Effect of far-infrared drying on the water state and glass transition temperature in carrots

• The Tg and water state in carrot tissues were explored using DSC and NMR.
• With increasing time, FID caused changes in the water state in dehydrated carrots.
• FID caused a shift from free water to immobilized water in carrot tissues.
• FID could elevate Tg values mainly by reducing immobilized water in carrot tissues.

The effect of far-infrared drying (FID) on the water state and glass transition temperature (Tg) of carrots were assessed by nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). Results showed that, with increasing time, FID caused dramatic changes in the water state in dehydrated carrots. The drastically decreased content of free water in vacuoles was accompanied by sharp increases in the content of immobilized water in the cytoplasm and extracellular space. Subsequently, the content of immobilized water decreased gradually with increasing time. FID elevated the Tg values appreciably by decreasing the content of immobilized water in carrot tissues. In carrots with moisture content <0.39 g/g dry matter, Tg values were increased by 21.36, 35.55 and 40.99 °C with the moisture content decreased by 0.20, 0.25 and 0.30 g/g dry matter at respective infrared power values of 400, 600 and 800 W.