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Fish sperm extracts have been shown to have various activities, but it has not been effectively developed and utilized at present due to the lack of effective methods for preparing edible grade products. This study proposed a method for preparing edible fish sperm DNA from Alaska pollock (PSD) and evaluated the hepatoprotective effect of the extracted DNA. Firstly, the preparation conditions of fish sperm DNA were optimized by response surface methodology. Under the ideal conditions that the ratio of solid to liquid was 3:1, the pH of extractant was 7.5, the purified solvent was saturated sodium carbonate solution and absolute ethanol was twice the volume of purified solvent, the yield of PSD was (13.657 ± 0.577) µg/mg. To evaluate the liver protective effects of the extracted DNA, the digestion products by three digestion enzymes (pepsin, DNase I and DNase II) compared using an alcohol-induced HepG2 cell model. The DNase I hydrolysis product was more effective in preventing cell alcohol damage, as shown by reducing the content of lipid peroxides. Transcriptomics and metabolomics data revealed that the DNase I hydrolysis product activated the Nrf2/HO-1 pathway through the PI3K/Akt signaling pathway and regulated abnormal lipid synthesis through the steroidogenic pathway. This study will provide an important basis for the evaluation and analysis of the hepatoprotective effect of fish sperm DNA in vivo. Overall, our findings will promote the comprehensive utilization of fish sperm and other aquatic wastes, and provide scientific guidance for the development of functional nucleic acid foods. [ABSTRACT FROM AUTHOR]

In this study, proteins were prepared from Schizochytrium pombe residue after oil extraction using isoelectric point precipitation, and their physicochemical and emulsifying properties were investigated. Our objective was to assess the suitability of these proteins for functional ingredient applications. Through a one-way experiment and optimization using response surface design, the effects of time, temperature, pH, and the material–liquid ratio of NaOH alkaline extraction were explored. The isoelectric point is verified by isoelectric point precipitation; the results revealed that crude protein from Schizochytrium (SCP) is minimally soluble at pH 4.2. Compared with whey protein (WP), it promotes better emulsion stability through the emulsification test. This study suggests that Schizochytrium oil-processing byproducts represent a promising source of protein, with potential applications as functional ingredients, offering implications for the usage of these byproducts in various industries. [ABSTRACT FROM AUTHOR]

In this study, proteins were prepared from Schizochytrium pombe residue after oil extraction using isoelectric point precipitation, and their physicochemical and emulsifying properties were investigated. Our objective was to assess the suitability of these proteins for functional ingredient applications. Through a one-way experiment and optimization using response surface design, the effects of time, temperature, pH, and the material–liquid ratio of NaOH alkaline extraction were explored. The isoelectric point is verified by isoelectric point precipitation; the results revealed that crude protein from Schizochytrium (SCP) is minimally soluble at pH 4.2. Compared with whey protein (WP), it promotes better emulsion stability through the emulsification test. This study suggests that Schizochytrium oil-processing byproducts represent a promising source of protein, with potential applications as functional ingredients, offering implications for the usage of these byproducts in various industries.

Proteins in either a native or denatured conformation often aggregate at an isoelectric point (pI), a phenomenon known as pI precipitation. However, only a few studies have addressed the role of pI precipitation in amyloid formation, the crystal-like aggregation of denatured proteins. We found that α-synuclein, an intrinsically disordered protein of 140 amino acid residues associated with Parkinson's disease, formed amyloid fibrils at pI (= 4.7) under the low-sodium phosphate conditions. Although α-synuclein also formed amyloid fibrils at a wide pH range under high concentrations of sodium phosphate, the pI-amyloid formation was characterized by marked amyloid-specific thioflavin T fluorescence and clear fibrillar morphology, indicating highly ordered structures. Analysis by heteronuclear NMR in combination with principal component analysis suggested that amyloid formation under low and high phosphate conditions occurred by distinct mechanisms. The former was likely to be caused by the intermolecular attractive charge-charge interactions, where α-synuclein has +17 and −17 charges even with the zero net charge. On the other hand, the latter was caused by the phosphate-dependent salting-out effects. pI-amyloid formation may play a role in the membrane-dependent amyloid formation of α-synuclein, where the negatively charged membrane surface reduces the local pH to pI and the membrane hydrophobic environment enhances electrostatic interactions. The results extend the supersaturation-limited mechanism of amyloid formation: Amyloid fibrils are formed under a variety of conditions of decreased solubility of denatured proteins triggered by the breakdown of supersaturation.