Microwave blanching impacts flavor compounds in peanuts.

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: [phone]; fax: [phone]; email: [e-mail].