engleski

Effects of different processing and preservation methods on some properties of sweet potato puree and powder

The aim of the study was to investigate the effects of thermal treatments, baking and steaming, of orange and purple-fleshed sweet potato cultivars (Ipomea batatas) on thermal behaviour of purees before and after freezing, and after freeze-drying. In addition, total and soluble solids, water activity and colour of sweet potato purees and powders were also determined. The results showed that purees prepared from baked orange and purple-fleshed sweet potatoes had higher total (19.11 and 29.15%) and soluble solids (11.11 and 14.15%), which contributed to the lowest freezing-Tfp (-13.20 and -17.52 °C) and melting peak temperatures-Tmp (3.44 and 2.10 °C), respectively. Purees made from steamed orange and purple-fleshed sweet potatoes had Tfp -12.10 and -14.44 °C, and Tmp 4.91 and 3.25 °C, respectively, and purees made from orange and purple-fleshed raw tubers had Tfp -11.83 and -13.93 °C, and Tmp 5.88 and 3.41 °C, respectively. Regardless the processing method, freeze-dried purple-fleshed sweet potato had higher glass transition temperatures (Tgmid), ranged from 41.27 to 42.06 °C, in comparison with freeze-dried puree made from orange-fleshed sweet potato (36.99 to 38.34 °C). The highest change in colour (ΔE) was observed in freeze-dried powders prepared from steamed orange (24.42) and baked purple-fleshed (15.53) sweet potatoes.

sweet potato, freezing, freeze-drying, thermal behaviour, colour

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