The objective of this study was to understand the microstructure, textural properties, and in-vitro starch digestibility of instant fried noodle enriched with cross-linked phosphorylated type 4 resistant wheat starch (CLWRS4). Pasting viscosity results showed that CLWRS4 granule had low swelling and high resistance to rupture during high-temperature steaming and frying. Scanning electron microscopic images showed that instant fried noodles prepared using wheat flours containing 20% and 40% CLWRS4 exhibited denser structure and lower porosity than their respective counterparts. The CLWRS4-enriched instant fried noodles had higher cooking resistance, harder texture of cooked noodles at 40% CLWRS4 level, and longer cooking time than their respective counterparts. The starch digestibility of uncooked/cooked instant fried noodles enriched with 20% and 40% CLWRS4 (82.5%/87.3% and 74.7%/78.8%, respectively) was lower than that of their respective counterparts (92.4%/94.6% and 94.5%/96.1%, respectively). Light microscopic images showed that the wheat starch granules were gelatinzed and broken into pieces, while the CLWRS4 granule remained as granular ghost shapes. The result suggested that low swelling ability of CLWRS4 remained after steaming and frying, which limited the accessibility of digestive enzymes and then reduced the starch digestibility of instant fried noodles. The study provides useful information for developing instant fried noodles with reduced starch digestibility by incorporating CLWRS4.
Keywords: In-vitro starch digestibility; Instant fried noodle; Microstructure; Textural properties; Type 4 resistant starch.
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