Electrophoresis, rheology and meltability of imitation cheese containing rice starch as influenced by storage time

The rheological and proteolytic changes in imitation cheeses containing 3% native (2.5, 15 or 28% amylose levels), pregelatinised, cross-linked or cross-linked and stabilised rice starch were compared to a control (0% starch) with storage time. After 180 days, the control had significant decreases in textural hardness (from 136.5 to 114.9 Newtons) and storage modulus (G'; 75.7 kPa to 63.3 kPa) as well as significant increases in tan δ values (0.447 to 0.476). The starch-containing imitation cheeses also had significant reductions in G' with storage as well as significant increases in tan δ values. Most of the starch types increased hardness after 90 days, possibly due to starch retrogradation. Meltability of the control imitation cheese increased significantly from 130.5 mm after 14 days to 144.6 mm after 180 days. Similar meltability increases were observed in products containing starch. Urea-polyacrylamide gel electrophoresis determinations showed that the protein fraction; α s1 -casein remained stable over 2 years storage, however, p-casein hydrolysed to γ-caseins probably due to the indigenous enzyme; plasmin. This breakdown of p-casein contributed to the weakening of imitation cheese structure and its increased melting capacity. The partial replacement of the protein matrix with starch lessened the effects of proteolysis on imitation cheese hardness.