Production and characterization of liposomes with encapsulated bioactive soy protein hydrolysate

Soy proteins known for their high nutritional value and pronounced techno-functional properties, can be hydrolyzed by using proteolytic enzymes and thus converted into hydrolysates rich in di-, tri- and oligopeptides. The resulting peptides are carriers of valuable biological activities, which make the soy hydrolysates very important in functional food applications as techno-functional and bioactive ingredients. However, commercial incorporation and application of soy protein hydrolysates can be hinderedby their low bioavailability and instability, bitter taste, hygroscopicity and possibility to interact with the food matrix. The aim of this research is encapsulation of the soy protein hydrolysate in liposomes in order to overcome the stated shortcomings, while preserving the biological activities that protein hydrolysates exhibit. The soy hydrolysate was prepared by a two-step enzymatic hydrolysis of a soy protein concentrate using commercial food-grade proteases, endoprotease from Bacillus amyloliquefaciens (Neutrase?) and egzo- and endoprotease from Aspergillus oryzae (Flavourzyme?) and encapsulated within liposomes. The liposomes were produced by a thin film method using a commercial lipid mixture (Phospolipon? 90G) containing mainly phosphatidylcholine. Next, the obtained multilamellar vesicles (MLV) with the soy protein hydrolysate were treated by high-intensity ultrasound waves generated by using (1) an ultrasonic probe at a frequency of 20 kHz and (2) an ultrasonic bath with a frequency 40 kHz. The smallest (310 nm) and uniform (unimodal size distribution) liposomes with the highest efficiency of peptide encapsulation (19 %) were obtained by the probe sonication. The presented results showed that incorporation of the soy protein hydrolysates was achieved within the liposome membrane and caused an increase in the liposome size in all tested formulations, namely: from 297 to 310 nm by using the ultrasonic probe, from 722 to 850 nm by using the ultrasonic bath, while in formulations without the ultrasonic treatments the increase from 2818 to 3464 nm was recorded. The entrapped peptides caused enlargement of all liposomes and the increase in negative charge of zeta potential values, which in the case of MLV liposomes was below -30 mV, indicating high stability of these liposomes. Significant antioxidant activity of the probe-sonicated liposomal formulation was confirmed by the ABTS scavenging ability and iron-chelating activity. Release studies conducted under simulated gastrointestinal conditions confirmed that liposomes provide prolonged release of encapsulated soy protein hydrolysates as compared to diffusion of the free hydrolysate. In the first 75 min, only 20 % of liposome encapsulated soy peptides diffused, which is 2.2-fold lower as compared to the diffusion of the non-encapsulated soy hydrolysate. Liposome encapsulated soy protein hydrolysates may provide the possibility for application in the areas such as food science and technology, with the aim to enhance the nutritional value and shelf life of food products, and develop functional foods.