Indian J. Fish., 65(3): 74-83, 2018 74 DOI: 10.21077/ijf.2018.65.3.78269-10 Peptides from white and red meat of yellowfin tuna (Thunnus albacares): A comparative evaluation U. PARVATHY, P. K. BINSI, A. A. ZYNUDHEEN, GEORGE NINAN AND L. N. MURTHY* ICAR-Central Institute of Fisheries Technology, Kochi - 682 029, Kerala, India *Mumbai Research Centre of ICAR- Central Institute of Fisheries Technology, Vashi, Navi Mumbai - 400703 Maharashtra, India e-mail: [email protected] ABSTRACT Dark muscle from yellowfin tuna is rich in proteins and is an important byproduct from tuna cannery. However, it has a low market realisation and is currently utilised for preparation of fertilisers and animal feeds. Recovery and utilisation of this biomass to bioactive protein hydrolysate is a promising alternative as it facilitates food and pharmaceutical applications. However, the extent to which the properties of the hydrolysate vary in red meat derived-hydrolysate is less investigated. Hence the current study was aimed at exploring the characteristics of protein hydrolysates derived from red meat of yellowfin tuna (Thunnus albacares) in comparison to its white meat. Protein hydrolysate was prepared using 1% (w/w) papain for one hour at optimised temperature of 60°C and pH of 6.5 from white and red meat of yellowfin tuna to derive tuna white meat protein hydrolysate (TWPH) and tuna red meat protein hydrolysate (TRPH), respectively. Nutritional evaluation of tuna meat indicated comparable protein content in both white and red portions with a value of 25.99±0.24% and 24.03±0.11%, respectively and a recovery of 50.34% from white meat and 44.67% from red meat protein to their hydrolysate forms was observed. Comparative evaluation of the functional as well as bioactive properties of hydrolysates from white and red meat of tuna indicated better antioxidative activity for TWPH. However, except oil absorption capacity (OAC), functional properties viz., protein solubility, foaming capacity and emulsifying properties were higher for TRPH. Present study explores the application potential of tuna red meat to its bioactive peptides for food and pharmaceutical sectors. Keywords: Antioxidative properties, Functional properties, Papain, Tuna protein hydrolysate, Yellowfin tuna Introduction chains with 2-20 amino acids obtained by hydrolysis either chemically or enzymatically. This process facilitates Tuna resources are considered to be significant recovery of essential nutrients viz., amino acids and has sources of seafood and are largely exploited on account immense scope in food, nutraceutical and pharmaceutical of their increased global demand for thermally processed industry on account of the excellent physicochemical, delicacies. However, tuna market mainly utilises the functional as well as bioactive properties (He et al., 2013; white meat thus resulting in the underutilisation of protein Halim et al., 2016). Hence with increasing knowledge of rich byproducts viz., red meat, head, skin, trimmings and these advantages, more research is being focused on the viscera, that are discarded without recovery attempts and development of fish-derived functional and nutraceutical accounts for more than 60% of biomass (Chalamaiah foods. The present study focused on deriving protein et al., 2012). Of these, 10-12% is the dark meat portion hydrolysates from white and red meat of yellowfin tuna which has nutrients especially proteins of high quality (Thunnus albacares) under similar hydrolytic conditions comparable to that of the white meat (Nishioka et al., using papain, to comparatively evaluate the characteristics 2007). Hence utilisation of these dark meat proteins is a of the derived hydrolysate for their further application serious matter to be addressed on account of the limited potentials. food resources for meeting nutritional security as well as increasing environmental pollution issues. Materials and methods Proper exploitation of these nutrient rich fish Fish, enzyme and chemicals processing discards could be achieved by enzymatic Fresh yellowfin tuna (T. albacares) was purchased conversion of these protein sources into its hydrolysates, from fish landing centre at Mumbai and brought to the facilitating its effective utilisation. Protein hydrolysates are laboratory in iced condition. The white and red meat the breakdown products of proteins viz., smaller peptide of tuna was separated and used as raw material for the U. Parvathy et al. 75 preparation of tuna white meat protein hydrolysate spray drying from the amount of raw material used for (TWPH) and tuna red meat protein hydrolysate (TRPH), hydrolysis. respectively. Enzymatic hydrolysis was carried out using Colour and browning intensity papain (Hi Media, India) obtained from papaya latex (proteolytic activity ≥ 4.5 ml of 0.1M NaOH). All the Hunter Lab colourimeter (Colorflex EZ 45/0, Hunter reagents used for the study were of analytical grade. Associates Lab inc., Reston, Virginia, USA) was employed to analyse the colour of the sample (1% hydrolysate Preparation of tuna protein hydrolysate solution) viz., L* (the degree of lightness), a* [redness(+)/ The separated white and red meat of tuna were greenness (-)] and b* [yellowness (+) or blueness (-)]. comminuted thoroughly using a kitchen blender and The browning intensity of hydrolysate samples added with twice the amount water to get fine slurry of were determined by measuring the absorbance of filtered meat which was further subjected to 80-90oC for 30 min samples (80 mg ml-1) spectrophotometrically (Lambda for complete endogenous enzyme inactivation. Further 25 UV/Vis, Perkin Elmer Life and Analytical Sciences, enzymatic hydrolysis was performed in a shaking water Singapore) at 420 nm. bath (Neolab Instruments, Mumbai, India) maintained at 60oC, employing papain at physiological pH (6.5). Ultraviolet absorption spectra Enzyme:substrate (E/S) ratio and duration of hydrolysis UV absorption spectra of the samples (2 mg ml-1), were maintained at 1.0% and 60 min, respectively. in the wavelength range of 200-330 nm and scan Termination of hydrolysis was brought out by raising speed of 2 nm sec-1 were determined using UV-VIS the process temperature to 80-90oC for 15-20 min and spectrophotometer (Lambda 25 UV/Vis, Perkin Elmer the resultant solution was course filtered and centrifuged Life and Analytical Sciences, Singapore) (Elavarasan and (K-24A, Remi Instruments, Mumbai) at 8000 g at 10oC Shamasundar, 2016). for 20 min to obtain protein hydrolysate solution which was further spray dried (Hemaraj Enterprises, Mumbai) Functional properties and subjected to quality analysis. Protein solubility Protein content and protein recovery Hydrolysate samples (10 mg ml-1, 20 ml) was well Analysis of the protein content of tuna meat and dispersed in distilled water by stirring at room temperature hydrolysates were done as per AOAC (2012) adopting for 30 min followed by centrifuging at 7500 g for 15 min micro-Kjeldahl method. The protein recovery in to collect the supernatant. Protein solubility was calculated hydrolysate was estimated as the percentage of protein as percentage of total protein in supernatant to the total recovered in hydrolysate to the total amount of protein in protein in sample (Morr et al., 1985). raw material. Foaming properties Degree of hydrolysis and proteolytic activity Foaming properties of the protein solution were Degree of hydrolysis (DH) was determined as determined by the methodology of Sathe and Salunkhe the percentage of α-amino nitrogen in hydrolysates, (1981). A known volume of protein solution (1%) was determined by formol titration method (Taylor, 1957) to homogenised (230 VAC T-25 digital Ultra-turrax, IKA, the total nitrogen content in the raw material (AOAC, India) at 16,000 rpm for 2 min at ambient temperature 2012). and the whipped sample was immediately transferred to a measuring cylinder and the volume read immediately and To estimate the proteolytic activity of papain, after 3 min to calculate the properties as: amount of tyrosine liberated in the sample was assessed. (A-B) A known quantity of diluted liquid hydrolysate solution Foaming capacity/Stability % = x100 was measured for its absorbance at 280 nm (Lambda B 25 UV/Vis, Perkin Elmer Life and Analytical Sciences, where, A = foam volume after whipping to determine Singapore). Standard curve of L-tyrosine (0.025 - 0.2 mg foaming capacity; foam volume after standing for 3 min ml-1) in 0.2 M HCl at 280 nm was used to determine the (foam stability) and B = volume before whipping. tyrosine content of sample and was expressed in µ mole Emulsifying properties of tyrosine liberated per mg of protein (Gajanan, 2014). A mixture containing oil (10 ml) and hydrolysate Yield solution (1%, 30 ml) were thoroughly homogenised (230 Yield of fish protein hydrolysate (%) was calculated VAC T-25 digital Ultra-turrax, IKA, India) at 20,000 rpm as the quantity of hydrolysate powder obtained after for 1 min. An aliquot of the emulsion (50 μl) pipetted from Peptides from yellowfin tuna 76 the bottom of the container at 0 and 10 min were mixed with centrifuged at 3000 rpm (K-24A, Remi Instruments, 0.1% sodium dodecyl sulphate solution (5 ml) to read the Mumbai) for 10 min and 2.5 ml of supernatant mixed with absorbance at 500 nm (Lambda 25 UV/Vis, Perkin Elmer equal volume of distilled water and 0.1% ferric chloride Life and Analytical Sciences, Singapore) immediately to read the absorbance at 700 nm (Lambda 25 UV/Vis, (A0) and 10 min (A10) after emulsion formation (Pearce Perkin Elmer Life and Analytical Sciences, Singapore) and Kinsella, 1978): (Oyaiza, 1986). 2 x 2.303 x A0 Ferric reducing antioxidant power (FRAP) EAI (Emulsion Activity Index) (m2 g-1) = 0.25 x wt of protein FRAP solution was prepared freshly by incubating a A10 x Δt premix containing 300 mm acetate buffer (pH 3.6) (25 ml), ESI (Emulsion stability index) (min) = ΔA 10 mm TPTZ (2,4,6-tripyridyl-s-triazine) solution (2.5 ml) in 40 mm HCl and 2.5 ml of 20 mm FeCl .