Spray Drying of Skim Milk Mixed with Milk Permeate: Effect on Drying Behavior, Physicochemical Properties, and Storage Stability of Powder

Abstract

The possibility of using milk permeate (MP) to lower the protein level of skim milk powder (SMP) in producing powders of 34% and lower protein is explored. Skim milk suspensions with various levels of MP were prepared by mixing SMP and MP powder (MPP) at the ratios of 1:0, 7:3, 3:7, and 0:1: from 34 to 5.3% protein. The suspensions were dried in a spray dryer with inlet and outlet temperatures of 180 and 80°C, respectively. Increasing permeate concentration in the mixture showed a greater tendency to stickiness manifested by lowered the cyclone recovery of the powder as more powder stuck on the wall of the dryer. Increasing permeate concentration in the resultant powder did not significantly affect the bulk density but led to a reduction in the particle size and also made the powder slight green and yellowish in color. It also found to lower the glass transition temperature (T_g ) of the skim milk powder (SMP) and induce crystallization of lactose at lower water activity (a_w  ≥ 0.328 for SMP:MPP of 3:7 and 0:1 compared to a_w  ≥ 0.0.432 for SMP:MPP of 1:0 and 3:7). Addition of MP in SMP lowered the T_g values of the resulting powders. The permeate fraction in spray-dried SMP/MPP mixtures found to lower the critical a_w and moisture content, suggesting the SMP mixed with MPP is more likely to become sticky than SMP alone (at 34% protein) when stored at a similar water activity and moisture content.

Keywords:

• Milk permeate
• Skim milk powder
• Spray drying
• Stickiness
• Storage stability

ACKNOWLEDGEMENT

The authors are gratefuel to the Dairy Ingredients Group of Australia (DIGA) for the funding of this research project (Project No. UQ3412) and Warren Cook and Michael Phillips of Murray Goulburn Cooperative Co. Ltd., Melbourne, Australia, for sending milk powder samples.

Notes

Source: From product specification.

¹Mean values±standard deviation (triplicates).

²Values followed by same letter within a column do not differ significantly (p > 0.05).

³Cyclone and total recovery (cyclone + sweep recovery), average of three trials.

⁴The volume mean [v(4,3)] diameter.

¹Mean values±standard deviation of triplicate samples.

²Moisture is presented as g H₂O/100 g dry solid.

³The values followed by same letter within a row do not differ significantly (p > 0.05).

⁴Water activity of samples kept in P₂O₅ was less than 0.034 (detection limit of water activity meter), so considered as zero.

¹Mean values±standard deviation of triplicate samples.

²The values followed by same letter within a row (of midpoint) do not differ significantly (p > 0.05).