In the dynamic world of starch processing, researchers have uncovered a realm of possibilities by manipulating temperature, pressure, humidity, and shear forces, as highlighted by the groundbreaking work of Eliasson and Gudmundsson (1996) and Bao et al. (2003).
Physical Transformation Without Chemicals
Unlike chemical modifications, physical alterations to starch involve changing its molecular structure without the use of chemicals. This is achieved through the application of heat, dynamic energy, or a combination of both. The outcome is a modified starch with transformed properties, exemplified by the classifications identified by Sair (1967).
Key Methods in Physical Modification:
1. Pregelatinized Starch: Ready-to-Eat Versatility
Pregelatinization, a straightforward method, involves cooking starch in water and subsequent drying. This results in starches ideal for ready-to-eat foods and adhesive applications, such as wallpaper glue. The process includes drying the slurry on a heated drum roller at high temperatures, yielding a final product with high transparency, viscosity, and favorable properties.
2. Granular Cold-Water Soluble Starch (GCWS): Instant Innovation
Developed for instant foods and microwave applications, cold-water soluble starches, also known as pregelatinized starches, undergo production methods like drum drying, extrusion, or firing followed by spray drying. To enhance the quality of dispersions, the last decade witnessed the development of Granular Cold-Water Soluble Starches (GCWS). These starches offer properties similar to freshly prepared pastes, overcoming some limitations of pregelatinized starch pastes.
3. Annealing Starch: Approaching the Glass Transition
In the annealing process, starch is treated with low amounts of water at temperatures below gelatinization. This approach aims to approach the glass transition temperature, enhancing molecular mobility without causing gelatinization. Annealing induces changes in various starch properties, including crystalline perfection, interaction between chains, and improvements in amylopectin regions.
4. Heat Moisture Treatment (HMT): Shaping Starch Structure
HMT, a physical modification process, involves treating starch granules at high temperatures and low humidity. This alters the association of starch chains and the crystalline order of granules. HMT induces structural changes in both amorphous and crystalline regions, allowing for increased derivatization and transformation of structural polymorphs.
5. Mechanical Milling Starch: Breaking Boundaries
Mechanical milling of starch granules, achieved through ball milling, leads to spontaneous gelatinization when exposed to cold water. This technique reduces granule size, gelatinization temperature, and enhances cold-water solubility. Ball milling also induces partial gelatinization and increases apparent viscosity.
6. Blends with Other Polymers: Finding Harmony
Blending starch with non-biodegradable plastics, while improving toughness, compromises complete biodegradability. To strike a balance, blending with biodegradable plastics is explored. Techniques are employed to enhance compatibility between starch and other polymers.
In the quest for sustainable and versatile starch applications, physical modifications stand as a gateway to unlocking new frontiers. From instant foods to enhanced biodegradability, these methods showcase the transformative power of harnessing starch’s inherent properties through innovative processing techniques.