Purpose: This study aims at defining boundaries for growth and mycotoxin production in order to optimize product formulation and shelf life.
Methods: A toxigenic isolate of Alternaria alternate (ITEM8176) isolated from tomato fruit affected by black mould and deposited at the ISPA collection, Italy (ITEM accession: http://www.ispa.cnr.it/Collection/) was used for growth and mycotoxin production assessment. Growth ability of the strain was determined after inoculating fungal ascospores (7 day-old culture) on cold break tomato purée supplemented with agar and followed by regular fungal development observations. A total of 6 levels of pH and 10 levels of temperature were tested, for 3 replicates, to define pH and temperature boundaries where fungal development and mycotoxin production occurred. The pH of tomato purée based medium was fixed at 2, 3, 4, 5, 6 and 7 while plates incubation was performed at 6.5, 10, 15, 20, 25, 30, 35 and 37°C. Analysis of mycotoxins (AOH, AME and TeA) was performed by HPLC with UV/DAD detection according to an adapted protocol.
Results: Stability of pH and water activity of tomato purée based media was checked throughout the experiments. Growth was observed above a pH of 3 whatever the incubation temperature. Growth optimum was determined at pH 5.5 and 24.5°C. Conditions where growth was not observed after 1 month incubation were considered not to allow fungal development as observed for pH lower than 3. Growth/no growth boundaries were compared with mycotoxin production/ no mycotoxin production boundaries for similar conditions on tomato purée based medium.
Significance: These results indicate the combination of pH and temperature where Alternaria mould development and mycotoxin production occurred. Knowing these boundaries will help industrials to optimize tomato product formulation and storage conditions to limit mould and mycotoxin development during shelf life.