title: Effect of inoculum composition and low KCl supplementation on the biological and rheological stability of an immobilized-cell system for mixed mesophilic lactic starter production.
abstract: Two strains of Lactococcus lactis subsp. lactis (L. lactis KB and KBP) and one of L. lactis subsp. lactis biovar. diacetylactis (L. diacetylactis MD) were immobilized separately in kappa-carrageenan-locust bean gum gel beads. Continuous fermentations were carried out in supplemented whey permeate in a 1-L pH-controlled stirred tank reactor inoculated with a 30% (v/v) bead inoculum and a bead ratio of 55:30:15 for KB, KBP, and MD, respectively. The process demonstrated a high productivity and microbial stability during the 7-week continuous culture. Compared with previous experiments carried out with an inoculum bead ratio of 33:33:33 for KB, KBP, and MD beads, respectively, the modification of the inoculum bead ratio had apparently little effect on free and immobilized, total and specific populations. A dominant behavior of L. diacetylactis MD over the other strains of the mixed culture was observed both with free-cell populations in the effluent and with immobilized-cell populations. Additional experiments were carried out with other strain combinations for continuous inoculation-prefermentation of milk. The data also confirmed the dominance of L. diacetylactis during long-term continuous immobilized-cell fermentations. This dominance may be tentatively explained by the local competition involved in the development of the bead cross-contamination and in citrate utilization by L. diacetylactis strains. The gel beads demonstrated a high rheological stability during the 7-week continuous fermentation even at low KCl supplementation of the broth medium (25 mM KCl).
authors.affiliation: Dairy Research Centre STELA, Pavillon Paul Comtois, Université Laval, Québec, QC, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Lamboley
authors.forename: C
authors.initials: C
authors.lastname: Lacroix
authors.forename: I
authors.initials: I
authors.lastname: Sodini
authors.forename: M J
authors.initials: MJ
authors.lastname: Lemay
authors.forename: C P
authors.initials: CP
authors.lastname: Champagne
mesh_terms: D000818:Animals; D002241:Carbohydrates / Q000032:analysis; D018914:Cells, Immobilized; D015169:Colony Count, Microbial; D003470:Culture Media; D005285:Fermentation; D019344:Lactic Acid / Q000096:biosynthesis*; D013294:Lactococcus lactis / Q000187:drug effects / Q000378:metabolism*; D008892:Milk / Q000737:chemistry / Q000382:microbiology; D011189:Potassium Chloride / Q000494:pharmacology*; D012212:Rheology
chemical_list: D002241:Carbohydrates; D003470:Culture Media; D019344:Lactic Acid; D011189:Potassium Chloride