RESUMEN
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%).
RESUMEN
The objective of this study was to investigate physicochemical properties of protein concentrate from skipjack tuna roe by a cook-dried (boiled or steamed-dried) process, and to evaluate their food functional properties. The yields of boil-dried concentrate (BDC) and steam-dried concentrate (SDC) prepared from skipjack tuna roe were 22.4 for BDC and 24.4% for SDC. Their protein yields were 16.8 and 18.4%, respectively. In terms of major minerals of the BDC and SDC, sulfur (853.2 and 816.6 mg/100 g) exhibited the highest levels followed by potassium, sodium and phosphorus. The prominent amino acids of roe protein concentrates (RPCs) were Glu, Asp, Leu and Val. The BDC and SDC showed a higher buffer capacity than egg white (EW) at the pH-shift range. The pH-shift treatment significantly improved the water holding capacities of RPCs, except pH 6. But they had a low solubility across the pH-shift range. The foaming capacities (104%-119%) of BDC and SDC were significantly lower than those of EW (p < .05), and their foam stabilities were not observed. Emulsifying activity index (m2/g protein) of RPCs and EW was 2.3 for BDC, 11.1 for SDC and 18.0 for EW. RPCs in the food and seafood processing industries will be available as egg white alternative protein sources and will be available as ingredients of surimi-based products in particular.
RESUMEN
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 (12.2m2/g protein) exceeded those of the BDC and SDC (2.2m2/g protein). Protein concentrates from yellowfin tuna roe may be useful as a potential protein source and as a high-value food ingredient.
