Review Tracking bioactive compounds with colour changes in foods e A review Voltaire Sant’Anna * , Poliana Deyse Gurak, Ligia Damasceno Ferreira Marczak, Isabel Cristina Tessaro Laboratory of Food Technology and Processing, Chemical Engineering Department, Rio Grande do Sul Federal University, DEQUI-UFRGS, Rua Engenheiro Luiz Englert, s/n  , 90040-040 Porto Alegre, Brazil article info Article history: Received 11 January 2013 Received in revised form 13 March 2013 Accepted 9 April 2013 Available online 17 April 2013 Keywords: CIELAB parameters Food Phenolics Carotenoids Chlorophylls Betalains abstract Colour is one of the major attributes that affect the consumer perception of food quality. Several pig- ments in foods, measurable by colourimetric instrumentation, possess biological activity. The present work is a review of studies that assessed the colour changes (by the CIELAB parameters) and the bioactive compound content, analysing statistically their correlation in a broad spectrum of foods. An emphasis was placed on the contribution of phenolics, carotenoids, chlorophylls and betalains on the food colour characteristics during different processing and storage conditions. The correlation between these compounds and the colour changes of some foods had r -values higher than 0.72, according to the Pearson correlation analysis. This suggests that colour instrumentation may be an efficient and practical technique to indirectly estimate the presence of bioactive components. This approach potentially facil- itates the real-time quality control of biological compounds during the food industry processes. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction In the past decades, the field of bioactive compounds has technologically advanced mainly due to an increasing consumer concern for human health. Studies involving biocompounds (e.g., phenolics, carotenoids, betalains, and vitamins) have revealed that the daily consumption of these compounds improves the health of humans by reducing plasma cholesterol levels, adnominal aortic atherosclerosis, cardio vascular risk factors, plaque aggregation and tendency of ischemic reperfusion injury, among other beneficial effects [1e4]. One of the challenges faced by scientists in the food and phar- maceutical industries is minimizing the industrial treatment effects on nutrients during processing and storage. In this context, a low- cost food quality control during processes is essential to attend this current demand. Usual methodologies to analyze bioactive com- pounds involve chromatography and/or chemical reactions turning them laborious, time consuming, destructive, expensive, and consequently, not interesting for industrial applications. Therefore, the development of alternative methods for an online quality control application is of utmost interest. Colour features can generally be retrieved from different colour spaces such as RGB (red, green, blue) and HSI (hue, saturation, intensity) using statis- tical methods, thereby allowing the assessment of parameters in a very short period of time. In the past years, many studies have focused on evaluating better colour instrumentation methods as an alternative to assess the presence of bioactive compounds with antioxidant activities such as carotenoids [5,6], anthocyanins and other polyphenols [7,8], betalain [9] and chlorophyll [10]. Thus, modern colour instrumentation methods might be fast and prac- tical during the different stages of production, processing and quality control of pharmaceutical and food products. The aim of the present paper is to correlate the presence of several bioactive compounds in a broad spectrum of foods to the CIELAB parameters. A detailed up-to-date summary of the potential applications of colour instrumentation as an alternative to the chemical reactions and the chromatography methods is presented in this review article. Furthermore, the future trends and the challenges faced in the food quality control field are discussed. 2. Theoretical background Colour is defined as the wavelengths of light in the visual spectrum (from 380 to 770 nm) that are detected by the human retina. All the colours detected by the human eye are associated * Corresponding author. Fax: þ55 51 3308 3277. E-mail addresses: voltairezs@yahoo.com.br , voltairezs@gmail.com (V. Sant’Anna). Contents lists available at SciVerse ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig 0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.dyepig.2013.04.011 Dyes and Pigments 98 (2013) 601e608