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Article

Effect of Addition of Tryptophan on Aggregation of Apo-α-Lactalbumin Induced by UV-Light

1
Department of Food Science, Faculty of Science, University of Copenhagen, Rolighedsvej 26, 1958 Frederiksberg, Denmark
2
Arla Foods Ingredients Group P/S—Innovation R&D, Discover Department, Sønderupvej 26, 6920 Videbæk, Denmark
3
Department of Biomedical Sciences, Faculty of Health and Medicine, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark
*
Author to whom correspondence should be addressed.
Academic Editors: Mario Estévez and Youling Xiong
Foods 2021, 10(7), 1577; https://doi.org/10.3390/foods10071577
Received: 24 May 2021 / Revised: 2 July 2021 / Accepted: 6 July 2021 / Published: 7 July 2021
UV-B illumination facilitates aggregation of alpha-lactalbumin (α-LA) by intramolecular disulfide bond cleavage followed by intermolecular thiol-disulfide exchange reactions. However, long term exposure to UV-B illumination may induce undesired oxidative modifications of amino acid residues in the protein. The purpose of this study was to examine the effect of UV-induced aggregation of apo-α-LA (a calcium-depleted form of α-LA) under aerobic and anaerobic conditions and by addition of tryptophan (Trp) as a photosensitizer. The addition of Trp to apo-α-LA illuminated under anaerobic conditions facilitated the highest level of free thiol release and disulfide-mediated aggregation as compared to without addition of Trp under both anaerobic and aerobic conditions. Addition of Trp under aerobic condition resulted in the lowest level of free thiols and disulfide-mediated aggregation and the aerobic conditions caused oxidation of the free Trp with formation of kynurenine and 5-hydroxy-Trp. Minor levels of the Trp oxidation product, 3-hydroxy-kynurenine (2% converted from Trp), was formed in apo-α-LA with added Trp under both aerobic and anaerobic conditions after UV-B treatment. View Full-Text
Keywords: UV illumination; tryptophan; aggregation; photooxidation; whey protein UV illumination; tryptophan; aggregation; photooxidation; whey protein
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MDPI and ACS Style

Zhao, Z.; Li, R.; Poojary, M.M.; Nielsen, S.B.; Lund, M.N. Effect of Addition of Tryptophan on Aggregation of Apo-α-Lactalbumin Induced by UV-Light. Foods 2021, 10, 1577. https://doi.org/10.3390/foods10071577

AMA Style

Zhao Z, Li R, Poojary MM, Nielsen SB, Lund MN. Effect of Addition of Tryptophan on Aggregation of Apo-α-Lactalbumin Induced by UV-Light. Foods. 2021; 10(7):1577. https://doi.org/10.3390/foods10071577

Chicago/Turabian Style

Zhao, Zichen, Renjie Li, Mahesha M. Poojary, Søren B. Nielsen, and Marianne N. Lund 2021. "Effect of Addition of Tryptophan on Aggregation of Apo-α-Lactalbumin Induced by UV-Light" Foods 10, no. 7: 1577. https://doi.org/10.3390/foods10071577

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