Moisture sorption isotherm and caking properties of infant formulas

Milk fat globule membrane regulates the physicochemical properties and surface composition of infant formula powders by improving the stability of the emulsion

The milk fat globules in infant formula (IF) are encapsulated by a component known as milk fat globule membrane (MFGM). However, it is currently unclear whether the improved emulsion stability of MFGM can have a profound effect on the finished IF. Therefore, this study investigated the effects of MFGM on the particle size, stability, rheology, and microstructure of emulsions prepared by dairy ingredients via wet mixing. Further, IF were processed using such emulsions, the physicochemical properties, surface composition of the powders were examined. The results showed that MFGM reduced the particle size of the emulsion, increased the viscosity, and improved the microstructure of the MFGM. Furthermore, MFGM reduced the moisture content of the powder, increased the glass transition temperature, and reduced the presence of surface fat. In conclusion, the addition of MFGM enhance the finished powder stability by improving the emulsion stability prepared during IF manufacturing.

Effects of different reducing carbohydrate types on the physicochemical characteristics of infant formula food stored for special medical purposes

The formula of food for special medical purpose has a direct impact on physicochemical stability, especially in hot climes and high temperature transport storage environments. An accelerated test (50 °C for 7 weeks) was used to analyze the mechanism of the physicochemical instability of formula A with lactose and maltodextrin, and formula B with maltodextrin. Deep dents and wrinkles were observed on the surface of the formula B, and more fat globules covered the surface of formula A particles after storage for a long time. Significantly higher amounts of furosine and Nε-carboxymethl-l-lysine (CML) were formed and the loss of available lysine was greater in formula A than in formula B. No significant difference was observed in lipid oxidation indicators between the two formulas. The results of this research demonstrated lactose was more active than maltodextrin and led to physicochemical instability.

Lactose crystallization and Maillard reaction in simulated milk powder based on the change in water activity

Maillard reaction (MR) and lactose crystallization (LC) are important reactions in the storage of milk powder. In this study, three models with different proteins based on skimmed milk powder were established to investigate the relationship between MR and LC at different water activities (a_w ). Moisture sorption isotherm, glass transition temperature (T_g ), and glycation products were evaluated, and the protein structure and lactose crystallinity were determined. The results indicated that MR product content, browning, and LC subsequently enhanced with the increase in a_w . The T_g value dropped lower than 0 at a_w 0.43 in whey protein isolate-lactose (WP-Lac) model and at a_w 0.54 in casein-whey protein isolate-lactose (CN-WP-Lac) model and casein-lactose (CN-Lac) model. The crystallinity of α-lactose monohydrate and anhydrous β-lactose in WP-Lac model was more significant than CN-WP-Lac and CN-Lac models (p < 0.05). The molecular band of whey protein gradually blurred in the Sodium dodecyl-sulfate polyacrylamide gel electrophoresis image, and the content of α-helix of WP-Lac model increased by 45.15% from a_w 0.33 to 0.53 (p < 0.05), while that of CN-WP-Lac model increased by only 3.95% (p < 0.05). With the increase in a_w , WP-Lac model formed more browning and crystallization products than CN-WP-Lac model, indicating that the presence of micelle macromolecules and the interaction between casein and whey proteins limited the browning and crystallization in CN-WP-Lac model. Practical Application Maillard reaction and lactose crystallization are important reactions in the storage of milk powder, and the result will provide theoretical guidance for the development of milk powder in the food industry.

Elucidating the physicochemical properties and surface composition of goat milk-based infant formula powders

This study investigated the characteristics of cow milk-based, goat milk-based, and mixed-based (using goat milk and cow whey powder)infant formulas (IF) with different sources of casein and whey protein, aiming to construct the properties of powders prepared using goat milk. Goat milk-based IF have different water activity, color, and glass transition temperature than other IF, whereas the crystallinity and solubility were similar. SDS-PAGE pattern showed that goat milk-based and mixed-based IF contained higher β-casein, while cow milk-based IF contained higher α_s1-casein. The differentials of casein affected the powder surface composition and free fat levels. Goat milk-based IF reduces the surface fat content and free fat levels of the particles. Further analysis showed that the surface of the particles was predominantly filled with saturated fatty acids. Our findings revealed that due to the different casein, goat milk-based IF have favorable characteristics and surface composition, thus promoting its particle stability.

Effect of powdering on critical water activity estimate from dynamic dewpoint isotherm of a crispy starch-based snack: a case study with fish cracker

The moisture sorption isotherm (MSI) and critical water activity (a _w,crit ) of a dry food determine the moisture barrier properties required of packaging for desired shelf life of starchy dry food. These can be obtained with the novel rapid dynamic dewpoint isotherm method (DDI), but with such rapid measurement incomplete equilibration is of concern, and this relates to suitable particle size of the sample tested. Further, an MSI curve without clear inflection point can make it difficult to extract the a _w,crit. The objective of this work was to investigate the effects of particle size of a starch based snack on its MSI and on a _w,crit . A novel model to fit the MSI data was also created to obtain the a _w,crit . Fish cracker samples were prepared in three particle sizes (< 180 µm, 250-425 µm, and ~ 3000 µm) and tested at 25 and 35 °C for MSI using DDI. The sample comminution by grinding had clear and consistent effects, with finer particles absorbing more moisture. For this crispy snack, the rapid dense measurements enabled estimating the critical point that was robust against a 10 °C temperature change with about 200 µm particle diameter. This suggests near complete equilibration by the lack of rate effects from temperature, which were seen with larger particles. The results indicate that powdering dry crispy foods enables proper DDI measurements, while without powdering the isotherms can be degraded by particle size effects. The broken-stick type model fit the data extremely well and showed the critical transition clearly as a jump discontinuity in the derivative (slope).

Effect of water activity on the functional, colloidal, physical, and microstructural properties of infant formula powder

We report on the physicochemical changes of infant formula (IF) powder and its macronutrients (lactose, fat, and proteins) under given storage conditions. Colloidal (particle size distribution, emulsion stability and sedimentation), morphological (scanning electron microscopy), thermal (differential scanning calorimetry), structural (synchrotron X-ray diffraction) as well as surface and chemical (X-ray photoelectron and Fourier transform infrared spectroscopies) data were used to elucidate the main cause-effect relationships for microstructural, functional, and other properties of the IF powder. The wetting behavior of the powder was found to be significantly affected by water activity (a_w) during storage (a_w in the range between 0.24 and 0.42). At the highest a_w (a_w = 0.42), lactose crystallization and fat migration took place, leading to changes on the surface of the particles that reduced powder wettability. We propose possible mechanisms to explain the observations, associated with changes in protein conformation. Interestingly, no major changes in the pH and colloidal characteristics, including particle size and distribution, stability, and sedimentation were observed in the reconstituted IF powder upon storage for 6 weeks. The results indicated a negligible contribution from possible Maillard reactions. We propose leading microstructural and wetting characterization to troubleshoot changes in the quality of IF powder, most relevant from the perspective of reconstitution after storage.

Inter-relationship between lactose crystallization and surface free fat during storage of infant formula

Inter-relationship between lactose crystallization (LC), the amount and composition of surface free fat (SFF); and their effect on physico-chemical properties of infant formula (IF) containing hydrolyzed and intact (non-hydrolyzed) whey protein in their composition were investigated at two temperatures (25 and 45 °C) and five RH (11-65%) conditions. Results varied with compositional variation of IF. LC increased exponentially with SFF in non-hydrolyzed IF powders. IF composition influenced LC and caused selective migration of triglycerides, resulting in higher proportion of unsaturated fats in SFF of powders with large lactose crystals and vice-versa. Increase in SFF with increased proportion of saturated fats in their composition, resulted in reduced wettability of powders. Overall, IF composition affects LC which influences the amount and type of fat migration to particle surface resulting in varying wettability of IF powders.

Effect of water activity on the thermal inactivation kinetics of Salmonella in milk powders

Persistence of Salmonella in milk powders has caused several foodborne outbreaks. The determination of proper pasteurization processing conditions requires an understanding of the thermal inactivation kinetics of Salmonella in milk powders. However, there is a lack of knowledge related to the effects of water activity (a_w) and fat content on Salmonella inactivation in milk powder during thermal processing. Two types of milk powders, nonfat dry milk and whole milk powder, with different fat contents (0.62 and 29.46% wt/wt, respectively) were inoculated with a 5-strain cocktail of Salmonella and equilibrated to 3 a_w levels (0.10, 0.20, and 0.30) for isothermal treatments at 75, 80, and 85°C to obtain D-values (the time required to achieve a 10-fold reduction of the bacteria at the isothermal treatment temperature) and z-values (the increase in temperature required to achieve a 90% reduction of the decimal reduction time D). Stability tests showed that the inoculation method used in this study provided a high and stable population of Salmonella for thermal inactivation studies. A moisture sorption isotherm was measured to understand the relationship between a_w and moisture content of milk powders. The thermal resistance of Salmonella was found to significantly increase as a_w decreased, which suggested that a higher temperature or longer processing time would be required at low a_w to achieve the desired inactivation of Salmonella. The microbial inactivation kinetics were not significantly different for the 2 milk powders; therefore, data were combined to develop a universal model. A response surface model was compared with a modified Bigelow model. The modified Bigelow model performed well to predict D-values [root mean square error (RMSE) = 1.47 min] and log reductions (RMSE = 0.48 log cfu/g). The modified Bigelow model developed here could be used to estimate D-value as a function of water activity and temperature to design a thermal pasteurization system for milk powders.

Physicochemical properties and surface composition of infant formula powders

Compositional difference in infant formula (IF) tends to influence its functionality and storage behaviour. The aim was to study the composition and physico-chemical properties of different stages of two commercial IF (A and B). Lactose crystallization measured by X-ray diffraction ranged between 2 and 32 % and was observed to decrease with increasing IF stages, which directly correlates with their composition. Scanning electron microscopy confirmed the presence of crystalline lactose which significantly (p < 0.05) increased the powder particle size. On the contrary, a negative correlation was observed between surface fat and lactose crystallization in all samples. Bulk and surface-free fat composition was significantly (p < 0.05) different for all samples. Surface free-fat analysis showed restricted presence (5-10% of surface fat) of unsaturated fatty acids (C18:1 and C18:2) in IF with higher crystalline lactose as opposed to >40% in others, suggesting a possible role of lactose crystallization in preferential migration of triglycerides to particle surface.