Tasting of traditional Polish fermented cucumbers: Microbiology, morpho-textural features, and volatilome

Correlation of physicochemical properties and volatile profiles with microbiome diversity in cucumber during lightly-pickling in seasoning liquid

Lightly-pickled cucumber is a popular pickled product in Asian countries. However, its quality and microbial alteration during pickling and its correlation between microorganisms and quality are still unclear. Changes in physicochemical properties, volatile organic compounds (VOCs), and microbial community during lightly-pickling cucumbers in seasoning liquid and their relationships were investigated. Results showed that the hardness and fracturability decreased with pickling time, modeled by a zero-order kinetic model. The color became brown and dark as pickling extended. Sixty-four VOCs were identified and 13 aroma-active compounds were found using GC-O and odor activity values. (E,Z)-2,6-nonadienal, hexanal, and (E,E)-2,4-heptadienal were the characteristic aroma markers essential for differentiating among the samples with different pickling times. At the genus level, Delftia and Stenotrophomonas dominated in the bacterial community, and Rhodotorula and Naganishia are the dominant fungal genera. The correlation analysis revealed that one bacteria (Acinetobacter) and two fungi (Naganishia and Rhodotorula) were strongly related to quality loss and off-flavors in cucumbers in the late pickling process. This study provides an important reference for facilitating the quality control of lightly-pickled cucumber during processing.

Regulation of the quality, flavour, and microbial community of industrially fermented split red sour soup by Lentilactobacillus buchneri and Pediococcus ethanolidurans

In order to study the changes in physicochemical properties, microbial diversity, and flavour substances during the industrial fermentation of split red sour soup (RSS) inoculated with lactic acid bacteria (LAB), two groups of samples from natural and inoculated fermentation were analyzed. The physicochemical properties in inoculated fermentation group were better than those of natural fermentation group. Compared to natural fermentation, inoculated fermentation led to rapid acidification, and the increased contents of key volatile compounds (isoamyl acetate, ethyl acetate, phenylethanol, acetic acid, etc.) in sour soup. The dominant bacterial genera in the inoculation group included Lentilactobacillus, Pediococcus, Lactobacillus and Lactiplantibacillus. The dominant bacterial genera in the natural fermentation group were Pediococcus, Lentilactobacillus, Levilactobacillus, and Weissella. The dominant fungal genera in the inoculated fermentation samples of tomato sour soup were Pichia and Hanseniaspora. The dominant genera in the remaining sour soup samples were Kazachstania. Spearman correlation analysis showed that Lentilactobacillus, Levilactobacillus, and other bacterial genera were positively correlated with phenylethanol, isoamyl acetate, and terpenoids in tomato sour soup, whereas Kazachstania, Pichia, Hanseniaspora, Candida, and other fungal spp. were positively correlated with alcohols 2-undecanol, cis-3-hexenyl acetate, etc. In chilli sour soup, most of the bacterial genera were negatively correlated with volatile flavour compounds. Acetic acid was positively correlated with Hanseniaspora and negatively correlated with Candida. This study revealed the effects of LAB fermentation on the flavour quality and microbial community of split RSS and laid the basis for the industrial production of split RSS.

Smoked sausages of bovine meat produced in North Macedonia as a source of pro-technological lactic acid bacteria and coagulase-negative cocci

Smoked bovine sausages, traditional meat products from the Balkan Peninsula, are rich in microbial diversity and represent potential sources of pro-technological microorganisms. This study aimed to characterize these sausages from three different producers collected in green markets of North Macedonia. The analyses included physico-chemical (proximate composition, pH, aw), morpho-textural (color and texture), and microbiological assessments (viable plate counts). Moreover, an isolation campaign was conducted to identify and characterize pro-technological microorganisms. Significant variability was observed in moisture content (ranging from 33.70 to 48.61 %), hardness, and color among samples from different producers. Samples from producer 2 showed the lowest pH (mean ∼4.90) and the highest loads of lactic acid bacteria (up to ∼9 log cfu g-1). Coagulase-negative cocci ranged between 4.84 and 7.47 log cfu g-1. No potential pathogenic bacteria were detected. A total of 30 isolates, primarily Latilactobacillus sakei, Staphylococcus equorum, and Staphylococcus casei, were identified. Isolates of L. sakei S7, S13, and S27 showed strong in-vitro acidification performance, together with the production of exopolysaccharides (EPS), and protease activity. S. equorum isolates S1 and S2 exhibited protease and lipase activities, while isolates S. casei S21 and S28 showed notable lipase and protease activities, along with the production of EPS. Additionally, all S. equorum isolates, except S2, showed nitrate reductase activity, one of the key features able to affect sausage color. These findings highlighted the pro-technological traits of these microbial isolates, suggesting their potential use as starter or adjunct cultures in the meat industry to enhance product quality and safety.

Lacto-fermented garlic handcrafted in the Lower Silesia Region (Poland): Microbial diversity, morpho-textural traits, and volatile compounds

The aim of the present study was to provide a first characterization of lacto-fermented garlic manufactured by local small-scale artisanal producers in the Lower Silesia Region (Poland). The lacto-fermented garlic samples showed high nutritional features in terms of antioxidant activity. A total of 86 compounds, belonging to various chemical classes, were identified by headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC/MS). Most of these compounds belonged to six main classes, being sulfur compounds, esters and acetates, oxygenated monoterpenes, monoterpene hydrocarbons, and alcohols. Aldehydes, acids, ketones, furans, and phenols were also identified. In the analyzed samples, counts up to 8 log cfu g-1 were observed for lactic acid bacteria. Metataxonomic analysis revealed the presence of Levilactobacillus, Lactiplantibacillus, Latilactobacillus, Secundilactobacillus, Weissella, Leuconostoc, Lactococcus, Pediococcus, and Lacticaseibacillus among the major taxa. These results were confirmed by the isolation and characterization of viable lactic acid bacteria. Indeed, the presence of the closest relatives to Lacticaseibacillus casei group, Pediococcus parvulus, Levilactobacillus brevis, Levilactobacillus parabrevis, and Lactiplantibacillus plantarum group was observed. A good acidification performance in salty garlic-based medium was observed for all the isolates that, between 8 and 15 days of fermentation, reached pH values comprised between 4 and 3.5, depending on the tested species. Of note, 15 out of the 37 lactic acid bacteria isolates (Levilactobacillus parabrevis, Pediococcus parvulus, Lactiplantibacillus plantarum group, and Lacticaseibacillus casei group) showed the presence of the hdcA gene of Gram-positive bacteria encoding for histidine decarboxylase. Furthermore, for 8 out of the 37 isolates the in-vitro exopolysaccharides production was observed. No isolate showed inhibitory activity against the three Listeria innocua strains used as surrogate for Listeria monocytogenes.

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.