Microalgae are rich in several nutritional and health-beneficial components, showing great potential as functional food ingredients. To this extent, knowledge of the biomass composition is essential in the selection of suitable microalgae species for specific food applications. Surprisingly, although cell wall polysaccharides are generally reported to play a role in functionality, limited attention has been given to the cell wall related polysaccharides of microalgae so far. Therefore, this study aimed to characterize dry biomasses of ten microalgae species with potential as functional food ingredients, with a particular focus on the composition of cell wall related polysaccharides. The investigated species were Arthrospira platensis, Chlorella vulgaris, Diacronema lutheri, Tisochrysis lutea, Nannochloropsis sp., Odontella aurita, Phaeodactylum tricornutum, Porphyridium cruentum, Schizochytrium sp. and Tetraselmis chuii. Lipids, proteins and ash made up a large fraction of the biomasses, except for the freshwater algae C. vulgaris and A. platensis which were mainly composed of proteins and polysaccharides. Generally, low amounts of storage polysaccharides (2-8%) were observed in the investigated microalgae species, while extracellular polymeric substances were only present in P. cruentum, O. aurita, C. vulgaris and A. platensis. Cell wall polysaccharides contributed approximately 10% of the biomass and were composed of heteropolysaccharides, showing at least five different monosaccharides. Moreover, the presence of uronic acids and sulfate groups provides anionic characteristics to the cell wall related polysaccharides of several microalgae. As a result, these polysaccharides show potential to display interesting functionalities as bioactive or technological substances.

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 NaHCO 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 NaHCO 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.

No abstract

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.

No abstract