Roasting Does More than Enhance Flavor in
Peanuts By Rosalie Marion Bliss
December 8, 2009
Agricultural Research Service
(ARS) scientists have shown that increasing roast color intensity steadily
ramps up the antioxidant capacities of peanuts, peanut flour and peanut skins.
The study was conducted by food technologist
P. Davis and his colleagues in the ARS
Quality and Handling Research Unit in Raleigh, N.C. ARS is the principal
intramural scientific research agency in the
U.S. Department of
The researchers characterized changes in antioxidant levels of roasted
peanuts and the
corresponding blanched skins across an industrially relevant range of
roast treatments. For the study, peanuts were incrementally roasted at 362
degrees Fahrenheit from zero to 77 minutes. The water- and oil-soluble
antioxidant activity levels of the roasted peanut product samples were then
Dark-roasting consistently increased water- and oil-soluble
antioxidant capacities for both commercially available peanut flours and
blanched peanuts. Peanut skins, currently considered a waste product of
industrial peanut processing, had remarkably high antioxidant capacities across
all roast conditions.
These antioxidant increases upon roasting were attributed to greater
concentrations of phenolic compounds and/or "browning" reaction products. The
latter result from thousands of complex chemical reactions in which proteins
and sugars interact, ultimately resulting in brown pigmentation. These
reactions, collectively termed Maillard browning, are also thought to
contribute in part to the characteristic flavor of roasted peanuts.
The researchers also measured vitamin E in the roasted peanuts.
Vitamin E degradation was most rapid in oil from lightly roasted peanuts;
however, oil from darker roasted peanuts had better vitamin E retention than
that of lightly roasted or even raw peanuts. This preservation of vitamin E
could be due to the increased concentration of oil-soluble Maillard reaction
products, which seem to protect vitamin E from oxidation.
While darker roasted peanuts are inappropriate for some applications
due to sensory considerations, these materials are utilized to prepare, for
example, darker roasted peanut flours and flavor extracts. The study expands
the fundamental knowledge of roasting as it relates to the antioxidant capacity
of peanuts and peanut ingredients, according to the authors. Davis reported the