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Development of a grain breakage susceptibility tester and a study of the effects of maize grain temperature
on breakage susceptibility and stress cracking. TAE HOON KIM (1), J. G. Hampton (2), Linus Opara
(3), A. K. Hardacre (4), and B. MacKay (5). (1) Seed Technology Centre, Massey University; (2) NZ Seed
Technology Institute, Lincoln University; (3) Institute of Technology and Engineering, Massey University;
(4) Crop & Food Research Institute; (5) Institute of Natural Resources, Massey University.
A breakage tester (HT-I breakage tester) was developed and single
grain breakage at various grain temperatures and times after drying was determined. Both a hard and a soft
maize hybrid had minimal breakage at high grain temperatures (78 to 110°C). Decreasing grain temperature
increased breakage exponentially. However, there was no significant difference in the percentage breakage
between the two hybrids after drying at various drying temperatures and cooling at ambient temperature.
Initially, the percentage breakage of the two maize hybrids increased rapidly within 10 minute after drying
at both 60°C and 120°C and they had reached the asymptotes after about 10 minutes cooling at ambient
temperature. Initial grain breakage was significantly higher at 60°C drying, but the asymptote was
significantly higher at 120°C drying. As drying temperature increased from 20 to 120°C, grain dimension
shrinkage (%) reduced significantly, but the shrinkage of length and width in both hybrids declined
generally to a lesser extent than that of thickness. Based on the results of this study, a possible mechanism
of stress cracking in maize grain after high temperature drying is suggested: When maize grain is exposed to
high drying temperatures (> 60°C), it is soft and plastic until the grain temperature nears that of the drying
temperature. As grain cools down quickly after high temperature drying, it hardens and becomes rigid. The
continuous and slow progress of thermal contraction of the maize endosperm over time after drying
collapses the connection between the starch granules and triggers the development of stress cracking.
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