Effect of selected pre-treatments on folate recovery of granule suspensions prepared from hen egg yolk

• Increasing ionic strength of the suspensions led to disruption of the granules.
• Folate (5-MTHF) content of granule was increased up to 21 μg/g at 0.15 M NaCl.
• Applying ultrasound treatments did not significantly alter granule composition.
• Phosphocalcic bridges keep the granule network compact and hardly breakable.

Fractionation of hen egg yolk allowed the concentration of 5-methyl-tetrahydro-folate (5-MTHF) in granule faction of yolk. Consequently, the pre-treatment methods naming as increasing ionic strength and power ultrasound was used to improve concentration of folate in granule fraction. The composition of granules after pre-treatment was characterized. The polyacrylamide gel electrophoresis showed that ionic strength modifications induced the loss of granule structure by solubilisation of proteins. Granule contained 21 μg of 5-MTHF/g granules extract on dry basis. However, by increasing ionic strength (>0.15 M NaCl) concentration of 5-MTHF was decreased in granule fraction due to integration of granule structure and release of folate in plasma fraction. Concerning ultrasound pre-treatments, the significant changes in total protein, lipid, cholesterol, fatty acid and 5-MTHF content of granules was not observed by increasing the ultrasound time. All results were indicative of the stable structure of granule and that its modification is difficult. The application of salt addition and increasing ionic strength indicates the importance of the existence of phosphocalcic bridges between phosphate groups of HDL-phosvitin and 5-MTHF which keeps folate (5-MTHF) stable in this compact network.