Team:Hong Kong JSS/Description

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Team:Hong Kong JSS/Description

Current Detoxification strategies of Aflatoxin B1 (AFB1)

1. Using heat or gamma rays
Studies have shown that high temperature, ultraviolet rays and gamma rays can destroy the molecular structure of aflatoxin, thereby reducing its toxicity. For example, treating contaminated corn at 260°C can reduce aflatoxin content by 85%.

  • Generally, temperatures and microwaves produced during cooking would not be sufficient to affect aflatoxin levels due to the high thermostability of AFB1.
  • The strong rays (ultraviolet rays and gamma rays) can also destroy nutrients structure.
  • Removal of AFB1 efficiency will be low and time consuming.

2. Using sorbent additives
Some minerals like aluminium silicate, active charcoal, and zeolite can be the adsorbents which have the ability to adsorb the AFB1. AFB1 will be directly excreted from our body with the binding adsorbent, instead of being absorbed when they pass through the digestive tract.

  • The adsorbility of them is so strong that they absorb the nutrients of food also.
  • This method cannot reduce the quantity of AFB1

3. Chemical method
Some acids are used as preservatives or antioxidants in foods to degrade AFB1. It is common to use inorganic salts, organic acids, ammonia vapor etc. in industrial detoxification processes to eliminate aflatoxins currently. Calcium propionate and sodium bisulfite are examples of antifungal agents to inhibit the yield of aflatoxin in animal feed. Treating corn, soybean meal, peanut meal, etc. contaminated by aflatoxin with ammonia or ammonia water can crack the toxin lactone under the action of ammonia to achieve the purpose of detoxification.

  • Many people believe that the chemical reagent will destroy the nutrients of the feed, causing secondary pollution on the feed.
  • Can be implemented in industrial processing only.

Physical and chemical treatment are the main detoxification methods nowadays. However, most of them are not efficient or will cause the loss of food nutrition. The use of biological methods, reducing AFB1 by binding or metabolism with the bacterial strain, has become a hot trend in the field of AFB1 degradation research recently, as it is non-polluting, has high specificity, consistency, mildness, and environmentally friendliness.

Microbiological degradation of AFB1 has gradually matured. Currently, a variety of microorganisms have been found to have a significant degradation of AFB1, for example, Lactobacillus sp., Bacillus subtilis. And the enzymes in these organisms that are responsible for the degradations, such as Manganese peroxidase, F420H2-dependent reductase, and laccase, were identified and studied by different researchers.

Our design to solve this problem

We aim to construct an ingestible probiotic E.coli that can preserve and detoxify food with potential of AFB1 contamination. The E. coli will be able to secrete AFB1-degrading enzymes - laccase or F420H2-dependent reductase (FDR).

To select the target laccase gene and FDR gene, literature review was done to compare the efficiency of different bacteria and enzymes in degrading AFB1. The Trametes versicolor laccase (tvLac) and FDR-A (MSMEG_5998) from Mycobacterium smegmatis were demonstrated by previous studies to have the highest efficiency in degrading AFB1 so they were selected as our candidate genes.

Laccase is a multicopper oxidase used for lignin degradation and melanin production which can be found in animals, plants, fungi, and bacteria. Meanwhile, FDR were shown to be involved in methanogenesis, antibiotic resistance, and other redox-related metabolic activities in bacteria. In laboratory conditions, both of them were reported to be able to degrade >90% of AFB1 within 48 hours.

The tvLac and FDR-A genes’ expressions were planned to be studied separately in our project and see which has a higher efficiency in expression, secretion and efficiency in degrading AFB1 in our testing condition. Then, the one with better performance will be utilized in our concept applications -

  1. The recombinant probiotic E. coli will be applied to the surface of food during storage. The enzymes secreted by the E. coli will be able to convert the AFB1 in food to a non-toxic or less toxic form and at the same time,they act as a competitor to the Aspergillus sp. that inhabit the surface of food.
  2. The extracted and purified enzymes will be used as a detoxifying spray that can detoxify food that’s potentially contaminated by AFB1.

  • The cost is low.
  • The method targets the storage process and thus less food waste will be produced.
  • The E. coli expression system has a short cycle, high expression yield and simple operation.
  • Most of the current detoxification methods are mainly used for reducing the aflatoxins in animal feed. We intend to make a probiotic that humans can use to ensure there is no AFB1 in the food before cooking or eating daily.
  • The probiotic E.coli is beneficial to the human body.
  • Due to bacterial competition and the presence of E.coli, the growth of other harmful microbes will also be reduced.

Verheecke, Carol and Liboz, Thierry and Mathieu, Florence Microbial degradation of aflatoxin B1: Current status and future advances. (2016) International Journal of Food Microbiology, 237. 1-9. ISSN 0168-1605

The Toxification and Detoxification Mechanisms of Aflatoxin B1 in Human: An Update DOI:

Lapalikar, G. V., Taylor, M. C., Warden, A. C., Scott, C., Russell, R. J., & Oakeshott, J. G. (2012). F420h2-dependent degradation of aflatoxin and other furanocoumarins is widespread throughout the actinomycetales. PLoS One. 2012;7(2):e30114. doi: 10.1371/journal.pone.0030114. Epub 2012 Feb 27. PMID: 22383957; PMCID: PMC3288000.

中國農業科學 2017,50(17):3422-3428

P.C. Okwara et al 2021 IOP Conf. Ser.: Mater. Sci. Eng. 1107 012178

Taylor, M. C., Jackson, C. J., Tattersall, D. B., French, N., Peat, T. S., Newman, J., Briggs, L. J., Lapalikar, G. V., Campbell, P. M., Scott, C., Russell, R. J., & Oakeshott, J. G. (2010). Identification and characterization of two families of F420H2-dependent reductases from mycobacteria that catalyse aflatoxin degradation. Molecular Microbiology, 78(3), 561–575.

Okwara, P. C., Afolabi, I. S., & Ahuekwe, E. F. (2021). Application of laccase in aflatoxin B1 degradation: A Review. IOP Conference Series: Materials Science and Engineering, 1107(1), 012178.