Eight different fruit juices were screened for heat-resistant mold (HRM). Heat was used, in the HRM screening method, to kill nonheat-resistant mold permitting the heat-resistant mold to survive. The HRM screening was beyond the commercial heat processing. An autoclave simplified the screening of large volumes of product and may be a novel use of an autoclave. To increase recovery from heat treatment, the medium was not acidified and surface plating was used in place of pour plating. To reduce cold shock, the product was cooled to ambient temperature and not below. A temperature controlled orbital shaker was used to enhance recovery by increasing aeration and preventing settling. The mold Talaromyces trachyspermus (Shear) Stolk & Samson, previously unreported as an HRM, was detected in retail packaged chilled and frozen pineapple juice but not in other fruit juices. Neosartorya fischeri (Wehmer) Malloch & Cain and Talaromyces flavus (Klöckner) Stolk & Samson were also isolated after a 30-min heat treatment at 80°C. Heat-resistant molds were found in both pure and mixed cultures. T. flavus and T. trachyspermus were growing in a mixed culture after heat treatment.
The interrelated factors that influence the effectiveness of SO 2 as a preservative against yeast were studied and the correct quantitative relationships of SO 2 molecular species determined. Widely differing pK values for SO 2 were found in the literature, compared with experimental data, and one set of values was selected. Undissociated H 2 SO 3 is the only effective form of SO 2 against yeast and can be calculated from measurement of free SO 2 and pH, and the correct dissociation constants. Duration of contact, pH, concentration of SO 2 and yeast, and binding of SO 2 all influence the preservative action of SO 2 . Lower total SO 2 concentrations can be used for food preservation by optimum control of these factors.