Review Hydrolyzable tannin analysis in food Panagiotis Arapitsas ⇑ Food Quality and Nutrition Department, Research and Innovation Centre, Fondazione Edmund Mach, via E. Mach, 1, 38010 San Michele all’Adige, Italy article info Article history: Received 1 February 2012 Accepted 24 May 2012 Available online 1 June 2012 Keywords: Tannins Food Gallotannins Ellagitannins Analytical chemistry abstract The discovery of plant polyphenols in food is perhaps one of the biggest breakthroughs in modern food science. Plant polyphenols are known for their role in food quality and safety, since they contribute sig- nificantly to taste, flavour, colour, stability etc., while they are increasingly recognised as important fac- tors in long-term health, contributing towards reducing the risk of chronic disease. Almost 200 years ago, hydrolyzable tannins (HTs) were the first group of plant polyphenols subjected to analytical chemical research. Despite the lack of commercially available standards, food analysis research offers a wealth of papers dealing with extraction optimisation, identification and quantification of HTs. The object of this review is to summarise analytical chemistry applications and the tools currently used for the analysis of HTs in food. Ó 2012 Elsevier Ltd. All rights reserved. Contents 1. Historical background – introduction .................................................................................... 1708 2. Classification........................................................................................................ 1710 3. Importance of food HTs ............................................................................................... 1710 4. Analytical chemistry ................................................................................................. 1711 4.1. Extraction..................................................................................................... 1711 4.2. Isolation ...................................................................................................... 1711 4.3. Chromatography – separation .................................................................................... 1714 4.4. Detection – Identification ........................................................................................ 1714 4.5. Quantification ................................................................................................. 1715 5. Concluding remarks and future aspects .................................................................................. 1715 References ......................................................................................................... 1716 1. Historical background – introduction With the start of the modern scientific revolution and the devel- opment of chemistry from alchemy, plant polyphenols became one of the first subjects of scientific research. Many of the fathers of chemistry worked in this field and provided the first results in rela- tion to the quantitative and qualitative analysis of HTs (Fischer, 1914; Haslam, 1989; Russell, 1935). Around 200 years ago, in the leather industry chemists were asked to improve leather processing techniques, due to the de- mand for greater quantities of leather and better quality. In this era, traditional techniques were the result of the application of empirical methods as well as reasoning, and most products were tanned with an infusion of oak bark for a period of three to six months. Probably for this reason, the first term used for these products, which is still adopted today, was vegetable tannins (tann in Celtic means oak tree). Over the centuries and around the world, other raw materials in addition to oak bark, all from the plant king- dom, were also used to tan hides, such as myrtle leaf extract in 17th century Rome. The quality of the final product was not always similar, even when exactly the same method was used. The first problem was finding the most efficient source of vegetable tannin, while the second step was standardisation. Since the most well- known and effective tanning material was oak bark extract, called tannic acid, numerous chemists tried to analyse it, discover its com- position and develop quantitative analytical methods, in order to produce a standard raw material (Darton, 1882a, 1882b; Fischer, 1914; Rau, 1887; Russell, 1935; Wilson, 1934). 0308-8146/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2012.05.096 ⇑ Tel.: +39 0461 615 564; fax: +39 0461 615 200. E-mail addresses: panagiotis.arapitsas@fmach.it, panagiotis.arapitsas@gmail. com Food Chemistry 135 (2012) 1708–1717 Contents lists available at SciVerse ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem