Purification and sweetness properties of egg white lysozymes from Indonesian local poultry of ayam kampung and Cihateup duck

Egg white lysozyme (EWL) is known to elicit a sweet response with the sweetness threshold was higher than sucrose. It, however, remains to be examined if EWL from different poultry exhibited similar sweetness properties. This study aims to characterize sweetness properties of EWL from Indonesian local poultry of ayam kampung (AK-EWL) and Cihateup duck (CD-EWL). Accordingly, AK-EWL and CD-EWL were purified from the egg white using an Amberlite FPC3500 resin. As a control, EWL of non-indonesian laying hen (hen-EWL) was also purified using the same method. Enzymatic activities of hen-EWL, AK-EWL and CD-EWL were found to be different, whereby AK-EWL exhibited the highest activity. The result confirmed that hen-EWL, AK-EWL and CD-EWL exhibited sweet responses with the threshold of 8.45, 10.39, and 7.66 µM, respectively. Amino acid composition analysis revealed that these three EWLs are dominated by non-polar amino acids. Nevertheless, the ratio of positively and negatively charged residues among them varied which might account for the differences on the sweetness threshold of hen-EWL, AK-EWL and CD-EWL. Further, pasteurization and sterilization were found to have significantly reduced the enzymatic activity, sweetness and structures of hen-EWL, AK-EWL and CD-EWL This suggested that the practical application of hen-EWL, AK-EWL and CD-EWL as sweeteners should not involve any heating treatments that might reduce their sweetness levels.