IMPROVED ISOLATION, MODIFICATION, AND FUNCTIONALITY OF GRAIN PROTEINS FOR NEW PRODUCT DEVELOPMENT
Location: National Center for Agricultural Utilization Research
Title: Oats Protein Isolate: Thermal, Rheological, Surface & Functional Properties
Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 26, 2008
Publication Date: June 15, 2009
Citation: Mohamed, A., Biresaw, G., Xu, J., Hojillaevangelist, M.P., Rayas-Duarte, P. 2009. Oats Protein Isolate: Thermal, Rheological, Surface, and Functional Properties. Food Research International. 42(1):107-114.
Interpretive Summary: The main objective of this work was to develop new uses for alternate crops. Oats is one of the most used cereals world wide, especially for a healthy diet. Oats contain 9-16% protein and are mostly used as a source of soluble fiber and feed. A comprehensive product development in the food industry is needed to expand oats protein utilization to attract investors. To complement agronomist effort, the protein group of the Cereal Products and Food Science Unit of the NCAUR participated by developing procedures to characterize and compare oat proteins to more popular cereals. This project was focused in determining thermal and rheological properties of oats protein isolates. Utilization of oat proteins in baked and pasta products, can also be considered to increase the nutritional value of these products. The use of oats in the snack industry can be explored by developing different extruded snacks with high protein content. Oat protein’s structure-function was also explored to increase chances for use in different types of foods (i.e., foaming properties, gel strength, heat stability) and interactions with other food components. Basic physical, mechanical and rheological properties and performances of oat proteins and oils were performed to provide information and direction for end-use food and non-food applications.
Oat protein isolate (OPI) was extracted in 0.015 N NaOH in a 10:1 ratio solvent:flour and was precipitated by adjusting the pH to 4.5 and freeze-dried. The thermal properties of OPI were determined using Differential Scanning Calorimetry (DSC). OPI with 6% moisture content exhibited a glass transition (Tg) at 43.4 deg C and delta Cp of 0.102 J/g/deg C. The chemical modification had a mixed effect on the Tg of OPI. The negative net charge of OPI and the modified OPI was apparent from the Free Capillary Zone Electrophoresis (FZCE) profiles. Acetylation significantly lowered foaming and emulsifying properties of OPI, while succinylation showed the highest foaming, foam stability, and emulsion stability. Acetylated OPI showed the highest surface hydrophobicity compared to the other samples, while OPI was the most soluble of all. The water holding capacity of all proteins was the same except for acetylated crosslinked (ACLOPI). The surface tension test confirmed that unmodified and modified OPI possessed surface activity and the equilibrium surface tensions decreased sharply with increasing protein concentration and leveled off to a constant value. The storage or elastic modulus, G’, for the acetylated oat protein suspension had the highest value among the five suspensions, while the G’ of the crosslinked (CLOPI) had the lowest value. The plateau of G’, were 2961 Pa, 920 Pa, 223 Pa, 41 Pa, and 1.8 Pa for the AOPI, ACLOPI, SOPI, and CL respectively. The phase shifts (delta) for all five suspensions were in the range of 10-42 degrees at the measured frequencies.