Judit Krisch

Anti yeast activities of some essential oils in growth medium, fruit juices and milk.

The anti-yeast activities of four essential oils (EOs) from clary sage, juniper, lemon and marjoram against wild-type isolates of the food-related yeasts Geotrichum candidum, Pichia anomala, Saccharomyces cerevisiae and Schizosaccharomyces pombe in malt extract (ME) medium, apple juice and milk were investigated. Minimal inhibitory concentrations (MICs) for the EOs and their main components were determined and the checkerboard method was used to calculate fractional inhibitory concentration (FIC) indices for the combinations of EOs or components. The most sensitive yeast was S. pombe (MICs of 0.0625-0.125 μl/ml) while G. candidum proved to be the most insensitive (MICs of 0.5-2 μl/ml). In general, the lag phases were lengthened by increasing EO concentrations, while significant reduction of growth rates was obtained only at the highest EO concentrations. The anti-yeast effects of the EOs were good in the acidic pH range optimal for yeasts growth. Combinations of juniper and clary sage EOs resulted in additive effects in the case of S. cerevisiae and G. candidum, but all other combinations showed no interaction. The combination of α-pinene and limonene led to synergism, while the combination of α-pinene with linalool resulted in an additive effect. Cloudy apple juice protected the yeasts against the effect of lemon EO: the lag phases were shorter and the growth rates higher than in clear apple juice. Lemon EO decreased the growth rate of G. candidum in skimmed milk in a dose-independent manner. Our results show that by adding lemon EO to clear apple juice a new, harmonic taste can be achieved and open storage time could be prolonged.

Anti‐biofilm forming and anti‐quorum sensing activity of selected essential oils and their main components on food‐related micro‐organisms

The aim of this study was to investigate the effect of clary sage, juniper, lemon and marjoram essential oils (EOs) and their major components on the formation of bacterial and yeast biofilms and on the inhibition of AHL‐mediated quorum sensing (QS).

Characterization of a β-glucosidase with transgalactosylation capacity from the zygomycete Rhizomucor miehei

An extracellular β-glucosidase from the zygomycete Rhizomucor miehei NRRL 5282 cultivated in a wheat bran-based solid state fermentation system was characterized. The purified enzyme exhibited an optimum temperature of 68-70 °C and pH of 5.0. It efficiently hydrolyzed oligosaccharides having β-(1→4) glycosidic linkages and exhibited some β- and α-galactosidase activity. The V(max) for p-nitrophenyl-β-d-glucopyranoside and cellobiose was 468.2 and 115.5 U/mg, respectively, while the K(m) was 0.12 mM for both substrates. The enzyme had transglucosylation and transgalactosylation activities resulting in the formation of glycosides from cellobiose, lactose and ethanol. The enzyme increased the amounts of free phenolic antioxidants in sour cherry pomace indicating that its hydrolyzing activity could potentially be applicable to improve the bioavailability of these compounds.

Anticandidal effect of berry juices and extracts from Ribes species

The biological activities of fruit juices and pomace (skin, seeds) extracts from blackcurrant (Ribes nigrum), gooseberry (Ribes uva-crispa) and their hybrid plant (jostaberry, Ribes × nidigrolaria) were evaluated against the most frequently isolated twelve human pathogenic Candida species by broth dilution tests. The phenolic content of juice, water and methanol extracts were measured and the relationship with antifungal activity was assessed. Growth of the most Candida species was inhibited, with the exception of C. albicans, C. krusei, C. lusitaniae and C. pulcherrima. R. nigrum, with the highest phenol content, was observed to have the highest anticandidal activity, indicating a positive correlation between phenol content and antifungal activity.

Antibacterial effect of essential oils and interaction with food components

The antibacterial effect of essential oils (EOs) derived from Citrus lemon, Juniperus communis, Origanum majorana, and Salvia sclarea, was investigated either alone or in combination, on 2 food related bacteria (Bacillus cereus and Escherichia coli). The influence of food ingredients — hydrolyzed proteins originating from animal and plant (meat extract and soy peptone) and sucrose — on the antibacterial effect of EOs was also tested. The most effective antibacterial activities were obtained with marjoram and clary sage oil, alone and in combination. High concentration of meat extract protected the bacteria from the growth inhibiting effect of marjoram oil, while soy peptone had no such effect. Sucrose intensified the lag phase lengthening by marjoram oil in a dose-independent manner.

IDENTIFICATION OF ACID- AND THERMOTOLERANT EXTRACELLULAR β-GLUCOSIDASE ACTIVITIES IN ZYGOMYCETES FUNGI

Extracellular beta-glucosidase activity of 94 strains, representing 24 species of the genera Gilbertella, Mucor, Rhizomucor , and Rhizopus was evaluated in submerged culture and under solid state fermentation on wheat bran. Gilbertella persicaria G1 isolate showed the highest activity (70.9 U ml -1 ) followed by other Gilbertella (58.6-59.0 U ml -1 ) and Rhizomucor miehei isolates (29.2-42.0 U ml -1 ). Optimum temperature for enzyme production was 25 degrees C for Gilbertella and Mucor , and 30 degrees C for Rhizomucor and Rhizopus strains. Enzymes of R. miehei strains proved to be thermotolerant preserving up to 92.8% residual activity after heating to 75 degrees C in the presence of cellobiose substrate. Enzymes of Mucor racemosus f. chibinensis, R. miehei and Rhizopus microsporus var. oligosporus strains were activated at acidic condition (pH 4). Glucose was a strong inhibitor for each fungal beta-glucosidase tested but some of them showed ethanol tolerance up to 20% (v/v). Ethanol also activated the enzyme in these strains suggesting glycosyl transferase activity.

Green tea and vitamin C ameliorate some neuro-functional and biochemical signs of arsenic toxicity in rats

Background/objectives: Nervous system damage is one of the consequences of oral exposure to waterborne inorganic arsenic. In this work, the role of oxidative status in the neurotoxicity of arsenic and the possible role of two foodborne antioxidants in ameliorating arsenic-related oxidative stress were investigated. Methods: Male Wistar rats were given 10 mg/kg b.w. of trivalent inorganic arsenic (in the form of NaAsO2), 5 day/week for 6 weeks by gavage, combined with vitamin C solution (1 g/l) or green tea infusion (2.5 g in 500 ml boiled water) as antioxidants given in the drinking fluid. Results: Body weight gain was reduced by arsenic from the second week and the antioxidants had no effect on that. Cortical evoked potentials had increased latency, tail nerve conduction velocity was reduced, and this latter effect was counteracted by the antioxidants. The effect of green tea was stronger than that of vitamin C, and green tea also diminished lipid peroxidation induced by As. There was fair correlation between brain As levels, electrophysiological changes, and lipid peroxidation, suggesting a causal relationship. Discussion: Natural antioxidants might be useful in the protection of the central nervous system against the toxicity of oral As.

Isolation and Characterization of Antagonistic Bacillus Strains Capable to Degrade Ethylenethiourea

In this study, more than 150 bacteria showing antagonistic properties against bacterial and fungal pathogens of the tomato plant were isolated and characterized. The most efficient agents against these phytopathogenic microorganisms belong to the genus Bacillus: the best biocontrol isolates were representatives of Bacillus subtilis, B. mojavensis and B. amyloliquefaciens species. They intensively produced fengycin or/and surfactin depsipeptide antibiotics and also proved to be excellent protease secretors. It was proved, that the selected strains were able to use ethylenethiourea (ETU) as sole nitrogen source. These antagonistic and ETU-degrading Bacillus strains can be applied as biocontrol and also as bioremediation agents.

Enhanced production of industrial enzymes in Mucoromycotina fungi during solid-state fermentation of agricultural wastes/by-products.

Cellulolytic, lipolytic and proteolytic enzyme production of zygomycetes Mucor corticolus, Rhizomucor miehei, Gilbertella persicaria and Rhizopus niveus were investigated using agro-industrial wastes as substrates. Solid-state cultures were carried out on untreated corn residues (stalk and leaf) as single substrate (SSF1) or corn residues and wheat bran in mixed fermentation (SSF2). Rapid production of endoglucanase (CMCase) was observed with maximal activity reaching after about 48-h fermentation, while cellobiohydrolase (CBH) and β-glucosidase enzymes generally had their peak after 72-h incubation. Highest filter paper degrading (FPase), CMCase, CBH and β-glucosidase activities obtained were (U g⁻¹ dss) 17.3, 74.1, 12.2 and 158.3, for R. miehei, G. persicaria, M. corticolus and Rh. niveus, respectively. M. corticolus proved to be the best lipolytic enzyme producer in SSF1 presenting 447.6 U g⁻¹ dss yield, while R. miehei showed 517.7 U g⁻¹ dss activity in SSF2. Rh. niveus exhibited significantly greater protease production than the other strains. Suc-AAPF-pNA hydrolyzing activities of this strain were 1.1 and 1.96 U g⁻¹ dss in SSF1 and SSF2, respectively. We conclude that the used corn stalk and leaf residues could potentially be applicable as strong inducers for cellulase and lipase production by Mucoromycotina fungi.

Latest about Spoilage by Yeasts: Focus on the Deterioration of Beverages and Other Plant-Derived Products.

Food and beverage deterioration by spoilage yeasts is a serious problem that causes substantial financial losses each year. Yeasts are able to grow under harsh environmental conditions in foods with low pH, low water activity, and high sugar and/or salt content. Some of them are extremely resistant to the traditional preservatives used in the food industry. The search for new methods and agents for prevention of spoilage by yeasts is ongoing, but most of these are still at laboratory scale. This minireview gives an overview of the latest research issues relating to spoilage by yeasts, with a focus on wine and other beverages, following the interest of the research groups. It seems that a better understanding of the mechanisms to combat food-related stresses, the characteristics leading to resistance, and rapid identification of strains of yeasts in foods are the tools that can help control spoilage yeasts.