Sweet spot: from coffee, peanut waste to milk chocolate

Australia produces around 75,000 tonnes of coffee ground waste annually, and coffee consumption is increasing by around 4.3% a year, according to Sustainable Gardening Australia (SGA).

Similarly, when manufacturers process peanuts to make peanut butter, candy and other products, they toss aside the papery red skins that encase the legume inside its shell. Thousands of tons of peanut skins are discarded each year, but since they contain 15% phenolic compounds by weight, they are a potential goldmine of antioxidant bioactivity. Not only do antioxidants provide anti-inflammatory health benefits, they also help keep food products from spoiling.

Now, researchers have found a new way to combine milk chocolate with waste peanut skins and other food wastes to boost its antioxidant properties. The project’s initial goal was to extract phenolics from peanut skins and find a way to mix them with food. It began with testing different types of agricultural waste for bioactivity. Phenolics are very bitter, so researchers had to find some way to mitigate that sensation.

To create their antioxidant-boosted milk chocolate, Lisa Dean PhD and her team of researchers at the US Department of Agriculture’s (USDA’s) Agricultural Research Service worked with peanut companies to obtain the peanut skins. From there, they ground the skins into a powder and extracted the phenolic compounds with 70% ethanol. The lignin and cellulose left behind can be used in animal feed as roughage. They also worked with local coffee roasters and tea producers to obtain used coffee grounds and tea leaves, using a similar methodology to extract the antioxidants from those materials. The phenolic powder is then combined with maltodextrin, a common food additive, to make it easier to incorporate into the final milk chocolate product.

To make sure their new confection would pass gastronomic muster, the researchers created individual squares of chocolate with concentrations of phenolics ranging from 0.1–8.1% and had a trained sensory panel taste each one. The goal was to have the phenolic powder be undetectable in the flavour of the milk chocolate. The taste testers found that concentrations over 0.9% were detectable but incorporating the phenolics at 0.8% resulted in a good compromise of a high level of bioactivity without sacrificing flavour or texture. In fact, more than half of the taste testers preferred the 0.8% phenolic milk chocolate over the undosed control milk chocolate. This sample had higher chemical antioxidant activity than most dark chocolates. The researchers presented their findings at the American Chemical Society (ACS) Fall 2020 Virtual Meeting & Expo.

While these results are promising, Dean and team also acknowledge that peanuts are a major food allergy concern. They tested the phenolic powder made from the skins for presence of allergens, and while none were detected, they say that a product containing peanut skins should still be labelled as containing peanuts.

Next, the researchers plan to further explore the use of peanut skins, coffee grounds, discarded tea leaves and other waste products into additional foods. Dean is hoping to test whether the antioxidants in peanut skins extend the shelf life of nut butters, which can go rancid quickly because of their high fat content. While commercial availability of their boosted chocolate is still a ways off and subject to corporate patents, they hope that their efforts will eventually lead to a better milk chocolate on supermarket shelves.

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