# Upgrading of Mixed Food Industry Side-Streams by Solid-State Fermentation with _P. ostreatus_
## 3 Results and Discussion
### P. orestatus Growth in the Mixed AISS  
In Table 3, the protein and sugar composition of the mixed AISS substrates before and after the growth of _P. orestatus_ by SSF at 25 \({}^{\circ}\)C, are presented. The moisture content of the substrates after fermentation was 62.6-88.7%, which is suitable for _P. orestatus_ growth. The fungus consumed most of the fermentable sugar in most cases. The reduction of sugars and the increase of protein are illustrated in Figure 1. The highest protein increase can be observed for the S7 substrate (5 mL whey, 20 mL molasses, 5 mL orange pulp, 20 mL potato pulp, 30 g BSG, 5 g MSR, and 20 mL water), which also had  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Metal (mg/Kg)** & **MSR** & **BSG** & **Whey** & **Molasses** & **Orange Pulp** & **Potato Pulp** \\ \hline Mg & 3970 & 605.6 & 2000 & 14,200 & 0.19 & 320.63 \\ Ca & 20.30 & 4.39 & 21.0 & 1636 & 285 & 1.10 \\ Fe & 96.02 & 4.56 & 0 & 70.9 & - & - \\ Cu & 19.38 & 24.62 & 3.66 & 6.03 & 3.21 & 3.34 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Metal elements contained in the used AISS.  
the highest sugar consumption. Generally, _P. ostreatus_ was able to grow on all of the substrates, which indicates the suitability of the mixed AISS as substrates for edible mushroom growth.  
Subsequently, the effects of substrate pH (4.0, 5.5, and 7.0, at 25 \({}^{\circ}\)C) and temperature (15, 25, and 37 \({}^{\circ}\)C, at pH 4.0) on _P. ostreatus_ growth on substrate S7 were studied. In this case, the biomass yield was expressed as g of mycelium/Kg of substrate, and the results are presented in Table 3. Higher mycelial yield was achieved at pH 4.0, while the lowest was at pH 7.0. This was expected as the optimal pH values for the growth of _Pleurotus_ fungi range from 4.0 to 6.5 [31]. From Table 3, it can also be seen that the fungus grows better at 25 \({}^{\circ}\)C. This is confirmed by other works that identified the optimal growth temperature of _P. ostreatus_ to be about 22 \({}^{\circ}\)C [32; 33; 34].  
For the scale-up experiments, the growth of _P. ostreatus_ on the S7 substrate was then studied using three different bioreactor systems, as described in paragraph 2.2. After two days of incubation, the formation of mycelium appeared in all three systems, and at five days, it had covered the entire surface of the substrate. The incubation temperature was then reduced to 16 \({}^{\circ}\)C to facilitate the fruiting  
Figure 1: Sugar consumption and protein increase during _P. ostreatus_ growth in the 25 mixed AISS substrates.  
of the mushrooms, since the optimum temperature reported in the literature is 15-18 \({}^{\circ}\)C [32; 33; 34]. The incubation was continued for a further 35 days during which (every seven days) water was added to maintain stable substrate moisture. At the end of the 40 days of incubation, no appearance of fruit from the edible fungus was observed, but the mycelium, on the contrary, showed alterations in color and gas (probably methane) formation. Thus, further research is needed on the conditions (moisture, temperature, addition on trace elements, etc.) for mushroom fruiting bodies using the proposed mixed AISS.