Fruit infected with Paecilomyces niveus: A source of spoilage inoculum and patulin in apple juice concentrate?

Abstract

Paecilomyces niveus has long been recognized as an important heat-resistant mold (HRM) causing spoilage in thermally processed apple products. With the recent discovery that P. niveus causes an apple disease called Paecilomyces rot, there is a need to evaluate the possibility that the spores can be introduced via infected fruit and survive thermal processing to contaminate apple products. Previously, research characterizing P. niveus survival and spoilage has been based on simple inoculation of cultured ascospores directly into juice. To determine whether ascospores formed in infected fruit survive through thermal processing with rotating vacuum evaporation (2.5 h, 70 °C), apples infected with P. niveus were used to make apple juice concentrate. Viable P. niveus was quantified in samples taken throughout the apple juice concentrate process: in cider, centrifuged juice, apple solids, and in juice made from concentrate. Additionally, the concentration of the mycotoxin patulin was determined in a subset of samples. Results show that P. niveus survived juice concentration. The thermal process used significantly reduced P. niveus (P = 0.0017); from an average of 5.5 log CFU L−1 in the initial cider made from diseased fruit to an average of 1.5 log CFU L−1 in single strength apple juice diluted from concentrate. Ascospores were observed at a greater abundance than intact asci throughout the concentration process. Patulin concentrations at all stages of apple juice concentration exceeded the United States’ regulatory defect action level of 50 ppb. This is the first report that apples infected with P. niveus can survive and remain viable in finished apple products and that patulin is produced in these apples. It raises important questions about the use of damaged and infected fruit as a source of HRM which contribute to spoilage and mycotoxins in apple juice concentrate.