Characterisation of fish tofu fortified with skipjack tuna (Katsuwonus pelamis) eyeball scleral cartilage biocalcium

Skipjack tuna eyeball scleral cartilage biocalcium (SCBC) with reduced particle can be fortified as the source of calcium in fish tofu. Ultrasonication at various times (0-30 min) was applied for the treatment of SCBC. No differences in mean particle size were observed, but the polydispersity index of SCBC decreased with augmenting ultrasonication times. SCBC without ultrasonication treatment at different amounts (0-10.0%) (w/w) was fortified into fish tofu. Breaking force, a* (redness) and b* (yellowness) increased, whereas deformation, L* (lightness) and whiteness index decreased as SCBC levels increased. Likeness scores of appearance, colour, texture, flavour, taste and overall likeness decreased with augmenting levels of SCBC (P < 0.05). No differences in likeness scores for odour and sandy mouth feel were attained, regardless of SCBC amounts added (P > 0.05). Fish tofu fortified with 7.5% (w/w) SCBC had a similar overall likeness score to the control. It showed a denser microstructure with greater ash and calcium contents than the control. Nevertheless, cross-linking of myosin heavy chain and actin became less when fish tofu was added with SCBC as witnessed by more retained protein bands. Therefore, the addition of SCBC up to 7.5 (w/w) increased the nutritive value of fish tofu without adverse effect on the sensory property.