植物 化学 英文 外文 文献翻译 热烫和干燥过程中山药粉颜色和功能特性的变化.doc

How blanching and drying affect the colour and functional characteristics of yam (Dioscorea cayenensis-rotundata) flour No?l Akissoé, Joseph Hounhouigan, Christian Mestresb, Mathurin Nagoa Abstract: Colour and texture are important features of amala, a traditional thick paste obtained from dry yam flour. Tubers from eight yam cultivars were blanched at 65 °C for 20 min and dried at 40 °C for 5 days to test biochemical, thermal and pasting changes occurring during traditional yam flour processing. Blanching reduced peroxidase activity and drying reduced polyphenoloxidase activity, but total phenol content and the brown index of flour and of amala increased dramatically during the latter operations. The brown index of amala was significantly correlated with the total phenol content of the flour (r = 0.84) and the peroxidase activity of the fresh tubers (r = 0.75). Amylose content and starch gelatinization enthalpy remained stable. For all cultivars, drying significantly increased the onset gelatinization temperature, suggesting the occurrence of starch annealing. The latter leads to a reduction in swelling power and solubility during pasting, and hence to a lower paste viscosity. @2003 Elsevier Science Ltd. All rights reserved. Keywords: Yam; Phenols; Polyphenoloxidase; Peroxidase; Blanching; Viscosity 1 Introduction Yams (Dioscorea spp.) are an important source of carbohydrate for many people of the sub-Sahara region, especially in the yam zone of west Africa. To overcome the high perishability of fresh yam tubers, due to their high moisture content and the seasonal nature of their production, in some west African countries (Benin and Nigeria) yams are processed into flour using a well established method. Tubers are peeled, sometimes sliced, blanched in hot water (around 65 ℃ for 15–50 min) and sun-dried (Akissoé, Hounhouigan, Bricas, Vernier, Nago, Olorunda, 2001). The resulting dried tubers or chips are then milled into flour, which is used to make a thick paste