To summarize, the highest quality HWEM is expected
to have moisture content less than 13%, high percentage
of PDIV, and low energy consumption. To achieve such
an expectation, the Expert Design 7.0 Trial program
was employed to deduce the optimum combination of
temperature and time for processing. The combination
of 65°C for 23 h was revealed as a superior condition
that would produce HWEM with a percentage of PDIV
of 90.7% and a percentage of DM of 87% (Table 3).
On the other hand, energy consumption would be only
80.8 kWh/60 kg of HWE. Furthermore, based on Equation
[4], with increases in time and temperature the
estimation of E. coli counts would be reduced to the
bottom (1.85 × 105 cfu/g) of an abruptly descending
surface shown in Figure 5. To demonstrate the quality
of HWEM produced by the predicted optimum combination,
3 batches of 60 kg of HWE were processed at
65°C for 23 h, and the consequent product of 25.8 kg
of each batch was analyzed. Similarities existed in the
qualities and energy consumption between the predicted
and real values (Table 3). Thus, RSM was proven
as an efficient methodology to optimize the processing
conditions of HWE.