肥皂的复兴？——如何在中性 pH 值和室温下制备澄清稳定的溶液。

A renaissance of soaps? - How to make clear and stable solutions at neutral pH and room temperature.

机构信息

Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany.

出版信息

Adv Colloid Interface Sci. 2016 Oct;236:28-42. doi: 10.1016/j.cis.2016.07.002. Epub 2016 Jul 21.

DOI:10.1016/j.cis.2016.07.002

Abstract

Soaps are the oldest and perhaps most natural surfactants. However, they lost much of their importance since "technical surfactants", usually based on sulfates or sulfonates, have been developed over the last fifty years. Indeed, soaps are pH- and salt-sensitive and they are irritant, especially to the eyes. In food emulsions, although authorized, they have a bad taste, and long-chain saturated soaps have a high Krafft temperature. We believe that most or perhaps all of these problems can be solved with modern formulation approaches. We start this paper with a short overview of our present knowledge of soaps and soap formulations. Then we focus on the problem of the lacking soap solubility at neutral pH values. For example, it is well known that with the food emulsifier sodium oleate (NaOl), clear and stable aqueous solutions can only be obtained at pH values higher than 10. A decrease in the pH value leads to turbid and unstable solutions. This effect is not compatible with the formulation of aqueous stable and drinkable formulations with neutral or even acidic pH values. However, the pH value/phase behavior of aqueous soap solutions can be altered by the addition of other surfactants. Such a surfactant can be Rebaudioside A (RebA), a steviol glycoside from the plant Stevia rebaudiana which is used as a natural food sweetener. In a recent paper, we showed the influence of RebA on the apKa value of sodium oleate in a beverage microemulsion and on its clearing temperature. In the present paper, we report on the effect of the edible bio-surfactant RebA, on the macroscopic and microscopic phase behavior of simple aqueous sodium oleate solutions at varying pH values. The macroscopic phase behavior is investigated by visual observation and turbidity measurements. The microscopic phase behavior is analyzed by acid-base titration curves, phase-contrast and electron microscopy. It turned out that even at neutral pH, aqueous NaOl/RebA solutions can be completely clear and stable for more than 50days at room temperature. This is for the first time that a long chain soap could be really solubilized in water at neutral pH at room temperature. At last, these findings were applied to prepare stable, highly translucent and drinkable aqueous solutions of omega-3-fatty acids at a pH value of 7.5.

摘要

肥皂是最古老的、也许是最天然的表面活性剂。然而，自从过去五十年间开发出“技术型表面活性剂”（通常基于硫酸盐或磺酸盐）以来，肥皂的重要性大大降低。实际上，肥皂对 pH 值和盐度敏感，而且具有刺激性，特别是对眼睛。在食品乳液中，虽然已被授权使用，但它们的味道不佳，并且长链饱和肥皂具有较高的克拉夫特温度。我们相信，通过现代配方方法可以解决大多数或几乎所有这些问题。我们从简要概述我们目前对肥皂和肥皂配方的了解开始。然后，我们专注于在中性 pH 值下缺乏肥皂溶解度的问题。例如，众所周知，对于食品乳化剂油酸钠（NaOl），只有在 pH 值高于 10 的情况下才能获得清澈且稳定的水溶液。pH 值降低会导致浑浊且不稳定的溶液。这种效果与中性甚至酸性 pH 值的水稳定且可饮用配方的配方不兼容。但是，可以通过添加其他表面活性剂来改变肥皂水溶液的 pH 值/相行为。这样的表面活性剂可以是甜菊糖 Rebaudioside A（RebA），它是植物甜叶菊 Stevia rebaudiana 中的一种甜菊糖苷，用作天然食品甜味剂。在最近的一篇论文中，我们展示了 RebA 对饮料微乳液中油酸钠的 apKa 值及其澄清温度的影响。在本文中，我们报告了食用生物表面活性剂 RebA 对不同 pH 值下简单油酸钠水溶液的宏观和微观相行为的影响。宏观相行为通过目视观察和浊度测量来研究。微观相行为通过酸碱滴定曲线、相差和电子显微镜分析来分析。结果表明，即使在中性 pH 值下，室温下，水相 NaOl/RebA 溶液也可以完全清澈且稳定超过 50 天。这是第一次在室温下，在中性 pH 值下真正将长链肥皂溶解在水中。最后，这些发现被应用于在 pH 值为 7.5 的情况下制备稳定，高度透明和可饮用的ω-3 脂肪酸水溶液。