Manipal: Researchers at the Department of Biophysics, School of Life Sciences, Manipal University, Manipal, India and Institute of Biophotonics, National Yang-Ming University, Taipei, Taiwan have developed a Stokes polarimeter based on nonlinear optical microscopy (second harmonic generation (SHG)) to investigate starch gelatinization. The findings are published in Nature Publishing Group (NPG) Journal "Scientific Reports" entitled "Investigating starch gelatinization through Stokes vector resolved second harmonic generation microscopy".
Starch breaks down under heat (cooked starch) and is more amenable for digestion. Using optical microscopy, the authors found that starch-water interaction environment was altered upon heating with diminishing signals. The fine structure of starch, organisation and arrangement is due to the molecular packaging of amylose and amylopectin in a network and organized as alternating concentric 120-400 nm thick growth rings which are thick amorphous and crystalline domains.
The hydrated starch upon heating alters the signal due to the micro-structural changes. These could be captured in traditional optical polarization microscope by using large number of images rather than single image of starch granule. "The slowly-digestible or resistant starch derived from uncooked food, whole grains, legumes, tubers and vegetables thus can be measured as an appropriate source of carbohydrates to provide as personalized nutrition to reduce risk of various conditions/diseases including cardiovascular diseases," said Dr. Nirmal Mazumder, the first author of the manuscript. This work was undertaken in collaboration with the imaging specialist, Dr. Jianjun Qiu from Key Laboratory of Biomedical Photonics, Huazhong University of Science and Technology, Wuhan, China.
Starch is made up of large number of glucose units joined by glycosidic bond which breaks down into glucose and used as energy source in the body. Starch is produced during photosynthesis in the plants and stored in the form of granules. When the starch is undigested in the small intestine, it is called resistant starch which is indigestible by the enzymes of the human body; however, in the large intestine it is fermented by the gut microbiota into metabolites such as short chain fatty acids, gases, organic acids and alcohols. The quality and quantity of resistant starch uptake may have several health benefits especially in disease conditions such as obesity and diabetes.