Microbiological Characterization of Greek Galotyri Cheese PDO Products Relative to Whether They Are Marketed Fresh or Ripened

Galotyri is the most popular traditional Greek PDO soft acid-curd cheese. This study compared the microbial numbers and types and characterized the lactic acid bacteria (LAB) biota of two artisan-type Galotyri PDO cheese varieties, one marketed fresh (Brand-K) and the other ripened (Brand-Z). Two retail batches of each cheese variety were analyzed, and a total of 102 LAB isolates were biochemically identified. LAB (7.2–9.3 log CFU/g) prevailed in all cheeses, followed by yeasts (5.8–6.8 log CFU/g). Typical starter strains of Streptococcus thermophilus and Lactobacillus delbrueckii were the most abundant species in all batches. However, the fresh Brand-K cheeses had 1–3 log units higher thermophilic starter LAB counts than the ripened Brand-Z cheeses, which contained a more diverse viable LAB biota comprising Lacticaseibacillus paracasei, Leuconostoc mesenteroides, Lentilactobacillus (L. diolivorans, L. kefiri, L. hilgardii), Pediococcus inopinatus/parvulus, few spontaneous nonstarter thermophilic streptococci and lactobacilli, and Enterococcus faecium and E. faecalis at higher subdominant levels.Conversely, the fresh Brand-K cheeses were enriched in members of the Lactiplantibacillus plantarum group; other LAB species were sporadically isolated, including Lactococcus lactis. All retail cheeses were safe (pH 3.9–4.0). No Salmonella spp. or Listeria monocytogenes were detected in 25-g samples by culture enrichment; however, Listeria innocua and coagulase-positive staphylococci (850 CFU/g) survived in one ripened batch. Gram-negative bacteria were <100 CFU/g in all cheeses. In conclusion, ripening reduced the starter LAB viability but increased the nonstarter LAB species diversity in the present Galotyri PDO market cheeses

Microbiological and Metagenomic Characterization of a Retail Delicatessen Galotyri-Like Fresh Acid-Curd Cheese Product

This study evaluated the microbial quality, safety, and ecology of a retail delicatessen Galotyri-like fresh acid-curd cheese traditionally produced by mixing fresh natural Greek yogurt with ‘Myzithrenio’, a naturally fermented and ripened whey cheese variety. Five retail cheese batches (mean pH 4.1) were analyzed for total and selective microbial counts, and 150 presumptive isolates of lactic acid bacteria (LAB) were characterized biochemically. Additionally, the most and the least diversified batches were subjected to a culture-independent 16S rRNA gene sequencing analysis. LAB prevailed in all cheeses followed by yeasts. Enterobacteria, pseudomonads, and staphylococci were present as <100 viable cells/g of cheese. The yogurt starters Streptococcus thermophilus and Lactobacillus delbrueckii were the most abundant LAB isolates, followed by nonstarter strains of Lactiplantibacillus, Lacticaseibacillus, Enterococcus faecium, E. faecalis, and Leuconostoc mesenteroides, whose isolation frequency was batch-dependent. Lactococcus lactis isolates were sporadic, except for one cheese batch. However, Lactococcus lactis, Enterobacteriaceae, Vibrionaceae, Salinivibrio, and Shewanellaceae were detected at fairly high relative abundances culture-independently, despite the fact that their viable counts in the cheeses were low or undetectable. Metagenomics confirmed the prevalence of S. thermophilus and Lb. delbrueckii. Overall, this delicatessen Galotyri-like cheese product was shown to be a rich pool of indigenous nonstarter LAB strains, which deserve further biotechnological investigation

Growth Inhibitory and Selective Pressure Effects of Sodium Diacetate on the Spoilage Microbiota of Frankfurters Stored at 4 °C and 12 °C in Vacuum

This study evaluated microbial growth in commercial frankfurters formulated with 1.8% sodium lactate (SL) singly or combined with 0.25% sodium diacetate (SDA), vacuum-packaged (VP) and stored at 4 °C and 12 °C. Standard frankfurters without SDA, containing 0.15% SL, served as controls (CN). Lactic acid bacteria (LAB) were the exclusive spoilers in all treatments at both storage temperatures. However, compared to the CN and SL treatments, SL + SDA delayed growth of LAB by an average of 5.1 and 3.1 log units, and 3.0 and 2.0 log units, respectively, after 30 and 60 days at 4 °C. On day 90, the SL + SDA frankfurters were unspoiled whereas the SL and CN frankfurters had spoiled on day 60 and day 30 to 60, respectively. At 12 °C, LAB growth was similar in all treatments after day 15, but strong defects developed in the CN and SL frankfurters only. Differential spoilage patterns were associated with a major reversal of the LAB biota from gas- and slime-producing Leuconostoc mesenteroides and Leuconostoc carnosum in the CN and SL frankfurters to Lactobacillus sakei/curvatus in the SL + SDA frankfurters. Thus, SL + SDA extends the retail shelf life of VP frankfurters by delaying total LAB growth and selecting for lactobacilli with a milder cured meat spoilage potential than leuconostocs, particularly under refrigeration

Role of Glucose in Enhancing the Temperature-Dependent Growth Inhibition of Escherichia coli O157:H7 ATCC 43895 by a Pseudomonas sp.

Growth of Escherichia coli O157:H7 strain ATCC 43895 was monitored at 5, 10, 15, and 25°C in both pure and mixed (1:1) cultures with a gluconate-producing Pseudomonas sp. found in meat to evaluate the effect of the absence and presence of 1% glucose in broth on temperature-dependent competition. The number of colonies of the Pseudomonas strain exceeded 9 log CFU/ml under all conditions tested. The pathogen grew better as the temperature increased from 10 to 15 and 25°C and grew better in pure culture than in mixed cultures. Pseudomonas sp. inhibited E. coli O157:H7 in cocultures with glucose at 10°C, while at 15°C the pathogen exhibited a biphasic pattern of growth with an intermediate inactivation period. Pathogen inhibition was much weaker in cocultures grown without glucose at 10 to 15°C and, irrespective of glucose, at 25°C. These results indicate that glucose enhances the growth inhibition of E. coli O157:H7 by some Pseudomonas spp., potentially due to its rapid uptake and conversion to gluconate, at low (≤15°C) temperatures

Growth and Biocontrol of Listeria monocytogenes in Greek Anthotyros Whey Cheese without or with a Crude Enterocin A-B-P Extract: Interactive Effects of the Native Spoilage Microbiota during Vacuum-Packed Storage at 4 °C

Effective biopreservation measures are needed to control the growth of postprocess Listeria monocytogenes contamination in fresh whey cheeses stored under refrigeration. This study assessed growth and biocontrol of inoculated (3 log10 CFU/g) L. monocytogenes in vacuum-packed, fresh (1-day-old) or ‘aged’ (15-day-old) Anthotyros whey cheeses, without or with 5% of a crude enterocin A-B-P extract (CEntE), during storage at 4 °C. Regardless of CEntE addition, the pathogen increased by an average of 2.0 log10 CFU/g in fresh cheeses on day 15. Gram-negative spoilage bacteria also increased by an average of 2.5 log10 CFU/g. However, from day 15 to the sell-by date (days 35–40), L. monocytogenes growth ceased, and progressively, the populations of the pathogen declined in most cheeses. This was due to an unmonitored, batch-dependent natural acidification by spoilage lactic acid bacteria, predominantly Leuconostoc mesenteroides, which reduced the cheese pH to 5.5, and finally to ≤5.0. The pH reductions and associated declines in pathogen viability were greater in the CEntE-treated samples within each batch. L. monocytogenes failed to grow in cheeses previously ‘aged’ in retail for 15 days. Overall, high population levels (&gt;7.5 log10 CFU/g) of psychrotrophic Enterobacteriaceae, particularly Hafnia alvei, were associated with an extended growth and increased survival of L. monocytogenes during storage.</jats:p