Mill RotovapExtraction Filter
EtOH DI water Retentate EtOH
Conversion of peanut skins, a current waste product, into a value-added ingredient
Chete, J.E., Orabone, E.L., Peatross, B.T., Troutman, C.A.
Data & Discussion
Peanut skins are a waste product and have virtually no value to
peanut processors. However, peanut skins are a rich source of
antioxidants which could be used in foods for added health benefits
or to prevent oxidative degradation. In this research, antioxidants
were successfully extracted from peanut skins with a 70% ethanol-
water solution, concentrated by removing the ethanol at 68°C with
a Rotovap, and then spray-dried using a laboratory spray dryer with
an inlet temperature of 160°C and an outlet temperature of 90°C.
The resulting powder was found to have an Oxygen Radical
Absorbance Capacity (ORAC) value comparable to other naturally
occurring agricultural sources high in antioxidants. The final product
has the potential to create another revenue stream for the peanut
industry, as well as to provide a way to add natural antioxidants to a
variety of food systems.
• Peanut seeds are surrounded by a thin, papery layer known as the peanut skin or
testae, which are removed during peanut processing by blanching or roasting.
• Current world production of peanut skins reaches 750,000 tons annually with a value
of approximately 15 cents per ton.
• Peanut skins are a good source of certain phenolic compounds which are excellent
antioxidants (Nepote et al., 2004).
• Food companies currently use synthetic antioxidants in their products because of price
and availability but because of health concerns, natural antioxidants are becoming more
• Natural antioxidants have the potential to be extracted and spray dried and could be
converted into a nutraceutical ingredient. While research has been done on antioxidant
extraction and consequent spray drying from several foods, no work has been
performed with peanut skins or with applying the final products to food systems as a
value-added nutraceutical ingredient.
• If natural antioxidants can be successfully extracted for use in foods, not only will the
value of peanut skins increase, but food companies will also have a better opportunity
to add health benefits to their foods and increase preservation techniques.
Nepote, V.; Grosso, N.R.; Guzman, C.A. Optimization of extraction of phenolic antioxidants from peanut
skins. Journal of the Science of Food and Agriculture [Online] 2004, 85, pp 33-38.
"Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods – 2007." USDA, Nov. 2007. Web. 20 Apr.
Goals & Objectives
Goal: To determine the feasibility of extracting and spray drying antioxidants from
1. Determine protein, oil, ash, and carbohydrate content of raw peanut skins and final
spray dried product.
2. Extract antioxidants from raw peanut skins using ethanol/water solvent.
3. Spray dry extraction to yield a powder, water-soluble product.
4. Measure antioxidant capacity for raw peanut skins and final spray dried product via
the ORAC assay.
1. Determine the relative allergenicity for raw peanut skins and the final product via
2. Determine which specific antioxidants are present in raw peanut skins and final
product via HPLC testing.
3. Conduct sensory analysis to document flavor profiles of the final product.
4. Add final product to a food system to determine plausibility of the application.
• Peanut skins were milled in a Model 4 Thomas-Wiley Laboratory Mill.
• Skins were then extracted in a 70% ethanol in water solution at a 5% extraction weight (5% milled skins, 95% solvent by weight).
• Vacuum filtration with Whatman # 4 paper filter was determined to be sufficient in removing all visible particulates, which were
removed as a retentate.
• A rotary evaporator (Büchi Rotovapor R-124) was used to remove ethanol from the solution.
• Before spray drying, maltodextrin was added to one repetition at a weight ratio of 4:1 (maltodextrin to total solids in solution).
• The Büchi Mini B-290 spray drier was used to spray dry one repetition with maltodextrin and one without. The temperatures that
were set for the spray drying process were an inlet temperature of 160°C and an outlet temperature of 90°C.
• Various assays were performed throughout the procedure such as, total suspended solids, density, total antioxidant capacity
through the Oxygen Radical Absorbance Capacity (ORAC) assay, total phenolic content, solubility, and amino acid content.
Contact us! JUSTIN CHETE: email@example.com ELLEN ORABONE: firstname.lastname@example.org BRETT PEATROSS: email@example.com COREY TROUTMAN: firstname.lastname@example.org
Clockwise starting with bottom left:
Extraction solution; Anatomy of a peanut,
with bag of milled skins; Rotovap;
Laboratory-scale spray dryer; Vacuum
filtration; Milled skins and spray dried
product without and with maltodextrin.
Acknowledgments: Dr. Jack Davis, Dr. Lisa Dean, and the entire USDA Peanut Lab at NC State, Dr. Brian
Farkas and the TAs for FS 475, Barrow-Agee Labs, NC State Soil Science Department
• Since there was no previous work with the extraction and spray drying of peanut skins,
the most important conclusion to take away from this project is that it is in fact possible
to concentrate antioxidants from peanut skins.
• The composition of the peanut skins and the spray dried final product was found
through proximate analyses, which will aid in the process of adding the product to food
• Further analysis of the final product, such as allergenicity testing and sensory testing,
will allow researchers to determine a food application.
Figure 3: ORAC comparison between different food samples
The data for milled peanut skins was determined by research performed in the USDA Peanut Laboratory in
Raleigh, North Carolina. Values for blueberries, chocolate powder, and ground cinnamon were determined
by the USDA (USDA, 2007). The spray dried products’ values are based on a gram for gram powder weight
basis, and therefore the product with maltodextrin was expected to have a much lower ORAC value.
ORAC Value Comparison
Figure 1: Methods to extract and spray dry antioxidants found in peanut skins.
Table 2: Solubility for a 2% solution for different treatments
Treatment % Solubility
Spray Dried Product 88.9 ± 1.0
Spray Dried Product with Maltodextrin 93.7 ± 0.8
Maltodextrin Alone 93.3 ± 2.0
36 g H2O
364 g solids
880 g H2O
220 g solids
105 g H2O
25 g solids
Powder + MD
Milled Peanut Skins Spray dried, no
Spray dried, with
Blueberries Chocolate, dutch
Table 1: Proximate analyses of milled skins, spray dried product with & without
% Moisture % Fat % Protein % Fiber % Ash % Carbohydrates Water Activity
Milled 8.9 17 16 19 1.5 57 0.54
Spray Dry 6.5 1.8 0.24
Spray Dry w/ Malto 4.1 0.5 0.14
• As the product is spray dried, the protein content decreases as well as the probability
• Increasing the solubility of the spray dried product will allow for an wider range of
Figure 2: Mass balance for experimental design.
• The extraction and spray drying procedure concentrated the antioxidants significantly.
Even compared to foods commonly associated with antioxidants, the final product has a
much higher ORAC value.