Kristberg Kristbergsson

Effect of surfactant surface coverage on formation of solid lipid nanoparticles (SLN)

The effect of surfactant surface coverage on formation and stability of Tween 20 stabilized tripalmitin solid lipid nanoparticles (SLN) was investigated. A lipid phase (10% w/w tripalmitin) and an aqueous phase (2% w/w Tween 20, 10 mM phosphate buffer, pH 7) were heated to 75 degrees C and then homogenized using a microfluidizer. The resulting oil-in-water emulsion was kept at a temperature (37 degrees C) above the crystallization temperature of the tripalmitin to prevent solidification of emulsion droplets, and additional surfactant at various concentrations (0-5% w/w Tween 20) was added. Droplets were then cooled to 5 degrees C to initiate crystallization and stored at 20 degrees C for 24 h. Particle size and/or aggregation were examined visually and by light scattering, and crystallization behavior was examined by differential scanning calorimetry (DSC). Excess Tween 20 concentration remaining in the aqueous phase was measured by surface tensiometry. Emulsion droplets after homogenization had a mean particle diameter of 134.1+/-2.0 nm and a polydispersity index of 0.08+/-0.01. After cooling to 5 degrees C at low Tween 20 concentrations, SLN dispersions rapidly gelled due to aggregation of particles driven by hydrophobic attraction between insufficiently covered lipid crystal surfaces. Upon addition of 1-5% w/w Tween 20, SLN dispersions became increasingly stable. At low added Tween 20 concentration (<1% w/w) the SLN formed gels but only increased slightly at higher surfactant concentrations (>1% w/w). The Tween 20 concentration in the aqueous phase decreased after tripalmitin crystallization suggesting additional surfactant adsorption onto solid surfaces. At higher Tween 20 concentrations, SLN had increasingly complex crystal structures as evidenced by the appearance of additional thermal transition peaks in the DSC. The results suggest that surfactant coverage at the interface may influence crystal structure and stability of solid lipid nanoparticles via surface-mediated crystal growth.

Changes in myofibrillar proteins during processing of salted cod (Gadus morhua) as determined by electrophoresis and differential scanning calorimetry

The effects of salt-curing, drying and rehydration on muscle proteins in cod (Gadus morhua) were studied during the processing of heavily salted cod or “bacalhau”. The aim was to observe conformational stability and possible degradation or denaturation, with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and differential scanning calorimetry (DSC). The salting process significantly decreased the heat stabilities of both myosin and actin. The decrease in water content during dry-salting did shift the transition temperatures slightly back to higher temperatures. The results, from the SDS-PAGE, showed that the myosin heavy chain (MHC) was cleaved into smaller sub fragments in the salting process with the two heavy meromyosin fractions (HMM S1 and S2) and the light meromyosin (LLM) fraction being the most abundant. Actin was less affected than myosin.

Impact of Surfactant Properties on Oxidative Stability of β-Carotene Encapsulated within Solid Lipid Nanoparticles

The impact of surfactant type on the physical and chemical stability of solid lipid nanoparticle (SLN) suspensions containing encapsulated beta-carotene was investigated. Oil-in-water emulsions were formed by homogenizing 10% w/w lipid phase (1 mg/g beta-carotene in carrier lipid) and 90% w/w aqueous phase (surfactant + cosurfactant) at pH 7 and 75 degrees C and then cooling to 20 degrees C. The impact of surfactant type was investigated using aqueous phases containing different water-soluble surfactants [2.4% w/w high-melting (HM) lecithin, 2.4% w/w low-melting (LM) lecithin, and 1.4% w/w Tween 60 or 1.4% w/w Tween 80] and a cosurfactant (0.6% taurodeoxycholate). The impact of the physical state of the carrier lipid was investigated by using either a high melting point lipid (tripalmitin) to form solid particles or a low melting point lipid (medium chain triglycerides, MCT) to form liquid droplets. A higher fraction of alpha-crystals was detected in solid particles prepared with high-melting surfactants (HM-lecithin and Tween 60) than with low-melting surfactants (LM-lecithin and Tween 80). With the exception of the HM-lecithin-coated solid particles, the suspensions were stable to particle aggregation during 21 days of storage. beta-Carotene degradation after 21 days of storage was 11, 97, 100, and 91% in the solid particles (tripalmitin) and 16, 21, 95, and 90% in the liquid droplets (MCT) for HM-lecithin, LM-lecithin, Tween 80, and Tween 60, respectively. These results suggest that beta-carotene may be stabilized by (1) LM- or HM-lecithin when liquid carrier lipids are used and (2) HM-lecithin when solid carrier lipids are used. The origin of this latter effect is attributed to the impact of the surfactant tails on the generation of a crystal structure better suited to maintain the chemical stability of the encapsulated bioactive.

Quality Index Method (QIM) scheme developed for farmed Atlantic salmon (Salmo salar)

Abstract The aim of the study was to develop a Quality Index Method (QIM) scheme for raw, farmed Atlantic salmon ( Salmo salar ) and to evaluate the scheme in a shelf life study. QIM is based on the evaluation of key parameters in the deterioration of seafoods. Demerit points are assigned to selected parameters according to their importance and a Quality Index (QI) is established by cumulating the resulting scores. The maximum storage time in ice was determined with Quantitative Descriptive Analysis (QDA) of the salmon after cooking and found to be 20–21 days. This was used as a reference to enable prediction of the remaining storage time of raw salmon in ice with QIM. The calculated QI evolved linearly with storage time in ice (QI=0.82x (days in ice)+0.18, R 2 =0.97). Individual salmon varied in QI within each storage day. However, the multivariate analysis (PLS1) demonstrated that storage time could be predicted with an accuracy of±1. 5 days, assuming that five salmon from each batch were included in the QIM assessment.

Formation of solid shell nanoparticles with liquid ω-3 fatty acid core

A major challenge for food and pharmaceutical industries is the engineering of nanostructures that can efficiently encapsulate bioactive compounds with enhanced physical and chemical stability, and high load. The influence of surfactant properties on the physical and chemical stability of (i) nanostructured lipid carriers (NLC) containing tristearin and ω-3 fish oil, (ii) tristearin solid lipid nanoparticles (SLN), and (iii) ω-3 fish oil-in-water emulsions was investigated. As surfactants we used low (LM)- and high-melting (HM) lecithins. Results indicated that the presence of fish oil reduced the crystallisation temperature, melting temperature, and melting enthalpy of tristearin. NLC stabilized with HM-lecithin inhibited the oxidation of ω-3 fatty acids ≥90% compared to those stabilized with LM-lecithin. This was attributed to the solidified surfactant layer of HM-lecithin inducing crystallisation of the shell by interfacial heterogeneous nucleation. The results showed that the saturated HM-lecithin was the key in controlling the crystallisation behaviour, and thereby enabled the formation of oxidatively and physically stable lipid nanoparticles.

Engineering Food Ingredients with High-Intensity Ultrasound

The use of ultrasound in the food industry has increased in the last decades. Ultrasound has been used both to analyze food structure and composition at low ultrasonic intensities and high frequencies and to modify ingredients at high ultrasonic intensities and low frequencies. Application of the latter is referred to as high-intensity (power) ultrasonication and is generally carried out at frequencies of =0.1 MHz and ultrasonic intensities of 10–100 W cm−2. In the food industry, power ultrasonication has proved to be a highly effective food processing and preservation technology, and use of high-intensity ultrasound with or without heat may be used, for example, to denature enzymes, aid in the extraction of valuable compounds from plants and seeds, tenderize meat, and homogenize or disperse two-phase systems such as emulsions or suspensions (Mason et al., 1996).

Influence of co-surfactants on crystallization and stability of solid lipid nanoparticles.

HYPOTHESIS The purpose of this study was to find a suitable co-surfactant to replace non-food grade bile salts in solid lipid nanoparticle (SLN) formulations. The hypothesis was that the molecular structure and physical properties of co-surfactant modulate the stabilization of SLNs upon polymorphic transition. EXPERIMENTS Tristearin SLNs were prepared by using two main surfactants: saturated high-melting lecithin, and unsaturated low-melting lecithin. As co-surfactants we used sodium taurodeoxycholate (i.e. bile salt), Pluronic F68, Tween 60 and 80, and amino acids tyrosine, tryptophan, and phenylalanine. The influence of co-surfactants on crystallization behavior and physical stability of SLNs was investigated by differential scanning calorimetry and static light scattering, respectively. FINDINGS The results showed that the aromatic amino acids had optimal structures and properties to act as effective co-surfactants in SLNs. Our study suggests that ideal co-surfactants are amphiphilic with pronounced hydrophobic areas, but highly water soluble so that they can have a reservoir of molecules readily available for interfacial stabilization. They adsorb fast to the interfaces, but without inducing polymorphic transition. This work demonstrates how the right structure can facilitate the desired function.

Examination of the Interaction of Chitosan and Oil-in-Water Emulsions Under Conditions Simulating the Digestive System Using Confocal Microscopy

ABSTRACT Chitosan is a cationic biopolymer that has been used extensively in dietary supplements to reduce fat absorption in the fight against obesity. The mechanism of fat binding of chitosan is still not fully understood and has been the subject of controversy. This study was designed to improve the understanding of the underlying mechanism by investigating the interaction of chitosan with oil-in-water emulsion droplets. Our results indicated that (0.1% w/w) chitosan adsorbed to a 20% w/w phosphatidylcholine-stabilized anionic primary emulsion to form a secondary cationic emulsion by electrostatic attraction forces under conditions resembling the stomach (pH 2). Bile salts (6 mM) were added to simulate secretion in the small intestine and pH increase. Bile salts adsorbed to the chitosan secondary emulsion, which resulted in aggregation of oil droplets followed by coalescence due to close packing of droplets. Increased viscosity (267–2531 cp) and increased degree of deacetylation (40–92% DDA) of chitosan enhanced emulsion breakdown. Increasing the pH to 7.5 without addition of bile salts yielded little aggregation. Pronounced aggregation is thought to decrease the accessibility of lipase to the oil resulting in lower bioavailability and reduced caloric intake. Understanding how chitosan interacts with oil droplets in the digestive tract is vital to developing a comprehensive model of the influence of chitosan on the bioavailability of dietary lipids. The information gained in this study may be useful for the interpretation and experimental design of animal and human feeding studies and for the rational design of chitosan-based functional foods for fat reduction.

Formation of transparent solid lipid nanoparticles by microfluidization: influence of lipid physical state on appearance.

HYPOTHESIS This study investigated the influence of liquid-solid transition and particle size on the optical properties of nanoemulsions. The hypothesis was that the crystallization of lipid droplets influences the nanoemulsion appearance. EXPERIMENTS Liquid and solid nanoemulsions (10 wt% octadecane, 1-5 wt% sodium dodecylsulfate) were formed by high-pressure microfluidization (5000-28,500 psi) at 45 °C. Solid lipid nanoparticles were formed by cooling the nanoemulsions to 5 °C and then heating to ambient temperature, whereas liquid nanoemulsions were formed by maintaining them at 25 °C. FINDINGS Results indicated that lipid nanoparticles ranging from 136 nm down to 36 nm were generated, and were stable to particle aggregation. The melting and onset temperatures of the nanoparticles decreased with decreasing particle diameter. Upon crystallization of the lipid, the absorbance increased by about 140% for nanoemulsions with 136 nm particle diameter, but only 5% for nanoemulsions with 36 nm particle diameter. These results were explained in terms of changes in refractive index upon droplet solidification that alter their scattering behavior. These results show that solidification of nanoemulsions results in a shift of the transparent-to-turbid transition regime. The practical consequences for emulsion manufacturers are that solid nanoemulsions must be smaller than liquid nanoemulsions to remain transparent.

Seasonal Changes in Chemical Composition and Quality Parameters in Capelin (Mallotus villosus)

Abstract Seasonal variation in capelin was examined by measuring chemical and lipid composition, including anti- and pro-oxidants. Lipid oxidation and other deterioration products were monitored. Results on chemical changes during landing of whole capelin indicated that the spoilage processes were intensive. This was evident by decomposition of endogenous antioxidants and gradual onset of rancidity and spoilage. Capelin from each season was found to have some distinctive chemical characteristics. High autolytic activity as well as high content of astax-anthin was found in the heavily feeding summer capelin. Autumn capelin contained the highest lipid content and the lowest stability towards lipid oxidation. The most uniform quality was observed in the winter capelin, while the spawning, fat depleted spring capelin contained the highest content of tocopherols.