超高甲氧基果胶在食品乳液中的应用

果胶或果胶-蛋白复合物材料具有良好的生物安全性和可利用性,因此近年来受到越来越多的关注。特别地,各种来源和结构特征的果胶被用于开发新型食品乳液,用作活性成分的保护或运输载体,有望在未来取代目前使用的化学材料。然而,由于果胶分子量一般达到数十万,用果胶制备的乳液粒径往往处于数十或数百微米,在储藏过程中容易失稳或凝聚,从而限制了其应用范围;另外果胶与蛋白质之间一般通过静电作用维持络合,容易受到环境pH变化影响而降解。我们把酯化度高于90%的果胶称为超高甲氧基果胶(ultrahigh methoxylated pectin,UHMP),其具有稳定的疏水/亲水基团比例(～1:2)和均匀的疏水基团分布,同时在酯化反应过程中其分子量会明显降解,从而提高其在溶液中的溶解度和运动速度,因此能克服天然果胶形成乳液时的弱点;同时UHMP能够不依赖蛋白质而单独使用,通过低能量法制备得到纳米级的乳液,其长程稳定性、透明度、对热和酸的抗性均好于普通果胶乳液,因此有望用于开发新型食品乳液,广泛用于食品、医药、化妆品及日化行业。

Application of ultrahigh methoxylated pectin in food emulsion

Pectin or pectin-protein complex has attracted rising attentions in recent years owing to their good biosafety and bioavailability. Particularly, pectins from different sources with various structure features have been frequently tested in developing novel food emulsions as the protector or vehicle for bioactive substances with the potency to replace chemical materials in near future. However, due to their high molecular weight of hundreds of thousands Daltons, pectin-based emulsion droplets usually were as big as tens to hundreds micrometers, which were both kinetically and thermodynamically unstable. This disadvantage greatly restricted its application. Besides, pectin-protein complex was usually maintained via electrostatic attraction, therefore easily could be decomposed with the variation of environment pH. Pectin with the degree of methoxylation over 90% prepared via esterification could be assigned as the ultrahigh methoxylated pectin (UHMP), which possesses stable hydrophobic/hydrophilic group ratio (~1:2) and homogeneous hydrophobic moieties distribution. Moreover, the molecular chains of UHMP have been degraded during the esterification reaction, which thereafter could promote the dissolving and movement of UHMP in aqueous medium. This improvement could help overcome the abovementioned shortness of natural pectin and facilitates the usage of UHMP in food emulsion. Meanwhile UHMP could be used alone as emulsifier without protein to prepare nanoemulsion by means of low energy method. The long-term stability, transparency, thermal and acidic resistance of UHMP emulsions are superior to those prepared by normal pectin. Conclusively, UHMP has potential utilization in developing novel emulsions, which can be widely used in foods, medicines, cosmetics and daily chemicals.