INFLUENCE OF ROASTING CONDITIONS ON VOLATILE FLAVOR OF ROASTED MALAYSIAN COCOA BEANS

ABSTRACT In this study, commercial Malaysian cocoa beans (SMC1A) were roasted in a forced airflow‐drying oven for 20, 30, 40 and 50 min at 120, 130, 140, 150, 160 and 170C. The products were evaluated for flavor compounds and sensory evaluation (as dark chocolate). The volatile fraction was isolated using the combined steam distillation–extraction procedure and was identified by gas chromatography–mass spectrometry. A quantitative descriptive analysis was used to evaluate the flavor intensity of the chocolates using a 9‐point rating scale for selected flavor attributes, namely astringency, bitter taste, sour taste, cocoa and burnt. Panelists were asked to smell and taste the sample against a standard chocolate. It was found that there were significant differences in flavor compounds between the different conditions of roasting. The main flavoring compounds identified composed of aliphatic and alicyclic groups such as alcohol and ester, and heterocyclic groups such as pyrazine and aldehyde. A total of 19 volatile major components were identified: nine pyrazines (2,5‐dimethyl‐, 2,3‐dimethyl‐, 2‐ethyl‐6‐methyl‐, trimethyl‐, 3‐ethyl‐2,5‐dimethyl‐, tetramethyl‐, 2‐ethenyl‐6‐methyl‐ and 3,5‐dimethyl‐2‐methylpyrazine); five aldehydes (5‐methyl‐2‐phenyl‐2‐hexenal, benzaldehyde, benzalacetaldehyde and α‐ethyliden‐benzenacetaldehyde); one methyl ketone (2‐nonanone); two alcohols (linalool and 2‐heptanol); and two esters (4‐ethylphenyl acetate and 2‐phenylethyl acetate). Based on the flavor profile of the compounds identified, an optimum production of the major flavoring compounds such as pyrazine, aldehyde, ketone, alcohol and ester occurred at 160C for 30 min of roasting. Trimethylpyrazine and tetramethylpyrazine compounds together with 5‐methyl‐2‐phenyl‐2‐hexanal were found to be good indicators for the evaluation of the roasting process. However, based on chocolate evaluation, the best roasting temperature was 150C for 30 min, which gave the lowest astringency and at the same time gave the lowest bitter taste and low level of sour and burnt tastes. At 150C roasting temperature, the desirable cocoa flavor was at its optimum. Correlation coefficients among certain volatile flavor and sensory characteristics of cocoa beans and dark chocolate were significant (P