For decades, the nut industry has treated the shell as an inconvenience, something to discard on the way to the kernel. We built RE-NUT® around the opposite idea. But what exactly is in there? The science is more interesting than most people realise.

Polyphenols: The Shell's Most Exciting Secret

If fibre is the structural story of the shell, polyphenols are the biological one and this is where the science gets fascinating.

Polyphenols are a large family of plant-derived compounds that include flavonoids, condensed tannins (also called proanthocyanidins), phenolic acids, and lignans. They are the compounds responsible for the antioxidant properties of red wine, green tea, and dark chocolate, and they are present in significant quantities in nut shells.

What the research shows:

Almond shells contain total phenolics, flavonoids, and condensed tannins in their ethanol-water extracts, with demonstrated antioxidant activity. Their polyphenol profile includes flavonoids, anthraquinones, phenolics, and lactones. Research on whole almonds has identified approximately 130 different polyphenols, including proanthocyanidins (the predominant class), hydrolysable tannins, flavonoids, and phenolic acids, many of which are concentrated in or around the outer layers of the nut.

Peanut shells are a particularly rich source. Studies on peanut shells report total polyphenol content of 428–740 µg gallic acid equivalents per gram, and total flavonoid content of 143–568 µg quercetin equivalents per gram. Key compounds include luteolin, carotene, resveratrol, and isosaponaretin. Notably, roasting, which is exactly how RE-NUT® processes its in-shell peanuts, has been shown to enhance total flavonoid content and antioxidant activity in peanut shells compared to raw material.

Peanut hull waste globally represents an annual loss of over 6.5 million tons of health-promoting dietary fibre and meaningful quantities of flavonoids such as luteolin and resveratrol, compounds commonly found in pharmaceutical-grade supplements and associated with cardiovascular and anti-inflammatory effects in research settings.

"Regular dietary intake of foods high in polyphenols and flavonoids — like those in abundance in nut hulls — have been associated with improved health outcomes including fewer cardiovascular events, less neurodegenerative and metabolic disease, and preserved cognitive function."

— Carballo-Casla et al., Frontiers in Nutrition, 2024 (reviewing peanut hull nutritional science)

What About the Tannins — Are They a Concern?

This is a question that comes up regularly — and it is a fair one. Condensed tannins and polyphenols are redox-active compounds, which means they can exhibit both antioxidant and, under certain conditions, pro-oxidant behaviour. This is one of the reasons genotoxicity testing was a necessary step for RE-NUT® ingredients before entering the market. The good news, and the reason we published our safety study in March 2026, is that the answer is clear: at the concentrations present in RE-NUT® Almond Solids, Almond Liquid Extract, and Peanut Paste, none of these compounds induce gene mutations or chromosomal damage. The ingredients passed both OECD 471 and OECD 487 testing with negative results across all conditions.

This is consistent with the broader scientific picture. At nutritionally relevant concentrations, polyphenols and tannins from nut sources behave as antioxidants — neutralising free radicals rather than generating them. It is only in experimental conditions at extreme concentrations, and in the presence of metal-catalysed oxidation, that pro-oxidant behaviour has been observed in laboratory settings.

What This Means for Food Formulators

RE-NUT® ingredients are not simply a sustainability story. They are a functional ingredient story with a sustainability backdrop.

Almond Solids, Almond Liquid Extract, and Peanut Paste each bring a richer, more complex nutritional and functional profile than their kernel-only counterparts — because they include what the industry has historically discarded. For a food product developer, this translates into:

· A natural source of dietary fibre that simultaneously delivers functional texture benefits.

· A cleaner label, since the fibre and antioxidant contribution comes from a single, recognisable ingredient.

· Genuine antioxidant capacity that can delay oxidation in fat-containing products, extending shelf life naturally.

· A compelling sustainability claim that is verifiable: we use the whole nut, produce zero by-product waste, and have the published science to back it.

All three RE-NUT® ingredients are water-soluble, which means they integrate cleanly into liquid and semi-liquid formulations (nut milks, plant-based beverages, spreads, yoghurt alternatives, and ice cream) as well as bakery, confectionery, and snack applications.