Effects of Refrigeration of Variable Frequency on Fracturability, Springiness, Adhesiveness and Pectin Nanostructure of Carrot during Shelf life

To investigate the effects of frequency conversion refrigeration on the textural properties and pectin nanostructure over the shelf life, the carrots were analyzed for textural indices such as fracturability, springiness, and adhesiveness using a texture analyzer. Additionally, the content of cell wall materials and the activity of cell wall-degrading enzymes over its shelf life were evaluated using spectrophotometric methods, and the nanostructure of pectin substances was examined with an Atomic Force Microscope (AFM). The results showed that frequency conversion refrigeration maintained the fracturability and springiness of carrots during shelf life, as well as the content of cell wall polysaccharides, including sodium carbonate soluble pectin (SSP), chelated soluble pectin (CSP), cellulose, and hemicellulose. The increase of water-soluble pectin (WSP) content was also delayed in carrots over the shelf life. Furthermore, frequency conversion refrigeration reduced the activity of carrot polygalacturonase (PG) during the middle of the pre-shelf life period, along with the activities of carrot pectinesterase (PME), cellulase (Cx), and β-galactosidase (β-Gal) throughout the entire shelf life. The increase in the number of CSP and SSP pectin aggregates was linked to the changes in Cx and β-Gal activities. Correlation analyses further indicated significant negative correlations between fracturability and PME activity, adhesiveness and PME activity, and springiness and β-Gal activity of the carrots during shelf life. It is concluded that frequency conversion refrigeration can preserve excellent textural qualities, such as fracturability, springiness, and adhesiveness, by delaying the depolymerization of pectin in carrots throughout its shelf life, thereby providing a theoretical basis and technical support for carrot cold storage aimed at preserving freshness.