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Carbohydrate Engineering for Enhanced Nutrition, Food Quality and Safety


The goal of this project is to design and prepare carbohydrate polymers, including starch and non-starch polysaccharides, for enhanced nutrition, food quality and safety. Genetic, enzymatic, physical, and chemical modifications will be conducted to control the structure and function of carbohydrates.
Specifically, we propose the following objectives. <OL> <LI> Study the functions of starch branching enzymes and debranching enzymes in vivo and conduct genetic starch modification through reciprocal crosses of corn mutants<LI>Establish the research program of "reconstituted starch granules", i.e. functional starch-based micro-particulate systems that can be used as carriers of hydrophilic and lipophilic food compounds <LI>Establish the research program of "phytoglycogen-based dendritic polysaccharide systems", and study the behavior of phytoglycogen as functional emulsifiers and nanocarriers.

</ol>As the outputs of this project, publications including scientific papers and patents will be generated. In the meantime, proposals will be submitted to federal agencies such as USDA and NSF. The technologies and materials created will be shared with the industry for potential innovations.

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NON-TECHNICAL SUMMARY: Carbohydrate polymers, such as starch and fibers, are major components of human diet and are indispensable in the modern industry. Principal applications of carbohydrate polymers include food, feed, carbohydrate conversions (corn syrup, maltodextrin, and modified starches), and ethanol manufacture. These applications constitute a multi-billion dollar industry that will benefit from advancing our knowledge of synthesis, degradation, and modification of carbohydrates. The carbohydrate-associated industry is undergoing profound transformations driven by important issues related to nutrition (glycemic response, obesity, and diabetes) and national energy security (biofuel ethanol). In addition, the applications of carbohydrates in nanotechnology are starting to show great potential in the food and non-food areas. With this background, our research team works in the fields of starch synthesis and genetic modifications, functional starch-based particulate systems, and carbohydrate nanotechnology. We strive to identify innovation opportunities addressing current industrial and research issues such as enhanced nutrition and food quality. These efforts are reflected in strategies of using effective and economic approach to modulate carbohydrate digestibility, increase the bioavailability of food nutrients, and improve the emulsion stability using novel food emulsifiers. In addition, the carbohydrate materials prepared are used to deliver antimicrobial compounds, which may substantially extend the shelf life of food and reduce the risk of pathogenic contaminations. We believe that these research efforts will show profound benefit for the economy, environment, and society.

APPROACH: To define the strategies of genetic starch modifications, we will study enzyme activities and starch structure of selected mutant genotypes containing ae, su1, and wx mutant alleles, and correlate the in vivo enzyme activity profiles with starch structures. We have designed experiments to generate 64 genotypes including all dosage combinations of ae, su1, and wx alleles, and to characterize the structure and functions of starches from these genotypes. The granular structure of starches will be imaged using scanning electronic microscope (SEM) and cryo-SEM. The fine structure of starch will be analyzed using high performance size-exclusion chromatography connected with refraction index detector and multiple angle laser light scattering detector. The thermal and rheological properties will be analyzed using differential scanning calorimetry and an oscillatory rheometer. The digestion behavior will be evaluated using Englyst assay. The physicochemical properties of starch will be correlated with the genotypes. "Reconstituted Starch Granules" (RSG) is a cutting-edge concept. The principle idea is to create starch-based micro-particulate as carriers for bioactive or functional compounds. RSG particulates are prepared using an emulsion-based methodology. Two mechanisms are used to solidify starch droplets: retrogradation and cross-linking. For the retrogradation-based mechanism, the starches have a strong tendency to form an inter-chain association. For the cross-linking based mechanism, cross-linking can be induced by food-grade chemical reactions. The primary application of the RSG system is to carry bioactive compounds that are either hydrophilic or lipophilic. For controlled release, RSG will be resistant to hydrothermal treatment (in food processing), oxidation (in storage), and low pH (in stomach). Meanwhile, RSG should be susceptible to amylases to ensure structural dissembling and compound release in enteric conditions. Phytoglycogen is the primary alpha-D-glucan replacing starch in mutant corns that lack starch debranching enzyme. It is water-soluble and usually shows a spherical shape with particle size ranging 30-100 nm. Phytoglycogen is susceptible to amylolytic and chemical modifications. Our work has demonstrated the superiority of phytoglycogen derivatives as emulsifiers to form O/W emulsion. In the next 2-3 years, our primary work will be to understand the effect of phytoglycogen structure on the properties and functions. Meanwhile, we have prepared phytoglycogen derivatives as nanocarriers of the antibacterial peptide nisin to deliver a prolonged inhibitory action against Listeria monocytogenes. In the next stage of this research, we will characterize the adsorption-desorption behavior of nisin with these nanoparticles. The data will allow us to engineer the structure of phytoglycogen nanoparticles for improved release profile.

Yao, Yuan
Purdue University
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