Pigment change of freeze-dried carotenoid powder during storage Y.C. Tang, B.H. Chen* Department of Nutrition and Food Science, Fu Jen University, Taipei 242, Taiwan, ROC Received 4 June 1999; received in final revised form and accepted 17 September 1999 Abstract The stability of pigment in freeze-dried carotenoid powder during dark storage at 4, 25, or 45  C, or under light at 25  C was studied. Carrot pulp waste was used as raw material for processing carotenoid powder by freeze-drying. The various carotenoids were analyzed by HPLC with photodiode-array detection. Results showed that the amounts of all-trans forms of all three com- pounds, a-carotene, b-carotene and lutein, decreased with increasing storage temperature or illumination time. The major isomers formed during dark storage were 13-cis-a-carotene, 13-cis-b-carotene and 13-cis-lutein, while 9-cis-a-carotene, 9-cis-b-carotene and 9-cis-lutein were favored during illumination. The degradation rate of the total amount of all-trans plus cis forms of each pigment ®ts a ®rst order model, and the highest rate constant (day 1 ) was found for b-carotene, followed by a-carotene and lutein. Both the Hunter L and b values of the powder decreased with increasing storage time and temperature, while the Hunter a value showed insigni®cant change (p>0.05). # 2000 Elsevier Science Ltd. All rights reserved. 1. Introduction Carotenoids such as b-carotene have long been demonstrated to be capable of providing some medical or health bene®ts, including the possible prevention and treatment of skin cancer and cardiovascular disease (Base, van den Berg, van der Plas & Haenen, 1996; Van Poppel, 1996). Although some controversial results have been reported regarding the potential treatment of lung cancer by b-carotene (Blumberg & Block, 1994; Nicol, Maudet & Savoure, 1994), b-carotene is still an impor- tant biological compound because of its provitamin A activity (Olsen, 1989). In recent years, carrot juice has become an important beverage commodity because it contains high amount of both a- and b-carotene (Chen, Peng & Chen, 1995, 1996). One of the major by-products during processing of carrot juice is carrot pulp waste, which was also reported to contain signi®cant amounts of a- and b- carotene (Chen & Tang, 1998). Thus it would be an advantage to the food industry if the carrot pulp waste could be reprocessed and utilized. In a recent study, Chen and Tang (1998) reprocessed carrot pulp waste into carotenoid powder by spray-drying, and found that the total amount of carotenoids decreased with both increasing time and temperature. Although spray drying is a promising technique for possible commercial pro- duction of carotenoid powder in the future, the stability of powder may be diminished because of disruption of powder granules under high temperature treatment during processing (Bhandari, Dumoulin, Richard, Noleau & Lebert, 1992). To remedy this problem, the application of some other processing methods such as freeze-drying can also be employed. The objectives of this study were to process carrot pulp waste into car- otenoid powder by freeze-drying and to determine the pigment stability during storage. 2. Materials and methods 2.1. Materials All-trans-a-carotene and all-trans-b-carotene stan- dards were purchased from Sigma Co. (St. Louis, MO, USA). Six working solutions of all-trans-a-carotene, 1, 5, 10, 25, 50 and 70 mg/ml, were each prepared by dis- solving an appropriate amount of all-trans-a-carotene in 100 ml of methanol/methylene chloride (99:1, v/v) in a brown volumetric ¯ask. Likewise, six working solu- tions of all-trans-b-carotene, 10, 25, 50, 75, 100 and 130 0308-8146/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0308-8146(99)00216-2 Food Chemistry 69 (2000) 11±17 www.elsevier.com/locate/foodchem * Corresponding author.