The importance of chocolate to human cultures the world over has far exceeded its culinary functions. Chocolate in its various forms has been revered as a symbol of love, elegance, and comfort. In some cultures, chocolate is even considered an aphrodisiac.

However, cocoa beans – the source of chocolate – only account for 15% of the plant matter harvested from the fruits of the cacao tree. Around 70% of the plant matter produced is cocoa pod husk. The remaining 15% consists of the shell from the cocoa beans and the protective jelly that surrounds the beans. Disposing of these waste products is proving to be a challenge. Many growers resort to storing the decomposing waste products on their cacao plantations, causing the rise and spread of devastating plant diseases.

The potential for recycling and reusing cocoa waste products has largely been neglected until now. Most cocoa bean production adheres to a linear economic model, which has led to sustainability concerns in the face of increasing pressures from climate change and habitat loss. As the main waste product, developing applications for cocoa pod husks is becoming increasingly critical for ensuring the sustainability of cocoa bean production.

Dr Piergiorgio Gentile from Newcastle University, Dr Joel Girón-Hernández from Northumbria University and collaborators have teamed up to explore potential uses for cocoa pod husks, which could help chocolate production become more economically efficient and sustainable. Their recent research has focused on a particularly promising compound derived from the cocoa pod husks, called pectin.

Owing to its unique physical and chemical characteristics, pectin could prove useful in the food industry as well as in biomedical applications. Its most well-known property is the ability to form gels when combined with water and other specific acids and sugars. It is this property of pectin, which is also found in a range of other fruits, that causes jams to thicken up and set. Its gelling and thickening ability enables it to provide texture and consistency in various foods.

Additionally, pectin acts as a stabiliser in the creation of emulsions – a combination of oil and water that otherwise wouldn’t mix. Common foods requiring an emulsion include mayonnaise and margarine. In fact, even milk chocolate includes an emulsion of cocoa butter and milk. Pectin also forms thin, edible films that can be used to create coatings on fruit and other food products to extend their shelf life and improve moisture control.

In biomedical fields, pectin is a valuable compound because it is non-toxic and compatible with living tissues. It has been demonstrated to improve the effectiveness of certain medications. It also slows the release of medications, meaning that fewer doses are required.

The gelling properties of pectin also give it great potential for use in 3D bioprinting – an advanced technique still in development that could enable living tissues and organs to be constructed in the lab. Dr Girón-Hernández and Dr Gentile suggest that pectin could provide the necessary precision and control to form gels within the tissues. This means it could be used to create the bioinks used in 3D bioprinting.

All pectin is not created equal, however. The researchers found that the plant it is derived from, the extraction method used, and several environmental factors all affect the physical and chemical structure of pectin, resulting in differences in its specific properties.

Their results demonstrate that the extraction method is particularly important in determining the characteristics of pectin. The process requires the input of the raw material, a solvent, and energy to produce the extract and any leftover waste products. Minimising the energy required for the extraction process and developing techniques to recover and reuse the extraction solvent are critical for reducing the cost and environmental impact of the process. However, this can’t come at a cost to the quality of the pectin extracted, particularly for biomedical uses.

Optimising the extraction process is vital. Through a series of experiments, Dr Girón-Hernández and Dr Gentile with their collaborators optimised the technique used for extracting the highest-quality pectin from cocoa pod husks. The team’s optimised technique achieved a pectin yield of around 20%, which surpasses the yields reported for other extraction methods. Importantly, the results showed that the pectin extracted using their technique was of medical-grade quality, making it suitable for use in 3D bioprinting as a versatile bioink ingredient.

To demonstrate, the researchers created a gel that could be used in bioinks with the extracted pectin. They opted to swap a compound commonly used in the process for calcium carbonate, investigating the effect of different concentrations of this compound on the gelling properties of the pectin. This technique enabled precise control of the speed at which the gel formed and the extent of swelling it underwent, making it suitable for biomedical uses.

Current cocoa bean production threatens the future of chocolate and the planet. By developing uses for cocoa bean byproducts, like cocoa pod husks, a sustainable and cost-effective circular economy model could be achieved for this industry.

Through their research, Dr Gentile and Dr Girón-Hernández with their collaborators show that developing uses for cocoa pod husk extracts could offer us so much more. The pectin derived from cocoa pod husks could provide valuable ingredients to the food industry and could help revolutionise the biomedical world. With their pectin extraction optimisation technique, perhaps 3D-printed organs and tissues will be widely available in our not-too-distant future.