Martina Lille

Nanofibrillar cellulose hydrogel promotes three-dimensional liver cell culture

Over the recent years, various materials have been introduced as potential 3D cell culture scaffolds. These include protein extracts, peptide amphiphiles, and synthetic polymers. Hydrogel scaffolds without human or animal borne components or added bioactive components are preferred from the immunological point of view. Here we demonstrate that native nanofibrillar cellulose (NFC) hydrogels derived from the abundant plant sources provide the desired functionalities. We show 1) rheological properties that allow formation of a 3D scaffold in-situ after facile injection, 2) cellular biocompatibility without added growth factors, 3) cellular polarization, and 4) differentiation of human hepatic cell lines HepaRG and HepG2. At high shear stress, the aqueous NFC has small viscosity that supports injectability, whereas at low shear stress conditions the material is converted to an elastic gel. Due to the inherent biocompatibility without any additives, we conclude that NFC generates a feasible and sustained microenvironment for 3D cell culture for potential applications, such as drug and chemical testing, tissue engineering, and cell therapy.

The role of hemicellulose in nanofibrillated cellulose networks

Cellulose nanofibrils show remarkable properties with applications in several fields of materials science, such as for composites, hydrogels, aerogels, foams, and coatings. Cellulose nanofibrils are typically produced by mechanical and enzymatic processing leading to fibrils having a width in the nanometer range and very high aspect ratios. The formation of percolating networks and interactions between fibrils lead to useful properties in for example gel formation and composites. In this work we studied how the residual xylan that is found in cellulose nanofibrils that have been produced from hardwood pulp affects these properties. We used enzymatic hydrolysis to specifically remove xylan and studied rheological properties, morphological features, and properties of paper-like films of cellulose nanofibrils. We found that removal of xylan enhances the formation of fibril networks, resulting in both stiffer gels and stronger films. However xylan also stabilizes the fibrils against flocculation. Also the history of processing of the preparations affects the results significantly.

Enzymatically structured emulsions in simulated gastrointestinal environment: impact on interfacial proteolysis and diffusion in intestinal mucus.

Fundamental knowledge of physicochemical interactions in the gastrointestinal environment is required in order to support rational designing of protein-stabilized colloidal food and pharmaceutical delivery systems with controlled behavior. In this paper, we report on the colloidal behavior of emulsions stabilized with the milk protein sodium caseinate (Na-Cas), and exposed to conditions simulating the human upper gastrointestinal tract. In particular, we looked at how the kinetics of proteolysis was affected by adsorption to an oil-water interface in emulsion and whether the proteolysis and the emulsion stability could be manipulated by enzymatic structuring of the interface. After cross-linking with the enzyme transglutaminase, the protein was digested with use of an in vitro model of gastro-duodenal proteolysis in the presence or absence of physiologically relevant surfactants (phosphatidylcholine, PC; bile salts, BS). Significant differences were found between the rates of digestion of Na-Cas cross-linked in emulsion (adsorbed protein) and in solution. In emulsion, the digestion of a population of polypeptides of M(r) ca. 50-100 kDa was significantly retarded through the gastric digestion. The persistent interfacial polypeptides maintained the original emulsion droplet size and prevented the system from phase separating. Rapid pepsinolysis of adsorbed, non-cross-linked Na-Cas and its displacement by PC led to emulsion destabilization. These results suggest that structuring of emulsions by enzymatic cross-linking of the interfacial protein may affect the phase behavior of emulsion in the stomach and the gastric digestion rate in vivo. Measurements of ζ-potential revealed that BS displaced the remaining protein from the oil droplets during the simulated duodenal phase of digestion. Diffusion of the postdigestion emulsion droplets through ex vivo porcine intestinal mucus was only significant in the presence of BS due to the high negative charge these biosurfactants imparted to the droplets. This implies that the electrostatic repulsion produced can prevent the droplets from being trapped by the mucus matrix and facilitate their transport across the small intestine mucosal barrier.

Versatile peroxidase as a valuable tool for generating new biomolecules by homogeneous and heterogeneous cross-linking.

The modification and generation of new biomolecules intended to give higher molecular-mass species for biotechnological purposes, can be achieved by enzymatic cross-linking. The versatile peroxidase (VP) from Pleurotus eryngii is a high redox-potential enzyme with oxidative activity on a wide variety of substrates. In this study, VP was successfully used to catalyze the polymerization of low molecular mass compounds, such as lignans and peptides, as well as larger macromolecules, such as protein and complex polysaccharides. Different analytical, spectroscopic, and rheological techniques were used to determine structural changes and/or variations of the physicochemical properties of the reaction products. The lignans secoisolariciresinol and hydroxymatairesinol were condensed by VP forming up to 8 unit polymers in the presence of organic co-solvents and Mn(2+). Moreover, 11 unit of the peptides YIGSR and VYV were homogeneously cross-linked. The heterogeneous cross-linking of one unit of the peptide YIGSR and several lignan units was also achieved. VP could also induce gelation of feruloylated arabinoxylan and the polymerization of β-casein. These results demonstrate the efficacy of VP to catalyze homo- and hetero-condensation reactions, and reveal its potential exploitation for polymerizing different types of compounds.

Relating microstructure, sensory and instrumental texture of processed oat

This study is a part of a larger project aiming to produce new, healthy, and tasty food ingredients from oat. Germination and different heating processes can be used to improve the texture and flavour of cereals. In this study effects of germination and wet and dry heating on the microstructure, instrumental structure and sensory properties of two oat varieties were assessed. The microstructure of native, germinated, autoclaved and extruded grains of the hulled cv. Veli and hull-less cv. Lisbeth was examined by light microscopy, the texture was measured by determining the milling energy and hardness of the grains and sensory characteristics were evaluated with descriptive sensory profile analysis. In cv. Veli the cells of the starchy endosperm were smaller than in cv. Lisbeth and β-glucan was concentrated in the subaleurone layer. In cv. Lisbeth β-glucan was evenly distributed in the starchy endosperm. The grains of cv. Lisbeth were more extensively modified in the germination process than the grains of cv. Veli, otherwise the effects of processing on the grains of the two cultivars were similar. Germination caused cell wall degradation, autoclaving and extrusion cooking caused starch gelatinization. Autoclaving resulted in the hardest perceived texture in oat. Gelatinization of starch appeared to contribute more to the hardness of oat groats than the cell wall structure. Of the instrumental methods used in this study the milling energy measurement appeared to be the most useful method for the analysis of the effects of processing on grain structure.

Crosslinking with transglutaminase does not change metabolic effects of sodium caseinate in model beverage in healthy young individuals

BackgroundPostprandial metabolic and appetitive responses of proteins are dependent on protein source and processing technique prior to ingestion. Studies on the postprandial effects of enzymatic crosslinking of milk proteins are sparse. Our aim was to study the effect of transglutaminase (TG)-induced crosslinking of sodium caseinate on postprandial metabolic and appetite responses. Whey protein was included as reference protein.MethodsThirteen healthy individuals (23.3 ± 1.1 y, BMI 21.7 ± 0.4 kg/m2) participated in a single-blind crossover design experiment in which the subjects consumed three different isovolumic (500 g) pourable beverages containing either sodium caseinate (Cas, 29 g), TG-treated sodium caseinate (Cas-TG, 29 g) or whey protein (Wh, 30 g) in a randomized order. Blood samples were collected at baseline and for 4 h postprandially for the determination of plasma glucose, insulin and amino acid (AA) concentrations. Gastric emptying (GE) was measured using the 13 C-breath test method. Appetite was assessed using visual analogue scales.ResultsAll examined postprandial responses were comparable with Cas and Cas-TG. The protein type used in the beverages was reflected as differences in plasma AA concentrations between Wh and Cas, but there were no differences in plasma glucose or insulin responses. A tendency for faster GE rate after Wh was detected. Appetite ratings or subsequent energy intake did not differ among the protein beverages.ConclusionsOur results indicate that the metabolic responses of enzymatically crosslinked and native sodium caseinate in a liquid matrix are comparable, suggesting similar digestion and absorption rates and first pass metabolism despite the structural modification of Cas-TG.

Cross-linking of sodium caseinate-structured emulsion with transglutaminase alters postprandial metabolic and appetite responses in healthy young individuals.

The physico-chemical and interfacial properties of fat emulsions influence lipid digestion and may affect postprandial responses. The aim of the present study was to determine the effects of the modification of the interfacial layer of a fat emulsion by cross-linking on postprandial metabolic and appetite responses. A total of fifteen healthy individuals (26.5 (sem 6.9) years and BMI 21.9 (sem 2.0) kg/m2) participated in a cross-over design experiment in which they consumed two isoenergetic (1924 kJ (460 kcal)) and isovolumic (250 g) emulsions stabilised with either sodium caseinate (Cas) or transglutaminase-cross-linked sodium caseinate (Cas-TG) in a randomised order. Blood samples were collected from the individuals at baseline and for 6 h postprandially for the determination of serum TAG and plasma NEFA, cholecystokinin (CCK), glucagon-like peptide 1 (GLP-1), glucose and insulin responses. Appetite was assessed using visual analogue scales. Postprandial TAG and NEFA responses and gastric emptying (GE) rates were comparable between the emulsions. CCK increased more after the ingestion of Cas-TG than after the ingestion of Cas (P< 0.05), while GLP-1 responses did not differ between the two test emulsions. Glucose and insulin profiles were lower after consuming Cas-TG than after consuming Cas (P< 0.05). The overall insulin, glucose and CCK responses, expressed as areas above/under the curve, did not differ significantly between the Cas and Cas-TG meal conditions. Satiety ratings were reduced and hunger, desire to eat and thirst ratings increased more after the ingestion of Cas-TG than after the ingestion of Cas (P< 0.05). The present results suggest that even a subtle structural modification of the interfacial layer of a fat emulsion can alter the early postprandial profiles of glucose, insulin, CCK, appetite and satiety through decreased protein digestion without affecting significantly on GE or overall lipid digestion.

Plant cells as food – A concept taking shape

Plant cell cultures from cloudberry, lingonberry and stoneberry were studied in terms of their nutritional properties as food. Carbohydrate, lipid and protein composition, in vitro protein digestibility and sensory properties were investigated. Dietary fibre content varied between 21.2 and 36.7%, starch content between 0.3 and 1.3% and free sugar content between 17.6 and 33.6%. Glucose and fructose were the most abundant sugars. High protein contents between 13.7 and 18.9% were recorded and all samples had a balanced amino acid profile. In vitro protein digestion assay showed hydrolysis by digestive enzymes in fresh cells but only limited hydrolysis in freeze-dried samples. The lipid analysis indicated that the berry cells were rich sources of essential, polyunsaturated fatty acids. In sensory evaluation, all fresh berry cells showed fresh odour and flavour. Fresh cell cultures displayed a rather sandy, coarse mouthfeel, whereas freeze-dried cells melted quickly in the mouth. All in all the potential of plant cells as food was confirmed.

Structural properties and foaming of plant cell wall polysaccharide dispersions

Water suspensions of cellulose nanofibres with xylan, xyloglucan and pectin were studied for foaming and structural properties as a new means for food structuring. The dispersions were analysed with rheological measurements, microscopy and optical coherence tomography. A combination of xylan with TEMPO-oxidized nanocellulose produced a mixture with well-dispersed air bubbles, while the addition of pectin improved the elastic modulus, hardness and toughness of the structures. A similar structure was observed with native nanocellulose, but the elastic modulus was not as high. Shear flow caused cellulose nanofibres to form plate-like flocs in the suspension that accumulated near bubble interfaces. This tendency could be affected by adding laccase to the dispersion, but the effect was opposite for native and TEMPO-oxidized nanocellulose. Nanocellulose type also influenced the interactions between nanofibers and other polysaccharides. For example, xyloglucan interacted strongly with TEMPO-oxidized nanocellulose (high storage modulus) but not with native nanocellulose.