Food Sci. Biotechnol. 20(1): 215-222 (2011) DOI 10.1007/s10068-011-0029-2 Effect of Water Activity and Temperature on the Color Change of Red Pepper (Capsicum annuum L.) Powder Jong-Whan Rhim and Seok-In Hong Received: 29 September 2010 / Revised: 5 November 2010 / Accepted: 6 November 2010 / Published Online: 28 February 2011 © KoSFoST and Springer 2011 Abstract Isotherm characteristics of red pepper powder and the effect of temperature and water activity (Aw) on its color change were investigated. Monolayer moisture contents of red pepper powder decreased from 0.1218 to 0.0912 g water/g solid with increasing temperature from 25 to 50 o C. The color change of red pepper powder was greatly dependent on temperature and Aw. As temperature and Aw increased, red color of pepper powder increasingly faded out to become brown and tarnish black, which is mainly attributed to the degradation of carotenoid pigments and development of browning compounds. Color parameters such as Hunter-L, a, b values and other color functions as well as browning index and ASTA color values represent color changes of red pepper powder as influenced by temperature and Aw. Keywords: red pepper, color, water activity, temperature, hunter color function Introduction Red pepper (Capsicum annuum L.) is extensively used through the world as a natural food colorant or a seasoning agent due to its attractive red color, unique sweet taste, and pungency. As the most important agricultural product in Korea with the market value of about one billion dollars a year, it is widely used as a main ingredient in traditional Korean foods such as gochujang and kimchi (1,2). Color is the most important quality attribute of red pepper products that determines their overall quality and consequently their final market price (1,3,4). The characteristic color of red pepper is due to ketocarotenoid compounds such as capsanthin, capsorubin, and cryptocapsin (1,5). Capsanthin is the major red pigment, which represent as much as 50% of the total carotenoids, followed by capsorubin (6). Other pigments are xanthophylls such as violaxanthin, zeaxanthin, β-cryptoxanthin, and β-carotene, which reflect a more yellow-orange color (5,7,8). Sometimes, color quality of red pepper products deteriorate during processing and storage resulting in decrease of market value. Usually, red pepper pods are dried using a natural solar drying or hot air drying methods and stored for several months, then ground to powder or flake forms before consumption. The color deterioration of dehydrated pepper products during drying and storage is attributed to the carotenoid destruction (9). Once the pods have been dehydrated and ground, the stability of the carotenoid pigments decreased (10-12). The stability of the pigments depends on cultivars, water activity, carotenoids level, and the endogenous antioxidants and enzyme activity (8). Non-enzymatic browning is recognized as another dominant factor for affecting degradation of color quality of red pepper products (13,14). Ramakrishnan and Francis (13) showed that a major color change in heated paprika was due to the increase in the content of browning compounds. A non-enzymatic browning, Maillard reaction, is expected to occur in the dried red pepper since it contains appreciable amounts of reducing sugars and amino acids. Lee et al. (14) reported that browning reaction in dried red pepper products followed zero order reaction and the reaction rate was strongly affected by water activity and temperature. To minimize undesirable color changes of dried red pepper products, it is necessary to have a good understanding of Jong-Whan Rhim ( ) Department of Food Engineering, Mokpo National University, Muan, Jeonnam 534-729, Korea Tel: +82-61-450-2423; Fax: +82-61-454-1521 E-mail: jwrhim@mokpo.ac.kr Seok-In Hong Korea Food Research Institute, Seongnam, Gyeonggi 463-746, Korea RESEARCH ARTICLE