The polyphenol level in Peanut skin extract was up to 380-450 mg GAE/g (gallic acid equivalent), which was much higher than grape seed extract (220 mg GAE/g) and green tea extract (160 mg GAE/g). Its principal constituents are proanthocyanidins (62-75%), resveratrol (0.8-1.2%) and quercetin (1.5-2.5%), of which proanthocyanidins B2 is 12.8 mg/g, and antioxidant activity (ORAC value) 15,000 μmol TE/g, i.e., 12 times the activity of vitamin C. The clearance rate of DPPH free radicals by peanut coated polyphenols was 98.7% at the concentration of 0.1mg/mL, which was 23% higher than synthetic antioxidant BHT, as per a study published in the Journal of Agricultural and Food Chemistry in 2021.
Plant defense mechanism is the main cause of polyphenol enrichment. In an attempt to repel ultraviolet (UV-B radiation intensity > 8W/m²) and pathogens (e.g., Aspergillus flavus infection rate decreased by 78%) during cultivation, peanut clothing will induce the phenylpropane metabolic pathway, and increase the activity of polyphenol synthetase (PAL, CHS) by 3-5 times. The tests showed that under the stress of drought (soil humidity < 30%), the value of total polyphenol of peanut coating would be increased to 410 mg/g from originally 280 mg/g. Through stress controlled cultivation technique, an agriculture corporation increased chlamydia anthocyanin production from peanut by 42%, decreased aflatoxin contamination risk by to 0.03ppb (limits at national scale is 20ppb).
Extraction technique has significant impact upon polyphenols yield. Supercritical CO2 extraction (pressure 35MPa, temperature 55℃) could extract 92% of peanut polyphenols, while traditional ethanol reflux technique was only 65%. A biological technology company implemented an enzymatic hydrolysis and ultrasonic technology (cellulase concentration 1.5%, ultrasonic power 800W), and the extraction efficiency of proanthocyanidin B2 was improved from 0.8mg/g to 1.6mg/g, and the production cycle was shortened by 40%. Nano encapsulation technology (particle size ≤100nm) increased bioavailability of polyphenols by 5% to 32%, and Cmax was obtained at 1.8μg/mL (standard preparation alone 0.4μg/mL).
Application in food industry to verify its anti-corrosion activity. The peroxidation value (PV) of fortified vegetable oils (such as soybean oil) with 0.05% Peanut skin extract rose to as low as 8.2 meq/kg after storage for 180 days, compared to 23.5 meq/kg in the control sample. A meat processing factory used it to substitute nitrite (the amount added is reduced from 150ppm to 50ppm), the TBARS value of lipid oxidation product of sausage reduced by 67%, and the content of nitrosamine formation was < 0.5ppb (national standard is 30ppb).
Anti-aging information radiant. In clinical trials with 2% Peanut skin extract, skin elasticity (Cutometer) was enhanced by 31% and wrinkle density was reduced by 44% after 8 weeks. Its inhibitory tyrosinase activity (IC50=0.18mg/mL) was 37% greater than that of arbutin, and a whitening mask (3% extract) lowered melanin index (MI) from 68.3 to 42.1, which was superior to that of 4% nicotinamide product (MI dropped to 47.5).
The economic benefit is enormous. As a by-product of the peanut processing industry (worldwide annual yield is over 6 million tons), the cost of extracting polyphenols is only 12/kg (purity ≥9585/kg). A company utilizes peanut clothing waste to produce antioxidants, with the profit increased by 1,200 per ton and 90.47 billion yuan reduced, at an annual growth rate of 21.3%, of which 58% belongs to the sector of food preservatives.
Safety studies favor diverse applications. The oral LD50 of peanut coat extract in rats was > 5,000mg/kg, and the mutagenicity test (Ames test) was negative. It is licensed by the European Union EFSA as a food additive (E 296) with an acceptable daily intake (ADI) of 4 mg/kg body weight. A 12-week human trial of a 150mg extract/can energy drink lowered the oxidative stress marker 8-OHdG by 39% in subjects with no allergic reactions observed (sample size n=500).
Environmental sustainability is the focal point. For every ton of peanut coat, it can provide 45kg of high-purity polyphenols, and the carbon footprint (LCA study) is only 18% of chemical antioxidants. With a carbon-neutral project where petroleum-based preservatives were replaced by Peanut skin extract, the carbon footprint of packaging material for food was reduced from 1.2kg CO2/kg to 0.3kg CO2/kg and was awarded the Global Green Chemistry Award 2023.