Changes in Viscoelastic Properties of Longan During Hot-Air Drying
Jatuphong Varith, Chanisara Oochauay, Tipaporn Khamdang, Adisorn Ponpai
Proceedings: Abstract Summary, International Conference on Agricultural, Food and Biological Engineering & Post Harvest/Production Technology, Sofitel Raja Orchid Hotel, Khon Kaen, Thailand, 21-24 January 2007. 204 p.
2007
บทคัดย่อ
Changes in viscoelastic properties are relevant to indentation of unpeeled longan (Dimocarpus Longan Lour.) in the drying process. The objective of this research was to determine the parameters from creep test to characterize viscoelastic properties of longan during a hot-air drying process. During drying with 65 °C hot air, the unpeeled longan was sampled every 2 hours to perform a creep test with a constant stress of 4.4 N/cm2 using the texture analyzer. Viscoelastic properties, such as retardation time )λret.( instantaneous compliance )J0,( retarded compliance )J1,( creep compliance)J ,(Newtonian viscosity )η(, and modulus of elasticity )E were analyzed using a six element Burger's model. Results showed that λret and E linearly decreased as moisture content decreased, from approximately 70% to a range of 64-57%(w.b.). Then, λret and E linearly increased as moisture content decreased from a range of 64-57% to 11% (w.b.). The J and J1 values linearly increased and then linearly decreased as moisture content decreased, yielding a transition moisture content of 64% (w.b.). The Jo value decreased as moisture content decreased. The η value did not markedly change, thus it did not involve the indentation of dried longan. The moisture content of 64 to 57% (w.b.) was a critical range susceptible to indentation of the longan during drying process.