Fat-filled Milk Powders Research Articles

Crystal size, a key character of lactose crystallization affecting microstructure, surface chemistry and reconstitution of milk powder

Lactose crystallization during storage deteriorates reconstitution performance of milk powders, but the relationship between lactose crystallization and reconstitution is inexplicit. The objective of this study is to characterize crystalline lactose in the context of formulation and elucidate the complex relationship between lactose crystallization and powder functionality. Lactose in Skim Milk Powder (SMP), Whole Milk Powder (WMP) and Fat-Filled Milk Powder (FFMP) stored under 23 %, 53 % and 75 % Relative Humidity (RH) at 25 ℃ for four months was compared. Lactose, surface chemistry and microstructure of FFMP stored at 25 ℃ and 40 ℃ at 23 % to 75 % RH for four months were also analyzed and interpreted. At the same RH, FFMP crystallized in the same pattern as WMP. At 53 % RH, FFMP and WMP differentiated from SMP in terms of lactose morphology as well as the ratio between anhydrous α-lactose and anhydrous β-lactose. Lactose remained amorphous at 23 % RH, crystallized predominantly to α/β-lactose (1:4) at 40 to 58 % RH and to α-lactose monohydrate at 75 % RH. The crystallinity index was similar for all powders containing crystalline lactose. The estimated crystallite size increased from approx. 0.1 to 20 µm with increasing RH and temperature. When amorphous lactose crystallized into crystals below approx. 0.1 µm at 25 °C and 43 % RH, the microstructure and surface lipid were comparable to that of the reference powder. This powder reconstituted into a stable suspension system comparable to that of reference (well performing) powders. These results demonstrate that crystallite size is the key property linking lactose crystallization and reconstitution. Our finding thus indicates limiting crystallite size is important for maintaining desired product quality.

An Experimental Study on the Dilute Phase Pneumatic Conveying of Fat-Filled Milk Powders: Particle Breakage

Powder breakage during pneumatic conveying negatively affects the properties of dairy products and causes increased dusting, reduced wettability, and decreased product performance. In particular, particle breakage is a serious issue for fat-filled milk powder (FFMP) which, if it breaks, releases fat that causes odours and leads to sticky blocked pipes. In this work, a conveying rig (dilute phase, positive pressure) with 50 mm diameter food grade stainless steel pipes (1.5 m high and 5 m conveying distance with three 90° bends, two in the vertical plane and one in the horizontal plane) was built as the test system. The effects of operating conditions (conveying air velocity and solid loading rate) on the attrition of FFMP in a dilute phase conveying system were experimentally studied. Four quality characteristics were measured before and after conveying: bulk density, particle size distribution, wettability, and solubility, to access the influence of particle breakage. Conveying air speed shows a significant impact on powder breakage. As air speed increased, more breakage occurred, and the volume mean diameter D[4,3] decreased by around 50%, using the largest conveying air speed of 38 m/s. Bulk density increased accordingly whereas wettability decreased with an increase in air speed, resulting from the higher breakage rate. On other hand, improving the solid loading rate can further reduce the breakage level, but the positive effect is not as good as decreasing air speed.

The Effect of Carnosol, Carnosic Acid and Rosmarinic Acid on the Oxidative Stability of Fat-Filled Milk Powders throughout Accelerated Oxidation Storage.

The in vitro antioxidant effects of the most potent antioxidants of rosemary, namely carnosol, carnosic acid and rosmarinic acid (c: ca: ra) were assessed in fat-filled milk powders (FFMPs) under accelerated conditions (40 °C and relative humidity (RH) 23%) over 90 days. Lipid oxidation was assessed in FFMPs by measuring peroxide values (PVs), thiobarbituric acid reactive substances (TBARS) and aroma volatiles using headspace (HS) solid-phase microextraction (SPME) coupled to gas-chromatography-mass spectrometry (GC-MS). The antioxidant potency of c: ca: ra exhibited a concentration-related effect (308 ppm > 200 ppm > 77 ppm), with the highest concentration being the most effective at controlling the formation of TBARS and PVs. At a concentration of 308 ppm c: ca: ra were particularly effective (p < 0.05) in inhibiting all the evaluated oxidation indices (primary and secondary) compared to the control samples, but in some cases less effectively (p < 0.05) than butylated hydroxyanisole: butylated hydroxytoluene (BHA: BHT) (200 ppm).

The influence of pre‐heat treatment of skim milk on key quality attributes of fat filled milk powder made therefrom

Key quality aspects of fat filled milk powders (FFMPs) produced with skim milk pre‐heated at 93 °C × 60 s and 105 °C × 15 s (medium whey protein nitrogen index; WPNI), and 116 °C × 60 s and 136 °C × 15 s (high WPNI) were examined. The 136 °C × 15 s treatment produced a FFMP with threefold higher free fat, showed significantly (P &lt; 0.05) lower solubility in coffee and exhibited extensive flecking on rehydration in water. Insoluble materials were observed using microscopy; flecks generated upon rehydration in water were composed of fat, whereas flecks/sediment in coffee were composed of undissolved powder particles.

Monitoring the composition, authenticity and quality dynamics of commercially available Nigerian fat-filled milk powders under inclement conditions using NIRS, chemometrics, packaging and microbiological parameters

Fat-filled milk powders (FMP) are inexpensive milk alternatives predominantly exported to developing countries to satisfy growing demands for dairy proteins. Harsh climatic and sanitary conditions, poor border controls and relatively long periods for distribution and storage enhance the inherent vulnerability of FMP to fraud and stability. Rapid, low-cost methods are needed for extensive routine authentication of FMP products. This study investigated, for the first time, the sample integrity and the quality dynamics of 7 Nigerian FMP brands stored for 7 weeks at 40 °C. The prominent melamine and urea absorption peaks were absent, but protein contents were below the permitted limit. The peak absorbance of the OH functional group increased while the tryptophan contents decreased with storage time. Multiclass analyses differentiated the fresh FMP brands from one another, and from those that were aged. Robust interval-PLS predictions obtained for storage time may be excellent indicators of FMP freshness and stability.

Influence of mechanical integrity during pneumatic conveying on the bulk handling and rehydration properties of agglomerated dairy powders

Agglomerated powders are susceptible to breakdown on handling, most notably, during powder conveying. In this study, three agglomerated dairy powders (whey protein concentrate powder, WPC; fat-filled milk powder, FFMP and infant formula powder, IF) were conveyed through a custom-fabricated dispersion rig to understand the effects of agglomerate breakdown on dairy powder handling and application. All samples displayed significant breakdown on dispersion, evidenced by reducing particle size and increasing bulk density. The resulting flowability of these powders was impaired (flow index: WPC: 9.3 to 5.1, FFMP: 5.7 to 4.9 and IF: 16 to 10) via increased particle-particle interactions. The initial stages of rehydration were impeded by agglomerate breakage (42.9–47.0% wettability reduction and 7.22–16.4% dispersibility reduction), while powder solubility remained relatively unchanged. This study provides insights into the alterations of agglomerated dairy powder properties on agglomerate breakdown, while identifying the effects these alterations have on the functional properties of these powders.

Characterisation of the quality alterations in model fat-filled milk powders under inclement conditions and the prediction of the storage time using near infrared spectroscopy

Fat-filled milk powders (FMP) are exported to tropical developing markets as inexpensive milk alternatives. Consequently, FMP are exposed to high temperature and humidity over long distribution and storage times, presenting challenges in preserving product quality and stability. Efficient and cost-effective methods for quality assurance under such conditions are needed. We utilised the changes in profile of the fatty acids, amino acids and near infrared spectra to investigate the quality alterations in 4 types of FMP produced onsite with 4 different vegetable oils (i.e., coconut, palm, soya-bean and sunflower) and stored for 7 weeks at 40 °C. Stearic acid decreased while the leucine content increased upon storage, but palm oil FMP appeared to be the most stable. Multiclass analyses offered substantive separation between fresh and aged samples. The models based on interval-PLS efficiently (NSE ≥ 0.90) predicted storage time with low errors (RSR ≤ 0.28), indicative of FMP freshness and stability.

Effective detection and quantification of chemical adulterants in model fat-filled milk powders using NIRS and hierarchical modelling strategies

Skimmed milk powder can be blended with indigenous vegetable oils to formulate fat-filled milk powder (FMP) to satisfy the growing demand of low-income consumers for dairy proteins in the developing countries where food control systems may be fragmented. Unscrupulous manufacturers may adulterate FMP with melamine or urea to give the false impression that it contains sufficient protein. This study investigated, for the first time, the efficacy of near infrared spectroscopy to detect and quantify melamine and urea (0.01–16.00%) in FMP formulated with 4 different vegetable oils (i.e., coconut, palm, soya-bean and sunflower). Multilevel analyses were able to detect, confirm and differentiate the adulterations with an efficiency ranging from 89.8 to 100.0%. The partial least square regression models yielded satisfactory predictions (R2p ≥0.96, RSR ≤0.19) at adulteration levels ≥1.00%. This study provides appropriate guidelines for cost-efficient screening of FMP products for adulterants to protect public health.

Pneumatic conveying of cohesive dairy powder: Experiments and CFD-DEM simulations

We performed an experimental and numerical investigation of pneumatic conveying of cohesive dairy powder. The experiments with fat-filled milk powder (FFMP) fines with an average particle size of 94 μm were carried out in a 2-inch diameter stainless steel pipe consisting of two 2.5 m horizontal sections connected to a 0.65 m vertical section by two bends of 0.4 m radius each. In addition to measurements of pressure drop and powder deposition, an optical technique was used to measure the dynamics (probability densities) of local particle volume fractions as a function of operating conditions. Numerical simulations were performed with a commercial discrete element modelling (DEM) software, EDEM®, coupled with the computational fluid dynamics (CFD) software, FLUENT®. The simulation results in terms of pressure drops and particle volume fractions were compared with the experimental data. A very satisfactory agreement was found. At low gas velocities, cohesive dairy powders easily re-agglomerate after the second 90° bend and then deposit at the bottom of the horizontal pipe. At higher gas velocities, results show intermittent dispersion of particles and less particle deposition is observed even at higher loading ratio.

Chemometric studies of the effects of milk fat replacement with different proportions of vegetable oils in the formulation of fat-filled milk powders: Implications for quality assurance

Bovine milk lipids can be replaced with cheaper indigenous vegetable oils to produce milk alternatives with healthier saturated/unsaturated fat balance for those in areas where milk supply is poor or even absent. A wide range of vegetable oils can be used, but their impacts when blended with skimmed milk powder to formulate filled milk powder (FMP) are still unknown. We investigate the baseline variances in 12 types of FMP produced onsite with 3 proportions (10%, 20% and 30%) of 4 different vegetable oils (i.e., coconut, palm, soya-bean and sunflower) using fatty acid- and near infrared spectra profiles. Chemometric analyses revealed 8 significant overlapping clusters of FMP types but 100% classification efficiency was achieved. Sunflower oil, and particularly soya-bean FMP types had statistically the lowest indices of atherogenicity and thrombogenicity. This appears to be the first chemometrics study of FMP; the spectral analytical models used may be effective for product monitoring.

Elucidation of factors responsible for formation of white flecks in reconstituted fat filled milk powders

Fat filled milk powders (FFMP) are formulated by blending skim milk and vegetable oil, to which lactose, permeate, sugar, maltodextrin, vitamins and minerals may also be added. The liquid mix is usually homogenised and spray dried, with agglomeration and lecithination, to produce powders for a range of end-user applications including drinking milk, yoghurt base and coffee whitening. Thus, it is important to avoid common powder defects such as inconsistent whitening, feathering or white flecking on reconstitution. The phenomenon of white flecking, and in particular, the underlying causes of fleck formation, are poorly understood. To better understand white fleck formation, six size fraction samples from two different FFMPs, a good (low level flecking) and a poor powder (high level flecking), were profiled. Most extensive flecking was observed in the coarse fraction of the poor powder, which also had an 8-fold higher free fat content than all other fractions and displayed poor emulsion stability (D3,2 = 15 ± 3.9 μm compared to 0.45-0.75 μm for all other fractions). Treatment of the reconstituted emulsions with an anionic surfactant or a reducing agent suggested that integrity of white flecks was based mainly on electrostatic interactions between proteins, with little contribution from covalent bonds. Although the extent of whey protein denaturation ranged between 22.6–47.5%, whey protein insolubility appeared to play a sub-ordinate role in white fleck formation. These results suggest that presence of flecks in FFMP was mainly associated with poor thermal stability of the emulsions.

Effect of fat replacement on flow and thermal properties of dairy powders

This paper presents the influence of fat replacement on flow and thermal properties of dairy powders. The research was undertaken by measuring flow properties of four different milk powders (whole milk powder, skim milk powder and two fat-filled milk powders with palm oil at 6.63 g/100 g and 25.5 g/100 g fat content, respectively) by using shear test. Fat content has a major influence on milk powder cohesiveness, with greater content resulting in greater cohesiveness. Fat content and type has also significant influence on flowability of milk powder. Fat-filled spray-dried milk powder is characterized by better flowability than whole milk powder with the same content of fat. The DSC curves showed that milk fat tended to melt in a lower temperature region than vegetable fat.

Evaluation of oil sources in whey-based calf milk replacers

Oil in fat-filled milk powders is the major source of energy in calf milk replacers. Choice of oil source is determined by nutritive value (chiefly digestibility), functionality (avoidance of breaking the emulsion) and, increasingly, customer preference for oils of purely vegetable origin. One alternative to the use of traditional oil sources such as lard and fish oil, is coconut oil, which is rich in highly digestible medium-chain length fatty acids (particularly C12:0), but relatively deficient in essential long-chain polyunsaturated fatty acids such as linolenic acid. The objective of this experiment was to compare the effects on calf performance of oil source within milk replacers.

Evaluation of oil sources in whey-based calf milk replacers

Oil in fat-filled milk powders is the major source of energy in calf milk replacers. Choice of oil source is determined by nutritive value (chiefly digestibility), functionality (avoidance of breaking the emulsion) and, increasingly, customer preference for oils of purely vegetable origin. One alternative to the use of traditional oil sources such as lard and fish oil, is coconut oil, which is rich in highly digestible medium-chain length fatty acids (particularly C12:0), but relatively deficient in essential long-chain polyunsaturated fatty acids such as linolenic acid. The objective of this experiment was to compare the effects on calf performance of oil source within milk replacers.

Influence of sample shape and size on self-ignition of a fat-filled milk powder

A lecithinated, 30% tallow fat-filled, milk-product powder, commercially-manufactured in Ireland, was used as the test material to assess the effect of sample shape and size on self-ignition in a thermostatically-controlled oven. Cubes of edge 25, 38 and 51 mm, spheres of diameter 26, 50, 77 and 102 mm, cylinders with diameter equal to length of 51, 76 and 100 mm and layers of 100 mm diameter and thickness of 10, 15 and 20 mm were tested. The minimum ignition temperature (MIT) varied from 206°C for the thinnest layer to 131°C for the largest sphere. For each shape, the results fitted the linear relationship ln( δ c T 2 r 2 ) = M− (N/T) , with close correlation. However, contrary to theory, the four straight lines did not coincide. Those for the spheres and layers were very close while those for cubes and cylinders had approximately 25% greater values for their slope (N). These results are shown to introduce significant differences when the values of M and N for the two most divergent lines within the test range are used to extrapolate estimates of critical layer thickness for the lower operating temperatures in parts of a milk spray dryer. M and N obtained from spheres gave the lowest estimates while those for cubes gave values up to 2·32 times, and those for cylinders, 2·85 times greater at 50°C. These results could also affect the safe design of silos for the storage of powder in the 40–50°C range to avoid self-ignition and allow the contents to cool to ambient temperature.