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Food Chem. 2019 Mar 30;277:463-470. doi: 10.1016/j.foodchem.2018.11.005. Epub 2018 Nov 2.

Physico-chemical chlorophyll-a species in aqueous alcohol solutions determine the rate of its discoloration under UV light.

Author information

1
Department of Health and Nutrition Sciences, Nishikyushu University, Kanzaki, Saga 842-8585, Japan. Electronic address: midori@nisikyu-u.ac.jp.
2
Department of Applied Biochemistry and Food Science Life Chemistry, Saga University, Honjo-machi, Saga 840-8502, Japan.
3
Department of Applied Biochemistry and Food Science Life Chemistry, Saga University, Honjo-machi, Saga 840-8502, Japan. Electronic address: uedat@cc.saga-u.ac.jp.
4
Department of Chemistry and Applied Chemistry, Graduate School of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502, Japan. Electronic address: tabatam@cc.saga-u.ac.jp.

Abstract

Chlorophyll-a (Chl-a) discolors when it is exposed to light, and such discoloration decreases food quality. To elucidate the discoloration mechanism of Chl-a, we determined discoloration rate in different Chl-a chemical species and assessed the size of Chl-a aggregates in mixed aqueous solutions of methanol and ethanol. Chl-a existed as monomer, J-aggregate, and random aggregate in solutions with different alcohol concentrations. The predominant species depended on the alcohol concentration. Monomeric Chl-a and J-aggregates discolored quickly, whereas random aggregates discolored slowly. Particle sizes of J-aggregates were 319 and 2305 nm in diameter in aqueous solutions of methanol and ethanol, respectively. The sizes of random aggregates were 51 and 79 nm in 10% (v/v) aqueous solutions of methanol and ethanol, respectively. The size of Chl-a aggregates positively correlated with the rate of Chl-a discoloration under UV light. Based on the results obtained, we propose a mechanism of Chl-a discoloration.

KEYWORDS:

Chlorophyll-a; Discoloration; J-aggregates; Particle size; Random aggregates

PMID:
30502172
DOI:
10.1016/j.foodchem.2018.11.005
[Indexed for MEDLINE]

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