Beer-battered fish

Our modern society produces lots of different kinds of organic waste, which has led many scientists to develop different ways for transforming this organic waste into useful products. Some of these scientists have then given presentations about these different ways at Spring meetings of the American Chemical Society (ACS).

The Spring meeting in 2016 included presentations on using damaged and spoiled tomatoes to power a microbial fuel cell and using eggshells to strengthen bioplastics (see Wake up to tomatoes and eggs). This year's Spring meeting, which took place online in April, included presentations on producing biofuels and chemicals from the waste generated by brewing beer, known as brewer's spent grains, and producing a bioplastic from waste fish oil.

As the name suggests, brewers spent grains comprise the material left over after all the flavor has been extracted from barley and other grains during the beer brewing process. Although this protein-rich material can be used as cattle-feed, a great deal is simply dumped in landfills, which inspired Haibo Huang and his colleagues at Virginia Tech in the US to try to find better uses for it.

Protein may account for up to 30% of brewers spent grains, but fiber accounts for much of the remainder of the material, which is why it can only be used as cattle feed, because most other animals lack the ability to digest the fiber. So Huang and his colleagues first decided to separate the protein from the fiber, which they did by exposing brewers spent grains to the enzyme alcalase. This enzyme broke the bonds attaching the proteins to the fibers, allowing the proteins to be dissolved in water and then separated from the fibers via filtration.

With the fiber removed, the protein makes an ideal feed for a much wider range of animals, including humans. Huang and his colleagues have already experimented with using it as a replacement for fish meal for feeding farmed shrimp, and are also exploring its potential as an ingredient in food products. Meanwhile, like other forms of plant biomass, the fibers can be converted into fermentable sugars by exposing them to sulfuric acid and then cellulase enzymes to break down the cellulose and hemicellulose. 

Huang and his colleagues tried giving the resulting sugars, including glucose, to a new strain of the bacteria Bacillus lichenformis, which a member of Huang's research group found in a spring at Yellowstone National Park. This strain fermented the sugars into 2,3-butanediol, which can be used to make several useful products, including synthetic rubber, plasticizers and the biofuel 2-butanol.

Beer often goes well with a nice piece of fish. As with brewing, producing that piece of fish generates a lot of waste material, in terms of the head, guts, bones and skin, which are generally thrown away. But in oily fishes such as salmon and haddock, this waste material is rich in easily extractable and potentially useful oil.

This led Francesca Kerton and her colleagues at Memorial University of Newfoundland, a region of Canada with a large fishing industry, to develop a method for converting the oil extracted from waste fish material into a sustainable form of polyurethane. Their method involves first oxidizing the oil with hydrogen peroxide to form epoxides, which they then react with carbon dioxide. 

Finally, they link these carbonated epoxides together with a nitrogen-containing amine to form a sustainable form of polyurethane. This amine is also derived from organic waste, in the form of cashew nut shells, but Kerton and her colleagues are investigating replacing the amine with amino acids, which are cheaper.

They have already shown that their process works with oils extracted from various different types of oily fish, including salmon and herring. The resulting sustainable form of polyurethane has similar physical properties to conventional polyurethane, but unlike conventional polyurethane, it naturally degrades in water. This degradation process can also be sped up by adding the enzyme lipase, which breaks down oils. Most importantly, however, their sustainable polyurethane doesn't smell of fish.

The views represented here are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd. or of the SCI.