Tony Savard

Selection and characterization of mixed starter cultures for lactic acid fermentation of carrot, cabbage, beet and onion vegetable mixtures

An evaluation of various lactic acid bacteria (LAB) for the fermentation of cabbage, carrot and beet-based vegetable products was carried out. As part of a screening process, the growth of 15 cultures in a vegetable juice medium (VJM) was characterized by automated spectrophotometry. Acidification patterns as well as viability during storage of the LAB were also established. There were greater differences between the pure cultures than the mixed ones with respect to growth in VJM and viability during storage. Reductions in viable cell counts during storage of the fermented VJM occurred more rapidly with a Leuconostoc strain than for pediococci or lactobacilli. Inoculation of vegetables was carried out with cultures of Lactobacillus plantarum NK-312, Pediococcus acidilactici AFERM 772 and Leuconostoc mesenteroides BLAC which were rehydrated in a brine. This rehydration procedure was not detrimental to viability. During fermentation of a carrot/cabbage vegetable mix, sugar metabolism was characterized by the assimilation of both glucose and fructose, but sugars remained in the fermented vegetables when acidification stopped. The pH in the LAB-inoculated vegetables after 72 h at 20 degrees C was significantly lower (by 0.2 units) than the uninoculated control. Inoculation with LAB designed for silage fermentation resulted in the inhibition of acetic acid production, and reduced the production of ethanol during fermentation. The selection process on VJM enabled the preparation of a mixed culture that was more rapid than the silage inoculants in acidifying the medium and was more effective in reducing the production of gas during the fermentation and storage of the fermented vegetables.

Antimicrobial Action of Hydrolyzed Chitosan against Spoilage Yeasts and Lactic Acid Bacteria of Fermented Vegetables

The antimicrobial properties of various chitosan-lactate polymers (ranging from 0.5 to 1.2 MDa in molecular weight) against two yeasts isolated from fermented vegetables and against three lactic acid bacteria from a mixed starter for sauerkraut on methylene blue agar (MBA) and in vegetable juice medium (VJM) were investigated. Chitosan-lactate reduced the growth of all microorganisms in solid (MBA) as well as in liquid (VJM) medium. In MBA, a concentration of 5 g/liter was needed to inhibit the growth of Saccharomyces bayanus, while 1 g/liter was sufficient to inhibit the growth of Saccharomyces unisporus. Lactic acid bacteria were also inhibited in this range of concentrations. The low-molecular-weight chitosan-lactate DP3 (0.5 kDa) was most efficient in solid medium (MBA), and inhibitory activities decreased with increasing hydrolysate lengths. In liquid medium (VJM), 0.5 g of chitosan-lactate per liter reduced the growth rates for both yeasts, but 10 g/liter was insufficient to prevent yeast growth. Intermediate-molecular-weight chitosan-lactate (5 kDa) was more efficient than chitosan of low molecular weight. Native chitosan (1.2 MDa) showed no inhibition in either medium. Microscopic examination of S. unisporus Y-42 after treatment with chitosan-lactate DP25 showed agglutination of a refractive substance on the entire cell wall, suggesting an interaction between chitosan and the cell wall. When chitosanase was added to the culture media containing chitosan-lactate, refractive substances could not be observed.

Evaluation of survival of murine norovirus-1 during sauerkraut fermentation and storage under standard and low-sodium conditions

Sodium reduction strategies have raised a few concerns in regards to possible outbreaks in unpasteurised raw fermented vegetables. Among potential outbreak agents, foodborne viruses are recognized as an important cause of food-borne illnesses. As most of them are acid-resistant, evaluation of the efficacy of lactic fermentation in inactivating enteric viruses must be considered to ensure the safety of these foods. In particular with the sodium reduction trend which could impair adequate fermentation in vegetables, we have challenged sauerkraut fermentation at a final concentration of 4 log TCID50/mL with the murine norovirus (MNV-1). Three sodium chloride concentrations (1.0%, 1.5%, 2.0%) were evaluated in spontaneous and starter fermentation of sauerkraut and were followed during fermentation and over a storage phase of 90 days. Detection of MNV-1 genetic material was carried out by real-time RT-PCR and the infectivity on cell culture. Real-time RT-PCR results showed that viral RNA was still detected after 90 day in sauerkraut under all the different conditions. Furthermore, MNV-1 viral particles were able to infect RAW cells after 90 days of storage with a non-significant viral charge reduction. Sodium reduction has a significant impact on the fermentation processing of sauerkraut but no influence on the destruction of norovirus particles or on their survival.

Population yields and vegetable juice fermentation of Leuconostoc mesenteroides cultures grown under free-cell or immobilized-cell technologies.

Leuconostoc mesenteroides BLAC cultures were produced using classical free-cell fermentation technology and immobilized cell technology (ICT). The ICT process consisted of entrapping the culture into alginate or pectin beads, adding them to a growth medium, and incubating for 14 h to allow growth of the culture inside the beads. Cell populations, survival to freeze-drying and specific acidifying activity (SAA) following inoculation in vegetable juices were examined. In free cell fermentations, 1.3 × 1010 cells/mL were obtained while 1.6 to 2.0 × 1011 cells/g were found in beads. The total cell counts recovered per fermentor were similar in free-cell and ICT systems. In the ICT process, the free-cell level was only of 1% or less. No difference in population yields were noted between alginate and pectin gels. Survival to freeze-drying was between 65 and 80% and was not significantly affected by the prior fermentation process nor the alginate or pectin matrix. A methodology was developed to ascertain the free-cell content of the freeze-dried ICT cultures, and data showed that they contained 97.5% of gel-entrapped cells. Freshly prepared free-cell suspensions had four times higher SAA than comparative free-cell freeze-dried cultures. The dried ICT cultures had lower SAA than free-cell equivalents, but there was no significant effect of the ICT matrix (alginate or pectin) on SAA. The powders of the ICT culture were ground and sieved to obtain particles ranging from 38 μm to 1000 μm in diameter. The smaller the particle, the higher was its SAA. Fermentation of vegetable juices or pastes were carried out with the free and ICT cultures. In the ICT fermentation, the free-cell content of the inoculum represented 2.5% of the total population, but this increased to 88% after the 22 h incubation in vegetable juice. Data are discussed in relationship with potential benefits of ICT cultures in vegetable fermentations.