Comparative Evaluation of Hot Water and Steam Blanching Methods on Quality Characteristics of Spinach (Spinacia oleracea)

Abstract

Aims: This study aimed to standardize hot water and steam blanching for the processing of Spinach, assessing their effectiveness in peroxidase (POD) enzyme inactivation and their impact on key quality attributes including color, pH, total soluble solids (TSS), antioxidant activity, ascorbic acid, oxalate content and microbial quality. Study Design: A completely randomized design (CRD) was employed, utilizing one-way ANOVA and Duncan's multiple range (DMR) tests to evaluate and compare the effect of the blanching method on spinach quality. Place and Duration of Study: College of Food Processing Technology and Bioenergy, Anand Agricultural University, Anand, between March and Oct 2024. Methodology: Various hot water blanching parameters (70 °C and 90 °C for 30 s and 60 s) and steam blanching durations (60 s, 120 s, and 180 s) were tested. Peroxidase (POD) activity was analyzed to determine inactivation. Hot water at 90 °C for 30 s and steam for 180 s were identified as optimal. These optimal parameters were then used to assess their impact on various quality attributes. Results: Statistical analysis revealed that hot water blanching (90 °C, 30 s) and steam blanching (180 s) were equally effective in peroxidase (POD) inactivation, with residual activities of 9.79 ± 1.05% and 10.50 ± 0.72%, respectively. Greenness (a* value) improved from −6.51 ± 0.21 (fresh) to −9.86 ± 0.04 (hot water) and −7.15 ± 0.05 (steam). Total oxalate content decreased significantly, from 454.66 ± 45.79 mg/100 g (fresh) to 220.00 ± 44.00 mg/100 g (hot water) and 286.00 ± 22.00 mg/100 g (steam), representing a reduction of nearly 50%. Both blanching methods significantly increased pH and simultaneously reduced total soluble solids (TSS), antioxidant activity, ascorbic acid content, and microbial load. Conclusion: Blanching significantly enhanced spinach greenness and reduced anti-nutrients (oxalates) and microbial load. This study provides food processors with scientific evidence for standardizing blanching methods ensuring maximum enzyme inactivation with minimal nutrient loss, thus supporting production of minimally processed, nutrient-rich spinach products.