3.1.2. Zinc retained in the final complex after crystallization
The major thrust of the study was to optimize a concentration of zinc on the basis of maximum binding efficiency of lactose to zinc. Zinc retained in the complex after crystallization at various levels of zinc sulphate is presented in Table 1. At zinc concentration of 1–5 mg/g of lactose, percent of zinc lost in washing was almost 0.3–1.4 mg/100 mL, yielding a maximum of zinc in final complex (16.3–78.9 mg/100 mL). Relatively lower proportion of zinc loss implied that lactose binding ability gradually increased at these levels. Further, increase in zinc concentration from 5.5 to 10 mg, resulted in maximum loss of zinc in washing i.e. from 3.6 to 29.1 mg/100 mL of zinc content in supernatant. At > 5 mg of added zinc/g of lactose level, the percentage of zinc in final complex significantly reduced (P < 0.05) as shown in Fig 1. It was also observed that zinc retained in the complex remained uniform even at higher concentration viz. 80 mg and 81.6 mg for 5.5 mg and 10 mg of added zinc/g of lactose. Therefore, 5 mg of added zinc/g of lactose level with 78.9 mg/100 mL of total zinc yield was selected for further characterization and application studies.