Research Of Quality Change Mechanism Of Wheat Damaged By Rhizopertha Dominica

The Rhyzopertha dominica is one of the important feeding moth of stored grain pests and it lays eggs in grain.Its larvae drills into grain,eats inside,then gets out w hen it grows up.The damage degree of different growth stages is different,among w hich,the most serious damage was the larval and adult stage[1].During the growth pr ocess,the Rhyzopertha dominica hides in wheat interior.It is difficult to clean and pre vent,so it will empty wheat and cause the loss,pollution and the deterioration of theq uality of wheat[2].At present,the researches of domestic and foreign on the effect of pests on whea t quality mainly concentrate in different insect mouth density and different time of inv asion.The researches find,because inoculation of insect pests and their offspring bothr emain in the wheat,it cann't explain the influence of the stored grain insect growth o n wheat quality.In this paper,by strictly controlling of temperature,humidity and insec t population density,to ensure the completion of one Rhyzopertha dominica growth cy cle and different insect state of infected wheat,we will explore the effects of proteinc omponents and characteristics,starch quality,lipid,enzymatic defense system and cell membrane permeability and the changes of processing and edible quality of eaten whe at and find the rule of wheat quality change and its inner mechanism after injured by the Rhyzopertha dominica in order to ensure national food security and guide the reas onable fumigation.The research results show that:(1)When moisture is about 13%,the optimum condition for Rhyzopertha domini ca is 30.28?,78%RH,8000 t per kilogram,in this condition,the pest prevalence a re more than 85%within three days and the average duration of the development of t he maize weevil is32.64 days,egg,larva,pupa,and the average duration to adult eme rgence 6.15 days,16.56days,7.24 6.98 days and 2.24 2.85days.(2)Along with the growth and development of Rhyzopertha dominica from egg to adult in wheat kernels,compared with the control,water reduced after increase;ashs amples showed a gradually increasing trend;hardness index,1000 grain weight,bulk density decreased;50%sucrose SRC(solvent retention capacity)increased gradually,5%lactic acid SRC decreased gradually,5%sodium carbonate and water SRC increas ed after reduced.Falling number decreasedand then increased,adult stage and then dcr eased;wheat grain microstructureshows as the infection and the development of Rhizo pertha dominica,wheat endosperm texture become loose,the protein matrix fracture and serious damaged starch gradually increased,adult stage matrix protein texture is h ard and serious fracture,most have been into pieces.(3)Compared with the control,crude protein content was first increased and the n decreased with Rhizopertha dominica from egg to adult in wheat kernels;albumin,globulin,alcohol soluble protein content increased,glutenin content decreased,the GM P content increased and then reached the highest in the pupal stage and then decrease d in the adult stage;Uric acid content has increased significantly as usual and the ori ginal sample;-SH-,S-S content decreased,Gluten moisture capacity decreased and then increased;alpha helices and beta-sheet content decreased gradually,the beta angle cont ent increased gradually,the random coil content increased gradually.The change of a mino acid compositionof wheat grain was changed,and the majority of the contents o f amino acidsreached the highest in the larvae and pupa stage,which had the greatest influence on the content of amino acids.Infection of Rhizopertha dominica result in serious change of wheat grain internal structure,the microstructure of glutenshowed th e surface of the gluten increased roughness,micro silk fibers increased,loose structure arranged irregularly.(4)The infection and the development of Rhizopertha dominica Lead to crude s tarch,amylopectin and amylose content increased in the egg stage and then decreased;Reducing sugar content higher than that of the control;Damaged starch content gradua lly increased;compared with the original sample,starchthe median diameter decreased significantly;Pasting properties of whole wheatflour and starch were significantly chan ged,different insect state of Rhizopertha dominica decay the whole wheat that flourba ck increased the biggest,the attenuation value increases the minimum,the maximuma mplitude of peak viscosity of starch,final viscosity reduction,low viscosity increased the maximum is not obvious;the difference of X-RD curve of wheat starch is not ob vious,cry-stallinity value fluctuations between 23.09%and 24.28%,indicating Rhizoper tha dominica against on crystallization of starch had no significant effect.Micrograph of the starch showed that the small size particles increased,damaged starch content in creased,granule surface of large size starch appear damage and large pits.(5)Compared with the sample,crude fat content of Rhizopertha dominica decay decreased gradually.The fatty acid value increased with lipid serious oxidation.Pest m etabolite uric acid and other substances resulting in water soluble acid value was grad ually increased,to the pupal stage and adult stage,increased more slowly.Whole whe at flour composition of fatty acids occurred different degrees of change,changes of th e fatty acid composition and species in different period of Rhyzopertha dominica infri ngement is significant and changes amplitude difference is remarkable.(6)The infection and the development of Rhizopertha dominica Lead to the perm eability of cell membrane increasing,conductivity value increased gradually,more slow ly increasing in the egg and larval stages than pupal stage and adult stage;lipid per-o xidation increased and MDA content increased gradually,the egg stage is almost the s ame,the larvae began to increased significantly.The infection and the development of Rhizopertha dominica Influence enzyme defense system:per-oxidase activity and catala se activity of intracellular importantantioxidant enzymes decreased gradually,lipase acti vity were higher than the same;poly-phenol o-xidase activity decreased gradually.(7)The infection and the development of Rhizopertha dominica result in signific antly decreased of wheat flour yield and whiteness;peak time increased and then decr eased,peak height and peak area decreased and then increased,peak width showed an overall increasing trend,Mix-ogram display dough resistance to stir,gluten strength an d elasticity were poor;when Mix-ograph 1.5min,dough becomes worse,loose seriously.Steamed buns smooth surface gradually became more poor,dark and full of variation,r educe the height;Steamed bread quality constitutive parameters:hardness,gumminess and chewing the trend of changes were similarity,the egg stage decreased,larval and pupal stage increased,decreased in the adult stage,elastic and visco poly and recover y decreased gradually;steamed bread sensory evaluation scores decreased gradually;Te xture parameters:elastic,cohesiveness,restore gradually decrease,indicating that steam ed bread quality of Rhizopertha dominica against wheat occurred obvious deterioration.