Understanding the characteristic changes of retrogradation behavior and edible quality of brown rice modified with inhibiting retrogradation enzymes of Ganoderma lucidum.

Abstract

Brown rice (BR) has gradually become a new choice for consumers due to its exceptionally nutritional value. Whereas starch retrogradation profoundly reduces its edibility, shelf-life and consumer acceptance, limiting the development of BR and even other starch-based food products. So, it is crucial for controlling the retrogradation properties of brown rice starch (BRS), and which has received significant attention in the food industry. Enzymatic modification is considered as an effective manner to retard starch retrogradation by degrading starch to an appropriate extent. Ganoderma lucidum can secrete various hydrolytic enzymes related to starch hydrolysis, providing a theoretical basis and feasibility for improving the starch retrogradation. Our study delves into characteristic changes of brown rice (BR) and its starch (BRS) when modified by the intracellular enzyme of Ganoderma lucidum, which contains several inhibiting retrogradation enzymes (GlIRE), mainly including α-amylase, β-amylase, and cellulase. GlIRE treatments significantly decreased the setback viscosity to 1544.33 ± 24.01 cP (2 h), diffraction intensities and relative crystallinity to 21.90 ± 0.06% (2 h) and 19.22 ± 0.19% (3 h) as per RVA and XRD analysis, accompanied with more pits and pores in surface morphology. The DSC analysis showed that GlIRE treatments significantly depressed the gelatinization enthalpy to 5.86 ± 0.46 J/g (2 h) and retrogradation enthalpy. FT-IR analysis also indicated the contribution of GlIRE treatments to retard starch retrogradation, including shifting the peaks of 3500 cm^-1-3200 cm^-1 to lower wave numbers and decreasing the transmittance, as well as R₁₀₄₇/R₁₀₂₂ values reducing from 0.87 to 0.73, mainly due to the shortening of starch chain length and the weakening of hydrogen bonding strength between or within the molecular chains. Simultaneously, it aslo found that GlIRE treatments effectively improved the textural properties of BR, with reducing of hardness, chewiness and gumminess, and increasing of adhesiveness. Interestingly, GC-MS analysis showed that GlIRE treatments could also significantly affect the types and contents of volatile compounds in BR. Our study highlights the efficacy of GlIRE in starch retrogradation and rice quality-improvement, showcasing a new expansion of the research and application of G. lucidum and a science-based strategy for developing the edible quality of starch-based food.