Macromolecular Interactions Of Konjac Dough During Dough Formation And Thermal Processing And Its Digestion

The recipes of many commercial functional wheat products,of which the polysaccrides classified as dietary fiber were increased,were developed to satisfy the increasing demands of consumers for health benefits.However,these products often fail to meet the market expectations.In addition to the taste and appearance defects,the health claims including but not limited to reducing blood sugar and blood fat,controlling weight are frequently challenged due to a lack of sound evidence.Understanding the mechanisms and dynamics of the forces and interactions involved in a food system is essential for predicting and controlling these systems not only for quality-improvement purpose,but also for comfirming its heath efficacy.This dissertation was to study the interactions during processing,both chemically and physically,of multiple components in a model system of one soluble dietary fiber,konjac glucomannnan(KGM).Both in vivo and in vitro studies were undertaken to investigate the hypothesis that the beneficial metabolic effects of KGM,related with in vivo digestion might be altered if the complicated food matrix was taken into consideration.Main results are as follows:1.An alkali-induced gelation of KGM including induction and two-step gelation will take place if heating KGM in an alkali solution.A molecular-level KGM structural evolution is considered in detail with the application of atomic force microscopy(AFM)and nuclear magnetic resonance(NMR)spectroscopy as the complementary methods to microrheology and thermoanalysis.It is shown that deacetylation of KGM chains occurs immediately upon mixing with Na2CO3,dehydrating KGM chains and inducing self-packaging.Partial unfolding of the packed loose structure of dehydrated KGM is observed immediately upon heating at a temperature much lower than the gel point.The configuration transition from random coils to self-assembling filament networks takes place around 50-70 ?,which is much lower than the temperature initiating a significant agglomeration between transitional fibrils to form junction zones around 70-90 ?.2.KGM can definetly modify the dough formation properties and rheological characteristics of dough,even though a lot of studies of this work confirm that KGM cannot cross-link with starch and protein during dough mixing and thermal processing.On one hand,KGM attributes to a significantly increase in water absorption,strengthens the dough structure and protects dough against softening and even collapsing when the dough is subject to over-mixing.On the other hand,addition of KGM induces negative effects on forming a continuous gluten network,which is principle for dough extension.The dough resistence significantly decreased,especially after dough recovery.The change of dough structure is thought to be an indirect result of KGM influencing water availability and phase related physical properties due to non-covalent bonding state.Entanged with protein,KGM reduces the flexibility of protein chains,leading to a reduction of content of disulfide bond,of which the protein conformation tends to be unstable.An overall low moisture system caused by KGM is unfavorable for forming stable secondary structure and folding correctly of gluten protein.With a laser confocal microscope,it could be found that KGM tends to be attached to the surface of starch granule,generates obvious phase separation phenomenon,elevates the concentration of each phase and largely increases the system viscosity when KGM and starch coexist in a system at the same time.During thermal processing,KGM can also delay the starch gelatinization and gluten denaturation.Starch granules swelling and collapsing are inhibited,so as the recrystallization of starch molecules.3.The attenuation of the overall rate and extent of in vivo digestion,are not due to the nature of KGM,but primarily because the interation between KGM,starch and gluten during processing.Although in vitro digestion indicates a higher concentration of KGM could slow the emzymatic digestion,the health promoting efficacy on glycemic response highly depends on the type of supplementation.Supplementing KGM with food,rather than KGM-added products,could cause a rapid gut negative feedback.The interation between KGM,starch and gluten during processing could slow the in vivo digestion and suppress hunger.In conclusion,the supermolecular structure of KGM will change a lot during processing.The non-covalent interation of KGM,starch and gluten is critical to the overall dough structure and its related processing properties and alleviated in vivo digestion.