Effects of critical fluctuations of storage temperature on the quality of a dry dairy product.

Discipline: milk powder; Keywords:  milk powder, storage requirement, long term storage, evaluation criteria, abiogenic loss of quality. 

Worldwide whole milk powder (WMP) is a dairy product which overcomes the problem of seasonality of raw milk. Additionally, it serves as a product with high nutritional value to remote areas. It has a long shelf life which depends on the conditions of storage and transportation, recommended to be in a range from 0 to 10°C. At higher temperatures, the quality of WMP deteriorates because of an increase in the degradation of fat and protein fractions. A range of low negative temperatures for storage have not been systematically investigated. Previous studies have shown that freezing WMP results in protein denaturation, crystallization of lactose and extraction of free fat, all of which reduce the quality characteristics thereof, including deterioration of solubility, quick rancidity and microbial changes. These studies, however, did not simulate possible transportation and storage conditions at low negative temperatures that may occur in practice. The volume  transported, the distance travelled and the climatic conditions during transportation, play an important role in WMP preservation. Thus, the objective of the study by Dr A.G. Galstyan and colleagues was to investigate the effect of changes in properties of WMP stored at unregulated temperatures from −20°C to 20°C. They published their results in the Journal of  Dairy Science, Volume 102 of 2019, page10779 to 10789. The title of the paper is: Effects of critical fluctuations of storage temperature on the quality of a dry dairy product.

In the study, they simulated storage and transport of WMP at −20°C. The samples were periodically thawed to 10 and 20°C and examined for physicochemical, functional-technological, thermodynamic, microbiological, and organoleptic parameters. 

The results showed that the storage of WMP at 20°C for 40 days did not affect the quality or quantitative yield of the thawed product. Also, the formation of a dew point following critical temperature fluctuations did not affect the quality of the WMP, whether the inner surface of the package was in contact with the product or separated from it by an air layer. The moisture in the packaged product was not redistributed by artificially contaminating the inner surface of the package with yeast and moulds and also showed an absence of yeast or mould growth after the WMP was thawed. In addition, no changes in technological and organoleptic characteristics of the thawed WMP were detected. There though was some compaction of the product and clumping, but this was reversible and the samples dispersed with little effort.                                                                                                                                                    

The results confirmed that the acceptable thermal conditions of milk powder storage could be expanded to range from −20°C to 10°C, since multiple (5) freeze/thaw cycles did not alter the technological and quality characteristics of the product.