Jes C. Knudsen

Transparent Films Based on PLA and Montmorillonite with Tunable Oxygen Barrier Properties

Polylactide (PLA) is viewed as a potential material to replace synthetic plastics (e.g., poly(ethylene terephthalate) (PET)) in food packaging, and there have been a number of developments in this direction. However, for PLA to be competitive in more demanding uses such as the packaging of oxygen-sensitive foods, the oxygen permeability coefficient (OP) needs to be reduced by a factor of ~10. To achieve this, a layer-by-layer (Lbl) approach was used to assemble alternating layers of montmorillonite clay and chitosan on extruded PLA film surfaces. When 70 bilayers were applied, the OP was reduced by 99 and 96%, respectively, at 20 and 50% RH. These are, to our knowledge, the best improvements in oxygen barrier properties ever reported for a PLA/clay-based film. The process of assembling such multilayer structures was characterized using a quartz crystal microbalance with dissipation monitoring. Transmission electron microscopy revealed a well-ordered laminar structure in the deposited multilayer coatings, and light transmittance results demonstrated the high optical clarity of the coated PLA films.

Synergistic cooperation of high pressure and carrot dietary fibre on texture and colour of pork sausages.

In order to investigate the synergistic cooperation between high pressure treatment (HP) and carrot dietary fibre, two formulations of pork sausages containing different percentage of carrot dietary fibre were pressurized at 500 and 600 MPa, for 1 second, 3, 6, and 9 min at 40, 50, and 60 °C. HP treatments significantly increase Youngs Modulus and affect Hencky strain values. We conclude that HP processing and carrot dietary fibre markedly improved emulsion strength resulting in firm sausages. Colour changes were investigated and significant increase in L* value and decrease in a* value were found, indicating that HP, temperature, and dietary fibre can affect physico-chemical properties of the meat matrix altering the intrinsic ability to absorb or reflect light. The sensory evaluation showed that HP treatment synergistically cooperate with carrot dietary fibre improving sensorial attributes like homogeneity, creaminess, fattiness, and firmness as detected by Napping in combination with Ultra-Flash Profile.

Reduction of salt in pork sausages by the addition of carrot fibre or potato starch and high pressure treatment

The combined effect of high pressure processing (HPP) (400, 600 and 800 MPa) and carrot fibre (CF) and potato starch (PS) on low salt (1.2%) pork sausages was investigated and compared with high (1.8%) salt sausages. Sausages had a marked increase in whitening with increasing content of fibre or starch, pressure level, and process temperature. The degree of redness was mainly affected by pressure level and heat treatment. An important finding regarding salt reduction was that the use of starch or fibre had more impact on textural properties than the level of salt since Youngs modulus and strain at fracture were mainly affected by formulation and HPP. Water binding capacity of low salt sausages was improved to the same level as high salt sausages with HPP and addition of CF or PS particularly by the addition of PS which produced sausages with better sensory properties than CF. The sensory analysis showed that this approach is promising for producing low salt sausages.

Acute Effect of Alginate‐Based Preload on Satiety Feelings, Energy Intake, and Gastric Emptying Rate in Healthy Subjects

Viscous dietary fibers such as sodium alginate extracted from brown seaweed have received much attention lately for their potential role in energy regulation through the inhibition of energy intake and increase of satiety feelings. The aim of our study was to investigate the effect on postprandial satiety feelings, energy intake, and gastric emptying rate (GER), by the paracetamol method, of two different volumes of an alginate‐based preload in normal‐weight subjects. In a four‐way placebo‐controlled, double‐blind, crossover trial, 20 subjects (age: 25.9 ± 3.4 years; BMI: 23.5 ± 1.7 kg/m2) were randomly assigned to receive a 3% preload concentration of either low volume (LV; 9.9 g alginate in 330 ml) or high volume (HV; 15.0 g alginate in 500 ml) alginate‐based beverage, or an iso‐volume placebo beverage. The preloads were ingested 30 min before a fixed breakfast and again before an ad libitum lunch. Consumption of LV‐alginate preload induced a significantly lower (8.0%) energy intake than the placebo beverage (P = 0.040) at the following lunch meal, without differences in satiety feelings or paracetamol concentrations. The HV alginate significantly increased satiety feelings (P = 0.038), reduced hunger (P = 0.042) and the feeling of prospective food consumption (P = 0.027), and reduced area under the curve (iAUC) paracetamol concentrations compared to the placebo (P = 0.05). However, only a 5.5% reduction in energy intake was observed for HV alginate (P = 0.20). Although they are somewhat contradictory, our results suggest that alginate consumption does affect satiety feelings and energy intake. However, further investigation on the volume of alginate administered is needed before inferring that this fiber has a possible role in short‐term energy regulation.

Droplet surface properties and rheology of concentrated oil in water emulsions stabilized by heat-modified beta-lactoglobulin B.

Effects of substituting native beta-lactoglobulin B (beta-lactoglobulin) with heat-treated beta-lactoglobulin as emulsifier in oil in water emulsions were investigated. The emulsions were prepared with a dispersed phase volume fraction of Phi=0.6, and accordingly, oil droplets rather closely packed. Native beta-lactoglobulin and beta-lactoglobulin heated at 69 degrees C for 30 and 45 min, respectively, in aqueous solution at pH 7.0 were compared. Molar mass determination of the species formed upon heating as well as measurements of surface hydrophobicity and adsorption to a planar air/water interface were made. The microstructure of the emulsions was characterized using confocal laser scanning microscopy, light scattering measurements of oil droplet sizes, and assessment of the amount of protein adsorbed to surfaces of oil droplets. Furthermore, oil droplet interactions in the emulsions were quantified rheologically by steady shear and small and large amplitude oscillatory shear measurements. Adsorption of heated and native beta-lactoglobulin to oil droplet surfaces was found to be rather similar while the rheological properties of the emulsions stabilized by heated beta-lactoglobulin and the emulsions stabilized by native beta-lactoglobulin were remarkably different. A 200-fold increase in the zero-shear viscosity and elastic modulus and a 10-fold increase in yield stress were observed when emulsions were stabilized by heat-modified beta-lactoglobulin instead of native beta-lactoglobulin. Aggregates with a radius of gyration in the range from 25 to 40 nm, formed by heating of beta-lactoglobulin, seem to increase oil droplet interactions. Small quantities of emulsifier substituted with aggregates have a major impact on the rheology of oil in water emulsions that consist of rather closely packed oil droplets.

The Effective Factors on the Structure of Butter and Other Milk Fat‐Based Products

Butter and other milk fat-based products are valuable products for the dairy industry due to their unique taste, their textural characteristics, and nutritional value. However, an increased consumer demand for low-fat-based products increases the need for an increased essential understanding of the effective factors governing the structure of milk fat-based products. Today, 2 manufacturing techniques are available: the churning method and the emulsification method. The first is typically used for production of butter with a globular structure, which has become increasingly popular to obtain low-fat-based products, typically without presence of milk fat globules. The microstructure of milk fat-based products is strongly related to their structural rheology, hence applications. Structural behavior is not determined by one single parameter, but by the interactions between many. This complexity is reviewed here. Parameters such as thermal treatment of cream prior to butter making, water content, and chemical composition influence not only crystal polymorphism, but also the number and sizes of fat crystals. The number of crystal-crystal interactions formed within the products is related to product hardness. During storage, however, postcrystallization increases the solid fat content and strengthens the fat crystal network. The fat crystal network is strengthened by the formation of more and stronger crystal-crystal interactions due to mechanically interlinking of fat crystals, which occurs during crystal growth. Postcrystallization is directly linked to chemical composition. The initially observed microstructural difference causing different rheological behavior will disappear during storage due to postcrystallization and formation of more crystal-crystal interactions.

Investigation of Consecutive Fouling and Cleaning Cycles of Ultrafiltration Membranes Used for Whey Processing

Abstract Development of resistance during multiple foulings and three-step Cleaning-In-Place (CIP) operations, simulating an industrial cleaning regime of polysulfone ultrafiltration membranes, was investigated. The study explored how trans-membrane pressure (150 and 300 kPa) and feed protein concentration (0.9 and 10%) influenced resistance reduction during filtration and flux recovery by the cleaning procedures. New membranes, pre-cleaned with a full CIP cycle, were used for each experiment. Subsequent fouling (simulating production) and CIP were done three times in a row and the development of fouling layer resistance was monitored and evaluated. Results show that filtration performance decreased during the first days of usage, possibly related to build-up of internal fouling. Cleaning success based on flux recovery was negatively influenced by a high protein concentration in the feed, but independent of the trans-membrane pressure during filtration.

Localized lipid autoxidation initiated by two-photon irradiation within single oil droplets in oil-in-water emulsions

The initiation of lipid autoxidation within single oil droplets in Tween-20-stabilized oil-in-water emulsion was achieved by highly focused two-photon (2P) irradiation at excitation wavelength (λex) 700 nm. The radical formation was enhanced by inclusion of the photo-cleavable radical initiator di-tert-butyl peroxide (DTBP) into the droplets, and demonstrated with confocal microscopy using radical-sensitive probe BODIPY(665/676). The radical chain reactions progressed up to 60 μm; however, there were no indications of oxidation in neighboring droplets demonstrating that radicals and oxidized probe molecules were not able to migrate between oil droplets. In addition, the spatial propagation of lipid autoxidation increased with the degree of oil unsaturation.

The effect of butter grains on physical properties of butter-like emulsions

Milk fat exists as globules in its natural state in milk. The potential of using globular fat to modulate the rheological properties and crystallization behavior in butter-like emulsions was studied in the present work. We conducted a comparative study of butter-like emulsions, with a fat phase consisting of 0, 10, 25, 50, or 100% anhydrous milk fat (AMF), the remaining fat being butter grains, and all samples containing 20% water, to obtain systematic variation in the ratio of globular fat. All emulsions were studied over 4wk of storage at 5°C. By combining small and large deformation rheology, we conducted a detailed characterization of the rheological behavior of butter-like emulsions. We applied differential scanning calorimetry to monitor thermal behavior, confocal laser scanning microscopy for microstructural analysis, and low-field pulsed nuclear magnetic resonance spectrometry to measure solid fat content. By combining these techniques, we determined that increasing the fraction of globular fat (by mixing with butter grains) decreases the hardness of butter-like emulsions up to an order of magnitude at d 1. However, no difference was observed in thermal behavior as a function of butter grain content, as all emulsions containing butter grains revealed 2 endothermal peaks corresponding to the high (32.7°C ± 0.6) and medium (14.6°C ± 0.1) melting fractions of fatty acids. In terms of microstructure, decreasing the amount of butter grains in the emulsions resulted in formation of a denser fat crystal network, corresponding to increased hardness. Moreover, microstructural analysis revealed that the presence of butter grains resulted in faster formation of a continuous fat crystal network compared with the 100% AMF sample, which was dominated by crystal clusters surrounded by liquid oil. During storage, hardness remained stable and no changes in thermal behavior were observed, despite an increase in solid fat content of up to 5%. After 28d of storage, we observed no difference in either microstructural or rheological properties, indicating that formation of primary bonds occurs primarily within the first day of storage. The rheological behavior of butter-like emulsions is not determined solely by hardness, but also by stiffness related to secondary bonds within the fat crystal network. The complex rheological behavior of milk fat-based emulsions is better characterized using multiple parameters.