The kokumi sensation of protein hydrolysates could be enhanced by γ-glutamylation through forming a series of γ-glutamyl di- and tri-peptides. In this study, porcine hemoglobin hydrolysate was γ-glutamylated using enzymes from Bacillus amyloliquefaciens (Ba) or Bacillus licheniformis (Bl), which are sold as glutaminases but identified as γ-glutamyltransferases (GGTs). To yield more γ-glutamyl peptides, reaction conditions were optimized in terms of GGT source (BaGGT and BlGGT), substrate concentration (10, 20, and 40%), reaction time (3, 6, 12, and 24 h), and glutamine supplementation (20, 40, and 80 mM). Results showed that both the GGTs had the highest transpeptidase activity at similar pH values but different temperatures. In addition, BaGGT had stronger catalytic ability to form γ-glutamyl dipeptides, while BlGGT was more capable to generate γ-Glu-Val-Gly. Adding glutamine was more efficient to obtain more target peptides than adjusting the hydrolysate concentration and reaction time. This study contributes to the valorization of animal side streams.