High performance liquid chromatographic (HPLC) determination of available lysine in milk protein-maize composite extrudates and its stability during storage

Effect of three processing variables: Milk protein sources (Rennet Casein and Whey Protein Concentrate-70 (WPC-70)), feed composition (4, 6 and 8% of milk protein source in addition to maize), feed moisture content (12,14,16%) on available lysine using HPLC was studied following extrusion processing of mixtures of milk protein and maize composite flour at extrusion temperature 100 degrees C with 340 rpm and optimized product was studied for storage stability at two different temperatures 25 degrees C and 37 degrees C. Results showed that rennet casein addition at 8% with 12% feed moisture content resulted in higher available lysine of 8.84 g/kg of sample whereas the WPC-70 addition at 8% with 14% feed moisture content had significantly (p < 0.05) lower available lysine content of 5.48 g/kg of sample due to higher denaturation at 100 degrees C. The available lysine content of the product on the initial day was found to be 8.36 (g/Kg of Sample) which reduced after one month of storage to 4.28 g/Kg of Sample and 2.97 g/Kg of Sample at 25 degrees C and 37 degrees C, respectively. Optimum extrusion parameters and storage conditions resulting in maximum available lysine was estimated.