Effects of fertilizer type and fruit diameter on firmness of pickled gherkin (Cucumis sativus L.) during vinegar fermentation

Abstract

Cell wall-modifying enzymes, activate during fruit development or triggered by environmental conditions such as heat and apoplasmic pH changes, degrade structural polysaccharides like pectin leading to reduced fruit firmness, a key quality trait in pickled products. This study aimed to evaluate the combined effects of fertilizer type and fruit diameter on the firmness of pickled gherkin. The experiment was conducted at the University of Ruhuna using two-factor factorial arrangement in a completely randomized design (CRD) with five replicates. The first factor was fertilizer type (urea and calcium nitrate-CN), and the second was fruit diameter (11 mm, 12 mm, 13 mm and 14 mm), forming eight treatment combinations: T1-Urea,11 mm; T2-Urea,12 mm; T3 Urea,13 mm; T4-Urea,14 mm; T5-CN,11 mm; T6-CN,12 mm; T7-CN,13 mm; and T8-CN,14 mm. After fruit setting, grade 1 gherkin fruits (standard fruit diameter 11- 14 mm) were harvested and fermented in vinegar. Firmness was measured using a digital force gauge after 45 days of fermentation. Data were analyzed using two-way ANOVA, and means were compared using Duncan’s Multiple Range Test at a 5% significance level. The interaction between fertilizer type and fruit diameter had a highly significant effect on firmness (p = 0.0006), indicating a diameter specific fertilizer response. However, neither fertilizer type nor fruit diameter alone had a significant effect (p > 0.05). The significantly highest firmness (22.07 N) was observed in urea treated fruits at 14 mm (T4). CN maintained consistent firmness (18.00–18.75 N) across 11–14 mm with low variability, while urea showed lower firmness at 11–13 mm (16.3- 17.0 N) but increased sharply at 14 mm, with higher variability. Therefore, when harvesting grade 1 gherkin fruits, it is recommended to harvest fruits with diameters of 11 to 14 mm when using CN, while only fruits with a diameter of 14 mm should be harvested when using urea to ensure optimal firmness during vinegar fermentation.