Effect of processing on flavor precursor amino acids and volatiles of sesame paste (tehina)
1997
Shahidi, F. | Aishima, T. | Abou-Gharbia, H. A. | Youssef, M. | Shehata, A. Adel Y.
The content of flavor precursor free amino acids in dehulled sesame seeds, subjected to roasting (R), steaming (S), roasting plus steaming (RS) and microwaving (M), was determined and compared with those of the raw (RW) seeds. R, RS, and S had major effects in reducing the content of free amino acids from 2360 μg/g to 582, 795 and 884 μg/g, respectively; M had no effect on the content of free amino acids. Meanwhile, flavor volatiles of the raw and processed seeds were compared by means of a dynamic headspace analyzer/gas chromatograph-mass spectrometer. Volatiles of RW seeds contained 85 compounds, whereas under the analytical conditions employed, seeds subjected to R, RS, S, and M had 117, 97, 93 and 87 compounds, respectively. Among volatiles identified in the RW seeds were 36 hydrocarbons, 8 aldehydes, 4 ketones, 8 alcohols, 2 acids, 2 esters, and 1 pyrazine. The only pyrazine identified in the RW seeds was 2,5-dimethylpyrazine. Pyrazines, generally recognized as contributors to the roasted aroma of foods, were more numerous (10 in R, 6 in RS, 2 in S, and 2 in M) and prevalent (8.71% in R, 2.97% in RS, 2.04% in S, 0.53% in M, and 0.25% in RW) in the volatiles of processed sesame seeds. The chemical nature of pyrazines also depended on the process employed. Multivariant analysis indicated a highly negative correlation between the loss of free amino acids and production of volatile flavor compounds in the R and RS samples, while the M sample remained unchanged. Furthermore, both R and RS seeds contained dimethyl sulfide and dimethyl disulfide, whereas no sulfur-containing compounds were present in other samples. Of the processed seeds, the flavors of R and RS samples were considered as acceptable, and the flavor intensity of the former was deemed stronger than that of the latter by the experimenters.
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