Characterization of biopolymers: starch and soy protein
Two biopolymers in food system, starch and protein, were studied in structures and properties. Four different types of barley starches were isolated from barley seeds. Bimodal size distributions and A-type x-ray diffraction pattern of all four barley starches were confirmed. Barley starches displayed similar onset gelatinization temperature ranging from 55.0 to 56.5°C. Apparent and absolute amylose contents, molecular size distributions of amylose and amylopectin, amylopectin branch-chian-length distributions, and Naegeli dextrin structures of the starches were analyzed. Results showed that amylose contents (9.1% to 44.7%) and total phosphorus contents (0.022% to 0.068%) varied among normal, waxy, and high amylose barley starches. 31P-NMR analysis showed that phosphorus in barley starches was mainly from phospholipids. All the barley starch varieties had short branch chain lengths and displayed a substantially reduced proportion of chains at DP 18--21. Waxy barley (W. B. Merlin) amylopectin had the longest detectable chain length of DP 67, whereas normal barley (glacier), high amylose glacier and high amylose hull-less glacier amylopectins had the longest detectable chain length of DP 82, 79, and 78, respectively;Different soy protein isolate samples were used to study the effect of protein conditions on mechanical properties and water absorption property after compression molding process. Results showed that all the soy protein isolate samples used in this study had good processability by compression molding. But properties of molded soy protein specimens varied among soy protein samples. The specimens made from the protein isolate samples with less denaturation and pH close to isoelectric point gave better dry and wet mechanical properties and low water absorption property. Physical properties of soy protein isolate samples could affect the properties of molded specimen counterparts;Rapid viscosity analysis showed the effect of addition of soy protein on pasting properties of different starches. The viscosity profiles varied among different starches and different soy protein concentrations. Potato starch and the interaction between potato starch and soy proteins were significantly affected by salt in the mixture of starch and protein. Soy protein could form helical complex with amylose through hydrophobic interactions, which retarded the swelling of starch granules. Protein could interact with phospholipids in starch and facilitated granule swelling. Decreased pasting temperature was observed in the mixture of normal maize starch and soy proteins. Pasting temperatures of waxy maize and potato starches were increased after soy proteins were added;The three studies showed that structures of both starch and soy protein affected their properties and applications in food and non-food systems.