Indigenous Lactic Acid Bacteria Isolated from Raw Graviera Cheese and Evaluation of Their Most Important Technological Properties

Technological and Enzymatic Characterization of Autochthonous Lactic Acid Bacteria Isolated from Viili Natural Starters

Viili, a Finnish ropy fermented milk, is traditionally manufactured through spontaneous fermentation, by mesophilic lactic acid bacteria and yeast-like fungi, or back-slopping. This study evaluated four natural viili starters as sources of lactic acid bacteria for dairy production. Back-slopping activation of the studied viili samples was monitored through pH and titratable acidity measurements and enumeration of mesophilic lactic acid bacteria. Sixty lactic acid bacteria isolates were collected, molecularly identified, and assayed for acidification performance, enzymatic activities, production of exopolysaccharides (EPSs), presence of the histidine decarboxylase (hdcA) gene of Gram-positive bacteria, and production of bacteriocins. A neat predominance of Lactococcus lactis emerged among the isolates, followed by Enterococcus faecalis, Enterococcus faecium, Enterococcus durans, Enterococcus lactis, and Lactococcus cremoris. Most isolates exhibited proteolytic activity, whereas only a few enterococci showed lipase activity. Five isolates identified as L. cremoris, L. lactis, and E. faecalis showed a good acidification performance. Most of the isolates tested positive for leucine arylamidase, whereas only one E. durans and two L. lactis isolates were positive for valine arylamidase. A few isolates also showed a positive reaction for beta-galactosidase and alpha- and beta-glucosidase. None of the isolates produced EPSs or bacteriocins. The hdcA gene was detected in five isolates identified as L. lactis and E. faecium. A few L. cremoris and L. lactis isolates for potential use as starter or adjunct cultures for dairy processing were finally identified.

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

Raw milk from native small ruminant breeds in Epirus, Greece, is a valuable natural source of autochthonous lactic acid bacteria (LAB) strains with superior biotechnological properties. In this study, two bulk milks (RM1, RM2) from two local sheep yards, intended for traditional Kefalotyri cheese production, were preselected for bacteriocin-like antilisterial activity by in vitro tests. Their antagonistic LAB biota was quantified followed by polyphasic (16S rRNA gene sequencing; IGS for Enterococcus; a multiplex-PCR for Leuconostoc) identification of 42 LAB (RM1/18; RM2/24) isolates further evaluated for bacteriocin encoding genes and primary safety traits. Representative isolates of the numerically dominant mesophilic LAB were Leuconostoc mesenteroides (10) in both RMs, Streptococcus parauberis (7) in RM2, and Lactococcus lactis (1) in RM1; the subdominant thermophilic LAB isolates were Enterococcus durans (8), E. faecium (6), E. faecalis (3), E. hirae (1), E. hermanniensis (1), Streptococcus lutetiensis (2), S. equinus (1) and S. gallolyticus (1). Based on their rpoB, araA, dsr and sorA profiles, six Ln. mesenteroides strains (8 isolates) were atypical lying between the subspecies mesenteroides and dextranicum, whereas two strains profiled with Ln. mesenteroides subsp. jonggajibkimchi that is first-time reported in Greek dairy food. Two RM1 E. faecium strain biotypes (3 isolates) showed strong, enterocin-mediated antilisterial activity due to entA/entB/entP possession. One E. durans from RM1 possessed entA and entP, while additional nine RM2 isolates of the E. faecium/durans group processed entA or entP singly. All showed direct (cell-associated) antilisterial activity only, as also both S. lutetiensis strains from RM2 did strongly. Desirably, no LAB isolate was β-hemolyrtic, or cytolysin-positive, or possessed vanA, vanB for vancomycin resistance, or agg, espA, hyl, and IS16 virulence genes. However, all three E. faecalis from RM2 possessed gelE and/or ace virulence genes. In conclusion, all Ln. mesenteroides strains, the two safe, enterocin A-B-P-producing E. faecium strains, and the two antilisterial S. lutetiensis strains should be validated further as potential costarter or adjunct cultures in Kefalotyri cheese. The prevalence of α-hemolytic pyogenic streptococci in raw milk, mainly S. parauberis in RM2, requires consideration in respect to subclinical mastitis in sheep and the farm hygiene overall.