The combined effect of water activity (aw), pH, storage temperature, headspace oxygen and carbon dioxide concentration on the growth of, and aflatoxin production by, Aspergillus flavus on synthethic media were examined using a multifactorial experimental design termed Response Surface Methodology. Regression analysis of the data indicated that aw pH, storage temperature and initial concentration of headspace oxygen in the gas mix were all highly significant factors (p<0·01) in controlling the growth of A. flavus on synthetic media. Mold growth was either completely inhibited or was visible after 1-2 days. Growth was more extensive in plates stored at higher storage temperatures (25-35°C) and package with 10-20% O2 (54-48% CO2). Growth of A. flavus was inhibited in certain treatment combinations stored at 25°C and completely inhibited in all plates stored at 15-20°C irrespective of the gas atmosphere. A curvilinear relationship was found between mold colony diameter (mm) and aflatoxin production. Aflatoxin production was maximum at a colony diameter of 7 mm and then decreased with increasing colony diameter. However, in all cases where growth occurred, the level of aflatoxin was less than the current regulatory standard of 20 ng g-1. This study has shown that A. flavus can grow in a CO2 enriched atmosphere if headspace oxygen is present. It also emphasizes the combined effect of several 'barriers' to either completely inhibit mold growth or to reduce aflatoxin in MAP products containing various levels of headspace oxygen to safe and acceptable levels (<20 ng g-1), particularly at temperature abuse storage conditions. © 1993 Academic Press. All rights reserved.
