HYDROLYSIS OF GINGER (ZINGIBER OFFICINALE ROSCOE) STARCH: SEARCH FOR PROCESS CONDITIONS USING THE SURFACE RESPONSE METHODOLOGY

摘要

The use of subcritical water hydrolysis can considerably decrease the reaction time for several systems. Ginger (Zingiber officinale) besides being a source of volatile oil and oleoresin has as much as 40% of starch. In the present work subcritical water was used to hydrolyze the ginger starch after the solid matrix was subjected to SFE using CO_2 and mixtures of CO_2 + ethanol or CO_2 + isopropyl alcohol. Because no information related to this system ginger starch + H_2O + CO_2 was found in literature, the surface response methodology was used to identify the best operation temperature and pressure. The reactions were carried out in a Spe-ed unit; the reactor mixture consisted of ginger bagasse with 30 % of water (mass); the reaction time was held constant at 15 minutes. The search for the best temperature and pressure started using a factorial experimental with 2 levels of pressure (100 and 200 bar), two levels of temperature (140 and 180℃) and a central point (150 bar and 160℃); the assays were made in triplicates and quintuplicate at the central point; the axial points were done at 132 and 188℃ and 80 and 220 bar. The reaction products were characterized with respect to the content of starch and reducing sugar. The maximum amount of reducing sugar was detected at 188℃ and 150 bar while the largest amount of hydrolyzed starch was obtained at 180℃ and 200 bar. These results indicate that part of the reducing sugar is being transformed to other reaction products such as furfural compounds, acids and gases.