Effect of oxidised phenolic compounds on the gel property of mackerel (Rastrelliger kanagurta) surimi

The effects of different oxidised phenolic compounds (ferulic acid, OFA; tannic acid, OTA; catechin, OCT and caffeic acid, OCF) at different levels (0-0.60% of protein content) on the properties of gels from mackerel (Rastrelliger kanagurta) surimi were investigated. Gels with addition of 0.40% OFA, 0.50% OTA, 0.50% OCF or 0.10% OCT had increases in breaking force by 45%, 115%, 46.1% and 70.3% and in deformation by 12.2, 27.5, 28.1 and 28.4%, respectively, compared with the control (without addition of oxidised phenolics). Lowered expressible moisture content without any change in the whiteness of resulting gels was found. Slightly lower myosin heavy chain (MHC) band intensity of gels added with oxidised phenolics at the optimal level was noticeable compared with that of the control. A sensory evaluation study indicated that addition of oxidised phenolic compounds had no negative impact on the colour and taste of the resulting gels (P > 0.05). Gels with addition of all oxidised phenolics had a finer matrix with smaller strands.     

Physicochemical properties and gel-forming ability of surimi from three species of mackerel caught in Southern Thailand

Physicochemical and gelation properties of surimi prepared from three species of mackerel were investigated. The highest whiteness with the lowest redness index corresponding to the lowest myoglobin content especially its oxidised form, metmyoglobin, was found in short-bodied mackerel (Rastrelliger brachysoma) surimi (p < 0.05). Frigate mackerel (Auxis thazard) surimi contained the highest lipid content (p < 0.05). The pH of all surimi was in the range of 6.58–6.80. The highest sulfhydryl group and Ca²⁺-ATPase activity was found in natural actomyosin extracted from short-bodied mackerel surimi (p < 0.05). The highest TCA-soluble peptide content was found in frigate mackerel surimi gels (p < 0.05). Kamaboko gel of short-bodied mackerel surimi exhibited the highest breaking force with the lowest expressible drip (p < 0.05). Heating regime had no effect on deformability of gels from Indian mackerel (Rastrelliger kanagurta) and short-bodied mackerel but not for frigate mackerel. The highest metmyoglobin content with the lowest whiteness was found in frigate mackerel surimi gel (p < 0.05). Therefore, short-bodied mackerel was the best suited for the production of surimi with superior functional attributes including whiteness and gel-forming ability.     

Impact of microbial transglutaminase on gelling properties of Indian mackerel fish protein isolates

Impacts of microbial transglutaminase (MTGase) (0–0.6 units/g sample) on gel properties of Indian mackerel unwashed mince, surimi and protein isolates with and without prewashing were studied. Generally, lower myoglobin and lipid contents were found in protein isolate with and without prewashing, compared to those of unwashed mince and surimi (P < 0.05). Protein isolate had the decreased Ca²⁺-ATPase and protein solubility, indicating protein denaturation. When MTGase was incorporated, breaking force and deformation of all gels markedly increased, especially as MTGase levels increased (P < 0.05). At the same MTGase level, gel from protein isolate with prewashing exhibited the highest breaking force and deformation (P < 0.05). The addition of MTGase could lower the expressible moisture content of most gels. No change in whiteness of gel was observed with the addition of MTGase (P > 0.05), but gel from protein isolate gels had decreased whiteness as MTGase at high level was added. The microstructure of protein isolate gels without prewashing showed a similar network to unwashed mince gels, whilst a similar network was observed between surimi gel and gel from protein isolate with prewashing. Nevertheless, a larger void was noticeable in gels from protein isolates. All gels incorporated with MTGase (0.6 units/g) showed a slightly denser network than those without MTGase. Thus, gel with improved properties could be obtained from protein isolate from Indian mackerel with added MTGase.     

Gel properties of croaker–mackerel surimi blend

Gel properties of croaker surimi blended with three types of mackerel surimi at different ratios were evaluated. The gel strength of the croaker–mackerel surimi blend was higher than that of the original mackerel surimi (p < 0.05). The presence of croaker surimi in the blend resulted in the increase in myosin heavy chain (MHC) band intensity. No differences in deformation of gels were observed in croaker surimi and croaker-short-bodied mackerel blend at all ratios (p > 0.05). The addition of short-bodied mackerel surimi into croaker surimi up to a ratio of 1:2 had no effect on whiteness and metmyoglobin content of the gel (p > 0.05). Marked decrease in expressible drip and TCA-soluble peptide of gel was noticeable in croaker–frigate mackerel surimi blend (p < 0.05). Therefore, the gel properties of croaker–mackerel surimi blend were governed by the type and content of mackerel surimi used.     

Color improvement by titanium dioxide and its effect on gelation and texture of proteins recovered from whole fish using isoelectric solubilization/precipitation

Whiteness is a critical attribute for restructured fish products such as surimi seafood. However, the whiteness of gels made from proteins recovered from fish processing by-products or whole fish using isoelectric solubilization/precipitation is poor. The by-products and whole fish contain bones, scales, skin, etc. that affect gel color. Therefore, whiteness needs to be improved if marketable products are to be developed from recovered proteins. The objectives of this study were to determine effects of titanium dioxide (TiO₂) on: (1) color; (2) texture; and (3) viscoelasticity (G′) of gels made from isolated carp proteins and Alaska pollock surimi. Carp proteins were recovered with isoelectric solubilization/precipitation. TiO₂ was added to carp proteins at 0-0.5 g/100 g. TiO₂ was not added to surimi. Due to much higher (P < 0.05) yellowness (b^∗) and lower (P < 0.05) lightness (L^∗), the whiteness of carp gels without TiO₂ was lower (P < 0.05) than surimi gels. TiO₂ at ≥ 0.2 g/100 g resulted in better (P < 0.05) whiteness of carp gels than surimi gels without chalky and artificially white appearance. TiO₂ did not affect texture or viscoelasticity. This research demonstrates that whiteness of restructured fish products based on proteins recovered from whole fish via isoelectric solubilization/precipitation can be similar to the whiteness of surimi seafood.     

Whey protein concentrate: Autolysis inhibition and effects on the gel properties of surimi prepared from tropical fish

Effects of whey protein concentrate (WPC) on autolysis inhibition and gel properties of surimi produced from bigeye snapper (Priacanthus tayenus), goatfish (Mulloidichthys vanicolensis), threadfin bream (Nemipterus bleekeri) and lizardfish (Saurida tumbil) were investigated. WPC (0–3%) showed inhibitory activity against autolysis in all surimi at both 60 and 65 °C in a concentration-dependent manner. Myosin heavy chain (MHC) of surimi was more retained in the presence of WPC. Breaking force and deformation of kamaboko gels of all surimi increased as added levels of WPC increased (P < 0.05). This was associated with lower levels of protein degradation, as evidenced by the decrease in trichloroacetic acid-soluble peptide content (P < 0.05). WPC at 3% (w/w) significantly decreased the whiteness of gels. However, water-holding capacity of kamaboko gels was improved with increasing concentration of WPC. The microstructure of surimi gels generally became denser with the addition of WPC.     

Effect of porcine plasma protein and setting on gel properties of surimi produced from fish caught in Thailand

Effects of porcine plasma protein (PPP) and high temperature setting on gel properties of surimi from bigeye snapper, bigeye croaker, threadfin bream and barracuda were investigated. PPP was effective in increasing breaking force and deformation of kamaboko gels set at 40°C for 30 min and heated at 90°C for 20 min. The optimum levels of PPP were 0.5, 0.5, 1.5 and 1.5 g/100 g and the optimum setting times were 2, 1.5, 1.5 and 2 h for bigeye snapper, bigeye croaker, threadfin bream and barracuda surimi, respectively. However, the addition of PPP significantly decreased whiteness (P<0.05). An increase in gel-forming ability of surimi with PPP coincided with a decrease in solubility in mixture of SDS, urea and β-mercaptoethanol, indicating the formation of nondisulfide covalent bond induced by both endogenous and plasma transglutaminase. The results supported that PPP improve the gelation of surimi in combination with setting.     

Changes of phenolic acids and antioxidant activities during potherb mustard (Brassica juncea, Coss.) pickling

Phenolic acids in potherb mustard (Brassica juncea, Coss.) were determined and the effects of pickling methods on the contents of total free phenolic acids, total phenolic acids, total phenolics, and antioxidant activities were investigated. Gallic acid, protocatechuic acid, p-hydroxybenzoic acid, vanillic acid, caffeic acid, p-coumaric acid, ferulic acid, and sinapic acid were identified in the present study. The contents of total free phenolic acids, total phenolic acids and total phenolics in fresh potherb mustard were 84.8 ± 0.58 μg/g dry weight (DW), 539 ± 1.36 μg/g DW, and 7.95 ± 0.28 mg/g DW, respectively. The total free phenolic acids increased during the pickling processes, but the total phenolic acids, total phenolics, and antioxidant activities decreased. However, after 5 weeks of fermentation, all the pickling methods retained over 70% of total phenolic contents and above 65% of antioxidant capacities. The results indicated that pickling processes were relatively good methods for the preservation of phenolic acids and antioxidants for potherb mustard.     

Effect of oxidised tannic acid on the gel properties of mackerel (Rastrelliger kanagurta) mince and surimi prepared by different washing processes

Effect of oxidised tannic acid (OTA) at different levels (0, 0.25, 0.50 and 0.75% of protein content) on the gel properties of mackerel (Rastrelliger kanagurta) mince and surimi prepared by different washing processes was investigated. Breaking force and deformation of gels varied with washing processes and concentrations of OTA. The gel of alkaline-saline washing process surimi (ASWPS) added with 0.25% OTA had the increases in breaking force and deformation by 166.2 and 45.9%, respectively, compared with that of conventional washing process surimi (CWPS) without OTA addition. Those increases were associated with the lowered expressible moisture content. Electrophoretic studies revealed that the greater polymerisation was found in ASWPS added with 0.25% OTA. Slight retention of myosin heavy chain (MHC) with lowered trichloroacetic acid (TCA) soluble peptide contents was observed in ASWPS gel added with 0.25% OTA, suggesting the decreased degradation induced by indigenous proteases. The microstructure of ASWPS gels became more ordered, compact and denser with the addition of 0.25% OTA. The use of OTA in conjunction with alkaline-saline washing process could improve the properties of gel from mackerel surimi without adverse effect on sensory properties.     

Effects of Bambara Groundnut Protein Isolates and Microbial Transglutaminase on Textural and Sensorial Properties of Surmi Gel from Sardine (Sardinella albella)

Effects of different bambara groundnut protein isolates (BGPIs) at a level of 6 % (w/w) in combination with microbial transglutaminase (MTGase) at a concentration of 0.6 U g^?1 surimi on gel properties of sardine (Sardinella albella) surimi were investigated. In the absence of MTGase, all BGPIs showed the adverse effect on gel-forming properties of surimi, as evidenced by the decreases in breaking force and deformation (P?<?0.05). When MTGase was incorporated, the increases in breaking force and deformation were found for all BGPIs used. Water-holding capacity of all gels was improved when BGPIs were added in combination with MTGase (P?<?0.05). Whiteness of gels slightly decreased with the addition of BGPIs; however, MTGase had no impact on whiteness (P?>?0.05). Surimi gel added with BGPI prepared from defatted flour with heat treatment in the presence of ethylenediaminetetraacetic acid (DF-BGPI-HE) and MTGase showed well-ordered network and exhibited the lowest peroxide value and thiobarbituric acid-reactive substances than those containing other BGPIs. Gel containing DF-BGPI-HE had negligible beany flavour. Additionally, DF-BGPI-HE had the lower amount of volatile compounds after storage of 30 days at room temperature than other BGPIs. Thus, the addition of DF-BGPI-HE and MTGase was an effective means to render sardine surimi gel with improved gel property and caused no beany flavour in resulting gel.     

Effect of zinc sulphate on gelling properties of phosphorylated protein isolate from yellow stripe trevally

Impacts of zinc sulphate (ZnSO₄) (0–140 μmol/kg) on gel properties of yellow stripe trevally surimi added with sodium tripolyphosphate (STPP) (0.25% and 0.5%, w/w) and protein isolate phosphorylated with STPP at 0.25% and 0.5% (w/w) were studied. Gels from surimi added with 60 μmol ZnSO₄/kg in the absence and presence of 0.5% STPP had the increases in breaking force and deformation by 20.9% and 33.3%, and 11.6% and 18.6%, respectively, compared with the control surimi gel (without additives). Gel of protein isolate phosphorylated with 0.5% STPP containing 100 μmol ZnSO₄/kg had the increases in breaking force and deformation by 14.87% and 5.6%, respectively, compared with the gel from non-phosphorylated protein isolate at the same ZnSO₄ level, suggesting that the phosphorylated protein isolate was more crosslinked by Zn²⁺. The addition of ZnSO₄ at the suitable level lowered the expressible moisture content, but increased whiteness of surimi or protein isolate gels (P < 0.05). Non-covalent bonds, more likely salt bridge and ionic interactions, played a major role in cross-linking of proteins in both surimi and protein isolate added with ZnSO₄, regardless of phosphates incorporated. Microstructure study revealed that a gel having highly interconnected and denser network with smaller voids was formed when protein isolate phosphorylated with 0.5% STPP was added with ZnSO₄ at a level of 100 μmol/kg. Thus, gel with improved properties could be obtained from protein isolate from yellow stripe trevally phosphorylated with STPP in conjunction with addition of ZnSO₄ at an appropriate level.     

Biochemical and gelling properties of tilapia surimi and protein recovered using an acid-alkaline process

The biochemical and gel properties of tilapia surimi prepared by a conventional washing method and protein isolated using alkaline-acid-aided processes were studied. Solubility and recovery of protein was found to be highest by using a conventional method, followed by an alkaline- and acid-aided process, respectively. Decreases in myoglobin and lipid contents were found in alkaline- or acid-aided process when compared to the conventional process (p < 0.05). The highest breaking force and deformation of kamaboko and modori gels was found in the gels prepared by the conventional washing method. Higher expressible water and whiteness were found in modori gels when compared to kamaboko gels. TCA-soluble peptide contents of conventional surimi gels were lower than those of acid- and alkaline-recovered protein gels. Degradation of myofibrillar protein was observed in acid-isolated protein. Microstructure of kamaboko gels showed more compact network than in modori gels in both conventional surimi and protein recovered using the pH-shift process.     

Effects of Hydrolysates from Silver Carp (Hypophthalmichthys molitrix) Scales on Rancidity Stability and Gel Properties of Fish Products

This study aimed to evaluate the effectiveness of hydrolysates, which were obtained from the scales of silver carp (Hypophthalmichthys molitrix) by papain, flavourzyme, and Alcalase 2.4 L, as natural antioxidants in silver carp mince and surimi gels during storage at 4 °C. The hydrolysates that possess greater in vitro antioxidant activities (DPPH radical-scavenging activity, Fe²⁺-chelating activity, and reducing power), including hydrolysates catalyzed by papain at 10 min (HP), flavourzyme at 5 min (HF), and Alcalase 2.4 L at 5 min (HA), were chosen as additives. Color, cooking loss, conjugated dienes (CDs), thiobarbituric acid reactive substances (TBARS), fatty acids, and sensory scores of mince were measured on days 0, 2, 4, 6, and 8 during 4 °C storage; additionally, whiteness, breaking force, deformation, gel strength, and sensory score of surimi gels were measured on days 1, 3, 5, 7, 9, and 11 during 4 °C storage. The results indicate that HA was conducive to lowering the cooking loss of mince and that HF significantly (P?<?0.05) reduced the CDs value of mince. For surimi gels, HF improved whiteness, deformation, and gel strength. Hence, HF could serve as a natural antioxidant during early oxidation and improve gel formation of silver carp products.     

The effect of whitening agents on the gel-forming ability and whiteness of surimi

The effect of different concentrations of the whitening agents, calcium carbonate, titanium dioxide and soybean oil, on the gel‐forming ability and whiteness of a mixture of bigeye snapper and mackerel surimi was investigated. The whiteness of the surimi gels increased as the concentration of all whitening agents increased (P < 0.05). Titanium dioxide was a good whitening agent and it had no detrimental effects on gel‐forming ability, while oil reduced the gel breaking force and deformation. The addition of calcium carbonate did not result in a marked increase in whiteness, but it did increase the breaking force and deformation to some extent. The different whitening agents showed different influences on the whiteness and gelling characteristics of surimi gel.     

The hydroxycinnamic acid content of barley and brewers’ spent grain (BSG) and the potential to incorporate phenolic extracts of BSG as antioxidants into fruit beverages

The hydroxycinnamic acid (HA) content of starting barley for brewers’ spent grains (BSG), whole BSG and phenolic extracts from BSG was measured using high performance liquid chromatography (HPLC) and correlated with antioxidant potential. The effect of BSG phenolic extracts on antioxidant activity of fruit beverages was also assessed (using the total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays). The concentration of HA present in barley extract and BSG was in the order of ferulic acid (FA), p-coumaric acid (p-CA) derivatives, FA derivatives, p-CA, caffeic acid (CA) and CA derivatives. Results suggested that brewing and roasting decreased the HA content. Antioxidant activity was significantly (P < 0.05) correlated with caffeic acid (R² = 0.8309) and total HA (R² = 0.3942) concentrations. Addition of extracts to fruit beverages resulted in a significant (P < 0.05) increase in antioxidant activity of cranberry juice, measured by the FRAP assay. In vitro digestion significantly (P < 0.05) reduced TPC, DPPH and FRAP activity of the fruit beverages.     

Phenolic profiles and antioxidant activities of commercial beers

The phenolic profiles and corresponding antioxidant activities of 34 commercial beers in Chinese markets were evaluated. Results found remarkable variations in total and individual phenolic contents as well as antioxidant activity across beer brands. Gallic and ferulic acids were the dominant phenolic compounds identified in the tested beer samples and both of them accounted for >50% of the total phenolic compounds. Results from Pearson correlation analysis suggested that five antioxidant activity assays positively correlated well (p < 0.01) with each other and showed significant positive correlations (p < 0.05) with (+)-catechin, protocatechuic, and caffeic acids contents. Stepwise linear regression further demonstrated that different phenolic components responsible for beer antioxidant activity were dependent on the method used, and that ferulic acid, syringic acid, (+)-catechin, caffeic acid, protocatechuic acid and (−)-epicatechin together made 55.0–88.1% of contribution to the antioxidant activity of beer.     

Effect of ferulic acid on inhibition of polyphenoloxidase and quality changes of Pacific white shrimp (Litopenaeus vannamei) during iced storage

Effects of ferulic acid (FA) on polyphenoloxidase (PPO) and the quality changes of Pacific white shrimp (Litopenaeus vannamei) during iced storage for 10 days were investigated. Both FA and oxygenated FA (OFA) with different concentrations (0.1%, 0.5%, 1% and 2% (w/v)) showed PPO inhibitory activity in a dose dependent manner. FA was generally more effective in PPO inhibition than was OFA. Based on activity staining, white shrimp PPO with an apparent molecular weight of 210 kDa was inhibited by FA. When whole shrimps were treated with FA solution with concentrations of 1% or 2% and stored in ice for up to 10 days, the increase in psychrophilic and mesophilic bacterial count were retarded, in comparison with the control and those treated with 1.25% sodium metabisulphite (SMS). The coincidental lower rates of increase in pH and total volatile base content were obtained. Additionally, shrimps treated with 2% FA possessed the lowest peroxide value and thiobarbituric acid reactive substances (TBARS) value during the storage. After 10 days of storage, shrimps treated with 2% FA had the lower melanosis score and higher score for colour, flavour and overall likeness, compared with the control and SMS treated shrimps (P < 0.05).     

Variation in antioxidant potential and total polyphenol content of fresh and fully-fermented Sri Lankan tea

Tea polyphenols possess antioxidant properties and have been shown to have a protective effect against several degenerative diseases. The study aimed to determine the amounts of polyphenols and antioxidant properties for teas grown in Sri Lanka, over a period of 10 months. Water extracts of freeze-dried fresh (unfermented) and fully-fermented tea leaves were made for a structured set of samples (fermented and unfermented teas from six plantations; teas representing two harvesting seasons from four plantations) collected from the main tea growing regions in Sri Lanka. Total phenolic content (TPC), the ferric reducing antioxidant power (FRAP) and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity were determined for each sample. The results highlight significant (P < 0.05) variations in antioxidant activity across the six plantations. FRAP and DPPH for both fermented and unfermented teas from the four highland plantations showed a significant (P < 0.05) interaction between season and plantation. A similar interaction between season and plantation was observed for total phenolics in unfermented teas from the four highland plantations. The variability of the total phenolics for fermented teas, however, was independent of seasonal variations. A significant correlation (r = 0.5, P < 0.05) was observed between FRAP and total phenolics.     

Inhibition kinetics of catechin and ferulic acid on polyphenoloxidase from cephalothorax of Pacific white shrimp (Litopenaeus vannamei)

Inhibition kinetics and mode of catechin and ferulic acid towards polyphenoloxidase (PPO) from cephalothorax of Pacific white shrimp were investigated. Catechin or ferulic acid inhibited quinone formation catalysed by PPO in a dose dependent manner. Catechin showed mixed type reversible inhibition with K_i value of 1.4 mM, whereas ferulic acid exhibited non-competitive reversible inhibition with K_i value of 37 mM. With increasing concentrations, both catechin and ferulic acid had higher copper (Cu²⁺) reduction and copper chelating capacity (P < 0.05). Catechin or ferulic acid could react with intermediated browning reaction products, thereby preventing dopachrome formation. Thus, catechin or ferulic acid could inhibit melanosis in Pacific white shrimp with different modes of inhibition towards PPO.     

Interactions of dietary fibre and omega-3-rich oil with protein in surimi gels developed with salt substitute

Most Western populations have insufficient intake of fibre and ω-3 polyunsaturated fatty acids (PUFAs), while sodium intake greatly exceeds the recommended maximum. Surimi seafood is not currently fortified with these nutraceutical ingredients. Alaska pollock surimi seafood was developed with salt substitute and fortified with either 6 g/100 g of fibre or 10 g/100 g of ω-3 oil (flax:algae:menhaden, 8:1:1) or fibre + ω-3 oil (6 g/100 g of fibre + 10 g/100 g of ω-3 oil). The objective was to determine effects of the dietary fortification on physicochemical properties of surimi. Fortification with either dietary fibre or ω-3 oil alone or in combination enhanced (P < 0.05) rheological and textural characteristics. The combined fortification had a synergistic effect on rheological properties. This indicates greater gelation of surimi in the presence of fibre + ω-3 oil, suggesting their interaction with surimi myofibrillar proteins. Fibre results in protein dehydration increasing protein concentration; while oil is immobilised by protein filling void spaces in the gel matrix. Differential scanning calorimetry showed that fibre and ω-3 oil did not interfere with normal denaturation of surimi proteins. Colour properties were only slightly affected (P < 0.05). Fortification of surimi with fibre and ω-3 oil resulted in a quality product that could be useful in developing surimi products with nutritional benefits.