In the intricate world of starch science, the semi-crystalline nature of native starches stands as a pivotal discovery that has evolved through decades of meticulous research. This article delves into the groundbreaking work of pioneers like Scherrer and Katz and Derksen, who, in the early 20th century, unraveled the mysteries of starch crystallinity. Their work laid the foundation for a classification system that categorizes native starches into distinct types, shedding light on their diffraction patterns and crystalline structures.
Scherrer’s Seminal Demonstration (1920): Unlocking Starch’s Crystalline Secrets
The year 1920 marked a milestone in starch research when Scherrer, for the first time, demonstrated the semi-crystalline nature of native starches. Through the lens of X-ray diffraction, Scherrer unveiled a world of ordered structures within starch granules. This groundbreaking revelation laid the groundwork for further exploration into the crystalline intricacies of different starch types.
Katz and Derksen’s Classification (1933): Categorizing Starch into Types A, B, and C
Building upon Scherrer’s foundational work, Katz and Derksen, in 1933, introduced a classification system that categorized native starches into three distinct types based on their diffraction patterns. This classification, particularly relevant for wild phenotypes, provided a framework for understanding the crystalline diversity within starches. The identified types were:
- Type A: Found prominently in cereals such as wheat and corn, Type A starch exhibited characteristic X-ray diffraction peaks at 20 angles (λ= 0.15405 nm): 10.1, 11.3, 14.9, 17, 18.1, 23, 23.9, and 26 degrees.
- Type B: Predominantly present in tubers and high-amylose starches, Type B starch displayed distinct diffraction peaks at 20 angles (λ= 0.15405 nm): 5.6, 10.1, 11.3, 14, 14.9, 17, 19.5, 22, 26, and 23.9 degrees.
- Type C: Encountered in legumes like smooth peas and beans, Type C starch showcased a unique complexity. It could either be a mixture of grain types A and B or a blend of crystallites A and B within the same grain, as observed in smooth pea starch.
Complexities Within Type C: A Blend of A and B Crystallites
Type C starch, commonly found in legumes, presented researchers with a fascinating puzzle. Some Type C starches were identified as mixtures of grain types A and B, while others exhibited a coexistence of crystallites A and B within the same grain. A notable example was smooth pea starch, revealing a composition with Type B crystallites at the grain center and Type A crystallites in the periphery.
Additional Complexity: The Emergence of Type V
For cereal starches containing lipids, such as corn, wheat, and barley, an additional crystalline type (V) surfaced. This type was characteristic of amylose-lipid complexes. Unlike the A type, these complexes generally did not exist in the crystalline state in native starches.
In conclusion, the historical journey of understanding starch crystallinity, from Scherrer’s pioneering demonstration to Katz and Derksen’s classification, has laid the groundwork for comprehending the diverse structures within native starches. This classification system remains a cornerstone in starch research, guiding scientists in unraveling the complexities of starch crystallinity and paving the way for innovations in food science and technology.