Roles of Water and Solids Composition in the Control of Glass Transition and Stickiness of Milk Powders (original) (raw)
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Food Chemistry, 2007
The effects of dilution of protein content in skim milk (34-8.5% protein content), by lactose addition, on the surface composition, water sorption property and glass transition temperatures of spray-dried powders were investigated. The X-ray photoelectron spectroscopy (XPS) study of spray-dried powders showed preferential migration of proteins toward the surface of the milk particles whereas the lactose remained in the bulk. Sorption studies showed that the lower protein concentration in milk powders is linked to an increased water adsorption property and lowering of water activity (a w ) for lactose crystallization. Analysis of glass transition temperature (T g ) of the powders sorbed at different humidities showed no distinct change in T g values, indicating the dominant effect of lactose on the glass transition temperature of all the powders.
Importance of glass transition and water activity to spray drying and stability of dairy powders
Le Lait, 2002
Spray-drying is a rapid dehydration method allowing production of high quality dairy powders. In dehydration and subsequent powder handling and storage, however, both chemical and physical changes, such as caking, lactose crystallisation, and nonenzymatic browning, may impair powder characteristics and result in loss of powder quality. Many of these changes are related to the physical state of lactose, as rapid removal of water in spray drying results in the formation of lowmoisture, amorphous, noncrystalline structures of lactose and other milk components. The amorphous components may exist as solid-like glasses or highly supercooled, viscous liquids. The formation of amorphous, glassy lactose during spray drying allows production of a free-flowing powder. High temperatures or residual water contents at the later stages of the drying process, however, may cause stickiness, caking, browning, and adhesion of the powder particles to the processing equipment. The glass transition of amorphous lactose occurs in the vicinity of room temperature at a water content of about 6.8 g (g × 100)-1 of lactose corresponding to an equilibrium relative humidity of 37% and 0.37 a w (water activity). At higher water contents, as the glass transition of amorphous lactose is well below storage temperature, dairy powders become sticky and the amorphous lactose may exhibit time-dependent crystallisation. Crystallisation of amorphous lactose may also release sorbed water from the amorphous material, which enhances other deteriorative changes, such as the nonenzymatic browning reaction. Amorphous lactose in dairy powders encapsulates milk fat, which, as a result of lactose crystallisation, is released and becomes susceptible for rapid oxidation. The glass transition and water activity are, therefore, important factors controlling processability, handling properties and stability of dairy powders. Glass transition / dairy powder / spray drying / stability / water Résumé-Importance de la transition vitreuse et de l'activité de l'eau pour le séchage par atomisation et la stabilité des poudres de lait. Le séchage par atomisation est une méthode de déshydratation rapide permettant la production de poudres de lait de première qualité. Cependant, au cours
Glass transitions and crystallization in milk powders
Effects of water content, storage time, and glass transition (physical state) on lactose crystallization and the resultant crystal forms in skim milk powder were investigated. Samples of freeze-dried skim milk containing amorphous lactose were stored at various relative humidities at room temperature (24°C). Crystallization was observed from time-dependent loss of sorbed water during storage and from increasing intensities and peak areas of X-ray diffraction patterns. Lactose was found to crystallize largely as an anhydrous mixture of a-and b-lactose in a molar ratio of 5:3. At high relative humidities, traces of other crystal forms were also found. The rate of crystallization, up to a maximum extent, which depended on crystallization conditions, increased as the relative humidity during storage increased. The rate of crystallization could be successfully modeled using the Avrami equation when relative humidity was ≥66.2%. The relationship between the extent of crystallization and relative humidity was parabolic; the maximum crystallization occurred at a relative humidity of 70%. The corresponding water content and temperature difference between storage temperature and glass transition temperature were predicted to be 17% (wt/ wt) and 61°C, respectively. Glass transition seems to control lactose crystallization in skim milk powder, and the data obtained can be used in predicting lactose crystallization in milk products containing lactose.
A novel technique for determining glass–rubber transition in dairy powders
Journal of Food Engineering, 2010
A novel rheological technique is described, for determining the glass-rubber transition temperature (T gr ) of spray dried dairy powders. The approach involves constant rate heating of powder under compression and measurement of changes in either gap distance (Method 1) or normal force (Method 2). Significant increases in the rate of change of these parameters was shown to correspond with T gr . The techniques were applied to skim milk, micellar casein and whey permeate powders and a range of fat-enriched micellar casein powders. T gr temperatures, so obtained, were compared with glass transition temperatures (T g ) determined by Differential Scanning Calorimetry (DSC). Methods 1 and 2 gave predictions for non-fat dairy powders of T g endset (T ge ) with SEP of 8.8 and 4.4°C, respectively. These novel techniques provide an accurate means of determining glass transitions in dairy powders, including high protein and fat-containing powders, whose relaxation properties can be difficult to measure by DSC.
Journal of Agricultural and Food Chemistry, 2007
The relationships between powder surface composition and powder rehydration properties under variable conditions of storage are investigated in this paper. A rheological approach was used to evaluate the modifications induced by storage on the rehydration properties of native phosphocaseinate powder. Concurrently, the powder surface composition (i.e., lactose, proteins, and lipids) was evaluated by X-ray photoelectron spectroscopy (XPS). A strong correlation was found between the powder wetting time lengthening and the migration of lipids on the powder surface during storage. XPS studies indicated also an over-representation of lipids on the powder surface (6%) in comparison with total lipids (0.4%) even on fresh powder before storage. Detailed investigation of powder lipids revealed the presence of high levels of polar lipids (66% compared with <1% in milk lipids). Their amphiphilic nature and their melting points could explain the extensive enrichment of lipids observed at the powder surface during processing and storage. The financial support of ARILAIT Recherche (Paris) and its scientific committee is gratefully acknowledged.
Water sorption and glass transition properties of spray dried lactose hydrolysed skim milk powder
Lwt - Food Science and Technology, 2007
The moisture sorption behaviour and glass transition temperature of spray dried skim milk powder with hydrolysed lactose (SMPHL) were determined. Spray drying of skim milk with hydrolysed lactose resulted in very low cyclone recovery of 25% and a large amount of powder remained stuck inside the spray dryer. The equilibrium moisture content of SMPHL was lower than that of lactose for each range of water activity when humidified for 21 days at 23 1C using saturated salt solutions. Unlike lactose, SMPHL did not lose water when the water activity exceeded 0.432 and no crystallization was noticed at water activity X0.753. The sorption isotherm data for SMPHL fitted well with the BET and GAB models with monolayer moisture contents of 7.55 and 8.27 g/100 g, respectively. The glass transition temperature of anhydrous SMPHL was 49 1C. The critical water activity and moisture content for SMPHL were 0.15 and 2.4 g/100 g dry solid, respectively. The low critical values indicated hydrolysis of lactose necessities maintenance of very low moisture of powder for its long-term stability.
International Dairy Journal, 2015
Surface composition, moisture sorption behaviour and glasserubber transition temperature (T gr) were determined for spray-dried milk protein concentrate (MPC) powders over a range of protein contents (35 e86 g 100 g À1). Surface characterisation of MPC powders indicated that fat and protein were preferentially located on the surface of the powder particles, whereas lactose was located predominantly in the bulk. Moisture sorption analysis at 25 C showed that MPC35 exhibited lactose crystallisation, whereas powders with higher protein contents did not and continually absorbed moisture upon humidification up to 90% RH. The GAB equation, fitted to sorption isotherms of MPCs, gave increases in monolayer moisture value (m m) with protein content. T gr , measured with a rheometer, decreased significantly (P < 0.05) with increasing water content and increased with increasing protein content (P < 0.05). In conclusion, increasing protein concentration of MPCs resulted in altered surface composition and increased m m value and T gr values.
Principles of lactose crystallization and rheology of milk protein concentrate
Research, Society and Development
Milk protein concentrate (MPC) is a commercial designation for dairy ingredients with higher protein and lower lactose content than conventional skim milk powder. Lactose in its amorphous form is found in several spray-dried dairy powders. Amorphous lactose is thermodynamically unstable and can mobilize and crystallize over time under adequate temperature and moisture content. Moisture sorption from the air precedes crystallization, enhancing MPC cohesiveness and caking. This increased humidity results in poor rehydration and dispersibility, lower yield during drying, operation problems, difficulties in handling and storage. Moreover, lactose crystallization in MPC can cause Maillard browning reaction and fat oxidation. To avoid this problem, it is necessary to pre-crystallize lactose as alpha-lactose monohydrate, which is non-hygroscopic, before spray drying. Such a procedure is essential in preventing deterioration of MPC resulting from lactose crystallization or chemical reaction...
Stickiness measurement techniques for food powders: a review
Powder Technology, 2004
The importance of sticky behaviour of amorphous food powders has been recognized over many decades in the food industry due to its influence on process and handling abilities and quality of the powders. This paper emphasizes the role of stickiness in the food powder industry as well as reviews the stickiness characterization techniques developed to date. This paper also attempts to correlate the stickiness behaviour of food powders to the instrumental analysis such as glass transition temperature. D