| China is the largest producer of shiitake mushrooms in the world.In the process of shiitake mushrooms picking,there are a large number of inferior by-products,which are basically the same as commercial shiitake mushrooms in chemical composition.However,these by-products are only used as nitrogen sources of fermented feed,resulting in a great waste of resources.Lentinan has been proved to have high nutritional value,which leads to the neglect of a large number of high-quality edible mushroom proteins in shiitake mushrooms.At the same time,in the extraction process of lentinan,a large amount of shiitake mushrooms protein is only used as fungus residue and has not been reasonably used.In order to reduce the waste of resources and fill the gap in the application research of shiitake mushrooms protein,the protein-polysaccharide complex(PPC)in shiitake mushrooms was obtained by alkali solution and acid precipitation method,and PPC was identified from the perspectives of microstructure,physical and chemical properties,spatial structure and functional characteristics.It was found that PPC formed a special ball-chain structure in aqueous solution.The hydrophobic(protein)and hydrophilic(polysaccharides)structures arranged in turn have excellent oil-water interface migration ability and interface curing ability,and are natural high internal phase emulsions(HIPEs)stabilizers.At the same time,the HIPEs were used to develop a transport system loaded with β-carotene,which significantly improved the storage stability and environmental stability of β-carotene.The main research contents and results are as follows:Structure identification and physicochemical properties analysis of PPC.PPC was isolated by alkali dissolution and acid precipitation,with a protein content of 82.07%(dry basis)and a polysaccharide content of 12.52%(dry basis).It was observed by frozen scanning electron microscope that PPC formed a unique ball-chain structure in aqueous solution.Through the experiment of proteolysis,it was found that the ball structure was protein(300nm)and the chain structure(50 nm)was polysaccharide.Zeta potential analysis showed that the isoelectric point of PPC was between 4.0 and 5.0.When p H was near the isoelectric point,the ball-chain structure of PPC disappeared and PPC aggregated into large particles.When p H<3.0,PPC formed particle structure and chain structure disappeared.Circular dichroism spectra,endogenous fluorescence and surface hydrophobicity indicated that the polarity of the microenvironment of PPC increased with the increase of p H.In addition,due to the alternating arrangement of hydrophilic(polysaccharide)and hydrophobic(protein)structures,PPC is an ideal oil-water interface stabilizer with a three-phase contact angle of 92.1°.The structural mechanism of PPC stabilizing HIPEs.The microstructure of HIPEs was observed by confocal laser focusing microscope.The results showed that the proteins in PPC formed a complete interface film on the surface of oil-water interface,while polysaccharides formed a dense network structure between oil droplets,which jointly maintained the stability of HIPEs.Through particle size analysis and rheological experiments,it was found that the gel performance of HIPEs was the best when p H 7.0,3%(w/v)PPC concentration and 80%oil phase volume fraction(φ)were used.Under this condition,HIPEs had both fluidity and gelation,and could be used as a 3D printing substrate to print various kinds of graphics with high structural resolution.The results of thermal stability and storage stability showed that after HIPEs were heated at 90 ℃ for 30 min and stored for 30 days,the gel structure of the emulsion remained stable and the particle size distribution changed little.A HIPEs delivery system loaded with β-carotene was developed.β-carotene was dissolved in peanut oil,and loaded β-carotene hips were prepared by PPC under the conditions of p H 7.0,3%(w/v)and 80% of φ.The load of β-carotene was 0.01% to 0.4%controllable.During the two-month storage,the emulsion maintained a complete gel structure and no obvious sensory change of β-carotene.The accelerated test was carried out by illumination,hydrogen peroxide and heating.The results showed that with the increase of PPC concentration(1%～3%),the retention rate of β-carotene increased,and the protective effect was better than that of small molecular surfactant Tween 80.In summary,this study identified the microstructure,physical and chemical properties,spatial structure and functional characteristics of PPC in shiitake mushrooms.Taking advantage of the excellent performance of PPC in oil-water interface stability,the stable HIPEs were developed,which were used as a carrier system for the embedding and protection of β-carotene.The study will provide research ideas and enrich theoretical basis for the comprehensive utilization and high-value production of by-products of shiitake mushrooms. |
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