Fred van de Velde

Confocal scanning light microscopy (CSLM) on mixtures of gelatine and polysaccharides

Abstract Demonstrations are given of the application of confocal scanning light microscopy (CSLM) on mixtures of gelatine with other food biopolymers. The various aspects of phase separation are visualised in two and three dimensional images. Contrast through fluorescence is obtained either by covalent labelling or non-covalent labelling. There is special focus on the system gelatine/dextran, which is shown to be a very suitable mixture for the study of the morphology of phase separated biopolymer mixtures.

Visualisation of biopolymer mixtures using confocal scanning laser microscopy (CSLM) and covalent labelling techniques

Abstract Confocal scanning laser microscopy (CSLM) has been used to study the behaviour of mixtures of proteins, gelatine, whey proteins and β-lactoglobulin, and polysaccharides, dextran, gellan gum, carrageenan, gum Arabic, and starch. CSLM proved to be a suitable technique to visualise the microstructure of these (phase separated) mixtures in two and three-dimensional images. Contrast through fluorescence is obtained either by covalent labelling (polysaccharides and proteins) or non-covalent labelling (proteins and starch). Double and triple labelling allows the visualisation of individual components in a complex mixture of biopolymers.

On the structure of κ/ι-hybrid carrageenans

Abstract The coil-to-helix transition and temperature dependence of the viscosity of commercial κ/ι-hybrid carrageenans produced by the red algae Sarcothalia crispata , Mazaella laminarioides , and Chondrus crispus were studied using rheometry and optical rotation. The structure of these κ/ι-hybrid carrageenans was determined by 1 H and 13 C NMR spectroscopy combined with monosaccharide composition analysis. The coil-to-helix transitions, measured by polarimetry and rheometry, of the κ/ι-hybrid carrageenans are significantly different from those of pure κ- and ι-carrageenan, and from hand-made mixtures thereof. This provides evidence that the κ/ι-hybrid carrageenans are mixed chains, containing both κ- and ι-repeating units.

Protein-Polysaccharide Interactions to Alter Texture

The sensory perception of texture is an important contributor of our general appreciation of foods. Food texture is mainly described in terms of mouthfeel and afterfeel attributes. The role of oral processing in the perception of texture and the role of microstructure therein have been reviewed regularly over recent years (Chen & Engelen 2012, Foegeding et al. 2011, Stieger & van de Velde 2013) and are not, therefore, addressed in this review. The scope of this review relates to the molecules that underlay the texture of foods. Protein, carbohydrate, and fat are the major structuring components in foods. In this review we focus on the physical interactions between proteins and polysaccharides that form the basis for the microstructure and texture of these foods. In general, food products are classified in four categories by their sensory and rheological properties: liquids, semisolids, soft solids, and hard solids (van Vliet et al. 2009). These four categories provide a useful classification framework, although they are not precisely defined by specific rheological properties. The current review focuses on semisolid and soft-solid foods.

High Resolution NMR of Carrageenans

Carrageenan is the generic name for a family of linear, sulphated galactans, obtained by extraction from certain species of marine red algae (Rhodophyta) [1]. They are composed of alternating 3-linked β-d-galactopyranose (G-units) and 4-linked α-d-galactopyranose (D-units) or 4-linked 3,6-anhydro-α-d-galactopyranose (DA-units), forming the disaccharide repeating unit of carrageenans (Figure 1). The sulphated galactans are classified according to the presence of the 3,6-anhydro-bridge on the 4linked galactose residue and the position and number of sulphate groups. The most common types of carrageenan are traditionally identified by a Greek prefix indicating the major component of the sample. To describe more complex carrageenan structures a uniform letter code nomenclature has been developed by Knutsen et al. [2]. The three commercially most important carrageenans are called ι (iota)-, κ (kappa)-, and λ (lambda)-carrageenan, the corresponding letter codes are G4S-DA2S, G4S-DA, and G2S-D2S,6S. Two other types, called μ (mu)and ν (nu)-carrageenan, which are the biological precursors of respectively κand ι-carrageenan, are often encountered in commercial carrageenan.

Application of whey proteins as coating ingredients

Technologies are described where activated whey proteins are used for encapsulating sensitive food materials. The mechanism, governing the solubility of whey protein films and coatings, on which these technologies are based was investigated.The building blocks for these films and coatings were aggregated whey proteins. Solubility was related to the continuity of the network of disulfide cross-links between the building blocks and the dynamics of rearrangements of disulfide bonds occurring via the socalled SH/S-S exchange reaction.By controlling either the accessibility of thiol groups or the accessibility of disulfide bonds within the whey protein aggregates, solubility of whey protein coatings and films could be tuned. These new insights will help to improve the properties of whey protein coatings promoting the applicability of whey proteins in films, encapsulates and coatings.The technologies have been intellectual property rights (IPR)-protected (1-5) by NIZO food research.

Formation Dynamics of Oral Oil Coatings and Their Effect on Subsequent Sweetness Perception of Liquid Stimuli.

Knowledge of the formation of oral coatings and their influence on subsequent taste perception is necessary to understand possible taste-masking effects by oil coatings. This study investigated (a) the dynamics of the formation of oral oil coatings formed by o/w emulsions and (b) the effect of oral oil coatings on subsequent sweetness perception of sucrose solutions. In vivo fluorescence was used to quantitate the oil fraction deposited on the tongue after oral processing of oil-in-water emulsions for different times. A trained panel evaluated sweetness perception of sucrose solutions after orally processing the emulsions. The oil fraction reached its maximum value within the first 3 s of oral processing. The oil fraction did not significantly affect subsequent sweetness perception of sucrose solutions. It is suggested that the oil droplets deposited on the tongue did not form a hydrophobic barrier that is sufficient to reduce the accessibility of sucrose to taste buds.

A Comparison of the lubrication behavior of whey protein model foods using tribology in linear and elliptical movement

Lubrication is an important factor in the sensory evaluation of food products. Tribology provides a theoretical framework and instrumental methods for evaluating frictional properties between two moving surfaces and the lubrication behavior of products between these surfaces. Relating frictional measurements to sensory properties detected during oral processing requires careful and pertinent choices in surface materials and testing conditions. The aims of this study were to investigate: (a) differences in lubrication behavior of a range of food textures and (b) the differences between linear and elliptical movement and added saliva to understand the contribution of food structure to friction. Six whey protein model food samples, ranging in texture from fluid to semisolid to soft solid, were analyzed using a pin on disk tribometer to determine the coefficient of friction (COF) across a range of sliding speeds. The samples were analyzed in their initial form and post-oral processing (n = 4) in both linear and elliptical movements. Elliptical movement slightly decreased coefficients of friction and extended the shape of the friction curve. Increases in test food viscosity decreased the COF but differences in viscosity were not apparent when test foods were mixed with saliva. Data correction for viscosity shifted the friction curves horizontally, indicating that lubrication had a greater impact upon friction than viscosity. This study provides initial insights for further comparison of linear and elliptical movement with a variety of sample compositions. PRACTICAL APPLICATIONS Sensory perception of smoothness and creaminess are often major contributors to overall hedonic food liking and are a major reason why products high in fat and sugar are more highly preferred over other foods. These parameters are influenced by friction and lubrication between the tongue, palate, teeth, food products, and saliva during oral processing. Tribology provides an instrumental method to evaluate friction between moving surfaces that mimic oral surfaces and the lubrication behavior of foods. Trends in frictional measurements can be correlated with sensory ratings of the same foods to better understand why preferences exist for certain foods or food compositions and how to effectively improve the acceptability and enjoyment of healthier foods.