Evaluation of growth quantification methods for modelling the growth of Penicillium expansum in an apple‐based medium

Abstract

Penicillium expansum isolates were grown on an apple concentrate-based medium modified to different water activity levels (0.83-0.99), and incubated at 3-29 • C for up to 14 days. The diameters of the growing colonies were measured and colonies were extracted for determination of ergosterol and N-acetyl-β-D-glucosaminidase activity. Results showed good correlation of measured diameters in the repeated treatments, but slightly lower repeatability for the ergosterol determination, and poor repeatability for the determination of N-acetyl-β-Dglucosaminidase activity. Primary and secondary models were built for colony diameter and ergosterol content of the colonies, which were similar for both isolates tested. Growth was prevented at low water activity values (0.83-0.85) outside the range 10-23 • C. However, given an unpreserved apple or apple product (a w > 0.97) left at room temperature growth may occur in a time as short as 1 day, probably leading to mycotoxin accumulation in a few days in the event of mycotoxigenic strains. This issue also highlights the importance of shortening the time of transport and storage operations when considering the use of culled apples unfit for other, higher quality and higher profit purposes to obtain apple by-products such as puree, juices or jam.

Patulin distribution in Fuji and Golden apples contaminated withPenicillium expansum

“…In Spain, juice concentrates are mainly produced from Golden apples, although Fuji apples are sometimes used when unsuitable for fresh consumption. Exposing P. expansum-infected apples, intended for juice production, to room temperature for short periods of time during postharvest operations has been shown to be critical for the accumulation of patulin (Marín et al 2006, Morales et al 2006a.…”

Effects of apple and pear varieties and pH on patulin accumulation by Penicillium expansum

“…Apple production is greater than pear production8 and, consequently, consumption of apple by‐products is higher. Thus, information about patulin contamination is mainly focused on apple and its by‐products which remain the major sources of patulin consumption in humans 9, 10…”

“…Patulin production appears to be dependent on factors such as water activity,10 pH11, 12 and other characteristics of the fruits 12, 13. Temperature also plays a role in patulin accumulation 14–17.…”

Risk Assessment and Safety Evaluation of Mycotoxins in Fruits

“…Growth of P. expansum was prevented at low a w values (0.83-0.85) and outside the range of 10-23°C, but in unpreserved apple or apple products (a w > 0.97) left at room temperature, growth may occur in a time as short as 1-day, probably leading to mycotoxin accumulation in a few days (Marin et al, 2006).…”