Mechanistic insight into softening of Canadian wonder common beans (Phaseolus vulgaris) during cooking.

The relative contributions of cotyledons and seed coats towards hardening of common beans (Phaseolus vulgaris) were investigated and the rate-limiting process which controls bean softening during cooking was determined. Fresh or aged whole beans and cotyledons were soaked and cooked in demineralised water or 0.1 M NaHCO3 solution, and texture evolution, microstructure changes and thermal properties were studied. Fresh and aged whole beans cooked in demineralised water had significantly different softening rate constants and so did fresh and aged cotyledons. The comparable softening rate constants of aged whole beans and cotyledons indicated an insignificant role of the seed coat in hardening during storage. All samples cooked faster in 0.1 M NaHCO3 solution. Disintegration of cooked tissues followed by microscopic examination revealed a transition from cell breakage through a phase of cell breakage and separation to complete cell separation with increased cooking time wherefore texture decayed. Therefore, progressive solubilization of pectin in the middle lamella greatly promoted texture decay. While residual birefringence even after substantial cooking time suggested some molecular order of the starch, calorimetric analyses revealed complete starch gelatinisation before complete cell separation occurred. This implies an insignificant role of starch in texture decay during cooking but its hindered uncoiling into a viscous gel after gelatinisation due to the restricting cell wall could promote its retrogradation. Therefore, we suggest that the rate-determining process in bean softening relates to cell wall/middle lamella changes influencing pectin solubilization.

Characterization and Degradation of Pectic Polysaccharides in Cocoa Pulp.

Microbial fermentation of the viscous pulp surrounding cocoa beans is a crucial step in chocolate production. During this process, the pulp is degraded, after which the beans are dried and shipped to factories for further processing. Despite its central role in chocolate production, pulp degradation, which is assumed to be a result of pectin breakdown, has not been thoroughly investigated. Therefore, this study provides a comprehensive physicochemical analysis of cocoa pulp, focusing on pectic polysaccharides, and the factors influencing its degradation. Detailed analysis reveals that pectin in cocoa pulp largely consists of weakly bound substances, and that both temperature and enzyme activity play a role in its degradation. Furthermore, this study shows that pulp degradation by an indigenous yeast fully relies on the presence of a single gene (PGU1), encoding for an endopolygalacturonase. Apart from their basic scientific value, these new insights could propel the selection of microbial starter cultures for more efficient pulp degradation.

Process-Structure-Function Relations of Pectin in Food.

Pectin, a complex polysaccharide rich in galacturonic acid, has been identified as a critical structural component of plant cell walls. The functionality of this intricate macromolecule in fruit- and vegetable-based-derived products and ingredients is strongly determined by the nanostructure of its most abundant polymer, homogalacturonan. During food processing, pectic homogalacturonan is susceptible to various enzymatic as well as nonenzymatic conversion reactions modifying its structural and, hence, its functional properties. Consequently, a profound understanding of the various process-structure-function relations of pectin aids food scientists to tailor the functional properties of plant-based derived products and ingredients. This review describes the current knowledge on process-structure-function relations of pectin in foods with special focus on pectin's functionality with regard to textural attributes of solid plant-based foods and rheological properties of particulated fruit- and vegetable-derived products. In this context, both pectin research performed via traditional, ex situ physicochemical analyses of fractionated walls and isolated polymers and pectin investigation through in situ pectin localization are considered.

Study of mango endogenous pectinases as a tool to engineer mango purée consistency.

The objective of this work was to evaluate the possibility of using mango endogenous pectinases to change the viscosity of mango purée. Hereto, the structure of pectic polysaccharide and the presence of sufficiently active endogenous enzymes of ripe mango were determined. Pectin of mango flesh had a high molecular weight and was highly methoxylated. Pectin methylesterase showed a negligible activity which is related to the confirmed presence of a pectin methylesterase inhibitor. Pectin contained relatively high amounts of galactose and considerable ß-galactosidase (ß-Gal) activity was observed. The possibility of stimulating ß-Gal activity during processing (temperature/pressure, time) was investigated. ß-Gal of mango was rather temperature labile but pressure stable relatively to the temperature and pressure levels used to inactivate destructive enzymes in industry. Creating processing conditions allowing endogenous ß-Gal activity did not substantially change the consistency of mango purée.

The impact of extraction with a chelating agent under acidic conditions on the cell wall polymers of mango peel.

The objective of this research was to evaluate whether mango peel is a potential source of functional cell wall polymers. To reach this objective, the native pectin polymers (NPP) extracted as alcohol insoluble residue from mango peel, were characterised in terms of uronic acid content, degree of methoxylation, neutral sugar content, and molar mass and compared to citric acid (pH 2.5, 2h at 80°C) extracted polymers, mimicking industrial pectin extraction conditions. Water-solubilised NPP were highly methoxylated having two populations with a Mw of 904 and 83kDa and a degree of methoxylation of 66%. Citric acid extraction with a yield higher than H2SO4 extraction resulted in a very branched pectin with an extremely high DM (83%) and a high molar mass. Comparing the Fourier Transform Infra-Red spectroscopy of extracted and native WSF showed that citric acid remained partially associated to the extracted pectin due to its chelating properties.