Combined effects of ultrasound and calcium on the chelate-soluble pectin and quality of strawberries during storage.

The combined effects of ultrasound and calcium on the water migration, quality, and chelate-soluble pectin (CSP) properties of strawberries were investigated using nuclear magnetic resonance (NMR), high-performance liquid chromatography (HPLC), and atomic force microscopy (AFM). The relationship among water migration, firmness, and CSP properties was also determined. Treatment with ultrasound and calcium (U + Ca) prevented the decrease in firmness of strawberries during storage (17 days). Measurements of physicochemical parameters (titratable acidity (TA), soluble solid content (SSC), CSP and Ca content) showed that U + Ca treatment maintained better fruit quality. AFM showed a larger percentage of wider and longer CSP molecules in the U + Ca group (width ≥90 nm; length ≥800 nm). These results, together with the HPLC results, confirmed that U + Ca treatment effectively inhibits CSP degradation. This study revealed that the application of ultrasound and calcium could preserve the quality of stored strawberries.