A. Sotirov*
Department “Agrotechnology, Plant Protection and Economics”, Institute of Agriculture-Kyustendil, Agricultural Academy-Sofia, Bulgaria
(Manuscript received 22 January 2026; accepted for publication 16 March 2026)
*e-mail: a_sotirov@iz-kyustendil.org
Abstract. This study investigates the biochemical changes occurring in Granny Smith apples after four months of uncontrolled winter storage, with a focus on the influence of preharvest soil fertilization using a 0.025% aqueous solution of ascorbic acid. Key biochemical and physicochemical parameters – including pH, electrical conductivity, total dissolved solids, sugars (glucose, fructose, total dissolved sugars), mineral salts, specific gravity, redox potential, vitamin C content, and juice yield were measured. The results show that uncontrolled storage leads to a decrease in fructose (3-6%), acidity (0.5), specific gravity (0.001), and redox potential (1/3), while glucose levels increase markedly due to sugar conversion (2%). Juice yield decreased (3%) in the control apples after storage but increased (3-20%) in most apples from the ascorbic-acid-treated trees, suggesting improved water retention and enhanced technological quality. Treated apples also exhibited slightly lower mineral salt content, higher electrical conductivity, and elevated vitamin C concentrations (75 mg/l) compared to controls. Correlation analysis confirmed strong relationships among key indicators such as Brix, pH, EC, TDS, and vitamin C. These results highlight the potential of vitamin C fertilization as a practical approach to improving postharvest fruit quality under non-regulated storage conditions.