Structural characterization, antioxidant activity, and immunological activity in vitro of polysaccharides from fruiting bodies of Suillus granulatus

Chemical Compounds, Bioactivities, and Potential Applications of the Mushroom Species of Genus Suillus (Agaricomycetes): A Review

The genus Suillus, also known as "Song mo," falls under the order Boletales and consists of various higher fungi. It establishes mycorrhizae primarily with pine trees and has a good taste and medicinal values. Herein, we reviewed the chemical compounds present in the genus Suillus, including polysaccharides, steroids, phenols, polyprenyl phenol derivatives, fatty acids, organic acids, and amino acids, and their reported bioactivities and potential applications. This review aims to promote the utilization of the resources belonging to the genus Suillus and serves as a theoretical basis for their future studies and clinical applications.

Preparation, chemical structure, and immunostimulatory activity of a water-soluble heteropolysaccharide from Suillus granulatus fruiting bodies

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A water-soluble heteropolysaccharide (SGP2-1) was purified from Suillus granulatus.

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SGP2-1with Mw of 150.75 kDa had the (1 → 4)-α-Glcp backbone structure.

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SGP2-1 could be recognized by toll-like receptor 2 in RAW 264.7 macrophages.

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SGP2-1 enhanced pinocytic capacity and promoted ROS, NO, and cytokine production.

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SGP2-1 exerted immunoregulatory activity through MAPKs, PI3K/Akt and NF-κB pathways.

A water-soluble heteropolysaccharide (SGP2-1) was purified from Suillus granulatus fruiting bodies by anion-exchange chromatography and gel permeation chromatography. The structural characteristics were analyzed by high-performance gel permeation chromatography, high-performance liquid chromatography, Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry, and nuclear magnetic resonance spectroscopy. The immunostimulatory activity was investigated using RAW 264.7 macrophages. Results showed that SGP2-1 with weight average molecular weight of 150.75 kDa was composed of mannose, glucose, and xylose. The backbone of SGP2-1 was mainly composed of → 4)-α-Glcp-(1→, and the terminal group α-d-Glcp → was linked to the main chain by O-6 position. SGP2-1 could significantly enhance pinocytic capacity, reactive oxygen species production, and cytokines secretion. SGP2-1 exerted immunomodulatory effects through interacting with toll-like receptor 2, and activating mitogen-activated protein kinase, phosphatidylinositol-3-kinase/protein kinase B, and nuclear factor-kappa B signaling pathways. These findings indicated that SGP2-1 could be explored as a potential immunomodulatory agent for application in functional foods.

Effects of drying temperature on umami taste and aroma profiles of mushrooms (Suillus granulatus)

Temperature is one of the most important factors for drying edible mushrooms. To evaluate the effects of different hot-air drying (HAD) temperatures on the umami taste and aroma profile of Suillus granulatus (S. granulatus) mushrooms, we measured umami substances and volatile compounds of S. granulatus dried at 40°C, 50°C, 60°C, 70°C, and 80°C. Results showed that when dried at 60°C, S. granulatus exhibited significantly higher (p < 0.05) equivalent umami concentration, taste activity values of glutamic acid (Glu) and 5'-guanosine monophosphate (5'-GMP), and electronic tongue umami sensory scores. The results identified a total of 71 volatile components of which geranylacetone, benzaldehyde, phenylethyl alcohol, and 3-methylbutanoic acid were the dominant compounds. Sensory evaluation and relative odor activity values (ROAVs) revealed that 16 volatile compounds were the key volatile organic compounds contributing mushroom-like and sweet odor to the overall aroma of S. granulatus; these included 1-octen-3-ol (ROAV: 15.11-62.06) and ethyl phenylacetate (ROAV: 13.62-79.11). The drying temperature changed the aroma profile of S. granulatus. Furthermore, the mushroom dried at 60°C had a more desirable mushroom-like and almond odor. It was, therefore, proposed that HAD at 60°C was optimal for retaining a pleasant flavor in S. granulatus. This study provides a theoretical basis for the optimal drying condition selection for the mushroom processing industry. PRACTICAL APPLICATION: Hot-air drying at 60°C can significantly retain the flavor of S. granulatus and is an optimal temperature for mushroom drying.

Polysaccharides production from soybean curd residue via Morchella esculenta

To minimize the serious environmental pollution caused by food byproducts, soybean curd residue was used as the substrate to ferment polysaccharides by Morchella esculenta. Water-soluble crude polysaccharides (CMP) were purified by different gradient concentrations (30%, 60%, and 90%) of ethanol into three precipitation fractions. The experimental results indicated that the precipitated polysaccharides by the ethanol concentration of 60% (PMP) had the highest purity, containing rhamnose, arabinose, xylose, mannose, glucose, and galactose, with the molar ratio of 0.08:0.25:0.16:0.07:0.28:1.00. The physicochemical properties were revealed by SEM, AFM, FTIR, NMR, and Congo red test. Furthermore, the measurement of antioxidant activities in vitro demonstrated that PMP exhibited higher antioxidant capacities with the dose-dependent manner than CMP and polysaccharides from unfermented soybean curd (USP). Overall, the results suggested that PMP had attractive functional activity which could be potentially utilized in functional food industries. PRACTICAL APPLICATIONS: The polysaccharides from fungi sources are increasingly being used in functional food and pharmaceutical industry. In allusion to the problem of polysaccharides fermented by edible fungi, such as low yield, high cost, and hard to controllable. Soybean curd residue (SCR), a food waste, has been successfully used for the production of polysaccharides and graded ethanol was used to enhance polysaccharides production, lower the difficulty and homologous costs of purity. The results indicated that the purified polysaccharides displayed excellent antioxidant activities on scavenging DPPH and hydroxyl radicals. The outcomes of this work can provide technical support for comprehensive utilization of SCR and references for promotion and application of polysaccharides fermented from SCR via Morchella esculenta in food and medicine fields.