CHARACTERISATION OF VOLATILE COMPOUNDS OF COCOA HUSK USING HEADSPACE SOLID-PHASE MICROEXTRACTION AND GAS CHROMATOGRAPHY-OLFACTOMETRY ANALYSIS

Abstract

Cocoa seeds (Theobroma cacao L.) are known for their variety of products exhibiting pleasant sensory properties. Cocoa husk is a residue from the cocoa industry which can be used as flavoring material. A headspace solid-phase microextraction (HS-SPME) procedure followed by gas chromatography-olfactometry (GC-O) analysis is proposed to determine aroma-active compounds in cocoa husk. To determine optimal extraction conditions of the HS-SPME technique: fiber type (100 µm polydimethylsiloxane, 85 μm Carboxen/polydimethylsiloxane, 65 μm polydimethylsiloxane/divinylbenzene and 50/30 µm divinylbenzene/Carboxen/polydimethylsiloxane), extraction time (15, 20 and 25 min) and temperature (40, 50 and 60 oC) were evaluated using surface response design. Response variables were global odor from the fibers and total chromatographic areas. GC-O in combination with HS-SPME using divinylbenzene/Carboxen/polydimethylsiloxane fiber operated at 60 oC for 22 min could isolate most of the volatile compounds from cocoa husk. A total of 169 of them were identified, including 28 acids, 23 esters, 22 pyrazines, 16 terpenes, 12 ketones, 8 alcohols, 3 aldehydes, among others. Among them, the most odor-active compounds were acetic acid, 2,3-diethyl-5-methylpyrazine, 2-ethyl-3,5-dimethylpyrazine, 3-methylbutanal, phenylacetaldehyde, 3,5-diethyl-2-methylpyrazine, 4-hidroxy-2,5-dimethyl-3(2H)-furanone, 3-methylbutanoic acid, 2-ethyl-5-methylpyrazine, 2,6-dimethylpyrazine, dimethyl trisulfide, 2,3,5,6-tetramethylpyrazine, 2,3,5-trimethylpyrazine, 2-methylbutanal, 2-methylpyrazine, 2-phenylacetic acid, linalool, butanoic acid, 2-methylbutanoic acid, 2,5-dimethylpyrazine and 2-phenylethyl acetate. The present method may be applied as a quality control tool for industrial laboratories.