Martin Michel

Dynamics of mixed protein–surfactant layers adsorbed at the water/air and water/oil interface

Abstract Drop and bubble shape tensiometry experiments are performed at the water/air and water/hexane interfaces in order to get more information about the differences in the adsorption layer structure of mixed protein/surfactant systems. For mixtures of β-lactoglobulin and sodium dodecyl sulphate the adsorption at the water/air interface is essentially a competitive process between protein/surfactant complexes and free surfactant molecules, while the water/oil interface is essentially covered by the complexes.

Aerated milk protein emulsions — new microstructural aspects

Abstract The formation of stable aerated products based on milk protein emulsions, such as whipped creams, depends on (i) the physical properties of the emulsion before the whipping step; and (ii) how the air is incorporated and the created air bubbles are stabilised. The final texture of the product is determined by the arrangement of the microstructural entities and the interaction among them. Advances are being made mainly in the better understanding of the destabilisation of the oil–water interface of the emulsion, which is a key point in the formulation process. However, the connection to the ‘real product’ has still to be made. Further investigations, especially with regard to the foaming behaviour, have to be encouraged in order to predict and control the physical quality and stability of aerated milk protein emulsions.

A Rapid tool for the stability assessment of natural food colours

Natural food colours lack stability under a number of conditions such as pH variation, oxidation, hydration, heat treatment and, most importantly, exposure to daylight. Stability tests to assess shelf life of natural colours under light irradiation can be time consuming. Thus, an accelerated test carried out under high light intensity irradiation that can be related to normal daylight irradiation conditions is highly desirable. Samples of various natural colouring solutions were prepared in aqueous model matrices at a range of pH values to mimic the majority of food matrices, pasteurised and irradiated under normal D65 light (0.2 W/m(2)) at 25°C, and in parallel under high light intensity irradiation (30 W/m(2)) at 3 different temperatures (25, 35 and 45°C). Similarly to the already known Q10 parameters for temperature, acceleration factors QL for irradiation, were determined and used for the first time to obtain a link between colour degradation under normal and accelerated conditions. It was possible, using these acceleration factors, to greatly reduce the time required to predict and compare the shelf life stability for a series of natural colours in aqueous model systems.

Monocomponent hexa- and dodecaethylene glycol succinyl-tocopherol esters: Self-assembly structures, cellular uptake and sensitivity to enzyme hydrolysis

We have chemically synthesized two water-soluble forms of tocopherol succinate linked via an ester bond to hexaethylene glycol and dodecaethylene glycol. The self-assembly structure of the former in water is vesicular, whereas the latter forms elongated micelles. We treated Caco-2 cells with these compounds in these physical forms, in addition to a mixed micelle form. The intact compounds were taken up into the cells, influenced by both the chain length and the physical structure. In addition, the tocopherol derivatives were also metabolized into tocopherol succinate and tocopherol inside the cell. The total hydrolysis and uptake into the cells was two-fold higher from tocopherol hexaethylene glycol succinate in the form of mixed micelles than in vesicular form as assessed by analyzing intracellular tocopherol and tocopherol succinate. The longer polyethylene glycol chain gave a higher intracellular tocopherol succinate/tocopherol ratio. The major intracellular esterase in Caco-2 cells is carboxyl esterase 1 (EC 3.1.1.1), and in silico modelling studies show that the position of docking and hence the site of hydrolysis is influenced by the chain length. The in silico prediction is consistent with the in vitro data, since a longer chain length is predicted to favour hydrolysis of the ester bond between the succinate and polyethylene glycol moieties.

An industry perspective on natural food colour stability

Abstract The Southampton six study revolutionized the way industry formulated natural colours in food products. The replacement of artificial dyes has been challenging due to compatibility issues of natural colours with other food components, and led to gaps, for example, blue colours in acidic pH matrices. In addition, natural colours or colouring foods are more expensive, at a parity of colouring strengths, when compared to artificial dyes. Finally, colour overdosing is almost inevitable due to fast degradation, over processing and shelf life, and it is accompanied by inconvenient taste/odour issues derived from the original ingredient used to produce the colour. This chapter describes recent developments in stabilization techniques to improve performances of natural colours, as well as formulation strategies to limit losses during processing with some of the most common solutions. The last part of this chapter focuses on the necessity to develop new rapid methods to determine whether natural solutions are suitable for use in relevant food matrices.

Dynamic interfacial tensions in the short time range by applying a fast capillary pressure technique

The capillary pressure technique is the method of choice for any tensiometry measurements in microgravity, as all bubbles and drops have a spherical shape. A combination of fast drop formation based on a known constant liquid flow and fast data acquisition of measured capillary pressure gives access to dynamic interfacial tensions in the range of milliseconds. Also the maximum drop pressure method, an equivalent to the maximum bubble pressure technique as fastest dynamic surface tension method, can be practised by the same set-up. The technique was developed already 15 years ago [ii] and now further refined during the MAP FASES* supported by the European Space Agency [ii]. Besides a detailed description of the technical parameters, experimental results for emulsion relevant systems are presented. The set-up presented here is based on a commercial drop and bubble profile analysis tensiometer which appears to be a kind of in-situ technique for membrane emulsification processes. The instrumental set-up is suitable also for oscillating drop and bubble experiments up to frequencies of several hundreds Hz.The capillary pressure technique is the method of choice for any tensiometry measurements in microgravity, as all bubbles and drops have a spherical shape. A combination of fast drop formation based on a known constant liquid flow and fast data acquisition of measured capillary pressure gives access to dynamic interfacial tensions in the range of milliseconds. Also the maximum drop pressure method, an equivalent to the maximum bubble pressure technique as fastest dynamic surface tension method, can be practised by the same set-up. The technique was developed already 15 years ago [ii] and now further refined during the MAP FASES* supported by the European Space Agency [ii]. Besides a detailed description of the technical parameters, experimental results for emulsion relevant systems are presented. The set-up presented here is based on a commercial drop and bubble profile analysis tensiometer which appears to be a kind of in-situ technique for membrane emulsification processes. The instrumental set-up is suitable also for oscillating drop and bubble experiments up to frequencies of several hundreds Hz.

Formation of 4-hydroxy-5-methyl-3(2H)-furanone (norfuraneol) in structured fluids

This study investigated the influence of structured fluids on Maillard-type reactions. The decomposition of xylose and the formation of volatile compounds were affected by the type of structured fluid used as reaction medium. In model systems based on xylose and glycine or leucine, xylose was preferably degraded in the hexagonal phase, compared to other mesophases and the aqueous sample. In parallel, norfuraneol was accumulated in the hexagonal phase. The data obtained indicate that molecular organisation of the reaction medium and flavour precursors can play an important role in food systems containing ingredients that tend to form self-assembly structures.

Vitamin A degradation in triglycerides varying by their saturation levels

Vitamin A deficiency has a widespread occurrence globally and is considered as one of the worlds most serious health risk factors. Potential solutions to address this deficiency include dietary diversification or supplementation, but food fortification is generally accepted as the most cost-effective solution. The main issue with food fortification of this vitamin is related to its high instability in food matrices. Dilution of vitamin A in triglycerides is a natural and appropriate way to stabilize this compound. We show here that vitamin A palmitate stability increases with increasing concentration of triglycerides. Moreover, we found that vitamin A palmitate displays improved stability in more saturated oils. Using various temperatures, and Arrhenius plots of experiments performed at storage temperatures between 30°C and 60°C for oils varying by their saturation and crystallinity, we demonstrate that crystallization is not responsible for this phenomenon. Additionally, we show by centrifugation that vitamin A is preferably solubilized in the liquid phase compared to the crystalline phase, explaining that triglyceride crystallization does not stabilize vitamin A palmitate. It is proposed that unsaturated fats generate more oxidation products such as radicals and peroxides, leading to a quicker degradation of vitamin A.

Strategies to limit colour changes when fortifying food products with iron

Iron, vitamin A, zinc and iodine have been recognized to be the micronutrients with the largest deficiencies worldwide. Among these, iron is highly reactive and may lead to negatively perceived organoleptic changes in products such as dull colour and off-taste. The colour change originated in fortified fruit-containing food products was confirmed to be the result of the complexation of iron and polyphenols. Phenolic compounds with two or more vicinal hydroxy benzyl moieties in their structure, such as catechols and pyrogallols were investigated for their ability to give bathochromic shift phenomena when mixed with iron salts. Furthermore, strategies for limiting colour development were based on: 1) pH adjustment; 2) saturation of polyphenols with unreactive divalent metal ions; 3) suppression of iron reactivity through complexation. Some of these strategies showed a significant improvement in colour stability, with the best results achieved by the latter. The findings in model systems gave a good insight of the mechanisms involved in colour changes, and results were transferable to iron fortified banana puree.

Colloids in Milk Products

Food, especially milk, is such a familiar material to all of us that it is easy to overlook the scientific input required to assure the quality of existing milk products and/or to come up with new and better processed dairy foods. A major input comes from the research fields of Colloid and Interface science and Soft Condensed Matter Physics, since it becomes more and more evident that relevant properties of foods, such as texture, taste, color, viscosity, stability, mouth-feel or nutritional functionality, are not simply the result of the presence of the ingredients mixed together during processing, but are also the result of the created three-dimensional structure. Recognizing that food materials can be described as colloidal systems allows food technologists to better control the quality of the end product. In the present work we discuss how colloidal concepts can be used to describe the behavior of milk products. We will consider the colloidal properties of milk characterized by the properties of its colloidal entities, i.e. the fat globules, the casein micelles and the whey protein aggregates.