Changes in structural, physicochemical properties and digestibility of partial hydrolyzed and annealed maize starch

Abstract

The objective of this study is to create modified starch with high RS content (especially heat resistant RS) through the combination of two techniques of restricted hydrolysis and annealing. Native maize starch was partially hydrolyzed in HCl solution at room temperature for 4, 14, 23, and 30h. Then, native starch (NC) and partially hydrolyzed starch (PAH) were annealed (ANN) at 50°C for 24h. The structural, physicochemical, and in vitro digestibility properties were measured. The apparent amylose content (AAC) was slightly increased at low hydrolysis level (HL) whilst decreased sharply at high HL. AAC was almost unchanged after annealing. Intrinsic viscosity, molecular weight and degree of polymerization decreased after PAH treatment whilst increased after ANN. The α-helix/amorphous ratio (AH/AMS) did not change much after PAH although it slightly increased after ANN. Relative crystallinity (DRC) increased slightly at low DH and decreased sharply at too high HL. Furthermore, ANN treatment increased DRC. The crystal pattern (A-type) did not change after PAH and ANN treatment. The gelatinization temperature of starch decreased after double modification. In terms of in vitro digestibility, the content of rapidly digested starch (RDS) increased but resistant starch (RS) significantly decreased after gelatinization pre-treatment. The content of resistant starch (RS) and boiling-stable resistant starch (bRS) increased sharply after PAH and ANN treatment. In particular, the highest bRS reached 24.2% under double treatment. While, the maximum bRS of PAH, ANN, and NC starches were 15.2%, 8.9%, and 4.2%, respectively. Actually, native starch contains poor properties and functions and is not suitable for industrial applications. In fact, the production of chemically modified starch with special technological features or high RS concentration is very interesting. In this study, the combination of the two processing techniques (PAH and ANN) significantly increased RS, especially bRS, which is capable of controlling blood glucose, body weight, and other benefits to human health.