Occurrence of Yeasts in White-Brined Cheeses: Methodologies for Identification, Spoilage Potential and Good Manufacturing Practices

Abstract

Yeasts are generally recognized as contaminants in the production of white-brined cheeses, such as Feta and Feta-type cheeses. The most predominant yeasts species are Debaryomyces hansenii, Geotrichum candidum, Kluyveromyces marxianus, Kluyveromyces lactis, Rhodotorula mucilaginosa, and Trichosporon spp. Although their spoilage potential varies at both species and strain levels, yeasts will, in case of excessive growth, present a microbiological hazard, effecting cheese quality. To evaluate the hazard and trace routes of contamination, the exact taxonomic classification of yeasts is required. Today, identification of dairy yeasts is mainly based on DNA sequencing, various genotyping techniques, and, to some extent, advanced phenotypic identification technologies. Even though these technologies are state of the art at the scientific level, they are only hardly implemented at the industrial level. Quality defects, caused by yeasts in white-brined cheese, are mainly linked to enzymatic activities and metabolism of fermentable carbohydrates, leading to production of metabolites (CO 2 , fatty acids, volatile compounds, amino acids, sulfur compounds, etc.) and resulting in off-flavors, texture softening, discoloration, and swelling of cheese packages. The proliferation of spoilage yeast depends on maturation and storage conditions at each specific dairy, product characteristics, nutrients availability, and interactions with the co-existing microorganisms. To prevent and control yeast contamination, different strategies based on the principles of HACCP and Good Manufacturing Practice (GMP) have been introduced in white-brined cheese production. These strategies include milk pasteurization, refrigeration, hygienic sanitation, air filtration, as well as aseptic and modified atmosphere packaging. Though a lot of research has been dedicated to yeasts in dairy products, the role of yeast contaminants, specifically in white-brined cheeses, is still insufficiently understood. This review aims to summarize the current knowledge on the identification of contaminant yeasts in white-brined cheeses, their occurrence and spoilage potential related to different varieties of white-brined cheeses, their interactions with other microorganisms, as well as guidelines used by dairies to prevent cheese contamination.

Characterization of Bacterial Microbiota of P.D.O. Feta Cheese by 16S Metagenomic Analysis

“…bulgaricus, Streptococcus thermophilus, Leuconostoc lactis [3,4]. However, like in any fermented food complex, the microbial communities that colonize the milk used for feta production play a significant role in forming the rich flavor and aroma of the final product [2,5,6]; for example, Enterococcus faecium may also be an important part of the microbiota of other traditional cheeses, although some strains may harbor genetic determinants of virulence [7]. The salting of the curd assists with the development of microbiota, and maturation is a twostage process after the curd is placed in containers and filled up with 7% (w/w) brine, lasting for a minimum of two months.…”

“…The salting of the curd assists with the development of microbiota, and maturation is a twostage process after the curd is placed in containers and filled up with 7% (w/w) brine, lasting for a minimum of two months. Recent studies exploring the microbiota of artisanal cheese with non-culturable methods have revealed highly heterogenous microbial ecosystems that could not be detected with the standard microbiological methods [5,8]. It is important to characterize the biodiversity of feta cheese at the species level since these various microorganisms can play vital roles in the development of the organoleptic properties of cheese, nutrient composition, ripening, taste, aroma, shelf life and safety [9,10].…”

Yeasts in different types of cheese

“…Yeast identification in milk and milk products was traditionally carried out using the characteristics of the colonies, microscopy, and phenotypical characteristics, such as growth requirements, and assimilation and/or fermentation of certain carbohydrates and nitrogen compounds [24] , [25] . However, these methods are laborious, complex and may give confusing results [26] .…”

“…Denaturing High-Performance Liquid Chromatography (DHPLC) has been applied for the identification of yeasts in bacterial surface ripened cheeses [31] and for the assessment of microbial diversity in natural whey cultures used for the manufacture of an Italian pasta-filata cheese [32] . Recently, advanced methods such as Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) and Fourier Transform Infrared Spectroscopy (FTIR) have applied for dairy yeast identification purposes [24] , [33] . MALDI-TOF MS generates protein-based spectral profiles, that is fingerprints acquired by desorption of specific peptide/protein biomarkers released from the cell surface by acidic treatment, while FTIR is based on the detection of functional biochemical groups directly from intact cells, producing metabolic spectral fingerprints unique for yeast species [24] , [34] .…”

“…Recently, advanced methods such as Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) and Fourier Transform Infrared Spectroscopy (FTIR) have applied for dairy yeast identification purposes [24] , [33] . MALDI-TOF MS generates protein-based spectral profiles, that is fingerprints acquired by desorption of specific peptide/protein biomarkers released from the cell surface by acidic treatment, while FTIR is based on the detection of functional biochemical groups directly from intact cells, producing metabolic spectral fingerprints unique for yeast species [24] , [34] . Quigley et al reviewed the application of molecular methods such as DHPLC, Temporal Temperature Gradient Gel Electrophoresis (TTGE) and Single Stranded Confirmation Polymorphisms (SSCP) for the identification of microbes, including yeasts, in dairy products from raw milk [35] .…”