## 2 Materials and Methods
### Laboratory Experiments
#### 2.2.1 Sample Preparation  
Overall, 174 substrate samples were prepared and tested. Air-dried soil was placed into acryl glass cylinder moulds (127 mm diameter, 50 mm height, 126.7 cm\({}^{2}\) sample surface area). Samples were gently shaken to ensure slight and uniform compaction. Subsequently, sample surfaces were levelled with a ruler so that they were flush with the edge of the \begin{table}
\begin{tabular}{l l l l l l} \hline
**Biopolymer** & **Product Name** & **Specification** & **Manufacturer** & **Appearance** &
\begin{tabular}{l} **Moisture** \\ **(wt\%)** \\ \end{tabular} \\ \hline Polysaccharides & & & & & \\ \hline Carboxymethyl cellulose & DTK NV CMC & Technical grade, low viscosity & Mikro-Technik-CMC & Light-yellowish & 8.6 \({}^{\text{a}}\) \\ Corn starch (CS) & C-Gel Instant & Pregelatinsed & Cargill GmbH & White powder & 5.8 \({}^{\text{b}}\) \\ Sodium lignocellulosic (NLS) & N18 & Cold-water soluble & Otto Dille GmbH & Brown powder & 8.6 \({}^{\text{a}}\) \\ Pea starch (PES) & Emcol EST (F11025) & Pregelatinsed & Emsland Group & Off-white powder & 10.4 \({}^{\text{b}}\) \\ Potato starch (POS) & KMC 18-09 & Pregelatinsed & KMC Germany & White powder & 9.4 \({}^{\text{b}}\) \\ Wheat starch (WS) & Tigel & & & & \\ Xanthan gum (XG) & XG TGRD & & & & \\  & & & & \\ \hline Proteins & & & & & \\ \hline Fava bean protein & ABPK 65\% & Enzyme activated & Aloja-Starkelsen & Creamy light-yellow & 8.8 \({}^{\text{d}}\) \\ concentrate (FBPC) & & & & powder & \\ Hen egg albumen (HEA) & Hen egg albumen & Cold-water soluble & Ovopol Sp. z. & Yellowish powder & 7.0 \({}^{\text{a}}\) \\ Haemoglobin protein (HG) & HG 92P & Haemoglobin powder, & Sonac & Dark red powder & 6.6 \({}^{\text{c}}\) \\ Plasma protein (PP) & PP 70P & Plasma powder, & Sonac & Cream-white & 7.5 \({}^{\text{c}}\) \\ Technical gelatine (TG) & TG 330 & Pitzer soluble at & Hellmann GmbH & Yellowish, & 13.0 \({}^{\text{a}}\) \\  & & \(\geq\)40 \({}^{\text{c}}\)C & & free-flowing & \\ Wheat protein (WP) & Glusol & Degraded, without & Kroner Stärke & Yellowish powder & 6.0 \({}^{\text{d}}\) \\  & & & & \\  & & & properties & & \\ \cline{2-5} Whey protein concentrate (WPC) & Instant WPC 80 & From fresh cheese & Lactoland GmbH & White to pale yellow & 6.2 \({}^{\text{d}}\) \\  & & & & powder & \\ \hline \end{tabular} Note. \({}^{\text{a}}\) = data provided by manufacturer, \({}^{\text{b}}\) = measured in accordance with DIN EN ISO 1666:1997 [43], \({}^{\text{c}}\) = measured in accordance with ISO 6496:1999 [44], \({}^{\text{d}}\) = measured in accordance with AOAC 930.15 [45].  
\end{table} 
Table 2: Biopolymers investigated by this study and their product data. The calculation of the biopolymer mass required for the preparation of the individual solutions also accounted for the biopolymers' respective dry mass (Table 2). The biopolymer powders were dissolved at room temperature in distilled water at the specified concentrations for 10 min using a magnetic stirrer until fully dissolved (Figure 2b). To avoid clumping of the biopolymers, powders were slowly added to the distilled water through a sieve. The TG solution required preparation in 40 \({}^{\circ}\)C warm water. The biopolymer solutions were sprayed onto the samples using a trigger sprayer with a nozzle suitable for viscous solutions (Ballistol hand atomizer, standard nozzle, Figure 2c). Uniform and accurate spray-on application was achieved by placing the untreated samples on a precision scale (Kern PES 4200-2M, 0.001 g resolution) and spraying the solution until the required application rate was achieved. Changes in solution density caused by the addition of biopolymer were considered negligible, so a fixed solution density of 1.0 g/mL was assumed for converting the required volumetric application rate (20.3 mL) to the gravimetric application rate (20.3 g). A 3D-printed splash guard was used to prevent the biopolymer solution from inadvertently touching the scale's weighing plate and thus distorting the scale readings (Figure 2c).