Effects Of Highland Barley Germination On Flour Nutritional Properties,Dough Rheological And Physicochemical Characteristics,and Bread-Making Quality

Highland barley is a cereal that has been cultivated in Chinese highlands for centuries.Farmers and herders in Tibetan regions used the highland barley for the main food,feed-processing,and brewing industries.However,highland barley is a low-use crop in the commercial food sector due to its poor gluten content and undesirable flavor.Nowadays,it is gaining more attention in food research due to its high concentrations of vital and functional compounds such asγ-aminobutyric acid（GABA）,β-glucan,and phenolic compounds.Therefore,there is an increasing interest in using highland barley for the human diet due to its high nutritional value and health benefits.Thus,this study focused on enhancing the use of highland barley as a vital source of functional compounds such as GABA,β-glucan,and phenolic compounds and as an essential starch source by screening different pretreatments.This study also focused on enhancing the bread-making performance properties of highland barley by germination treatment.Furthermore,the effects of highland barley germination time on in-vitro digestion,extractability,and bioavailability of functional compounds（GABA,phenolic compounds,and other antioxidants）were evaluated.The main results of this study are concluded as follows:Firstly,this thesis aimed to apply non-chemical and simple pretreatment methods in order to enhance GABA,β-glucans,total phenolic compounds（TPC）,and antioxidant properties of highland barley.Different approaches were used to accomplish this aim:soaking,germination,fermentation,germination prior to fermentation,and fermentation prior to germination.All pretreatments enhanced the quality of highland barley and significantly increased the quantity of GABA.However,germinated barley（GB）and germinated-then-fermented barley（GFB）had the highest GABA contents of 11.9 mg/100 g and 10.3 mg/100 g,respectively,and maintained the highest level ofβ-glucan（5.41 and 5.66%,respectively）along with improving the antioxidant properties and TPC content.Results indicated that germination could be utilized further as a practical approach for enhancing the functional components in cereals.Secondly,this thesis evaluated the effect of highland barley germination time on dough thermomechanical,pasting,fermentation,dynamic rheological,molecular mobility,and protein structural properties.Highland barley was germinated for 24,48,and 72 h.Mixolab results indicated that germination decreased flour water absorption and increased protein weakening.Germination significantly decreased the freezable water,melting enthalpy,and all pasting properties as compared to the native barley（NB）samples.LF-NMR results showed that germination decreased the relaxation time T₂,in which it had the shortest T₂₁ and T₂₂,while it increased the free water(T₂₃)compared to the NB dough samples.Moreover,germination increased the protein’s extractability,surface hydrophobicity,and damaged starch-protein network,while it decreased bread-specific volume.However,germination for 24 h showed minor effects on dough and bread samples compared to 48 and 72 h.Therefore,germination for 24 h under well-controlled conditions could be used to avoid the adverse rheological effects.Thirdly,this thesis evaluated the impact of highland barley germination time on bread-making performance,shelf-life,and nutritional value.Results showed that germination produced a functional bread with significantly enhanced nutritional value,as well as antimicrobial and antioxidant properties.Excessive germination（48 and 72 h respectively）negatively affected the gluten network formation,which decreased flour water absorption,dough development time,and stability.Additionally,LF-NMR results suggested that germination decreased T₂₁,T₂₂,and T₂₃populations during storage.Significantly,bread made with germinated barley（24h）had the best impact on bread-making performance,shelf-life,sensory attributes,and overall acceptability.This study confirmed that germination under controlled conditions for 24 h could improve bread quality and properties.Fourthly,this thesis evaluated the effects of highland barley germination time on the in-vitro digestibility,extractability,and bioavailability of GABA,TPC,and other antioxidants of highland barley bread.After in-vitro digestion,germination enhanced GABA extractability by 1.13,1.25,and 1.52 folds in GB24,GB48,and GB72,respectively.In addition,germination increased the bioavailability of GABA in GB24,GB48,and GB72 bread to 81.67,88.20,and 89.49%,respectively,compared to 72.59%in NB samples.In GB24,GB48,and GB72 bread,germination enhanced TPC extractability by 1.43,1.50,and 1.57 folds,respectively,and increased bioavailability by 79.92,83.59,and 81.63%.Similarly,germination improved antioxidants’extractability and bioavailability of all germinated highland barley bread.Therefore,germination could be a recommended pretreatment for highland barley before incorporating it into food to enhance these beneficial components.Finally,this thesis investigated the effect of germination time on molecular,physicochemical,and morphological properties of highland barley starch.The results of this study revealed that germination for 72 h（GB72）significantly increased amylose content and gelatinization temperatures（T_o and T_c）to 26.3%,59.79°C,and 68.19°C as compared to 22.81%,57.56°C,and67.05°C in NB starch,respectively,and a significant decrease in total starch contents was noticed（31.67%）in GB72 as compared to 45.70%in NB.After germination,the FT-IR intensity ratio of995/1022 and 1047/1022 bands,pasting temperatures,particle size,and swelling capacity were also decreased.Moreover,average molecular weight,relative crystallinity,gelatinization temperature ranges,and gelatinization enthalpy were reduced compared to NB starch,and the decrease was more evident in GB72 starches（0.49×10⁸g/mol,17.64%,8.40°C,and 6.41J/g）,respectively.This study indicates the effectiveness of germination for the modification of highland barley starch and its potential to affect starch-based products.