Sakin-Yilmazer Melike, Dirim S Nur, Di Pinto Davide, Kaymak-Ertekin Figen
Faculty of Engineering, Department of Food Engineering, Ege University, 35100 Bornova, Izmir Turkey.
J Food Sci Technol. 2014 Dec;51(12):3949-55. doi: 10.1007/s13197-012-0890-x. Epub 2012 Nov 17.
As a novel product, yoghurt powder was produced by freeze drying and with added candied chestnut puree at ratios of 5, 10, and 20 % by weight. During the freeze drying process, mass loss, water activity, and the moisture content of the samples were determined and the colour (Hunter L, a, b) of the yoghurt powder products was measured. Results showed that increasing the percentage of candied chestnut puree resulted in an increase in water activity, moisture content, and colour change values of the end product. The drying behaviour, drying rate versus free moisture content, was also investigated. It was observed that yoghurt with or without added candied chestnut puree could be satisfactorily freeze-dried. Moreover, the performance of the dried product was observed in a ready-to-use, reconstituted form. For this purpose, the obtained powders were reconstituted to their original moisture contents. Shear stress and apparent viscosity against shear rate in a range of 1-1,000 (1/sec) was then measured by a Haake-Mars rotary viscometer. According to the results, the apparent viscosities of reconstituted products, as plain yoghurt and the one with an added 5 % chestnut puree were lower than that of fresh yoghurt. However, reconstituted yoghurts containing 10 % and 20 % chestnut puree had apparent viscosities higher than fresh yoghurt. Power Law explained well the rheological behaviour of reconstituted yoghurt samples for the applied shear rate range. Based on rheological data and sensory analysis, it was concluded that the freeze dried yoghurt containing 10 % (w/w) candied chestnut puree was an acceptable novel product.
作为一种新产品，酸奶粉通过冷冻干燥制成，并添加了重量比为5%、10%和20%的糖渍栗子泥。在冷冻干燥过程中，测定了样品的质量损失、水分活度和水分含量，并测量了酸奶粉产品的颜色（亨特L、a、b值）。结果表明，增加糖渍栗子泥的百分比会导致最终产品的水分活度、水分含量和颜色变化值增加。还研究了干燥行为，即干燥速率与自由水分含量的关系。观察到添加或未添加糖渍栗子泥的酸奶都能令人满意地进行冷冻干燥。此外，还观察了干燥产品以即用型复水形式的性能。为此，将获得的粉末复水至其原始水分含量。然后用哈克-马尔斯旋转粘度计测量在1-1000（1/秒）范围内的剪切应力和表观粘度与剪切速率的关系。根据结果，复水后的纯酸奶产品以及添加了5%栗子泥的产品的表观粘度低于新鲜酸奶。然而，含有10%和20%栗子泥的复水酸奶的表观粘度高于新鲜酸奶。幂律很好地解释了在所施加的剪切速率范围内复水酸奶样品的流变行为。基于流变学数据和感官分析，得出结论，含有10%（w/w）糖渍栗子泥的冷冻干燥酸奶是一种可接受的新产品。
