# Preparation and Characterization of Flavored Sauces from Chinese Mitten Crab Processing By-Products
## 1 Introduction  
The Chinese mitten crab (_Eriocheir Sinensis_), which is primarily found in North Asia and the Thames Valley region, is a significant freshwater economic crab in China [1]. Due to its detectable meat, high protein content, complete and optimal amino acid composition, and a wide variety of fatty acids, minerals, and vitamins that are crucial for human metabolism, the Chinese mitten crab has a high nutritional value in the aquaculture business [2]. According to the statistical report of the Chinese Ministry of Agriculture, the production of Chinese mitten crab was 808,000 tons in 2021 [3]. The extraction of crab roe is one of the important processing methods for crabs, and the processing of crabs (crab roe processing) produces a large number of by-products, including crab legs and bodies, which account for about 65% of the weight of the crab. As a result, the comprehensive utilization of the large number of by-products generated during processing is becoming increasingly urgent.  
Studies have shown that the by-products of Chinese mitten crab contain nutrients, such as protein (15-30%), minerals (30-50%), chitin (15-30%), fat (1-10%), and rich vitamins [4]. Currently, research on Chinese mitten crab by-products is primarily concentrated on chitin extraction; the utilization of other components has not received attention. Making maximum use of the protein and lipid-based components in crab by-products to generate sauces is, thus, a crucial step toward developing high-value biotransformation and the recycling of crab by-products.  
In the process of the green biotransformation of aquatic by-products, the demand for seafood seasonings produced by extraction, fermentation, and enzymatic digestion has continued to grow in recent years. Compared with extraction and fermentation methods, enzymatic digestion is an important tool for modernizing the production of seafood seasonings because of its simplicity, efficiency, and ease of control [5]. However, the enzymatic digestion of crab by-products is often harsh, lacking in freshness and mellowness, and deficient in overall flavor. The Maillard reaction could be employed to solve these problems. Under the appropriate reaction conditions, the Maillard reaction can remove the bitterness while also removing other unpleasant flavors [6]. The Maillard reaction has been widely used in the preparation of meat seafood seasonings, such as the Maillard reaction system, composed of blue bass, scallop, and other seafood enzymatic hydrolysis products, and the reduction of sugar to prepare rich seafood seasonings [7; 8]. However, as peptides and proteins are practically incapable of Maillard reactions, and most Maillard reactions occur when they are rich in free amino acids, good enzymatic digestion of crab by-products is required for the taste enhancement process. At present, the by-products of Chinese mitten crab have been used in the extraction of chitin and its derivatives and the production of feed, and there are few reports on the preparation of seasonings with the by-products of crab [4]. Moreover, there are few reports on the systematic study and evaluation of the effects of the enzymatic hydrolysis decoupled Maillard reaction on aquatic sauces.  
In this study, two kinds of sauces were created from two types of by-products, utilizing enzymatic digestion and flavor enhancement techniques based on the Maillard reaction. These sauces were then objectively assessed using current scientific analytical methodologies. The goal was to find a novel, effective approach to using crab processing by-products, increase their overall worth, and offer theoretical backing for the high-value utilization of crab sauces.