Browsing by Subject "Elintarviketieteet"

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  • Arte, Elisa (Helsingin yliopisto, 2019)
    Wheat is the world’s most important staple food, providing one-fifth of the daily protein consumed globally. However, the majority of wheat is used as refined flour, in which the nutritionally superior bran layers and germ are removed during milling, thus producing yearly a massive amount of underutilised food side streams. Better exploitation of the side streams and development of new plant-based protein ingredients are required to ensure the future global demand for food protein. This study aimed to examine hydrolytic enzymes and lactic acid fermentation as tools to improve the bioavailability, nutritional quality and technological properties of wheat bran proteins for food applications. The study showed that proteolytic activity, either by endogenous or exogenous enzymes, was crucial for increasing protein liberation and solubilisation from wheat bran, whereas microbial activity was required for improving the nutritional quality of the proteins. The application of commercial carbohydrases or proteases was able to either solubilise the bran cell walls or the proteins from the residues of endosperm in bran but was not effective in liberating proteins within aleurone cells. The endogenous enzymes of wheat bran, activated by chemical acidification, increased the protein solubilisation up to 75% with a simultaneous increase in in vitro protein digestibility (from 14% to 20%). However, bioprocessing by lactic acid bacteria (LAB), yeast and cell wall-degrading enzymes (Depol 761P and Viscoferm) was found as the most beneficial and microbiologically safe method to improve the solubilisation and nutritional quality of bran proteins. This bioprocessing meth-od resulted in a protein solubilisation of 52% and significantly improved the in vitro protein digestibility to 39%. In this work, the bioprocessing of wheat bran by LAB and yeast, with and without cell wall-degrading enzymes and phytase prior to the production of protein isolates, was found to influence the biochemical and technological properties of the bran proteins. The bioprocessed protein isolates had significantly higher protein content (80%), presumably due to the degradation of starch and soluble arabinoxylans during the bioprocessing. In general, the bioprocessing of bran resulted in a lower protein solubilisation of the protein isolates and had no influence on the emulsifying properties of the isolates in oil-in-water emulsions. However, bioprocessing by lactic acid fermentation together with cell wall-degrading enzymes almost doubled the foaming stability. Furthermore, wheat breads were made by substituting 20% of the total energy by proteins from the isolates. Wheat breads enriched with the lactic acid fermented bran protein isolate was found to have the most optimal technological characteristics, showing delayed staling and lower firmness during four days’ storage in comparison to bread enriched with a protein isolate produced without bioprocessing. In conclusion, by utilising lactic acid fermentation in combination with selected hydrolytic enzymes, the aleurone cell walls can be degraded and the proteins liberated for microbial modification, leading to improved protein bioavailability, nutritional quality and technological functionality. This study is the first to show the potential of using bioprocessing for the development of new wheat bran-based protein ingredient for food applications.