Hongwu Ji

Response surface methodology for autolysis parameters optimization of shrimp head and amino acids released during autolysis

Protein hydrolysates were prepared from the head waste of Penaens vannamei, a China seawater major shrimp by autolysis method. Autolysis conditions (viz., temperature, pH and substrate concentration) for preparing protein hydrolysates from the head waste proteins were optimized by response surface methodology (RSM) using a central composite design. Model equation was proposed with regard to the effect of temperature, pH and substrate concentration. Substrate concentration at 23% (w/v), pH at 7.85 and temperature at 50°C were found to be the optimal conditions to obtain a higher degree of hydrolysis close to 45%. The autolysis reaction was nearly finished in the initial 3h. The amino acid compositions of the autolysis hydrolysates prepared using the optimized conditions in different time revealed that the hydrolysates can be used as a functional food ingredient or flavor enhancer. Endogenous enzymes in the shrimp heads had a strong autolysis capacity (AC) for releasing threonine, serine, valine, isoleucine, tyrosine, histidine and tryptophan. Endogenous enzymes had a relatively lower AC for releasing cystine and glycine.

Physical and chemical analysis of Passiflora seeds and seed oil from China.

The physical and chemical properties of seeds and seed oil from ‘Tainung No. 1’ passion fruit in China have been analyzed in order to evaluate their nutritional value. Proximate analysis shows that the seeds have a high amount of protein (10.8±0.60%) and are rich in oil (23.40±2.50%). The seeds are found to be a good source of minerals. They contain considerable amounts of sodium (2.980±0.002 mg/g), magnesium (1.540±0.001 mg/g), potassium (0.850±0.001 mg/g), and calcium (0.540±0.002 mg/g). The passion fruit seeds contain the 17 amino acids that are found naturally in plant protein (tryptophan is not analyzed). The essential amino acids account for 34% of the 17 amino acids. The amino acid score of passion fruit seeds protein is 74 and the first limiting amino acid is methionine and cystine. The oil extracted by solvent and supercritical dioxide carbon is liquid at room temperature and the color is golden–orange. The specific gravity of the oil is about 0.917. Comparing the chemical properties of the oil extracted by solvent with that by supercritical dioxide carbon, the latter may be suitable as edible oil directly, while the former will be edible after it must be refined to improve on clarity. Fatty acid composition of the seed oil indicates that the oil contains two essential fatty acids (linoleic acid and linolenic acid), but the content of linoleic acid (72.69±0.32%) is by far greater than that of linolenic acid (0.26±0.00%). The present analytical results show the passion fruit seed to be a potentially valuable non-conventional source for high-quality oil.

Optimization of peptic hydrolysis parameters for the production of angiotensin I-converting enzyme inhibitory hydrolysate from Acetes chinensis through Plackett–Burman and response surface methodological approaches

BACKGROUND Angiotensin I-converting enzyme (ACE) plays an important physiological role in regulating blood pressure. The elevation of blood pressure could be suppressed by inhibiting ACE. ACE inhibitory peptides derived from food proteins could exert antihypertensive effects without side effects. Acetes chinensis is a marine shrimp suitable for the production of ACE inhibitory peptides. The principal objective of this study was to screen for the significant variables, and further to optimize the levels of the selected variables, for the enzymatic production of ACE inhibitory peptides from Acetes chinensis. RESULTS Plackett-Burman design and response surface methodology were employed to optimize the peptic hydrolysis parameters of Acetes chinensis to obtain a hydrolysate with potent ACE inhibitory activity. The peptic hydrolysis variables were subject to a Plackett-Burman design for screening the main factors. The selected significant parameters such as pH, hydrolysis temperature and enzyme/substrate (E/S) ratio were further optimized using a central composite design. The optimized conditions were: pH 2.5, hydrolysis temperature 45 °C, E/S ratio 17 800 U kg(-1) shrimp and substrate concentration 200 g L(-1). The results showed that 3-5 h hydrolysis could result in a hydrolysate with ACE inhibition IC(50) of 1.17 mg mL(-1) and a high DH of 25-27%. CONCLUSION Plackett-Burman design and RSM performed well in the optimization of peptic hydrolysis parameters of Acetes chinensis to produce hydrolysate with ACE inhibitory activity. A hydrolysate with potent ACE inhibitory activity and high degree of hydrolysis was obtained, so that the yield of ACE inhibitory peptides in it was high.

Optimization of microbial inactivation of shrimp by dense phase carbon dioxide

Microbial inactivation of Litopenaeus vannamei by dense phase carbon dioxide (DPCD) treatment was investigated and neural network was used to optimize the process parameters of microbial inactivation. The results showed that DPCD treatment had a remarkable bactericidal effect on microorganism of shrimp. A 3×5×2 three-layer neural network model was established. According to the neural network model, the inactivation effect was enhanced with pressure, temperature and exposure time increasing and temperature was the most important factor affecting microbial inactivation of shrimp. Cooked appearance of shrimp by DPCD treatment was observed and seemed to be more positively acceptable by Chinese diet custom. Therefore, color change of shrimp by DPCD treatment could have a positive effect on quality attributes. Moderate temperature 55 °C with 15 MPa for 26 min treatment time achieved a 3.5-log reduction of total aerobic plate counts (TPC). The parameters combination might be appropriate for shrimp process by DPCD.

Mussel-inspired synthesis of polydopamine-functionalized calcium carbonate as reusable adsorbents for heavy metal ions

A new high-efficiency adsorbent (PDA-CaCO3) is fabricated via simple thermal calcination of ostracean shells and chemical modification with dopamine. The adsorption capacity for Pb(II) and Cd(II) was 336.32 and 175.48 mg g−1, respectively. Importantly, it can be easily regenerated by low-cost reagents, and exhibited a high adsorption capacity after multiple adsorption–desorption cycles.

A GRAPHENE/ENZYME-BASED ELECTROCHEMICAL SENSOR FOR SENSITIVE DETECTION OF ORGANOPHOSPHORUS PESTICIDES

A sensitive and fast sensor for quantitative detection of organophosphorus pesticides (OPs) is obtained using acetylcholinesterase (AChE) biosensor based on graphene oxide (GO)–chitosan (CS) composite film. This new biosensor is prepared via depositing GO–CS composite film on glassy carbon electrode (GCE) and then assembling AChE on the composite film. The GO–CS composite film shows an excellent biocompatibility with AChE and enhances immobilization efficiency of AChE. GO homogeneously disperses in the GO–CS composite films and exhibits excellent electrocatalytic activity to thiocholine oxidation, which is from acetylthiocholine catalyzed by AChE. The results show that the inhibition of carbaryl/trichlorfon on AChE activity is proportional to the concentration of carbaryl/trichlorfon. The detection of linear range for carbaryl is from 10nM to 100nM and the correlation coefficients of 0.993. The detection limit for carbaryl is calculated to be about 2.5nM. In addition, the detection of linear range for trichlorfon is from 10nM to 60nM and the correlation coefficients of 0.994. The detection limit for trichlorfon is calculated to be about 1.2nM. This biosensor provides a new promising tool for trace organophosphorus pesticide detection.

Changes in the myosin secondary structure and shrimp surimi gel strength induced by dense phase carbon dioxide

Dense phase carbon dioxide (DPCD) could induce protein conformation changes. Myosin and shrimp surimi from Litopenaeus vannamei were treated with DPCD at 5-25MPa and 40-60°C for 20min. Myosin secondary structure was investigated by circular dichroism and shrimp surimi gel strength was determined using textural analysis to develop correlations between them. DPCD had a greater effect on secondary structure and gel strength than heating. With increasing pressure and temperature, the α-helix content of DPCD-treated myosin decreased, while the β-sheet, β-turn and random coil contents increased, and the shrimp surimi gel strength increased. The α-helix content was negatively correlated with gel strength, while the β-sheet, β-turn and random coil contents were positively correlated with gel strength. Therefore, when DPCD induced myosin to form a gel, the α-helix of myosin was unfolded and gradually converted to a β-sheet. Such transformations led to protein-protein interactions and cross-linking, which formed a three-dimensional network to enhance the gel strength.