Department of Food Science, University of Wisconsin, Madison 53706.
Department of Food Science, University of Wisconsin, Madison 53706.
J Dairy Sci. 2019 Oct;102(10):8691-8695. doi: 10.3168/jds.2019-16393. Epub 2019 Aug 14.
Potato pectin has unique molecular characteristics that differentiate it from commercially available pectins sourced from citrus peels or apple pomace, including a higher degree of branching and a higher acetyl content. The objective of this study was to evaluate the ability of potato pectin to stabilize milk proteins at an acidic pH above their isoelectric point, pH 5.5, at which no citrus- or apple-derived pectins are functional. Potato pectin was extracted from raw potato tubers by heating at pH 4.5 and 120°C for 30 min after removing starch solubilized using a dilute HCl solution adjusted to pH 2. The potato pectin was found to have a galacturonic acid content of 17.31 ± 3.29% (wt/wt) and a degree of acetylation of 20.20 ± 0.12%. A portion of the potato pectin was deacetylated by heating it in an alkaline condition. The deacetylation resulted in a galacturonic acid content of 19.12 ± 4.64% (wt/wt) and a degree of acetylation of 3.03 ± 0.03%. Particle size distributions in acidified milk drink (AMD) samples adjusted to pH 5.5 demonstrated that the acetylated and deacetylated potato pectins were capable of inhibiting the aggregation of milk proteins to the largest degree at a pectin concentration of 1.0 and 0.25% (wt/wt), respectively. Pectin molecules that were not bound to milk proteins in these AMD samples were quantified after centrifugally separating milk proteins and pectin bound to them from the serum. We found that, for the acetylated and deacetylated potato pectins, all or approximately half of the pectin molecules were bound to milk proteins at a pectin concentration of 0.25 or 1.0% (wt/wt), respectively. These results suggest that the presence of acetyl groups is a critical factor that determines how potato pectin molecules bind electrostatically to milk protein surfaces, form 3-dimensional structures there, and function as a stabilizer. The present results demonstrate that potato pectin can stabilize milk proteins at pH 5.5 and potentially enable the development of novel AMD products with improved functionality for casein-containing products with moderately acidic pH profiles.
马铃薯果胶具有独特的分子特性，使其有别于市售的来源于柑橘皮或苹果渣的果胶，包括更高的支化度和更高的乙酰基含量。本研究的目的是评估马铃薯果胶在高于其等电点 pH5.5 的酸性条件下稳定乳蛋白的能力，在该 pH 下，没有柑橘或苹果来源的果胶具有功能。马铃薯果胶是通过在 pH4.5 和 120°C 下加热 30 分钟从生马铃薯块茎中提取的，在使用稀 HCl 溶液调节至 pH2 溶解淀粉后进行。马铃薯果胶的半乳糖醛酸含量为 17.31±3.29%（wt/wt），乙酰化度为 20.20±0.12%。部分马铃薯果胶在碱性条件下进行脱乙酰化。脱乙酰化导致半乳糖醛酸含量为 19.12±4.64%（wt/wt），乙酰化度为 3.03±0.03%。将 pH 调至 5.5 的酸化乳饮料（AMD）样品的粒度分布表明，在果胶浓度为 1.0%和 0.25%（wt/wt）时，乙酰化和脱乙酰化的马铃薯果胶能够最大程度地抑制乳蛋白的聚集。在这些 AMD 样品中，离心分离乳蛋白和与其结合的果胶后，定量了未与乳蛋白结合的果胶分子。我们发现，对于乙酰化和脱乙酰化的马铃薯果胶，在果胶浓度为 0.25%或 1.0%（wt/wt）时，所有或大约一半的果胶分子与乳蛋白结合。这些结果表明，乙酰基的存在是决定马铃薯果胶分子如何通过静电作用与乳蛋白表面结合、在那里形成三维结构以及作为稳定剂发挥作用的关键因素。本研究结果表明，马铃薯果胶可以在 pH5.5 下稳定乳蛋白，并有可能为具有适度酸性 pH 分布的含酪蛋白产品开发具有改善功能的新型 AMD 产品。
