Physico-chemical chlorophyll-a species in aqueous alcohol solutions determine the rate of its discoloration under UV light. (30th March 2019)

• Record Type: Journal Article
• Authors: Yasuda, Midori; Oda, Keisuke; Ueda, Toshihisa; Tabata, Masaaki
• Is Part Of: Food chemistry. Volume 277(2019)
• Page Start: 463
• Page End: 470
• Publication Date: 2019-03-30
• Subjects: Chlorophyll-a -- Discoloration -- J-aggregates -- Random aggregates -- Particle size; Food -- Analysis -- Periodicals; Food -- Composition -- Periodicals; 664
• DOI: 10.1016/j.foodchem.2018.11.005
• Languages: English
• ISSNs: 0308-8146

Abstract

Highlights: UV light discolored chlorophyll-a in solutions with high alcohol concentrations. The particle size of chlorophyll-a aggregates depended on alcohol concentration. Monomer chlorophyll-a and its J-aggregates discolored easily. Chlorophyll-a random aggregates maximally resisted discoloration caused by UV light. 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.