## 2 Materials and Methods
### Laboratory Trials  
Experimental analyses were carried out at the Laboratory for Food Chemistry and Technology of the Estonian University of Life Sciences and at the Laboratory of the School of Natural Sciences and Health of Tallinn University in 2020-2021. A schematic diagram for meat and protein separation is shown in Figure 1. Before starting the experiment, mussels were defrosted and then rinsed with tap water to reduce salts. In the first set of experiments, the mussels were crushed with water in a blender (Philips HR3652, 1400 W) for 2 min at full power. In this experiment, different ratios of raw mussels (uncleaned) to water were used (1 volume of mussels and 2, 3, or 4 volumes of water). After 2 min, the top portion of the suspension (without the crushed shells) was decanted into a 1000 mL measuring cylinder (height 45 cm, internal diameter 6.3 cm) and allowed to settle for 1, 5, and 15 min. Next, 10 mL of the mussel suspension was removed from the upper third of the cylinder by pipetting and used for the dry-matter content determination (by drying for 24 h at 60 \({}^{\circ}\)C). The mass of the residue was then recorded. For the determination of protein content, 50 mL of the sample was pipetted from the upper third of the cylinder, and the protein content of the sample was then determined spectrophotometrically by the Bradford assay (according to the manufacturer's instructions). To achieve this, the protein content of the sample was diluted to between 0.1 and 1.4 mg/mL. Then, 900 \(\mu\)L of Bradford reagent (Sigma-Aldrich B6916, Saint Louis, MO, USA) was added to 900 \(\mu\)L of the diluted sample and the absorbance of the solution was measured at 595 nm after 25 min. For calibration, bovine serum albumin (BSA) was used. The content of calcium ions was determined by the complexometric titration method directly from the untreated sample by titrating the test samples with ethylenediaminetetraacetic acid (EDTA) solution using Patton and Reeder's indicators. In the second set of the experiment, the filtration of the liquid meat mass was tested to assess whether there could be an economic advantage in removing excess liquid prior to drying, i.e., whether the higher concentration of the filtered meat mass, and hence, lower potential drying energy input, would compensate for the dry matter that is discarded during filtration. In this experiment, the raw mussel samples were crushed on a Grindomix GM200 homogenizer (RETSCH, Haan, Germany). The crushing speed was selected to be 6000 rpm between 7 and 9 s. From a visual assessment, 7-9 s appeared sufficient to separate the meat from the shells while leaving a fraction of the shells that were practically clean from meat particles and not too fine. Prior to the test, 250 mL of deionized water was added for every 100 g of shell mass. The water was added in three stages, each time settling the shells and decanting the liquid meat mass. The shells are heavier than the meat and settle quickly, so each sedimentation process took only a few seconds. Half of the material was then filtered. The filtration of the liquid meat material was carried out using a 100 \(\upmu\)m cloth mesh. The mesh was placed on a Bunsen flask and excess water was removed by vacuum. The filtered mass was placed on a tray and weighed. In order to heat dry the filtered and unfiltered samples, the liquid meat mass was poured into porcelain tubes and dried in a thermal oven until the liquid was completely removed. Then, the content of dry matter was found. The total protein content of the samples was determined by the Kjeldahl method [23] by heating the sample with concentrated sulfuric acid at 360-410 \({}^{\circ}\)C.  
Figure 1: Schematic diagram for meat and protein separation. Dashed boxes represent optional processing steps. In addition, control samples were taken to measure the dry weight and protein content in the clean mussel meat before the experiments started. For this purpose, three batches of mussels were separated, 10 g per batch.