Local Hong Kong Starbucks branches have teamed up with researchers to boil old baked goods down to their core chemical components in order to extract recycled ingredients used in plastics, laundry detergents and other ubiquitous products.
“We’d go collect bakery waste from Starbucks outlets once a week and process it in our lab to convert the waste into useful chemicals, like succinic acid and bioplastic,” says Carol S. K. Lin, a biochemical engineer at the City University of Hong Kong who led and presented the project at the 244th National Meeting and Exposition of the American Chemical Society.
“Succinic acid is a popular molecule, and there are already plants built in Europe, Thailand and the States,” she says.
Starbucks kicked off the experiment earlier this year with their “Care For Our Planet” campaign in Hong Kong. The coffee chain advertised charity sets of cookies and cups, and for each one sold Starbucks donated HK$8 (about US$1) to the university for research support. By the end of the campaign, Lin’s school collected about US$6,400. Along with a grant from the Innovation and Technology Commission, Lin had enough resources to perform a thorough investigation of the pastries’ recycling potential.
Rather than rely on petroleum for creating plastics, succinic acid is a sustainable feedstock
The goal is to find a use for the 1.3 billion tons of food waste that is dumped each year.
She and her colleagues used biorefinery technologies – or the process of converting organic materials into bio-based products like animal feed, chemicals or biofuels – to break down the pastries. To achieve this, they undertook a method called acid hydrolysis.
First, they tossed some fungi into the blended baked goods in order to convert the carbohydrate bases into the simple sugars glucose and – additionally for cake – fructose. They then loaded the sugary fermentation broth, along with a pinch of nitrogen, into a fermentation vat, which promoted bacterial growth. The microbes munch on the sugars and produce a compound called succinic acid as their waste – which is what the researchers were aiming for. They distilled the broth to separate the acid from its byproducts, then crystallized and filtered it to yield vials of the pure, powdery white compound.
(Being surrounded by the tasty treats was tempting, and the researchers themselves would sometimes take a nibble of an old scone or cookie, Lin admits. But after several months of crusty croissants they were “sick of it.”)
The U.S. Department of Energy lists succinic acid as one of the 12 key materials yielded by sugars that can make high-value products. “It really has a wide range of applications,” Lin says. This includes pigments and resins, automobile parts, laundry detergents, plastics and medicines. Rather than rely upon non-renewable petroleum as a base for creating plastics, the researchers consider succinic acid a sustainable, renewable feedstock for making bio-plastics and other commodities.
Succinic acid is a popular molecule
Lin and her colleagues also tested the method on other food items from local restaurants and the university cafeteria, such as noodles, rice, mixed vegetables and meats. All of these scraps and leftovers proved adept for the new recycling method. Coffee grounds, however, were the exception. “It seems there’s another product in coffee grounds that inhibits growth of the bacteria for succinic acid production,” Lin notes. “The method works well for things that contain starchy and protein-rich materials.”
Though Lin and her team proved their technique works, scaling it up to serve the entire city of Hong Kong or beyond is a challenge. Lin thinks her lab would need industrial or governmental support in order to achieve the feat, and they are currently investigating whether or not the process is profitable enough to lure private investors into getting involved. She’s hopeful, however. “Worldwide, there’s great interest.”
Top image: Croissant innards, courtesy Flickr user Roboppy