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ABSTRACTIn this study, a high-calcium and high-amino acid fish frame hydrolyzate (FFH) was prepared from channel catfish (Ictalurus punetaus) through ultrasound-assisted enzymatic hydrolysis (UAEH). A 4-factor and 3-level Box-Behnken design of response surface methodology was employed to optimize the hydrolysis conditions, where the independent variables were sonication power (W), sonication time (min), enzyme activity (U) and water-substrate ratio (v/w). The degree of hydrolysis (DH) and soluble calcium content (SCC) were used as response factors. The optimal hydrolysis conditions were found to be sonication power (X1) = 492.91 W, sonication time (X2) = 15.01 min, enzyme activity (X3) = 6677.88 U, and water-to-substrate ratio (X4) = 3.56 v/w. Under these conditions, UAEH effectively disintegrated fish frame collagen and converted bound calcium to soluble calcium. Nevertheless, this study investigated the pattern of collagen transformation into short peptides and free amino acids throughout the degradation process. These findings highlight the potential of the FFH from channel catfish to serve as a foundation for creating highly nutritious food additive. The outcomes of this study further enhance the food industry’s ability to capitalize on the nutritional benefits offered by fish frame hydrolyzates. This expansion of health-focused product options and endorsement of the sustainable use of fish by-products harmonizes seamlessly with the industry’s evolving goals of waste reduction and value optimization.

To investigate the effect of dietary fiber on batter characteristics and oil penetration in deep-fried battered and breaded fish nuggets (BBFNs) from silver carp surimi, deep-fried BBFNs were prepared with model batters (composed of wheat starch and gluten) added with 8% apple fiber, 6% soybean fiber or 12% wheat bran fiber. The moisture adsorption isotherms of dietary fiber, wheat starch and gluten, and the pick-up of BBFNs were evaluated, the viscosity, rheological behavior and calorimetric properties of batters were measured, and the thermogravimetric properties of the crust, the water state and oil penetration of deep-fried BBFNs were also evaluated. The results showed that the moisture absorption capacity of wheat starch was the largest, followed by soybean fiber, apple fiber, wheat bran fiber, and gluten. Compared to that the control group (without dietary fiber), the addition of 8% apple fiber, 6% soybean fiber or 12% wheat bran fiber significantly increased the viscosity of batters and the pick-up of BBFNs (P < 0.05). The loss modulus (G’) and storage modulus (G”) of batters were decreased firstly, then increased rapidly and ultimately remained stable with an increase in oil temperature, and soybean fiber resulted in the highest G’ and G”, which contributed to the fastest formation of gels and the highest thermal stability of the crust after frying. The addition of each of the dietary fibers resulted in transformation of free water into bound water and increased the total moisture content of the crust. Soybean fiber resulted in the lowest oil penetration in deep-fried BBFNs, followed by apple fiber, wheat bran fiber and the control group. This study indicated that the addition of the three dietary fibers in model batter systems can accelerate the formation of gels, significantly improve the strength of the gels formed, and ultimately inhibit oil penetration in deep-fried BBFNs.

Crayfish (Procambarus clarkii) is nutritious and delicious, but its safety always worries consumers. This study aimed to investigate the microbial safety of frozen cooked crayfish. The total volatile basic nitrogen (TVB-N) content and pH of crayfish samples were measured to determine the end point of the shelf life. The structure and diversity of the microbial communities in the viscera and gills, muscle and shell of crayfish and the marinade were analyzed by high-throughput sequencing. The results showed that during the frozen storage of cooked crayfish, the pH of the viscera, gills and muscle decreased slowly, while the pH of the marinade and the shell increased first and then decreased. The TVB-N contents of all four samples showed an upward trend. On the 180th day, the TVB-N values of the muscle as well as the viscera and gills were 32.42 and 31.26 mg/100 g, respectively, which were higher than the accepted upper limit. The results of high-throughput sequencing showed that there were differences in the bacterial community structure of the four crayfish samples at the end of the shelf life. The decreasing order of the abundance of bacteria in these samples were marinade > viscera and gills > shell > muscle. The dominant bacterial genera in these samples were also different; Lactobacillus was dominant in the marinade. Psychrobacter and Vibrio were dominant in the viscera and gills, the dominant bacteria in the shell were Vibrio, Lactobacillus and Psychrobacter, and the dominant bacteria in the muscle were Psychrobacter and Acinetobacter. In conclusion, the microbial safety risk of the marinade and the viscera and gills in frozen cooked crayfish products was relatively high and could be reduced by combined use of various cleaning methods, adjusting the acidity of the marinade and using antibacterial agents.

This study addressed the effect of polysaccharide hydrocolloids on the crust characteristics and oil penetration of fried battered and breaded fish nuggets (BBFNs). Fish pieces were battered with a mixture of wheat starch (WS) and wheat gluten (WG) at a ratio of 11:1 (m/m) added with 0.3% sodium carboxymethyl cellulose (CMC-Na), 0.2% guar gum (GG), or 0.2% xanthan gum (XG), breaded, and fried at 170 ℃ for 40 s followed by 190 ℃ for 30 s. The fluorescence intensity, surface hydrophobicity (H0), sulfydryl and disulfide bond contents, and secondary structure of WG and the crystal structure of WS in the crust were determined, and the oil penetration in the crust was evaluated. Results showed that the H0, fluorescence intensity, disulfide bond content, relative contents of β-sheet and β-turn in the crusts with the three polysaccharide hydrocolloids were greater than those in the control (without the addition of any polysaccharide hydrocolloids), while the free sulfydryl content and the relative contents of α-helix and random coil of WG, and the relative crystallinity of WS were lower than those in the control. The H0, fluorescence intensity, sulfydryl content and relative α-helix content of WG and the relative crystallinity of WS were lowest for the crust with XG, followed by CMC-Na and GG, while an opposite trend was observed for the disulfide bond content and relative β-sheet content. Furthermore, Sudan red staining area was largest for the control, and smallest for fried BBFNs with XG (present only in the crust), followed by CMC-Na and GG. These results indicated that due to their high hydrophilicity and unique structures, the three polysaccharide hydrocolloids can interact with WG to improve the stability of the crust, thereby inhibiting the oil penetration of fried BBFNs.

In order to uncover the growth and decline of microorganisms during the processing of frozen cooked crayfish and to determine the critical control points, the traditional microbial culture method combined with high-throughput sequencing was used to analyze the changes in the microbial community at different processing stages, namely, raw materials, sand spitting, washing, cooking and finished products. The results showed that the sand spitting process could significantly reduce the number of microbes in the gills by 98.9%, but did not change the number of microbes in the intestine. The total number of colonies in the gills and intestines of crayfish decreased by 4.22 and 4.64 (lg(CFU/g)), respectively during the cooking process. The microbial load in crayfish meat was below the detection limit. Besides, the coliform bacteria and Pseudomonas were killed completely. The high-throughput sequencing results showed that the species abundance and diversity in the gills and intestine of raw crayfish were lower than those in cooked crayfish meat. The microbial community in the crayfish gills was dominated by Proteobacteria, while that in the intestine was dominated by Firmicutes. The species abundance and diversity of crayfish were reduced during sand spitting, and the relative abundance of Proteobacteria in the crayfish intestine was decreased significantly. The relative abundance of Flavobacterium in the meat and gills of crayfish was more significantly decreased after cooking compared with washing. The key control points of microorganisms during the processing of frozen cooked crayfish were determined as sand spitting and cooking, which will provide a theoretical basis for improving the quality and safety of and preserving crayfish products.

In the present study, the effect of the interaction between wheat starch and gluten on oil distribution in deep-fried battered and breaded fish nuggets (BBFNs) from silver carp surimi was investigated. Deep-fried BBFNs were prepared using batters consisting of wheat starch (WS) and gluten (WG) blends (at mass ratios of 15:1, 13:1, 11:1, 9:1 and 7:1), and then the surface hydrophobicity (H0), free sulfydryl content, disulfide bond content, secondary structure of WG and the crystalline structure of WS in the crust, as well as the surface oil and penetrated surface oil contents of deep-fried BBFNs were evaluated. The microstructure and oil distribution in the crust were also observed. The results showed that as the WS/WG ratio decreased, the H0 value increased firstly then decreased, and the free sulfydryl and disulfide bond contents gradually decreased and increased, respectively. Meanwhile, the β-turn structure of WG was gradually converted into β-sheet, and the surface oil and penetrated surface oil contents of deep-fried BBFNs as well as the relative crystallinity of WS decreased firstly then increased. The size of pores in the crust and oil distribution decreased at first and then increased. Among the tested WS/WG ratios, deep-fried BBFNs with a WS/WG ratio of 11:1 had the highest H0 (8 990), and the lowest surface oil (2.1%) and penetrated surface oil contents (5.8%), and the lowest relative crystallinity of WS (17.8%), and the crust exhibited the most compact microstructure and the least oil distribution. Therefore, the interaction between WS and WG is affected by changes in WS/WG ratio, which can in turn affect oil distribution in deep-fried BBFNs.

Fluorescent probe labeling is easy to operate and the sensitivity of fluorescence detection is 3–4 orders of magnitude higher than traditional methods such as ultraviolet visible (UV-Vis) spectroscopy. The absorption and distribution of chitosan oligosaccharide (COS) monomers with different degrees of polymerization (DPs) in mice was analyzed by fluorescent probe labeling. In this study, we analyzed the differences in the absorption and distribution of COS monomers with DPs of 2–5 in mice gavaged with fluorescein isothiocyanate (FITC) labeled COS monomers through fluorescence signal detection by a small animal intravital optical imaging system and fluorescence quantification. The results showed that at 1 h after administration, the fluorescence signal in the mice reached its peak level. COS could be absorbed into the blood and cross the blood-brain barrier to distribute into the brain tissue. COS mainly distributed into the kidney and liver, followed by the heart and spleen, and a small amount of COS distributed into the lung and brain. The distribution of COS monomers in the kidney and liver was positively correlated with the DP, while the peak distribution in serum, heart, spleen, lung, and brain in decreasing order was as follows: chitobiose > chitotetraose > chitotriose > chitopentose. The findings of this study are meaningful for guiding future study of the structure-activity relationship of functional COS and provide a reference for further study of the functional mechanism of COS, which will accelerate the development and application of COS in functional foods.