(2012) reported that carbohydrate was the main substrate to pro-
duce more organic acids through biological fermentation than
proteins because protein quantity increased due to cell growth in
the degradation of carbohydrate. Based on the above results, car-
bohydrate reduction seems to provide some significant information
about the following steps during the fermentation process.
Hydrolysis occurs when insoluble organic polymers are broken
into simple sugars, fatty acids and amino acids. Becausemost of the
organics in food waste are in particulate form, hydrolysis is the first
step of the anaerobic fermentation process. As shown in Fig. 1b, the
hydrolysis rate of food waste reached 47% at 55 C, which is higher
than the rates of 32.8% and 32.4% at 25 C and 35 C, respectively.
Liu et al. (2013a) also observed that a higher degree of hydrolysis
occurred in thermophilic fermentation than mesophilic fermenta-
tion; however, the acidogenesis rate of 3.2% was the lowest at 55 C
in the study. Higher temperature can accelerate the activity of
extracellular enzymes; meanwhile, acidogenesis bacterial are
inhibited at higher temperature. It has been reported that the for-
mation of various organic acids should be associated with carbo-
hydrate reduction (Liu et al., 2013a). Based on the preceding results,
the carbohydrate reduction degreewas the highest at 25 C, and the
same result was obtained with the greatest acidogenesis rate of
6.9% at 25 C.
Therefore, these data show that the hydrolysis rate at 25 Cwas
close to the rate that occurred at 35 C but lower than that at 55 C;
however, the acidogenesis rate was highest at 25 C. Hence, 25 C
was the most efficient temperature for organic acids preparation in
this study