Dept. of Food, Bioprocessing and Nutrition Sciences, North Carolina State Univ., Box 7624, Raleigh, NC 27695, USA.
J Food Sci. 2013 Feb;78(2):C145-51. doi: 10.1111/1750-3841.12036. Epub 2013 Jan 18.
The ability of food gels to hold water affects product yield and organoleptic quality. Most researchers believe that water is held by capillarity such that gels having smaller mean pore diameter and a more hydrophilic surface hold water more tightly. To date, however, only qualitative evidence relating pore size to water holding (WH) properties has been provided. The present study sought to provide quantitative confirmation of this hypothesis. Scanning electron microscopy coupled with image analysis was used to measure pore size, and water contact angle with the gel surface was measured by the captive bubble method, in both model polyacrylamide gels and heat-induced protein (minced chicken breast) gels. These were related to water lost during cooking of meat pastes to form gels (cooking loss (CL)), as well as water lost upon centrifugation (expressible water (EW)) or by capillary suction (CSL) of all prepared gels, as inverse measures of WH. As predicted by the Young-Laplace equation for calculating capillary pressure, the presumed mechanism of WH, gels with lower water losses exhibited a more hydrophilic surface (smaller contact angle). Yet, both lower CL and CSL correlated with larger mean pore diameter of gels, not smaller as had been expected. Polyacrylamide gels varied more in WH than did prepared meat gels, yet only the capillary suction method was sensitive enough to detect these differences.
The ability of gels to hold water is important for economics of processing, food quality, and food safety. This study investigated the prevailing theory for how gels hold water, capillarity. Both the pore sizes of gel microstructures and the degree of hydrophilicity of the polymers comprising each gel were quantitatively assessed and related to water holding (WH) properties, and this was the first report using such methodologies. It appeared that the degree of hydrophilicity was much more important explaining WH properties than pore size, and that future research of this kind should be carried out.
食物凝胶保持水分的能力会影响产品的产量和感官质量。大多数研究人员认为，水分是通过毛细作用保持的，因此具有较小平均孔径和更亲水表面的凝胶能更紧密地保持水分。然而，到目前为止，只有与保水（WH）性能相关的孔径的定性证据。本研究旨在提供对这一假说的定量确认。通过扫描电子显微镜结合图像分析来测量孔径，通过俘获气泡法测量凝胶表面与水的接触角，分别在模型聚丙烯酰胺凝胶和热诱导蛋白质（绞碎鸡胸肉）凝胶中进行。这些与肉糊形成凝胶时的烹饪损失（CL）、离心（EW）或所有制备凝胶的毛细抽吸（CSL）过程中损失的水分（作为 WH 的反测）有关。正如计算毛细压力的 Young-Laplace 方程所预测的那样，这是 WH 的假定机制，具有较低水分损失的凝胶表现出更亲水的表面（较小的接触角）。然而，CL 和 CSL 都与凝胶的平均孔径较大有关，而不是预期的较小。聚丙烯酰胺凝胶的 WH 变化比预制肉凝胶更大，但只有毛细抽吸法足够灵敏以检测到这些差异。
凝胶保持水分的能力对加工经济、食品质量和食品安全都很重要。本研究调查了凝胶保持水分的流行理论，即毛细作用。凝胶微观结构的孔径大小和构成每个凝胶的聚合物的亲水性程度都进行了定量评估，并与保水（WH）性能相关联，这是首次使用这种方法进行的报告。似乎亲水性的程度比孔径更能解释 WH 性能，未来应该进行这类研究。
