Browsing by Author "Lius, Elina"

Finding new plant-based protein sources is important from a sustainable development perspective. Ethanol and starch production from barley results in fiber and protein side-stream fractions that are currently utilized for animal feed. Nonetheless, it would be more profitable if the barley protein side-stream was used as a human food ingredient. The main storage proteins in barley are known as hordeins. They are polymeric proteins and have low solubility, due to their inter-chain and inter-molecular disulfide bridges and hydrophobic side-chains. In food technology applications protein solubility is an important property for emulsifying and foaming functionality. Proteins are sensitive to the surrounding environment, especially to pH, which could be used to alter the solubility. In this thesis the literature review examined barley (Hordeum vulgare) proteins, especially the hordeins, functionality and effect on food materials. The review includes previous studies concerning cereal proteins functionality in general and their effect on food materials and a discussion on protein stabilized emulsions. The aim of the study was to determine the protein composition of two barley protein concentrates, OP1 and OP2, and to evaluate protein solubility and emulsifying properties. Furthermore, the aim of the study was to compare the functionality of the concentrates. According to SDS gel electrophoresis the protein concentrates consisted mostly of hordeins, especially C-hordein and some B-hordein. Minor amounts of other proteins where also identified. The protein solubility was determined by Lowry’s method. The proteins were more soluble in sodium phosphate buffer than in deionized water. In sodium phosphate buffer at pH 3,8 the solubility of OP1 proteins was 100 mg/g ± 11 mg/g and in deionized water at pH 3,9 the solubility was 45 mg/g ± 1,1 mg/g. The solubility of the OP2 proteins in sodium phosphate buffer at pH 3,8 was 47 mg/g ± 1,5 mg/g and in deionized water at pH 3,7 the solubility was 45 mg/g ± 1,1 mg/g. In both samples the proteins solubility increased as the pH increased. Most proteins were solubilized at pH 11: the solubility for OP1 and OP2 proteins were 240 mg/g ± 11 mg/g and 140 mg/g ± 12 mg/g respectively, which is problematic regarding food products, but could be used as a treatment to improve solubility. The smallest oil droplets were formed in emulsions were the pH was adjusted to 7 with sodium phosphate buffer. The stability of emulsions was however poor in all samples because of phase separation, which was already significant after one day of storage. The phase separation was considered to be flocculation which finally resulted in creaming or sedimentation. The flocculation may have occurred due to hydrophobic interactions between the proteins on the oil/water interface. However, shaking of the emulsion causes the flocculated oil droplets to separate, forming an even emulsion. No coalescence was observed in all samples, except for OP1-emulsions with 1 % (w/v) dry matter. These results confirm that these protein concentrates can be used in food products, especially in milk type drinks that need to be shaken before usage.