Abstract
Flaxseed oil cake extract (residual from cold-press oil production and rich in proteins and polysaccharides) was evaluated as a potential substrate for the preparation of spray-dried powders with emulsifying activity. Three variants of powders were obtained using different spray-drying process inlet temperatures: 160 °C, 180 °C, and 200 °C. The influence of temperature on physicochemical features (water holding capacity, oil binding capacity, water activity, solubility, color, chemical composition, antioxidant activity, and surface morphology) of the powders was estimated. Additionally, the emulsifying activity of the powders and the stability of oil-in-water emulsions prepared with their various content (0.5%, 1%, and 3%) were determined. Results showed that inlet temperature had significant influence on all physicochemical and functional properties of the powders. Increased inlet temperature decreased solubility and antioxidant activity but increased water-holding capacity, oil-binding capacity, and emulsifying activity. The emulsions prepared with the powder obtained at 200 °C showed the highest stability. SEM images showed the production of relatively spherical particles which were folded or wrinkled with a lot of dentures. This study could open a promising pathway for producing natural and plant-based spray-dried powders for food applications as emulsion stabilizers.
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Key Points
Proteins are natural amphiphilic molecules with interfacial activity and colloid-stabilizing characteristics; hence, proteins are increasingly used as emulsifiers. Proteins preferentially adsorb to the oil–water interface and form a viscoelastic film, which provides physical stability to the emulsion during subsequent processing and storage. Plant proteins are increasingly used in various food applications due to their acceptable emulsifying, fat- and water-absorbing, texture-modifying, and whipping properties. Oil cakes/oil meals are by-products obtained after oil extraction from oilseeds. There are two types of cakes: edible and nonedible. Edible cakes have a high nutritional value, i.e., their protein content ranges from 15% to 50%. Their composition varies depending on their variety, growing conditions, and extraction methods.
Flaxseed oil cake (FOC) is a cheap by-product of flaxseed (Linum usitatissimum L.) oil pressing and is rich in omega-3 fatty acids, proteins, soluble and insoluble fibers, phytoestrogenic lignans, different types of antioxidant compounds, vitamins (A, C, D, and E), and minerals (Mg, K, Na, Fe, Cu, Mn, and Zn). Flaxseed seeds contain 10 to 30% protein, which is mainly composed of amino acids such as glutamic acid, arginine, valine, leucine, tyrosine, and phenylalanine. Flaxseed proteins are composed of salt-soluble 11–12S globulins and water-soluble 1.6–2S albumins, which are referred to as linin and conlinin, respectively. Flaxseed globulin has an overall molecular mass of ~320 kDa, a pI (isoelectric point) of ~4.75, and is comprised of at least five subunits having molecular masses ranging from 11 to 61 kDa held together by disulfide linkages [31,35]. In contrast, flaxseed albumin is a basic protein containing a single polypeptide chain that has a molecular mass between 16 and 18 kDa.
There are no reports about utilization of flaxseed oil cake obtained via cold-press technique to produce spray-dried extract. Thus, the aim of the present study was to produce spray-dried powders from FOC extract and to examine the influence of inlet temperature on their physicochemical and emulsifying properties. The spray-dried powders reported in this study are novel in the functional food additives sector as final, ready to use products, and their evaluation in practical contribution as emulsifiers has not been previously reported in a scientific way.
The results of this research indicated the potential of FOCE for production of spray-dried functional powders with different emulsifying activity. It was shown that inlet temperature has significant influence on both physicochemical features of powders and emulsions prepared with various contents. As the emulsions prepared with powder obtained at 200 °C were characterized by the highest stability and particles size distribution, it can be concluded that higher inlet temperature enhances functional properties of FOCE powders. This study could open a promising pathway for producing natural and plant-based spray-dried powders for food applications as emulsion stabilizers.