Factors affecting rapid visco analyser curves for the determination of maize kernel hardness

The effects of grinding condition, solids content and beating rate on apparent viscosity measured with a Rapid Visco Analyzer (RVA) For maize kernel varieties with different endosperm hardness were investigated, Maize hardness was measured with a tangential abrasive dehulling device (TADD), density, flotation, and subjective ratings. Harder maize kernels gave rise to coarser particles that took longer to reach peak viscosity and had lower peak heights than the finer particles from soft kernels. Finely ground samples produced distinct viscosity curves. Higher solids content increased peak viscosity. A low heating rate produced the highest peak viscosities. The viscosity characteristics of decorticated, degermed maize kernels were similar to those observed for whole maize samples. Peak viscosity and slope were significantly correlated with kernel hardness values. Evaluation at 18 % solids concentration with 10 degrees C/min heating rate for soft kernels and 2.4 degrees C/min for hard kernels resulted in the greatest sensitivity to differences in endosperm hardness. Maize samples can be initially separated into hard and soft categories by flotation or density. RVA parameters can then be adjusted to distinguish between samples within each group. The RVA technique is sensitive to differences in maize kernel endosperm hardness with the advantages of small sample size, short testing time, simple procedure, easy data management and versatility for screening kernels. (C) 1997 Academic Press Limited