Effects on pasting viscosity of starch and flour from different operating conditions for the Rapid Visco Analyser

Three wheat flours, three wheat starches, a regular maize starch and a waxy maize starch were subjected to a number of different RVA profiles. Five different initial temperatures were used, 40, 50, 55, 60, and 65 degreesC, with different initial holding times (0-3 min), heating times (2fl-10 min), holding times at 95 degreesC (0-6 min), cooling times (2-6 min), and final hold times (0-10 min) being applied. A range of final temperatures of 30-60 degreesC was also utilized. Significant variations in viscosity were observed with these conditions, particularly in wheat starch and flour. The most important parameters causing these variations were the initial temperature, the heating rate, and the final holding time. Short initial holding times also resulted in a wider spread of values for peak viscosity although there was little effect on the mean value and no significant effect on the holding strength or final viscosity. The final temperature was also important in that lower temperatures gave more viscous gels. Provided that the desired cooling rate could be achieved, varying the cooling time had no effect on the peak or trough viscosities and only a very minor effect on the final viscosity. If final temperatures of 40 degreesC or lower are to be used, the cooling conditions and final hold time would need to be adjusted so that maximum viscosity could be achieved. A proposal for a standard Rapid Visco Analyser (RVA) procedure is: at least 1 min at 50 degreesC, heat to 95 degreesC over 4 min, hold at 95 degreesC for 4 min, cool to 50 degreesC in 3 min, and hold at 50 degreesC for 4 min. These conditions should minimize variation within samples and should allow a better comparison between samples.