Martin E. Leser

Bio: Martin E. Leser is an academic researcher from Nestlé. The author has contributed to research in topics: Adsorption & Emulsion. The author has an hindex of 40, co-authored 106 publications receiving 5459 citations. Previous affiliations of Martin E. Leser include Hebrew University of Jerusalem & Chalmers University of Technology.

Lipases at interfaces : a review

Abstract: Lipases are acyl hydrolases that play a key role in fat digestion by cleaving long-chain triglycerides into polar lipids Due to an opposite polarity between the enzyme (hydrophilic) and their substrates (lipophilic), lipase reaction occurs at the interface between the aqueous and the oil phases Hence, interfaces are the key spots for lipase biocatalysis and an appropriate site for modulating lipolysis Surprisingly enough, knowledge about the effects of the interfacial composition on lipase catalysis is still limited and only described by the term "interfacial quality" Recent systematic studies based on a biophysical approach allowed for the first time to show the effects of the interfacial microenvironment on lipase catalysis These studies demonstrate that lipase activity as a function of interfacial composition is more attributed to substrate inaccessibility rather than to enzyme denaturation or inactivation, as it is often hypothesized A detailed analysis of the interfacial properties of all compounds involved in triglyceride digestion revealed that lipolysis is a self-regulated reaction This feedback mechanism can be explored as a new avenue to control lipase catalysis To substantiate this hypothesis, oil hydrolysis in a model gastro-intestinal system was performed, which can be seen as an interfacial engineering approach to enzyme reactivity control The presented characterization of the interfacial composition and its consequences provide a new approach for the understanding of lipase reactions at interfaces with direct impact on biotechnological and health care applications

Delivery systems for liquid food products

Abstract: One of the present challenges of the food industry is to deliver nutrition and health benefits to the consumer while keeping, or improving the taste and aroma impact. Adding active ingredients to liquid food products for fortification is in most cases not possible or not sufficient to achieve the desired goal, due to the fact that many interesting micronutrients are only hardly soluble in aqueous systems and show (i) a limited stability against chemical or physical degradation, (ii) an incompatibility between the active ingredient and the food matrix, or (iii) reveal an uncontrolled release or bioavailability. Therefore, encapsulation systems, also denoted as ‘delivery systems’, are typically used to solve these formulation problems. The task to find the appropriate delivery system is especially challenging for the food industry compared to other fields such as pharmacy, medical products or cosmetics, since only a limited amount of ingredients can be used as encapsulation and stabilization material. In the present review we will discuss the delivery systems available for (semi)-liquid foods and comment on existing advantages and limitations. The remaining technical challenges to solve in the future concern mainly the facts that (i) most of the available delivery systems for aqueous products do not yet allow to significantly stabilize degradation sensitive ‘encapsulated’ active ingredients against e.g. oxidation, (ii) the ‘encapsulation’ (solubilization) capacity of some delivery systems is still quite poor and (iii) off-taste generation is possible above certain concentrations of added delivery systems.

Formation and stability of emulsions using a natural small molecule surfactant: Quillaja saponin (Q-Naturale®)

Abstract: Q-Naturale® is a natural food-grade surfactant isolated from the bark of the Quillaja saponaria Molina tree The major surface active components of Q-Naturale® are believed to be saponin-based amphiphilic molecules In this study, we compared the effectiveness of this natural surfactant for forming and stabilizing emulsions with a synthetic surfactant (Tween 80) that is widely used in the food industry We examined the influence of homogenization pressure, number of passes, and emulsifier concentration on the particle size produced Q-Naturale® was capable of forming relatively small droplets (d < 200 nm) at low surfactant-to-oil ratios (SOR < 01) using high pressure homogenization (microfluidization), but the droplets were not as small as those produced using Tween 80 under similar conditions (d < 150 nm) Q-Naturale®-coated droplets were stable to droplet coalescence over a range of pH values (2–8), salt concentrations (0–500 mM NaCl) and temperatures (20–90 °C) However, some droplet flocculation was observed under highly acidic (pH 2) and high ionic strength (≥400 mM NaCl) conditions, which was attributed to screening of electrostatic repulsion Indeed, Q-Naturale®-coated droplets had a relatively high negative charged at neutral pH that decreased in magnitude with decreasing pH These results indicate that Q-Naturale® is an effective natural surfactant that may be able to replace synthetic surfactants in food and beverage products

Monoglyceride self-assembly structures as delivery vehicles

Abstract: Monoglyceride molecules spontaneously self-assemble into various liquid crystalline structures when present in an aqueous environment The various phases can be used to achieve different functionalities, eg to protect molecules from chemical degradation, to solubilize drugs and nutrients, to control release of flavours and drugs or to increase the yield in Maillard reactions We will review (1) the typical characteristics of monoglyceride self-assembly structures, (2) the most common characterisation techniques, (3) how introduction of guest molecules influences the self-assembly structures, (4) their use for drug delivery and (5) how commercial food grade monoglycerides obtained from sunflower oil can be applied to achieve unique delivery functionalities in food systems

Stability of emulsions containing sodium caseinate and dextran sulfate: Relationship to complexation in solution

Abstract: The effect of addition of the anionic polysaccharide dextran sulfate (DS) on the properties of n -tetradecane-in-water emulsions containing sodium caseinate (CN) has been studied under different pH and ionic strength conditions. Two methods were used for preparation of the emulsions (20 vol% oil, 0.5 wt% CN, 0.1–1 wt% DS). In ‘bilayer emulsions’, the DS was added to a CN-stabilized emulsion after emulsification; in ‘mixed emulsions’, the oil was directly emulsified into the mixed biopolymer solution. At pH=6, DS was found to adsorb onto CN-coated droplets, and extensive aggregation due to bridging flocculation occurred at 0.1 wt% DS. Polymeric stabilization was observed at higher polysaccharide concentration (1 wt% DS). In the mixed emulsions, no bridging flocculation was observed at any DS concentrations. These contrasting results for the two preparation methods indicate that strong interactions are present already at a pH value above the isoelectric point of the protein, and that the structure of the adsorbed layer at the oil–water interface is different for the two sets of systems. When the pH of emulsions containing 0.5 wt% DS or less was lowered towards acidic values, precipitation was observed. The mixed and bilayer emulsions containing 1 wt% DS were found to be more stable at pH=2 than the emulsion without DS. Mixed emulsions containing 1 wt% DS exhibited good shelf-life stability on quiescent storage for 3 weeks, especially when the emulsion was prepared at low pH. Complexes were found to dissociate when 0.1 or 0.5 M NaCl was present, suggesting that associative interactions between CN and DS are mainly electrostatic.

Surface and Colloid Science

Abstract: 1: Magnetic Particles: Preparation, Properties and Applications: M. Ozaki. 2: Maghemite (gamma-Fe2O3): A Versatile Magnetic Colloidal Material C.J. Serna, M.P. Morales. 3: Dynamics of Adsorption and Oxidation of Organic Molecules on Illuminated Titanium Dioxide Particles Immersed in Water M.A. Blesa, R.J. Candal, S.A. Bilmes. 4: Colloidal Aggregation in Two-Dimensions A. Moncho-Jorda, F. Martinez-Lopez, M.A. Cabrerizo-Vilchez, R. Hidalgo Alvarez, M. Quesada-PMerez. 5: Kinetics of Particle and Protein Adsorption Z. Adamczyk.

Microemulsion-based media as novel drug delivery systems

Abstract: Microemulsions are clear, stable, isotropic mixtures of oil, water and surfactant, frequently in combination with a cosurfactant. These systems are currently of interest to the pharmaceutical scientist because of their considerable potential to act as drug delivery vehicles by incorporating a wide range of drug molecules. In order to appreciate the potential of microemulsions as delivery vehicles, this review gives an overview of the formation and phase behaviour and characterization of microemulsions. The use of microemulsions and closely related microemulsion-based systems as drug delivery vehicles is reviewed, with particular emphasis being placed on recent developments and future directions.

Potential of Different Enzyme Immobilization Strategies to Improve Enzyme Performance

Abstract: Enzyme biocatalysis plays a very relevant role in the development of many chemical industries, e.g., energy, food or fine chemistry. To achieve this goal, enzyme immobilization is a usual pre-requisite as a solution to get reusable biocatalysts and thus decrease the price of this relatively expensive compound. However, a proper immobilization technique may permit far more than to get a reusable enzyme; it may be used to improve enzyme performance by improving some enzyme limitations: enzyme purity, stability (including the possibility of enzyme reactivation), activity, specificity, selectivity, or inhibitions. Among the diverse immobilization techniques, the use of pre-existing supports to immobilize enzymes (via covalent or physical coupling) and the immobilization without supports [enzyme crosslinked aggregates (CLEAs) or crystals (CLECs)] are the most used or promising ones. This paper intends to give the advantages and disadvantages of the different existing immobilization strategies to solve the different aforementioned enzyme limitations. Moreover, the use of nanoparticles as immobilization supports is achieving an increasing importance, as the nanoparticles versatility increases and becomes more accessible to the researchers. We will also discuss here some of the advantages and drawbacks of these non porous supports compared to conventional porous supports. Although there are no universal optimal solutions for all cases, we will try to give some advice to select the optimal strategy for each particular enzyme and process, considering the enzyme properties, nature of the process and of the substrate. In some occasions the selection will be compulsory, for example due to the nature of the substrate. In other cases the optimal biocatalyst may depend on the company requirements (e.g., volumetric activity, enzyme stability, etc).

Statics and dynamics of worm-like surfactant micelles

Abstract: In certain surfactant solutions, such as aqueous cetyltrimethylammonium bromide (CTAB) in 0.1 M KBr, the amphiphiles are found to assemble reversibly into long, flexible worm-like micelles. Above a few per cent surfactant, these form an entangled viscoelastic fluid, reminiscent of a polymer solution. The authors review some recent experimental and theoretical progress concerning the equilibrium statistics and dynamics of these systems, which differ from normal polymer solutions in that the chains can break and reform reversibly.