-Dairy propionibacteria are important organisms for the manufacture of Swiss-type cheese, for the biological production of propionate and vitamin 8 12 and have probiotic properties. In ail the se applications, their metabolic activities play a critical role. A complete understanding of propionate fermentation and of the metabolic routes used is therefore necessary. Dairy propionibacteria have a complex metabolism and involves several cycles. Lactate or sugars utilisation yields pyruvate which can be reduced to produce propionate via the transcarboxylase cycles, or oxidised to yield acetate and CO 2 • During the coupled oxidation-reduction, ATP is produced by an electron transport system and fumarate acts as the final acceptor. Although propionibacteria are mainly anaerobes, the electron transport system can be used in the presence of oxygen and they possess the citrate cycle, but can not grow under normal atmospheric oxygen pressure. The proportions of propionate acetate and CO 2 produced vary depending on the strain used and this can be explained, to sorne extent, by their relative ability to utilise pyruvate via reactions of the citrate cycle. The physicochemical environ ment during growth affects propionic acid fermentation; it is impaired by the presence of oxygen and nitrate, but fermentation at acidic pHs enhances propionate production. Fermentation in presence of more than one substrate is complex and still poorly understood. When both L-and D-lactate isomers are available, L-lactate is used preferentially. Although sugar fermentation is more efficient, in the presence of lactate and sugars, there is evidence that lactate is used preferentially. Propionic acid fermentation is affected by the utilisation of amino acids, especially aspartate; co-metabolism of lactate and aspartate results in a lower propionate production and a decrease of the ratio propionate:acetate. There is evidence that the utilisation of the products of proteolysis is an important event in the ripening of Swiss-type chee se and could account for the low propionate:acetate ratios observed in Swiss-type cheese. © Inra/Elsevier, Paris.propionic acid bacteria {lactate { sugar { metabolism Résumé -Métabolisme du lactate et des sucres par les bactéries propioniques laitières: une revue. Les bactéries propioniques laitières sont importantes pour la fabrication de fromages de type emmental, pour la production biologique de propionate et de vitamine 8 12 ainsi que pour leurs propriétés probiotiques. Dans ces domaines, leurs activités métaboliques ont un rôle crucial. Il est donc Oral communication at the 2nd Symposium on Propionibacteria, Cork, Ireland, June 25-27, 1998. * Correspondence and reprints. P.Piveteau@hotmail.com 24 P. Piveteau nécessaire de comprendre de façon approfondie la fermentation propionique et les voies métabo-liques empruntées. Les bactéries propioniques possèdent un métabolisme complexe impliquant plusieurs cycles. Le pyruvate issu de l'utilisation du lactate et des sucres peut être réduit, ce qui conduit à la pr...

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Growth of propionibacteria in complex media was independent of the initial number of cells; in contrast, growth of propionibacteria in milk and whey did not occur if the initial level of cells was <106 cfu/ml. Addition of vitamins, minerals or complex nitrogen sources to the milk or whey, or incubation under anaerobic conditions had no effect on the lack of growth. Addition of freeze-dried whey, prepared from skim milk reconstituted from powder, to a complex medium prevented growth from low inocula in the complex medium, demonstrating the presence of an inhibitor or inhibitors in the whey. The inhibitor(s) was heat stable, had a low molecular mass and retained its activity for at least 4 weeks at 20 °C. Pregrowth of some lactic acid bacteria, used as starter cultures in Swiss-type cheese manufacture, in milk for 2 weeks at 20 °C removed the inhibition, which explains how propionibacteria develop in Swiss-type cheese from low numbers even though they are inhibited in milk.

-Growth of P. freudenreichii DPC 3801 in whey was stimulated by peptone, tryptone, pre-growth of Lactobacillus helveticus DPC 4571 in milk and by sodium caseinate hydrolysed with the crude proteinase of Lb. helveticus DPC 4571. Addition of vitamins (riboflavin, thiamine, PABA, Ca panthothenate, biotin and nicotinic acid) and minerals (MgSO 4 and MnCl 2 ) to control whey did not improve the growth of P. freudenreichii. CoCl 2 and CuSO 4 inhibited growth. Growth of the lactobacillus in milk resulted in significant increases in peptide and amino acid production but the amino acids produced did not stimulate the growth of the PAB. Several chromatographic procedures, including ion-exchange, gel permeation and reverse-phase, high-pressure liquid chromatography failed to categorically identify the peptide(s) responsible for the stimulation of the PAB. In some of these chromatographic systems, the stimulatory activity was shown to be present in several peaks implying that different peptides were involved. Several tetra-, penta-and hexa-peptides produced by other strains of Lb. helveticus from α s -and β-casein had a small but significant effect on growth of P. freudenreichii DPC 3801. Based on these results it was concluded that stimulation of P. freudenreichii was due to production of peptides by Lb. helveticus from casein. Propionibacterium freudenreichii / Lactobacillus helveticus / peptide / wheyRésumé -Caractérisation des stimulants produits par Lactobacillus helveticus dans le lait pour Propionibacterium freundenreichii. La croissance de Propionibacterium freudenreichii DPC 3801 dans du lactosérum était stimulée par la peptone, la tryptone, une pré-croissance de Lactobacillus helveticus DPC 4571 dans le lait et un caséinate de sodium hydrolysé par la protéase purifiée de L. helveticus DPC 4571. L'ajout de vitamines (riboflavine, thiamine, PABA, Ca panthothenate, biotine et acide nicotinique) et de minéraux (MgSO 4 et MnC1 2 ) au lactosérum témoin ne stimule pas la croissance de P. freudenreichii ; CoC1 2 et CuSO 4 l'inhibent. La croissance de L. helveticus dans le lait entraîne une augmentation significative en peptides et acides aminés, mais les acides aminés produits ne stimulent pas la croissance des PAB. Différentes méthodes chromatographiques, incluant l'échange d'ions, la perméation sur gel, et la phase inverse ne permirent pas d'identifier le(s) peptide(s) responsables de la stimulation. L'activité stimulante était présente dans plusieurs pics chromatographiques indiquant que différents peptides sont impliqués. Plusieurs tetra-et hexapeptides produits par d'autres souches de L. helveticus à partir de caséines α et β ont un effet stimulant faible mais significatif sur la croissance de P. freudenreichii DPC 3801. Sur la base de l'ensemble de ces résultats, la stimulation de P. freudenreichii serait due à la production par L. helveticus de peptides à partir des caséines.Propionibacterium freudenreichii / Lactobacillus helveticus / peptide / lactosérum