# Hyperspectral Imaging as a Rapid Quality Control Method for Herbal Tea Blends
## 1 Introduction  
The use of fresh and dried herbs for the preparation of herbal infusions (tisanes) that are popularly consumed for the pleasant taste and most importantly their perceived health benefits, dates back to antiquity. Today, tea is the most consumed beverage worldwide, second only to water. In 2013, the total retail sales of bagged, loose and concentrated teas in the United States increased by 5.9% reaching a figure of USD$1,751,055,302. In 2012, the total consumption of tea was shown to comprise of 85% black tea and 15% green tea, with oolong and white tea making up the remainder. The 2013 statistics for bagged, loose and concentrated tea annual sales reported sales of USD$579,974,381 for black tea (bags), an increase from 2012 of 2.5%. The sales of herbal beverage tea (bags), medicinal teas (bags) and African red tea (bags) increased by 11.0%, 15.4% and 3.5%, respectively. A trend towards the increased consumption of loose tea was noted, especially in specialty tea and coffee shops. This is reflected in the 11.1% increase in African ted tea (loose) sales for example [1]. Worldwide, the largest consumer of tea is China (1.6 billion pounds per year). However, the consumption per person statistics tells a differentstory. The top consumers of tea per person per year are Turkey (6.961 pounds), Ireland (4.831 pounds) and the UK (4.281 pounds) [2]. A widely accepted definition of a herbal tea is a non-caffeine-containing hot beverage prepared through infusion of any plant other than the leaves _Camelia sinensis_ (L.) Kuntze or 'true tea'. True teas including black, green, yellow and oolong teas are all prepared exclusively from _Camelia sinensis_ (Theaceae) [3,4]. In recent years, consumers have become more health conscious, both in terms of prevention and treatment of disease, which has led to an escalation in the use and development of plant-based health products including herbal teas [5]. Herbal teas are important dietary sources of anti-oxidants, especially phenolic compounds, which are capable of preventing free-radical-induced damage in biological systems, thereby preventing disease manifestation and progression [4]. Herbal tea blends are mixtures of two or more plant species (herb or spice) with the same or different medicinal uses blended together. The quest to improve the aesthetic properties of herbal teas has seen the introduction of different herbal tea flavors such as vanilla, lemon and mint. More recently, the introduction of herbal tea ingredients to produce blends with the intention of improving health properties, taste and sometimes masking unpleasant herbal aromas has become popular [6]. The list of top herbal ingredients in herbal beverage teas (bags) include chamomile, mints, ginger, valerian, licorice, aloe and lavender etc. while the top herbal ingredients in medicinal tea (bags) include chamomile, senna, ginger, Echinacea, dandelion and kava, etc. [1]. On the \"world's biggest tea drinkers\" list, South Africa occupies 11 th place, with consumption of 1.789 pounds per person per year [2]. A number of plants have traditionally been used in South Africa as \"teas\". Two Cape fynbos plants, rooibos (African red tea) and honeybush, widely cultivated in the Eastern and Western Cape have enjoyed commercial success. Rooibos tea is sold in more than 37 countries with 86% of the export market being represented by Germany, the Netherlands, the UK, Japan and the USA [7]. Anecdotal evidence reports the use of herbal teas such as rooibos and honeybush teas for the relief of colic, vomiting, stomach cramps, indigestion, heartburn and nausea [8,9]. Studies in support of these claims and other biological activities have been documented [7,10,11]. Herbal teas are mostly available on the market as ground or crushed loose products often packaged in tea bags. In this form it is difficult to verify the botanical origin of a product by its appearance [3].