Growth Control of Listeria monocytogenes in Raw Sausage via Bacteriocin-Producing Leuconostoc carnosum DH25.

The current study addresses the critical issue of Listeria monocytogenes growth in raw sausage/meat products leading to human infections, most commonly listeriosis, which is known for its high fatality rate. This research focuses on the isolation, identification, and screening of lactic acid bacteria from various meat and fish products in Switzerland. In total, 274 lactic acid bacteria strains were isolated from 30 different products and were screened for their ability to inhibit Listeria monocytogenes growth, with 51 isolates demonstrating anti-Listeria activity at 8 °C, 15 °C, 25 °C, and 37 °C. Further experiments, using a meat model and a raw sausage challenge test, demonstrated that Leuconostoc carnosum DH25 significantly inhibited Listeria monocytogenes growth during the ripening and storage of the tested meat/sausage. This inhibitory effect was found to be attributed to the bacteriocins produced by Leuconostoc carnosum DH25 rather than factors like pH or water activity. The stability of the anti-Listeria substances was examined, revealing their resistance to temperature and pH changes, making Leuconostoc carnosum DH25 a promising protective culture for raw sausages. The genome sequencing of this strain confirms its safety, with no antibiotic resistance genes or virulence factors detected, and reveals the presence of the structural genes for the production of the bacteriocin LeucocinB-Ta11a. This study underscores the potential of LAB strains and their bacteriocins as effective tools for enhancing food safety and preventing Listeria monocytogenes growth in meat products, offering valuable insights into biocontrol strategies in the food industry.

Variations in Ecuadorian Cocoa Fermentation and Drying at Two Locations: Implications for Quality and Sensory.

In Ecuador, various processes are applied during cocoa post-harvesting. This study, therefore, explored fermentation parameters across two locations with 2-7 independent runs, focusing on temperature, microbial counts, pH during fermentation and drying, and their impact on cocoa bean quality. Factors including fermentation devices (jute bags, plastic bags, and wooden boxes), pre-drying, turning during fermentation, fermentation duration, and drying temperature were investigated. Fermenting in plastic bags without pre-drying or turning and fermenting in jute bags for only 40 ± 2.0 h yielded low maximal fermentation temperatures Tmax (31.1 ± 0.4 °C and 37.6 ± 1.8 °C), leading to bitter, astringent, woody, and earthy cocoa liquor. Longer fermentation (63 ± 6 h) in wooden boxes with turning (Wt) and in jute bags with pre-drying and turning (Jpt) achieved the highest Tmax of 46.5 ± 2.0 °C, and a more acidic cocoa liquor, particularly in Wt (both locations) and Jpt (location E). Therefore, it is recommended to ferment for a minimum duration from day 1 to 4 (63 ± 6 h), whether using plastic bags (with mandatory pre-drying) or jute bags (with or without pre-drying or turning). Furthermore, this study underscores the risks associated with excessively high drying temperatures (up to 95.2 ± 13.7 °C) and specific dryer types, which can falsify cut-tests and introduce unwanted burnt-roasted off-flavors in the cocoa liquor.

Monitoring of cocoa post-harvest process practices on a small-farm level at five locations in Ecuador.

Cocoa post-harvest practices were monitored on a small-farm scale (ca. 50 kg fresh beans) at five intermediaries from four provinces in Ecuador: (A) in Manabí, (B) and (E) in Los Ríos, (C) in Cotopaxi, (D) in Guayas. Temperature, pH (pulp, cotyledon), cell counts (yeasts, lactic acid bacteria, acetic acid bacteria) were recorded daily, and cut-tests and sensory descriptive analysis evaluated end quality. An overall inconsistency and variability in processing were observed with different fermentation devices (jute/plastic bags, wooden boxes), pre-drying, turning during fermentation, fermentation duration, and different drying processes (temperatures, direct/indirect). Key parameters (maximum temperature, pH cotyledon development) revealed a significant impact of the fermentation device on the post-harvest process and, therefore, on the fermentation development. 67-74 h in jute bags without turning was sufficient to reach well-fermented cocoa beans without moldy off-flavors, whereas 133 h in plastic bags without turning resulted in 3 ± 1% moldy beans and cocoa liquor with moldy off-flavor. Drying at high temperatures (80 ± 10 °C) with direct heat contact resulted in beans roasted to burnt off-flavor. Conclusively, the whole post-harvest process was crucial for well-fermented beans without off-flavor. Plastic bags seemed unsuitable, while jute bags could be an alternative to wooden boxes.

MALDI-TOF MS profiling and exopolysaccharide production properties of lactic acid bacteria from Kunu-zaki - A cereal-based Nigerian fermented beverage.

MALDI-TOF MS is a technique for high-throughput characterization of foodborne microbiota, however, its application for studying African traditional fermented foods is limited. A total of 164 out of 220 lactic acid bacterial (LAB) isolates from Kunu-zaki were identified using MALDI-TOF MS, with 100% identity of representative strains compared to 16S rRNA gene sequencing. MALDI-TOF MS profiling combined with 16S rRNA gene sequencing revealed a total of 15 LAB species in Kunu-zaki, where the most predominant species were Lactiplantibacillus plantarum (40.46%), Weissella confusa (27.27%), and Pediococcus pentosaceus (15.00%). Phenotypic screening of all isolates revealed strains of W. confusa (57), Lactiplantibacillus sp. (9), Companilactobacillus musae (1), Ligilactobacillus saerimneri (1) and Leuconostoc citreum (1) that are capable of producing dextran and/or fructan. Dextransucrase genes were detected in all EPS-producing strains by PCR. Weissella confusa YKDIA1 and YKDIA4 produced 11.93 and 11.70 g/L dextran from millet-sorghum flour hydrolysate-sucrose, respectively. Kunu-zaki produced using W. confusa YKDIA1 had high water holding capacity (100%) and viscosity ranging from 49.46-139.24 mPas. In this study, MALDI-TOF MS adequately revealed the LAB species composition in Kunu-zaki in a high-throughput strategy and further, the dominant occurrence of EPS-producing LAB strains and their potentials to influence the rheological properties of Kunu-zaki were demonstrated.

Screening of lactic acid bacteria and yeast strains to select adapted anti-fungal co-cultures for cocoa bean fermentation.

Contamination with filamentous fungi during cocoa bean fermentation and drying reduces the quality of cocoa beans and poses a health risk for consumers due to the potential accumulation of mycotoxins. The aim of this study was to develop anti-fungal lactic acid bacteria (LAB)-yeast co-cultures by selecting anti-fungal strains best adapted to the cocoa bean fermentation process from 362 LAB and 384 yeast strains isolated from cocoa bean post-harvest processes. The applied multiphasic screening approach included anti-fungal activity tests in vitro and in vivo and assessment of the carbon metabolism and stress tolerance of the anti-fungal strains in a cocoa pulp simulation medium. The anti-fungal strains, Lactobacillus fermentum M017, Lb. fermentum 223, Hanseniaspora opuntiae H17, and Saccharomyces cerevisiae H290, were selected based on their high fungal growth inhibition capacity and their well-adapted metabolism. Up to seven filamentous fungal strains of the genera Aspergillus, Penicillium, and Gibberella were inhibited on average by 63 and 75% of the maximal inhibition zone by M017 and 223, respectively, and by 25 and 31% by the strains H17 and H290, respectively. Both Lb. fermentum strains converted the medium's glucose, fructose, and citric acid into 20.4-23.0 g/l of mannitol, 3.9-6.2 g/l acetic acid, and 8.6-10.3 g/l lactic acid, whereas the two yeast strains metabolized glucose and fructose to produce 7.4-18.4 g/l of ethanol. The Lb. fermentum strains were further characterized as particularly tolerant towards ethanol, acetic acid, and heat stress and both yeast strains tolerated high amounts of ethanol and lactic acid in the medium. Finally, the anti-fungal in vivo assays revealed that the two Lb. fermentum strains completely inhibited growth of the citrinin-producing strain, P. citrinum S005, and the potentially fumonisin-producing strain, G. moniliformis S003, on the surface of cocoa beans. Furthermore, growth of the aflatoxin-producer A. flavus S075 was inhibited after 10-14 days by all four selected anti-fungal strains, i.e. Lb. fermentum M017, Lb. fermentum 223, H. opuntiae H17, and Sacc. cerevisiae H290, at 51-95% when applied as single cultures and at 100% when the strains were combined into four co-cultures, each composed of a Lb. fermentum and one of the two yeast strains. As a conclusion, these four LAB-yeast co-cultures are recommended for future applications to limit the growth of filamentous fungi and the concomitant mycotoxin production during the fermentation of cocoa beans.