Oil from skipjack tuna (ST) eyeballs is extracted by the wet rendering method at 121 °C for different holding times (5–60 min) using an autoclave. Yield increases as heating time increases up to 20 min (p < 0.05); no further increase is obtained with a longer heating time (p > 0.05). Conversely, acid value and total polar compounds increase. However, peroxide value (PV), thiobarbituric acid reactive substances, and anisidine value (AnV) decrease up to 30 min. No changes in unsaponifiable matter (UM) or conjugated diene (CD) are attained, regardless of heating time. Polar components (PC) increase with heating time (p < 0.05). All oil samples have a high polyunsaturated fatty acids (PUFA) content (40.46–41.00%), with monounsaturated fatty acids (MUFA) and saturated fatty acids (SFA) in the range of 20.94–21.26% and 37.77–38.45%, respectively. PUFA content is reduced slightly with a heating time of 60 min. Docosahexaenoic acid (DHA) (C22:6, n3) is the dominant fatty acid in all samples (31.67–32.24%). Based on FTIR spectra, heating for longer time results in lower intensity at wavenumbers of 3015 and 1740 cm−1. Thus, light yellow oil from ST eyeballs prepared by a green process for an appropriate time can serve as an excellent source of DHA and other PUFA.Practical Applications: Tuna oil is known to be a rich source of DHA and PUFA with health benefits. However, precooked tuna heads, generally used as raw material, yield oils with a very dark color and offensive odor, which require several refinery processes. To reduce the number of steps in the refinery process, tuna eyeballs which are separated from tuna heads can render higher quality fish oil. Moreover, the wet rendering process, a green process without toxic substances, can be used without causing environmental problems.

Summary Nanoliposomes loaded with skipjack tuna eyeballs oil (STEO‐NL) were prepared using an ethanol injection method, without and with the aid of ultrasonication. Higher amplitude (80%) and longer time (15 min) of ultrasonication reduced particle size (from 192.20 to 150.70 nm) and zeta‐potential (from −40.43 to −47.29 mV) of STEO‐NL but increased peroxide value (PV), conjugated diene (CD) and thiobarbituric acid reactive substances (TBARS) of STEO‐NL. However, encapsulation efficiency was not different among all the samples (96.82‐97.70%) (P > 0.05). Cow milk was fortified by addition of STEO‐NL (without ultrasonication) at different final levels (0, 2.5 and 5.0% w/w). Subsequently, high‐temperature short‐time (72 °C, 15 s) process was employed to pasteurize the fortified milk, which were further stored up to 10 days at 4 °C. Microbiological quality and pH of pasteurized fortified cow milk were still acceptable. Addition of STEO‐NL at higher level (5%) resulted in higher PV and TBARS and lower acceptability than the control and that fortified with 2.5% STEO‐NL throughout the storage of 10 days, but sensorial acceptability was still obtained. In general, no differences in colour, and viscosity were attained among all samples. Moreover, pasteurized cow milk fortified with STEO‐NL had an increased amount of n‐3 polyunsaturated fatty acids.

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.

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Oil from skipjack tuna eyeballs is produced by wet rendering method under mild conditions (70–90 °C for 30–60 min). Suitable condition (70 °C for 30 min) provides the oil having yield of 13.95% and acceptable color (L* = 92.26, a* = −2.17, and b* = 22.37) along with less hydrolytic and oxidative deteriorations. To increase oxidative stability, lecithin (200 and 400 ppm), α‐tocopherol (200 and 400 ppm), and their combination (1:1 ratio) at the same concentrations are added in the oil and stored for 30 d at 30 °C. Oil added with α‐tocopherol at 400 ppm shows the highest stability within the first 2 d (peroxide value = 339.28 mEq peroxide kg−1, anisidine value = 34.15, thiobarbituric acid reactive substances = 0.74 mg of MDA kg−1 of oil). However, at day 30, oil incorporated with α‐tocopherol at 400 ppm shows no differences in n‐3 fatty acids, particularly eicosapentaenoic acid and docosahexaenoic acid from the control. Also, no significant differences in FTIR spectral intensity between both samples at day 30 at wavenumbers 3013 and 1743 cm−1, representing cis‐double bond and carbonyl group, respectively, are observed. Therefore, other appropriate techniques, e.g., packaging or additives are still required for enhancement of oxidative stability of oil from skipjack tuna eyeball. Practical Applications: Wet rendering method is an environmental friendly method for tuna oil production. However, high temperature of extraction can generate darker color and induce lipid oxidation. To increase the qualities of rendered oil, milder temperature and shorter time for oil extraction should be applied. Moreover, the use of high potential antioxidant in combination with other techniques such as packaging, etc., should be implemented for extending the shelf‐life of oil having high susceptibility toward oxidation.