Proteomics reveals the mechanism of protein degradation and its relationship to sensorial and texture characteristics in dry-cured squid during processing.

Proteolysis in dry-cured squid contributes to the development of sensory and textural attributes. In this study, label-free quantitative proteomics was conducted to study the mechanism of proteolysis and its correlation with quality changes. The results showed that the protein profile of dry-cured squid changed markedly during processing, which was confirmed by the quantification of myofibrillar protein, amino nitrogen and total free acids, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. Thirty-two key differentially abundant proteins were found to be correlated with sensory and texture characteristics, including myofibrillar protein, tubulin beta chain, collagens, heat shock proteins and cytochrome c. The correlation analysis indicated that myosin regulatory light chain and tubulin beta chain played the most important role in the development of texture and sensory attributes in squid samples during the dry-curing process. The results offered novel insights into proteolysis in dry-cured squid and its relationship to quality changes.

Ester Bonds for Modulation of the Mechanical Properties of Protein Hydrogels.

Hydrogels are soft materials constructed of physically or chemically crosslinked polymeric net-works with abundant water. The crosslinkers, as the mechanophores that bear and respond to mechanical forces, play a critical role in determining the mechanical properties of hydrogels. Here, we use a polyprotein as the crosslinker and mechanophore to form covalent polymer hydrogels in which the toughness and fatigue fracture are controlled by the mechanical unfolding of polyproteins. The protein Parvimonas sp. (ParV) is super stable and remains folded even at forces > 2 nN; however, it can unfold under loading forces of ~100 pN at basic pH values or low calcium concentrations due to destabilization of the protein structures. Through tuning the protein unfolding by pH and calcium concentrations, the hydrogel exhibits differences in modulus, strength, and anti-fatigue fracture. We found that due to the partially unfolding of ParV, the Young's modulus decreased at pH 9.0 or in the presence of EDTA (Ethylene Diamine Tetraacetic Acid), moreover, because partially unfolded ParV can be further completely unfolded due to the mechanically rupture of ester bond, leading to the observed hysteresis of the stretching and relaxation traces of the hydrogels, which is in line with single-molecule force spectroscopy experiments. These results display a new avenue for designing pH- or calcium-responsive hydrogels based on proteins and demonstrate the relationship between the mechanical properties of single molecules and macroscopic hydrogel networks.

Effects of Iron-Peptides Chelate Nanoliposomes on Iron Supplementation in Rats.

The objective of this study was to investigate the effects of iron nanoliposomes on iron supplementation and toxicity in SD rats induced by a low-iron diet. The size and infrared spectroscopy of a liposomal oral delivery system were investigated. The particle size of nanoliposomes embedded with chelates was increased. Infrared spectra proved that peptides-iron and blank nanoliposomes were bonded by interaction forces, including the fracture of hydrogen bonds, C = C bonds, hydrophobic interaction, and C-N bonds. We found that iron supplementation chelates had a certain protective effect on viscera after being embedded by nanoliposomes. After 10 days of treatment, the concentration of hemoglobin could be gradually increased. Nanoliposome encapsulated peptides-iron has a better effect than other groups. At the same time, SOD, MDA, and CAT reached normal levels after 20 days. Histological results showed that the sections of the nanoliposomes groups were clearer than those of the other groups. There was a little inflammation in the liver without obvious pathological changes, which also proved that the iron chelates embedded by nanoliposomes had no obvious side effects on iron supplementation in rats. Nanoliposome encapsulated peptides-iron has a small side effect and a significant curative effect of iron supplementation. It maybe has a good application prospect in the clinical medical field.

Physicochemical, digestive and rheological properties of protein from tuna by subcritical dimethyl ether: Focus on process-related indexes.

The process-related physicochemical, digestive and rheological properties of protein prepared by subcritical dimethyl ether extraction (SDEE) were comprehensively investigated and compared with those obtained by pH-shift, to study the industrial potential of SDEE. Two different materials from tuna (meat and liver) were studied in parallel, and SDEE had similar effects on the proteins in them. The protein component was almost unchanged before and after SDEE, while the content of water-soluble protein and alkali-soluble protein was substantially reduced and increased after pH-shift, respectively. We also found that SDEE had superior ability to pH-shift to conserve light metals, remove lipids and heavy metals, and maintain protein structure. Furthermore, SDEE-produced protein powders were easier for humans to digest, and their gelation and emulsification were also superior to those prepared by pH-shift. The aforementioned results suggest that SDEE can remove more impurities, and the obtained protein has outstanding potential in industrial applications.

Extraction of oil from wet Antarctic krill (Euphausia superba) using a subcritical dimethyl ether method.

In this study, a novel method for obtaining high-quality krill oil from wet Antarctic krill by using subcritical dimethyl ether (SDE) was proposed. A response surface design was used to obtain the best SDE extraction parameters. The optimum extraction efficiency of 93.77 ± 0.92% was obtained at a stirring speed of 1030 rpm, temperature of 47 °C and dynamic extraction time of 90 min. Compared with n-hexane, ethanol, supercritical CO2 and subcritical n-butane extraction, the krill oil extracted by SDE exhibited low peroxide values (1.46 ± 0.26 mmol kg-1), high astaxanthin (218.06 ± 4.74 mg kg-1), phosphatidylcholine (PC) (33.95 ± 0.65%), and phosphatidylethanolamine (PE) (11.67 ± 0.23%) content. Moreover, krill oil extracted by SDE has high levels of EPA (16.38 ± 0.05%) and DHA (7.91 ± 0.07%). SDE extraction proved to be an efficient and safe method for extraction of quality krill oil from wet Antarctic krill, and it could be a promising method for oil extraction in wet food in future.

Extraction of oil from high-moisture tuna liver by subcritical dimethyl ether: feasibility and optimization by the response surface method.

The purpose of this paper is to explore the possibilities of subcritical dimethyl ether extraction (SDME) of oil from tuna liver with high-moisture content. The results showed that the oil and water were successfully co-extracted from the liver, and could be easily separated by centrifugation. In addition, the response surface method was employed to optimize the process parameters of SDME, including temperature/pressure, time and stirring speed. It was predicted that a temperature/pressure of 42/0.80 °C/MPa, time of 50 min and stirring speed of 925 rpm were the optimum within the experimental ranges, with an oil yield of 17.46 ± 0.23%. Furthermore, supercritical carbon dioxide extraction (SC-CO2) was studied comparatively. Only minor differences were observed between the oils extracted by SDME and SC-CO2, which indicated the high-quality of the SDME-oil. With no freeze-drying procedure and the relatively low pressure used in SDME, SDME could be a promising technique for extraction of marine fish liver oil.