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Sammy Heung

The laboratory at the Chinese University of Hong Kong’s department of chemistry is filled with the rich aroma of tea as Professor Ngai To and his students get down to work.
They produce copious quantities of kombucha, the fizzy, fermented drink made from sweetened black tea which has become popular with claims of health benefits.
But the team’s focus is not on the trendy drink itself or concocting new flavours.
Ngai and his students hope an essential ingredient for brewing kombucha can create a new environmentally friendly material to replace plastic food packaging and even natural leather.
Kombucha is made by fermenting tea and sugar with bacteria and yeast, a days-long process that uses a pancake-shaped gelatinous mass called “Scoby” – which stands for “symbiotic culture of bacteria and yeast”.
The team has used that to produce bacterial cellulose, a type of polymer that can be used as a biodegradable packaging material that disintegrates in soil within three to five months.
“We are able to make the new material waterproof and oilproof,” said Ngai, who is assistant dean for research at the university’s science faculty.
“The ingredients we use are not very expensive, as we primarily use tea leaves and sugar. Additionally, the cultures can be reused.”
Explaining the process, he said about seven days after a batch of kombucha was made, the gelatinous Scoby layer secreted bacterial cellulose.
The team adds soy protein into the cellulose structure and applies a coating made with an oil-resistant composite. After drying, the cellulose becomes a thin film that is biodegradable, non-toxic, edible and flexible.
The sheet can be used to make a bag for snacks or street food, or a seal or cover for drinks cups or sandwich boxes.
Ngai said the material could also be used to create a synthetic leather to replace natural animal skin leather with a potential impact to reduce deforestation and greenhouse gas emissions.

The cellulose can be crushed, spread out, dried and solidified to create a leather-like structure.
“There are leather alternatives on the market, but they are made with plastic which can also lead to environmental pollution,” he said.
His team has sent samples to a company in Switzerland which is carrying out tests to see how the material compares with natural leather and its potential for use.
Among other things, the company will test if the material swells when submerged in water, is breathable, and prone to wear and tear.
Ngai said other researchers had integrated bacterial cellulose into packaging materials, but there were limitations.
For example, it was found to be not strong enough for some uses, and became less effective when exposed to air and water.
Since his team started work in 2020, the biggest challenge was finding a way to modify the properties of the film to make it suitable for food packaging.
They eventually found the solution by adding soy protein and alginate salt derived from seaweed.

Ngai said some food packaging companies had already expressed interest in the product, but the film’s transparency and ability to block oxygen and water vapour needed improving.
“If the film is used on a sushi or sandwich container, it has to be more transparent so that customers will be able to see what is inside,” he said.
“A longer shelf life is required for food, so it is better if the film can block oxygen or water vapour.”
One drawback was that producing the film currently cost more than plastic, so the team was looking for ways to automate the production process and enable larger-scale production.
To reduce costs, it was hoping to collaborate with the food industry to obtain unwanted tea leaves used for other drinks, or leftover sugar.
Hong Kong last year introduced measures to reduce the use of plastic as one of its efforts to reduce waste.
Since April 22 last year, retailers and restaurants could no longer sell or use polystyrene tableware or plastic cutlery for takeaway and dine-in services.
In the second phase that could start as early as this year, there will be a ban on throwaway plastics in restaurants, and on plastic food containers, six-pack yokes for canned drinks, tablecloths, disposable gloves and plastic-stemmed dental floss.


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Professor Ngai To says the film’s transparency and ability to block oxygen and water vapour need to be improved. Photo: Sun Yeung

The ingredients used to make the product, such as tea leaves and sugar, are not expensive. Photo: Sun Yeung

Researcher Dr Jiang Zhoulun (left) and Professor Ngai To display some of their packaging film. Photo: Sun Yeung

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News

Hong Kong

Health & Environment

Team’s waterproof, oilproof polymer can be used as a biodegradable packaging material for food and drinks


Team’s waterproof, oilproof polymer can be used as a biodegradable packaging material for food and drinks.
