Lai Hao Li

Application of Response Surface Methodology to Optimise Preparation High Antioxidant Activity Product from Pinctada fucata Muscle

The high antioxidant activity product was isolated from Pinctada fucata muscle by a method of Alcalase hydrolysis. Optimization using response surface methodology was performed and 3D response surfaces were plotted from the mathematical model. The results indicated that the optimal extraction conditions were as follows: pH 7.0, temperature 61°C, E/S 3.01%, hydrolysis time 3h, under the conditions of hydrolysis products of the DPPH radical scavenging rate of 67.3% and the degree of hydrolysis of 31.2%, which was in good agreement with the predicted model value.

Extraction, Purification and Partial Characterizations of Polysaccharides from Gracilaria lemaneiformis

In the present study, the crude polysaccharides were extracted from the microalgae Gracilaria lemaneiformis with ultrasonic-assisted extraction method and purified by DEAE-52 cellulose chromatography and Sephadex G-100 size-exclusion chromatography in that order. Two main fractions, GPC-1and GPC-2, were obtained through the extraction and purification steps. Then partial characterizations, such as chemical composition, ultraviolet (UV) spectrum and infrared (IR) spectrum of the two fractions were analyzed in this study. The results indicated that the total sugar contents of GPC-1and GPC-2 were 89.32% and 88.79%, and the protein contents of these two fractions were only 0.35% and 0.76%, compared with that of crude polysaccharides of 75.49% and 1.92%, respectively. Moreover, both the UV spectrum and the IR spectrum demonstrated that the two fractions were typical purified polysaccharides. As a consequence, these investigated characterizations could be considered as a favorable evidence for the identification of polysaccharides from Gracilaria lemaneiformis.

Study of Ultrasonic-Freeze-Thaw-Cycle Assisted Extraction of Polysaccharide and Phycobiliprotein from Gracilaria lemaneiformis

Ultrasonic-freeze-thaw-cycle assisted extraction was used to synchronously extract polysaccharide and phycobiliprotein from Gracilaria lemaneiformis. Firstly, different solvents (deionized water, sodium hydroxide, phosphate buffer solution (PBS) and calcium chloride solution) were screened, and PBS (1 mM, pH 6.8) was considered as the best solvent for its OD565 value (0.086±0.0003) and OD595 value (0.471±0.002), which was significantly higher than any other solvents (p<0.05). Moreover, an L9 (3)4 orthogonal test was carried out to optimize extraction conditions, based on the single-factor test. The results indicated that the optimized conditions were fixed as follows: the ratio of solid to liquid 1:25 (w/v), 2 times of freeze-thaw cycles, ultrasound power 320 W and ultrasound time 10 min, which obtained the optimum yield and purity of polysaccharide and phycobiliprotein, 30.54%, 1.36% and 0.296, respectively. As a result, ultrasonic-freeze-thaw-cycle assisted extraction is considered to be an effective, economic and eco-environmental method to extract polysaccharide and phycobiliprotein.

Extraction of Fish Oil from the Muscle of Sturgeon Using Supercritical Fluids

This study evaluated the extraction of oil from sturgeon (Acipenser baeri) muscle using supercritical fluids. Response surface methodology (RSM) was used to identify and quantify the variables, namely extraction pressure, extraction time and CO2 flow rate on the yield of oil. Statistical analysis indicated that for all three variables, the quadratic terms and interactions between the variables had significant effects on yield (p < 0.05). Polynomial regression model predictions were in good agreement with the experimental results, with a coefficient of determination of 0.9936 for yield. Maximum yield from sturgeon muscle was 26.83% with a pressure of 315.8 bar, extraction time of 10.8 min and CO2 flow rate of 3.5 l/min, which closely matched the predicted value (26.70%). The characteristics of the fish oil extracted with the supercritical fluids were superior to those of oil obtained by other methods.

Desalination of Antioxidant Peptides from Pinctada fucata Using C18 Chromatographic Column

Antioxidant peptides crude product from Pinctada Fucata desalination technology by C18 chromatographic column was studied. The desalination rate and the antioxidant activity were used to analyze the effect of desalination conditions. The results show that the optimum conditions for desalting are loading 2ml of sample with concentration of 100 mg/ml, flow rate of 2 ml/min, 0.1% TFA as mobile phase with pH 6.5 in 0-4.5min and 80% methanol in 4.5-30min. Under these conditions, the desalination rate is 68.75% and the peptide recovery rate is 76.53%. The inhibitory content (IC50) expressed by antioxidant peptides is 11.421mg/ml in the system of DPPH radical.

Isolation and Identification of Nitrite-Degrading Lactic Acid Bacteria from Salted Fish

Lactic acid bacteria commonly used in fermented meat products, dairy products and smoked products such as pickled food industry. They can make the products have a special flavor and color, inhibit the growth of pathogenic bacteria, and reduce the nitrite content of products, improve food security. 12 strains of lactic acid bacteria were isolated from the salted fish. Some of their biochemical characteristics were studied and compared, as well as their abilities on the tolerance and degradation of nitrite. 3 strains named b2、j2、j5 were approved to degrade nitrite quickly with good biochemical characteristics. After amplification and sequencing of 16S rDNA gene, the isolated strains were identified by sequence homology as Lactobacillus plantarum, Leuconostoc mesenteroides and Pediococcus pentosaceus. Strainb2, j2 and j5could degrade 96.2%, 85.6%, 91.2%.

Optimization of Nitrite Reductase Production Conditions in Lactobacillus plantarum from Salted Fish

The conditions for nitrite reductase (NiRs) produced by Lactobacillus plantarum from salted fish were optimized. Enzyme activity of nitrite reductase was used as evaluation index. The results showed that the pH value had greatest influence on enzyme activity. The optimum conditions of producing nitrite reductase were inoculate quantity 4 %, pH 6.3, culture temperature 35 °C, incubation time 48 h. The enzyme activity of nitrite reductase reached to 89.672 U/mL, which increased by 71 % after optimization. This work provided the foundation for the research of enzymatic properties of nitrite reductase. This may be useful to the production of salted fish products.

Effects of Inoculating Compound Lactic Acid Bacteria on the Quality of Cured Fish

Inoculation with compound lactobacillus in the low-salt pickled fish, fermented and dried to produce cured fish. The paper studied the effects of inoculating compound lactobacillus on the pH, total volatile basic nitrogen (TVB-N), amino acid nitrogen content (AA-N) and total acid content of salted fish quality. The results showed that, compared with the non-vaccinated groups (CK), The cured fish inoculated lactobacillus had a lower pH and TVB-N content, higher the amino acid nitrogen content and total acid content. Inoculated compound lactic acid bacteria into salted fish, to a certain extent, could improve the nutritional value and edible value, which had positive effects on the fish quality.

Different Temperatures of Frozen Storage Effects on Proteins of Crisp Grass Carp (Ctenopharyngodon idellus C.et V)

This article focused on the study of frozen storage temperatures effect on protein of crisp grass carp, and then induced changes of texture of crisp grass carp muscle. During frozen storage, lower temperature, better texture of crisp grass carp muscle. The little changes of texture characteristics of crisp grass carp were related to lower changes of drip loss, cooking loss, protein solubility and thermal stability. The results indicated that lower temperature of frozen storage was beneficial to maintain the mastication of crisp grass carp.

Mathematical Modeling of Drying Kinetics of Salted Otolithes Ruber at the Different Temperature

Salted Otolithes ruber with 80 (±5) g weight on dry basis were dried in the blast electric oven using different temperature (20, 30, 40 and 50°C) until the humidity fell down to 0.6 from 1.23 on dry basis. Drying processes were completed between 20-48h. In this study, experiment values were compared with predicted values obtained from twenty thin layer drying theoretical/ semi-empirical/ empirical equations. Models whose coefficient of correlation (R2) values are highest were chosen to be the best models. According to this, Midillis Model was defined as the most suitable model in which predicted value is closest to experimental data for 20°C level, Weibulls model was for 30°C level, Weibull distributions model was for 40°C level and Alibas model was for 50°C level.