Milk chocolate is a consumer favorite worldwide and is praised for its sweet taste and creamy texture. This treat comes in many varieties, but it's not exactly healthy. Dark chocolate, on the other hand, is high in phenolic compounds, which may provide antioxidant health benefits, but it's also a harder, more bitter chocolate. Today, researchers report a new way of combining milk chocolate with peanut shells and other waste to boost its antioxidant properties.
“The idea for this project started with testing different types of agricultural waste for bioactivity, especially peanut shells,” said Lisa Dean, Ph.D., the project's principal investigator. “Our original goal was to extract phenols from the skin and find a way to mix them with food.”
When manufacturers roast and process peanuts to make peanut butter, candy and other products, they throw aside the papery red skins that encase the legume in the shell. Thousands of tons of peanut shells are thrown away every year, but given that they contain 15% phenolic compounds by weight, they are a potential gold mine of antioxidant bioactivity. Not only do antioxidants provide anti-inflammatory health benefits, they also help prevent food items from spoiling.
“Phenols are very bitter, so we had to find a way to soften that feeling,” Dean says. In fact, the natural presence of phenolic compounds is what gives dark chocolate its bitterness, along with less fat and sugar compared to its milk chocolate cousin. Dark varieties are also more expensive than milk because of their higher cocoa content, so the addition of a waste product such as peanut shells offers similar benefits at a fraction of the price. And peanut shells aren't the only food waste that can enhance milk chocolate in this way; The researchers are also investigating the extraction and uptake of phenolic compounds from used coffee grounds, discarded tea leaves and other food waste.
To create their antioxidant milk chocolate, Dean and her team of researchers from the United States Department of Agriculture (USDA) Agricultural Research Service teamed up with peanut companies to obtain the peanut shells. From there, they ground the hides into a powder and extracted the phenolic compounds with 70% ethanol. The residual lignin and cellulose can be used as roughage in animal feed. They also worked with local coffee roasters and tea producers to obtain used coffee grounds and tea leaves, using a similar method to extract the antioxidants from those materials. The phenolic powder is then combined with maltodextrin, a commonly used food additive, to make it easier to incorporate into the final milk chocolate product.
To make sure their new treat would make it through gastronomy, the researchers created individual chocolate squares with concentrations of phenols ranging from 0.1% to 8.1% and had a trained sensory panel taste them all. The aim was not to detect the phenolic powder in the taste of the milk chocolate. The taste testers found that concentrations above 0.9% were detectable, but including the 0.8% phenols resulted in a good compromise of a high level of bioactivity without sacrificing taste or texture. In fact, more than half of the taste testers preferred 0.8% phenolic milk chocolate over the undosed control milk chocolate. This sample had a higher chemical antioxidant activity than most dark chocolates.
While these results are promising, Dean and team also recognize that peanuts are a major problem in food allergies. They tested the phenolic powder made from the skin for the presence of allergens, and although none were detected, they say a product containing peanut shells should still be labeled as peanuts.
Next, the researchers plan to further explore the use of peanut shells, coffee grounds, and other waste products in supplemental foods. In particular, Dean hopes to test whether the antioxidants in peanut shells extend the shelf life of nut butters, which can quickly go rancid due to their high fat content. While the commercial availability of their fortified chocolate is still a long way off and subject to company patents, they hope their efforts will eventually lead to better milk chocolate on supermarket shelves.
