Recycling of orange waste for single cell protein production and the synergistic and antagonistic effects on production quality

Abstract The daily output of orange residue from the orange juice production enterprise in the Three Gorges Reservoir Area (TGRA) of China is approximately 100 t/d, which seriously pollutes the environment of the TGRA. The key challenge of handling this waste is maximizing profitability. In this study, high-protein feed with low levels of crude fiber and pectin was produced by solid fermentation of orange waste. The synergistic and antagonistic effects of microorganisms on one another significantly influenced the quality of single cell protein (SCP) feed. The added true protein (ATP) content increased gradually as pectin degradation (PD) and crude fiber degradation (CFD) were enhanced because of the synergistic effects. However, ATP decreased because of antagonistic effects as PD and CFD were increased beyond certain values. Aspergillus oryzae ( A. oryzae ) and Trichoderma koningii ( T. koningii ) mutually promoted each other, but the growth of Candida tropicalis was inhibited by A. oryzae and T. koningii as polygalacturonase and carboxymethyl cellulase accumulated. Synergistic and antagonistic effects existed simultaneously during microorganic fermentation of orange wastes. In large-scale fermentation, ATP, PD, and CFD were increased by 14.20%, 15.80%, and 9.15%, respectively, in comparison with the flask test. The profit achieved by reusing orange waste in the Chongshou Agricultural Park as SCP feed was calculated to be 48500 USD per year, whereas the cost of disposing of the orange waste was 7560 USD. This study provides insight into how microorganic synergistic and antagonistic effects influence the quality of SCP feed and provides a potential route for recycling agricultural waste into valuable materials.