Temperature and water activity effects on growth and temporal deoxynivalenol production by two Argentinean strains of Fusarium graminearum on irradiated wheat grain

The ability of six strains of Pichia anomala, four strains of Pichia kluyveri and two strains of Hanseniaspora uvarum predominant during coffee processing to produce polygalacturonase (PG), pectin esterase (PE) and pectin lyase (PL) in yeast polygalacturonic acid medium (YPA) and in coffee broth (CB) was studied. For comparison, a reference strain of Kluyveromyces marxianus CCT 3172 isolated from cocoa and reported to produce high amount of PG was included.

Initial screening of PG activity using YPA medium showed that K. marxianus CCT 3172, P. anomala S16 and P. kluyveri S13Y4 had the strongest activity. Enzymatic assays showed that the four yeast species secreted PG, but none of the yeasts investigated was found to produce PE or PL. P. anomala S16 and P. kluyveri S13Y4 were found to produce higher amounts of PG when grown in CB than in YPA. When K. marxianus CCT 3172, P. anomala S16 and P. kluyveri S13Y4 were grown in YPA broth adjusted to pH of 3.0–8.0 and incubated at temperatures of 15–40 °C, the three yeast species secreted the highest amount of PG at pH 6.0 and at 30 °C. For PG secreted by K. marxianus CCT 3172 and P. anomala S16, the optimum pH and temperature for the enzymatic activity were 5.5 and 40 °C, respectively. On the other hand, PG produced by P. kluyveri S13Y4 showed the highest activity at pH 5.0 and 50 °C.

Significant differences in the extracellular activity of PG were found between the yeasts species as well as between strains within same species. High amounts of PG were produced by two strains of P. anomala and P. kluyveri. It is therefore likely that strains of those two species may be involved in the degradation of pectin during coffee fermentation.