| The Chinese giant salamander is a traditional food ingredient in China and has great nutritional and medicinal value.The technology for the artificial breeding of commercial giant salamanders is now mature,and the number of breeding is increasing.To achieve effective use of commercial giant salamander resources,its deep processing technology is a key issue that needs to be addressed.However,there are currently few deep-processed products on the market,and the development of salamander fish mince for leisure food has not yet been reported.This paper firstly assesses the edible quality and nutritional value of fish tofu from different raw materials(crucian carp,silver carp,carp,grass carp and giant salamander)based on the differences in raw materials;secondly,the processing process of giant salamander fish tofu is optimized using response surface testing in order to solve the problems of insufficient gel strength,difficult forming and rough taste during processing;Finally,psyllium husk powder(PHP)is a new food resource that can be used as a fat and gel substitute in the traditional process.Therefore,this study focuses on the systematic investigation of the effect mechanism of PHP-MP composite gel,which provides a theoretical basis for the development of healthy and high-quality leisure salamander fish tofu.The main findings are as follows:(1)Analysis of the textural properties showed that there were significant differences in the textural properties of fish tofu from different raw materials,with giant salamander fish tofu being harder at 755.33 ± 18.76 g,but less elastic,with less gel strength and less pronounced network organization;Secondly,the analysis of free amino acids in fish tofu from different raw materials showed that EAA/TAA was 51.6% and EAA/NEAA was107.0% in giant salamander fish tofu,and according to the FAO/WHO ideal model,the ratio of amino acids in giant salamander fish tofu is more in line with human nutritional requirements,while the two nucleotides(AMP+IMP)that contribute most to freshness in giant salamander fish tofu had the highest content,56.68 ±3.52 mg/100g;Finally,GC-IMS analysis of fish tofu from different raw materials revealed that the key components of the volatile flavour substances of giant salamander fish tofu were dominated by aldehydes and that the aromatic volatile flavour substances of giant salamander fish tofu were more intense compared to other raw materials.(2)The results of water migration showed that with the increase of PHP concentration,the relaxation time of free water(T23)was significantly shortened and the peak area was significantly reduced,and the T23 peak area reached the minimum value at 2% of PHP addition,indicating that the addition of moderate amount of PHP can promote the hydration of mixed gels,eliminate the formation of interconnected water channels,promote the formation of tight gel network of mixed gels,better trap water molecules and increase the water holding capacity of gels.The results of water migration showed that with the increase of PHP concentration,the relaxation time of free water(T23)was significantly shortened and the peak area was significantly reduced,and the T23 peak area reached the minimum value at 2% of PHP addition,indicating that the addition of moderate amount of PHP can promote the hydration of mixed gels,eliminate the formation of interconnected water channels,promote the formation of tight gel network of mixed gels,better trap water molecules and increase the water holding capacity of gels.The optimal process conditions for giant salamander fish tofu were determined by single-factor and response surface optimisation tests,based on the quality of giant salamander minced meat,with the addition of psyllium husk powder(PHP)at 2.0%,soy protein isolate(SPI)at 1.0% and transglutaminase(TGase)at 4.0%.The process validation test and microstructure analysis before and after the optimization showed that the gel strength and textural properties of the fish tofu of giant salamander were significantly improved.(3)Previous experiments have shown that the addition of PHP to salamander fish tofu may promote cross-linking between protein molecules,but the exact mode of action and mechanism of action are unclear.Therefore,different concentrations(0.5%～3.0%)of PHP were added to salamander MP to prepare mixed gels by two-stage heating,and the rheological properties,chemical action,SDS-PAGE,protein secondary structure and water migration were used as evaluation indexes to analyze the effect of PHP addition on salamander MP and its mechanism of action.The results of rheological and chemical interaction force analysis showed that the addition of 1.5%～2.0% PHP could improve the functional properties of MP of giant salamander at low ionic strength;when PHP was added at 2.0%～3.0%,the molecular interaction force of the gel was significantly reduced,indicating that PHP would interfere with the cross-linking of MHC through covalent bonds of ionic,hydrogen and hydrophobic interactions;SDS-PAGE results showed that the addition of PHP promoted the cross-linking and aggregation of protein molecules and facilitated the formation of covalent bonds between promyosin and actin,but this facilitation effect was reduced when PHP was added in excess(>2.5%);The results of the secondary structure analysis of the proteins showed a decrease in α-helix content and an increase in β-fold content at PHP additions of 1.0% to 2.0%,indicating a conversion of the α-helix structure to a β-fold structure and an increase in gel strength,when PHP addition is greater than 2.5%,the content of α-helix and β-fold significantly decreases,while the irregularly coiled structure increases,resulting in irregular aggregation of MP protein and transformation of protein structure from stable to unstable structure;The results of water migration showed that with the increase of PHP concentration,the relaxation time of free water(T23)was significantly shortened and the peak area was significantly reduced,and the T23 peak area reached the minimum value at 2% of PHP addition,indicating that the addition of moderate amount of PHP can promote the hydration of mixed gels,eliminate the formation of interconnected water channels,promote the formation of tight gel network of mixed gels,better trap water molecules and increase the water holding capacity of gels. |
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