According to the growth pattern of yeast cells under non-sterile
conditions, a 3-log decrease in the initial microbial population
within 24 h of SSF occurred (Fig. 1). Over the same cultivation
period, it was observed that yeast cells remained viable in populations
of more than 8-log10cfu/g substrate in the process with the
autoclave sterile OP. To better understand the effect of autoclave
sterilization process on OP, the amount of limonene in raw and pretreated
OP was determined. The estimated values (0.52±0.02 vs
0.20±0.01%, v/w of raw and autoclave sterile matrix) indicated that
the loss of limonene observed during the autoclave sterilization of
OP was rather high (62%) due to its evaporation. The inhibitory
effect of limonene has been reported in chemically defined liquid
media at very low levels (0.01–0.20%, v/v) [30,31]. A greater minimum
inhibitory concentration of limonene (0.28%, v/w) was found
in the study of Wilkins et al. [29], in which satisfactory ethanol
yields could be obtained from citrus peel waste after saccharification
and fermentation.