## 2 Materials and Methods
### Methods  
The antioxidant activity in water extracts of the test material was determined by the ABTS+\(\bullet\) (2,2\({}^{\prime}\)-Azino-bis(3-ethylbenzothazoline-6-sulphonic acid) diammonium salt) radical cation assay according to the modified method of [PERSON] et al. (1999) [37]. The results were given as umol TEAC (Trolox Equivalent Antioxidant Capacity) in g of dry matter (d.m.) of the powder. The content of the individual polyphenols was determined using the HPLC method described by [PERSON] (2017) [38]. A weighed amount of powder (100 mg) was put into a plastic test tube, and then 1 mL of methanol containing 1 g/100 mL ascorbic acid was added. The solution was mixed thoroughly by vortexing, and was incubated in an ultrasonic bath (15 min at 30 \({}^{\circ}\)C). The samples were then swirled at a speed of 5000 rpm. From the test tube, 1 mL of extract was collected and re-swirled at a speed of 12,000 rpm. An aliquot of 500 \(\upmu\)L of extract was taken for analysis by HPLC (high-performance liquid chromatography), and the polyphenols were all determined using the same HPLC set-up. A Synergi Fusion-RP 80i column (\(250\times 4.60\) mm) was used, and elution was carried out using a gradient flow with two mobile phases: acetonitrile/deionised water at pH 3.00. The analysis time was 36 min, the flow rate was 1 mL min\({}^{-1}\) and the wavelength range for detection was 250-370 nm. Polyphenols were identified based on Fluka and Sigma Aldrich external standards. A Shimadzu HPLC (USA Manufacturing Inc., USA) was used, consisting of two LC-20 AD pumps, a CMB-20A system controller, an SIL-20 AC autosampler, an SPD-20 AV UV/VIS detector and a CTD-20 AC controller. The results are expressed in \(\upmu\)g of the total content of the polyphenols g\({}^{-1}\) d.m. The assay was performed with three replicates. The total vitamin C sample content was determined following extraction of the ascorbic acid and dehydroroscorbic acid, and then reduction using dithiothreitol reagent. HPLC was performed using a UV 2487 detector, and separation was carried out by an RP Symmetry C18 5 \(\upmu\)m 4.6 \(\times\) 150 mm column at a temperature of 25 \({}^{\circ}\)C, while the injection volume varied between 10-30 \(\upmu\)L. The results were expressed in mg of vitamin C g\({}^{-1}\) d.m. of powder. The Water Holding Capacity (WHC) was determined according to the procedure of [PERSON] et al. (2007) [39]. The WHC was expressed as g water g\({}^{-1}\) d.m. of powder. The Water Solubility Index (WSI) was measured using the method of [PERSON] et al. (1996) [40]. The results were expressed as g of the dissolved powder out of the kg of powder. The pH was measured using a Laboratory pH-meter (Elmetron CP-511). Dry matter was measured by a gravimetric method according to AOAC (2000) [41] methodology. The a\({}_{\mathrm{w}}\) value was measured using a manual AquaLab Water Activity Meter (Decagon Devices. Inc. Pullman, USA). The microstructure of the strawberry powders was investigated using a Quanta 200 XL series scanning electron microscope (FEI, Oregon, USA). Computer image analysis using Visual Analyzer 400 (Alpha M.O.S., Toulouse, France) was used to instrumentally assess the colour of the powders. The tested powder samples were placed in a measuring chamber, which controlled the lighting conditions. Upper and lower lighting was used to avoid the shadow effect on the tested samples. To take pictures, a 16 mm diameter lens, focus 0.1 m by Fujifilm (Tokyo, Japan), was used. Measurements were made using the CIE L*a*b* system (L* - brightness, +a* - red, -a* - green, +b* - yellow, -b* - blue) and RGB (R - red, G - green, B - blue). The results of the colour analysis are given in graphs showing the share of individual colour shades to which the relevant codes are assigned. The codes correspond to the values of the colour parameters in both L*a*b* and RGB space.