3.2. Relationship between mechanical properties difference and
milling quality
Milling quality indices, head rice yield, brown rice yield and
broken rice yield, are presented in Table 1. The relationship between
breaking force difference and head rice yield is shown in Table
3. The head rice yield increased linearly with the increase in
the breaking force difference between the ventral side and the
dorsal side. The broken rice yield was always related to head rice
yield, the head rice yield increased with the decrease in the broken
rice yield. The broken rice yield was also related to the breaking
force difference between the ventral side and the dorsal side, the
broken rice yield decreased with the increase in the breaking force
difference between the ventral side and the dorsal side.
The correlation coefficient between the breaking force difference
and the head rice yield was larger than that between the
average breaking force and head rice yield (Table 3). The breaking
strength difference between the dorsal side and the ventral side
and average breaking strength were all related to the head rice
yield. But the correlation coefficient between the breaking
strength difference and head rice yield was still larger than that
between the average breaking strength and head rice yield. The
elasticity modulus difference and average elasticity modulus
were all not related to the head rice yield. The fracture energy difference
was not related to the head rice yield, but the average
fracture energy was related to the head rice yield. The correlation
coefficient between the mechanical properties and broken rice
yield was wholly lower than that between the mechanical properties
and head rice yield. It was more accurate to predict the
head rice yield by the breaking force difference between the ventral
side and the dorsal side than by the average breaking force.
When brown rice kernel is mechanically milled, rice kernels
experience the compound acting force, which include compressive,
frictional and shearing force. Thus the mode of force acting
on rice at milling still remains unknown. The correctly establishing
the relationship between the mechanical properties and milling
quality is an important basis for an improving design of
milling machine. Rice kernels which have larger breaking force
difference will absorb more fracture energy at milling under the
same milling condition, and these rice kernels do not easily break