Association of Aflatoxin B1 and Microbial Contamination in Traditional Curry Pastes from Local Markets in Nonthaburi, Thailand

Abstract

Background: Curry paste is a blend of natural ingredients, such as chilli and various herbs,
that are pounded and ground into a paste. It is a popular and widely used ingredient in
cooking. However, curry paste products, which are commonly sold in convenience stores
and market stalls, are at risk of contamination by toxic substances, particularly aflatoxins
produced by the fungus Aspergillus spp. Long-term exposure to these toxins can lead to
liver cancer. The World Health Organisation (WHO) classifies aflatoxins as one of the most
potent carcinogens. In Thailand, the Ministry of Public Health has established a food
standard, setting the maximum permissible limit for aflatoxin contamination at 20 ug/kg.
Therefore, controlling the quality and safety of curry paste is crucial for consumer protection.

Objectives: To screen curry paste samples for aflatoxin B1 contamination and to analyze
microbial contamination, including Aspergillus spp., yeast, and bacteria. Additionally,
to investigate the relationship between the presence of aflatoxin B1 and the detection
of Aspergillus spp., yeast, and bacteria in curry paste samples.

Methods: This descriptive, field-based study was conducted in February 2025. A total of
32 curry paste samples were collected from various local markets in Mueang district,
Nonthaburi province. Aflatoxin B1 contamination was screened using a rapid test kit
(Aflatoxin B1-Precise Rapid Test Kit) with a Limit of Detection (LOD) of 5 μg/kg. Microbial
contamination by Aspergillus spp., yeast, and bacteria was assessed through standard
culture methods using appropriate media. The data were analysed using descriptive
statistics to determine contamination percentages, and Fisher’s exact test was used to
examine the relationship between variables, with a significance level set at p<0.05.

Results: An investigation of samples from 11 market stalls revealed that samples were
contaminated with aflatoxins and microorganisms at rates at 72.00% and 81.00%, respectively.
Considering of types of contamination across all samples, bacterial contamination was
the most prevalent, found in 81.00%, followed by contamination with aflatoxins (72.00%),
Aspergillus spp. (50.00%), and yeast (50.00%), respectively. The top three types of aflatoxin
contaminated-curry paste were Southern Sour Curry Paste and Red Curry Paste, followed
by Sour Curry Paste and Massaman Curry Paste, at 100.00%, 80.00% and 67.00%, respectively.
For bacterial contamination, the top three contaminated-curry pastes were Southern
Sour Curry Paste and Panang Curry Paste, followed by Green Curry Paste and Red Curry
Paste, at 100.00%, 88.00% and 83.00%, respectively. Statistical analysis revealed a significant
correlation between the contamination of Aflatoxin B1 and the presence of Aspergillus spp.
by 16 samples from 23 samples with p-value = 0.001, whereas no statistically significant
correlation was found between the presence of yeast (p-value = 1.000) and between
bacteria (p-value = 0.150).

Conclusions: This study confirms the high prevalence of aflatoxin B1 and Aspergillus spp.
contamination in local curry pastes, with a clear and significant association between the two.
This suggests that the aflatoxin contamination likely originates from fungal growth in the raw
ingredients or due to unhygienic storage conditions. The findings highlight the urgent need
for continuous food safety monitoring and quality control throughout the supply chain.
It is recommended that producers and vendors improve hygiene practices in handling
raw materials and storing finished products to mitigate the risks of both mycotoxin and
microbial contamination.