Solid state fermentation of apple pomace for livestock feed

Apple pomace is the main by-product of apple cider and juice processing industries. It is composed of apple pulp, seeds, stems and skins and contains 66.4 to 78.2% moisture, 9.5 to 22.0% carbohydrates and 1.03 to 1.82% proteins.; Solid state fermentation was used to convert apple pomace to a protein enriched animal feed. To achieve this goal, we studied on the selection of potential microorganisms, fermentation optimization to improve cell growth and protein synthesis, cell growth kinetics on solid substrate and heat generation and transfer in solid state fermentation system; Kluyveromyces marxianus NRRL Y-1196 and Rhodotorula glutinis AP10 were selected as the best performers increasing the protein content of the pomace about 3 times to 9.7% on the dry weight basis. They showed the highest protein content when supplemented with 0.5% urea. Optimum temperature for K. marxianus and R. glutinis AP10 were 30°C and 27°C respectively.; Kinetic parameters of R. glutinis growing on apple pomace were estimated by Levenburg-Marquardt least-squares method. Maximum growth temperature (T_max) was estimated to be approximately 314.3 K. Correlations of maximum specific growth rate (μ_max) and maximum cell mass (X_max) versus temperature were described by a Ratkowsky model. The highest values of μ_max and X_max were respectively 6.05E-05 s−1 at 302.9 K and 80 g biomass kg−1 initial dry matter. The specific death rate depended on temperature according to the Arrhenius equation. The specific death rate (μ_d,m ) was 4.12E-05 at 309.16 K and the activation energy (E_a) for R. glutinis was 196.21 kJ mol−1.; Dynamic two-dimensional modeling was used in a theoretical analysis of the overheating problem in SSF within a multi-level tray reactor. The model described the growth and death of R. glutinis as a function of temperature, the generation of metabolic heat, and the transfer of heat within the reactor bed by conduction and convection.; Significant death occurred in the upper region of the bed where the highest temperature was reached. The temperature rise at the top of the bed could be minimized by using high superficial air velocities or low inlet air temperatures. The most effective strategy for heat removal from the reactor was to use a high superficial air velocity at lower temperature than the optimum temperature for cell growth. The air velocities should be determined empirically to avoid a severe substrate drying by evaporation.