Bulk properties of palm kernel cake for solid-state fermentation

The bulk volumes of hydrated palm kernel cake (PKC) were investigated to generate information on bulk properties for solid-state fermentation (SSF). Measurements were made under ambient conditions as regards the range of moisture level, sieved and unsieved PKC and two substrate handling procedures, viz. loading, tapping and hydration (LTH) and hydration, loading and tapping (HLT) methods. Because of the combined effects of particle size, inconsistent particle surface characteristics, moisture level and particle agglomeration caused by substrate hydration before loading, different trends in volume changes were observed. Empirical models were developed to predict the bulk volume changes with information on three measurable parameters, namely, moisture level, initial volume of a known quantity of dry PKC and particle size. For sieved PKC in the LTH method, unsieved PKC in the LTH method and unsieved PKC in the HLT method, three models were derived respectively. As for sieved PKC in the HLT method, significant scatters in the volume changes restricted the establishment of a single model. Instead, six models were proposed for six particle sizes for more precise estimation. The findings from this work are useful, first, in assisting the determination of dimensions of SSF equipment for substrates of different particle sizes and moisture levels and, second, for the interpretation of fermentation results, e.g. effects of particles swelling and handling procedures on microbial performance. (c) 2011 Curtin University of Technology and John Wiley & Sons, Ltd.