M. Boulet

Observations on the heat-induced salt balance changes in milk I. Effect of heating time between 4 and 90°C

Milk permeate was separated at various temperatures by means of a hollow fibre ultrafiltration unit coupled to a stainless steel heat exchanger. Milk samples conditioned at 4°C were heated to 20, 40, 60, 80, 85 or 90°C prior to ultrafiltration. Ca, P, Mg, Na, K and citrate concentrations were measured in the permeate samples. Ca and P contents of the permeate decreased as the temperature increased. The pH was measured after cooling the permeate to room temperature. Smaller losses of Mg and citrate were also observed with increase in temperature. Na and K levels were not affected. A two-step time-concentration relationship was apparent for the species under study. An initial sharp decrease in concentration occurred in the first minute of holding time and was followed by a slower reaction. The possible occurrence of a two-step mechanism in the heat-induced salt balance changes is discussed. Dicalcium phosphate precipitation is believed to be coupled with tricalcium citrate precipitation upon heating.

Deposit formation on heated surfaces: effect of interface energetics

Deposit formation was measured in a model laboratory plant in which whole milk was in contact with a heated surface at 100 °C for 1 h. The effect of the interfacial properties of various poly mer-coated surfaces on the amount and the adhesion strength of deposit was determined. The nature of the surface influenced the formation of deposit only slightly, but had a large effect on its adhesion strength. From correlation analysis, the polar contribution to surface energy was identified as the main factor influencing the deposit adhesion strength. These results suggest that the type of interactions at the surface govern the ease of removal of deposit.

Fractionnement des Protéines de Soya, de Féverole de Colza et de Feuilles de Luzerne par “Dissolution Fractionnée”

Abstract A new protein fractionation method has been developed on the basis of solubility differences of fractions in solutions of ammonium sulfate. It is shown that for each of the fractions of soybean, fababean, rapeseed and alfalfa leave proteins there is a zone of ammonium sulfate concentrations at which the fraction is preferentially extracted. In the method, a protein mixture is subjected to a series of successive extractions with ammonium sulfate solutions of decreasing concentrations. The isolated fractions are homogeneous according to the ultracentrifugation test. The method can be used for large scale fractionation.

A Study of the Chemical Composition and Nutritive Value of Leaf Protein Concentrates

Abstract Leaf protein concentrates from alfalfa and from clover obtained by solvent-precipitation and by heat-coagulation have been examined for their chemical composition, their nutritive value and their digestibility. The amino acid composition is not affected by the process of precipitation except that solvent precipitation seems to retain more methionine and less leucine than the heat process. Alfalfa and clover have similar amino acid patterns except that alfalfa has more cystine, aspartic acid and serine than clover. The lipids retained with the protein by the heat process contain much more linolenic and less palmitic, stearic, oleic and linoleic acids than those by the solvent process. Acetone retained more linoleic and linolenic acids and less stearic and palmitoleic acids than alcohol. The lipids of clover had more stearic and oleic acids than those of alfalfa. More mineral elements except Na and Fe and more carbohydrates were found in the solvent-precipitated concentrates than in the heat-coagula. Alfalfa protein concentrate was more digestible and had a higher P.E.R. value than clover protein concentrate. Both, however, were inferior to casein. Dispersibility in water was greater for solvent-precipitated than for heat-precipited concentrates.

Etude De La Séparation Électrophorétique En Gel De Polyacrylamide Des Protéines Extraites De Soja, De Féverole, De Colza, De Feuilles De Luzerne E De Leurs Fractions Isolées

Abstract Proteins and protein fractions extracted from soybeans, fababeans, rapeseed and alfalfa leaves have been examined by polyacrylamide gel electrophoresis using gels of various densities. Results have shown that both soybean and fababean proteins have the same number of fractions and sub-fractions and have similar physical dimensions. It has been shown that the number of sub-fractions appearing on the gel and their apparent molecular dimensions are influenced by the nature of the separation buffer used.

Observations on the seasonal variations in the salt balance of concentrated milk

Abstract Seasonal variations in the salt balance of raw bulk milk and its 3:1 concentrate were studied over a one-year period. A marked increase in the level of colloidal calcium was found between December and February in raw milk, whereas the other components remained unchanged. Evaporative concentration shifted the soluble-colloidal equilibrium towards the colloidal phase as the Ca, PO4, Mg and citrate content increased. Thermal stabilization of the concentrates by pH adjustment or Na2HPO4 addition had little effect on salt balance at any time of the year. The colloidal Ca PO 4 ratio was the only compositional parameter that could be correlated to the heat stability of concentrated milk.

Propriétés Physico-Chimiques et Composition en Acides Aminés des Fractions de Protéines de Soya, de Féverole, de Colza et de Feuilles de Luzeme

Abstract Fractions were prepared and purified from proteins of four different vegetable sources by a method based on differences of solubility in ammonium sulfate solutions. Sedimentation coefficient SW25, distribution of amino-acid residues, absorption coefficient at 280 and 260 nm and solubility in ammonium sulfate solutions of various concentrations have been determined with the isolated fractions. Results indicated that solubility decreased logarithmically with increases in concentration of ammonium sulfate. It is shown for the five fractions studied that solubility is related to the ratio of the number of polar/neutral residues.

Etudes des Variations du Coefficient de Sédimentation et des Dimensions Moléculaires de la Globuline 11S de Soya en Fonction de la Force Ionique aux pH Acide et Alcalin et en Présence de n-Butanol.

Abstract Solutions of the 11S soybean globulin have been treated with different agents and their effects on the sedimentation coefficient (S) and molecular dimensions (a/b axial ratio and molecular weight) of the protein have been examined. At pH 2 and 11 and low ionic strengths (0.01 to 0.03) the protein dissociated into sub-fractions of 1 to 1.1 S having molecular weights between 15,000 and 20,000 and these assume a much elongated form as indicated by the axial ratios between 13 and 17. Increases in ionic strength at constant pH favored reassociation of the sub-fractions into molecules of larger molecular weight and more symmetrical in shape. In the presence of sodium dodecylsulfate (2%) the protein is also dissociated into small units (1.5S) having an axial ratio of 12. In the presence of n-butanol (5%) the protein is incompletely dissociated into fractions 2, 6 and 9S. These effects are discussed in relation to the electrostatic charges on the protein molecules and the linkages between the sub-fractions.

Effect of Extreme pH and Salt Concentration on Intrinsic Viscosity and Huggins' Constant (k′) of 7S and 11S Soybean Globulins

Abstract Intrinsic viscosities of 7S and 11S soybean proteins have been measured at various concentrations, 0.5–2.0%, pH 2.0 and 11.0 and in the presence of salt at 0.01–0.5 ionic strength. Sedimentation coefficients were also measured. The results indicated that extreme pH caused molecular dissociation and extensive unfolding which were partially reversed by the addition of salt. The 7S protein was much more resistant to dissociation and unfolding than the 11S protein.

Estimation of casein micelles' surface energy by means of contact angle measurements

The surface energies of highly hydrated casein micelle layers isolated from variously pretreated skim milks have been determined by means of contact angle measurements. The long range Lifshitz-Van der Waals (LW) and the short range hydrogen bonding (SR) components of surface energy were determined using α-bromonaphthalene and water for contact angle measurements. Casein micelles isolated from untreated and heat treated milks showed similar surface energy values of about 63·5 mJ.m -2 with an LW component of 19·2 mJ.m -2 and an SR component of 44·3 mJ.m -2 . The calculated attraction potential energy was − 0·7 mJ.m -2 . Casein micelles isolated from renneted milk showed a surface energy of 33·0 mJ.m -2 with an LW component of 30·7 mJ.m -2 and an SR component of 2·3 mJ.m -2 . The attraction potential energy of renneted micelles was nearly two orders of magnitude higher than those of micelles from other milks ( − 63·3 mJ.m -2 ). The SR component of interfacial energy accounted for 98% of this attraction potential. The importance of attractive forces in relation to casein micelle stability is discussed.