Mould infection and aflatoxin contamination in foodgrains in Vietnam

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Tran Van An, Nguyen Thi Minh Tam and Hoang thi Loc
Postharvest Technology Institute
Hanoi, Vietnam

Vietnam is a tropical agriculture country. The climate conditions are favourable for the year-round agriculture practice but at the same time they make a good environment for moulds and insects to develop. Moulds proliferation leads to the production of mycotoxins and to the spoilage of food, both in quantity and quality.

The study on mycotoxins and methods for their prevention and control has become a prominent problem in our country and in recent years it retains the interest of our scientists. Lucas et al. determined the content of aflatoxin in rice in different stores in Saigon (1971), Bui xuan Dong did some preliminary researches about moulds infection in groundnut in Hanoi stores and poisoning effect of moulds that produce mycotoxins in ducklings (1976). Pham van Phung, Nguyen Lan Dung and Nguyen van Ngoan reported that from 15 strains of isolated Aspergillus flavus, 6 have the potential of aflatoxin production. Le van To reported about mould infection in animals feed: 7 from 9 strains isolated produce mycotoxins and the perspective to use Athrobactor sp. to test the activity of Dicoumarolmycotoxin. Veterinary Doctor Nguyen van Phong (1984) found degenerative lesions and tumors in liver of ducklings and ducks suspiciously died from mycotoxin poisoning (1984).

These facts clearly showed that in Vietnam, there are problems of mould infection and consequently aflatoxin contamination on foodgrains.

Thanks to the encouragement of FAO and UNDP and their supply of analytical standard reference samples of aflatoxin, our Post-harvest Technology Institute could carry out well a national research subject about the level of mould infection, methods of elimination of moulds and about aflatoxin contamination on foodgrains.

The title of the research is "Study on the level of moulds contamination on foodgrains and methods for prevention of mycotoxins caused by moulds".

Research was carried out on three main kinds of foodgrains: paddy, rice and maize, aiming at the following objectives:

1. Determination of moulds infection in foodgrains in Vietnam especially of the moulds that produce mycotoxins.
2. Preliminary application of some processes for moulds prevention and control in the warehouses.
3. Determination of Aflatoxin contamination on foodgrains in Vietnam.
4. Selection of appropriate methods for determination of Aflatoxin contamination level on foodgrains in order to establish the standard level of permitted aflatoxin contamination on human food and animal feed in Vietnam.

Several obtained results are as follows:

MOULDS INFECTION IN RICE GRAINS

• The paddy grains of rainy crop (Summer-Autunm crop) stored for 3 months were used as sample for the study, the moisture content from 15, 7 to 17%. We have isolated moulds from Aspergillus and penicillis. A. flavus infected is 20% and A. fumigatus 15% .
• With the rice samples that are infected by moulds, we have isolated 21 species from Aspergillus, penicilia, curcularis, aureobasidius and cladosporium. A. flavus infection is about 28%.

MOULDS INFECTION IN MAIZE GRAINS

Maize harvested in rainy season is very difficult to be dried and stored properly. Therefore, it could be infected by moulds with a very high percentage. In many tested samples, nearly 100% were infected by moulds.

STUDIES IN SOME METHODS FOR PREVENTION AND CONTROL OF MOULDS IN WAREHOUSES

Methyl bromide and phosphine are two common chemicals usually used for grain disinfection from insects. We tried to use these substances to kill moulds in an attemp to combine with the disinfection effect on moulds as well as on insects. The results showed that:

• Methyl bromide: In laboratory conditions, the dose of 32 b/m³ can kill 100% of moulds. Unfortunatelly, in field conditions, only 78-82% of moulds were killed. This lower result is due to the chemical adorption by the grain mass. In field application, we used doses of 40 mg/m³ and 48 mg/m³. Both doses have similar results to the 32 mg/m³ dose but 48 mg/m³ can kill 94-98% of mould in the foodgrains warehouses with the capacity of hundred tons.
• Phosphine: dose of 50 g/m³ can kill only the growth period of moulds and cannot kill Spores of moulds.

By using the mixture of phosphine and amoniac, at the dose of 50 mg/m³ +50 mg/m³, we found that all the moulds were killed. Thus, we can use methyl bromide and the mixture phosphine and amoniac to disinfect paddy grains in big capacity warehouses.

AFLATOXIN CONTAMINATION IN FOODGRAINS IN VIETNAM

• On the 35 rice samples, tested by using DD. Doromina and L Makaimenko method, we were not able to detect Aflatoxin presence.
• On mould infected maize samples, we discovered aflatoxin with high level > 19 ppb. Yellow maize is infected more heavily than white maize. Using the analytical reference standards of aflatoxin given by FAO, we can test aflatoxin in exported foodgrains.

We believe that with the results obtained from this training course on new methods for testing aflatoxin and with further assistance of FAO/UNDP and RAS/86/189 project we could intensify our control activities of foodgrains including the control of aflatoxin.

On behalf of all staff members of Post-harvest Technology Institute and its branch in Ho Chi Minh City, I would like to express once again our grateful acknowledgements to FAO/UNDP and Project RAS/86/ 189 and to all our colleagues here. We hope that our cooperation will be well developed.

Thank you very much.

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