Natural Antimicrobials: A Reservoir to Contrast Listeria monocytogenes.

Natural environments possess a reservoir of compounds exerting antimicrobial activity that are forms of defence for some organisms against others. Recently, they have become more and more attractive in the food sector due to the increasing demand for natural compounds that have the capacity to protect food from pathogenic microorganisms. Among foodborne pathogens, Listeria monocytogenes can contaminate food during production, distribution, or storage, and its presence is especially detected in fresh, raw food and ready-to-eat products. The interest in this microorganism is related to listeriosis, a severe disease with a high mortality rate that can occur after its ingestion. Starting from this premise, the present review aims to investigate plant extract and fermented plant matrices, as well as the compounds or mixtures of compounds produced during microbial fermentation processes that have anti-listeria activity.

Valorization of orange peels exploiting fungal solid-state and lacto-fermentation.

BACKGROUND: Orange peels can serve as a cost-effective raw material for the production of lactic acid. Indeed, given their high concentration of carbohydrates and low content of lignin, they represent an important source of fermentable sugars, recoverable after a hydrolytic step. RESULTS: In the present article, the fermented solid, obtained after 5 days of Aspergillus awamori growth, was used as the only source of enzymes, mainly composed of xylanase (40.6 IU g-1 of dried washed orange peels) and exo-polygalacturonase (16.3 IU g-1 of dried washed orange peels) activities. After the hydrolysis, the highest concentration of reducing sugars (24.4 g L-1 ) was achieved with 20% fermented and 80% non-fermented orange peels. The hydrolysate was fermented with three lactic acid bacteria strains (Lacticaseibacillus casei 2246 and 2240 and Lacticaseibacillus rhamnosus 1019) which demonstrated good growth ability. The yeast extract supplementation increased the lactic acid production rate and yield. Overall, L. casei 2246 produced the highest concentration of lactic acid in mono-culture. CONCLUSION: To the best of our knowledge this is the first study exploiting orange peels as low-cost raw material for the production of lactic acid avoiding the employment of commercial enzymes. The enzymes necessary for the hydrolyses were directly produced during A. awamori fermentation and the reducing sugars obtained were fermented for lactic acid production. Despite this preliminary work carried out to study the feasibility of this approach, the concentrations of reducing sugars and lactic acid produced were encouraging, leaving open the possibility of other studies for the optimization of the strategy proposed here. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Pseudomonas fluorescens and Escherichia coli in Fresh Mozzarella Cheese: Effect of Cellobiose Oxidase on Microbiological Stability during Refrigerated Shelf Life.

Background: Mozzarella cheese possesses a high moisture content (50−60%) and a relatively high pH (around 5.5) and is therefore considered a perishable food product characterized by high quality deterioration and the potential risk of microbial contamination. Moreover, it can be spoiled by Pseudomonas spp. and coliform bacteria, which may be involved in different negative phenomena, such as proteolysis, discolorations, pigmentation, and off-flavors. To prevent these, different methods were investigated. In this context, the present study aims to assess the antimicrobial effect of cellobiose oxidase on Pseudomonas fluorescens (5026) and Escherichia coli (k88, k99) in mozzarella cheese during refrigerated shelf life. Methods: microbiological challenge tests were designed by contaminating the mozzarella covering liquid containing different cellobiose oxidase concentrations with P. fluorescens (5026) and E. coli (k88, k99). The behavior of these microorganisms and the variation of hydrogen peroxide concentrations were then tested under refrigerated conditions for 20 days to simulate the mozzarella cheese shelf life. Results and Conclusions: The data obtained demonstrated the effect of cellobiose oxidase on microbial growth. In particular, E. coli (k88, k99) was inhibited over the entire shelf life, while P. fluorescens (5026) was only partially affected after a few days of refrigerated storage.

Antimicrobial Activity of Fermented Vegetable Byproduct Extracts for Food Applications.

To prevent foodborne diseases and extend shelf-life, antimicrobial agents may be used in food to inhibit the growth of undesired microorganisms. In addition to the prevention of foodborne diseases, another huge concern of our time is the recovery of agri-food byproducts. In compliance with these challenges, the aim of this work was to more deeply investigate the antimicrobial activity of extracts derived from fermented tomato, melon, and carrot byproducts, previously studied. All the fermented extracts had antimicrobial activity both in vitro and in foodstuff, showing even higher activity than commercial preservatives, tested for comparison against spoilage microorganisms and foodborne pathogens such as Salmonella spp., L. monocytogenes, and B. cereus. These promising results highlight an unstudied aspect for the production of innovative natural preservatives, exploitable to improve the safety and shelf-life of various categories of foodstuff.

Fermentation of Agri-Food Waste: A Promising Route for the Production of Aroma Compounds.

Food waste and byproducts are generated along the entire food processing and storage chain. The large amount of waste deriving from the whole process represents not only a great economic loss but also an important ethical and environmental issue in terms of failure to recycle potentially reusable materials. New, clear strategies are needed to limit the amount of waste produced and, at the same time, promote its enhancement for further conversion and application to different industrial fields. This review gives an overview of the biological approaches used so far to exploit agri-food wastes and byproducts. The application of solid-state fermentation by different microorganisms (fungi, yeasts, bacteria) to produce several value-added products was analyzed, focusing on the exploitation of lactic acid bacteria as workhorses for the production of flavoring compounds.

Levetiracetam Prophylaxis Therapy for Brain Tumor-Related Epilepsy (BTRE) Is Associated With a Higher Psychiatric Burden.

Purpose: Brain tumor-related epilepsy (BTRE) is a condition characterized by the development of seizures in the context of an undergoing oncological background. Levetiracetam (LEV) is a third-generation anti-seizure medication (ASM) widely used in BTRE prophylaxis. The study evaluated LEV neuropsychiatric side effects (SEs) in BTRE prophylaxis. Method: Twenty-eight patients with brain tumors were retrospectively selected and divided into two groups. In one group, we evaluated patients with a BTRE diagnosis using LEV (BTRE-group). The other group included patients with brain tumors who never had epilepsy and used a prophylactic ASM regimen with LEV (PROPHYLAXIS-group). Neuropsychiatric SEs of LEV were monitored using the Neuropsychiatric Inventory Questionnaire (NPI-Q) at the baseline visit and the 6- and 12-month follow-up. Results: Eighteen patients of the BTRE-group and 10 patients of the PROPHYLAXIS-group were included. Compared to the BTRE-group, the PROPHYLAXIS-group showed a higher severity of neuropsychiatric symptoms. According to Linear Mixed Models (LMM), a multiplicative effect was observed for the interaction between group treatment and time. For the caregiver distress score (CDS), only a time-effect was observed. Conclusion: Prophylactic ASM with LEV is associated with an increased frequency of neuropsychiatric SE. Accurate epileptological evaluations in patients with brain tumors are mandatory to select who would benefit most from ASM.

How Periodontal Disease and Presence of Nitric Oxide Reducing Oral Bacteria Can Affect Blood Pressure.

Nitric oxide (NO), a small gaseous and multifunctional signaling molecule, is involved in the maintenance of metabolic and cardiovascular homeostasis. It is endogenously produced in the vascular endothelium by specific enzymes known as NO synthases (NOSs). Subsequently, NO is readily oxidized to nitrite and nitrate. Nitrite is also derived from exogenous inorganic nitrate (NO3) contained in meat, vegetables, and drinking water, resulting in greater plasma NO2 concentration and major reduction in systemic blood pressure (BP). The recycling process of nitrate and nitrite to NO (nitrate-nitrite-NO pathway), known as the enterosalivary cycle of nitrate, is dependent upon oral commensal nitrate-reducing bacteria of the dorsal tongue. Veillonella, Actinomyces, Haemophilus, and Neisseria are the most copious among the nitrate-reducing bacteria. The use of chlorhexidine mouthwashes and tongue cleaning can mitigate the bacterial nitrate-related BP lowering effects. Imbalances in the oral reducing microbiota have been associated with a decrease of NO, promoting endothelial dysfunction, and increased cardiovascular risk. Although there is a relationship between periodontitis and hypertension (HT), the correlation between nitrate-reducing bacteria and HT has been poorly studied. Restoring the oral flora and NO activity by probiotics may be considered a potential therapeutic strategy to treat HT.

Development of Lactic Acid-Fermented Tomato Products.

BACKGROUND: lactic acid fermentation was recently proposed to produce fruit and vegetable beverages with high nutritional value. In this study, a wide screening of strains and fermentation parameters was carried out to develop fermented tomato-based drinks containing viable cells and potentially bioactive metabolites. METHODS: six different products (three extracts, two tomato juices and one tomato puree) were used as substrate for fermentation. After preliminary testing, eight fermentation conditions for each tested product were selected. The final products were stabilized with pasteurization or refrigeration and further characterized in terms of (i) antioxidant activity and (ii) total polyphenols. RESULTS: selected strains were able to grow in almost all tomato-based products except for one extract. Antioxidant activity and total phenolic content depend on products and fermentation conditions used and, except for tomato puree, an overall increase was observed. The best nutritional profile was reached in fermented samples stored at refrigerated temperature without thermal stabilization. CONCLUSION: an integrated data vision allowed to choose, for each substrate, the best combination of strains to produce novel fermented tomato-based products with different application perspectives.

Antimicrobial and Fermentation Potential of Himanthalia elongata in Food Applications.

Himanthalia elongata is a brown oceanic seaweed rich in bioactive compounds. It could play an important role in food production because of its antimicrobial and antioxidant properties. Three strains belonging to the Lactobacillus casei group (Lactobacillus casei, Lactobacillus paracasei, and Lactobacillus rhamnosus) and a Bacillus subtilis strain were used for the solid-state fermentation of commercial seaweeds, and bacterial growth was monitored using the plate count method. High-pressure processing (HPP) was also employed (6000 bar, 5 min, 5 °C) before extraction. The antimicrobial activity of the extracts was tested in terms of the main food pathogenic bacteria (Salmonella spp., Listeria monocytogenes, Escherichia coli, Staphylococcus aureus, and Bacillus cereus), and the phenolic content was estimated using the Folin-Ciocalteau method. In addition, targeted UHPLC-MS2 methods were used to unravel the profile of phlorotannins. H. elongata allowed the growth of the L. casei group strains and B. subtilis, showing the fermentability of this substrate. Significant antimicrobial activity toward L. monocytogenes was observed in the extracts obtained from unfermented samples, but neither fermentation nor HPP enhanced the natural antimicrobial activity of this seaweed species. The content in the phenolic compounds decreased because of the fermentation process, and the amount of phenolics in both the unfermented and fermented H. elongata extracts was very low. Despite phlorotannins being related to the natural antimicrobial activity of this brown seaweed, these results did not support this association. Even if fermentation and HPP were not proven to be effective tools for enhancing the useful compounds of H. elongata, the seaweed was shown to be a suitable substrate for L. casei group strains as well as for B. subtilis growth, and its extracts exhibited antimicrobial activity toward foodborne pathogens.

Heat Resistance of Listeria monocytogenes in Dairy Matrices Involved in Mozzarella di Bufala Campana PDO Cheese.

The presence of Listeria monocytogenes in Mozzarella di Bufala Campana Protected Designation of Origin cheeses may depend on curd stretching conditions and post contaminations before packaging. To avoid cross-contamination, thermal treatment of water, brines and covering liquid may become necessary. The present study aimed to improve knowledge about L. monocytogenes thermal resistance focusing on the influence of some cheese making operations, namely curd stretching and heat treatment of fluids in contact with cheese after molding, in order to improve the safety of the cheese, optimize efficacy and sustainability of the processes. Moreover, the role that cheese curd stretching plays in L. monocytogenes inactivation was discussed. The 12 tested strains showed a very heterogeneous heat resistance that ranged from 7 to less than 1 Log10 Cfu/mL reduction after 8 min at 60°C. D-values (decimal reduction times) and z-values (thermal resistance constant) calculated for the most heat resistant strain among 60 and 70°C were highly affected by the matrix and, in particular, heat resistance noticeably increased in drained cheese curd. As cheese curd stretching is not an isothermal process, to simulate the overall lethal effect of an industrial process a secondary model was built. The lethal effect of the process was estimated around 4 Log10 reductions. The data provided may be useful for fresh pasta filata cheese producers in determining appropriate processing durations and temperatures for producing safe cheeses.

Vegetable By-Product Lacto-Fermentation as a New Source of Antimicrobial Compounds.

BACKGROUND: One of the main objectives of the food industry is the shelf life extension of food products, taking into account the safety requirements and the preference of consumers attracted by a simple and clear label. Following this direction, many researchers look to find out antimicrobials from natural sources. METHODS: Tomato, carrot, and melon by-products were used as substrates for lactic acid fermentation using seven strains belonging to the Lactobacillus genus, L. plantarum, L. casei, L. paracasei, and L. rhamnosus. The obtained fermented by-products were then extracted and the antimicrobial activity toward fourteen pathogenic strains of Listeria monocytogenes, Salmonella spp., Escherichia coli, Staphylococcus Aureus, and Bacillus cereus was tested through agar well diffusion assay. RESULTS: All the extracts obtained after fermentation had highlighted antimicrobial activity against each pathogen tested. In particular, a more effective activity was observed against Salmonella spp., L. monocytogenes, S. aureus, and B. cereus, while a lower activity was observed against E. coli. CONCLUSION: Lactic acid fermentation of vegetable by-products can be a good strategy to obtain antimicrobials useful in food biopreservation.

From Byproduct to Resource: Fermented Apple Pomace as Beer Flavoring.

One of the main struggles of the large-scale apple processing industry is pomace disposal. One solution for this problem is to convert this waste into a resource. Apple pomace could be used as a substrate for lactic acid bacteria and could induce the formation of a more complex aroma profile, making this fermented product an innovative aromatizer for alcoholic beverages, such as beer. In this study, for the first time, the effect of lacto-fermented apple pomace addition in beer was evaluated. Three bacterial strains (Lactobacillus rhamnosus 1473 and 1019, and L. casei 2246) were tested for apple pomace fermentation, and L. rhamnosus 1473 was the strain that best modified the aromatic profile. The addition of fermented apple pomace to beer increased the complexity of the aroma profile, demonstrating the potential of this byproduct as an aromatizer in the alcoholic beverage industry.

Orange peels: from by-product to resource through lactic acid fermentation.

BACKGROUND: Considering the large amounts of by-products derived from orange processing, which are generally discarded, the present study aimed to explore the feasibility of using orange peel for lactic acid production in solid state fermentation. RESULTS: Different species of lactic acid bacteria were employed, singly and in co-culture, to evaluate their ability to ferment orange peel and produce lactic acid. Among the single cultures tested, Lactobacillus casei 2246 was the most efficient strain, reaching the highest concentration of lactic acid (209.65 g kg-1 ) and yield (0.88 g g-1 ). The use of Lactobacillus plantarum 285 and Lactobacillus paracasei 4186 in co-culture produced a comparable amount of lactic acid, showing a better performance than the same strains in single cultures. CONCLUSION: Orange peels represent a suitable raw material for solid state fermentation employing lactic acid bacteria. Lactic acid was obtained that consumed the most of sugars available, leading to high yields. Despite all the strains tested showing the same growth ability, different peculiarities in lactic acid production were revealed, dependent on the species/strains, suggesting the relevance of strain selection. © 2019 Society of Chemical Industry.

Use of Dairy and Plant-Derived Lactobacilli as Starters for Cherry Juice Fermentation.

BACKGROUND: Lactic acid bacteria (LAB) exhibit a great biodiversity that can be exploited for different purposes, such as to enhance flavours or metabolize phenolic compounds. In the present study, the use of dairy and plant-derived LAB strains to perform cherry juice fermentation is reported. METHODS: The growth ability of Lactobacillus plantarum, Lactobacillus casei, Lactobacillus paracasei and Lactobacillus rhamnosus was studied in cherry juice. Profiling of sugars, organic acids and volatile compounds was performed by GC-MS (Gas Chromatography-Mass Spectrometry), while the phenolic fraction was characterized using UHPLC (Ultra High Performance Liquid Chromatography) equipped with a linear ion trap-mass spectrometer. RESULTS: Sucrose significantly decreased in all fermented samples as well as malic acid, converted to lactic acid by malolactic fermentation. The total amount of volatile compounds increased. Specifically, propyl acetate, an ester with fruit notes, reached the highest concentration in L. rhamnosus and L. paracasei (dairy strains) fermented juices. Phenolics were extensively metabolized: caffeic acid was converted into dihydrocaffeic acid, p-coumaric acid into 4-ethylphenol and phenyllactic acid was produced. CONCLUSION: Lactic acid fermentation confer fruit notes to the juice and enhance phenyllactic acids, especially employing dairy strains (L. rhamnosus and L. paracasei). The level of dihydrocaffeic acid, a compound with putative biological activity was also increased (in particular with L. plantarum).

In vitro metabolism of elderberry juice polyphenols by lactic acid bacteria.

In this study, ten strains of Lactobacillus were used to assess the in vitro metabolism of elderberry juice polyphenols. Total polyphenolic compounds increased after starter addition, especially with three L. rhamnosus and one L. plantarum strains, of dairy origin: quercetin-3-O-rutinoside was the most abundant compound (from 39.02 ±â€¯5.28 to 127.56 ±â€¯11.34 µg/mL) and hydroxycinnamic acids, flavonols and anthocyanins reached the highest amounts. When L. plantarum were used phenyllactic acids presented a value of 7.05 ±â€¯2.38 µg/mL, while in the other samples it was around 5.56 ±â€¯1.65 µg/mL. Hydroxycinnamic and hydroxybenzoic acids were subjected to lactic acid bacteria metabolism: caffeic and protocatechuic acids were consumed during fermentation while dihydrocaffeic acid and catechol were produced. Anthocyanins increased in a strain-specific way. So, by this study we highlighted that dairy strains can produced (phenyllactic acids), modified (hydroxycinnamic acids) or increased (flavonols glycosides and anthocyanins) phenolic compounds.

The Influence of Viable Cells and Cell-Free Extracts of Lactobacillus casei on Volatile Compounds and Polyphenolic Profile of Elderberry Juice.

In this study, four strains of Lactobacillus casei, as viable cells or cell-free extracts (CFE), were added to elderberry juice in order to evaluate their effect on phenolic and aromatic profile. Two of them were able to grow in juice while the others showed zero-growth. The same strains were lysed and added as extracts in elderberry juice. Multivariate statistical analysis show a separation among samples containing growing cells, non-growing cells, CFE, highlighting the particularities of specific strains. Juices added with CFE presented the highest amount of esters. The strains showing growth phenotype cause an increase of phenyllactic acids. The highest concentration of volatile compounds, particularly of alcohols, terpenes and norisoprenoids (responsible for typical elderberry notes) was observed in samples with strains showing zero-growth. Moreover, a significant increase in anthocyanin content was observed in these samples, suggesting the possible use of Lactobacillus for increasing specific molecules, even for non-multiplying bacterial cell. Considering that this is the first study concerning the use of non-growing cells in fruit juice, the potential of strains is still to be explored and it may have a significant technological application in the development of a microbial collection useful for fruit juice industry.

Volatile profile of elderberry juice: Effect of lactic acid fermentation using L. plantarum, L. rhamnosus and L. casei strains.

In this study we explored, for the first time, the lactic acid fermentation of elderberry juice (EJ). A total of 15 strains isolated from dairy and plant matrices, belonging to L. plantarum, L. rhamnosus and L. casei, were used for fermentations. The volatile profile of started and unstarted EJ was characterized by HS-SPME/GC-MS technique after 48h of fermentation and 12days of storage at 4°C. All L. plantarum and L. rhamnosus strains exhibited a good capacity of growth while not all L. casei strains showed the same ability. The aromatic profile of fermented juices was characterized by the presence of 82 volatile compounds pertaining to different classes: alcohols, terpenes and norisoprenoids, organic acids, ketones and esters. Elderberry juice fermented with L. plantarum strains showed an increase of total volatile compounds after 48h while the juices fermented with L. rhamnosus and L. casei exhibited a larger increase after the storage. The highest concentration of total volatile compounds were observed in EJ fermented with L. plantarum 285 isolated from dairy product. Ketones increased in all fermented juices both after fermentation and storage and the most concentrated were acetoin and diacetyl. The organic acids were also affected by lactic acid fermentation and the most abundant acids detected in fermented juices were acetic acid and isovaleric acid. Hexanol, 3-hexen-1-ol (Z) and 2-hexen-1-ol (E) were positively influenced during dairy lactic acid bacteria strains fermentation. The most represented esters were ethyl acetate, methyl isovalerate, isoamyl isovalerate and methyl salicylate, all correlated with fruit notes. Among terpenes and norisoprenoids, ß-damascenone resulted the main representative with its typical note of elderberry. Furthermore, coupling obtained data with multivariate statistical analyses, as Principal Component Analysis (PCA) and Classification Trees (CT), it was possible to relate the characteristic volatile profile of samples with the different species and strains applied in this study.

The effect of sub-inhibitory concentrations of rifaximin on urease production and on other virulence factors expressed by Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa and Staphylococcus aureus.

Rifaximin, a topical derivative of rifampin, inhibited urease production and other virulence factors at sub-MIC concentrations in strains involved in hepatic encephalopathy and the expression of methicillin resistance in Staphylococcus aureus. In particular, urease production was affected in all Proteus mirabilis and Klebsiella pneumoniae strains as well as in all tested Pseudomonas aeruginosa isolates. Other exotoxins, synthesized by P. aeruginosa, such as protease, gelatinase, lipase, lecithinase and DNAse were also not metabolized in the presence of rifaximin. This antibiotic inhibited pigment production in both P. aeruginosa and Chromobacterium violaceum, a biosensor control strain. Lastly, rifaximin affected haemolysin production in S. aureus and was able to restore cefoxitin susceptibility when the strain was cultured in the presence of sub-MICs of the drug. The present findings confirm and extend previous observations about the beneficial effects of rifaximin for the treatment of gastrointestinal diseases, since in this anatomic site, it reaches a large array of concentrations which prevents enterobacteria from thriving and/or producing their major virulence factors.