Free and bound patulin in cloudy apple juice

During validation of an HPLC-UV method for patulin analysis, a time and concentration dependent recovery of patulin was observed. Spiked cloudy apple juice was analysed on successive days, which resulted in recoveries on day 3 which were up to 20% lower than on day 1. This reduction was caused by an interaction between patulin and the solid parts of cloudy apple juice. Since these solid parts are richer in proteins compared to the liquid phase of cloudy apple juice, and the binding of patulin to proteins has been described in the literature, patulin will most probably interact with the proteins in the solid parts. As a consequence, up to 20% of the present patulin is bound and not detected during HPLC-UV analysis, which can lead to an underestimation on toxicological level.