The Construction of a Low-Odor Background Model of Silver Carp (Hypophthalmichthys molitrix) Surimi

In the Healthy China Strategy context, fish are increasingly in demand as a source of high-quality protein. Silver carp (Hypophthalmichthys molitrix) is a resource-rich and highly productive freshwater fish species found in China that is not edible raw or cooked in its original form due to its many boney spines. However, due to its advantages of being low-cost, low in fat, and high in protein, it is an ideal choice for surimi production. Currently, it is widely used in the industrial production of surimi products. The development of the freshwater surimi industry can significantly improve the added value of freshwater fish utilization, which has attracted extensive attention. Freshwater surimi is high in protein and low in fat and has a smooth and delicate taste, making it extremely popular with consumers. It has a high output, low price, is growing in demand, and is gradually being accepted throughout domestic and foreign markets. It has also driven the development of some related industries and produced significant economic and social benefits. As domestic consumers experience improved living standards and a faster pace of work, premade dishes containing surimi products as well as recreational snack surimi products with increased shelf-life are more attractive, as they save the consumer processing time, are enjoyed by the consumer, and meet their nutritional demands, affording these products great market potential. With the development of surimi products and related industries, specific requirements are being put forward for its production. Although China supplanted Japan as the largest producer of surimi products worldwide in 2006, ushering in a period of nearly 10 years of high production growth, the annual production of surimi products in China since 2014 has stagnated or even slightly decreased. Moreover, the surimi industry has entered a bottleneck period for quality enhancement caused by the expansion of quantity. The fishy odor of freshwater surimi is one of the industrial problems that affect the quality and efficiency of surimi. The flavor of surimi products (such as fish balls, fish intestines, fish cakes, and others in hot pot) has become one of the quality attributes that consumers are extremely concerned about. However, the adsorption and release laws of key odor-active substances are still unclear. There are existing research technologies for surimi odor, mainly including instrumental analysis (gas chromatography-mass spectrum, gas chromatography-olfactometry, gas chromatography-olfactometry- mass spectrum, electronic nose technology, etc.), sensomics analysis (odor activity value (OAV), aroma extract dilution analysis, odor recombination, odor omission test, etc.), and enzyme-linked immunosorbent assay. The research objects of odor sensory experiments are mostly rice wine, oil, vegetables, fruits, and fungi. Moreover, present odor research is mainly carried out in a prepared solution, mainly using odor recombination of a liquid simulation system, which is different from the interaction between the real odor active substance-solid surimi. Therefore, constructing an odor model based on solid surimi is necessary to better simulate the sensory characteristics of surimi. To build an odor model based on solid surimi, an odorless or low-odor surimi background model must be established in order to investigate the interaction between various odor components and surimi. There are several fishy substances and complex components in freshwater fish and surimi products, including aldehydes, alcohols, ketones, esters, sulfur compounds, nitrogen compounds, and alkanes.At present, most studies on rinsing surimi reported worldwide are based on how to better apply it to the food system, ignoring interactions between components in the complex system of surimi, which creates certain limitations in establishing a background model of surimi. Therefore, salt, salt-alcohol, acid, alkali, and other rinsing media were selected in this study, which was not limited to food systems. By comparing the removal effects of different rinsing media on the odor residue of surimi, an odorless or low-odor background model of surimi could be constructed. Here, the effect of different rinsing media on the odor residue of a surimi background model was studied. Specific rinsing media were as follows: 0.5% NaCl (W/W) + 0.35% Na2CO3 (W/W) + 4.0% C2H5OH (W/W) solution (group A), 0.5% NaCl (W/W) + 0.35% Na2CO3 solution (group B), 0.5% CaCl2 (W/W) + 0.35% Na2CO3 (W/W) + 4.0% C2H5OH (V/W) solution (group C), 0.5% CaCl2 (W/W) + 0.35% Na2CO3 (W/W) solution (group D), 1% NaCl (W/W) + 1% Na2CO3 (W/W) + 4.0% C2H5OH (V/W) solution (group E), 1% NaCl (W/W) + 1% Na2CO3 (W/W) solution (group F), 1 mol/L HCl solution (group G), and 1 mol/L NaOH solution (group H), respectively. The results showed that SPME-GC-MS detected 65 volatile compounds in silver carp surimi, including 22 aldehydes, 13 alcohols, 9 ketones, and 7 hydrocarbons, among which the contents of aldehydes and alcohols were high, which had a major contribution to the odor of silver carp surimi. A total of 18 odor-active substances were detected by the OAV (≥1) method, which helped illustrate that odor-active compounds contribute to the overall odor of surimi. After treatment with eight kinds of rinsing media, the residual amount of the odor-active substances in the silver carp surimi was washed or released to varying degrees, affecting the sample's overall odor contribution. The rinsed surimi samples contained 6,8,7,9,6,12,9, and 9 odor active compounds and residual rates of volatile odor compounds were (0.380±0.120)%, (0.610±0.086)%, (0.280±0.033)%, (0.480±0.037)%, (0.150±0.018)%, (4.330±0.160)%, (18.680±0.081)%, and (0.490±0.003)%, respectively. According to the SPME-GC-MS analysis results, due to the synergistic effect of ethanol, the content of volatile compounds detected in group E was the lowest, the total residual amount of odor-active compounds was reduced to (6.57±0.77) μg/kg, and the total residue rate was only 0.15%. Meanwhile, the total OAV decreased to 2.52±0.25, there were 17 odor-active substances with an OAV<1, and the OAV of nonanal was only 1.34±0.05, which could establish a low-odor background model of surimi. Furthermore, electronic nose and sensory evaluations distinguished the overall odor characteristics between different rinsed samples and fresh surimi.This study took silver carp surimi as the research object and studied the influence of volatile odor compounds and salts, salt-alcohols, acids, alkalis, and other rinsing media in surimi on the residual rate of odor substances through SPME-GC-MS, electronic nose, and sensory evaluation methods, which will significantly contribute to the establishment of an odorless or low-odor solid surimi model and provide a novel idea for sensory analysis.