| Summary: | 碩士 === 國立臺灣大學 === 園藝學研究所 === 89 === Hsian-tsao has been a popular herb used for food and folk medicine in Taiwan. The alkali extract of hsian-tsao herb forms jelly with the addition of food starch which make it a popular dessert in the summer time. The objectives of this study are: (1) to compare the hsian-tsao flavor volatiles obtained from different extraction method; (2) to identify flavor impact compounds of hsian-tsao extracts; (3) to investigate the effect of pH on the constitution and amount of flavor volatile in the extracts; (4) to compare the difference of flavor volatiles among the hsian-tsao extracts which the dried herbs have been stored for one year and five years; (5) to investigate the differences of flavor compositions between open-air and airtight extraction methods.
Comparison of the extraction methods, which included Amberlite XAD-2 adsorption, headspace purge-and-trap method, and solid-phase microextraction using by three adsorption fibers, steam distillation-solvent extraction demonstrated it capability of obtaining the highest flavor volatiles. Five esters、seven aldehydes、sixteen ketones、six alcohols、three acids、fifty-eight hydrocarbons, and seven miscellaneous compounds were identified from the hsian-tsao extract from a five-year storage herb with 0.5% Na2CO3 solution (SC-5). Among the identified compounds, hexanal、2-pentyl furan、1-octen-3-one and 2-octenal have also been identified as impact compounds using Gas Chromatography-Olfactometry (GCO). They present the characteristic aroma of fresh, green grass and mushroom sweet of the hsian-tsao extract sample.
Little qualitative difference of the flavor compounds were found among the extracts obtained from 0.5% Na2CO3 solution (pH =11)、water (pH =6) and pH5.0 buffer solution extractions, however quantitative differences are significant. Volatile compounds extracted by different pH solutions were in the order of 0.5% Na2CO3 solution (pH =11)>pH5.0 buffer solution>water (pH =6). The flavor of 0.5% Na2CO3 solution extract is also favorable by panelists under preference sensory test.
Both extracts from one-year storage hsian-tsao herb and five-year storage herb have little difference qualitatively among different pH solution. Quantitatively, water extract of one-year storage herb contains twice as much flavor volatiles as five-year storage herb. The results of sensory evaluations show that one-year storage hsian-tsao possess fresh and green grassy flavor, five-year storage herb smells mild and pleasant hsian-tsao jelly flavor and is favorable by the panelists.
In comparison of open-air and airtight extraction, little difference is found qualitatively. Quantitatively, airtight extraction resulted in twice as much flavor volatiles as compared to open-air extraction. Sensory results indicate the flavor of open-air extract is more favorable to airtight extract.
In conclusion, one-year storage dried hsian-tsao herb with 0.5% Na2CO3 solution under airtight extraction obtained the hightest quantity of flavor volatiles. However, five-year storage herb extracted with 0.5% Na2CO3 solution under open-air extraction resulted in better flavor of hsian-tsao extract.
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