| Agar is widely used in food,medicine and daily chemical fields because of its good gel properties.However,agar has poor solubility due to its large molecular weight like many macromolecular polysaccharides,which limits its application range.Therefore,it is necessary to prepare a low-temperature instant agar with a certain gel strength to expand the application range and effect of agar.In this paper,the effects of three modification methods on the physicochemical properties such as the solubility and gel properties of agar were studied,and the preparation method of carboxymethylation modification for low-temperature instant agar was determined.Carboxymethyl agar with different substitution degrees and physicochemical properties was efficiently synthesized by microwave-assisted technology,and the differences in physicochemical properties of carboxymethyl agar with different substitution degrees and preparation methods were analyzed.The application effect of carboxymethyl agar in tilapia surimi was further studied.This study aims to provide technical basis for the development of quick soluble agar preparation technology and its product development.The main research contents and results are as follows:(1)The effects of three modification methods on the physicochemical properties of agar were compared,and the carboxymethylation modification was determined as the optimal method.The agar was modified by carboxymethylation,hydrogen peroxide oxidation and hydroxypropylation.The solubility,color,gel transparency,gel texture,IR molecular structure and thermal stability of agar before and after modification were compared to study the effects of different modification methods on the physicochemical properties of agar.The results showed that after carboxymethylation and hydroxypropylation,the dissolution temperature,gel temperature,gel re-dissolution temperature and gel strength of agar decreased significantly(p<0.05),and the soft elasticity and water holding capacity of agar gel increased.Oxidation significantly increased the gel strength(p<0.05),from 984 g/cm~2 to 1 463 g/cm~2.Oxidation modification and hydroxypropylation modification significantly increased the whiteness of agar(p<0.05),while carboxymethylation modification decreased the whiteness of agar(p<0.05).The transparency of agar gel was significantly improved by the three modification methods(p<0.05).Carboxymethylation reduced the thermal stability of agar,oxidation and hydroxypropylation improved the thermal stability of agar.Three modification methods can change the physical and chemical properties of agar in varying degrees,and the effect of carboxymethylation is the most obvious.(2)In order to further improve the carboxymethyl reaction efficiency,microwave-assisted and conventional modification technologies of carboxymethyl agar and their effects on physicochemical properties and microstructure were compared and studied.The effects of microwave power,reaction time,temperature,molar ratio and reaction medium on the degree of carboxymethyl substitution were studied by microwave-assisted method.The results showed that when other reaction conditions were the same,the time required for preparing carboxymethyl agar with the same degree of substitution was shortened from 240 min to 45 min under 400 W microwave irradiation.The physical and chemical properties of the agar prepared by the two methods were determined.It was found that there was no significant difference in the dissolution temperature,color and texture characteristics between the two methods,but the gel strength of the carboxymethyl agar prepared by microwave-assisted method was higher than that of the conventional method.With the increase of substitution degree,the dissolution temperature and whiteness of carboxymethyl agar gradually decreased,while the gel transparency showed an upward trend,and the gel texture became soft and elastic.Zeta potential and particle size decreased with increasing degree of substitution.The molecular weight of carboxymethyl agarose was significantly affected by microwave-assisted method,and the higher the degree of substitution,the more serious the cleavage of the molecular.The SEM results showed that the surface of carboxymethylated agarose molecules became rough and porous.(3)In order to broaden the application of low temperature fast dissolving agar,the application of carboxymethyl agar in tilapia surimi was studied.With tilapia surimi as raw material,the gel properties,chemical force,protein composition,infrared spectrum and scanning electron microscope microstructure of surimi were investigated by adding different doses of carboxymethyl agar.The results showed that the gel strength of surimi increased first and then decreased with the increase of carboxymethyl agar content,but the effect on the water holding capacity of surimi was not significant.The addition of 1.0%?2.0%carboxymethyl agar improved the gel properties of surimi to varying degrees.The results of protein chemical interaction showed that carboxymethyl agar had a great influence on the ionic bond and hydrophobic interaction between surimi proteins.With the increase of addition amount,the ionic bond decreased,and the hydrophobic interaction increased first and then decreased.Carboxymethyl agarose can participate in the cross-linking of actin,making the?-helix structure of surimi protein transform to?-turn structure;SEM images showed that the microstructure of the composite surimi gel was more closely and orderly than that of the control group.Carboxymethyl agarose after swelling played a role in filling the surimi gel results. |
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