Evaluation of pectin nanostructure by atomic force microscopy in blanched carrot

Low-temperature blanching (LTB) is a very attractive method for preserving the texture of fresh vegetables; however, the molecular basis of this treatment remains to be elucidated. The mechanism of textural change in carrots by LTB was investigated. Carrot samples were treated using three kinds of blanching: high-temperature blanching (HTB), LTB, and LTB followed by HTB. Fresh and treated samples were evaluated conventionally for firmness, galacturonic acid content, and the activity of pectin methylesterase. In addition, Raman microscopy was also used to describe the pectin distributions in the samples. However, the Raman maps did not show obvious differences among the samples, but they coincided with the results of galacturonic acid content. Furthermore, the nanostructures of water-soluble pectin (WSP), chelator-soluble pectin (CSP), and diluted alkali-soluble pectin (DASP) fractions were observed by atomic force microscopy. The median length of CSP molecules was shortened from 44.76 nm to 12.57 nm by HTB. On the other hand, LTB induced elongation of CSP molecules (median length: 58.12 nm) and maintaining ability of DASP to form a regular network on mica.