Deshpande S S, Cheryan M, Salunkhe D K
Crit Rev Food Sci Nutr. 1986;24(4):401-49. doi: 10.1080/10408398609527441.
Phenolic substances occur primarily in fruits and vegetables and in the seeds of certain pigmented cultivars of sorghum, millets, and legumes. One of the major difficulties encountered in polyphenol research is the lack of a standard quantitative method for the analysis of phenolics that would be suitable for a wide range of seeds, forage crops, and food products and under a variety of experimental conditions. Some methods measure "total phenol", which may not be a true index of the nutritional quality of foods and thus does not distinguish polyphenols of nutritional concern from other low-molecular-weight phenols that also occur naturally in these products. Tannic acid (a hydrolyzable gallotannin) is commonly used as a "reference standard", but this may be a questionable practice since its biological properties differ from those of tannins of flavonoid origin. Polyphenols of cereals and legumes are predominantly of the latter type. Also, commercially available tannic acid has been shown to be a mixture of four phenolic compounds, the relative proportions of which vary with the samples. Thus, the choice of a suitable standard for tannin analysis is also important. The quantitative extraction of the condensed tannins from plant tissue is always difficult, since it may be complexed to a carbohydrate or protein matrix which could be quite insoluble due to a high degree of polymerization. The literature on tannin methodology is diverse and at times conflicting. Currently available methods for tannin analysis range from simple colorimetric, UV spectrophotometric, chromatographic, and enzymic to more sophisticated and expensive nuclear magnetic resonance (NMR) techniques. None of these methods of analyses is completely satisfactory nor can it be applied to different food products with the same degree of success. This review covers physical and chemical methods for tannin analysis of different food products, the problems in analysis and interpretation of data, and future research needs in this area.
酚类物质主要存在于水果、蔬菜以及某些高粱、小米和豆类的有色品种种子中。多酚研究中遇到的一个主要困难是缺乏一种适用于广泛种子、饲料作物和食品以及各种实验条件的酚类物质标准定量分析方法。一些方法测量“总酚”，但这可能不是食品营养质量的真实指标，因此无法区分具有营养意义的多酚与这些产品中天然存在的其他低分子量酚类。单宁酸（一种可水解的没食子单宁）通常用作“参考标准”，但这可能是一种有问题的做法，因为其生物学特性与黄酮类单宁不同。谷物和豆类中的多酚主要是后一种类型。此外，市售单宁酸已被证明是四种酚类化合物的混合物，其相对比例因样品而异。因此，选择合适的单宁分析标准也很重要。从植物组织中定量提取缩合单宁总是很困难，因为它可能与碳水化合物或蛋白质基质络合，由于高度聚合，这种基质可能非常不溶。关于单宁分析方法的文献多种多样，有时相互矛盾。目前可用的单宁分析方法从简单的比色法、紫外分光光度法、色谱法和酶法到更复杂、更昂贵的核磁共振（NMR）技术。这些分析方法都不完全令人满意，也不能以相同的成功程度应用于不同的食品。这篇综述涵盖了不同食品中单宁分析的物理和化学方法、数据分析和解释中的问题以及该领域未来的研究需求。
