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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVEMENT & MAINTENANCE OF FLAVOR & SHELF-LIFE, FUNCTIONAL CHARACTERISTICS & BIOCHEM/BIOACTIVE PROCESS, & USE OF GENETIC/GENOMIC RESOURCE

Location: Market Quality and Handling Research

Title: Evaluation of Oil from Roasted Peanut Skins

Authors
item Hathorn, Chellani -
item Dean, Lisa
item Sanders, Timothy

Submitted to: Institute of Food Technology
Publication Type: Abstract Only
Publication Acceptance Date: June 8, 2012
Publication Date: N/A

Interpretive Summary: In order to determine if other uses are possible for peanut skins other than animal feed, the oil present in the skin was characterized. After grinding to reduce the size of the skin material, the oil was removed using cold hexane. The hexane was evaporated and the remaining oil was tested. Although the fatty acid present were nearly identical to those found in peanuts themselves, there was very little vitamin E in the oil from the skins. This is very different from the amount of vitamin E normally found in whole peanuts. Also, the stability of the oil from peanut skins was much less than that of whole peanuts when oxygen was introduced. This indicates that peanut skins may cause rancidity problems when used added back to peanut products at higher levels than is naturally found.

Technical Abstract: The skins from peanuts are a low-value material from peanut processing and literature suggests it is an excellent source of phenolic compounds. Peanut skins do not have any significant uses other than as a small component of animal feed. Studies indicate that the compounds in the skin have high antioxidant activity, while little is known specifically about the oil composition from these skins. The purpose of this research was to evaluate peanut skins and oil from the skins. Roasted peanut skins were ground using a Thomas Wiley laboratory mill fitted with a 0.5 mm sieve. The color, moisture content, oil content, fatty acid profile and tocopherols were determined. Oxidative stability index was used to determine the resistance of the oil to oxidation. The color (L value), moisture and oil content were 28.6, 7.6% and 11.9%, respectively. Cold solvent extracted oil was used for all analyses. The fatty acid profile of the oil from the skins was similar to published findings on peanut oil. Specifically, the oil contained 55.6±0.3 and 23.2±0.2 g/100g of oleic and linoleic acid, respectively. Alpha-tocopherol was not detected, while beta, gamma and delta-tocopherols were present at 53.0±0.5, 57.1±0.5, and 13.6±1.1 mcg/g, respectively. These results were unexpected since peanut oil typically has a higher concentration of alpha-tocopherol. Gamma-tocopherol was present in the highest concentration in the oil from peanut skins. Oxidative stability index was very low at 1.7 hrs. These findings indicate that oils in peanut skins and the seed have similar fatty acid profiles, while tocopherols and oxidative stability were different from peanut oil.

Last Modified: 4/24/2014
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