The effect of different drying methods on the physicochemical and technological properties of hazelnut protein isolates

Animal based proteins, especially meat and meat products, can meet our basic protein needs. However, the increasing tendency of consumers to easily accessible, healthy and economical foods and special consumer preferences (veganism/vegetarianism, religious beliefs, etc.) have made plant-based proteins more popular in recent years. Hazelnut is an important plant-based protein source. In this study, the protein isolate was obtained from hazelnut using by-product of cold press, by alkali extraction and isoelectric precipitation method. Then, the hazelnut protein isolates were dried with different drying methods. For this purpose, the spray drying (SD) method, in which the inlet and outlet temperatures were applied as 180 and 75°C, respectively, and the refractance window drying (RWD) method at four different temperatures (60, 70, 80 and 90°C) were used. Dry matter content, water activity, protein content, color, solubility (pH 1, 3, 5, 7 and 9), particle size, density, water and oil holding capacity, surface hydrophobicity, emulsification (pH 1, 7 and 9) and foaming (pH 1, 7 and 9) properties were investigated. The solubility, emulsification and foaming properties of protein isolates showed different trends depending on varying pH levels. In both drying methods, minimum solubility was observed at pH 5 due to its closeness to the isoelectric point, while maximum solubility was reached at pH 1 with values of 100% and 98.30-66.58% for SD and RWD methods, respectively. In addition to higher solubility, the surface hydrophobicity and foaming properties of the sample dried by the SD method were found to be better compared to RWD. On the other hand, the particle size and bulk density of the sample dried by RWD method were found to be higher, and it was determined that the flow properties and emulsifying properties (except pH 1) were superior. Both drying methods presented similar products in terms of water activity, protein content, water and oil binding values. As a result of the study, it was determined that hazelnut protein isolates could show different physicochemical and technological properties according to the drying method.