Structural Characterization of Porphyra Haitanensis Extracts and Their Effects on Structure, Physicochemical Properties, and in Vitro Digestibility of Corn Starch

Porphyra haitanensis with many bioactive components has great prospects for application in the functional food, pharmaceutical, and cosmeceutical industries. In this study, two sequentially extracted fractions (PhE1 & PhE2) were isolated and structurally characterized. The results showed that PhE1 was mainly composed of protein (36.82%) and neutral sugar (32.43%), while PhE2 was mainly composed of neutral sugar (58.70%). Both are mainly composed of galactose, PhE2 also contains a small amount of glucose. To widen the application of PhEs in starchy foods, they were added to corn starch (CS) system and co-gelatinized. Rheological tests indicated that PhEs could effectively affect gel strength of CS. The addition of PhEs effectively inhibited the content of leached amylose in CS gelatinization system except those at an addition of 5% PhE1 and 5% PhE2. FT-IR data suggested that PhE1 could improve the short-range order, but PhE2 showed no significant effects. SEM images showed that the pore wall of the composites thickened, and the network structure became relatively ordered. In in vitro tests, PhEs significantly reduced the contents of rapidly digestible starch, and PhE1 presented better effects. Therefore, PhEs may be used as potential materials to delay the digestion of CS and related products.