Effect of oxidoreduction potential and of gas bubbling on rheological properties and microstructure of acid skim milk gels acidified with glucono-delta-lactone.

Milk oxidoreduction potential was modified using gases during the production of a model dairy product and its effect on gel setting was studied. Acidification by glucono-delta-lactone was used to examine the physicochemistry of gelation and to avoid variations due to microorganisms sensitive to oxidoreduction potential. Four conditions of oxidoreduction potential were applied to milk: milk was gassed with air, nongassed, gassed with N(2), or gassed with N(2)H(2). The rheological properties and microstructure of these gels were determined using viscoelasticimetry, measurement of whey separation, and confocal laser scanning microscopy. It appeared that a reducing environment led to less-aggregated proteins within the matrix and consequently decreased whey separation significantly. The use of gas to modify oxidoreduction potential is a possible way to improve the quality of dairy products.

Influence of drug polarity upon the solid-state structure and release properties of self-emulsifying drug delivery systems in relation with water affinity.

To overcome low oral bioavailability of poorly water-soluble drugs, self-emulsifying drug delivery systems (SEDDS) have been noted as a promising strategy. However, incorporation of drugs into SEDDS composed of Gelucire44/14 could induce interactions not yet well understood. The aim of this study was to investigate the influence of drug polarity upon the solid-state structure of SEDDS formulation, particularly in terms of wettability, thermal behaviour and microscopic aspects and their effect upon the release properties of the SEDDS. Model drugs were naproxen and sodium naproxen (10% w/w), two drugs with similar chemical structure but different water solubilities. Both drugs had an effect on the structure and behaviour of SEDDS: sodium naproxen mainly increased surface wettability while naproxen modified its thermal behaviour. Moreover, influence of Gelucire44/14 as self-emulsifying matrix was very marked for naproxen with a huge increase of naproxen release, the less water-soluble drug in condition where the solubility was the limiting parameter (at pH 1.2). Study of SEDDS structure and its physico-chemical properties using different techniques brought novel findings about the behaviour of SEDDS with different kinds of drugs (various water solubilities) and could be linked to their performances during in vitro dissolution.

Improvement of rheological properties of firm acid gels by skim milk heating is conserved after stirring.

The enhancement of the strength of set acid gels by heating milk was related to rheological parameters (water retention capacity, storage modulus) of corresponding stirred gels. To obtain accurate rheological data from stirred gel it was necessary to maintain a constant granulometry of gel particles and to recognize time after stirring as a contributing factor. Two hours after stirring, the gel exhibited a higher storage modulus when milk was heated above 80 degrees C. A measurement of viscosity of just-stirred yoghurt was sufficient to predict correctly the quality of a stirred gel analysed by viscoelastic measurements. Increased resistance to syneresis of just-stirred gels was related to higher viscosity. The quantity of beta-lactoglobulin (beta-Ig) bound to casein micelles explains the improvement of these gel qualities. We have considered that the structure of the initial firm gel (mesostructure level) was conserved in fragments within the stirred gel. Consequently, the explanation given by various authors for the effect of heating milk on the properties of set gels can also be applied to stirred gels. The same mechanism, described in literature for structure formation of set gels from acidified milk is purposed to explain the role of heating milk on the recovery of gel structure after stirring. The beta-Ig association with casein micelles during heating favoured micelle connections during the acidification. It also favoured the association of gel fragments after stirring during the recovery in gel structure.

Electrochemical modifications of proteins. 1. Glycitolation.

When an electrochemical method is tentatively applied for N-alkylation of proteins, some Maillard reactions occur on the counter electrode. A low level of reductive N-alkylation of casein was obtained on a cathodic electrode, but the method unfortunately remains poorly efficacious in comparison with those using a hydride donor such as sodium cyanoborohydride. Electroassisted reductive N-alkylation is suitable only for basic proteins such as histones or lysozyme. For other proteins, an alternative consists of either methylating carboxylic residues to increase the value of their isoelectric pH or coating them with a cationic detergent.

The quantification of protein amino groups by the trinitrobenzenesulfonic acid method: a reexamination.

Trinitrobenzenesulfonic acid (TNBSA) is the reagent in a well-known method for quantification of primary amino groups, but even at room temperature, N-trinitrophenylation of primary amines is concomitant with hydrolysis of the reagent. The production of picric acid, the product of TNBSA hydrolysis, lowers the sensitivity of the method. Heating accelerates hydrolysis more than condensation on amino groups. The optimal pH range is centered on the value 10. The optical density is generally evaluated at 340 or 420 nm. The former value corresponds to the maximal absorption of the final product, N-trinitrophenylamines. The latter value is relative to the Mesenheimer pi-complex, the well-known intermediate of the overall reaction. Both wavelengths are suitable for quantification of amines, but 420 nm seems to be the best. Further addition of sulfite is not necessary. The quantification of amines is somewhat hampered by compounds such as area and sodium dodecyl anions. The relative rates of reaction of diaminoacyl groups of protein with TNBSA differ depending on the substitution degree of the neighboring groups. Some of them do not react. The trinitrophenylation kinetic seems to be more dependent on protein structure than reactivity. In evaluation of the available lysine in glycated proteins, the distinction between reductive alkylation and Maillard-type condensation necessitates quantitative evaluation of nonalkylated lysine in protein hydrolysate, compared to results with the TNBSA method. Our results are confirmed by complete guanidization of the protein and subsequent determination of homoarginine in hydrolysates.