Compositional Characteristics of Materials Recovered from Headed Gutted Silver Carp (Hypophthalmichthys molitrix) by Isoelectric Solubilization and Precipitation Using Organic Acids

Effect of pH-Shifting Process on the Cathepsin Activity, Muddy Off-Odor Compounds' Content and Gelling Properties of Isolated Protein from Silver Carp

Silver carp (Hypophthalmichthys molitrix) is a potential source for making surimi products. However, it has the disadvantages of bony structures, high level of cathepsines and muddy off-odor which is mainly caused by geosmin (GEO) and 2-methylisoborneol (MIB). These disadvantages make the conventional water washing process of surimi inefficient (low protein recovery rate, and high residual muddy off-odor). Thus, the effect of the pH-shifting process (acid-isolating process and alkali-isolating process) on the cathepsins activity, GEO content, MIB content, and gelling properties of the isolated proteins (IPs) was investigated, comparing it with surimi obtained through the conventional cold water washing process (WM). The alkali-isolating process greatly boosted the protein recovery rate from 28.8% to 40.9% (p < 0.05). In addition, it removed 84% GEO and 90% MIB. The acid-isolating process removed about 77% GEO and 83% MIB. The acid-isolated protein (AC) displayed the lowest elastic modulus (G'), the highest TCA-peptide content (90.89 ± 4.65 mg/g) and the highest cathepsin L activity (65.43 ± 4.91 U/g). The AC modori (60 °C for 30 min) gel also demonstrated the lowest breaking force (226.2 ± 19.5 g) and breaking deformation (8.3 ± 0.4 mm), indicating that proteolysis caused by the cathepsin deteriorated the gel quality of AC. The setting (40 °C for 30 min) considerably increased the breaking force (386.4 ± 15.7 g) and breaking deformation (11.6 ± 0.2 mm) of the gel made from the alkali-isolated protein (AK) (p < 0.05). In AC and AK gel, a clearly visible cross-linking protein band with a molecular weight greater than MHC was seen, demonstrating the presence of endogenous trans-glutaminase (TGase) activity, that improved the gel quality of AK. In conclusion, the alkali-isolating process was an effective alternative method for making water-washed surimi from silver carp.

Cryoprotective Effects of Protein Hydrolysates Prepared from By-Products of Silver Carp (Hypophthalmichthys Molitrix) on Freeze-Thawed Surimi

The cryoprotective effects of different amounts of protein hydrolysates prepared from by-products of silver carp using Protamex and Alcalase on surimi that were subjected to six freeze-thaw cycles were investigated. Commercial cryoprotectant (8% w/w 1:1 sucrose-sorbitol blend, SuSo) and control (without cryoprotectant) groups were used for comparison. After six freeze-thaw cycles, the lowest actomyosin extractability, Ca2+-ATPase activity and total sulfhydryl content, along with the highest surface hydrophobicity of actomyosin, were observed in the control group (P < 0.05). On the contrary, the group with addition of 2 g of hydrolysate prepared by Protamex hydrolysis (PH-2) displayed the highest actomyosin extractability, Ca2+-ATPase activity and correspondingly, lowest surface hydrophobicity of actomyosin (P < 0.05). Total sulfhydryl content of actomyosin and textural properties of heat-set surimi gels were similar between samples with PH-2 and those with SuSo (P > 0.05). Differences in molecular weight distribution, total and free amino acid compositions between the hydrolysates prepared by Protamex and Alcalase hydrolysis were possible reasons attributing to their variable cryoprotective effects on freeze-thawed surimi. Results from this study clearly support that hydrolysate prepared by Protamex hydrolysis at an appropriate amount could serve as an effective cryoprotectant without increasing the sweetness of surimi products. Furthermore, our findings suggest that the hydrolysates follow a different cryoprotection mechanism compared to SuSo (sucrose-sorbitol blend).

Nutritional Quality and Physical Characteristics of Soluble Proteins Recovered from Silver Carp

The objective of this study was to evaluate the nutritional quality and physical characteristics of soluble proteins separated from silver carp at 4, 20, and 40 °C. Ground silver carp was diluted, and soluble proteins were separated by centrifugation and dried. The proximate composition (dry wt) of the protein powders averaged 82.42% protein, 3.25% lipid, and 14.50% ash. Average protein recovery yield was 11.78% with the better yields occurring at 20 °C (P < 0.05). Mineral profile revealed greater concentrations of Fe, Mg, P, and Na when compared to the initial homogenate. More saturated and monounsaturated fatty acids were recovered in the 4 °C powder and the least in the 40 °C powder (P < 0.05). Polyunsaturated fatty acids displayed a reverse trend, with the greatest concentration in the 40 °C powder and the least in the 4 °C powder (P < 0.05). The amino acid profile revealed that the protein powder met all FAO/WHO/UNO amino acid requirements for adults. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed high amounts of low and medium molecular weight (MW) proteins (10-15 and 25-50 kDa, respectively). Two-dimensional (2-D) electrophoresis indicated that the low MW proteins possessed a neutral isoelectric point relative to that of the medium MW proteins. The protein powder was significantly less soluble (P < 0.05) than whey protein concentrate 80 at every pH tested (pH 3.0 to 11.0). Similar tendencies were seen when ionic strength was shifted (0.0 to 1.1 I; P < 0.05). Soluble protein powders derived from silver carp are nutrient rich and have physical characteristics resembling whey protein concentrate. Changes in process temperature had limited effects on protein powder composition.

PRACTICAL APPLICATION

Soluble proteins contribute to 20 to 40% of fish protein and are soluble in neutral salt solutions. Much of the sarcoplasmic proteins are lost when they solubilize in processing water and are discarded similarly to how whey protein was once discarded during dairy processing. When government regulations on whey disposal were implemented, the dairy industry responded by repurposing the high-quality protein for human use and it is now a billion dollar industry. The aim of this research project was to verify the composition of an otherwise overlooked protein source.

Effects of starch concentration on calcium-enhanced black bullhead catfish protein gels

Calcium‐enhanced protein recovered from black bullhead catfish was used to develop gels containing increasing amounts of potato starch (0–20 g/kg protein paste) and the effects of starch on functional, textural, and color properties were tested. Energy required to unfold protein groups was greater with the addition of 5 g starch/kg protein paste. Gels containing starch were harder, chewier, and less springy (p < .05) than gels without starch. For most measurements, regression analysis showed that increasing the starch concentration beyond 5 g/kg did not contribute to further significant textural changes. Torsional shear stress and strain along with Kramer shear force increased as the concentration of starch increased (R² = .79, .79, and .53, respectively). The addition of ≥10 g starch/kg protein paste resulted in darker gels and gels got darker as more starch was added (R² = .71). Results showed no benefit to increasing starch concentration in gels beyond 5 g starch/kg protein paste.

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.

Nutritional and Digestive Properties of Protein Isolates Extracted from the Muscle of the Common Carp Using pH-Shift Processing

This study details the nutritional and digestive properties of protein isolates that are extracted from carp (Cyprinus Carpio L.) muscle using pH shifting methods. Alkaline (ALPI) and acid (ACPI) protein isolates exhibit higher protein yields (87.6%, 76.3%, respectively). In addition to the high recovery of myofibrillar protein, a portion of the water-soluble proteins is also recovered. The moisture contents of ACPI and ALPI are 85.5% and 88.5%, respectively, and the crude protein contents of these two fractions are 83.20% and 83.0%, respectively, both contents of which are higher than those for fresh muscle. Most part of the ash and fat are removed in the separation process. The protein isolation is also found to be lighter and whiter than the fresh muscle and there is no difference between amino acid content of protein isolation and that of fresh muscle. The maximum solubility of water washed surimi is 73.21%, while solubility of ACPI-2 and ALPI-2 (pH 7.0) are 66.67% and 62.08%, respectively. The digestibility of ALPI and ACPI is improved after being treated with chymotrypsin, which is about 7-8 times as that of fresh muscle. The results indicate that the protein isolates have better nutritional and digestive properties than the fresh muscle does in food processing.

PRACTICAL APPLICATIONS

Common carp is a lower additional value fish that exists in large amount in China. This study investigates nutritional and digestive properties of protein from carp extracted by pH shifting methods. According to the obtained data in this study, pH shifting method is a good protein recovery method that can effectively remove bone spurs, skin, fat and other impurities. In addition, sarcoplasmic proteins can also be recovered. The nutritional properties of protein isolates of carp were suitable for supplementing as an ingredient for human consumption. The pH-shift process greatly improves the protein digestibility. Therefore, there are broad application prospects of the protein isolation as protein ingredients in food industry.

Influence of pre-cooking protein paste gelation conditions and post-cooking gel storage conditions on gel texture

BACKGROUND

Gelation conditions affect the setting of myofibrillar fish protein gels. Therefore the impact of widely applied pre-cooking gelation time/temperature strategies and post-cooking period on the texture and color of final protein gels was determined. Four pre-cooking gelation strategies (no setting time, 30 min at 25 °C, 1 h at 40 °C or 24 h at 4 °C) were applied to protein pastes (fish protein concentrate and standard functional additives). After cooking, texture and color were analyzed either directly or after 24 h at 4 °C on gels adjusted to 25 °C.

RESULTS

No-set gels were harder, gummier and chewier (P < 0.05) when analyzed immediately after cooling; however, gel chewiness, cohesiveness and firmness indicated by Kramer force benefited from 24 h at 4 °C gel setting when stored post-cooking. Gel-setting conditions had a greater (P < 0.05) effect on texture when directly analyzed and most changes occurred in no-set gels. There were significant (P < 0.05) changes between directly analyzed and post-cooking stored gels in texture and color, depending on the pre-cooking gelation strategy.

CONCLUSION

Pre-cooking gelation conditions will affect final protein gel texture and color, with gel stability benefiting from a gel-setting period. However, post-cooking storage may have a greater impact on final gels, with textural attributes becoming more consistent between all samples.

pH shift protein recovery with organic acids on texture and color of cooked gels

BACKGROUND

Isoelectric solubilization and precipitation (ISP) processing uses pH shifts to separate protein from fish frames, which may increase commercial interest for silver carp. Texture and color properties of gels made from silver carp protein recovered at different pH strategies and organic acid types were compared. ISP was applied to headed gutted silver carp using 10 mol L(-1) sodium hydroxide (NaOH) and either glacial acetic acid (AA) or a (1:1) formic and lactic acid combination (F&L). Protein gels were made with recovered protein and standard functional additives.

RESULTS

Texture profile analysis and the Kramer shear test showed that protein gels made from protein solubilized at basic pH values were firmer, harder, more cohesive, gummier and chewier (P < 0.05) than proteins solubilized under acidic conditions. Acidic solubilization led to whiter (P < 0.05) gels, and using F&L during ISP yielded whiter gels under all treatments (P < 0.05).

CONCLUSION

Gels made from ISP-recovered silver carp protein using organic acids show potential for use as a functional ingredient in restructured foods.