Powdered Milk Replacer Reconstitution - Solubility Test Results
Objective of the solubility test
The objective of the solubility test conducted by WildAgain was to measure the solubility of the various powdered milk replacers in the final stage of the reconstitution process (dissolution). The test methodology is described at this link.
The methodology produced results, in terms of dry pellet formation, as expected. The image below is a sampling of 8 of the 24 trials that were performed. The pellets consist of the dry residue of the powder that did not go into dissolution during the reconstitution process.
The chart below shows the quantified solubility index (SI) scores for the various products (some with multiple lots tested). As the chart indicates, smaller scores (%'s) are better in terms of more complete solubility.
Specific test results and analysis (click for PDF's):
For reference, human grade whole milk powders should have a SI not exceeding 1% if spray dried, and not exceeding 15% if roller dried. The type of drying process used by PetAg® and Fox Valley for their respective products is not disclosed on their product labels. But PetAg® has disclosed in other forms in the past that they utilize a multi-step spray drying process, largely to agglomerate the milk particles to deliver a product with better reconstitution properties.
Conclusion and observations
For all of the samples tested above, the average value for SI was 3.0% with a median value of 2.3%. Because these products are not human grade in quality, it is not surprising that only 17% of the samples (4 of 24) met the SI standard for spray dried products of <1%. The fact that two-thirds (16 of 24) of the samples scored an SI of 3% or less seems acceptable for the grade and intended use of the products. The samples that scored an SI above 3% should not necessarily be cause for concern, but should be used more as an indicator for those products that perform less well than those with a lower SI score.
For all of the products, the literature consistently suggests that powdered milk products will achieve a higher and more complete degree of dissolution with hotter water temperatures and longer reconstitution (resting) time. This is especially true for the casein-rich milk replacer powders used by rehabilitators.
Remember that the test results described above were performed at 110°F water and a total resting time of only 20 minutes, according to the prescribed test procedure. It seems reasonable to assume that the SI scores would see improvement if the samples were retested with hotter water and a longer total resting time period. The products that should see most improvement based on the chart above would be Fox Valley 30/50 and 20/50, and Esbilac® and KMR®.
References (not intended as an exhaustive list)
Anema, S. G., D. N. Pinder, R. J. Hunter, and Y. Hemar. Effects of storage temperature on the solubility of milk protein concentrate (MPC85). Food Hydrocolloids (2006) 20:386-393.
Baldwin, Alan J., Fonterra Research Centre, Palmerston, NZ. Insolubility of milk powder products- a minireview. Dairy Science Technology (2010) 90:169-179.
Boiarkina, I., N. Depree, W. Yu, D. I. Wilson, and B. R. Young. Rapid particle size measurements used as a proxy to control instant whole milk powder dispersibility. Dairy Science and Technology (2017) 96:777-786.
Forny, Laurent and Stefan Palzer (Food Science and Technology Department, Nestlé Research Centre, Vers-Chez-Les-Blanc, CH-1000 Lausanne, Switzerland). Wetting, disintegration and dissolution of agglomerated water soluble powders. Conference Paper · June 2009
Ilari, Jean-Luc and Laila Mekkaoui. Physical properties of constitutive size classes of spray-dried skim milk powder and their mixtures. Le Lait, INRA Editions, 2005, 85 (4-5), pp.279-294. hal-00895603
International Diary Federation. In determination of insolubility index, Standard 129A. Brussels, IDF (1988)
Pugliese, Alessandro, Giovanni Cabassi, Emma Chiavaro, Maria Paciulli, Eleonora Carini, and Germano Mucchetti. Physical characterization of whole and skim dried milk powders. Journal of Food Science Technology (2017) 54(11):3433-3442.
Sharma, Anup, Atanu H. Jana, and Rupesh Shrikant Chavan. Functionality of milk powders and milk-based powders for end-use applications - a review. Comprehensive Reviews in Food Science and Food Safety (2012) 11:518-528.