Drying characteristics of thin layer hot air drying for preparation of ready-to-reconstitute protein enriched spongy snack (khaman)

Khaman is a widely enjoyed traditional protein enriched snack known for its short shelf life, primarily due to its high moisture content. To convert traditional khaman into a ready-to-reconstitute product, moisture was removed by drying it in thin layers at temperatures ranging from 60 to 75 °C, with air flow rates between 4.5 and 18 m3/h. The physical characteristics of the reconstituted tray-dried samples showed variations in thickness (3.48–3.68 cm), density (0.189–0.230 g/cm3), color parameters (L*: 18.08–23.51; a*: 0.94–1.59; b*: 38.34–43.93), and hardness (2.53–3.07 kgf) with respect to 3.6 cm, 0.234 g/cm3, 24.85, 0.72, 37.72 respectively of the fresh khaman. In terms of chemical properties, the pH ranged from 5.85 to 7.23, total soluble solids (TSS) from 3.07 to 4.13°Brix, total sugar content from 9.74 to 11.37%, and protein levels from 18.34 to 21.41% in the reconstituted samples with respect to 7.65, 4.32°Brix, 11.64% and 21.98% respectively of the fresh khaman. For optimal retention of physical, chemical, and sensory attributes, the ideal drying conditions were determined to be a temperature of 70 °C and an air flow rate of 4.5 m3/h. The maximum drying rate, effective diffusivities and activation energy were 3.5 mg water/g dry matter/min, 7.4–10.7 × 10−7 m2/s and 21.12 kJ/mol respectively. The thickness and sensory attributes of freshly prepared khaman and optimized reconstituted khaman were also very close, reflecting their similarity in texture and overall quality. The Midilli model demonstrated a good fit for the drying characteristics, as indicated by statistical parameters including an R2 value of 0.99, χ2 of 0.000098, and RMSE of 0.00806. This study provides a practical approach to extending the shelf life of khaman while preserving its key sensory and nutritional qualities. The findings offer valuable insights for the food industry, enabling the commercialization of ready-to-reconstitute khaman as a convenient, high-protein snack with enhanced storage stability.