Incidence and management of aflatoxin contamination in groundnut under different postharvest storage systems

Introduction

It's been observed across multiple surveys that 40-80% of groundnut samples from West African markets exceed safe aflatoxin limits, making this the most contaminated food commodity in the region [5,16] . Aflatoxin B1, produced primarily by Aspergillus flavus and A. parasiticus, is the most potent naturally occurring carcinogen, classified as Group 1 by IARC [1] . Chronic exposure through contaminated groundnut contributes to liver cancer and growth stunting, particularly in children [10] . Pre-harvest contamination is driven by drought stress during pod filling, which cracks pod walls and facilitates fungal invasion [6,12] . But the majority of aflatoxin accumulation occurs postharvest, when improper drying and storage allow fungal growth to accelerate [3,8] . Traditional storage in jute or polypropylene sacks permits moisture re-absorption and poor aeration, creating conditions ideal for Aspergillus proliferation [5,15] . Hermetic storage technologies like Purdue Improved Crop Storage (PICS) bags restrict oxygen diffusion, suppressing fungal metabolism and insect activity [7,11] . Few studies have tracked aflatoxin kinetics over time in groundnut under contrasting storage systems in West Africa. This research monitored AFB1, fungal populations, and kernel moisture at four-week intervals over 12 weeks across three storage systems at two sites in northern Ghana.

Materials and Methods

Study area description

The research was conducted at two sites in the Northern Region of Ghana: Tamale (9.40° N, 0.84° W) and Yendi (9.44° N, 0.01° W) during November 2021 to February 2022 (dry season). Mean temperature during storage was 31.4 °C with relative humidity fluctuating between 28% (December) and 72% (February). Groundnut variety Samnut 22 was sourced from local farmers immediately after harvest and sun-drying to ~8% moisture [9] .

Performance evaluation

AFB1 was quantified at weeks 0, 4, 8, and 12 by HPLC with fluorescence detection following immunoaffinity column cleanup (VICAM AflaTest). Kernel moisture was measured by oven method (130 °C, 72 h). Fungal isolations used dilution plating on Aspergillus Flavus and Parasiticus Agar (AFPA) with identification by colony morphology and UV fluorescence [2,14] . Results were compared against EU maximum limits: 4 µg/kg AFB1 for direct consumption and 20 µg/kg for processing [17] .

Materials

Three storage systems were tested: (1) traditional jute sacks stored on bare floor under thatched roof; (2) improved ventilated structures with raised wooden pallets and metal mesh sides; (3) hermetic PICS triple-layer bags (80 µm polyethylene inner layers + woven outer) stored on pallets. Each treatment had four replicates of 50 kg bags at each site. Total: 3 systems × 4 replicates × 2 sites = 24 experimental units.

Methods

Data were analyzed by repeated-measures ANOVA with storage system as the between-subjects factor and sampling time as the within-subjects factor, using GenStat 20. Means were separated by LSD at p≤0.05. Correlation analysis tested relationships between AFB1 and kernel moisture, temperature, and Aspergillus colony counts [9] .

Results

Comprehensive Interpretation

Traditional storage exceeded the 20 µg/kg EU processing limit by week 5 and reached 112.6 µg/kg by week 12 (Table 1, Figure 1). Improved storage delayed the exceedance to week 11 (21.7 µg/kg). Hermetic bags kept AFB1 at 3.7 µg/kg, below the strict 4 µg/kg direct-consumption limit throughout the trial. Kernel moisture rose to 12.4% in traditional bags versus 7.8% in hermetic bags (Table 2). A. flavus dominated isolations at 48.3% (Figure 2). Correlation between moisture and AFB1 was r = 0.91 (p<0.001).

Discussion

The 30-fold AFB1 difference between traditional and hermetic storage after 12 weeks underscores the role of oxygen and moisture control in aflatoxin prevention. PICS bags reduce internal O₂ to 2-5% within two weeks, which suppresses aerobic Aspergillus metabolism [7] . Murdock and Baoua [7] reported similar results for cowpea, and Villers [8] demonstrated the principle for multiple grain types. The improved ventilated structure performed moderately, suggesting that better airflow alone reduces but doesn't eliminate fungal growth when ambient humidity is high [3,15] . The dominance of A. flavus (48.3%) over A. parasiticus (22.7%) matches the typical species distribution in West African groundnut systems [4,16] . The strong moisture-AFB1 correlation (r = 0.91) confirms that maintaining kernel moisture below 8-9% is the most important single factor in aflatoxin management, consistent with Turner et al. [11] and Hell and Mutegi [5] .

Conclusion

Hermetic PICS bag storage limited aflatoxin B1 to 3.7 µg/kg over 12 weeks well within EU safety limits compared with 112.6 µg/kg in traditional jute sacks. Kernel moisture was the strongest predictor of contamination. PICS bags are a practical, affordable intervention for smallholder groundnut farmers in West Africa, requiring no electricity or chemicals. Extension programs should promote hermetic storage alongside proper sun-drying to below 8% moisture as a two-step strategy for aflatoxin management. Longer-term storage trials (6-12 months) would confirm the durability of hermetic protection.

References

1. International Agency for Research on Cancer (IARC). Aflatoxins. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. 2012;100F:225-248.
2. Klich MA. Aspergillus flavus: The major producer of aflatoxin. Mol Plant Pathol. 2007;8(6):713-722.
3. Waliyar F, Kumar PL, Traore A, Ntare BR, Diarra B, Kodio O. Pre-and postharvest management of aflatoxin contamination in peanuts. In: Leslie JF, Bandyopadhyay R, Visconti A, editors. Mycotoxins: Detection Methods, Management, Public Health and Agricultural Trade. Wallingford: CABI; 2008. p. 209-218.
4. Bandyopadhyay R, Ortega-Beltran A, Akande A, Mutegi C, Atehnkeng J, Kaptoge L, et al. Biological control of aflatoxins in Africa: Current status and potential challenges. World Mycotoxin J. 2016;9(5):771-789.
5. Hell K, Mutegi C. Aflatoxin control and prevention strategies in key crops of sub-Saharan Africa. Afr J Microbiol Res. 2011;5(5):459-466.
6. Guo B, Chen ZY, Lee RD, Scully BT. Drought stress and preharvest aflatoxin contamination in agricultural commodity: Genetics, genomics, and proteomics. J Integr Plant Biol. 2008;50(10):1281-1291.
7. Murdock LL, Baoua IB. On Purdue Improved Cowpea Storage (PICS) technology: Background, mode of action, future prospects. J Stored Prod Res. 2014;58:3-11.
8. Villers P. Aflatoxins and safe storage. Front Microbiol. 2014;5:158.
9. Gomez KA, Gomez AA. Statistical procedures for agricultural research. New York: John Wiley and Sons; 1984. p. 1-680.
10. Williams JH, Phillips TD, Jolly PE, Stiles JK, Jolly CM, Aggarwal D. Human aflatoxicosis in developing countries: A review of toxicology, exposure, potential health consequences, and interventions. Am J Clin Nutr. 2004;80(5):1106-1122.
11. Turner PC, Sylla A, Gong YY, Diallo MS, Sutcliffe AE, Hall AJ, et al. Reduction in exposure to carcinogenic aflatoxins by postharvest intervention measures in West Africa. Lancet. 2005;365(9475):1950-1956.
12. Cotty PJ, Jaime-Garcia R. Influences of climate on aflatoxin-producing fungi and aflatoxin contamination. Int J Food Microbiol. 2007;119(1-2):109-115.
13. Waliyar F, Reddy SV, Subrahmanyam P, Reddy TY, Rachaputi NC, Lava Kumar P, et al. Management of grain legume aflatoxin problem in semi-arid tropics. ISB News Rep. 2003;1-4.
14. Amaike S, Keller NP. Aspergillus flavus. Annu Rev Phytopathol. 2011;49:107-133.
15. Okello DK, Kaaya AN, Bisikwa J, Were M, Oloka HK. Management of aflatoxins in groundnuts: A manual for farmers, processors, traders, and consumers in Uganda. Kampala: National Agricultural Research Organisation; 2010. p. 1-28.
16. Mutegi CK, Ngugi HK, Hendriks SL, Jones RB. Prevalence and factors associated with aflatoxin contamination of peanuts from western Kenya. Int J Food Microbiol. 2009;130(1):27-34.
17. European Commission. Commission Regulation (EC) No. 1881/2006 setting maximum levels for certain contaminants in foodstuffs. Off J Eur Union. 2006;L364:5-24.
18. Bhatnagar-Mathur P, Sunkara S, Bhatnagar-Panwar M, Waliyar F, Sharma KK. Biotechnological advances for combating Aspergillus flavus and aflatoxin contamination in crops. Plant Sci. 2015;234:119-132.