۱- Introduction

۲- Materials and methods

۳- Results and discussion

۴- Conclusion

References

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.

Introduction

China is the foremost orange producer in the world. In 2014, the orange planting area of China was 2.211
۱۰۱۰ m2 , and the annual output was 2.75
۱۰۱۰ kg (Shan, 2014). Oranges are consumed worldwide in the forms of pulp, peel and juice. Approximately 8
۱۰۹ -۲
۱۰۱۰ kg of solid and liquid residue is produced as waste during orange processing every year (Tripodo et al., 2004; Rezzadori et al., 2012). In most instances, this enormous amount of waste is scattered on soil in areas adjacent to the production facility, incinerated, placed in a land fill, or used as raw material for animal feed production (Martín et al., 2010; Patsalou et al., 2017). However, incineration of orange waste was found to lead to highly polluted surface and ground water with altered chemical oxygen demand and biological oxygen demand, as well as polluted soil (Rezzadori et al., 2012; Braddock, 1995). The term SCP refers to dead, dry cells of microorganisms such as yeast, bacteria, fungi and algae, which are utilized as a protein supplement in foods for humans or animal feed (Ofodile et al., 2011; Mahmood, 2012). SCP is made up of carbohydrates, fats, vitamins, minerals, and other cellular constituents (Mondal et al., 2012), and it can be produced from relatively inexpensive material or waste material (Santamaría-Fernandez et al., 2017).