To analyze umami peptides in the water extract of straw mushroom, fractionation guided by sensory evaluation and an electronic tongue of the extract was performed through sequential ultrafiltration and gel filtration chromatography. Fraction F1, which was found to make the greatest contribution to the overall umami, was further fractionated by reversed-phase high performance liquid chromatography combined with principal component analysis. Subfraction F1-a was found to have similar taste to straw mushroom. In addition the umami peptides from F1-a were identified by ultra-high performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry. The synthetic counterparts of the identified umami peptides were evaluated for their taste characteristics through sensory evaluation and electronic tongue analysis. The results showed that the umami peptides were identified as Asp-Asp-Cys-Pro-Asp-Lys, Leu-Val-Asp-Lys-Pro-Arg, Gln-Ala-Asp-Lys-Arg-Lys, and Asp-Thr-Phe-Asn-Asp-Lys, with umami taste threshold of 0.10, 0.33, 0.42, and 0.17 mg/mL, respectively. The flavor characteristics of these four umami peptides were attributed to the formation of specific structures by amino acids through peptide bonds. Among them, the umami peptide Asp-Asp-Cys-Pro-Asp-Lys was the most effective in enhancing the umami taste of monosodium glutamate (MSG) solution at a concentration of 20 mg/mL.

Flammulina velutipes polysaccharide (FVP) was added to soy protein isolate (SPI) hydrogels and subjected to heat treatment to improve the gel strength, water-holding capacity and thermal stability. The stability of FVP-SPI hydrogels was further analyzed in terms of their secondary and tertiary structures and intermolecular forces. The results showed that heat treatment and addition of FVPsignificantly improved the water-holding capacity of SPI hydrogels, and increased the enthalpy change of denaturation (ΔH) by 25.46%, thereby significantly improving hydrogel stability. Hydrophobic interactions, disulfide bonds and electrostatic interactions were the major driving forces for the formation of heat-induced FVP-SPI hydrogels. The addition of FVPimproved the electrostatic interactions and caused transformation of α-helix into β-sheets in the hydrogels, surface exposure of the tryptophan residues in SPI and enhanced hydrophobicity. The enhancement of SPI hydrogels by FVPprovides a reference for the development and application of SPI hydrogels.

Hot water extraction (H), ultrasonic extraction (U) or ultrasonic-assisted hot water extraction (U + H) was used to extract polysaccharides from Pleurotus eryngii, which were then evaluated for physicochemical and structural characteristics and immunomodulatory activity. Results indicated that all three polysaccharides showed absorption peaks characteristic of polysaccharides. The polysaccharide prepared by ultrasonic extraction (U) was composed of mannose, glucose, galactose, xylose and fucose in a molar ratio of 8.60 : 80.90 : 7.41 : 2.68 : 0.57. The polysaccharide obtained by hot water extraction (H) was composed of mannose, glucose, galactose, xylose and fucose in a molar ratio of 9.36 : 79.72 : 8.18 : 2.60 : 0.42. The polysaccharide obtained by ultrasonic-assisted hot water extraction (U + H) was composed of mannose, glucose, galactose, xylose and fucose in a molar ratio of 6.75 : 82.66 : 7.14 : 2.30 : 1.12. The molecular mass distribution of U consisted of 13152 (83.61%), 281 (3.02%), and 53 kDa (13.37%). The molecular mass distribution of H consisted of 10232 (93.15%), 281 (1.94%) and 61 kDa (4.90%). The molecular mass distribution of U + H consisted of 10471 (98.59%), and 60 kDa (1.40%). The results of cell counting kit-8 (CCK-8) showed that the polysaccharide extracted by ultrasonic extraction at low concentrations of 5 and 10 μg/mL had a slightly toxic effect due to the degradation of large molecular mass polysaccharide fractions, while the other concentrations of U and all concentrations of H and U + H had no significant toxicity to macrophages. Neutral red test results showed that the three polysaccharides could enhance the phagocytic activity of macrophages significantly but differently (P < 0.05). The phagocytic rate of macrophages treated with U was 193.45% compared to 163.64% and 187.62% with H and U + H, respectively. This study provides a theoretical foundation for the directional preparation of P. eryngii polysaccharides with specific functional activities.

Peanut is an important oilseed crop, susceptible to quality deterioration under harsh storage conditions because of its high oil content. In order to explore the effects of different storage temperatures on peanut quality under normal humidity conditions, in-shell peanuts were stored at 15, 25 or 35 ℃ for up to 30 weeks. Indicators of lipid oxidation: acid value (AV), peroxide value (PV), and malondialdehyde (MDA) content; indicators of protein oxidation: carbonyl, sulfhydryl, disulfide bond contents; and the activities of oxidation-related enzymes: lipase (LPS), lipoxygenase (LOX) and peroxidase (POD) were tested. The results showed that the AV increased from (0.48 ± 0.01) to (1.78 ± 0.02) mg/g and the carbonyl content from (3.19 ± 0.24) to (118.61 ± 6.41) μmol/g over the storage period at 25 ℃. Meanwhile, at the end of storage, the highest lipase and lipoxygenase activities were observed in the sample stored at 35 ℃, which were (59.00 ± 1.70) and (1287.17 ± 98.45) U/g, respectively; the AV increased from (0.48 ± 0.01) to (3.15 ± 0.10) mg/g, the MDA content from 23.03 to 1039.63 nmol/g, and the carbonyl content from (3.19 ± 0.24) to (124.86 ± 3.07) μmol/g. At 15 ℃, the highest lipase and lipoxygenase activities were only (41.60 ± 1.23) and (1036.14 ± 34.49) U/g, respectively and the peroxide and carbonyl contents increased by 18.4 and 17.1 times after 30 days of storage, respectively, reaching much lower levels than those at the other temperatures. In conclusion, storage at normal humidity and at 15 ℃ can effectively suppress the oxidase activity at a low level at all time points, resulting in a low degree of oxidation of peanut oil and protein, while high ambient temperature increases the oxidase activity, and the higher the temperature, the higher the enzyme activity, and the higher the contents of primary and secondary oxidation products in oil, indicating a higher degree of peroxidation. Moreover, protein oxidation also occurs due to the oxidation of amino acid side chains and protein structural damage, ultimately leading to a decline in peanut quality.

Soy protein isolate (SPI) is a commercial protein with balanced amino acids, while the poor solubility impedes its use in traditional foods. To overcome the problem, the complex coacervation of SPI/Flammulina velutipes polysaccharide (FVP) were investigated. Initial results revealed that the suitable amounts of FVP contributed to reducing the turbidity of SPI solution. Under electrostatic interaction, the formation of SPI/FVP coacervates were spontaneous and went through a nucleation and growth process. Low salt concentration (C_NaCl = 10, 50 mmol/L) led to an increase in the critical pH values (pHc, pH_φ1) while the critical pH values decreased when C_NaCl ≥ 100 mmol/L. The concentration of NaCl ions increased the content of α-helix. With the increase of FVP, the critical pH values decreased and the content of β-sheet increased through electrostatic interaction. At SPI/FVP ratio of 10:1 and 15:1, the complex coacervation of SPI/FVP were saturated, and the coacervates had the same storage modulus value. SPI/FVP coacervates exhibited solid-like properties and presented the strongest storage modulus at C_NaCl = 50 mmol/L. The optimal pH, SPI/FVP ratio and NaCl concentration of complex coacervation were collected, and the coacervates demonstrated a valuable application potential to protect and deliver bioactives and food ingredients.