Effects of processing and storage on aflatoxins levels in processed cheese from cheddar and fresh cheese.

Aflatoxins are secondary metabolites produced by some fungi such as Aspergillus parasiticus, A. flavus and A. nomius. They are the most potent carcinogenic compounds produced naturally (IARC, 1993). Aflatoxins M1 is a hydroxylated derivative of aflatoxin B1 which is secreted in the milk from animals fed with a contaminated feed. The dairy products, including cheese, are very suitable for the growth of fungi able to produce aflatoxins. Many controversial results have been published concerning the effects of processing and storage on the level of aflatoxin M1 in dairy products. The effect of manufacturing processes and storage on the level of aflatoxins has been studied, taking into consideration the lack of researches made in Syria about this topic, the climate, the poor storage conditions in a lot of stores. The work had two objectives: 1) isolation and morphological identification of fungi from cheddar and fresh cheese incubated at two different temperatures (4° and 25°C); 2) determination of B1,B2,G1,G2,M1,M2 aflatoxin levels by HPLC (Sharman et al.,1993) in: a) A. flavus strain isolated from cheddar and fresh cheese; b) cheddar and fresh cheese samples inoculated with isolated A. flavus strain; c) the main components of processed cheese (i.e. inoculated cheese, butter, dry milk); d) processed cheese samples submitted at different treatments based on three parameters: d-1) temperatures of processing - one part of the samples were melted at 90 °C, the other part after melting were transferred to 140°C (UHT); d-2) temperatures of storage 4° and 25°C; d-3) time of storage 1 and 30 days. The results brought to evidence the presence in the cheddar and fresh cheese samples assayed of a strain of toxigenic A. flavus, that was compared to a toxigenic strain used as reference. The toxin characterized was aflatoxin B1. The level of this toxin was less in the cheese inoculated compared to that of A. flavus strain grown in vitro. In the main components it was found aflatoxin M1. A significant reduction of aflatoxins levels was detected in both types of processed cheeses compared to the mix of the main components. The aflatoxin levels did not statistically differ in the parameters checked: temperatures of processing and storage, time of storage in both cheese, except in the case of M1 in processed cheese from fresh cheese.