The supercooling-facilitating (SCF) activities, that is, the anti-ice nucleation activity of the hot water extracts from five types of processed food refuse was examined. The extract with the highest activity among five hot water extracts was coffee refuse, showing 1.50℃ of SCF activity at a final concentration of 0.1 mg/ml. From the hot water extract of coffee refuse, the coffee refuse extract containing various polyphenols was prepared by the ultrafiltration (less than MWCO 10,000), a solvent fractionation of ethyl acetate. The yield of coffee refuse extract was 0.9% (w/w) from dried coffee refuse. The SCF activity of the coffee refuse extract at a final concentration of 1.0 mg/ml was 4.2℃. HPLC analysis of the coffee refuse extract showed that caffeine and chlorogenic acid, which are major components of coffee, could be found at 173 and 62.3 µg/ml, respectively. However, the SCF activities of both compounds (0.70 and 1.06℃) at a final concentration of 0.1 mg/ml were lower than those of ferulic acid and coumaric acid, respectively at 3.40 and 2.35℃. This is the first report to our knowledge on the SCF activity of caffeine. The SCF activity of caffeine at a final concentration of 1.0 mg/ml was 2.3℃. The specificity of caffeine against various ice nuclei containing calcium oxalate, 9-fluorenon, and ice nucleating bacteria was examined. Caffeine at a final concentration of 1.0 mg/ml could inhibit the ice nucleation activity of calcium oxalate, and Pseudomonas fluorescens KUIN-1 at the same level that of as silver iodide. From these results, it was suggested that the extract could be able to be applied to the field to control the frost damage of the vegetables and that the harvested vegetables might be stored unfrozen even at 0℃ or less.
Keywords: Anti-ice nucleation activity; Caffeine; Coffee refuse.