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. 2016 Feb 26;17(3):302.
doi: 10.3390/ijms17030302.

Co-Production of Fungal Biomass Derived Constituents and Ethanol from Citrus Wastes Free Sugars without Auxiliary Nutrients in Airlift Bioreactor

Behzad Satari  1   2 , Keikhosro Karimi  3 , Mohammad J Taherzadeh  4 , Akram Zamani  5
Affiliations

Co-Production of Fungal Biomass Derived Constituents and Ethanol from Citrus Wastes Free Sugars without Auxiliary Nutrients in Airlift Bioreactor

Behzad Satari et al. Int J Mol Sci. .

Abstract

The potential of two zygomycetes fungi, Mucor indicus and Rhizopus oryzae, in assimilating citrus waste free sugars (CWFS) and producing fungal chitosan, oil, and protein as well as ethanol was investigated. Extraction of free sugars from citrus waste can reduce its environmental impact by decreasing the possibility of wild microorganisms growth and formation of bad odors, a typical problem facing the citrus industries. A total sugar concentration of 25.1 g/L was obtained by water extraction of citrus waste at room temperature, used for fungal cultivation in shake flasks and airlift bioreactor with no additional nutrients. In shake flasks cultivations, the fungi were only able to assimilate glucose, while fructose remained almost intact. In contrast, the cultivation of M. indicus and R. oryzae in the four-liter airlift bioreactor resulted in the consumption of almost all sugars and production of 250 and 280 g fungal biomass per kg of consumed sugar, respectively. These biomasses correspondingly contained 40% and 51% protein and 9.8% and 4.4% oil. Furthermore, the fungal cell walls, obtained after removing the alkali soluble fraction of the fungi, contained 0.61 and 0.69 g chitin and chitosan per g of cell wall for M. indicus and R. oryzae, respectively. Moreover, the maximum ethanol yield of 36% and 18% was obtained from M. indicus and R. oryzae, respectively. Furthermore, that M. indicus grew as clump mycelia in the airlift bioreactor, while R. oryzae formed spherical suspended pellets, is a promising feature towards industrialization of the process.

Keywords: Mucor indicus; Rhizopus oryzae; chitosan; citrus waste; ethanol; oil; pellet; protein.

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Figures

Figure 1
Figure 1
Lab-scale study on fungal conversion of citrus waste sugars.
Figure 2
Figure 2
Concentration of (▲) sucrose, (♦) glucose, (■) fructose, and (×) ethanol in cultivation of (a) M. indicus and (b) R. oryzae on CWFS without any nutrient in baffled shake flasks. Data are means ± SD, n = 2.
Figure 3
Figure 3
Concentration of (▲) sucrose, (♦) glucose, (■) fructose, and (×) ethanol in (a) CWFS supplemented with full nutrients and (b) CWFS supplemented with KH2PO4 in baffled shake flasks during the growth of M. indicus. Data are averages of two replicates ± SD.
Figure 4
Figure 4
Concentration of (▲) sucrose, (♦) glucose, (■) fructose, and (×) ethanol in the cultivation of CWFS supplemented with all required nutrients in a 4-L airlift bioreactor using M. indicus. Data are means ± SD, n = 2.
Figure 5
Figure 5
Concentration of (▲) sucrose, (♦) glucose, (■) fructose, and (×) ethanol in cultivation of (a) M. indicus and (b) R. oryzae in a 4-L airlift bioreactor on CWFS without nutrients supplementation. Data are means ± SD, n = 3.
Figure 6
Figure 6
(A) Pellet type growth by R. oryzae and (B) mycelial type growth by M. indicus in airlift bioreactor on CWFS without any nutrients supplementation. The photos are taken after 72 and 48 h cultivation, respectively.
Figure 7
Figure 7
Microscopic morphology of M. indicus in airlift bioreactor after cultivation for (A) 0 h, (B) 24 h, and (C) 48 h. The D–F pictures belonged to R. oryzae growth (D) at the beginning, (E) after 48 h, and (F) 72 h. Both fungi were cultivated on CWFS in airlift reactors with no additional nutrients. The bars correspond to 20 μm.
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