Volume changes, food materials

Tab. 9.3 Some correlations for the change of volume of food materials during microwave-assisted drying (see volume and chapter notation for symbols).

The second term between parentheses is a measure of the change in volume v upon application of a tensile stress on the material. The relative volume change is quite small for most solid foods, implying that the Poisson ratio is close to 0.5, leading to Eu = 3G, etc. Foods of a spongy nature, like bread crumb, may have /i close to zero. 

Bonazzi, C., Dumoulin, E. (2011). Quality changes in food materials as influtaicedby drydng processes. In E. Tsotsas A. S. Mujumda (Eds.), Modern drying technology. Volume 3 Product quality and formulation (Chapter 1) (pp. 1-20). Weinheim Wiley-VGH. 

Saponification. Before solvent is added for extraction, saponification (alkaline hydrolysis) is a step used in most extractions of tocopherols and tocotrienols. It should be noted that acetate forms of tocopherols or tocotrienols in a sample are changed to free tocopherols and tocotrienols after saponification. This process breaks down the ester bonds of lipids and sample matrices as well. In most extraction procedures, a 60% to 80% (w/v) aqueous solution of KOH is used to perform the saponification. The volume of KOH required varies according to the amount of lipid contained in the sample. Also, ethanol is needed to stabilize the saponified solution and prevent the precipitation of soap material. Usually, the ratio of KOH, ethanol, and fat (in sample) during saponification is 3 (g) 15 (ml) 1 (g), respectively (Ball, 1988). The ratio may need to be adjusted based on the types of fats in the sample. Although ethanol concentration has no effect on the extraction of a-tocopherol by hexane, a concentration above 30% may cause lower recoveries of other tocopherols (Ueda and Igarashi, 1990). For most food samples, saponification for 30 min at70°C is sufficient. 

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