Effect Of Germination On The Physical And Chemical Properties Of Millet Starch

Millet is the product of millet hulls,which is rich in nutrition and health ingredients.Starch is the main component of cereals,including millet,which is widely used in various fields.Its physical and chemical properties also affect the processing method,edible quality and nutritional value of cereals.Germination is a green economical bioprocessing technology.The endogenous enzymes can not only improve the nutritional composition and potency of grains,but also change the physical and chemical characteristics of the main ingredients in the grain,thereby improving the processing quality.At present,the research on germinated millet mainly focuses on the changes of nutritional components,enrichment of functional components and development and analysis of sprouted millet food.There are few systematic studies on the effects of germination on the physical and chemical properties of millet starch,which has important theoretical and practical guiding significance for the application and promotion of germinated millet and its starch.In this paper,the variation law of water distribution,amylase activity,main nutrient components,starch structure,basic physicochemical and thermal characteristics of starch during the germination of millet were systematically studied.The main findings are as follows:（1）Low-field nuclear magnetic resonance was used to study the distribution of water during immersion and germination of millet.The results showed that the internal water in the soaking process of millet was mainly bound water,and the bound water was converted into free water;the internal water during germination were mainly bound water and semi-bound water,and the bound water and free water were converted into semi-bound water;the optimum soaking time at 25℃was 10 h.The content of starch,crude protein,crude fat,and ash in millet decreased after germination,with decreases of 29.36%,23.92%,43.45%,and 42.45%.The contents of reducing sugar andγ-aminobutyric acid both increased,increasing by 88.58%and 599%,respectively.The content of most amino acids,total non-essential amino acids,total essential amino acids,and total amino acids reached or approached the highest at 24 h after germination,and were lower than that of untreated millet after 72 h or 96 h after germination,and the proportion of essential amino acids decreased.The proportion of essential amino acids decreased;the amylase activity increased continuously;the color of millet became lighter and the color difference became more and more obvious.（2）The content of amylose in millet starch decreased after germination,which decreased the most at 96 h（5.42%）.The degree of crystallinity increased,which increased at 120 h（8.10%）.The pores on the surface of the starch increased and the number increased,orderliness in the crystalline region and the state of the double helix structure were improved.The crystal structure of the starch has not been destroyed,and the internal functional groups have not changed.The starch particle size,the molecular weight of amylose and amylopectin decreased,and the molecular weight of amylose decreased more than amylopectin（3）The swelling of millet starch increased and the solubility of millet starch decreased after germination.The retrogradation resistance property,transparency and water holding capacity were both enhanced,achieving optimal performance at 72 h,96 h and 24 h after germination,respectively.The gelatinization stability and anti-retrogradation property of starch paste increased.The content of fast-digested starch,slow-digested starch and blood glucose index both increased to varying degrees,and increased the most at 96 h,48 h and96 h after germination,by 2.12%,1.70%and 2.22%,respectively.The content of resistant starch decreased and maximized at 48 h after germination,decreased by 3.08%.Millet starch paste was pseudoplastic fluid before and after germination,and the fluidity of starch paste decreased after germination.（4）DSC and DSC-TG were used to study the gelatinization,regeneration and thermal decomposition characteristics of millet starch during germination.The gelatinization temperature increased,gelatinization enthalpy value,retrogradation degree and rate of millet starch decreased after germination.The thermal decomposition activation energy,pre-finger factor,enthalpy change and gibbs free energy of millet starch thermal decomposition all increased after germination.The mechanism of raw and after 24 h germinated millet starch thermal decomposition was G（α）=[-ln（1-α）]^2/3,the most probable reaction mechanism was random nucleation and subsequent growth.The mechanism of raw and after 0 h,48～120 h germinated millet starch thermal decomposition was G（α）=α,the most probable reaction mechanism was phase boundary reaction.