Characterization of Volatile Compounds in Raw, Boiled and Roasted African Walnuts (Tetracarpidium conophorum)

Abstract

The volatile constituents of African walnuts play an important role in the flavour quality characteristics of this nut. Research on African walnut volatiles is very limited (raw, boiled, and roasted), thus this research study was undertaken. In this study, volatile aroma components of boiled and roasted African walnuts were analyzed using gas chromatography-mass spectrometry (GC-MS) in comparison with the volatiles from raw African walnut. A total of 150 volatiles were identified in raw, boiled and roasted African walnuts. Among these were 70% amines, 4% esters, 2% acids, 6% amides, 2% aldehydes/ketones and 16% other additional compounds in raw African walnuts. For the boiled sample the compounds identified include 58% amines, 2% esters, 12% amides, 2% aldehydes/ketones, 2% sulphur-containing compounds and 24% other compounds while the roasted African walnuts had 10% amines, 2% esters, 4% pyrazines, 24% amides, 14% aldehydes/ketones, 8% sulphur-containing compounds and 38% additional compounds identified. The predominant volatile compound identified in raw and boiled African walnuts were the amines (70% and 58%, respectively) followed by amides (6 and 12%) and esters (4 and 2%). Acids (2%) were identified only in the raw African walnuts. Pyrazines (4%) were only detected in the roasted African walnuts. The major volatile components of raw African walnut, the isobutylamine (amine) increased consistently at different retention times.

Key words: African walnut, raw, boiled, roasted, volatiles.