Vacuum impregnation of apple assisted by high hydrostatic pressure

Apple was impregnated with pigment solution by vacuum heat sealing (VS) and/or high hydrostatic pressure treatment (HHP; 100-600 MPa, 25 degrees C, 5 min). Impregnation efficacy was evaluated as impregnation ratio (%) by image analysis, while damages of cell membrane and texture were quantified by electrical impedance spectroscopy and texture analysis, respectively. Combinations of VS and HHP exclusively achieved 100% impregnation. Meanwhile, the damage was comparable between the samples after VS and VS+100 MPa treatment and aggravated by elevated levels of HHP. As for the texture, breaking stress (hardness) decreased after VS and VS+HHP (100-600 MPa) comparably. Meanwhile, breaking strain (deformability) significantly increased after VS+HHP (200-600 MPa), indicating further damage of strain texture as compared with that after VS and VS+100 MPa treatment. It was indicated that impregnation of apple was fully achieved by a combination of VS and 100 MPa treatment, while minimizing the cell membrane and texture damages.