Previous studies have shown that the use of a continuous microwave
system for blanching peanuts can reduce processing time, compared to
using a traditional hot air, multi-zone oven. However, at microwave
blanching temperatures exceeding 110 C, off-flavors can occur.
Scientists at North Carolina State University wanted to
characterize the chemical components responsible for the development of
off-flavors in peanuts caused by high-temperature microwave blanching.
The researchers conducted descriptive sensory analysis to characterize
the sensory differences between non-microwave blanched and
high-temperature microwave-blanched peanuts.
The investigators used solvent-assisted flavor evaporation (SAFE)
with gas chromatography olfactometry (GC-O) and GC-mass spectrometry
(GC-MS) techniques to extract, characterize and identify aroma-active
compounds in peanuts. Aroma extract dilution analysis (AEDA) was used to
select the compounds with the most potential flavor impact.
The off-flavor in high-temperature microwave-blanched peanuts was
characterized by certain sensory attributes--ashy, bitter, cardboardy
and stale. The researchers used AEDA to identify differences in the
number and intensities of compounds between the control and off-flavored
peanuts. More than 25 compounds were found in each sample with flavor
dilution factors between 5 and 10.
All samples contained nutty compounds, such as
2-ethyl-3,5-dimethylpyrazine and 2,3-diethyl-5-methylpyrazine;
chocolate-malty compounds like 2-methylbutanal; as well as rosy
compounds--phenylacetaldehyde. Off-flavor samples were characterized by
a larger number of compounds that imparted fatty and floral notes and
fewer compounds that imparted brothy and roasted notes.
The combination or concentrations of these compounds may be
responsible for the off-flavor that develops in high-temperature
microwave-blanched peanuts. Being able to chemically identify this
off-flavor will ultimately aid in the development of an alternative
blanching method for peanuts using microwave technology.
Further information. Timothy Sanders, Department of Food Science,
North Carolina State University, 120 Schaub Hall, Box 7624, Raleigh, NC
27695; phone: 919-515-6312; fax: 919-515-7124; email:
tim_sanders@ncsu.edu.
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