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Effect of moisture content on glass transition and sticky point temperatures of sugarcane, palmyra-palm and date-palm jaggery granules

Sorption isotherms of sugarcane (SC), palmyra-palm (PP) and date-palm (DP) jaggery granules were obtained at 25 and 35 °C following isopiestic vapour transfer technique. Glass transition temperatures (Tg) and sticky point temperatures (Tsc) at different moisture contents were determined using DSC and rotational viscometer, respectively. All sorption isotherms fitted well to the GAB equation while no apparent difference in equilibrium moisture content (EMC) was seen among them at either of the temperatures. Tg values for dry granules were 316.89, 335.24 and 325.07 K for SC, PP and DP respectively. Tg could be predicted well with both Gordon and Taylor equation, and combined Gordon and Taylor and GAB equations. Tsc for palmyra-palm was highest (347.3 K), followed by DP (339.6 K) and SC (334.9 K). A generalised linear equation correlates Tg and Tsc. Critical moisture contents for SC, PP and DP are 1.0–2.0, 3.1–4.3 and 1.9–2.9% db, respectively.

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