Peanut skins, coffee wastes enhance antioxidant properties of milk chocolate

Phenolic compounds – in chocolate, for example – can provide valuable antioxidant health benefits, but also a harder, more bitter chocolate. The antioxidants in turn provide anti-inflammatory health benefits to the consumer and notably, help keep food products from spoiling. Researchers have recently found a new way to combine the less bitter milk chocolate with waste peanut skins and waste coffee grounds to boost its antioxidant potential.

To create their antioxidant-boosted milk chocolate, researchers at the US Department of Agriculture’s (USDA’s) Agricultural Research Service worked with peanut manufacturers to obtain the peanut skins. When manufacturers roast and 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 tonnes of peanut skins are discarded each year, which contain 15% phenolic compounds by weight.

Afterwards, they ground the skins into a powder and extracted the phenolic compounds with 70% ethanol, while the lignin and cellulose (plant fibres) left behind were used in animal feed as roughage. The phenolic powder is then combined with maltodextrin, a common food additive, to make it easier to incorporate into the final milk chocolate product.

The researchers 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.

They finally created individual squares of chocolate with concentrations of phenolics ranging from 0.1% to 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 idea for this project began with testing different types of agricultural waste for bioactivity, particularly peanut skins,” said Lisa Dean, Ph.D., the project’s principal investigator.She explained that the natural presence of phenolic compounds gives dark chocolate its bitterness, along with less fat and sugar compared to its cousin milk chocolate. “Dark varieties are also more expensive than milk ones because of their higher cocoa content, so the addition of a waste like peanut skins provides similar benefits for a fraction of the price.”

The results were promising: the taste-testers found that 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 also had higher chemical antioxidant activity than most dark chocolates.

As for the major food allergy concern that peanuts present, the researchers tested the phenolic powder made from the peanut skins for presence of allergens. None were detected, but the researchers say that a product containing peanut skins should still be labeled as containing peanuts for consumer reference.

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