Investigating the role of pectin in carrot cell wall changes during thermal processing: A microscopic approach

• A new microscopy approach was used to assess changes in carrot cell wall integrity.
• Cell wall polysaccharide accessibility by molecular probes was hampered by pectin.
• Only the accessibility of galactomannan was independent of the presence of pectin.
• Carrot cell wall integrity can be modulated by thermal processing.
• Pectin was leached out from the cell wall due to thermally-induced β-elimination.

Changes in cell wall integrity upon thermal treatment were assessed in carrot cells using novel microscopic approaches using Congo red and different cell wall polysaccharide specific probes (JIM7, LM10, LM11, LM15, LM21, LM22 and CBM3a). Strong thermal processing induced an increased accessibility of cellulose and hemicelluloses by Congo red and the specific probes, except galactomannan, which detection was not affected by the thermal processing. Detection of pectin by JIM7 disappeared upon thermal processing, pointing at the leaching out effect of pectin from cell wall due to β-elimination. Changes observed after thermal processing were moreover similar to changes observed after enzymatic degradation of pectin, and a combination of thermal and pectinases treatments did not cause additional effects. These observations indicated that the presence of native pectin is the main factor governing cell wall polysaccharides accessibility and overall cell wall integrity in carrot, which can be modulated through thermal processing.Industrial relevanceThis work provides new evidences on the specific role of pectin in carrot cell wall integrity, more specifically on how it can be modulated by thermal processing. New light microscopy approaches to assess changes in cell wall integrity are presented. This information is important for food industry since plant cell wall acts as a structural barrier for the release of carotenoids and other micronutrients in plant-based food products.