Vacuum-assisted sucrose impregnation improves frozen pineapple quality through water-state modification

Freezing-induced ice recrystallization is a major limitation in preserving the quality of high-moisture fruits because of its adverse effects on cellular structure, texture, and nutritional stability. This study investigated vacuum-assisted sucrose impregnation as a cryostabilization approach for improving the quality of frozen pineapple stored at -18 °C for 21 days. Pineapple cubes were subjected to untreated control, atmospheric sucrose impregnation (AI; immersion in 60% (w/w) sucrose solution for 30 min at atmospheric pressure), and vacuum-assisted impregnation (VI; 31.8 kPa for 20 min followed by 10 min relaxation). Mass transfer, thermal characteristics, physicochemical properties, color, texture, and microstructural changes were evaluated. Vacuum treatment significantly enhanced solute incorporation, increasing cryoprotectant uptake to 11.2%. Differential scanning calorimetry revealed that VI reduced the onset freezing temperature from -1.8 to -3.6 °C and decreased melting enthalpy by approximately 52% compared with untreated samples. Freezable water content decreased from 72.4% to 38.6%, while bound water increased from 27.6% to 61.4%, indicating enhanced water immobilization within the fruit matrix. During frozen storage, VI-treated samples exhibited lower ion leakage (9.1%), greater retention of total phenolic content (67.5 mg GAE/100 g), higher antioxidant activity determined by DPPH scavenging (73.9%) and FRAP (581.3 μmol Fe²⁺ equivalents/100 g fresh weight), and improved textural stability, maintaining hardness at 21.4 N compared with 10.2 N in control samples after 21 days. SEM observations further confirmed reduced tissue disruption and preservation of cellular architecture. These findings demonstrate that vacuum-assisted sucrose impregnation effectively improves cryostability by regulating water distribution and preserving structural integrity in frozen pineapple.