Jacques Goulet

Attachment of Listeria monocytogenes to stainless steel, glass, polypropylene, and rubber surfaces after short contact times

This study was carried out to investigate the attachment capabilities of Listeria monocytogenes strain Scott A to stainless steel, glass, polypropylene, and rubber surfaces after short contact times at ambient (20°C) and cold storage temperatures (4°C) using scanning electron microscopy technique. Surface energy value of each surface was estimated by contact angle measurements. All surfaces displayed many possible harborages for L. monocytogenes attachment. Our results indicated that L. monocytogenes cells could attach to all surface types at both temperatures after contact times as short as 20 min or 1 h. Extracellular materials could be observed on the surfaces especially polypropylene and glass incubated at 4 and 20°C for 1 h respectively.

Batch fermentation of whey ultrafiltrate by Lactobacillus helveticus for lactic acid production

SummaryCheese whey ultrafiltrate (WU) was used as the carbon source for the production of lactic acid by batch fermentation with Lactobacillus helveticus strain milano. The fermentation was conducted in a 400 ml fermentor at an agitation rate of 200 rpm and under conditions of controlled temperature (42° C) and pH. In the whey ultrafiltrate-corn steep liquor (WU-CSL) medium, the optimal pH for fermentation was 5.9. Inoculum propagated in skim milk (SM) medium or in lactose synthetic (LS) medium resulted in the best performance in fermentation (in terms of growth, lactic acid production, lactic acid yield and maximum productivity of lactic acid), as compared to that propagated in glucose synthetic (GS) medium. The yeast extract ultrafiltrate (YEU) used as the nitrogen/growth factor source in the WU medium at 1.5% (w/v) gave the highest maximum productivity of lactic acid of 2.70 g/l-h, as compared to the CSL and the tryptone ultrafiltrate (TU). L. helveticus is more advantageous than Streptococcus thermophilus and Lactobacillus delbrueckii for the production of lactic acid from WU. The L. helveticus process will provide an alternative solution to the phage contamination in dairy industries using Lactobacillus bulgaricus.

Optimal conditions for production of lactic acid from cheese whey permeate by Ca-alginate-entrapped Lactobacillus helveticus

Abstract Whole cells of Lactobacillus helveticus were immobilized in calcium-alginate beads to produce lactic acid from cheese whey ultrafiltrate. Ca-alginate-entrapped cells were characterized by higher fermentation rates and optimum pH than free cells. No difference could be observed in the profile of cell activity against temperature for either type of cells. After a heat treatment, cell activity was higher for free cells than for immobilized cells. Continuous lactic acid fermentation using a packed bed reactor was investigated.

β-casomorphin 4 from milk fermented by a mutant of Lactobacillus helveticus

Abstract Hydrophobic peptides were isolated from milk fermented by a wild-type strain and a mutant strain of Lactobacillus helveticus L89 deficient in X-prolyl-dipeptidyl aminopeptidase (X-PDAP, EC.3.4.14.5) which is specific for peptide bonds on the carboxyl side of proline residues. Peptides were fractionated by RP-HPLC. Chromatogram profiles showed differences in peptide elution time, concentration and number. An opioid peptide, β-casomorphin 1–4 (60–63), was detected in a peptide extract derived from milk fermented with an X-PDAP-deficient mutant of L. helveticus . The molecular weight of this tetrapeptide was confirmed by mass spectrometry. A tetradecapeptide present in the wild-type culture (β-cas 106–119) was absent in the mutant strain culture after 24 h of fermentation with the pH controlled at 6.

Adhesion of Pathogenic Bacteria to Food Contact Surfaces: Influence of pH of Culture.

The adhesion of Aeromonas hydrophila, Escherichia coli O157:H7, Salmonella Enteritidis, and Staphylococcus aureus to hydrophobic and hydrophilic surfaces in cultures with different pHs (6, 7, and 8) was studied. The results indicated that the type of material had no effect on the attachment capacity of microorganisms, while environmental pH influenced the adhesion of A. hydrophila, E. coli, and S. aureus to both solid substrates. The attachment of S. Enteritidis (P > .05) was not affected by the type of substrate or the culture pH, whereas E. coli displayed the weakest affinity for both polystyrene and glass surfaces. No correlation was established between the physicochemical properties of the materials, or the bacterial and the rate of bacterial adhesion, except for S. aureus. Photomicrographs have shown that surfaces were contaminated by small clusters of S. Enteritidis while S. aureus invaded the food contact surfaces in the form of small chains or cell aggregates.

Growth of Lactobacillus paracasei ssp. paracasei on tofu whey

The liquid by-product of the soybean product tofu, tofu whey (TW), was used as a growth medium for the production of Lactobacillus paracasei ssp. paracasei LG3 cultures. The TW used in this study contained stachyose, raffinose, sucrose, fructose and glucose, but the strain used could only utilize the three latter. The lactobacilli population obtained in MRS broth was three times higher than that in TW alone, and supplementation of TW was thus examined. Of 19 mixtures of yeast extracts (YE), peptones and potato extracts examined, the best nitrogen sources were YE and tryptone. The addition of YE, salts (phosphates, citrates, Mg and Mn), glucose as well as Tween to TW tripled the populations to 2.9 x 10(9) cfu/ml, which was as high as that obtained in MRS broth. Growth of L. paracasei LG3 in cow rehydrated skim milk was inferior to that in TW.

Production of alginate beads by a rotative atomizer

The use of a rotative flat disc atomizer for the production of biocatalysts immobilized in alginate gel was investigated. The influence of viscosity (0.28 to 1.53 Pa · s), disc diameter (5 to 20 cm), flow rate (0.5 to 2 L/min) and rotational speed (1.6 to 5 rev/s) on drop formation mechanisms, bead diameter and their distributions were investigated. Bead diameters ranging from 1 to 3 mm were been obtained. Flow rate and viscosity increases resulted in higher bead diameters but increasing disc diameter and rotational speed had a decreasing effect. A viscosity of 0.65 Pa · s would prove best for production of beads with good size distribution and mechanical strength. Predictive equations for the mean volumetric bead diameter were determined.

Production of Propionibacterium freudenreichii subsp. shermanii in Whey-based media

Diluted cheese whey permeate supplemented with FACMP (Fermented Ammoniated Condensed Milk Permeate) was used as a culture medium for the production of Propionibacterium freudenreichii subsp. shermanii. FACMP was obtained through a mixed fermentation of milk permeate by Lactobacillus helveticus and Streptococcus thermophilus under pH control with gaseous ammonia. Uptake of carbon substrates (lactose and lactic acid) and production of organic acids (propionic, acetic, pyruvic) were followed by HPLC. Addition of yeast extract and KH2PO4 increased the growth rate; a cell population of 1.3 × 1010 colony forming units/ml was obtained within 48 h (3% v/v inoculum). Replacing FACMP by commercial sodium lactate or full strength whey permeate was investigated. Overall, the lactose medium (whey) was less efficient than the lactate supplemented media (FACMP, sodium lactate) in promoting bacterial growth and acid production. The use of FACMP instead of commercially available synthetic lactate improved the bacterial growth of P. shermanii by 25%.

Effect of intermittent CO2 enrichment during nutrient starvation on tertiary treatment of wastewater by alginate-immobilized Scenedesmus bicellularis

A method of accelerating the removal of ammonium and phosphate by the unicellular microalga Scenedesmus bicellularis is presented for municipal tertiary wastewater treatment using immobilized cells to obtain a high quality of effluents. Microalgal cells grown in defined medium were harvested by centrifugation and stored at 4°C in the dark for 8 months before immobilization. The concentrated cell suspension was then immobilized in alginate films supported on polypropylene screens. Immobilized cells were incubated in a water-saturated air stream enriched with CO2 at 750, 1,000, or 1,500 ppm for 3 h periods followed by 2 h periods without enrichment. The quantitative effects of these three CO2 enrichments on nutrient uptake from secondary municipal wastewater effluent were compared to a control laboratory air at 320 ppm under the same conditions of illumination, photoperiod, and humidity. The exposure cycle of 48-h nutrient deprivation in air with CO2 enrichment followed by 2 h of nutrient uptake from wastewater was repeated three times with a residual NH4N content dropping to 0% after 105 min for the 1,500 ppm CO2 treatment and to 34% of the initial level after 120 min for the control treatment. Complete PO4P removal required more than 2 h. The chlorophyll a contents obtained with 1,000 and 1,500 ppm CO2 enrichments were comparable. This study establishes that intermittent CO2 enrichment during nutrient deprivation of immobilized microalgal cells in a water-saturated air stream may accelerate tertiary wastewater treatment.

Continuous production of small peptides from milk proteins by extracellular proteases of free and immobilized Serratia marcescens cells

Abstract The continuous production of small peptides from buttermilk protein proteolysis has been studied using whole free and immobilized Serratia marcescens cells as an enzyme source. The hydrolysis reaction was carried out in a reactor at various dilution rates from 0.15 to 0.50 h−1. Results showed that the cell population was stable, even at high flow rates, but the extent of hydrolysis varied as a function of residence time, and decreased as the dilution rate increased. Data from the distribution of the resulting peptides according to molecular weight and aromatic residues showed that the hydrolysates obtained result from the common action of an endopeptidase system favored by low flow rate, and an exopeptidase system that preferentially hydrolysed on aromatic terminal peptide and that was favored by high flow rate. In both reactors, the large protein residues were hydrolysed extensively, but more free amino acids were liberated in the immobilized cell system than in the free cell system. We obtained the best production of useful peptides corresponding to the characteristics of a dietary product in the free cell system, at a dilution rate of 0.25 h−1 (57% peptides with 2–10 amino acid residues in the hydrolysate).