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

Abstract

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, Leuconostocmesenteroides, Lentilactobacillus (L. diolivorans, L. kefiri, L. hilgardii), Pediococcusinopinatus/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.

Antilisterial activity of raw sheep milk from two native Epirus breeds: Culture-dependent identification, bacteriocin gene detection and primary safety evaluation of the antagonistic LAB biota

“…Because the present raw sheep milks were expected to contain numerous undesirable gram-negative bacteria apart from LAB contaminants, two series of 20-mL samples from each RM batch were challenged at 0 and 48 h, the first series without and the second with added 4 % NaCl. Salt addition aimed to favor growth of indigenous mesophilic LAB, such as wild lactococci, leuconostocs, lactobacilli, and enterococci capable of growing well in 4 %, 6.5 % and/or 8 % salt in vitro ( Vandera et al., 2019 ; Sameli et al., 2021 ; Samelis and Kakouri, 2022 ), in raw milk and/or in the well assays during incubation. All ‘culture-enriched’ curdled RM samples were tested after a 1:1 dilution with Ringer to facilitate diffusion around the wells.…”

“…Of note, KAA agar used to selectively enumerate enterococci also supports growth of kanamycin-resistant, esculin-positive Lactiplantibacillus spp. when present in milk ( Samelis et al., 2009 ) or cheese ( Samelis and Kakouri, 2022 ) samples.…”

“…So, after enumeration, 60 presumptive LAB colonies (30 from each inhibitory RM batch; 5 from each agar medium) were randomly picked from one high dilution MPCA/37 °C, MRS/30 °C, MRS/45 °C, M17/22 °C M17/42 °C; KAA/37 °C agar plate, by following the same isolation protocol we applied in previous milk or cheese LAB ecology studies ( Vandera et al., 2018 , 2019 ; Samelis and Kakouri, 2022 ). Depending on their isolation medium, colonies were grown in MRS or M17 broth at 30 °C or 37 °C, purified by streaking on MRS or M17 agar plates, checked for their Gram-staining, catalase and oxidase reactions to separate the LAB (Gram-positive, catalase-negative) isolates, and kept in MRS broth supplemented with 20 % (w/v) glycerol (Merck, Darmstadt, Germany) at -30 °C ( Samelis and Kakouri, 2022 ). For the purposes of this study, only the LAB isolates obtained from RM batches that showed in vitro bacteriocin-mediated antilisterial activity in the aforementioned well diffusion assays ( Section 2.2 ) were characterized further ( Fig.…”

“…For the purposes of this study, only the LAB isolates obtained from RM batches that showed in vitro bacteriocin-mediated antilisterial activity in the aforementioned well diffusion assays ( Section 2.2 ) were characterized further ( Fig. 1 ): initially, they were differentiated in main LAB groups at the genus level by basic phenotypic criteria (cell-shape by phase contrast microscopy; CO 2 from glucose; NH 3 from arginine hydrolysis; growth at 10 °C and 45 °C; growth in 4 % and 6.5 % salt; growth on KAA agar), performed according to Samelis and Kakouri (2022) , followed by their identification at the species by genotypic methods ( Fig. 1 ).…”

Biogenic Amine Formation in Artisan Galotyri PDO Acid-Curd Cheeses Fermented with Greek Indigenous Starter and Adjunct Lactic Acid Bacteria Strain Combinations: Effects of Cold (4 °C) Ripening and Biotic Factors Compromising Cheese Safety

“…Amongst them, the development of novel 'regional' craft-made cheese starter cultures with improved performance was attempted in the course of the BIOTRUST (2018-2022) research project [50]. For several practical reasons, including the selection of a convenient traditional PDO cheese technology that offers simple and fast production, easy final product packaging and distribution, and rapid income circulation, Galotyri PDO, the oldest soft, Acid-Curd Greek cheese produced exclusively in the regions of Epirus and Thessaly from boiled ewes' or goat's milk and consumed either fresh or ripened [51,52], has served as a real-cheese model to evaluate the in situ performance of newly designed starter and adjunct LAB strain combinations under artisan manufacturing conditions.…”