## 2 Starch Modification Processes
### Physical Modifications  
The physical properties of the starch can be modified using physical processes. Physical processes are generally divided into thermal and non-thermal treatments [45]. Table 3 summarizes the physical starch modification techniques and their basic features. Usually, physically modified starch is considered natural as opposed to chemically modified starch [45]. Physical modifications are more accessible and often less expensive than chemical modification techniques and produce no effluents containing salts, reagents, or reagent by-products [46]. In general, physical treatments destroy the arrangements of the starch molecules within granules. Even though the properties of physically treated starch are the same as in native starch, they are not as thermostable as the starch obtained through chemical modification [47]. Thermal treatment, including annealing, microwave radiation, pre-gelatinization, and heat-moisture treatment (HMT) [48], are the most widely applied physical processes, as shown in Table 3. The microwave-assisted treatment is commonly applied during the preparation of films from starch. Generally, microwave-assistant treatment increases water solubility and decreases the crystallinity, viscosity, and transparency of starch [49]. In addition, the microwave-assisted treatment has several advantages such as energy-saving, high conversion, and rapidity [50]. [PERSON] et al. [51] prepared cassava starch-based biodegradable films using the microwave-assistant method. The authors also reported the use of clay nanoparticles as a reinforcement material to develop cassava starch-based biodegradable packaging materials. [PERSON] and coworkers investigated the effectiveness of the combination of microwave treatment and chemical modification techniques. The authors reported improvements in the degree of substitution, structural, and physicochemical properties of potato starch esters obtained by microwave pretreated esterification [52]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Enzyme**} & \multirow{2}{*}{\begin{tabular}{c} **Enzyme** \\ **Activity (U)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Optimum** \\ **Conditions** \\ \end{tabular} } & \multirow{2}{*}{**Substrate**} & \multirow{2}{*}{
\begin{tabular}{c} **Concentration of** \\ **Enzyme (g)** \\ **Required per** \\ **10 mL of Solution** \\ \end{tabular} } & \multirow{2}{*}{**References**} \\  & & & & & **10 mL of Solution** \\ \hline Pullulanase & \multirow{2}{*}{\(\geq\)1000} & \multirow{2}{*}{pH 6.5 at 50 \({}^{\circ}\)C} & Oligosaccharides & \multirow{2}{*}{5} & \multirow{2}{*}{[38]} \\ EC 3.2.1.41 & & & & & \\ Isoamylase & \multirow{2}{*}{\(\geq\)10,000,000} & \multirow{2}{*}{pH 6.5 at 40 \({}^{\circ}\)C} & \multirow{2}{*}{Polysaccharides} & \multirow{2}{*}{0.00050} & \multirow{2}{*}{[38]} \\ EC 3.2.1.68 & & & & & \\ \hline Oligo-1,6- & \multirow{2}{*}{\(\geq\)100} & \multirow{2}{*}{pH 6.8 at 37 \({}^{\circ}\)C} & \multirow{2}{*}{Polysaccharides} & \multirow{2}{*}{50} & \multirow{2}{*}{[38]} \\ glucosidase & \multirow{2}{*}{\(\geq\)100} & \multirow{2}{*}{pH 6.8 at 37 \({}^{\circ}\)C} & \multirow{2}{*}{Polysaccharides} & \multirow{2}{*}{50} & \multirow{2}{*}{[38]} \\ EC 3.2.1.10 & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Enzymatic activity and optimum conditions of starch debranching enzymes. [PERSON] et al. [57] studied the effect of microwave treatment on the structure, surface, and porous nature of starch granules. For example, the pores created during microwave treatment may facilitate the movement of plasticizers and other additives added to the starch granules. The authors also investigated the effect of microwave radiation on the physicochemical properties of the cassava starch-stearic acid complex. This work demonstrated that microwave radiation improved the complexation of stearic acid with cassava starch, giving high thermal stability and viscosity.