Influence of Oil Load and Maltodextrin Concentration on Properties of Tuna Oil Microcapsules Encapsulated in Two-Layer Membrane

The two layers of tuna oil-in-water emulsions containing different oil loads (5–10 wt%) and maltodextrin concentrations (10–20 wt%) were stabilized by a lecithin–chitosan membrane. The liquid emulsions were then spray dried at an inlet air temperature of 180 ± 2°C and an outlet air temperature of 85 ± 5°C. The characteristics of liquid emulsion (creaming and mean droplet size) and spray-dried microcapsules (moisture content, water activity, color, morphology, glass transition temperature, and encapsulation efficiency) were measured. The results suggest that two-layer oil-in-water emulsions are an effective system to produce high oil-loaded microcapsules, which may lead to its wide application for use in food products.     

Isolation,characterisation and stability of myoglobin from Eastern little tuna (Euthynnus affinis) dark muscle

This study aimed to purify and characterise the myoglobin from the dark muscle of Eastern little tuna (Euthynnus affinis). Myoglobin purified by ammonium sulphate precipitation (65–100% saturation), followed by Sephadex G-75 chromatography had a molecular weight of 15,680 Da. The isoelectric point (pI) of both oxymyoglobin (OxyMb) and metmyoglobin (MetMb) was estimated to be 5.25, as determined by zeta potential analysis. Transition temperatures were 61 and 60 °C, for OxyMb and MetMb, respectively. The colour values (L∗, a∗ and b∗) and absorption spectra of the myoglobin solutions differed significantly, depending upon the form of myoglobin. OxyMb and MetMb had the Soret bands at 413 and 407 nm, respectively. The pH and thermal stability of myoglobin were tested under a pH range of 3–11 and a temperature range of 4–70 °C, respectively. Loss of haem–globin complex and autoxidation were dominant at pH 3, as evidenced by the disappearance of the Soret band and the formation of MetMb. Heating at temperature above 60 °C had a great impact on myoglobin denaturation. With increasing temperature and incubation time, OxyMb was susceptible to oxidation and conformational changes, whilst MetMb tended to be more stable. Thus, the form of myoglobin governed its properties and stability.     

Changes in heme proteins and lipids associated with off-odour of seabass (Lates calcarifer) and red tilapia (Oreochromis mossambicus × O. niloticus) during iced storage

Changes in heme proteins and lipids associated with off-odour development in seabass (Lates calcarifer) and red tilapia (Oreochromis mossambicus × O. niloticus) muscles during 15 days of iced storage were studied. Fresh seabass contained the higher contents of myoglobin and heme iron, compared with red tilapia (P < 0.05). An increase in metmyoglobin proportion was observed during storage. After 3 days of storage, a decreased heme iron content and a concomitant increase in non-heme iron content were noticeable in both fish (p < 0.05). Oxidation of myoglobin and released non-heme iron were associated with lipid oxidation. The increases in oxidation products and free fatty acids were observed as the storage time progressed. Fishy and rancid odours were detected at day 6 of storage for both fish and a higher intensity was found in seabass muscle. Thus, the off-odour in fish muscle was mostly governed by lipid oxidation and species specific.     

The effect of different atmospheric conditions on the changes in myoglobin and colour of refrigerated Eastern little tuna (Euthynnus affinis) muscle

BACKGROUND: Oxidation of myoglobin is responsible for the undesirable appearance and loss in acceptability of fish and fish products. The retardation of such a change by a modification of the surrounding atmosphere would be a means to maintain the quality of fish during the refrigerated storage. RESULTS: The changes in oxymyoglobin and metmyoglobin from dark muscle of Eastern little tuna (Euthynnus affinis) as affected by different atmospheric systems (closed system, opened system and flushed oxygen system) were determined. A saturated oxygen atmosphere more likely weakened the haem–globin complex, especially as the exposure time increased. Autoxidation of the oxy form proceeded rapidly in the presence of oxygen with the concomitant formation of the met form. When the oxygen was excluded, oxidation of oxymyoglobin was retarded. With flushed oxygen and increasing exposure time, conformational changes of globin occurred, mainly associated with protein oxidation. Generally, oxymyoglobin was more susceptible to oxidation and conformational change than did metmyoglobin. After keeping the samples at 4 °C for 3 days, dark muscle of tuna fillet kept in vacuum packaging had a slight decrease in redness and it was still acceptable. The fillets stored in exposed air or packed in 100% O₂ atmosphere turned brown, most likely due to myoglobin oxidation. CONCLUSION: The oxygen level of the packaging atmosphere had a profound impact on myoglobin alteration, which was governed by the forms of myoglobin. Copyright © 2011 Society of Chemical Industry     

Influence of chitosan and NaCl on physicochemical properties of low-acid tuna oil-in-water emulsions stabilized by non-ionic surfactant

An influence of low molecular weight (LMW) chitosan on physicochemical properties and stability of low-acid (pH 6) tuna oil-in-water emulsion stabilized by non-ionic surfactant (Tween 80) was studied. The mean droplet diameter, droplet charge (ζ-potential), creaming stability and microstructure of emulsions (5 wt% oil) were evaluated. The added chitosan was adsorbed on the surface of oil droplets stabilized by Tween 80 through electrostatic interactions. Such addition of chitosan at different concentrations (0–10 wt%) to emulsions showed slight effect on the mean droplet diameter. However, the degree of flocculation was a function of chitosan concentration assessed by emulsions' microstructure and creaming index. The impact of chitosan on the strength of the colloidal interaction between the emulsion droplets increased with increasing chitosan concentration. The mean diameter of droplet in emulsions increased with increasing NaCl because of the electrostatic screening effect. The addition of LMW chitosan could be performed to create tuna oil emulsions with low-acid to neutral character, as well as various physicochemical and stability properties suitable for health food products.     

Retardation of myoglobin and haemoglobin-mediated lipid oxidation in washed bighead carp by phenolic compounds

Antioxidative activities of phenolic compounds (caffeic acid, gallic acid and tannic acid; 200 ppm) in washed mince (pH 6), with added myoglobin (Mb) and haemoglobin (Hb), from bighead carp (Hypophthalmichthys nobilis), during 9 days of iced storage, were studied. Tannic acid exhibited the preventive effect on discolouration of washed mince containing Mb or Hb during storage (P < 0.05). High peroxide value (PV) was found and large amount of, thiobarbituric acid-reactive substances (TBARS) and hexanal were formed in washed mince containing haem proteins, especially Hb. As determined by apo Streptococcal haem-associated protein, Hb had the lower haem affinity than Mb. Phenolic compounds, especially caffeic acid and gallic acid, could lower lipid oxidation induced by Mb or Hb throughout storage (P < 0.05). Prevention of haem release, as well as inhibition of lipid oxidation induced by haem proteins with selected phenolic compounds, should be an alternative means in lowering discolouration and lipid oxidation in fish muscle.     

The effect of Fenton’s reactants and aldehydes on the changes of myoglobin from Eastern little tuna (<Emphasis Type="Italic">Euthynnus affinis</Emphasis>) dark muscle

The influences of Fenton’s reactants (H₂O₂ and FeCl₂) and aldehydes (hexanal and hexenal) on changes of oxymyoglobin and metmyoglobin from Eastern little tuna (Euthynnus affinis) dark muscle were studied. In the presence of H₂O₂, both oxymyoglobin and metmyoglobin were rapidly oxidized into ferrylmyoglobin based on spectra patterns. In the presence of Fe²⁺ and/or H₂O₂, the changes in fluorescent intensity of myoglobin were noticeable, but there were no changes in aggregation ratio. Release of non-heme iron from myoglobin was mainly governed by H₂O₂. When aldehydes were incorporated, the oxidation of oxymyoglobin and conformational changes of globin were more pronounced. No release of non-heme iron was noticeable, suggesting the stability of heme moiety toward aldehydes. Hexenal had a great impact on cross-linking of oxymyoglobin and metmyoglobin via covalent modification. Alteration of myoglobin redox state might be enhanced by conformational changes of globin induced by both Fenton’s reactants and aldehydes.     

Characteristics of gelatin from the skins of bigeye snapper, Priacanthus tayenus and Priacanthus macracanthus

Gelatins extracted from the skins containing fine scales of two species of bigeye snapper, Priacanthus tayenus (GT) and Priacanthus macracanthus (GM), were characterised. Both gelatins had the protein as the major component with high content of imino acids (proline & hydroxyproline) (186.29–187.42 mg/g). GT and GM contained calcium at levels of 6.53 and 2.92 g/kg, respectively. Both gelatins contained α1 and α2 chains as the predominant components and some degradation peptides. The absorption bands of both gelatins in Fourier transform infrared (FTIR) spectra were mainly situated in the amide band region (amide I and amide II). GT and GM had a relative solubility greater than 90% in the wide pH ranges (1–10). The bloom strength of GM (254.10 g) was higher than that of GT (227.73 g) (P < 0.05), but was slightly lower than that of commercial bovine gelatin (293.22 g) (P < 0.05). Finer gel structure with smaller strands and voids was observed in GM gel, in comparison with that observed in GT counterpart.     

Characteristics of myoglobin and haemoglobin-mediated lipid oxidation in washed mince from bighead carp (Hypophthalmichthys nobilis)

Myoglobin (Mb) and haemoglobin (Hb) accounted for 61% and 39% of the total haem-protein in bighead carp (Hypophthalmichthys nobilis) dark muscle, respectively. Molecular weight of Mb and monomeric-Hb was ∼16 kDa. Haemin loss from metHb was more rapid, compared to metMb (pH 6.0, 4 °C). Pro-oxidative activities of oxyMb/Hb and metMb/Hb were examined in washed mince during 9 days of iced storage (pH 6.0). Soret measurements suggested the existence of holoMb throughout storage. For Hb, weakening of haem-globin linkage was observed, especially for metHb which had undetectable Soret after 3 days of storage. Loss of redness was more rapid and extensive in washed mince containing Hb, compared to Mb. During storage, Hb induced larger amounts of peroxides, thiobarbituric acid-reactive substances and hexanal than did Mb (p < 0.05), especially for met-form. Thus, Hb had lower haemin affinity and was a stronger pro-oxidant than Mb.