Author:

Keywords:

Science & Technology, Physical Sciences, Life Sciences & Biomedicine, Chemistry, Applied, Food Science & Technology, Chemistry, Pectin, De-esterification, Absolute degree of blockiness, Ca2+-pectin gels, Rheology, "Egg-box" model, Pectin gels classification, CALCIUM SENSITIVITY, HOMOGALACTURONAN, METHYLESTERASE, CONFORMATIONS, ASSOCIATION, GELATION, CHAIN, 0904 Chemical Engineering, 0908 Food Sciences, 0912 Materials Engineering, Food Science, 3006 Food sciences, 4004 Chemical engineering

Abstract:

Pectins of varying degree and pattern of methylesterification were produced through controlled de-esterification of highly esterified citrus pectin, using carrot pectin methylesterase (PME) (P-pectins), Aspergillus aculeatus PME (F-pectins) or sodium hydroxide saponification (C-pectins). Estimation of the degree of methylesterification (DM) and quantification of the pattern of methylester distribution in terms of absolute degree of blockiness (DBₐbₛ) enabled the characterisation of pectins. Characterised pectins were used for the preparation of Ca²⁺-pectin gels with varying calcium ion (Ca²⁺) concentration. The rheological characteristics of produced gels were evaluated by means of small-amplitude oscillatory tests. During gel formation, gel strength was monitored so as to allow assessment of network development. Based on the evaluation of mechanical spectra, the nature of the cured gels was established. Depending on Ca²⁺ concentration as well as DM and DBₐbₛ, gels prepared from specific C-pectins (48≥DM≥26%; 9≤DBₐbₛ≤37%) and F-pectins (64≥DM≥29%; 9≤DBₐbₛ≤50%) showed a striking decrease of the gel strength with time, while gel networks produced from other pectins either displayed a continuous increase of the gel strength or verged towards pseudo-equilibrium within the observation time of 5h. Furthermore, the DM, DBₐbₛ and Ca²⁺ concentration influenced the evolution of Ca²⁺-pectin networks from “structured liquids” to “strong gels”. Based on the experimental results, specific mechanisms of Ca²⁺ interactions with pectins were (also) considered.