Silva J V C, Peixoto P D S, Lortal S, Floury J
INRA, UMR1253 Science and Technology of Milk and Eggs, F-35042, Rennes, France.
J Dairy Sci. 2013 Oct;96(10):6186-98. doi: 10.3168/jds.2013-6552. Epub 2013 Aug 16.
During cheese ripening, microorganisms grow as immobilized colonies, metabolizing substrates present in the matrix and generating products from enzymatic reactions. Local factors that limit the rates of diffusion, either within the general cheese matrix or near the colonies, may influence the metabolic activity of the bacteria during ripening, affecting the final quality of the cheese. The objective of this study was to determine the diffusion coefficients of solutes as a function of their different physicochemical characteristics (size, charge, and shape) in an ultrafiltrate (UF) model cheese (based on ultrafiltered milk) to enable better understanding of the ripening mechanisms. Diffusion coefficients of fluorescein isothiocyanate (FITC)-dextrans (4 kDa to 2 MDa) and FITC-labeled dairy proteins (α-lactalbumin, β-lactoglobulin, and BSA) were measured using the technique of fluorescence recovery after photobleaching (FRAP). This study showed that macromolecules up to 2 MDa and proteins could diffuse through the UF model cheese. The larger FITC-dextrans were not more hindered by the structure of the UF model cheese compared with the smaller ones. Any decrease in the diffusion coefficients of solutes was related only to their hydrodynamic radii. The FITC-dextran diffusion data were fitted to an obstruction model, resulting in a constant obstruction factor (k ~0.42). Diffusion in the model cheese was sensitive to the physicochemical characteristics of the solute. The FITC-dairy proteins studied (rigid and negatively charged molecules) were hindered to a greater degree than the FITC-dextrans (flexible and charge-neutral molecules) in the UF model cheese. The existence of steric and electrostatic interactions between the protein matrix of the UF model cheese and the FITC-dairy proteins could explain the decrease in diffusion compared with FITC-dextrans.
在奶酪成熟过程中，微生物以固定化菌落的形式生长，代谢基质中存在的底物并通过酶促反应产生产物。限制扩散速率的局部因素，无论是在一般的奶酪基质中还是在菌落附近，都可能影响成熟过程中细菌的代谢活性，从而影响奶酪的最终品质。本研究的目的是在超滤（UF）模型奶酪（基于超滤牛奶）中确定溶质的扩散系数与其不同物理化学特性（大小、电荷和形状）之间的函数关系，以便更好地理解成熟机制。使用光漂白后荧光恢复（FRAP）技术测量了异硫氰酸荧光素（FITC）-葡聚糖（4 kDa至2 MDa）和FITC标记的乳蛋白（α-乳白蛋白、β-乳球蛋白和牛血清白蛋白）的扩散系数。这项研究表明，高达2 MDa的大分子和蛋白质可以在超滤模型奶酪中扩散。与较小的FITC-葡聚糖相比，较大的FITC-葡聚糖在超滤模型奶酪结构中的受阻程度并没有更高。溶质扩散系数的任何降低仅与其流体动力学半径有关。FITC-葡聚糖的扩散数据拟合到一个阻碍模型，得到一个恒定的阻碍因子（k~0.42）。模型奶酪中的扩散对溶质的物理化学特性敏感。在超滤模型奶酪中，所研究的FITC-乳蛋白（刚性且带负电荷的分子）比FITC-葡聚糖（柔性且电荷中性的分子）受到更大程度的阻碍。超滤模型奶酪的蛋白质基质与FITC-乳蛋白之间存在空间和静电相互作用，可以解释与FITC-葡聚糖相比扩散降低的原因。
