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The Kinetics and Mechanism of Caffeine Infusion from Coffee: the Temperature Variation of the Hindrance Factor
Author(s) -
Spiro Michael,
Chong Yuen Ying
Publication year - 1997
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/(sici)1097-0010(199707)74:3<416::aid-jsfa868>3.0.co;2-0
Subject(s) - caffeine , chemistry , diffusion , green coffee , chromatography , chlorogenic acid , reaction rate constant , kinetics , food science , thermodynamics , endocrinology , medicine , physics , quantum mechanics
The rates of infusion of caffeine into water at 25.5°C were measured for green and medium roast Kenyan arabica coffees in the particle size range 0.85–1.00 mm. Each type of coffee was employed in three forms: dry (as received), water‐filled but still containing the original amount of solubles, and water‐filled and free of solubles other than caffeine. Intra‐bean diffusion coefficients of caffeine were calculated from the rate constants and compared with the known diffusion coefficients of caffeine in water to provide hindrance factors. These were much larger than the corresponding hindrance factors obtained at 80°C (Spiro et al , J Sci Food Agric 46 , 349–356 (1989)). Examination of these results and of partition constants determined at both temperatures enabled the factors contributing to slow internal diffusion to be separated and identified. Factors which were more pronounced at 25°C were the finite rate of caffeine dissolution within the bean, complexation of caffeine with chlorogenic acid and other coffee solubles, and the adsorption of caffeine molecules within the bean matrix. © 1997 SCI