Functional properties of gonad protein isolates from three species of sea urchin: a comparative study.

Sea urchin Mesocentrotus nudus, Glyptocidaris crenularis, and Strongylocentrotus intermedius gonad protein isolates (mnGPIs, gcGPIs, and siGPIs) were extracted by isoelectric solubilization/precipitation (ISP) from the defatted gonads, and their functional properties were compared. Sodium dodecyl sulfate polyacrylamide gel electrophoresis results showed the similar protein pattern between each protein isolate and defatted gonad, indicating the high efficiency of ISP processing for protein recovery. Amino acid profileconfirmed that the mnGPIs and siGPIs could be potential sources of essential amino acid in nature. As regard to functional properties, mnGPIs showed higher water- and oil- holding capacities followed bysiGPIs and gcGPIs and all protein isolates presented great foaming property. As for emulsifying activity index (EAI), mnGPIs, gcGPIs, and siGPIs showed the minimum solubility and EAI at pH 5, 3, and 4, respectively, and behaved a pH-dependent manner. The gcGPIs revealed the highest EAI from pH 6 to 8 among the samples. In addition, circular dichroism showed increased content of ß-sheet at the expense of α-helix and ß-turn, suggesting the structure denaturation of the protein isolates. Indeed, no statistical difference was observed between secondary structure of mnGPIs and siGPIs. Moreover, ISP processing increased free sulfhydryl content of sea urchin protein isolates, but no difference was observed among the samples. Furthermore, siGPIs revealed the highest amount of total sulfhydryl and disulfide bonds, whereas both defatted gonads and protein isolates from G. crenularis presented the maximum surface hydrophobicity. These results suggest that gonad protein isolates from three species of sea urchin possess various functionalities and therefore can be potentially applied in food system. PRACTICAL APPLICATION: Sea urchin M. nudus, G. crenularis, and S. intermedius gonads are edible, whereas the functional properties of protein isolates from sea urchin gonad remain unknown. In this case, the extraction and comparison of three species of sea urchin gonad protein isolates will not only confirm functional properties but also screen food ingredients with suitable functions. In this study, functionalities of protein isolates derived from M. nudus, G. crenularis, and S. intermedius gonads would provide potential application in bakery food and meat products or as emulsifier candidates in food system.

Simultaneous extraction by acidic and saline solutions and characteristics of the lipids and proteins from large yellow croaker (Pseudosciaena crocea) roes.

The objective of this study was to simultaneously obtain protein isolates and lipids from the dried powder of large yellow croaker (Pseudosciaena crocea) roes (pcRs) to achieve high-value utilization. Protein isolates and lipids were extracted simultaneously from pcRs by saline and acidic solutions. The purity of the protein isolates from the pcRs (pcRPIs) was greater than 70%, with vitellogenin, vitellogenin B and vitellogenin C as the main proteins. The lipids from pcRs (pcRLs) were mainly composed of triglycerides with high levels of EPA and DHA. The pcRPIs exhibited a higher surface hydrophobicity, water/oil holding capacity and emulsifying ability than those of the pcRs. Moreover, pcRPIs had a better oil holding capacity and emulsifying ability than soy protein isolate. These results suggest that protein isolates and lipids can be simultaneously extracted by saline and acidic solutions, and pcRPIs and pcRLs can be used as functional materials in the food industry.

Quantitative Proteome Reveals Variation in the Condition Factor of Sea Urchin Strongylocentrotus nudus during the Fishing Season Using an iTRAQ-based Approach.

To investigate the variation in the condition factor of the sea urchin Strongylocentrotus nudus (S. nudus), gonads were collected in May (MAY), June (JUN), and July (JUL), at the beginning (AUG-b) and end of August (AUG-e). Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) detection of the gonads revealed an obvious enhancement of the band at about 37 kDa from July, which was identified as transforming growth factor-beta-induced protein ig-h3 (TGFBI) by nanoLC-ESI-MS/MS. Gonadal proteins were identified by isobaric tagging for relative and absolute quantitation (iTRAQ), and regulation of the identified proteins in pairs of the collected groups was observed. A total of 174 differentially expressed proteins (DEPs) were identified. Seven of the DEPs showed significant correlations with both the gonad index (GI) and protein content. These correlations included 6-phosphogluconate dehydrogenase, decarboxylating isoform X2 (6PGD), CAD protein, myoferlin isoform X8, ribosomal protein L36 (RL36), isocitrate dehydrogenase [NADP], mitochondrial isoform X2 (IDH), multifunctional protein ADE2 isoform X3, sperm-activating peptides (SAPs) and aldehyde dehydrogenase, and mitochondrial (ALDH). However, TGFBI had no correlation with gonad index (GI) or protein content. 6PGD, IDH, multifunctional protein ADE2 isoform X3, and ALDH were shown to interact with each other and might play key roles in changing the condition factor of S. nudus gonads.

Involvement of DNA in Gel Formation of Scallop (Patinopecten yessoensis) Male Gonad Hydrolysates and Corresponding Hybrid Gel with κ-Carrageenan.

Involvement of DNA in gelation and microstructural properties of scallop (Patinopecten yessoensis) male gonad hydrolysates (SMGHs) and corresponding hybrid gel with κ-carrageenan (SMGHs/κ-C) was studied using DNase pretreatment. Although DNase pretreatment significantly transformed SMGHs from weak gels to liquid, it made SMGHs have a superior synergistic effect on gel formation with κ-C by evidence of 2.7-fold G' and 1.1-fold melting temperature. However, the relaxation time (T21 and T23), functional groups, and flocculation behavior were comparable between SMGHs/κ-C and SMGHs/DNase/κ-C. Moreover, SMGHs/DNase/κ-C exhibited a denser network with more numerous patches and larger void spaces. These results suggest that DNA contributes to the gel formation of SMGHs whereas restricts more cationic peptides in SMGHs to bind sulfate groups in κ-C during gel formation.

Physiochemical Properties and Functional Characteristics of Protein Isolates from the Scallop (Patinopecten yessoensis) Gonad.

Protein isolates were recovered from scallop (Patinopecten yessoensis) gonads to develop a novel functional matrix by investigating their physiochemical and functional properties. Scallop gonad protein isolates (SGPIs) were prepared from degreased scallop gonads (DSGs) by an alkali extraction and isoelectric solubilization/precipitation (ISP) process. The protein compositions of the SGPIs were mainly vitellogenin and beta-actin with molecular weights of 266 and 42 kDa, respectively, as determined using Nano-liquid chromatography-mass/mass (Nano-LC-MS/MS). After the ISP process, the protein solubility of the SGPIs was significantly improved, and the surface hydrophobicity of SGPIs intensely increased by 1.1-fold, which were attributed to the exposure of aromatic residues such as phenylalanine, tyrosine, and tryptophan. However, the content of total/reactive sulfhydryl in SGPIs was decreased compared with that of DSGs. Meanwhile, the ISP process caused partial protein unfolding, as indicated by circular dichroism analysis, which exhibited a remarkable rise in the ß-sheet content with a parallel decline in the α-helix and random coil contents (P < 0.05). SGPIs exhibited a better oil absorption capacity and foaming property than both DSGs and soybean protein isolates (SPIs). Moreover, the emulsifying capacity of SGPIs was greatly enhanced by the ISP process, which was superior to the effect of commercial SPIs and was ascribed to its favorable solubility as well as surface characteristics. PRACTICAL APPLICATION: During the processing of scallop (Patinopecten yessoensis) adductors, scallop gonad, a high-protein part, is usually discarded as processing by-products despite its edibility. In recent years, scallop gonads are regarded as good sources to develop protein matrices due to their high protein content and numerous nutrients. In this study, scallop gonad protein isolates (SGPIs) were isolated by isoelectric solubilization/precipitation (ISP) process. The preferable solubility, foaming property coupled with high emulsifying property of SGPIs indicated that the SGPIs could be potentially utilized as a good protein emulsifier and additives in production of kamaboko gels, hamburger patties, sausages, and pet foods.

Bioaccessibility and cellular uptake of ß-carotene in emulsion-based delivery systems using scallop (Patinopecten yessoensis) gonad protein isolates: effects of carrier oil.

Emulsion-based delivery systems were structured by using scallop gonad protein isolates (SGPIs) as novel food-grade emulsifiers. The effects of carrier oil, including the long chain triglycerides (LCT) and medium chain triglycerides (MCT), on the bioaccessibility and cellular uptake of ß-carotene (BC) were investigated. Both LCT and MCT delivery systems remained stable at pH 7-8 but aggregated at lower pH values (3-6) according to the results of light scattering and microscopy measurements. LCT droplets fabricated within SGPIs were digested and released more slowly than MCT droplets during the simulated gastrointestinal tract digestion. The LCT emulsion showed higher BC bioaccessibility (65.5%) than the MCT emulsion (23.1%) as a result of the greater solubilization of BC in mixed micelles fabricated from long-chain fatty acids. Moreover, the LCT emulsion produced higher cellular uptake of BC as compared with the MCT emulsion in intestinal epithelial cells. These results demonstrated that SGPIs could be used as novel food-grade emulsifiers to protect lipophilic bioactive compounds in emulsion-based delivery systems, in which LCT is more suitable to encapsulate and deliver BC than MCT.

In silico assessment and structural characterization of antioxidant peptides from major yolk protein of sea urchin Strongylocentrotus nudus.

Sea urchin gonads have been demonstrated to contain major yolk protein (MYP), which can be hydrolyzed by enzymes to release biologically active peptides. The in silico analysis of the MYP sequence in the BIOPEP database showed the presence of fragments with antioxidant activity. The sequence was hydrolyzed by 21 kinds of proteases and 23 antioxidant peptides were obtained. Eight peptides, including Leu-Trp (LW), Arg-Trp (RW), Ala-Trp (AW), Thr-Trp (TW), Ala-Asp-Phe (ADF), Leu-Trp-Lys (LWK), Ser-Asp-Phe (SDF) and Leu-Tyr (LY), were screened and a score over 0.5 was obtained using PeptideRanker. The peptides LW, TW and LWK showed a stronger antioxidant capacity with IC50 values of 8.85, 9.59 and 9.62 mmol L-1, respectively, compared to that of glutathione (10.81 mmol L-1). Furthermore, AW, LW and LY showed Trolox equivalent antioxidant capacity (TEAC) values of 3.07, 1.87 and 1.52 mmol TE per mmol peptide, respectively. These results suggest that the MYP from sea urchin (S. nudus) gonads is a good source of antioxidant peptides with abundant tryptophan.

Characteristic antioxidant activity and comprehensive flavor compound profile of scallop (Chlamys farreri) mantle hydrolysates-ribose Maillard reaction products.

The objective of the present study was to improve the utilization of scallop (Chlamys farreri) byproducts by using Maillard reaction. Scallop mantle hydrolysates (SMHs) were prepared using neutrase then reacted with ribose. Thirty-four peptides were identified from SMHs by UPLC-Q-TOF-MS, and the abundance of Asp and Lys suggested the strong Maillard reactivity. The formation of Schiff's base as well as modification of amide I, II and III bands in Maillard reaction products (MRPs) was confirmed by ultraviolet-visible, fluorescence, and Fourier transform infrared spectroscopy. Thirty volatile compounds were produced by the reaction of SMHs with ribose. Moreover, MRPs with enhanced radical scavenging and anti-linoleic acid peroxidation activities over SMHs promoted the survival and reduced the DNA damage of HepG2 cells treated with hydrogen peroxide. These results suggest that SMHs-ribose MRPs can be potentially used as food antioxidant for suppressing of lipid oxidation or protecting of cell from oxidative damage.