Extraction Optimization And Structure Identification Of Phlorotannins And Its Effect On Physical Properties Of Surimi Gel

Phlorotannins is a class of phloroglucinol polymers that are found primarily in brown algae and structural components of cell walls.The alginate polyphenols have various activities such as antioxidative,antibacterial,antiviral,anti-inflammatory,anti-tumor,anticoagulant,anti-diabetic syndrome,and liver protection activity.Therefore,phlorotannins are extracted from brown algae as a natural active ingredient and have great potential for becoming novel drugs and health products.Surimi products are make from seawater or freshwater fish with low value as a raw material are processed with certain elasticity,which is deeply popular by consumers.Some gel enhancers such as polysaccharides and non-muscle proteins are often added as excipients to increase the gel strength of surimi products.Phlorotannins can oxidize proteins and form covalent bonds with them,having the potential as gel enhancers and nutritional improvers for surimi.Therefore,brown algae was selected as the experimental raw material in this study to study the structure of polyphenols in brown algae,and to explore the influence of the addition of phlorotannins on the physical properties of the gel.Sargassum horneri was selected as the highest content of phlorotannins from four brown algae.Ultrasonic-assisted extraction was selected as the optimal extraction method.The extraction conditions of phlorotannins in the algae were optimized.With the yield of phlorotannins,the ultrasonic-assisted extraction method was used to analyze the volume fraction of ethanol,liquid-solid ratio and ultrasonic extraction time by single factor test and response surface analysis.Folin-Ciocalteu method and 2,4-dimethoxybenzaldehyde assay(DMBA method)were used to determine the content of total phenols and phlorotannins in the polyphenols extracts from Sargassum horneri and analyze its relevance.The results showed that the optimum extraction conditions for the response surface test of phlorotannins were:ethanol volume fraction 55%;liquid-solid ratio 42:1 mL/g;ultrasonic extraction time 58 min.Under optimized conditions,the yield of phlorotannins in the Sargassum horneri was25.16±0.34 mg/100g.For the obtained Sargassum horneri phlorotannins extracts,the total phenol yield measured by the Folin-Ciocalteu method was positively correlated with the yield of the phlorotannins measured by the DMBA method.To study the structure of phlorotannins in different brown algae,ethyl acetate extraction of phlorotannins extracts was separated and isolated by the silica gel column,and was identified by liquid chromatography coupled with a time-of-flight mass spectrometer(LC-TOF-MS).The results showed that the Sargassum horneri contained Diphlorethol and Triphlorethol A..To study the effect of phlorotannins extracts on the properties of surimi products,various concentrations of phloroglucinol or copper algae polyphenol extracts were added to the hairtail surimi to determine the physical properties of surimi products.The results showed that the extract of phlorotannins could increase the breaking strength and gel strength of the surimi gel(p<0.05).When the addition amount was 0.05%,0.3%,and 1%,the gel strength of the surimi was increased by 9.08%,18.32%,and 40.49%.It was observed that the extract of the phlorotannins of Sargassum horneri can change the microscopic structure of the surimi gel and form a stable network structure.It was found by electron scanning microscopy that the phlorotannins extracts from the brown algae had a significant effect on the surimi gel.The dielectric constant and dielectric loss of the surimi gel were analyzed using a dielectric constant analyzer.It was found that the phlorotannins extract of the Sargassum horneri can reduce the dielectric constant and dielectric loss of the surimi gel,reflecting the fact that the phlorotannins extract.The material can change the microstructure of the surimi gel and increase the binding force of the water.Analysing the transverse relaxation time using nuclear magnetic resonance technology,it can be seen that adding phlorotannins extract can make the retained water in the surimi more constrained.The degree of freedom decreases.This thesis mainly explores the extraction and identification of phlorotannins and their effects on the gel properties of surimi.The study found that phlorotannins in the Sargassum horneri had a significant effect on the gel of the surimi and improved the gel structure of the surimi,making the trapped water more closely associated with the surimi structure.