Yogurt and other fermented milks

Yogurt and other fermented milk

The effects of adding lactococcal proteinase on the growth rate of Lactococcus lactis in milk depend on the type of enzyme

3 tables 5 graph.International audienc

Secondary and adjunct cultures

Chapter 11International audienceTwo types of cultures are used in cheesemaking: primary and secondary. The primary cultures include all the starter lactic acid bacteria that are involved in acid production during cheese manufacturing. The secondary and adjunct cultures are involved in cheese ripening. They are called secondary cultures to distinguish them from the primary acid–producing starters, and are as important as the primary ones in those cheeses in which they are found. They include yeasts, for example, Geotrichum candidum; molds, for example, Penicillium camemberti and Penicillium roqueforti; and bacteria, for example, Brevibacterium, Corynebacterium, Staphylococcus, Propionibacterium sp., and heterofermentative lactobacilli. They are added to provide well-defined functions, such as, gas production, aspect, coloration, and development of the typical flavor. In the present chapter, the most important groups of secondary microbiota, the species found in cheeses, the properties used in their selection, and the form and use of these cultures as adjuncts will be described

Cheese rind microbial communities: diversity, composition and origin

Cheese rinds host a specific microbiota composed of both prokaryotes (such as Actinobacteria, Firmicutes and Proteobacteria) and eukaryotes (primarily yeasts and moulds). By combining modern molecular biology tools with conventional, culture-based techniques, it has now become possible to create a catalogue of the biodiversity that inhabits this special environment. Here, we review the microbial genera detected on the cheese surface and highlight the previously unsuspected importance of non-inoculated microflora-raising the question of the latter's environmental sources and their role in shaping microbial communities. There is now a clear need to revise the current view of the cheese rind ecosystem (i.e. that of a well-defined, perfectly controlled ecosystem). Inclusion of these new findings should enable us to better understand the cheese-making process

Charged casein-derived oligopeptides competitively inhibit the transport of a reporter oligopeptide by Lactococcus lactis

26 ref.International audienceAim: To study the effect of casein-derived peptides, accumulated during growth of Lactococcus lactis in milk, on its oligopeptide transport (Opp) function.Methods and Results: This effect was estimated by analysing the ability of casein-derived peptides to compete for the transport of a reporter peptide by whole L. lactis cells. The transport of the reported peptide was monitored by determining the intracellular concentrations of the corresponding amino acids by means of reverse-phase high-performance liquid chromatography (HPLC). Uptake of the reporter peptide was competitively inhibited by casein-derived peptides. The competition was only because of charged casein-derived peptides, including anionic peptides. The design of specific pure peptides made it possible to evidence for a positive (or negative) influence exerted by the positively (or negatively) charged side chain of the N-terminal amino acid on the competition.Conclusions: Charged casein-derived peptides impaired the oligopeptide transport function of L. lactis .Significance and Impact of the Study: These results demonstrate an inhibition of Opp when too many peptides are produced by the proteinase. Peptide transport by Opp therefore represents a bottleneck for increasing the growth rate of L. lactis in milk

Amino acid supply of Lactococcus lactis during growth in milk

69 ref. 8 tables 6 graph.International audienc

Debaryomyces hansenii, Proteus vulgaris, Psychrobacter sp and Microbacterium foliorum are able to produce biogenic amines

The occurrence of biogenic amines (BAs) produced by the microbiota of fermented foods is a source of health concern. The three bacteria Microbacterium foliorum, Proteus vulgaris and Psychrobacter sp. and the yeast Debaryomyces hansenii, isolated from surface-ripened cheeses, are known to contribute to their aromatic properties. The potential of each of these strains to produce BAs was investigated, both in pure cultures of each bacterium in a laboratory medium supplemented with amino acids and in mixed cultures with D. hansenii in a model cheese during the ripening process. BAs were quantified using HPLC. In the laboratory medium, all microbial strains produced at least one biogenic amine. P. vulgaris produced the highest amount of BAs, mainly putrescine and isoamylamine, with a total of 195 mg.L-1. In all of the model cheeses, the highest levels of BAs were determined at the end of ripening. With D. hansenii and M. foliorum, the total levels of BAs were below 10 mg.kg(-1) of cheese. Gram-negative bacteria, in association with D. hansenii, produced up to 25 mg.kg(-1) of BAs. Histamine was produced when Psychrobacter sp. was present, and isoamylamine, when P. vulgaris was present in the cheese ecosystem. Though these strains are able to catabolise amino acids into flavour compounds, they are also able to produce BAs, particularly putrescine, isoamylamine and histamine, showing the simultaneous expression of the two catabolic pathways. This study is a preliminary work on the assessment of the impact of all ripening microorganisms on the sanitary quality of cheese

The effect of reduced sodium chloride content on the development of fluorescent Pseudomonas in a Reblochon-like cheese

The effect of reduced sodium chloride content on the development of fluorescent Pseudomonas in a Reblochon-like cheese. Microbial Spoilers in Food 201

Behavior of Escherichia coli O26:H11 in the presence of Hafnia alvei in a model cheese ecosystem

This study was designed to evaluate the capacity of three Hafnia strains to inhibit the growth of an E. coli strain O26:H11 in an uncooked pressed model cheese, in the presence or absence of a microbial consortium added to mimic a cheese microbial community. Inoculated at 2 log CFU/ml into pasteurized milk without Hafnia, the E. coli O26:H11 strain reached 5 log CFU/g during cheese-making and survived at levels of 4 to 5 log CFU/g beyond 40 days. Inoculated into milk at 6 log CFU/ml, all three tested Hafnia strains (H. alvei B16 and HA, H. paralvei 920) reached values close to 8 log CFU/g and reduced E. coil O26:H11 counts in cheese on day 1 by 0.8 to 1.4 log CFU/g compared to cheeses inoculated with E. coil O26:H11 and the microbial consortium only. The Hafnia strains slightly reduced counts of Entero coccus faecalis (similar to-0.5 log from day 1) and promoted Lactobacillus plantarum growth (+02 to 0.5 log from day 8) in cheese. They produced small amounts of putrescine (similar to 1.3 mmol/kg) and cadaverine (similar to 0.9 mmol/kg) in cheese after 28 days, and did not affect levels of volatile aroma compounds. Further work on H. alvei strain B16 showed that E. coil O26:H11, inoculated at 2 log CFU/ml, was inhibited by H. alvei 816 inoculated at 6 log CFU/ml and not at 4.5 log CFU/ml. The inhibition was associated neither with lower pH values in cheese after 6 or 24 h, nor with higher concentrations of lactic acid. Enhanced concentrations of acetic acid on day 1 in cheese inoculated with H. alvei B16 (4 to 11 mmol/kg) could not fully explain the reduction in E. coil O26:H11 growth. A synergistic interaction between H. alvei B16 and the microbial consortium, resulting in an additional 0.7-log reduction in E. coli O26:H11 counts, was observed from day 8 in model cheeses made from pasteurized milk. However, E. coil O26:H11 survived better during ripening in model cheeses made from raw milk than in those made from pasteurized milk, but this was not associated with an increase in pH values. In vitro approaches are required to investigate the mechanisms and causative agents of this interaction. H. alvei B16 appears to be a. promising strain for reducing E. coil O26:H11 growth in cheese, as part of a multi-hurdle approach. (C) 2012 Elsevier B.V. All rights reserved

Ecological and aromatic impact of two Gram-negative bacteria ( Psychrobacter celer and Hafnia alvei) inoculated as part of the whole microbial community of an experimental smear soft cheese

The impact of the growth of two Gram-negative bacteria, Psychrobacter celer and Hafnia alvei, inoculated at 10(2) and 10(6) cfu/g, on the dynamics of a multispecies community as well as on volatile aroma compound production during cheese ripening was investigated. Results showed that P. celer was able to successfully implant itself in cheese, regardless of its inoculation level. However, when it was inoculated at a high level, the bacterial biodiversity was drastically lowered from day 25 to the end of ripening. Overall, the presence of P. celer led to the higher production of volatile aroma compounds such as aldehydes, ketones and sulfur compounds. Regardless of its inoculation level, H. alvei barely affected the growth of the bacterial community and was subdominant at the end of ripening. It influenced total volatile aroma compound production with volatile sulfur compounds being the most abundant. Overall, these two bacteria were able to implant themselves in a cheese community and significantly contributed to the aromatic properties of the cheese. Their role in flavoring and their interactions with the technological microorganisms must be considered during cheese ripening and should be further investigated