Cross-linked resistant starch from high-amylose corn starch, and structures of phosphate esters in cross-linked resistant wheat starch determined by phosphorus-31 spectroscopy

Grain-based foods with increased levels of slowly digestible starch (SDS) and resistant starch (RS) appear to provide nutritional benefits for humans. Such foods may be produced by adding specialty starches having high levels of SDS and RS. High-amylose (∼70%) corn starch (Hylon VII) was simultaneously heat-moisture treated and phosphorylated with concomitant cross-linking in a semi-dry reaction using a 99/1 (w/w) mixture of sodium trimetaphosphate/sodium tripolyphosphate (STMP/STPP) at pH 11.5. Mathematical modeling related the reaction conditions to the levels of phosphorylation and resistant starch. Reacting Hylon VII with 10% of STMP/STPP (sb) at 45% of{09} moisture (total mixture basis) for 4 h at pH 11.5 and 110°C gave a product with 0.39% P and 43% RS in the freshly cooked starch compared to 0.03% P and 25% RS for untreated Hylon VII, and 32% RS for either modification alone. The doubly modified Hylon VII resistant starch in the raw state contained 90% dietary fiber by the AOAC International Method compared to 16% for Hylon VII, and had a higher gelatinization temperature by ∼20°C.; alpha,gamma-Dextrins produced from Type-IV resistant (RS4) wheat starch were examined by 31P NMR spectroscopy. The alpha,gamma-dextrins from RS4 prepared at pH 11.5--12.5 showed a ∼1/1 molar mixture of distarch monophosphate (DSMP) and monostarch monophosphate (MSMP), whereas those prepared at pH 9.5--10.5 showed a decreasing ratio of DSMP/MSMP plus an increasing level of monostarch diphosphate (MSDP). Starch triphosphate ester was not detected in any RS4 sample. In a standard reaction to produce RS4 wheat starch, 31P NMR spectroscopy showed that STMP initially present at 0.15M reacted to an extent of ∼5% with hydroxide ion to give pyrophosphates, orthophosphates, and tripolyphosphates, and ∼15% with wheat starch to produce starch phosphates. A series of RS 4 wheat starches were prepared all containing ∼0.4% P but with varying levels of DSMP from 47 to 80 mole % of total starch phosphates. Digestion of the raw RS4 starches by pancreatin at 37°C (Englyst method) gave a positive correlation between the level of DSMP and the level of RS 4.