Antimicrobial and antioxidant activity of pressurized liquid extracts from oenological woods

The main goal of this study was to evaluate the antimicrobial activity of a collection of oenological woods extracts (non-toasted and toasted American oak wood, non-toasted and toasted French oak wood, non-toasted and toasted Rumanian oak wood, chestnut, cherry and wine grape wood) isolated by pressurized liquid extraction in order to control the microbial spoilage of wines. Inhibition of the growth of six wine lactic acid bacteria (LAB) (Lactobacillus hilgardii CIAL-49, Lactobacillus casei CIAL-52, Lactobacillus plantarum CIAL-92, Pedioccocus pentosaceus CIAL-85, Oenococcus oeni CIAL-91 and CIAL-96), two acetic acid bacteria (AAB) (Acetobacter aceti CIAL-106 and Gluconobacter oxydans CIAL-107) and three Brettanomyces yeast (Brettanomyces bruxellensis CIAL-108, CIAL-109 and CIAL-110) by the oenological wood extracts was assessed. The antioxidant activity and the total phenol index of wood extracts were also evaluated. Results confirmed differences in bacteria and yeast susceptibility to oenological wood extracts among different genera and species. Among them, AAB were especially sensitive to the phenolic inactivation from oenological woods extracts. Contrarily, amongst LAB, L. hilgardii CIAL-49 was the most resistant strain to the action of the wood extracts. Cherry wood was active against 9 of the 11 strains tested meanwhile French, Rumanian oak wood and chestnut show the lowest values of IC₅₀ for A. aceti CIAL-106. No significant correlation was found between antimicrobial activity either with antioxidant activity or with the total phenol content, suggesting that structure-function of the phenolic extracts has a greater influence on the antimicrobial activity than the total phenol content.     

Antimicrobial activity of lacticin 3147 against oenological lactic acid bacteria. Combined effect with other antimicrobial agents

This study investigated the potential use of lacticin 3147 to control growth of wine lactic acid bacteria (LAB) aiming to develop new approaches for reducing the content of sulphites in wine. Lacticin 3147, potassium metabisulphite and eucalyptus extract interactions were also evaluated. Inhibitory activity of the bacteriocin demonstrated to be strain-dependent and the highest antimicrobial effect was established at the exponential growth phase. Low lacticin 3147 IC₅₀ values (10.46–57.97 UA/mL) were measured for most of the strains, except for Lactobacillus casei CIAL-51 which were remarkably resistant (IC₅₀ = 141.70 UA/mL); Oenococcus oeni CIAL-117 were the most sensitive strain (IC₅₀ = 10.46 UA/mL). A synergistic effect of either lacticin 3147 or eucalyptus extract in combination with metabisulphite in inhibiting LAB growth was measured. Addition of lacticin 3147 to growing cultures of Lactobacillus plantarum CIAL-92 caused effective cell lysis, decrease of cell viability and extensive membrane damage, differing from the effects detected after addition of eucalyptus extract. To our knowledge, this is the first study that reports the inhibitory activity of this bacteriocin against oenological LAB and its potential role in the wine industry. The potential of eucalyptus extract as antimicrobial agent in winemaking is also highlighted. A combination of these two antimicrobials with metabisulphite could represent a promising approach to preserve LAB spoilage in wine and, consequently, eliminate or reduce the addition of SO₂.     

Novel biocompatible silver nanoparticles for controlling the growth of lactic acid bacteria and acetic acid bacteria in wines

This paper reports the inhibitory potential of two new silver-based biocompatible nanoparticles (Ag NPs), specifically synthesized for this study, against Gram-negative and Gram-positive bacteria, such as Escherichia coli and Staphylococcus aureus, and different wine lactic acid bacteria (LAB) (Oenococcus oeni, Lactobacillus casei, Lactobacillus plantarum and Pediococcus pentosaceus) and acetic acid bacteria (AAB) (Acetobacter aceti and Gluconobacter oxydans). Both solid nanoparticles, dried PEG-Ag NPs 1 (20.01% silver content) and glutathione-stabilized GSH-Ag NPs 2 solution (0.197 mg/mL silver content), showed homogeneous size distribution and physicochemical properties compatible with their use as antimicrobial agents. The nanoparticles showed different antimicrobial spectra, with PEG-Ag NPs 1 being more effective (lower IC₅₀ values) against Gram-negative strains, whereas GSH-Ag NPs 2 showed similar efficiency against Gram-negative and Gram-positive strains, with the exception of O. oeni strains, which turned out to be notably susceptible to them (IC₅₀ ∼1 μg/mL, Ag concentration). For the LAB and AAB tested, these nanoparticles showed IC₅₀ values (particle concentration) of the same order as those for the widely used additive potassium metabisulphite, at least as calculated for PEG-Ag NPs 1. These results confirm the potential of Ag NPs in controlling microbial processes in winemaking, and open new investigations on the design and use of antimicrobial-specific silver-based nanoparticles in oenology.     

Effects of extraction methods of shiitake by-products on their antioxidant and antimicrobial activities in fermented sausages during storage

Two different solvents (water and ethanol/water at 50/50 ratio) were used for extraction of phenolic contents in shiitake by-products, and the antioxidant and antimicrobial efficacies of fermented sausages incorporated with these two extracts were investigated during storage. Also, shelf-life stability of fermented sausages fortified with these two extracts was compared with those fortified with BHT (0.02%) or nitrite (0.01%)/nitrate (0.005%). Significantly higher antioxidant activities (e.g., ferrous ion chelating and DPPH scavenging) and inhibitory capacity against lipid oxidation (e.g., TBARS reduction) were observed in the fermented sausages made with ethanolic extract (shiitake by-products extracted with ethanol/water) compared with those added with aqueous extract (extracted with water) or BHT, nitrite/nitrate and control throughout storage. The ethanolic extract treated-samples also showed a significantly slower increasing rate of total aerobic count (6.54–6.95 log₁₀ cfu/g) than the ones treated with aqueous extract (6.74–7.16 log₁₀ cfu/g) during storage. Otherwise, extract obtained from the ethanolic extract treated-samples had stronger antimicrobial activities against pathogens than the one obtained from aqueous extract treated-samples (e.g., minimum inhibitory concentrations, MIC = 2.05 & 3.64, 3.12 & 5.20 and 7.29 & 10.41 mg/mL for S. aureus, L. monocytogenes and E. coli O157, respectively). Especially, the antimicrobial activity against S. typhimurium (MIC = 37.50 mg/mL) was observed only in the extract of ethanolic extract treated-samples. Our study demonstrates that the extraction with ethanol/water solvent is a more effective method to obtain bioactive compounds enriched-extract which better improved the shelf-life stability of fermented sausages during storage without defects in quality in comparison to the extraction method with water.     

Antimicrobial effect of blueberry (Vaccinium corymbosum L.) extracts against the growth of Listeria monocytogenes and Salmonella Enteritidis

This study examined the antimicrobial effect of blueberry (Vaccinium corymbosum L.) extracts obtained from four cultivars (Elliott, Darrow, Bluecrop, and Duke) on the growth of Listeria monocytogenes and Salmonella Enteritidis. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the extracts against L. monocytogenes and S. Enteritidis in tryptic soy broth were determined. Concentrations of total phenolic compounds and four individual phenolic (chlorogenic acid, ellagic acid, quercetin, and quercetin-3-galactoside) in the extracts were determined using Folin-Ciocalteau method and HPLC analysis, respectively. All four extracts at 112.5–900 mg/mL exhibited a dose-dependent growth-inhibitory effect against L. monocytogenes and S. Enteritidis. L. monocytogenes was significantly more sensitive to the antimicrobial effect of the extracts than S. Enteritidis. Phenolic compounds in the extracts such as chlorogenic acid, quercetin, ellagic acid, and quercetin-3-galactoside were the active antimicrobial compounds in the blueberry extracts. The results of this study suggest that blueberry extract or extract-derived components may be used to control pathogenic microorganisms. More studies on the use of blueberry as a natural antimicrobial in food products are warranted.     

Effect of sulfur dioxide and ethanol concentration on fungal profile and ochratoxin a production by Aspergillus carbonarius during wine making

Fungal profiles and ochratoxin A (OTA) accumulation during wine making were investigated using five different wine grape cultivars, Cabernet Sauvignon, Pinot Noir, Merlot, Syrah and Petit Verdot and the intrinsic influences caused by sulfur dioxide, ethanol and combine effect of ethanol and reducing sugar were analyzed using Cabernet Sauvignon and inoculation of Aspergillus carbonarius. Aspergillus spp. and Penicillium spp. were found as the major fungi in all winemaking processes and were highly correlated with OTA accumulation in wine. Most fungi died and OTA production decreased after 48 h of alcoholic fermentation, being consistent with the period when ethanol accumulation increased. The addition of SO₂ significantly inhibited the growth and OTA production of A. carbonarius with complete inhibition at 500 mg/L. When the ethanol concentration in the must increased to the range of 2–4%, growth and OTA production of A. carbonarius were significantly inhibited. Reducing sugar concentration had no significant effect on the growth and OTA production of A. carbonarius within the levels changing during the winemaking. Therefore, the increase of ethanol concentration played an important role in causing the decrease of fungal contamination and OTA accumulation during winemaking.     

Antimicrobial effect of cranberry juice and extracts

The antimicrobial effect of cranberry juice and of three cranberry extracts (water-soluble (E1) and apolar phenolic compounds (E2), and anthocyanins (E3)) was investigated against seven bacterial strains (Enterococcus faecium resistant to vancomycin (ERV), Escherichia coli O157:H7 EDL 933, Escherichia coli ATCC 25922, Listeria monocytogenes HPB 2812, Pseudomonas aeruginosa ATCC 15442, Salmonella Typhimurium SL1344, and Staphylococcus aureus ATCC 29213). Each cranberry sample was analyzed to determine the minimum inhibitory concentration (MIC) and the maximal tolerated concentration (MTC) at neutral pH. The results, reported in μg phenol/mL, indicated that all the bacterial strains, both Gram-positive and Gram-negative, were selectively inhibited by the cranberry phenolic compounds. The extract rich in water-soluble phenolic compounds caused the most important growth inhibitions. The bacteria ERV, and to a lesser degree, P. aeruginosa, S. aureus and E. coli ATCC 25922, were the most sensitive to the antimicrobial activity of extract E1. The growth of P. aeruginosa and E. coli ATCC was also affected by the presence of the anthocyanin-rich cranberry extract E3, although the observed antibacterial effect was not as important as with extract E1. In general, L. monocytogenes, E. coli O157:H7 and S. Typhimurium were the most resistant to the antibacterial activity of the cranberry extracts. Within 30 min of exposure with pure neutralized cranberry juice, L. monocytogenes and ERV were completely inactivated.     

Antioxidant and antimicrobial activities of various leafy herbal teas

We evaluated the antioxidant and antimicrobial activities of various leafy herbal tea (LHT) extracts, including rooibos, green tea, black tea, rosemary, lemongrass, mulberry leaf, bamboo leaf, lotus leaf, peppermint, persimmon leaf, and mate tea. To compare the antioxidant activities of various LHTs, samples of each were extracted with 80 °C water or 20 °C ethanol, and their total phenolic content (TPC), total flavonoid content (TFC), 2,2-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, 2,2-azinobis-3 ethyl benxothiazoline-6-sulphonic acid (ABTS) radical cation decolorization activity, ferric reducing power, and ferrous ion chelating effect were measured. Green tea ethanol extract showed the highest antioxidant activity in all assays except the ferrous ion-chelating assay. Water extracts of green tea and black tea and ethanol extracts of rosemary, mate, and persimmon leaf teas also exhibited considerable antioxidant potential, followed by the green tea ethanol extract. Minimum inhibitory concentrations (MIC) and minimum lethal concentrations (MLC) were determined to verify the antimicrobial activities of the LHT extracts against two oral pathogens (Streptococcus mutans and Streptococcus sobrinus) and three food-borne pathogens (Listeria monocytogenes, Shigella flexneri, and Salmonella enterica). Among the tested LHTs, green tea ethanol extract had potent antimicrobial activity against all five pathogens, and the mate tea water extract was the most effective against Gram-positive bacteria. Consequently, green tea ethanol extracts had the most powerful antioxidant and antimicrobial properties, suggesting their potential application as a health-promoting functional ingredient or natural preservative in foods.     

Addition of phytochemical-rich plant extracts mitigate the antimicrobial activity of essential oil/wine mixtures against Escherichia coli O157:H7 but not against Salmonella enterica

Marinades for preparing raw meats for cooking are frequently made of wine and herbs. We simulated several formulations of potential antimicrobial marinades with these components and other food compatible/food derived extracts. Red wine formulations containing essential oils from oregano or thyme, or their primary active components carvacrol and thymol, respectively, and a mixture of plant extract powders from phytochemical-rich apple skin, green tea, and olive, were evaluated for inhibitory activity against the foodborne pathogens Escherichia coli O157:H7 and Salmonella enterica. Red wine alone exhibited low activity, as did the plant extract suspended in the wine. Surprisingly, the high activity of oregano or thyme essential oils in red wine was reduced in E. coli, but not in Salmonella, by addition of the plant extract. This study shows that essential oils in red wine can be an effective antimicrobial in food, however the possibility exists that phytochemicals, added to the treatment solution or natively present in the food itself, could adversely impact the antimicrobial activity and should be addressed with future studies.     

Effect of ethanol on the ability of Oenococcus oeni to remove ochratoxin A in synthetic wine-like media

The study focused on the changes in bacterial population, malolactic fermentation and ochratoxin A (OTA) levels in cultures of Oenococcus oeni performed in synthetic medium supplemented with ethanol and OTA. Growth was better in cultures containing 5% ethanol and was not observed in cultures containing 15% ethanol. The OTA removal ability of O. oeni depended on ethanol and initial OTA levels. The highest toxin removal percentage was observed in cultures containing 5% ethanol and 2 μg OTA/l. In ethanol-containing medium part of OTA was not sorbed by O. oeni and remained in the liquid medium. Thus, it cannot efficiently eliminate OTA in acidic ethanol-containing beverages, such as wine. The effect of ethanol on the OTA removal ability of O. oeni is described for the first time.     

A new fear in wine: Isolation of Staphylococcus epidermidis histamine producer

Biogenic amines (BAs) are undesirable compounds in all foods and beverages because they may induce food-borne intoxications when consumed at high concentrations. The aim of this study was to identify the organism responsible for the synthesis of histamine in a Tempranillo red wine from Ribera de Duero D.O. (Denomination of origin), Spain. Bacteria present in wines after malolactic fermentation were isolated, identified and typed. Four strains of the species Oenococcus oeni and two strains of Staphylococcus epidermidis were found. None of the O. oeni strains produced histamine, cadaverine or putrescine, but one of the S. epidermidis strains (Pa) was able to produce all three in synthetic medium and grape must, although not in wine. From the data obtained in this work, histamine present in Tempranillo wine B was produced by the S. epidermidis strain Pa. This is the first report in which the presence of S. epidermidis has been reported in wine and whose ability to produce histamine, putrescine and cadaverine has been demonstrated in grape must.     

Antioxidant and antimicrobial activities of leafy green vegetable extracts and their applications to meat product preservation

Leafy green vegetables (LGV) are rich in phenolic compounds that have a wide range of biological functions, including antioxidant and antimicrobial activities. Our first goal was to evaluate the antioxidant and antimicrobial activities of 70% ethanolic extracts of ten LGV commonly consumed in East Asia. To determine antioxidant activity, we measured total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, 2,2-azinobis-3 ethyl benxothiazoline-6-sulphonic acid (ABTS) cation decolorization activity, and reducing power. For the analysis of antimicrobial activity, the inhibitory effects of the extracts against Escherichia coli, Salmonella enterica, Shigella flexneri, Listeria monocytogenes, Staphylococcus aureus, and Bacillus subtilis were evaluated using agar well diffusion and broth-microdilution tests. Among all LGV, extracts of chamnamul (Pimpinella brachycarpa) and fatsia (Aralia elata) exhibited outstanding antioxidant and antimicrobial properties, and we thus investigated the influences of these extracts on lipid oxidation and microbial criteria in raw beef patties. The extracts and butylated hydroxytoluene (BHT, a positive control) were individually added to patties at both 0.1% and 0.5% (w/w) concentrations and the patties were stored at 4 °C for 12 days. The color parameters and thiobarbituric acid reactive substances (TBARS) values were monitored periodically, and a microbial analysis was performed. The addition of extracts and BHT resulted in concentration-dependent decreases in TBARS values and in the number of microorganisms in the beef patties and also improved meat color stability. The fatsia extract had more effective antioxidant and antimicrobial activities than the chamnamul. We conclude that extracts of LGV, especially fatsia, have potential as natural preservatives for meat products.     

In vitro antimicrobial activity of less-utilized spice and herb extracts against selected food-borne bacteria

In this study we compared the antimicrobial activities of extracts from four under-utilized spices and herbs including goraka (Garcinia quaesita), galangal (Alpinia galanga), lemon iron bark (Eucalyptus staigerana) and mountain pepper (Tasmannia lanceolata) to the three common spices and herbs pepper (Piper nigrum), rosemary (Rosmarinus officinalis), and oregano (Oreganum vulgare). Different extraction solvents were used (water, ethanol and hexane) and extracts were tested against four food-borne bacteria (Escherichia coli, Salmonella Typhimurium, Listeria monocytogenes and Staphylococcus aureus) using agar disc diffusion and broth dilution assays. Solvent type greatly influenced the antimicrobial activity of the spice and herb extracts except for those of P. nigrum, which had little or no activity. In general the spice and herb extracts with antimicrobial activity were more effective against Gram-positive than Gram-negative bacteria. Extracts from the under-utilized herbs and spices had significant activity. In particular, A. galanga hexane and ethanol extracts and E. staigerana ethanol and water extracts had strong antimicrobial activity against S. aureus and/or L. monocytogenes. Interestingly the minimal inhibitory concentrations determined using the broth dilution method and the diameter of inhibition zones using the disc diffusion assay were not strongly correlated (r² ranged from 0.10 to 0.70) in most extracts, suggesting that choosing just one method for antimicrobial testing may lead to indefinite conclusions. The total phenolic content of two extracts from each spice and herb was assayed to establish any relationship between antimicrobial activity and phenolic compound levels, however this was found to poorly correlated (r² < 0.30). This study has demonstrated that simple extracts of novel under-utilized herbs and spices have potential antimicrobial activity against food-borne bacterial species. Further it is indicated that the antimicrobial activity in some herbs and spices may be due to the presence of substances other than phenolic compounds.     

The antimicrobial effect of wine on Bacillus cereus in simulated gastro-intestinal conditions

This study aimed to evaluate the antimicrobial activity of wine against Bacillus cereus vegetative cells and spores. The results clearly show that wine exerts a strong inactivation effect against vegetative cells of B. cereus. The red wine tested inactivated stationary phase cultures to undetectable numbers in less than 10 s. Thus, further inactivation assays were carried out with wine diluted with water (1:4 and 1:8). Diluted wine 1:4 caused a reduction of approximately 5 log cycles on viable cell counts in 20 s. On the other hand, B. cereus spores were found to be highly resistant to wine exposure. The influence of wine components (organic acids, ethanol and phenolic compounds) was investigated on vegetative cells. The wine organic acids tested exhibited a strong inactivation effect, and, when combined with ethanol, a slight synergistic effect was observed. The wine phenolic compounds assayed displayed no activity against the vegetative cells at the concentrations tested. At the simulated gastric conditions studied (in the presence of food), wine diminished considerably the number of B. cereus viable cells in addition to the effect of the synthetic gastric fluid. The behaviour of B. cereus spores under gastro-intestinal conditions was also evaluated. In a consumption-like scenario, the addition of wine led to lower total counts (vegetative cells + spores) of B. cereus in the simulated intestine conditions, showing that wine inhibits the proliferation of the vegetative cells obtained from the germination of spores. This work provides evidence that consumption of wine during a meal may diminish the number of viable cells of B. cereus and reduces the impact of the germination of spores that may occur in the small intestine, thus lowering the risk of toxi-infection that may be caused by this pathogen.     

Antimicrobial activity of phenolic compounds of wine against Campylobacter jejuni

Campylobacter jejuni is a food pathogen which causes gastrointestinal conditions with an ever-increasing incidence at a global level. The antimicrobial power of wine and its components has been studied. Wines having 11.5% ethanol significantly reduced the viability of C. jejuni when they were diluted to 25% in water. The microbicidal power of red wine was higher than that of white wine. While pH does not seem to affect the viability of this pathogen, different phenolic compounds have an effect on it when tested at concentrations from 0 to 1000 mg/L. Gallic acid and p-hydroxybenzoic acid reduced the viability of C. jejuni at concentrations as low as 1 mg/L, but quercetin and catechin did not even affect it at concentrations of 1000 mg/L. Methyl gallate, epicatechin, synaptic acid, vanillic acid, and caffeic acid were microbicidal at concentrations starting at 10 mg/L. Tryptophol, ferulic acid, and cumaric acid were effective starting at 100 mg/L. According to this, wine constitutes an adverse environment for the survival of this pathogen. Furthermore, it would be interesting to study the possible use of phenolic compounds in wine as an alternative to the use of antimicrobial growth promoters against these bacteria in broilers.     

Pomegranate peel (Punica granatum L) extract and Chinese gall (Galla chinensis) extract inhibit Vibrio parahaemolyticus and Listeria monocytogenes on cooked shrimp and raw tuna

Vibrio parahaemolyticus and Listeria monocytogenes are bacterial pathogens associated with raw or ready-to-eat seafood products. Many compounds extracted from plant material have shown promise for inhibiting bacterial pathogens when applied to some foods. In this study, aqueous methanol extracts from pomegranate peel (Punica granatum L.) and Chinese gallnut (Galla chinensis) were tested against V. parahaemolyticus and L. monocytogenes on cooked shrimp and raw homogenized tuna. The extracts were applied to the shrimp by soaking for 2 min (5 mg/ml). The extracts (1.7 mg ml) were added to homogenized tuna and stirred. The antimicrobial assay on V. parahaemolyticus was conducted at 12 °C, and the assay on tuna was conducted at both 4° and 12 °C. Both Chinese gall and pomegranate peel extracts significantly inhibited the growth of V. parahaemolyticus in both shrimp and tuna. Only Chinese gall extract significantly inhibited growth of L. monocytogenes. Overall V. parahaemolyticus was more sensitive to both plant extracts compared with L. monocytogenes. Both plant extracts had stronger antimicrobial activity on shrimp compared with the tuna. Neither extract completely inhibited the growth of V. parahaemolyticus or L. monocytogenes.     

Antimicrobial efficacies of plant extracts and sodium nitrite against Clostridium botulinum

This study was conducted to evaluate the antibotulinal activities of some plant extracts, alone or in combination with nitrite (NaNO₂). Water- and 99.5% ethanol-soluble extracts (1:9 plant material weight-by-solvent volume, 25 °C, 48 h) of 90 kinds of fresh and dehydrated herbs and spices were tested. The aqueous extract of clove and alcohol extracts of lemon eucalyptus, mace and licorice exhibited greater antibotulinal activities in TPGY medium with MIC ranging from 0.05% to 0.2%. However in TPGY, only the aqueous extract of Coptis rhizome exhibited synergistic antibotulinal activity with NaNO₂, reducing the individual MIC of NaNO₂ from 6–8 ppm to 2 ppm with 0.05% Coptis extract. In a model meat food, the alcohol-soluble extracts of nutmeg (0.05%) and sage (0.02%), and the aqueous fraction of clove extract (0.05%) exhibited antibotulinal activities in combination with 10 ppm NaNO₂. The observed synergy between plant extracts and NaNO₂ that resulted in lower MIC of both additives have significant repercussion in the control of botulism in minimally processed meat products without compromising organoleptic properties.     

Inhibition of Fusarium culmorum by carboxylic acids released from lactic acid bacteria in a barley malt substrate

The effect of carboxylic acids, composed by both organic and phenolic acids, released in a barley malt substrate fermented by lactic acid bacteria was tested against Fusarium culmorum macroconidia and compared under different fermentation conditions. Phenolic acids released by Lactobacillus plantarum FST1.7 and Lactobacillus brevis R2Δ were quantified using a QuEChERS method coupled with a HPLC-UV/PDA system. Their concentration improved with increasing extract content of the barley malt-based substrate and reached maximal concentrations after 48 h of fermentation performed at optimum growth temperature. Generally, phenolic acids were produced at levels far below their minimal inhibitory concentration (MIC), and limited synergistic effects were observed when mixed with organic acids. The fungal growth suppression by the wort fermented by Lb. brevis R2Δ (95 ± 9 h total inhibition) could be fully explained by the presence of antifungal carboxylic acids, whereas only partially accounted for Lb. plantarum FST1.7 (198 ± 19 h). Organic acids were mainly responsible for the ability of LAB fermented wort to cause fungal inhibition, whereas phenolic acids took only a secondary role at the low concentrations released. Longer fermentation times favoured primarily organic acid release, whereas fermentation of higher malt extract substrates encouraged both organic and phenolic acids production. The understanding on how synergy works between antifungal compounds could help to identify strategies to further increase their concentration in wort, with potential to replace synthetic broths and for direct application in food application.     

Antimicrobial effects of fractions from cranberry products on the growth of seven pathogenic bacteria

The antimicrobial effect of thirty HPLC fractions of different polarity obtained from two cranberry juices and three extracts (anthocyanins, water-soluble and apolar phenolic compounds) isolated from frozen cranberries and pomace was investigated against seven bacterial strains (Enterococcus faecium resistant to vancomycin (ERV), Escherichia coli O157:H7 EDL 933, Escherichia coli ATCC 25922, Listeria monocytogenes HPB 2812, Pseudomonas aeruginosa ATCC 15442; Salmonella Typhimurium SL1344 and Staphylococcus aureus ATCC 29213) The minimum inhibitory concentration (MIC) and the maximal tolerated concentration (MTC) of each fraction were determined for each pathogen using a 96-well microtiter plate method. The results, reported in μg phenol/mL, indicated that all the bacterial strains, both Gram-positive and Gram-negative, were selectively inhibited by the cranberry phenolic compounds. All pathogens were very sensitive to at least seven fractions with MTCs below 2 μg phenol/mL and five fractions with MICs below 10 μg phenol/mL. In addition, four fractions rich in apolar phenolic compounds were very efficient against all bacteria with MICs below 10 μg phenol/mL, and twenty five fractions completely inhibited microbial growth with MICs below100 μg phenol/well. L. monocytogenes exhibited the highest sensitivity with twelve very active fractions (MTCs and MICs below 1 and 10 μg phenol/mL, respectively) while E. coli O157H7 was the least sensitive to twenty seven fractions (with the highest MICs). Also, it appears that the technological process to manufacture cranberry juice can reduce the antimicrobial activity of phenolic fractions.     

Mould growth and mycotoxin production as affected by Equisetum arvense and Stevia rebaudiana extracts

Cereals are very important for human and animal diet. However, agricultural products can be contaminated by moulds and their mycotoxins. On the other hand, natural plant products with antimicrobial properties could be a possibility to control mycotoxigenic fungi in foods and feeds. In this study, Equisetum arvense and Stevia rebaudiana extracts were tested for their efficacy against a range of mycotoxigenic fungi. Maize agar medium (MAM 2%) was used for this study and E. arvense and S. rebaudiana extracts were added at different concentrations (1–3%) under different water activity (a_w) levels (0.85–0.95). Six mycotoxigenic moulds were inoculated and incubated at different temperatures (15–30 °C) during 21 days. In general, no growth was observed with E. arvense extract at 3% in all studied conditions for all isolates. However, with S. rebaudiana extract at 2–3%, growth was not significantly decreased (p < 0.05) in most of the cases. Finally, in terms of toxin production, results were not conclusive. The use of E. arvense extracts as antifungals and antimycotoxigenics and their application should be further explored.