The Effect of Water Type and Reconstitution Temperature on the Solubility of Commercially Available Milk Powders in Sri Lanka

Abstract

The objective of this study was to investigate the effect of water type and water temperature levels on the solubility of commercially available milk powders in Sri Lanka. In addition to that, chemical properties of milk powders were analyzed and compared with international quality standards. Solubility was measured using insolubility index method and three water types were used including distilled water, deionized water and nano-water at two different temperature levels as 24 °C and 80 °C. Altogether 30 milk powder samples were tested including two locally produced and four imported milk powder brands. According to the insolubility index values, imported milk powder brands possessed higher solubility (0.49±0.05) than the locally produced ones (0.82±0.03) in all the three water types and temperature levels. When comparing the three different water types, solubility of milk powders were significantly lower (p<0.05) in de-ionized water, compared to nano-water and distilled water at 24 °C temperature in both imported and local milk powders. At 80 °C temperature level, imported milk powder brands showed a lower solubility in de-ionized water while local milk powder brands showed significantly lower solubility (p<0.05) in nano-water. All the milk powders had much higher solubility at 80 °C when compared to that of 24 °C. Present study results revealed that Free Fatty Acid levels in imported milk powders exist within the acceptable range (1.57±0.5 mmol/100 g fat) while it is much higher than acceptable limits in locally produced milk powders (4.43±0.1 mmol/100 g fat). All the other chemical properties including fat, protein, ash, Ca, pH, moisture and water activity were within the acceptable standard levels in both local and imported milk powders and it can be concluded that compositional changes of milk powders also affect on the solubility other than water type and temperature levels during reconstitution.