Towards a better understanding of the pectin structure–function relationship in broccoli during processing: Part I—macroscopic and molecular analyses

Abstract

To investigate the structure–function relationship of pectin during (pre)processing, broccoli samples ( Brassica oleracea L. cultivar italica) were subjected to one of the following pretreatments: (i) low-temperature blanching (LTB), (ii) LTB in combination with Ca 2+ infusion, (iii) high-pressure pretreatment (HP), (iv) HP in combination with Ca 2+ infusion, or (v) no pretreatment (control sample), whether or not in combination with a thermal treatment of 15 min at 90 °C. The macroscopic attributes of broccoli were linked to the chemical structure of broccoli pectin. By enhancing the cross-linking of pectic polymers, both LTB and HP reduced the texture loss that occurred during thermal processing of broccoli. During these pretreatments, homogalacturonan was de-esterified by pectin methylesterase, which led to changes in pectin solubility. When LTB or HP was combined with Ca 2+ infusion, changes in the structure of pectin occurred, however not always reflected at the macroscopic level. The degree of esterification of pectin in Ca 2+-soaked broccoli samples was lower compared to non-Ca 2+-soaked samples and, in addition, a higher amount of ionically cross-linked pectin was retrieved.