The effect of heating conditions on polyphenol oxidase, proteases and melanosis in pre-cooked Pacific white shrimp during refrigerated storage

Pre-cooked Pacific white shrimp (Litopenaeus vannamei) is an important shrimp product. However melanosis, especially in the cephalothorax including carapace and internal organs, is more likely caused by the remaining polyphenol oxidase (PPO) after pre-cooking. Thus, PPO from carapace and proteases from hepatopancreas of Pacific white shrimp were characterised and the remaining activities of both enzymes were monitored in pre-cooked shrimp during storage at 4 °C. Based on activity staining using L-β-(3,4 dihydroxylphenyl) alanine as a substrate, PPO consisted of two isoforms with apparent molecular weight of 210 and 220 kDa. No difference in activity band was observed when analysed under reducing and non-reducing condition. Proteases from hepatopancreas were able to activate PPO to some degree. For the in vitro study, both enzymes were quite stable when heated at temperature up to 70 °C but the loss in activities increased with increasing heating time (0-120 s). When Pacific white shrimp were pre-cooked to obtain different core temperatures (50-90 °C), different PPO and protease activities were retained. Higher core temperatures were associated with lower PPO and protease activities, but higher cooking loss. When the shrimp were pre-cooked at 80 °C, the residual PPO and protease activities were 3.9% and 5.4%, respectively and cooking yield of 95.6% was obtained. The resulting pre-cooked shrimp possessed lower melanosis score during 7 days of storage at 4 °C. Thus, pre-cooking of shrimp to obtain a core temperature of 80 °C, with a holding time of 30 s, could prevent the severe cooking loss and lower melanosis during subsequent storage.     

Effect of Treating of Squid with Sodium Chloride in Combination with Oxidising Agent on Bleaching,Physical and Chemical Changes During Frozen Storage

Pink discolouration is a problem faced in the squid processing industry, and some treatments have been implemented to tackle such a problem. The study aimed to elucidate the impact of NaCl in combination with oxidising agents on the quality changes of squid during frozen storage. The effects of treatment of pink squid using 3% (w/v) NaCl solution containing oxidising agents (0.05–0.5% (w/v) H₂O₂ or 0–10 ppm NaOCl) on colour and chemical and physical changes of squid during frozen storage were investigated. The lowest decreases in a*, b* values, ∆E* and ∆C* of squid were obtained with the treatment using 3% NaCl solution containing 0.5% H₂O₂. Nevertheless, NaOCl (0–10 ppm) had no impact on a* and b* values. During frozen storage at −18 °C for 10 weeks, fresh squid, pink squid samples without and with treatments with 3% NaCl solution containing 0.5% H₂O₂ had no changes in a* and b* values during frozen storage. Nevertheless, thiobarbituric acid reactive substances value, disulphide bond content, thaw drip and shear force were more pronounced in treated pink squid, compared with pink squid without treatment (control) and fresh squid, respectively, during the extended storage (p < 0.05). Higher denaturation and aggregation of muscle proteins during frozen storage were observed in treated pink squid than that without treatment and fresh squid, respectively. Therefore, pink squid treated with oxidising agent was prone to protein aggregation and denaturation during the extended frozen storage, though it could lower the pink colour. Therefore, fresh squid without treatment using oxidising agent is recommended for production of frozen squid with negligible loss in quality during extended storage.     

Autolysis of goatfish (Mulloidichthysmartinicus) mince: Characterisation and effect of washing and skin inclusion

Autolysis of goatfish mince and washed mince incubated at different temperatures (30–70 °C) was investigated. The highest autolytic activity was generally observed in mince and washed mince at 60 °C as evidenced by the highest trichloroacetic acid (TCA) soluble peptide content and the greatest disappearance of myosin heavy chains (MHCs). Autolysis of both mince and washed mince was maximised at pH 4, and lower autolytic activity was observed at pH 7. trans-epoxysuccinyl-l-leucyl-amido (4-guanidino) butane (E-64) showed the greatest inhibition of autolysis at pH 4, showing that at least one cysteine protease was active in goatfish muscle. Nevertheless, soybean trypsin inhibitor effectively inhibited the autolysis at neutral pH (pH 7), suggesting that goatfish muscle also contained at least one serine protease. Generally, autolysis of mince was more pronounced than that of washed mince, indicating that washing could lower the autolytic activity of mince. In the presence of skin, a higher autolysis was obtained with the goatfish mince. Therefore, both sarcoplasmic and myofibril-associated proteases in muscle as well as the contamination of skin likely contributed to the degradation of muscle proteins of goatfish.     

Comparative studies on chemical composition and thermal properties of black tiger shrimp (Penaeus monodon) and white shrimp (Penaeus vannamei) meats

Chemical composition and thermal properties of meat from two species of shrimps, black tiger shrimp (Penaeus monodon) and white shrimp (Penaeus vannamei), were comparatively studied. White shrimp meat had higher protein and ash contents than had black tiger shrimp meat (p < 0.05). Fractionation of nitrogenous constituents revealed that myofibrillar protein was the major component in the muscles; myosin heavy chain (MHC) and actin were the predominant proteins. White shrimp meat comprised higher stromal protein with greater pepsin-soluble collagen and insoluble collagen contents than did black tiger shrimp meat. Muscle proteins from black tiger shrimp, especially MHC, had higher thermal stability than those from white shrimp as indicated by the higher transition temperature (T_max) as well as the lower inactivation rate constant (K_D). Phospholipid was the predominant lipid (72–74%) in both shrimps, followed by triglyceride. Polyunsaturated fatty acids were found as the major fatty acids with the range of 42.2–44.4%. DHA (22:6)/EPA (20:5) ratio in black tiger shrimp (2.15) was higher than that in white shrimp (1.05). Mg was the dominant mineral in both shrimps. Ca and Fe were also found at high concentrations. Arginine was the most abundant amino acid, while leucine, isoleucine and proline were predominant in both shrimps. Glutamic acid and glycine contents were greater in black tiger shrimp meat; however, white shrimp meat had higher hydroxyproline content. Different compositions might govern the different characteristics as well as thermal properties of both species.     

Thermal properties and heat-induced aggregation of natural actomyosin extracted from goatfish (Mulloidichthys martinicus) muscle as influenced by iced storage

Thermal properties and aggregation of natural actomyosin (NAM) extracted from fresh and 9 days ice-stored goatfish were comparatively studied. Myosin of fresh goatfish had the higher thermal stability than that of ice-stored counterpart as indicated by the higher maximum transition temperature (T_max). Additionally, the thermal inactivation rate constant (K_D) of Ca²⁺-ATPase in NAM from fresh goatfish was lower than that of ice-stored counterpart when incubated at the temperature range of 20–40 °C, indicating the lower thermal stability of the latter NAM. NAM from fresh goatfish exhibited the higher turbidity, surface hydrophobicity and disulfide bond formation than did NAM of iced-stored sample when heated at temperature from 35 to 75 °C, suggesting the higher extent of aggregation of the former. However, goatfish NAM showed the lower extent of heat-induced aggregation than did bigeye snapper NAM. As visualized by transmission electron microscopy, network strands of aggregates from bigeye snapper NAM were finer and more uniform than those from goatfish. NAM from goatfish stored in ice showed the lower extent of heat-induced aggregation than did NAM from fresh counterpart. Therefore, heat-induced aggregation of goatfish muscle proteins was governed by freshness.     

Properties, translucence, and microstructure of Pacific white shrimp treated with mixed phosphates as affected by freshness and deveining

ABSTRACT:  Effects of freshness and deveining on some properties, translucence, and microstructure of Pacific white shrimp ( Litopenaeus vannamei ) soaked in 2.5% NaCl containing different phosphates were studied. Shrimp soaked in all solutions had increases in weight gain and cooking yield with lowered cooking loss, compared with the control ( P < 0.05). However, efficacy of mixed phosphates in quality improvement of ice-stored shrimp was lower than fresh shrimp. Deveining resulted in increased weight gain and yield ( P < 0.05). Nevertheless, samples treated with phosphates became more translucent. Shrimp stored in ice for 7 d and treated with mixed phosphates were generally more translucent than fresh counterparts ( P < 0.05). Shrimp soaked in 2.5% NaCl containing 0.875% sodium acid pyrophosphate (SAPP) and 2.625% tetrasodium pyrophosphate (TSPP) were generally less translucent and had high weight gain and cooking yield along with low cooking loss. The microstructure study revealed that the muscle fibers were less attached with the loss of Z-disks after being treated with mixed phosphates. Cooked meats of fresh shrimp and ice-stored shrimp had more compact fiber arrangement with the shrinkage of sarcomere compared with raw samples. Disintegration was observed at the M-line in ice-stored shrimp treated with mixed phosphates after cooking, while such a phenomenon was not found in the cooked fresh sample treated with phosphates. T _max and enthalpy of both myosin and actin peaks shifted to lower values when shrimp were treated with mixed phosphates ( P < 0.05). Those changes were generally more pronounced in ice-stored shrimp. Therefore, freshness and deveining process had an impact on the quality of Pacific white shrimp treated with phosphates.     

Effects of colorant concentration and ‘natural colour’ or ‘sodium content’ claim on saltiness perception,consumer liking and emotion,and purchase intent of dipping sauces

Natural colorant (no colorant, NC = 0%; moderate colorant, MC = 1.2%; high colorant, HC = 3.6% w/w) and salt (regular salt, RS = NaCl; reduced sodium, ReS = KCl; no salt, NS) were added in mayonnaise‐based dipping sauces to evaluate effects of colorant concentration and ‘natural colorant’ or ‘sodium content’ claim on saltiness expectation, consumer liking and emotion, and purchase intent (PI) of these products. Regardless of the salt type and content, increasing colorant concentration decreased colour liking scores while saltiness expectation tentatively increased as indicated by higher % of ‘too much’ responses for saltiness on a JAR (Just‐About‐Right) scale. At a given salt type and content, liking scores of salty taste decreased with increasing colorant concentration, both before and after the ‘sodium content’ claim was given to consumers. Emotion scores elicited by consuming dipping sauces were affected by colorant concentration. Positive emotions (good, interested, satisfied) decreased while negative emotions (guilty, unsafe, worried) increased with increasing colorant concentration. Statements of ‘natural colorant’ and ‘sodium content’ claim had minimal effects on elicited emotions and PI.     

Influences of a natural colourant on colour and salty taste perception,liking, emotion and purchase intent: a case of mayonnaise‐based dipping sauces

Effects of colourant and a ‘natural source’ statement on sensory liking, emotion, saltiness expectation and purchase intent (PI) of three dipping sauces containing shrimp head colourant [no‐colourant (NC); moderate‐colourant (MC, 1.2% colourant); high‐colourant (HC, 3.6% colourant)] were evaluated. Consumers disliked colour of HC compared to MC (4.65 vs. 6.24). Despite the same NaCl level, saltiness liking decreased with increasing colourant [6.38 (NC), 5.43 (MC), 3.97 (HC)]. Correspondence analysis biplot revealed that sauces with or without natural colourant were associated more with positive emotions. Positive emotion (good, interested, satisfied) scores decreased while negative emotion worried increased with increasing colourant concentration. The ‘natural source’ statement decreased guilty and unsafe scores but minimally affected PI of NC and MC. Saltiness expectation was not different between NC (off‐white colour) vs. MC (lighter orange) and between NC vs. HC (darker orange); however, consumers expected HC to be saltier than MC.     

Comparative studies on the effect of the freeze–thawing process on the physicochemical properties and microstructures of black tiger shrimp (Penaeus monodon) and white shrimp (Penaeus vannamei) muscle

The effects of different freeze–thaw cycles (0, 1, 3 and 5) on the physicochemical properties and microstructures of black tiger shrimp (Penaeus monodon) and white shrimp (Penaeus vannamei) muscle were investigated. White shrimp had greater exudate loss and higher α-glucosidase (AG), as well as β-N-acetyl-glucosaminidase (NAG) activities, than did black tiger shrimp, especially when the number of freeze–thaw cycles increased (P < 0.05). The decreases in Ca²⁺-ATPase activity, sulfhydryl group content and protein solubility with concomitant increases in disulfide bond formation and surface hydrophobicity were more pronounced in white shrimp muscle, than in black tiger shrimp muscle, particularly after five cycles of freeze–thawing (P < 0.05). The shear force of both shrimps was decreased after five freeze–thaw cycles (P < 0.05). The microstructure study revealed that the muscle fibers were less attached, with the loss of Z-disks, after subjection to five freeze–thaw cycles. Therefore, the freeze–thawing process caused denaturation of proteins, cell disruption, as well as structural damage of muscle in both shrimps. White shrimp generally underwent physicochemical changes induced by the freeze–thawing process to a greater extent than did black tiger shrimp.