Chitosan from Shrimp Shells: BAEC Research on a Safer Alternative to Formalin

In June 2014, police teams in Dhaka destroyed nearly 200 tonnes of fruit in two days, among them 120 tonnes of mangoes and more than half a million litchis, saying the fruit had been treated with formalin. A question hung over every mango season after that: is there a safe way to keep fruit and fish fresh without a toxic chemical?

One answer came from a laboratory at Savar. Dr Mubarak Ahmad Khan, then chief scientific officer of the Bangladesh Atomic Energy Commission (BAEC), reported that chitosan, a natural substance made from discarded shrimp shells, could be used to preserve food in place of formalin. This report sets out what he and his colleagues said they had achieved, how chitosan is made, what the published experiments showed, why formalin worries health authorities, and what was still unproven.

According to Dr Mubarak, chitosan can be made naturally from shrimp shells that processing plants and kitchens throw away. He described it as cheap and harmless to people, and said he had already used it successfully on several fruits and vegetables. Next would come fish, then commercial use.

He reported that after three years of research, chitosan treatment had kept mangoes fresh for two to three weeks, litchi for 12 to 13 days, pineapple for 10 to 12 days, frozen bitter gourd for about 18 days and tomatoes for 21 days. He said quality, shape, colour and taste did not change.

Prothom Alo, which visited the Institute of Radiation and Polymer Technology (IRPT) at the Atomic Energy Research Establishment in Savar in December 2016, reported that the team had first produced chitosan from shrimp shells in 2008, about eight years earlier. The research coordinator was Zahid Md. Mahbub Islam. In a 2012 trial in Chapainawabganj, treated mangoes stayed in good condition for 14 days, and pineapple could be kept for up to 10 days. The team had also tested jam (black plum), strawberry and jackfruit.

Prothom Alo reported that treated mola fish kept for 18 hours in the open and tilapia for 21 hours. A December 2016 letter in The Financial Express mentioned a trial at a pineapple farm in Madhupur, Tangail.

Dr Mubarak also said that his discovery had been presented at a meeting at the Prime Minister's Office, and that a 13-member committee had been formed to take it forward. In his account, the committee included secretaries of the ministries concerned, directors general of departments, chemical engineers from BUET and professors of Dhaka University. Other research institutes were asked to examine the results, and permission was given to begin work on fish. He said he was also considering patenting the Bangladeshi process for making chitosan.

A shrimp's hard outer shell is rich in chitin, a natural polymer. Chitosan is obtained from chitin by removing part of its acetyl groups, a process chemists call deacetylation. A 2018 review in the peer-reviewed journal Frontiers in Microbiology, by Gianfranco Romanazzi, Erica Feliziani and Dharini Sivakumar, describes chitosan as a linear polysaccharide of glucosamine and N-acetylglucosamine units, and notes that it is among the most abundant natural polymers after cellulose.

Dr Mubarak described the steps used at Savar. The shells are first washed in a 3 per cent solution of sodium hydroxide (caustic soda) and cleaned, which yields chitin. Radiation is then used in making the chitosan. He said that other countries mostly make chitosan by a costly chemical method, while his team used gamma radiation, which he described as cheap. Because no other chemicals are added at that stage, he said, it does not pollute.

Professor Sitesh Chandra Bachar, chairman of the Department of Pharmacy at Dhaka University, explained the chemistry to Prothom Alo in 2016: the components of shrimp shell are reacted with acid and alkali to produce chitosan. The team's published papers show where the radiation comes in. In a study by Md. Abdul Kader, Nehar Parvin, Md. Elias Molla and Mubarak A Khan in the AUST Journal of Science and Technology (volume 7, 2015 issues), chitosan extracted from prawn shell at the IRPT was dissolved at 2 per cent in 2 per cent acetic acid, and that solution was irradiated with gamma rays at 40 kGy from a 120 kilocurie source, at 3.2 kGy per hour. The irradiated chitosan had a degree of deacetylation of about 79 per cent.

Dr Mubarak pointed out that radiation processing of food is approved by the World Health Organization (WHO) and the US Food and Drug Administration (FDA). In 1980 the Joint FAO/IAEA/WHO Expert Committee on Food Irradiation concluded that irradiating any food commodity up to an average dose of 10 kGy presents no toxicological hazard. In the Savar process, however, it is the chitosan solution that is irradiated, not the fruit itself.

In 2013, Ashna Islam, Mahfuza Sharifa Sultana, Fahmida Parvin and Mubarak A Khan published a paper titled "Effective γ-radiation Dose on Chitosan for Preservation of Mangoes" in the Jahangirnagar University Environmental Bulletin (volume 2, pages 35 to 40). It reports that chitosan irradiated at 50 kGy and 100 kGy was superior in extending the shelf life of mango.

The later AUST study gives more detail. The researchers used green Amropali mangoes collected from a garden in Manikganj district. The fruit were dipped for two minutes in irradiated chitosan solutions of 500, 750 and 1,000 parts per million, air dried, and stored in the open or in zip bags at room temperature and at freezing temperature. Untreated mangoes served as controls.

• At room temperature, untreated mangoes began to shrink and spoil after six days, and all were spoiled by day 12.
• Treated mangoes stayed completely fresh up to 12 days before some began to spoil.
• After 18 days in the open, mangoes treated with 750 or 1,000 ppm had lost 27.3 per cent of their weight and those treated with 500 ppm 28.9 per cent.
• Of the three strengths, 750 ppm gave the least weight loss on average, and the authors named it the most promising.

The authors explained the effect by chitosan's antimicrobial activity and by the thin film it forms on the fruit surface, which slows the exchange of oxygen and carbon dioxide and acts as a barrier to water loss. Citing earlier work, they noted that mango keeps only 4 to 8 days at room temperature and 2 to 3 weeks in cold storage at 13 degrees Celsius, and that producers and traders lose about 20 to 30 per cent of the crop through poor storage and handling.

Dr Mubarak said that chitosan could be produced to meet demand from local raw materials. In his account, chitosan worth one taka was enough to treat a kilogram of mangoes commercially, while vegetables would cost 40 paisa a kilogram. A kilogram of shrimp yields about 60 grams of shell, he said, and six kilograms of shell make a kilogram of chitosan, at a production cost of about 20,000 taka. He compared this with about one lakh taka for chitosan made chemically in India. The Daily Star, reporting his work in 2016, quoted the same six-to-one ratio and the 20,000 taka cost, and said that in some countries a kilogram of chitosan cost as much as five lakh taka.

Prothom Alo's December 2016 report gave different figures: ten kilograms of shell for one kilogram of chitosan, a production cost of about 2,000 taka a kilogram against about one lakh taka for imported chitosan, and about 500 litres of liquid preservative from each kilogram. The reports did not explain the difference; both are the scientists' estimates at the time, not market prices.

On raw material, the original report said that the shrimp Bangladesh produces each year leaves about 15,000 tonnes of shell, and that scientists considered the chitosan that could be made from it enough for the country's food preservation needs. Prothom Alo reported in 2016 that Bangladesh had no factory producing chitosan and that talks on commercial production were being held with the Bangladesh Chemical Industries Corporation (BCIC).

Formalin is a solution of formaldehyde in water. The US National Cancer Institute describes formaldehyde as a colourless, flammable, strong-smelling chemical used in building materials and many household products. In 2004 the International Agency for Research on Cancer (IARC), part of the WHO, classified formaldehyde as a human carcinogen, and in 2011 the US National Toxicology Program listed it as a known human carcinogen in its 12th Report on Carcinogens. Studies of exposed workers link it most strongly with myeloid leukaemia, and several with nasopharyngeal cancer.

Most of that evidence concerns breathing it. On swallowing, the US Agency for Toxic Substances and Disease Registry (ATSDR) reports that animals given 50 to 100 mg per kilogram of body weight a day by mouth suffered weight loss, stomach and gut ulcers, and liver and kidney damage. Hong Kong's Centre for Food Safety, in a 2009 report, said that swallowing large amounts can cause severe abdominal pain, vomiting, coma, kidney injury and death, and that adding formaldehyde to food is prohibited there.

The same Hong Kong report makes a point that matters for testing: formaldehyde also occurs naturally in food. It found natural levels of 6.3 to 22.3 mg per kilogram in apples and 38.7 to 60 mg per kilogram in pears, and noted that natural levels in some foods can reach 300 to 400 mg per kilogram. A positive test does not therefore by itself prove that a trader added formalin. Anyone concerned about the health effects of a chemical in food should consult a doctor.

Formalin fears peaked in 2014. According to The Financial Express, the Dhaka Metropolitan Police drives of June 2014 found readings of 2 ppm in mangoes, 5.07 ppm in plums and 143.94 ppm in papayas, and several people were fined a total of 50,500 taka. The environmental group Poribesh Bachao Andolan (POBA) collected 263 fruit samples from 35 points in Dhaka between 1 and 10 June 2014 and reported formaldehyde in most of them, including 66 per cent of mangoes and 95 per cent of litchis.

The testing itself was questioned. Both the police and POBA had used the Z-300 formaldehyde meter. The Daily Star reported in 2014 that a Bangladesh Council of Scientific and Industrial Research (BCSIR) report found the meter not appropriate for testing fruit: it is designed to measure formaldehyde in air, and other volatile substances such as acetone, acetic acid and methanol, as well as fruit kept at high temperature, could give false readings.

The government answered with law. Parliament passed the Formalin Control Act on 16 November 2015, and the Ministry of Commerce issued its rules on 29 December 2015. The law does not ban formalin, which laboratories, hospitals, tanneries, textile mills and hatcheries use, but requires a licence for its import, production, transport, storage, sale and use. The Ministry of Commerce licenses imports and the Ministry of Industries permits production. The heaviest penalty is life imprisonment with a fine of up to 20 lakh taka; importing without a licence can bring two and a half years in prison and a fine of up to three lakh taka.

Food safety as a whole sits under the Safe Food Act of 10 October 2013, which created the Bangladesh Food Safety Authority (BFSA) on 2 February 2015.

Chitosan coatings on fruit are not unique to Bangladesh. The 2018 Frontiers in Microbiology review describes three ways chitosan protects harvested produce: it acts against fungi and bacteria by inhibiting spore germination and pathogen growth; it triggers the fruit's own defence responses; and it forms an edible film that slows respiration and ripening. It notes that chitosan was the first compound approved as a "basic substance" for plant protection in the European Union, under Regulation (EU) No 563/2014, for both organic agriculture and integrated pest management.

The same review also sets out limits. Chitosan works best at around 1 per cent concentration, and weaker solutions protect less. It must be dissolved in an acid before use, and early preparations took one to two days to make. Its effect declines as fruit ripens, because ripe tissue responds less. Cost is another hurdle compared with conventional fungicides.

Experts in Bangladesh urged caution too. Professor A B M Faruque of the Department of Pharmaceutical Technology at Dhaka University told Prothom Alo in 2016 that chitosan is an inert natural substance with no health risk, but that further tests were needed before commercial production. Dr Mubarak's own plan, as he described it, was to have other research institutes verify the results and to complete the work on fish before any commercial use.

Mubarak Ahmad Khan was born in 1958. He studied chemistry at Jahangirnagar University, earning his BSc and MSc there, and took a PhD in polymer and radiation chemistry. At BAEC he rose to chief scientific officer and director general, and led the chitosan research at the Institute of Radiation and Polymer Technology. He is best known for work on jute: in 2009 he developed Jutin, a corrugated sheet made from a blend of jute and polymer, and he later developed the Sonali Bag, a biodegradable bag made from jute. He received the Bangladesh Academy of Sciences gold medal in 2015, the National Jute Award in 2016 and the Federation of Asian Chemical Societies award in 2017.

The Bangladesh Atomic Energy Commission was established on 27 February 1973. Its Atomic Energy Research Establishment at Savar houses several institutes, among them the Institute of Food and Radiation Biology. BAEC has worked with radiation processing for many years: in 1993 a commercial gamma irradiation plant, Gamatech, began operating in Chattogram as a joint venture with BEXIMCO.

Shrimp is one of Bangladesh's most important fisheries products. Banglapedia records 56 species of shrimp and prawn in the country's waters, 37 of them in salt water, 12 in brackish water and 7 in fresh water. The main farmed species are the tiger shrimp or bagda (Penaeus monodon) and the giant freshwater prawn or golda (Macrobrachium rosenbergii).

Banglapedia puts the area under tiger shrimp at about 145,000 hectares and golda at about 30,000 hectares in some 60,000 ponds and paddy fields, mainly in Khulna, Satkhira, Bagerhat and Cox's Bazar. Shrimp processing plants have been set up in Khulna, Chattogram and Dhaka.

The wider fisheries sector set the scale for any new preservative. According to the Department of Fisheries' Yearbook of Fisheries Statistics of Bangladesh 2019-20, as reported by The Financial Express in November 2021, the country produced 45.03 lakh tonnes of fish in fiscal year 2019-20, 57.38 per cent of it from aquaculture, and exported 70,950 tonnes of fish and fishery products worth Tk 39,851.50 million.

Photo: Pelagic / Wikimedia Commons (CC BY-SA 4.0)

Sources: The Agro News (Staff Correspondent), Prothom Alo, The Daily Star, The Financial Express, AUST Journal of Science and Technology, Jahangirnagar University Environmental Bulletin, Frontiers in Microbiology, US National Cancer Institute, ATSDR, Centre for Food Safety (Hong Kong), FAO/WHO Codex Alimentarius Commission, Banglapedia, Wikipedia