ORIGINAL PAPER Degradation patterns and stability predictions of the original reds and amino acid derivatives of monascus pigments Heeyong Jung • Deokyeong Choe • Ky-Youb Nam • Kwang-Hwi Cho • Chul Soo Shin Received: 8 July 2010 / Revised: 30 December 2010 / Accepted: 10 January 2011 / Published online: 28 January 2011 Ó Springer-Verlag 2011 Abstract The original red isomers and L-phenylalanine derivative isomers of monascus pigment, which have a side chain of either C 5 H 11 or C 7 H 15 , were produced via Mon- ascus fermentation, and then purified. The degradation patterns of the pigments relating to incubation conditions were investigated. For all tested compounds, a total of seven major fragments were formed during incubation, five in presence of sunlight irradiation and two with no sunlight. The red isomers R5 and R7 showed the same pattern whereas the L-Phe derivative isomers P5 and P7 exhibited another pattern. All of the pigments appeared to be highly sensitive to sunlight irradiation considering that with sun- light, diverse fragments were produced and the side chains C 5 H 11 and C 7 H 15 were degraded. The fragments are thought to be formed via degradation and combination reactions of pigments based on a comparison of the frag- ment molecular masses. Theoretically stable isomers of an original red pigment and some amino acid derivatives were selected based on a comparison of their Hartree confor- mational energies, which were estimated using geometric optimization based on ab initio molecular orbital calculations. The greater stability of amino acid derivatives was confirmed based on maximum UV-absorption wave- lengths and isomer population rates. Keywords Monascus  Red pigment  Amino acid derivatives  Sunlight stability  Degradation pattern Introduction Strains of Monascus species that usually produce pigments have traditionally been used for manufacturing red alco- holic beverages and red bean curd in eastern Asian coun- tries such as Taiwan, China, Japan, The Philippines, Korea, and Indonesia [1]. In the food industry, monascus pigments have been used for coloring processed meats (sausages and hams), marine products (fish paste, surimi), and tomato ketchup. There are reports that different strains of Monascus species produce six major pigment compounds consisting of the yellows of monascin [2–4] and ankaflavin [5], the oranges of monascorubrin [6, 7] and rubropunctatin [8], and the reds of monascorubramine [9] and rubropuncta- mine [10]. These compounds are a type of polyketide with different solvent solubilities. In solid cultivations using rice, the produced pigments are known to bind the rice proteins of the medium [11]. There are reports of synthesis of monascus derivatives that are made from original monascus pigments by addition of nitrogenous compounds, such as amino acids, peptides, amino sugars, amino alco- hols, chitosan, and nucleic acids [12]. It has been proposed that the oxygen moiety of the orange monascus pigment is replaced by the nitrogen moiety of a nitrogenous com- pound [12–14], with a subsequent color shift from orange to red [14, 15]. K.-Y. Nam is Co-first author. H. Jung  D. Choe  C. S. Shin (&) Department of Biotechnology, College of Life Science and Biotechnology, Yonsei University, Seodaemun-gu, Seoul 120-749, South Korea e-mail: csshin@yonsei.ac.kr K.-Y. Nam Bioinformatics and Molecular Design Research Center, YERP, Yonsei University, Seodaemun-gu, Seoul 120-749, South Korea K.-H. Cho Department of Bioinformatics, Soongsil University, Dongjak-gu, Seoul 156-743, South Korea 123 Eur Food Res Technol (2011) 232:621–629 DOI 10.1007/s00217-011-1427-7