## 2 Materials and Methods
### Quality Prediction Test
#### 2.4.1 Flotation Test  
The flotation test is one of the simpler and more straightforward methods to observe the catalase activity and is based on the gas formation when catalase is reacting with hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)). This test was carried out as described by [PERSON] et al. [26] with some modifications. The direct flotation test is a rapid assessment method performed directly on dried mangoes. The underlying principle of this approach is that dried mango with more catalase enzymes can react faster with hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) solution and rise to the top of the solution in less time by generating more O\({}_{2}\) bubbles on the fruit surface. The color of mango slices dried at 40 \({}^{\circ}\)C, 60 \({}^{\circ}\)C and 80 \({}^{\circ}\)C seemed closer to each other, were selected at random and kept separately at room temperature. The slices were cut into small quadratic cuboids (10 \(\times\) 10 mm), as shown in Figure 1.  
Three 200 mL beakers containing 130 mM hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) substrate (pH 7.0) were placed at a height of 50 mm on the heating plates set at 25 \({}^{\circ}\)C. Twenty cuboids from different mango slices dried at 40 \({}^{\circ}\)C, 60 \({}^{\circ}\)C and 80 \({}^{\circ}\)C were tested separately by placing them at the bottom of the beaker with clean forceps. The solution started bubbling on the fruit surface due to the reaction between H\({}_{2}\)O\({}_{2}\) and catalase. The dried samples gradually floated up to the surface of the H\({}_{2}\)O\({}_{2}\) solution. The rising time of the samples was recorded once they reached the surface of the solution. The rate of enzyme activity was calculated using the following equation:  
\[k=\left( \begin{array}{c}\frac{s}{t}\\ \end{array} \right), \tag{2}\]  
where \(k\) is the rate of enzyme activity (mm s\({}^{-1}\)), \(s\) is the distance (mm) and \(t\) is the rising time of the mango pieces (s). The influence of density on the rising time was determined by randomly selecting 10 cuboids from the mango slices dried at 40 \({}^{\circ}\)C, 60 \({}^{\circ}\)C and 80 \({}^{\circ}\)C. The density was calculated as described by [PERSON] et al. [27]:  
\[\rho=\left( \begin{array}{c}\frac{m}{V}\\ \end{array} \right), \tag{3}\]  
where \(m\) is the mass of the sample (g) and \(V\) is the volume (cm\({}^{3}\)). The volume was measured using a pycnometer (BLAUBRAND, Wertheim, Germany) with an inner volume of 25 mL. The methodology was conducted based on [PERSON] et al. [28]. Toluene was used as a non-water-soluble liquid. At 22 \({}^{\circ}\)C ambient temperature, the density of toluene was noted as 0.862 g cm\({}^{-3}\). The volume of the samples was calculated as:  
\[V=V_{f}~{}-~{}\left( \begin{array}{c}\frac{m_{f+s+tol.}-m_{f}~{}-~{}m}{\rho_{ tol.}}\\ \end{array} \right), \tag{4}\]  
where \(V_{f}\) is the volume of the weighing glass (cm\({}^{3}\)), \(m_{f+s+tol. }\) is the mass of the weighing glass, sample and toluene (g), \(m_{f}\) is the mass of the weighing glass (g), \(m\) is the mass of the sample (g) and \(\rho_{tol. }\) is the density of toluene (g cm\({}^{-3}\)). In addition, the surface changes of dried mangoes were characterized using scanning electron microscopy (JSM-IT100, JEOL GmbH, Freising, Germany). The samples of approximately 3 mm \(\times\) 3 mm obtained from the central zone of the dried mango slices were fixed on a gold-plated cylinder and placed on the sample platform. Several images were captured from different surface areas of the samples at magnifications of \(\times\)50-250 under high vacuum conditions with an accelerating voltage of 2.5 kV. Indirect Flotation Test  
For the indirect flotation test, filter discs soaked with catalase extracts were used instead of directly dried mango to exclude the influence of density, air entrapment and  
Figure 1: Dried mango slices and cuboids (10 \(\times\) 10 mm) of 40 \({}^{\circ}\)C, 60 \({}^{\circ}\)C and 80 \({}^{\circ}\)C.  
surface changes of dried mango on the flotation time.