Abstract
This thesis investigated how germination impacts the protein quality of oat flour and influences the physicochemical and nutritional properties of an oat beverage across subsequent processing steps. Germination increased protein content by 16%, boosted water-extractable protein by 62%, and elevated free amino groups five-fold. Fourier transform infrared spectroscopy (FTIR) and compositional data showed a shift toward more disordered, hydrated protein structures (reduced β-sheets; increased α-helix and random coil), decreased intact polysaccharides and lipids, and reduced phytic acid and trypsin inhibitors. Together, these changes improved in vitro protein hydrolysis by 42% (greatest at 25 °C). Oat flour from germinated grains (GOF) also contained higher branched-chain, aromatic, and several dispensable amino acids, increasing amino acid scores for histidine, valine, and threonine to >1 compared with 0.80–0.87 in oat flour from ungerminated grains (UGOF). GOF and UGOF were processed into oat beverage and showed divergent volatile profiles: germinated samples (G) exhibited lower lipid- oxidation volatiles (e.g. furans and lipid-derived aldehydes) and higher amino acid- derived aldehydes and esters than ungerminated samples (UG), indicating distinct biochemical pathways during processing.
Sequential high-pressure homogenisation (HPH) of the oat beverage followed by heating (80 °C, 30 min) and fermentation (Lactiplantibacillus plantarum 299v) revealed that germination strongly influenced structural and nutritional properties of oat beverages. HPH at 50–75 MPa reduced particle size in both matrices, but viscosity and FTIR responses differed between UG and G samples. Germinated samples showed nonlinear viscosity responses at 25 and 75 MPa and more pronounced matrix loosening at 75 MPa, consistent with increased accessibility of hydrophilic domains and higher total digested protein compared with the corresponding UG samples. In contrast, UG samples showed faster gastric and intestinal protein hydrolysis rates at 75 MPa without corresponding improvement in TDP. Total amino acids decreased in G samples but remained stable in UG samples at 75 MPa.
Heating further reduced particle sizes at 75 MPa (He75) and differentially altered viscosity independent of HPH processing parameters: decreased in UG but increased in G iisamples. FTIR indicated more intact carbohydrate structures in UGHe75, whereas GHe75 showed increased lipid-associated absorbances. Protein-associated regions exhibited minimal shifts in peak intensity for both matrices. Heating decreased the gastric protein hydrolysis rate in UG samples, independent of HPH pressure. In G samples, however, this decrease was observed only at 75 MPa. Nevertheless, the intestinal protein hydrolysis rate increased in G samples and was accompanied by higher TDP compared with the unhomogenised control and 25 MPa-treated G samples. However, total amino acids decreased in G samples, while remaining stable in UG samples. Heating also intensified lipid-oxidation volatiles in both matrices, though less in G samples. Additionally, Strecker aldehydes increased in G samples.
Fermentation produced higher microbial counts in G samples than in UG samples, with a lower endpoint pH (< 3.5). Fermentation markedly reduced TDP across matrices, with greater losses in homogenised UG samples accompanied by significant reductions in gastric and intestinal rate. In contrast, fermented samples pre-treated at 50–75 MPa retained TDP comparable to unfermented controls and showed increases in several amino acids, including BCAAs and lysine, whereas UG samples exhibited reductions. FTIR indicated aggregation (decrease in Amide II) in UGFe75 and enrichment of fatty acid and organic-acid bands in GFe75. Volatile profiles shifted strongly toward fermentation products (acetic acid, acetoin) and were more abundant in G samples; UG samples showed elevated lipid-derived volatiles. In G samples, Strecker aldehydes and esters decreased.
Overall, this work demonstrates that germination is an effective strategy to enhance protein quality (total digestible proteins, indispensable amino acids) in whole-oat beverages and fundamentally alters the oat matrix’s response to homogenisation, heating, and fermentation. Germination shows strong potential for integration with HPH and fermented beverage production, though optimisation is required to prevent losses in amino acid quality.