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

Abstract

Aims: To study the effects of water activity (a_W ; 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 a_W , temperature and time of incubation were used to examine growth and mycotoxin production. All strains were able to grow at 0·95 a_W , but maximum growth rates were obtained at 0·99 a_W and 25°C. Maximum levels of AOH, AME and TA were obtained at 0·99 a_W and 25°C, but high amounts of TA were also obtained at 0·96 a_W 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 a_W 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.

Keywords: Alternaria alternata; growth; mycotoxins; temperature; water activity; wine grapes.