Post-harvest Treatment Of High-amylose Maize And Its Application In Food

High-amylose maize contains a large amount of resistant starch and has been widely used in low glycemic/low GI(glycemic index)foods abroad;in China,the lack of highamylose maize germplasm resources,slow breeding,yield,and quality have limited the commercial use of high-amylose maize.In recent years,some high-yielding amylose maize has been available for industrialization research.In this paper,we focus on the drying,processing,quality optimization,and food application of high-amylose maize in the deep processing chain of maize.In this paper,hot-air drying,heat-moisture treatment,and annealing treatments were applied to the harvested high-amylose maize kernels to explore the effects of processing methods on the digestibility and physicochemical properties of high-amylose maize flour;to study the effects of the addition of high-amylose maize flour and processing methods on the quality and taste of noodles,with the aim of making highamylose maize noodles with high palatability and low-glycemic requirements;and to provide theoretical support for the industrialization of high-amylose maize.Theoretical basis and data support for the industrialization of high-amylose maize.This study was conducted as follows:1)The effects of drying freshly harvested high-amylose maize kernels at different drying temperatures on the digestibility and physicochemical properties of their maize flour were investigated.Freshly harvested high-amylose maize kernels(28.2% moisture content)were dried at 50°C,70°C,90°C,and 110°C with hot-air drying to 10%～13% moisture content.The digestibility of the dried high-amylose maize flour decreased with the increase of drying temperature,especially at 110°C.The digestibility of high-amylose maize flour decreased to 41.1%.The termination temperature of starch crystals of high-amylose maize flour increased with the increase of drying temperature,which indicated that the starch molecules in the starch granules rearranged during the drying process.It observed by polarized light microscopy that with the increase in drying temperature of high-amylose maize kernels,the residual birefringence after digestion of high-amylose maize flour increased,the aggregation of granules increased,and the starch granules within the aggregates did not change significantly during the digestion process.These results suggest that the elevated heat and digestibility resistance of high-amylose maize after hot-air drying is due to the aggregation of starch granules and the rearrangement of starch molecules to form a more stable crystal structure,resulting in reduced starch digestibility.2)The effects of heat-moisture treatment of high-amylose maize kernels on the digestibility and physicochemical properties of high-amylose maize flour were investigated.The results showed that the digestibility of high-amylose maize flour kernels after heatmoisture treatment showed a decreasing trend with increasing treatment temperature and treatment time,and the digestibility decreased after heat-moisture treatment from 63.6% to36.6%.The digestibility of high-amylose maize flour also showed decreasing swelling power from 8.5 g/g to 6.2 g/g,decreasing final viscosity from 3204 c P to 218 c P,and increasing termination temperature form 81.2°C to 107.5°C with increasing time and temperature of heat-moisture treatment.and an increase in the enthalpy change of pasting 5.8J/g to 10.7 J/g);the morphology of the starch granules was not significantly changed by the hygrothermal treatment as observed by optical microscopy images.The starch birefringence intensity of some starch granules was weakened at 100°C and 120°C.The results indicated that the reduction in digestibility of high-amylose maize flour after heat-moisture treatment was due to the rearrangement of starch molecules to make its structure more compact.3)The effects of annealing high-amylose maize kernels on the digestibility and physicochemical properties of high-amylose maize flour were investigated.Annealing of high-amylose maize kernels: high-amylose maize kernels were soaked in water baths at50°C,60°C,70°C,and 80°C for 24 h or 48 h,respectively.Compared to untreated highamylose maize,the digestibility of high-amylose maize kernels with an annealing treatment time of 24 h was reduced from 63.6% to 57.1%,while the digestibility of high-amylose maize kernels with an annealing treatment time of 48 h was lower than that of untreated maize(60.1%～61.8%).The degree of digestibility at 48 h of annealing treatment was lower than that of untreated and higher than that of 24 h treated high-amylose maize flour,indicating that the digestibility resistance was more enhanced at 24 h of annealing treatment;the swelling power of high-amylose maize flour decreased after annealing treatment compared to untreated high-amylose maize flour from 8.5 g/g to 6.0 g/g,decrease in final viscosity from 3204 c P to 297,increase in finally paste temperature from 81.2°C to 130.3°C and increase in paste enthalpy change from 5.8 J/g to 10.4 J/g after annealing treatment;the birefringence of annealed high-amylose maize flour was observed under optical microscope gradually weakened with the increase of treatment temperature,and some starch granules were aggregated.The results showed that after annealing treatment,the granules were more compact and the starch molecules rearranged to form a more stable crystal structure at 50°C and 60°C annealing treatment temperatures,while some starch granules were pasted and the crystal structure was destroyed at 70°C and 80°C treatment temperatures.The starch granules that were not pasted during the treatment process had a more perfect and stable crystal structure,leading to the enhancement of their heat resistance and digestibility.4)The effects of the addition of high-amylose maize flour and the processing method on the quality characteristics and digestibility of the noodles were investigated.Highamylose maize flour was formulated by adding 30%,40%,and 50% of untreated or adjusted moisture and steaming for 20 min,and the noodles were prepared with it.The results showed that as the amount of high-amylose maize flour added increased,the cooking loss of noodles increased from 4.16% to 10.57%,the cooking time increased,the shelf life increased,the hardness decreased from 6222 g to 5311 g,the sensory score decreased from 92.4 to 62.3and the digestibility decreased at the same amount of addition.Under the same amount of addition,the high-amylose maize flour steamed with adjusted moisture for 20 min resulted in reduced cooking loss,increased water absorption and stretch,softer texture,improved sensory quality,and decreased stretching force and distance.When the amount of highamylose maize flour steamed with adjusted moisture for 20 min was 30%,the sensory score of the noodles was closest to the control and had the highest degree of acceptance by the evaluators.The results showed that the addition of high-amylose maize flour could reduce the digestibility of the noodles,improve the shelf life of the noodles,impart a unique corn flavor to the noodles,and be accepted by the public.They concluded that the pretreatment of steaming with adjusted moisture for 20 min could indeed improve the quality of highamylose maize noodles.