Mycotoxin contamination of foods and feeds in Nepal

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T. B. Karki and B. P. Sinha
Central Food Research Laboratory
Ministry of Agriculture, Nepal

SUMMARY

Monitoring of mycotoxins in food commodities was first initiated in Nepal in the year 1978 as a consequence of FAO/UNEP Regional Monitoring of Food Contaminants Project involving four countries in which Nepal and India were placed in one group and Pakistan and Sri Lanka on the other. Since then 850 food samples mainly comprising of Cereals, Pulses, Oilseeds and Spices and about 150 samples of feed and feed ingredients were monitored for aflatoxin content covering the period of 1980 -1987. Result has indicated that corn and peanut are the two commodities most prone to aflatoxin contamination. Ecologically, Terai Southern Plain area is more susceptible to aflatoxin hazard compared to hills and mountainous area. Coincidentally, toxigenic fungi (Aspergillus flavus) predominated in Terai since from the onset of storage as contrary to hills and mountainous areas. Further, A. flavus spp. isolated from Terai area produced higher amount of aflatoxin B. (6334 ppb) than from the hills and mountains. Thus, the potency of the strains has shown altitude bias. Maximum level of aflatoxin B. is found in corn (321 ppb) and peanut as raw shelled (634 ppb). Aflatoxin content in feed and feed ingredients are relatively higher because low quality cereals or damaged grains are usually used for feed and feedstocks. Maximum level of aflatoxin B. in Poultry feed is found to be 1100 ppb.

INTRODUCTION

Mycotoxin are considered to be potent liver carcinogens. A host of toxigenic fungi produce varieties of toxic metabolities contaminating foods and compel them unsuitable for consumption. Meagre resources of developing countries need to be channelled to increased production by avoiding unwanted natural contaminants like mycotoxins. Increasing production is the national goal of every developing nation and therefore the measures to avert losses during preservation, processing, storage and marketing, have to be afforded due priority in the developmental plans particularly with regard to the invasion of toxic fungi. Mycotoxin monitoring programme has been integrated with the study of causative fungi for developing a viable strategy to control the mycotoxin contamination in food and feed.

Central Food Research Laboratory (CFRL) under the Ministry of Agriculture has taken the lead in the study of mycotoxin and toxigenic fungi in coordination with other related agencies like Rural Save Grain Project and Teaching Hospital for finding clues to disease syndrome by consuming suspected food commodities.

OBJECTIVES

1. To monitor aflatoxin content in different food and feed products.
2. To investigate causative micro-organism and study their growth pattern and potency to form aflatoxin.
3. To determine ecological distribution of toxic fungi in relation to aflatoxin production.
4. To investigate aflatoxin production in various storage system of corn in Kathmandu Valley for recommending suitable one for the intended purposes.

INCIDENCE OF AFLATOXINS IN FOOD AND FEEDS

Karmacharya et al (1988) reports the analytical data of aflatoxin in food and feeds.

Table 1. shows the occurrence of aflatoxin contamination in different food commodities. Out of total 582 samples of corn and peanuts products, and wheat flour, and parboiled rice, 109 (18.7%) samples were contaminated with aflatoxin. Further, the number of samples which exceeded permissible limit of 30 ppb of aflatoxin B1 as suggested by FAO, were 35 (6%) samples of tested food commodities. Aflatoxin problem as revealed by this study is of no serious magnitude. However, it warrants careful monitoring of mycotoxin for controlling mould infection in stored products.

Table 1 Occurrence of aflatoxin B1 in food commodities (1980 -1987)

Corn and peanut are the two risk commodities from the point of aflatoxin contamination. Out of 35 samples exceeding 30 ppb of aflatoxin, 90 of contaminated samples comprised of corn and peanut products. Thus special impetus should be given to prevent aflatoxin hazard in these commodities.

Table 2. shows list of 255 samples of different food commodities mainly comprising of raw rice, beaten rice, wheat, flour, pulses, spices etc; which did not show presence of aflatoxin. The sampling period covered almost seven years. However, it suffers from some deficiencies of basic informations with regard to the exact origin of samples. Therefore, it has been planned to collect appreciable number of samples from different ecological areas to determine the extent of problem and thereby to employ counter measures to avert it.

Table - 2 Aflatoxin negative samples of different food commodities (1980 - 1987)

ND = Not Detected.

Table 3. shows the occurrence of aflatoxin in feed products. 116 samples of different feeds comprising mainly of poultry, cattle and pig were tested for aflatoxin content. 55 (47.4%) samples showed positive aflatoxin content ranging from trace to 1100 ppb in case of poultry feed. Further, it indicates that 20 (12.9%) samples exceeded the permissible limit suggested by EEC countries for animal feed. Data presented here mainly refer to poultry feed. Therefore, it is necessary to collect more samples of feed and feed ingredients to ascertain the safe product of feed and hence minimise aflatoxin problems in these products.

Table 3 Occurrence of aflatoxin In different feeds (1983-1987)

TOXIGENIC FUNGI ISOLATED FROM CORN

Nepal has a varied topography stretching from the plain area of Terai to the rugged terrace of hills and mountains. Most of the surplus cereals are produced in the plain of terse where ambient temperature and humidity are relatively high. These grains are supplied to deficit hilly areas, after nearly six month's storage. Corn is also grown in plain, hills and mountains. Corn cob is harvested at high moisture content (18-21), dried and then stored cob with husk for about six month before being shelled. milled and consumed. Thus, it is not surprising that most of the corn samples are occasionally infected by mould producing toxin. Earlier studies by Karki et al (1979) also conforms that corn might be the prominent problem area of aflatoxin contamination especially during storage and movement of grains from the plain Terai to the deficit hilly areas. Thus, corn can be a problem from food safely standpoint and hence this aspect has to be dealt with utmost care and attention.

In Hills/Mountains and Kathmandu areas, the predominant mould flora were in the order of Fusarium spp., followed by Aspergillus spp (A. flavus A. niger, A. fumigates), Penicillium spp. and Rhizopus, Where as this trend was different in Terai and inner Terai regions and therefore the prominent flora were in the order of A. flavus, Fusarium spp. Penicillium spp, A. niger A. fumigatus, and Rhizopus spp. (Table 4). While Fusarium spp. was found dominant in hills/mountain, and Kathmar du Terai samples showed preponderance of A. flavus However, these data reveal that Fusarium toxin may prevail in the hills/mountain area as contrary to the aflatoxin problem in Terai. Therefore, occurrence of various toxin as a metabolic product of causative fungi has to be investigated in order to arrive at a practical solution of this natural contaminant.

Table 4 Occurrence and identification of internal mold flora in corn samples.

POTENCY OF ASPERGILLUS FLAVUS SPP. FOR AFLATOXIN PRODUCTION

Nineteen representative strains of A. flavus isolated from corn grown at different altitudes, were selected for their toxin production. Corn grown from the following localities were collected for investigation.

1. Hills/Mountain: Elevation 1517-2300 meter (Khopasi, Dhading, Kavre, Jumla)
2. Kathmandu Valley: Elevation 1330-1350 meter (Kathmandu, Lalitpur, Bhaktapur)
3. Terai /Inner Terai: Elevation 72-474 meter (Biratnagar, Mahendranagar, Nijgadh & Hetauda)

A. flavus isolated from Terai and inner Terai produced aflatoxin B1 & B2 at the concentration of 6 gm/kg and 0.9 mg/kg respectively (Table 5). This finding has indicated that A. flavus isolated from hills/mountain and Kathmandu region seem to have lower potency of aflatoxin production. Two strains from Kathmandu Valley produced all four aflatoxins B1, B2, G1 and G2. However, two strains from Terai, one from Kathmandu Valley and one from mountain areas did not produce aflatoxin. A. flavus isolated from terse produced the highest amount of aflatoxin compared to valley and other hills/mountainous region.

This result shows that there is a need of precautionary post-harvest measures to minimise the possible aflatoxin hazards. In short, aflatoxin can become a big menace in Terai area where temperature is relatively high and the humidity is also favourable for the growth of A. flavus. However, a careful strategy needs to be initiated to determine the extent of damage caused by A. flavus along the coastal area of river belt. These areas seem to be prone to A. flavus invasion. For instance, the Terai and inner Terai area extending to river beds of Gandaki, Koshi and Karnali need to be investigated for probable hazards of A. flavus and subsequent toxin production. Also the use of other additives like spices and mould inhibitors and even some acid producing bacteria should be investigated from the point of controlling aflatoxin contamination in food products.

AFLATOXIN CONTENT IN CORN AT DIFFERENT STORAGE SYSTEM AFTER 10 MONTH'S STORAGE AT KATHMANDU

Karki et al (1988) reports the occurrence of A. flavus and subsequent aflatoxin production in corn at different storage structures of Kathmandu Valley.

Table 5 Variation in potentiality of A. flavus strains isolated from corn grown at different altitude In Nepal.

Fig. 1 shows the distribution pattern of A. flavus propaguels and aflatoxin production at different storage systems employed in Kathmandu Valley. No aflatoxin was detected on the sample stored at Thangro (outdoor open storage system around a pole and four support base). The sample stored at Bhakari (bamboo bins) contained 1.5 ppb aflatoxin B.. However, the aflatoxin content in Ghyampo (clay jar) and metal bin was found to be 40 and 125 ppb aflatoxin B1 respectively. This clearly indicates that Thangro seems to be an appropriate storage system for corn as evidenced by absence of A. flavus and aflatoxin production. Furthermore, Bhakari type of storage can be improved for preventing mold infection and relative toxin production. It needs further elaboration in different agro-climatic regions.

AFLATOXIN IN RELATION TO LIVER CANCER

In order to establish a close relationship of human mycotoxicoses with that of the aflatoxin content in the diet intake, it is very important to employ a comprehensive screening programme. For this purpose, daily consumption of aflatoxin is needed to analyse a large number of foodstuffs collected from market and domestic households. Rensburg (1977) reports a significant statistical relationship between the incidence of liver cancer and the intake of aflatoxin as shown in Table 6.

Table 6 Incidence of liver cancer (cases per 100,000 people per annum) and aflatoxin Intake (mg/kg body weight per day) In Africa and Asia.

Source: S.J. Van Rensburg p699, in R.J. Rodricks, C.W. Hesseltine M.A. Mehlamann: Mycotoxins in Human and Animal Health. Path. tox. Fubl. Inc. Fark Forrest, IL, 1977.

The following inferences can be drawn :

1. Highland areas are relatively dry and thus mold infection are reduced producing low level of aflatoxin.
2. The daily aflatoxin intake in these regions is less than 5 mg/kg body weight. If the daily intake is doubled to 10 mg/kg as observed in several humid lowland areas (Kenya), the incidence of liver cancer increased by 100.

This information is highly pertinent to our conditions and the findings on toxigenic mould and aflatoxin content in corn. In our studies, aflatoxin content and A. flavus propaguels are found to be increased in lowlands than in the highlands. However, there is dearth of information with regard to liver cancer cases according to altitude ranges. However, it reflects two main issues to be considered.

1. Consumption pattern of two risk commodities (corn and peanut) in different area.
2. Liver cancer cases amongst the consumers of this area.

In Nepal, most people living in hills consume corn as the staple food. But Terai is the risk area for aflatoxin production, Thus the magnitude of problems concerning production, storage, and consumption of risk commodities in different areas have to be carefully determined to monitor the level of toxin present in food and the probable mycotoxin cases in different areas.

Future Course of Action:

1. To prepare aflatoxin mapping of different food commodities at different localities.
2. To initiate monitoring of other mycotoxins (Ochratoxin, Zeralenone etc) in view of their causative fungi for possible intervention.
3. To introduce efficient post-harvest technology systems through existing networks.
4. To employ mould inhibitors for effective conservation and control of aflatoxin production.
5. To communicate crucial matters of health hazards to farmers, grain handlers, and marketing people for exhancing safety & minimising losses.
6. To enforce the regulation of aflatoxin level in foods and feeds.
7. To use heat treatment (roasting) for decontaminating aflatoxin level in foods through extension system.

REFERENCES:

Karmacharya, S. - Aflatoxin content in foods and feeds. National Conference on Science and Technology, 24-29 April, 1988. Royal Nepal Academy of Science & Technology (RONAST), Nepal.

Karki, T.B.: Note on Microbiological and Aflatoxin Analyses of Bothast, R.J.: Cereal grains from Terai plain of Southern Nepal.& Stubblefield, R.D.: Cereal Chemistry, Vol. 56, No.1 (1979) (USA).

Karki, T.B. & : Ecological distribution of toxigenic mould flora

Joshi, R. : during storage of corn in Nepal. National Conference on Science and Technology, 24 - 29 April, 1988, RONAST, Nepal.

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