Machinery mold (galactomyces geotrichum) survival following thermal and hydrostatic pressure processing

Abstract

Machinery mold is a foodborne fungus associated with spoilage of fruit and vegetable products, as well as colonization of the food production environment. Galactomyces spp. are not considered heat-resistant molds, although their sensitivity to mild heat treatments, like blanching and pasteurization, as well as to nonthermal treatments, like high pressure processing (HPP), remains unknown. Cultures of two Galactomyces spp. isolates, Galactomyces geotrichum and Galactomyces candidum, were heat treated at 50, 53, and 55°C and HPP treated at 4°C for 90 s at 300, 400, and 600 MPa. The 2-day-old G. geotrichum had a D-value of 0.99 ± 0.04 min and 28-day-old G. geotrichum had a D-value of 1.28 ± 0.07 min at 558C. Meanwhile, 2-day-old G. candidum had a D-value of 3.13 ± 0.20 min and 28-day-old G. candidum had a D-value of 1.60 ± 0.01 min at 558C. Overall, the significant differences in D-values between the two cultivation times were modest, and statistical significance was not consistent across all three temperatures. However, the differences were more pronounced at higher processing temperatures. G. geotrichum was only reduced by 0.32 ± 0.07 log CFU/mL after 90 s at 300 MPa. However, increasing the treatment level to 400 MPa for 90 s decreased the counts for G. geotrichum to below the limit of detection (<1 log CFU/mL) following HPP treatment. Meanwhile, the counts for G. candidum survivors at 400 MPa were 1.36 ± 0.08 log CFU/mL and were under the limit of detection at 600 MPa for 90 s. Based on the findings in this study, machinery mold contaminants would be readily inactivated by the processing conditions used to target a 5-log reduction in the bacterial pathogen of concern. HIGHLIGHTS • The D-value for machinery mold at 55°C was determined to be 0.99 min. • Differences in thermoresistance was minimal between cultures of varying ages. • A ≥5-log reduction was achieved by pressure treatments of 300 MPa for 90 s.