Photo credit: David Bares
Imagine walking into a superstore and buying foods packaged in biofilms made with coffee grounds that completely dissolve in water. New research indicates this possibility is fast becoming a reality!
According to ICO, the world consumed about 10.3 billion kg of coffee in 2022-23, and the consumption in 2023-24 is expected to go up a further 2%. The growth in demand and consumption of coffee is accompanied by a greater accumulation of coffee by-product waste, such as spent coffee grounds (SCG). Every gram of coffee beans produces about 0.9g of spent coffee grounds, making SCG the most abundant waste generated in coffee beverage preparation. Estimates show that at least 60 million tons of SCG are accumulated annually. Most of these SCG, are incinerated or make their way to landfills, in recent times, new applications are being discovered for the same.
From working as an effective natural dye for Nylon 6.6 to conversion into rich synthesis gas, as a bio-nutrient through microbial transformation to a novel green concrete, spent coffee grounds are being used in different ways to minimize their impact on the environment. Often used as a fertilizer by gardening enthusiasts and small farmers, SCG when decomposing uses oxygen and produces methane, which makes them a bigger problem for the environment.
One novel way to use SCG is as a substrate for the production of edible, biodegradable films with K-Carrageenan as the base polymer.
On a dry weight basis, SCG has as much as 66% polysaccharides, mostly galactomannans (50%), cellulose (25%), and arabinogalactans (25%). The high galactomannan content makes SCG a suitable raw material for edible biodegradable biofilm production as they are highly soluble in water, are thermostable up to 200°C even at prolonged exposure, and can form a stable, viscous, aqueous solution with film-forming capacity. SCG is rich in phenolic compounds, especially chlorogenic acids (85%) and caffeic acid (6%). They also contain up to 17% proteins, and 13 to 15% lipids, a significant chunk of which (20%) are extractable coffee oils. Due to this composition, SCG is easily adaptable for biofilm production with the polysaccharides helping improve the mechanical parameters of film texture.
The new research exploring the potential for biofilm production used a blend of oils pressed from a blend of robusta and arabica coffee grounds as it had the best quality and highest antioxidant properties compared to arabica or robusta alone. This oil was emulsified and used as a filler while K-Carrageenan was used as a base polymer. First, K-Carrageenan was dissolved in distilled water at 50°C, after which the emulsified SCG oil was added, and homogenized.
When this solution was cast in petri dishes and dried at room temperature, it resulted in a biodegradable, edible biofilm with high antioxidant and polyphenol content and lesser water content than pure Carrageenan films. The SCG oil is hydrophobic, reducing the water solubility of the film, though it was completely soluble in seawater over time, demonstrating that the biofilm is fully biodegradable. The oils also enhance the level of polyphenols and the antioxidant capacity in the films.
After thorough analysis, SCG can be considered a great plasticizer for K-Carrageenan, reducing the brittleness of the biofilm while also enhancing the elongation at the break. By using SCG oils, the resulting biofilms can be strengthened, and loaded with antioxidants and polyphenols, and the overall environmental impact is significantly minimized compared to the commonly used plastic films for food packaging.
As this research goes commercial, SCG biofilms could offer a more sustainable and functional alternative to plastics for the food packaging industry.