The effects of water activity (aw) and temperature on growth of and ochratoxin A (OA) production by strains of Aspergillus ochraceus, Penicillium cyclopium, and Penicillium viridicatum were investigated. On agar media in which the aw had been adjusted by addition of sucrose or glycerol, the minimum aw values for OA production by A. ochraceus, P. cyclopium and P. viridicatum lay between 0.83–0.87, 0.87–0.90, and 0.83–0.86, respectively. At 24 C, optimum aw values for OA production by A. ochraceus and P. cyclopium were 0.99 and 0.95–0.99, respectively, whereas that of P. viridicatum varied and was 0.95 and 0.99 for the two strains tested. At optimum aw, the temperature range for OA production by A. ochraceus was 12–37 C, whereas that of P. cyclopium and P. viridicatum was 4–31 C. Optimum temperature for OA production by A. ochraceus was 31 C, whereas that of P. cyclopium and P. viridicatum was 24 C. On Edam cheese of 0.95 aw the minimum temperature for OA production by P. cyclopium was 20 C. On barley meal, P. viridicatum produced maximal quantities of OA at 0.97 aw and could produce OA at temperatures as low as 12 C.

The optimum and limiting conditions of water activity (aw) and temperature for growth of and aflatoxin B1 production by various Aspergillus flavus strains were determined. Agar media were used in which the aw was adjusted by addition of sucrose or glycerine. Optimum temperatures for aflatoxin B1 production at high aw varied with the strain tested being 13–16, 16–24, or 31 C. Strains with a low temperature optimum for aflatoxin B1 production showed fast growth at 37 C without aflatoxin B1 production. A reduced aw (0.95 and less) together with a moderate or low temperature inhibited toxin production more than growth. However, at a high temperature one strain showed stimulation of aflatoxin B1 production on the glycerine medium at reduced aw No differences were noted between aflatoxinpositive and aflatoxin-negative strains with respect to growth under various conditions.

The effect of water activity (aw) on growth and aflatoxin production by Aspergillus parasiticus NRRL 2999 was determined using submerged cultures in which the aw was adjusted by addition of glycerine, glucose, or a mixture of salts. At a sub-optimal aw aflatoxin production was low in the glycerol and glucose media while no strong inhibition of mycelial growth occurred. A similar effect was obtained in surface cultures on agar media in which the aw was adjusted by addition of glycerine or sucrose. The effect of a sub-optimal temperature was the reverse; compared to inhibition of mycelial growth in surface cultures, the effect on aflatoxin production was slight. No detectable quantities of aflatoxin B1 were formed at 0.83 aw and at 10 C nor at four combinations of higher aw and temperature. The aw was measured by a recently developed device using the dewpoint principle.

The combined effects of water activity (aw) and temperature on growth and patulin production by strains of Penicillium expansum, Penicillium patulum, and Aspergillus clavatus were determined. Malt agar media were used, in which the aw was adjusted by addition of sucrose or glycerine. The minimum aw values for patulin production by P. expansum, P. patulum, and A. clavatus were 0.99, 0.95, 0.99, respectively. The temperature ranges for patulin production by P. expansum, P. patulum, and A. clavatus were 0–24, 4–31, and 12–24 C, respectively. The optimum temperatures for patulin production by P. expansum and A. clavatus were low compared with those for growth. Optimum temperatures for patulin production at high aw by P. patulum varied with the strain tested and were 8 or 31 C. The temperature range for patulin production in apples by P. expansum was determined. The minimum temperatures for rotting and patulin production were 1 C in Cox Orange cv. and 4 C in Golden Delicious cv. The amount of patulin accumulating in rotten tissue of six apple varieties differed greatly. The invasiveness of and patulin production by various strains of four patulin-producing fungal species were tested. All P. expansum strains tested caused rot containing patulin. The increase of rot and patulin production by P. crustosum and A. clavatus depended on the strains tested. None of the P. patulum strains was able to invade Golden Delicious apples.

Evaluation of the enzyme-linked immunosorbent assay (ELISA) for detecting a mold-specific, heat-stable and water-soluble antigen demonstrated the potential of the method for detecting molds in food products. The mold antigen, as produced by Penicillium spp. and Aspergillus spp., was present in all food samples containing aflatoxin B1. The amount of mold antigen present in the test samples was related in each case to the aflatoxin B1 content. Experiments done with samples artificially inoculated with mycotoxin-producing molds revealed that mold contamination could be detected by ELISA at a very early stage. The minimum detectable amount of mold mycelium for three different species of Penicillium was 38 ng/g of sample.