## 3 Results and Discussion  
### Potential of Biowastes as Culture Media  
As listed in Table 1, a mixture of discarded vegetable residues can yield a liquid fraction after a simple crushing and centrifugation process with a total carbohydrate content of 31.3 g/L. Glucose and fructose are major sugar monomers of this stream, accounting for more than 95% of these carbohydrates. These sugar components are easily assimilated by most microorganisms, thus making these streams a promising feedstock for microbial-based processes. The production of vegetables under horticulturally intensive systems, such as greenhouse-type industries, is one of the major producers of organic waste. It is important to note that currently, agro-food residues are poorly exploited, often directly discharged into the environment and/or landfilled [14]. In addition, during its treatment, 80% of this biowaste is converted into bacterial biomass with no added value and with associated treatment and disposal costs [26]. Using agro-food biowaste as feedstock in bioprocessing will therefore benefit its sustainable management as a valuable raw material. Lignocellulosic residues are another sugar-rich source that can represent an important raw material for bioprocessing. In contrast to agro-food biowastes, lignocellulosic residues require pretreatment and enzymatic hydrolysis to obtain a sugar-rich stream or hydrolysate. As highlighted in Table 2, the water-insoluble fraction recovered after steam explosion pretreatment of a lignocellulosic urban pruning residue is made of 48% carbohydrates, considering both cellulose and hemicellulose components. After the enzymatic hydrolysis of the pretreated solid fraction and a subsequent vacuum evaporation step, a glucose-rich stream was obtained with a final total sugar concentration of about 250 g/L (Table 1). Before vacuum evaporation, a glucose concentration of around 60 g/L was obtained, corresponding to an enzymatic hydrolysis yield of about 70%. [PERSON] et al. [19] have previously reported similar yield values during the enzymatic hydrolysis of a steam-exploded urban pruning residue obtained under similar pretreatment conditions. The use of residual lignocellulosic biomass as feedstock for SCO production has been previously investigated. Sugarcane bagasse, rice straw, or wastepaper are some examples [27; 28; 29]. [PERSON] et al. [28] reported the production of lipids using the hemicellulose hydrolysate obtained after dilute acid pretreatment of sugarcane bagasse and the yeast _Lipomyces starkeyi_. The resulting lipids showed a similar fatty acid (FAMEs) profile to palm oil, commonly used in biodiesel production. [PERSON] et al. [27] subjected rice straw to a glycerol-FeCl\({}_{3}\) pretreatment. The resulting enzymatic hydrolysate was used as media for lipid production with the yeast _Cryptococcus curvatus_ ATCC 20509, obtaining 8.8 g/L of lipids with conversion yields of 0.17 g/g. On the other hand, [PERSON] et al. [16] obtained 5.4 g/L of lipids using an enzymatic hydrolysate of pretreated waste office paper (5% (_w/v_) substrate concentration \begin{table}
\begin{tabular}{c c c c} \hline
**Carbohydrate** & **Agro-Food Biowaste** & **Concentrated Agro-Food Biowaste** & **Concentrated Enzymatic Hydrolysate from Lignocellulosic Urban Residue** \\ \hline Glucose & 14.40 \(\pm\) 0.04 & 28.54 \(\pm\) 0.18 & 244.13 \(\pm\) 3.21 \\ Xylose & 0.11 \(\pm\) 0.02 & 0.27 \(\pm\) 0.02 & 9.17 \(\pm\) 0.02 \\ Galactose & 0.27\(\pm\) 0.02 & 0.43 \(\pm\) 0.05 & 0.46 \(\pm\) 0.02 \\ Arabinose & 0.71 \(\pm\) 0.03 & 0.39 \(\pm\) 0.04 & 0.16 \(\pm\) 0.02 \\ Mannose & 0.16 \(\pm\) 0.01 & 0.26 \(\pm\) 0.01 & 0.52 \(\pm\) 0.02 \\ Fructose & 15.64 \(\pm\) 0.30 & 31.16 \(\pm\) 0.47 & n.d. \\ \hline \end{tabular}
\end{table} 
Table 1: Carbohydrate composition of the biowaste streams resulting from a mix of discarded vegetables (agro-food waste) and the hydrolysate obtained after pretreatment and enzymatic hydrolysis of a lignocellulosic urban pruning residue. in a 0.5% hydrogen peroxide solution; 121 \({}^{\circ}\)C, 30 min).