Three kinds of roe protein concentrates (RPCs: boil-dried concentrate, BDC; steam-dried concentrate, SDC; freeze-dried concentrate, FDC) were prepared from yellowfin tuna to produce value added products for food applications. The buffer capacities of the RPCs were higher under alkaline than under acidic conditions. The water holding capacities of the RPCs were in range 4.5-4.7 g/g protein at pH 6.0. The protein solubility of the FDC (14.2%) was higher than those of the BDC (5.4%) and SDC (5.5%) at pH 6.0. The foaming capacity of the FDC (156.8%) was higher than those of the BDC (109.7%) and SDC (109.4%); the FDC foam was stable for 60 min. The oil-in-water emulsifying activity index of the FDC (12.2m/g protein) exceeded those of the BDC and SDC (2.2m/g protein). Protein concentrates from yellowfin tuna roe may be useful as a potential protein source and as a high-value food ingredient.
Isoelectric solubilization/precipitation (ISP) processing allows selective, pH-induced water solubility of proteins with concurrent separation of lipids and removal of materials not intended for human consumption such as bone, scales, skin, etc. Recovered proteins retain functional properties and nutritional value. Four roe protein isolates (RPIs) from yellowfin tuna roe were prepared under different solubilization and precipitation condition (pH 11/4.5, pH 11/5.5, pH 12/4.5 and pH 12/5.5). RPIs contained 2.3-5.0 % moisture, 79.1-87.8 % protein, 5.6-7. 4 % lipid and 3.0-3.8 % ash. Protein content of RPI-1 and RPI-2 precipitated at pH 4.5 and 5.5 after alkaline solubilization at pH 11, was higher than those of RPI-3 and RPI-4 after alkaline solubilization at pH 12 (P < 0.05). Lipid content (5.6-7.4 %) of RPIs was lower than that of freeze-dried concentrate (10.6 %). And leucine and lysine of RPIs were the most abundant amino acids (8.8-9.4 and 8.5-8.9 g/100 g protein, respectively). S, Na, P, K as minerals were the major elements in RPIs. SDS-PAGE of RPIs showed bands at 100, 45, 25 and 15 K. Moisture and protein contents of process water as a 2'nd byproduct were 98.9-99.0 and 1.3-1.8 %, respectively. Therefore, yellowfin tuna roe isolate could be a promising source of valuable nutrients for human food and animal feeds.
Roe is the term used to describe fish eggs (oocytes) gathered in skeins and is one of the most valuable food products from fishery sources. Thus, means of processing are required to convert the underutilized yellowfin tuna roes (YTR) into more marketable and acceptable forms as protein concentrate. Roe protein concentrates (RPCs) were prepared by cooking condition (boil-dried concentrate, BDC and steam-dried concentrate, SDC, respectively) and un-cooking condition (freeze-dried concentrate, FDC) from yellowfin tuna roe. The yield of RPCs was in the range from 22.2 to 25.3 g/100 g of roe. RPCs contained protein (72.3-77.3 %), moisture (4.3-5.6 %), lipid (10.6-11.3 %) and ash (4.3-5.7 %) as the major constituents. The prominent amino acids of RPCs were aspartic acid, 8.7-9.2, glutamic acid, 13.1-13.2, and leucine, 8.5-8.6 g/100 g of protein.Major differences were not observed in each of the amino acid. K, S, Na, and P as minerals were the major elements in RPCs. No difference noted in sodium dodecyl sulfate polyacrylamide gel electrophoresis protein band (15-100 K) possibly representing partial hydrolysis of myosin. Therefore, RPCs from YTR could be use potential protein ingredient for human food and animal feeds.
Four roe protein isolates (RPIs) from skipjack tuna were prepared using isoelectric solubilization (pH 11 and 12) and precipitation (pH 4.5 and 5.5) (ISP) at different pH points to evaluate their physicochemical and functional properties and in vitro bioactivities. Moisture (<6.3%) and protein (71%–77%) content were maintained. Sulfur, sodium, phosphorus, and potassium were the major elements, and glutamic acid and leucine were the prevalent amino acids (12.2–12.8 and 9.6–9.8 g/100 g protein, respectively) in RPIs. RPI‐1 showed the highest buffering capacity at pH 7–12. RPIs and casein showed similar water‐holding capacities. At pH 12, RPI‐1(pH 11/4.5) showed the highest solubility, followed by RPI‐3(pH 12/4.5), RPI‐2(pH 11/5.5), and RPI‐4(pH 12/5.5) (p < .05). Oil‐in‐water emulsifying activity indices of RPI‐1 and RPI‐3 significantly differed. At pH 2 and 7–12, pH‐shift treatment improved the food functionality of RPIs, which was superior to positive controls (casein and hemoglobin). RPI‐1 showed ABTS+ radical scavenging (102.7 μg/ml) and angiotensin‐converting enzyme inhibitory activities (44.0%).
To facilitate the effective use of butter clam shell as a natural calcium resource, we determined the optimal conditions for calcium lactate (BCCL) preparation with high solubility using response surface methodology (RSM). The polynomial models developed by RSM for pH, solubility and yield were highly effective in describing the relationships between factors (P<0.05). Increased molar ratios of calcined powder (BCCP) from butter clam shell led to reduced solubility, yield, color values and overall quality. The critical values of multiple response optimization to independent variables were 1.75 M and 0.94 M for lactic acid and BCCP, respectively. The actual values (pH 7.23, 97.42% for solubility and 423.22% for yield) under optimization conditions were similar to the predicted values. White indices of BCCLs were in the range of 86.70-90.86. Therefore, organic acid treatment improved color value. The buffering capacity of BCCLs was strong, at pH 2.82 to 3.80, upon the addition of less than 2 mL of 1 N HCl. The calcium content and solubility of BCCLs were 6.2-16.7 g/100 g and 93.6-98.5%, respectively. Fourier transform analysis of infrared spectroscopy data identified BCCL as calcium lactate pentahydrate, and the analysis of microstructure by field emission scanning electron microscopy revealed an irregular form.
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