Chemical composition of volatiles from coconut sap (neera) and effect of processing

摘要

Volatiles from (ⅰ) fresh, (ⅱ) clarified and (ⅲ) fermented coconut sap neera were isolated by a simultaneous distillation and solvent extraction method using a Likens-Nikerson apparatus and subjected to GC-MS analysis for identification of chemical constituents. Twenty-one compounds (5.33 ppm), constituting more than 98% of the volatiles from fresh neera, were characterised. Typical major flavour compounds found in volatiles of fresh neera were ethyl lactate, phenyl ethyl alcohol, ethyl lactate, 3-hydroxy-2-pentanone, farnesol, 2-methyl tetrahydrofuran, and tetradecanone. Clarified neera contained lower quantities of volatiles, in which 13 compounds (1.31 ppm), constituting more than 97%, were identified. However, the typical flavour components retained were ethyl lactate, phenyl ethyl alcohol, 1-hexanol, 2-methyl tetrahydrofuran, 3-hydroxy-2-pentanone and 2-hydroxy-3-pentanone. Fermented neera contained a greater quantity of volatiles, in which 12 compounds (37.4 ppm), representing more than 95% of the volatiles, were characterised. Ethyl lactate, phenyl ethyl alcohol and farnesol were among the seven compounds retained from fresh neera. The astringency and harsh note of the fermented neera could be due to the increased amounts of acids (19.0 mg/l), such as palmitoleic acid and dodecanoic acid, along with higher concentrations of ethyl alcohol and ethyl esters.