This chapter describes the interactions of microorganisms with dairy foods that lead to commonly encountered product defects. The major microbial inhibitors in raw milk are lactoferrin and the lactoperoxidase system. Fluid milk, cheese, and cultured milks are the major dairy products susceptible to spoilage by non-spore-forming fermentative bacteria. Non-spore-forming bacteria responsible for fermentative spoilage of dairy products are mostly in either the lactic acid-producing or coliform group. The most common fermentative defect in fluid milk products is souring caused by the growth of lactic acid bacteria. The defect in noncultured fluid milk products is usually caused by growth of specific strains of lactococci. Spore-forming bacteria that spoil dairy products usually originate in the raw milk. The defect in milk products is described as sweet curdling, since it first appears as coagulation without significant acid or off flavor being formed. The major heat-resistant species in milk is Geobacillus stearothermophilus (formerly Bacillus stearothermophilus). A practical means to prevent sporeformers from spoiling nonfermented liquid dairy products given sub-ultrahigh-temperature (UHT) heat treatments has not been developed. The most common yeasts present in dairy products are Kluyveromyces marxianus and Debaryomyces hansenii (the teleomorph) and their asporogenous counterparts (the anamorph), Candida species, and Zygosaccharomyces microellipsoides. Yeasts and molds that spoil dairy products can usually be isolated in the processing plant on packaging equipment, in the air, in salt brine, on manufacturing equipment, and in the general environment (floors, walls, ventilation ducts, etc.).

Milk and Dairy Products

The diversity of the microbial community on cow teat skin was evaluated using a culture-dependent method based on the use of different dairy-specific media, followed by the identification of isolates by 16S rRNA gene sequencing. This was combined with a direct molecular approach by cloning and 16S rRNA gene sequencing. This study highlighted the large diversity of the bacterial community that may be found on teat skin, where 79.8% of clones corresponded to various unidentified species as well as 66 identified species, mainly belonging to those commonly found in raw milk (Enterococcus, Pediococcus, Enterobacter, Pantoea, Aerococcus, and Staphylococcus). Several of them, such as nonstarter lactic acid bacteria (NSLAB), Staphylococcus, and Actinobacteria, may contribute to the development of the sensory characteristics of cheese during ripening. Therefore, teat skin could be an interesting source or vector of biodiversity for milk. Variations of microbial counts and diversity between the farms studied have been observed. Moreover, Staphylococcus auricularis, Staphylococcus devriesei, Staphylococcus arlettae, Streptococcus bovis, Streptococcus equinus, Clavibacter michiganensis, Coprococcus catus, or Arthrobacter gandavensis commensal bacteria of teat skin and teat canal, as well as human skin, are not common in milk, suggesting that there is a breakdown of microbial flow from animal to milk. It would then be interesting to thoroughly study this microbial flow from teat to milk.

https://hal.archives-ouvertes.fr/hal-01137155/document

Cow Teat Skin, a Potential Source of Diverse Microbial Populations for Cheese Production

Predominant Microflora of Downgraded Danish Bulk Tank Milk

An Ecological Study of the Psychrotrophic Bacteria of Soil, Water, Grass and Hay

Modification of Milk Proteins by Psychrotrophic Bacteria

Investigation of factors contributing to the bacterial count of bulk tank milk. II. Bacteria in milk from individual cows.

Investigation of factors contributing to the bacterial count of bulk-tank milk. I. Influence of two-day storage and effect on results of preliminary incubation.

Investigation of Factors Contributing to the Bacterial Count of Bulk Tank Milk. III. Increase in Count, from Cow to Bulk Tank, and Effects of Refrigerated Storage and Preliminary Incubation

C.K. Johns

Papers

Investigation of factors contributing to the bacterial count of bulk tank milk. II. Bacteria in milk from individual cows.

Investigation of factors contributing to the bacterial count of bulk-tank milk. I. Influence of two-day storage and effect on results of preliminary incubation.

Investigation of Factors Contributing to the Bacterial Count of Bulk Tank Milk. III. Increase in Count, from Cow to Bulk Tank, and Effects of Refrigerated Storage and Preliminary Incubation