Preparation, Properties, And Mechanism Of Granular Starch-lipid Complex

Starch is the major components of human diet and plays an important role in the texture of food products and the glycemic response. Frequent consumption of rapidly digestible starchy food is associated with the development of insulin resistance and metabolic syndrome. Resistant starch and slowly digestible starch have been recommended for diets to prevent metabolic syndrome. The digestion rate of starchy food is related to amylose content, branch chain length of amylopectin, lipids and protein contents. Starch-lipid complex is resistant to enzyme hydrolysis, lowering postprandial plasma-glucose and insulin responses.A series of starch-lipid complexes were prepared using waxy cornstarch, normal cornstarch, and high-amylose cornstarch(Hylon V) with different amylose contents at different complexation temperatures. The effect of amylose contents and complexation temperatures on the formation and physicochemical properties of starch-lipid complex was investigated. Waxy cornstarch has low complexation degree for little amylose content, short branch chain-length of amylopectin and steric hindrance. Hylon V was restricted by large amount of amylose, unable to swell and complex with lauric acid. Normal cornstarch was more favorable to complex with lauric acid. The complexation temperature has a positive relation with the complexation degree of starch-lipid complex.Granular starch-lipid complexes were prepared using normal cornstarch and lauric acid through two different adding methods of lauric acid. Method I is heating starch slurry prior to adding lauric acid. Method II is adding lauric to starch slurry prior to heating. Effect of the distribution of amylose-lipid complex in starch granules on the physicochemical properties and digestion rate was studied. The distribution of amylose-lipid complex in starch granules was confirmed by using confocal laser scanning microscopy. Amylose-lipid complex prepared by method I was distributed throughout granules. Amylose-lipid complex prepared by method II was mainly distributed on the surface of granules. The results of X-ray diffraction and DSC show that method I was more favorable to the formation of amylose-lipid complex and slow the digestion rate of starch.Starch-lipid complexes with different moisture contents(10%, 20%, 30%, 40%, and 50%) were prepared using two different methods(heating starch slurry prior to mixing with lauric acid(HM); mixing with starch prior to heating(MH)). The effect of moisture conents and order of adding lauric acid to starch on the physicochemical properties and digestibility was investigated. The results of X-ray diffraction, DSC, and RVA show that when the moisture content was 40%, amylose, amylopectin, and lauric acid have larger chance to complex with lauric acid for good mobility. When the moisture content increased continuously, most of starch granules gelatinized forming viscos texture, which would retard the formation of amylose-lauric acid complex. The formation of amylose-lauric acid complex is the key reason for slowing digestion rate. Mixing lauric acid with starch prior to heating favored the formation of slowly digestible starch and resistant starch.Native normal cornstarch, potato starch, and pea starch were characterized by A-type, Btype, and C-type crystalline polymorph, respectively. The effect of annealing and crystalline structure on the formation, physicochemical properties, and digestion rate of granular starchlipid complex was studied. The resistant starch content of uncooked potato starch, annealed potato starch, and annealed potato starch-lipid complex was siganificantly higher than the counterparts of normal cornstarch and pea starch. Cooked potato starch, annealed potato starch, and annealed potato starch-lipid complex showed higher rapidly digestible starch. Pea starch is more favorable to complex with lauric acid to slow its digestion rate for higher amylose content. Granular potato starch is not easy to complex with lauric acid for rigid crystalline structure and smooth surface.Granular starch-lipid complexes were prepared by using normal cornstarch and saturated fatty acids with different chain length(lauric acid, myristic acid, palmitic acid, and stearic acid). The effect of oven drying and freeze-drying on the physicochemical properties and digestion rate of starch-lipid complex was investigated. The introduction of fatty acids increased pasting temperature, decreased peak viscosity, retarded gelatinization and retrogradation. Compared to long carbon chain fatty acid, short chain fatty acid was much easier to complex with amylose and formed unstable crystalline structure, which contributed to slowly digestion rate. Long chain fatty acid complexed amylose contributed to the ability of enzyme resistance. Freeze-drying facilated retrogradation of starch and the formation of unperfect crystalline structure. Oven drying is more favorable to the formation of slowly digestible starch.