Shulai Liu

Combined Effect of Ozonized Water Pretreatment and Ozonized Flake Ice on Maintaining Quality of Japanese Sea Bass (Lateolabrax japonicus)

The effect of the combined application of ozonized water pretreatment and ozonized flake ice (O+OIce) as compared with traditional flake ice (CK), ozonized flake ice (OIce), and ozonized water pretreatment and traditional flake ice (O) was investigated for the storage of Japanese sea bass. Microbiological, chemical, and sensory analysis and moisture content were carried out throughout a storage period of 18 days. A slower increase of total viable mesophilic count (TVC), total volatile base nitrogen (TVB-N), and thiobarbituric acid reactive substances (TBARS) was observed for O+OIce as compared with OIce, O, and CK. Treatment of O+OIce also allowed a better control of pH as compared with OIce, O, and CK. None of the treatments resulted in a significant difference in myofibrillar protein extractability and moisture content. The shelf life of Japanese sea bass treated with CK, OIce, O, and O+OIce, determined by sensory evaluation, was 9, 15, 12, and more than 18 days, respectively. Principal component analysis results showed that the treatments significantly affected the fish quality during storage, and the sensory attributes had a significant correlation with TVB-N, TVC, and TBARS. In conclusion, the combined application of ozonized water and ozonized flake ice had the best effect on fish quality maintenance.

Comparative study of basic characteristics of ordinary and dark muscle in skipjack tuna (Katsuwonus pelamis)

Differences between ordinary and dark muscle of skipjack tuna (Katsuwonus pelamis) including proximate composition, flavor, color, texture, and freshness were investigated. Ordinary muscle had a higher crude protein content, but a lower crude lipid content than dark muscle. Alcohols (30.41%) and aldehydes (25.56%) were the prominent flavor compounds present in ordinary muscle, whereas hydrocarbons (39.51%) and ketones (21.81%) were more abundant in dark muscle. Different L*, a*, and b* values were also observed. Texture profile analysis (TPA) showed that dark muscle had higher values for adhesiveness, and lower values for cohensiveness, chewiness, and resilience. After mechanical breaking, large myofibril fragments were observed in ordinary muscle under phase contrast microscopy, but not in dark muscle. Freshness indices, including K values, total volatile basic nitrogen (TVB-N), and thiobarbituric acid (TBA) values of dark muscle were higher than for ordinary muscle.

Deodorisation of fish oil by nanofiltration membrane process: focus on volatile flavour compounds and fatty acids composition

This study focuses on the investigations for the deodorisation of tuna oil and squid oil through n-hexane extraction and nanofiltration membrane process with a molecular weight cut-off of 360 Da. The change of the odour and the fatty acids composition were analysed. Volatile components analysed by monolithic material sorptive extraction (MMSE) combined with gas chromatography–mass spectrometry (GC-MS) suggested that nanofiltration membrane process could remove the majority of the volatile components, and the removal rate was approximate to 80%. The odour activity values (OAVs) of the volatile components in tuna oil and squid oil were significantly reduced from 125.23 to 17.47 and 129.76 to 10.06 (P < 0.05), respectively. On the other hand, the contents of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were increased as expected. These results indicated that the organic solvent nanofiltration technique had obvious effects on deodorisation of fish oil, and it would be a promising deodorisation method in fish oil refining industry.

Extraction of oil from high-moisture tuna liver by subcritical dimethyl ether: feasibility and optimization by the response surface method

The purpose of this paper is to explore the possibilities of subcritical dimethyl ether extraction (SDME) of oil from tuna liver with high-moisture content. The results showed that the oil and water were successfully co-extracted from the liver, and could be easily separated by centrifugation. In addition, the response surface method was employed to optimize the process parameters of SDME, including temperature/pressure, time and stirring speed. It was predicted that a temperature/pressure of 42/0.80 °C/MPa, time of 50 min and stirring speed of 925 rpm were the optimum within the experimental ranges, with an oil yield of 17.46 ± 0.23%. Furthermore, supercritical carbon dioxide extraction (SC-CO2) was studied comparatively. Only minor differences were observed between the oils extracted by SDME and SC-CO2, which indicated the high-quality of the SDME-oil. With no freeze-drying procedure and the relatively low pressure used in SDME, SDME could be a promising technique for extraction of marine fish liver oil.

A comparative study of physicochemical and functional properties of silver carp myofibrillar protein glycated with glucose and maltodextrin

Myofibrillar protein (Mf) from silver carp (Hypophthalmichthys molitrix) was incubated with glucose and maltodextrin for 0–96 h at 50 °C and 75% relative humidity to obtain glycoconjugates in different periods of the Maillard reaction. Physicochemical properties, including molecular weight, sugars bound to Mf, available amino acid content and FT-IR properties all indicated that glycation occurred successfully. In addition, SDS-PAGE analysis and available amino acids of Maillard reaction productions (MRPs) suggested that glucose reacted more easily with Mf than maltodextrin. Functional properties of MRPs were superior to Mf and reached the highest value at 8–12 h, and then decreased significantly. Heat stability and solubility of Mf–maltodextrin in 0.5 M NaCl was better than for Mf–glucose, while the solubility in 0.1 M NaCl, and the emulsifying and foaming properties of Mf–glucose were in general better than for Mf–maltodextrin. The variety of saccharides and the process of the Maillard reaction had a great influence on the physicochemical and functional properties of MRPs.

Decrease of Lipid Oxidation for Dried Shrimp (Acetes chinensis) Preservation Using Alkaline Lipase Hydrolysis Technology

ABSTRACT In this study, the degreasing technology using alkaline lipase hydrolysis for Chinese dried shrimp (Acetes chinensis) was investigated, with the purpose of decreasing lipid oxidation during dried shrimp preservation. The salt, moisture, and lipid contents of the shrimp were 6.01, 32.51, and 2.95%, respectively. The optimum enzymatic hydrolysis condition for effective decrease of shrimp lipid was obtained: lipase concentration 40 U/mL, pH 10, soaking time 60 min, soaking temperature 30°C, and shrimp/liquid ratio 1:20 (w:v). Under this optimum condition, the residual lipid of the shrimp was reduced to 2.28%, and the degreasing rate reached 49%. During 30-day preservation, the thiobarbituric acid-reactive substances (TBARS) value (0.185 mg/kg of dried shrimp and 0.131 mg/kg of degreased dried shrimp at Day 30) of degreased shrimp was lower than the shrimp without degreasing, indicating alkaline lipase hydrolysis could effectively prevent lipid oxidation and inhibit oxidative rancidity during dried shrimp preservation.