid. 2-Butanol was also detected in the fermented pulps; but no relation was found with the microorganisms looked for. Among the factors tested, the rise in temperature led to a decrease in the production of acetic acid, ethanol and D-lactic acid.
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