Microencapsulation of bee pollen protein hydrolysate by whey protein concentrate and fibersol and evaluation of stability and structur of microcapsuls

Microencapsulation is the most commonly used method of preserving proteins and peptides, which increases the stability in different conditions. Bee pollen with 10–40% protein, is a valuable source of protein that has functional and nutraceutical properties. By hydrolysis and producing bioactive peptides, their functional and health effects will be improved. Fibersol is a dietary fiber that can be used in many foods and supplements. This carbohydrate compound is actually non-digestible maltodextrin and has recently been used as a wall material in encapsulation. Few studies have conducted on the microencapsulation of hydrolysed proteins and their stability during accelerated conditions. On the other hand, by-products of honey bees such as pollen have been less noticed; therefore the aim of this study was the microencapsulation of bioactive bee pollen protein hydrolysate by fibersol and WPC and to study the changes of structure and stability of resulted microcapsules during the exposure to UV radiation.

Bee pollen was hydrolysed by Alcalase (1.5%) for 4 h in shaking incubator. The protein hydrolysate was microencapsulated using WPC, fibersol, and their combination by spray drying. The wall materials and hydrolysed protein were used in ratio of 10:1 (w/w). WPC 2%, fibersol 2%, as well as WPC and fibersol mixtures with 1:3 ratio, were the wall materials. For accelerating the oxidation reactions, the obtained capsules were exposed to UV radiation for 48 h. During the exposure to UV radiation, the DPPH radical scavenging activity of microcapsules and hydrolysed protein was measured. Interactions between hydrolysed protein compounds, WPC and fibersol were identified by the FTIR spectroscopy. The SEM was used to investigate the morphology of the microcapsules.

Almost at all experimental time, the highest DPPH radical scavenging during exposure to UV radiation was related to the capsules prepared using fibersol and WPC mixture and after that the capsule with WPC as wall material. The FTIR spectroscopy of the hydrolysed protein was changed significantly when it was exposed to UV radiation. This change caused by  losing the hydrogen bonds in the secondary structure of proteins, including the separation of two polypeptide chains or the opening of the αhelix and loss of β-sheet structure. The FTIR profile of capsulated hydrolysed protein by fibersol showed that the adhesion of protein and polysaccharide changed the absorbance of C–H bending and N–H stretching bands of amide groups in the hydrolysed protein in 3000–3500 cm-1 and the stretching band of C–H and O–H group in the region of 2000–3000 cm-1 for fibersol in the wall. After exposure to UV, because of cross-linking in fibersol and more involving the molecules of fibersol to protein, the absorbance was increased in the region of 1500–3500 cm-1. The number of peaks and absorbance in the FTIR spectra of hydrolysed proteins microencapsulated in WPC were more than number of peaks and absorbance in the FTIR spectra of WPC. There was no significant difference in the FTIR spectra of hydrolysed protein encapsulated with WPC before and after exposure to UV. The peaks in FTIR spectra of hydrolysed protein microencapsulated with the mixture of WPC and fibersol, showed higher absorbance level than the peaks of fibersol and lower than peaks of WPC. None of the peaks of microencapsuls with the wall of mixture of WPC and fibersol, were changed after exposure to UV radiation. Results of SEM showed that the microcapsules prepared with mix of fibersol and WPC had a uniform and smoother wall than microcapsules prepared with only fibersol. Finally, the mix of WPC and fibersol was selected as the best wall with a proper protective ability for the microencapsulation of hydrolysed proteins and protection against UV radiation.