*2.7. Polarized Light Microscopy (PLM)*

The birefringence of starch samples was observed under polarized light with a binocular microscope (BA310 Pol, Motic, Xiamen, China) at a magnification of 100×. The starch samples were transferred onto a slide glass and a drop of water was then added to each sample before observation.

#### *2.8. Rheological Measurement*

The rheological properties of the starch samples were determined using a rheometer (Physica MCR301; Anton Paar, Graz, Austria). Starch suspensions at 10% (*w/w*) concentration after hydrothermal treatment (as described in the Section 2.2) were loaded onto the measuring apparatus after rapid cooling to room temperature. The 5 cm in diameter parallel-plate geometry with a 1 mm gap was used for all the measurements. The outer edge of the sample was coated with silicone oil to minimize water loss during measurements [23]. Temperature was controlled using a water bath system connected to a Peltier system in the bottom plate to accurately control temperature during rapid heating and cooling.

### 2.8.1. Steady Shear Viscosity Measurement

Steady shear tests were programmed to increase the shear rate from 0.01 s−<sup>1</sup> to 100 s−<sup>1</sup> with six points per decade. Apparent viscosity values were obtained as a function of shear rate. The flow behaviors of mixed starch samples were analyzed using a power law equation [25,26].

$$
\sigma = \mathbb{K} \cdot \gamma^n \tag{3}
$$

where σ (Pa) is the shear stress, K (Pa sn) is the consistency index, γ (s<sup>−</sup>1) is the shear rate, and n is the flow index [26].

#### 2.8.2. Temperature Sweep

In the temperature sweep test, the strain and frequency were set at 0.5% and 1 Hz, respectively (within the linear viscoelastic region). The temperature was set from 25 ◦C to 75 ◦C at a heating rate of 2 ◦C/min and cooled from 75 ◦C to 25 ◦C at a rate of 5 ◦C/min. The storage modulus (G- ), loss modulus (G--), and loss tangent (tanδ = G--/G- ) were obtained as a function of temperature [27].

#### 2.8.3. Frequency Sweep

Frequency sweep tests were conducted in situ after the temperature sweep. Mechanical spectra of starch gel samples were recorded in the range of 0.1–100 rad/s with 10 points per decade, and the controlled variable was set at 5% strain (within the linear viscoelastic region) [26,28]. All frequency sweep tests were performed at 25 ◦C. G- , G--, and tanδ were obtained by changing the frequency. The power law models represented in Equations (4) and (5) were applied to describe the frequency dependence of G and G--, respectively.

$$\mathbf{G}' = \mathbf{K}' \cdot \boldsymbol{\omega}^{\mathrm{n}'} \tag{4}$$

$$\mathbf{G}^{\prime\prime} = \mathbf{K}^{\prime\prime} \cdot \boldsymbol{\omega}^{\mathbf{n}^{\prime}} \tag{5}$$

In Equations (4) and (5), K- , K--, n- , and n- are the corresponding fitting parameters, respectively, and ω is the angular frequency (Hz). K and K- reflect the elastic and viscous properties, respectively. n and n- are referred to as the frequency exponents and can provide useful information regarding the viscoelastic nature of materials [25].
