Impact of antagonistic yeasts from wine grapes on growth and mycotoxin production by Alternaria alternata.

AIMS: Alternaria alternata is a major contaminant of wine grapes, meaning a health risk for wine consumers due to the accumulation of toxic metabolites. To develop a successful biofungicide, the effectiveness of epiphytic wine grape yeasts against A. alternata growth and toxin production was assessed in vitro under temperature and aW conditions that simulate those present in the field. METHODS AND RESULTS: The effect of 14 antagonistic yeasts was evaluated on growth and alternariol (AOH), alternariol monomethyl ether (AME) and tenuazonic acid (TA) production by three A. alternata strains in a synthetic medium with composition similar to grape (SN) at three temperatures (15, 25 and 30°C). All Metschnikowia sp. yeast strains evaluated completely prevented A. alternata growth and mycotoxin production at all temperatures in SN medium. Meanwhile, the growth inhibition exerted by Starmerella bacillaris yeast strains was higher at 30°C, followed by 25 and 15°C, being able to show a stimulating or inhibiting effect. Hanseniaspora uvarum yeast strains showed a growth promoting activity higher at 15°C, followed by 25 and 30°C. Even at conditions where A. alternata growth was stimulated by the S. bacillaris and H. uvarum yeasts, high inhibitions of mycotoxin production (AOH, AME and TA) were observed, indicating a complex interaction between growth and mycotoxin production. CONCLUSION: There is a significant influence of temperature on the effectiveness of biocontrol against A. alternata growth and mycotoxin production. Metschnikowia sp. strains are good candidates to compose a biofungicide against A. alternata. SIGNIFICANCE AND IMPACT OF THE STUDY: Among the different antagonistic yeasts evaluated, only Metschnikowia sp. strains were equally effective reducing A. alternata growth and mycotoxin at different temperatures underlining the importance of considering environmental factors in the selection of the antagonists.

Water activity and temperature effects on growth and mycotoxin production by Alternaria alternata strains isolated from Malbec wine grapes.

AIMS: To study the effects of water activity (aW ; 0·99, 0·98, 0·97, 0·96 and 0·95), temperature (15, 25 and 30°C), incubation time (7-28 days), and their interactions on mycelial growth and alternariol (AOH), alternariol monomethyl ether (AME) and tenuazonic acid (TA) mycotoxin production on a synthetic nutrient (SN) media similar to grape composition by three strains of Alternaria alternata isolated from wine grapes from Argentina. METHODS AND RESULTS: Interacting conditions of aW , temperature and time of incubation were used to examine growth and mycotoxin production. All strains were able to grow at 0·95 aW , but maximum growth rates were obtained at 0·99 aW and 25°C. Maximum levels of AOH, AME and TA were obtained at 0·99 aW and 25°C, but high amounts of TA were also obtained at 0·96 aW and 15 or 30°C. Production of AOH and AME was favoured over TA at 25°C. TA levels were more sustained than AOH and AME. CONCLUSION: The optimum and marginal conditions for growth and mycotoxin production by A. alternata on a SN media similar to grape composition were in agreement, but certain stressful conditions for growth evaluated also promote mycotoxin production. SIGNIFICANCE AND IMPACT OF THE STUDY: Temperature and aW conditions that allows growth and mycotoxin production are those normally found during wine grape ripeness in the field. Therefore, efforts should be made to prevent Alternaria presence and mycotoxin production in wine grapes.

Highly cold-active pectinases under wine-like conditions from non-Saccharomyces yeasts for enzymatic production during winemaking.

UNLABELLED: The influence of oenological factors on cold-active pectinases from 15 preselected indigenous yeasts belonging to Aureobasidium pullulans, Filobasidium capsuligenum, Rhodotorula dairenensis, Cryptococcus saitoi and Saccharomyces cerevisiae was investigated. Pectinolytic enzymes were constitutive or partially constitutive; and high glucose concentration (200 g l(-1) ) did not affect or increased pectinase production at 12°C and pH 3·5 (up to 113·9 U mg(-1) ) only in A. pullulans strains. SO2 (120 mg l(-1) ) slightly affected the growth of A. pullulans strains but did not affect pectinase production levels. Ethanol (15%) barely affected pectinase activity of A. pullulans strains but diminished relative activity to 12-79% of basidiomycetous yeasts. Moreover, non-Saccharomyces strains showed promising properties of oenological interest. This study demonstrates that cold-active pectinases from some A. pullulans strains were able to remain active at glucose, ethanol and SO2 concentrations usually found in vinification, and suggests their potential use as processing aids for low-temperature winemaking. SIGNIFICANCE AND IMPACT OF THE STUDY: Nowadays, there is increasing interest in low-temperature winemaking. Nevertheless, commercial oenological pectinases, produced by fungi, are rarely active at low temperatures. Cold-active pectinases that are stable under vinification conditions are needed. This study indicated that cold-active and acid-tolerant pectinases from non-Saccharomcyes yeasts were able to remain active at glucose, ethanol and SO2 concentrations usually found in winemaking. Furthermore, not only are these yeasts a source of cold-active pectinases, but the yeasts themselves are also potential adjunct cultures for oenology to produce these enzymes during cold-winemaking.

Study of adhesion of Lactobacillus casei CRL 431 to ileal intestinal cells of mice.

It is well known that the cell wall of Lactobacillus casei CRL 431, a strain present in probiotics, presents lectinlike surface molecules. Presence of these molecules stimulates the immune system. Given the role that lectins and lectinlike substances play in the adhesion phenomenon, it is probable that this is an initial stage in the immunostimulation produced by this bacterium. To confirm this, adhesion of this microorganism to exfoliated mouse ileal epithelial cells was studied in vitro. Other L. casei strains isolated from adult human intestines and one of dairy origin were also examined for their ability to adhere to ileal epithelial cells. Another strain, which was included in the present study, was Lactobacillus acidophilus CRL 730. L. casei strains isolated from humans showed good ability to adhere to ileal epithelial cells, whereas L. casei isolated from dairy origin did not. Adhesion was only observed at 37 degrees C and at a pH between 6 and 7.5. The exposure time needed for highest adhesion was 30 min. Presence of lectinlike substances on the surface of L. casei CRL 431 is important to this adhesion phenomenon, since adherence capacity was lost after removal of these substances.