The Concentrations of Phenolic Compounds and Vitamin C in Japanese Quince (Chaenomeles japonica) Preserves

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) fruit preserves in terms of the content of vitamin C and phenolic compounds, as well as to discuss the effects of processing on the concentrations of these compounds in Japanese quince fruit. Research materials consisted of seven different products: a 100% Japanese quince fruit pressed juice, syrups with added honey, cane sugar, and xylitol, and three products sweetened with white sugar: jam, fruits in syrup, and candied fruits. The content of vitamin C and polyphenolic compounds (phenolic acids and flavonoids) was determined by high-performance liquid chromatographic method. The study confirmed that the Japanese quince fruit preserves can be considered a rich source of vitamin C and selected phenolics. At the same time, the tested products differed significantly in terms of the levels of the analyzed phenolic compounds, e.g., the syrups sweetened with xylitol were characterized by significantly higher concentrations of the analyzed phenolics than the syrups sweetened with other sweeteners. It is noteworthy to explore the possibilities for quince fruit processing, taking into account various processing methods and conditions, and using sweeteners alternative to white sugar.