Separation of membranes from acid-solubilized fish muscle proteins with the aid of calcium ions and organic acids

Effects of calcium ion on gel properties and gelation of tilapia (Oreochromis niloticus) protein isolates processed with pH shift method

The effect and mechanisms of calcium chloride and citric acid addition on the acid method of processing tilapia protein isolates and surimi gels were studied. The alkaline method shows better gel quality than the acid method with lower yield and high lipid content. The addition of calcium chloride increased the breaking force to 494.56 g and citric acid helped reducing the lipid content by 85.85%, resulting in a higher yield of 75.36%. Gels with calcium maintained low levels of expressible moisture (2.30%), indicating a well-organised gel matrix. The decrease in -SH content and increase in ionic bonds content suggested increased formation of disulphide bonds and ionic bonds. Oscillatory dynamic measurement indicated that more heat resistant bonds were formed. The morphology of myofibril proteins studied by atomic force microscopy (AFM) showed that the height of the proteins in the calcium-added gels decreased 79.4%, which suggested that the protein structure was "suppressed".

Calcium hydroxide as a processing base in alkali-aided pH-shift protein recovery process

BACKGROUND

Protein may be recovered by using pH shifts to solubilize and precipitate protein. Typically, sodium hydroxide is used as the processing base; however, this has been shown to significantly increase sodium in the final recovered protein.

RESULTS

Protein was extracted from black bullhead catfish (Ameiurus melas) using a pH-shift method. Protein was solubilized using either sodium hydroxide (NaOH) or calcium hydroxide (Ca(OH)₂ ) and precipitated at pH 5.5 using hydrochloric acid (HCl). Protein solubility was greater when Ca(OH)₂ was used compared to NaOH during this process. Using Ca(OH)₂ as the processing base yielded the greatest lipid recovery (P < 0.05) at 77 g 100 g^-1 , whereas the greatest (P < 0.05) protein recovery yield was recorded as 53 g 100 g^-1 protein using NaOH. Protein solubilized with Ca(OH)₂ had more (P < 0.05) calcium in the protein fraction, whereas using NaOH increased (P < 0.05) sodium content.

CONCLUSION

Results of our study showed that protein solubility was increased and the recovered protein had significantly more calcium when Ca(OH)₂ was used as the processing base. Results showed both NaOH and Ca(OH)₂ to be an effective processing base for pH-shift protein recovery processes. © 2016 Society of Chemical Industry.

Effect of pretreatment on lipid oxidation and fishy odour development in protein hydrolysates from the muscle of Indian mackerel

Impact of different pretreatments on chemical compositions of Indian mackerel mince was studied. Mince prepared using washing/membrane removal/alkaline solubilisation process (W-MR-Al) contained the lowest remaining myoglobin and haem iron content and also showed the lowest total lipid and phospholipid contents. When mince and W-MR-Al were hydrolysed using Alcalase for up to 120 min, a higher degree of hydrolysis (DH) was found in W-MR-Al after 30 min of hydrolysis. Furthermore, hydrolysate from W-MR-Al had lower peroxide value (PV), thiobarbituric acid reactive substances (TBARS) and non-haem iron content throughout hydrolysis period (P<0.05). When hydrolysate powder produced from mince and W-MR-Al (0-0.3%w/v) were fortified in milk, the former resulted in the lower likeness score (P<0.05) at all levels used. The addition of the latter, for up to 0.2%, had no effect on likeness of all attributes, compared with milk without fortification (P>0.05). Therefore, the appropriate pretreatment of mince yielded hydrolysate with lower fishy odour.

Interactions between hemoglobin and cod muscle constituents following treatment at extreme pH values

Acid and/or alkaline solubilization is a recent method developed to separate proteins from muscle foods with good functional properties. However, exposure of the muscle and its components to low pH values has been shown to promote lipid oxidation, limiting therefore the applications of this novel method. This research aimed primarily to study the physicochemical changes of the fish membranes brought about during acid or alkali solubilization processes. The effect on lipid oxidation and the possible role of the water soluble fraction of the muscle (press juice) as a potent antioxidant were also investigated. Model systems comprising minced cod muscle or cod microsomal suspensions were used. Results showed that acid or alkaline treatment (pH < 3.5 or pH > 10.5) of cod membranes significantly delayed lipid oxidation. Added triacylglycerols to washed cod system treated at low pH did not enhance hemoglobin-mediated lipid oxidation. Decreased precipitation of hemoglobin was observed with the alkali-treated membranes at all protein concentrations compared to the acid-treated and the untreated membranes. Finally, the addition of press juice to washed cod muscle tissue or to the membrane model system, significantly delayed hemoglobin lipid oxidation.

PRACTICAL APPLICATION

The results of this study can be used to improve pH-shifting technologies to avoid or decrease lipid oxidation problems. Also, the use of press-juice from cod muscle as means of protecting the muscle against lipid oxidation is suggested.

Compositional characteristics of materials recovered from whole gutted silver carp (Hypophthalmichthys molitrix) using isoelectric solubilization/precipitation

Isoelectric solubilization/precipitation (ISP) at acidic and basic pH was applied to whole carp, yielding proteins, lipids, and insolubles. The objective was to characterize composition of recovered materials. Crude protein was concentrated to 89-90% in proteins recovered at acidic pH and to 94-95% at basic pH. Basic pH yielded proteins with more (P < 0.05) essential amino acids (EAAs). EAA content in recovered proteins met FAO/WHO/UNO requirements. ISP did not affect fatty acid (FA) composition. Lipids recovered at acidic pH contained 88-89% of total fat and at basic pH, 94-97%. Total fat in recovered proteins was low, with EPA and DHA at the highest (P < 0.05) percentage for pH 11.5. ISP, particularly basic pH, effectively removed impurities such as bones and scales from whole carp. This is indicated by 3.8-5.8% of ash in recovered proteins compared to 11.2% for whole carp and 5.4% for boneless/skinless carp fillets. Basic pH yielded less (P < 0.05) Ca, P, and Mg in recovered proteins. These minerals were more (P < 0.05) concentrated in insolubles recovered with basic pH. This study indicates that materials recovered from whole carp using ISP have high nutritional value and may be useful in the development of human food and animal feeds.

Plasma phospholipids implicated in the matrix effect observed in liquid chromatography/tandem mass spectrometry bioanalysis: evaluation of the use of colloidal silica in combination with divalent or trivalent cations for the selective removal of phospholipids from plasma

The feasibility of the use of colloidal silica in combination with a number of divalent or trivalent cations for the removal of plasma phospholipids was evaluated by sequentially adding the two reagents (i.e., colloidal silica and a cation) directly to blank plasma samples or plasma samples spiked with analytes. Three representative plasma phospholipids were monitored to determine the efficiency of the phospholipids removal under different reagent combinations. The recovery of each spiked analyte was also monitored under each condition in order to determine if any of the analyte was removed along with the phospholipids. By optimizing the amounts of the reagents used and the sequence of the addition of the reagents, quantitative and reproducible removal of the phospholipids was achieved. Using the finally selected lanthanum cation, the removal of phospholipids was achieved with minimal concomitant loss of the ten investigated analytes which were carefully selected to incorporate functional groups that could potentially interact with the added reagents and hence could be removed along with the phospholipids.

Removal of lipids and diarrhetic shellfish poisoning toxins from blue mussels (Mytilus edulis) during acid and alkaline isolation of proteins

Diarrhetic shellfish poisoning (DSP) toxins pose a serious health risk for consumers of bivalves and other shellfish, as well as a huge economic burden for the bivalve-producing farmers. In this work, the aim was to utilize a solubilization-based protein-isolation method to produce a low-DSP toxin protein isolate from toxic blue mussels that are unsuitable for the whole shellfish market. A homogenate of whole mussel meat was solubilized at low pH (2.8) or high pH (11.1), followed by centrifugation and reprecipitation of the solubilized mussel proteins at the isoelectric pH. In a second centrifugation, precipitated proteins were collected. These processes resulted in 81 (acid solubilization) and 72% (alkaline solubilization) reduction in the initial DTX-1 toxin content of the mussel meat. No other DSP toxins were found in the protein isolates. Acid processing of mussel meat resulted in 50% reduction in the total lipid content, while alkaline treatment did not significantly affect the lipid content. The effect of citric acid and calcium chloride addition to the mussel meat-water homogenate on lipid and toxin content was also investigated. A poor correlation factor was surprisingly obtained between reductions in DTX-1 toxin and lipids in protein isolates from processed toxic mussels. Results from an analytical mass balance of the DTX-1 toxin during acid processing showed that 61% of this toxin ended up in the aqueous supernatant after the second centrifugation. The present study presents a promising alternative way of utilizing mussels for food production in periods when they are toxic.

Amino acid, fatty acid, and mineral profiles of materials recovered from rainbow trout (Oncorhynchus mykiss) processing by-products using isoelectric solubilization/precipitation

Protein, lipid, and insolubles (bones, skin, scales, fins, insoluble protein, and more) were recovered from rainbow trout processing by-products by means of isoelectric solubilization/precipitation at basic pH and acidic pH. Isoelectric solubilization/precipitation of the trout processing by-products resulted in the recovery of protein that was higher (P < 0.05) in essential amino acids (EAAs), non-EAAs, and total EAA/total AA ratio when compared to the processing by-products. Basic pH treatments yielded a higher (P < 0.05) content of EAAs than the acidic pH treatments. Nutritional quality of the recovered protein was high based on EAAs meeting the FAO/WHO/UNU recommendations for adults. The presence of omega-3 and omega-6 fatty acids (omega-3, omega-6 FAs) and the omega-3/omega-6 ratio in the recovered lipids were similar to the trout processing by-products, indicating that the pH treatments had no effect on these FAs. Ca and P contents of the processing by-products exceeded the recommended dietary allowances (RDA), but Fe and Mg did not. Basic pH treatments yielded protein with the lowest (P < 0.05) amount of minerals and the highest (P < 0.05) amount of Ca, P, and Mg in the insolubles when compared to acidic pH. The isoelectric solubilization/precipitation of the processing by-products effectively removed minerals from the recovered protein without removal of the bones, skin, scales, fins, and so on, prior to processing. The results indicated that isoelectric solubilization/precipitation, particularly at basic pH, permitted recovery of high-quality protein and lipids from fish processing by-products for human food uses; also, the recovered insolubles may be used in animal feeds as a source of minerals.

Effect of low pH on the susceptibility of isolated cod (Gadus morhua) microsomes to lipid oxidation

During the extraction of muscle to produce protein isolates by acid or alkali solubilization, membranes are exposed to abnormally low or high pH. Low but not high pH treatment induces rapid oxidation of membrane phospholipids in the presence of hemoglobin. The goal of this research work was to study the oxidative stability of microsomes under the conditions met during acid solubilization. Isolated microsomes from cod muscle were used as a model system. At pH 5.3 or lower, 99% of isolated cod membranes sedimented at low centrifugation speeds. Isolated membranes that were exposed to pH 3.0 were less susceptible to hemoglobin-mediated lipid oxidation. Cod hemoglobin exposed to pH 3 was rendered less pro-oxidative than the untreated cod hemoglobin. However, when microsomes and hemoglobin were together exposed to low pH, oxidation was promoted. Citric acid and calcium chloride, as well as press juice isolated from cod muscle, were able to inhibit lipid oxidation of microsomal suspensions.