Electrical conductivity of reconstituted milk affected by temperature and composition

Introduction: Among the foods consumed on a daily basis, milk has the most appropriate and balanced ingredients, that is the reason milk called whole food. Milk is the only known substance in nature that can provide the human body with complete and balanced nutrition. Recombined milk is a milk replacement product. Recombined milk components are more easily adjustable than milk components. The electrical conductivity is referred to as conductivity of specific material against the electric current, which is expressed in micro Siemens units per cm (mS/cm). Using electrical conductivity, valuable information is available about the quality of different materials, including food. In addition, by this method, as a simple and practical tool, the quality of many foods can be controlled. The aim of this study was to investigate the electrical conductivity of recombined milk affected by temperature, protein percentage, and lactose content. Materials and methods: In order to investigate the effect of protein percentage (1, 2 and 3%) and percentage of lactose or sugar content (4, 6 and 8%) on the electrical conductivity of milk, pure dry milk powder without dietary supplementation was used. Lactose powder was used to increase the lactose content of dry milk powder. Sodium caseinate was used to increase the protein content of dry milk powder. Distilled water was used to increase the volume of samples. Total experiments were carried out at three temperature levels (50, 55 and 60 ºC). Data analysis was also done using SPSS 16 software. Results and discussion: The results showed that temperature, protein percentage, and lactose percentage had a significant effect on the electrical conductivity of recombined milk. The electrical conductivity of the recombined milk ranged from 2.31 to 5.7 mS/cm at 50°C, 8% lactose, 1% protein, and 60°C, 4% lactose, 3% protein, respectively. The greatest and least effect on the electrical conductivity of recombined milk was related to the effect of protein percentage and lactose percentage, respectively. By increasing the temperature, the electrical conductivity of the reconstituted milk has increased significantly. The greatest changes in electrical conductivity (16%) of recombined milk occurred by the influence of temperature factor in protein 1% and lactose 4% and its value ranged from 2.44 to 2.83 mS/cm. In addition, the lowest changes in electrical conductivity (6%) of recombined milk were obtained by the temperature factor of 3% protein and 8% lactose, and it was increased from 4.68 to 4.95 mS/cm. By increasing protein content, the electrical conductivity of recombined milk has increased significantly. The most changes in electrical conductivity (107%) of recombined milk occurred by the influence of protein percentage at 55 °C and 6% lactose and its value ranged from 2.42 to 5.6 mS/cm. In addition, the lowest changes in the electrical conductivity (100%) of reconstituted milk occurred by the influence of protein percentage at 55 °C and 4% lactose, and its content increased from 2.5 to 5 mS/cm 5. These results indicate that the protein percentage factor has the most effect on the electrical conductivity of recombined milk (compared to two temperature factors and lactose percentage). By increasing lactose content, the electrical conductivity of recombined milk has decreased significantly. The greatest changes in electrical conductivity (13%) of recombined milk occurred by the influence of lactose percentage at 60 °C and protein 3% and its content decreased from 5.7 to 4.95 mS/cm. Also, the smallest changes in electrical conductivity (1.5%) of reconstituted milk occurred by the influence of lactose percentage at 55 °C and 2% protein, and its content decreased from 5.55 to 4.48 mS/cm. The maximum and minimum amount of electrical conductivity of reconstituted milk was 5.7 mS/cm at 60°C, 4% lactose and 3% protein, and 2.31 mS/cm at 50°C, 8% lactose and 1% protein, respectively.