Jun Cai

The polysaccharide/protein/polyphenol-based composite films were successfully developed by blending chitosan (CS), porcine small intestinal mucosal protein (PSIMP) and curcumin (CUR) for the short-term refrigerated preservation of chicken breasts. The results showed that the addition of 2% CUR increased the elongation at break by 18.4%, and 3% CUR significantly raised the water contact angle from 53.4° to 72.5°. The water vapor transmission rate and oil absorption rate of CS/PSIMP/CUR3 films were reduced by 30% and 64%, respectively. Throughout the entire refrigerated storage period of chicken breast, packaging with the CS/PSIMP/CUR3 composite film decreased bacterial proliferation by 34% relative to the control group. After 7 days of storage, chicken breast packaged with CS/PSIMP/CUR3 film exhibited a total viable count of 5.57 log CFU/g and a total volatile basic nitrogen level of 13.36 mg/100 g, both remaining below the spoilage thresholds of 6 log CFU/g and 15 mg/100 g, respectively. Additionally, the centrifugal loss and cooking loss decreased by 19% and 32%, respectively. Furthermore, CS/PSIMP/CUR film packages significantly reduced the degradation of inosine monophosphate of refrigerated chicken breasts during storage. The proposed strategy would provide suggestions for developing the novel packaging with antimicrobial and barrier properties for the preservation of perishable meat.

The efficiency and accuracy of the synthesis of structural lipids are closely related to the regiospecificity of lipases. Understanding the structural mechanism of their regiospecificity contributes to the regiospecific redesign of lipases for meeting the technological innovation needs. Here, we used a thermostable lipase from Streptomyces sp. W007 (MAS1), which has been recently reported to show great potential in industry, to gain an insight into the structural basis of its regiospecificity by molecular modelling and mutagenesis experiments. The results indicated that increasing the steric hindrance of the site for binding a non-reactive carbonyl group of TAGs could transform the non-specific MAS1 to a α-specific lipase, such as the mutants G40E, G40F, G40Q, G40R, G40W, G40Y, N45Y, H108W and T237Y (PSI > 80). In addition, altering the local polarity of the site as well as the conformational stability of its composing residues could also impact the regiospecificity. Our present study could not only aid the rational design of the regiospecificity of lipases, but open avenues of exploration for further industrial applications of lipases.

An alkaline lipase strain of Pseudomonas aeruginosa HFE733 was isolated from soil samples of domestic waste. The alkaline lipase from P. aeruginosa HFE733 was purified and characterized. The enzyme was purified 9.97-fold by means of ammonium sulphate precipitation, Sephadex G-25 and diethylaminoethyl (DEAE) cellulose chromatography. Purified alkaline lipase protein was analyzed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), the molecular mass was 51.0 kDa. The enzyme exhibited maximum activity at 40 °C and pH 8.5. The enzyme is stable at pH 7.0–8.5. It was remarkably activated by some metal ions and chemical reagents, such as Fe³⁺, Al³⁺, β-mercaptoethanol, cysteine, DL-dithiothreitol (DTT), Tween 80 and Triton X-100, but suppressed by sodium dodecyl sulfate (SDS) at 10 mmol/L. The P. aeruginosa HFE733 strain and lipase exhibited remarkable potential for biodegradation of oil and organics (measured as chemical oxygen demand (COD)). We demonstrated that it can be used for biodegradation of food wastewater from restaurants.

Helicoverpa armigera sterol carrier protein-2 (HaSCP-2) is a validated target for development of novel insecticides due to its divergent protein structure and function from the vertebrate SCP-2. HaSCP-2 is important for normal development and fertility in Helicoverpa armigera (Hübner). The discovery of chemical inhibitors of HaSCP-2 through a structure-based virtual screening is reported here. Bioassay indicated that H1 and H14 had inhibitory effect on the growth of H. armigera larvae. The results suggest that H1 and H14 are promising as useful lead compounds for further optimization and development of novel SCP-2-specific pesticides.

Aflatoxin contamination of food and grain poses a serious economic and health problem globally. Aflatoxin B₁ (AFB₁) is extremely mutagenic and toxic as well as a potent carcinogen to both humans and livestock. In this study, the degradation of AFB₁ by extracellular extract of Cladosporium uredinicola was examined using high-performance liquid chromatography (HPLC), thin-layer chromatography (TLC), and liquid chromatography mass spectrometry. Within 24 h of incubation, AFB₁ was efficiently eliminated by the culture supernatant of C. uredinicola (84.5±5.7%) at 37°C; the elimination was proven to be enzymatic, and the enzyme was thermostable. The biotransformation products of AFB₁ detected by HPLC and TLC were proven to be the same compound. Analysis with LCMS showed that AFB₁ was bio-transformed to a structurally different compound (m/z=365 [M+Na]⁺), which is first reported. The cytotoxicity study to HeLa cells indicated that culture supernatant-treated AFB₁ is less toxic as compared with AFB₁.

The purification and characterization of the extracellular polygalacturonase from Zygoascus hellenicus V25 submerged culture using orange peel waste were investigated. This polygalacturonase, with a molecular weight of 75.28 kDa, was purified to 16.89 purification fold with a recovery of 18.46% and specific activity of 2469.77 U/mg protein by ammonium sulfate precipitation, DEAE cellulose chromatography, and Sephadex G-100 gel filtration. The enzyme exhibited maximum activity at 60°C and pH 5.0 and was stable over a wide range of pH levels (3.0-11.0). Moreover, enzyme activity was enhanced by Cu²⁺ and cysteine, whereas it was strongly inhibited by Hg²⁺. The extent of enzymatic hydrolysis was negatively correlated with the degree of pectin esterification. K_m and V_max values of the polygalacturonase were 5.44 mg/mL and 61.73 μmol/(min·mg), respectively. The polygalacturonase was applied in the juice clarification of four fruits, and results showed that the percentage transmittance at 660 nm increased by 3.51, 4.36, 8.04, and 12.2%.

β-Mannanases are the second most important enzymes for the hydrolysis of hemicelluloses. An endo-β-mannanase from Enterobacter ludwigii MY271 was purified at 11.7 ± 0.2-fold to homogeneity with a final recovery of 15.2 ± 0.2 %. Using purified β-mannanase protein and SDS-PAGE, the molecular mass was found to be 43.16 kDa. The optimal pH and temperature of the enzyme was found to be 7.0 and 55 °C, respectively. The β-mannanase activity was stable over a broad pH range of pH 2.0–10.0. In addition, the purified enzyme was highly activated by several metal ions and chemical reagents, such as Mg²⁺, l-cysteine, glutathione (GSH) and β-mercaptoethanol. Whereas the enzyme was strongly inhibited by Hg²⁺, Cu²⁺, N-bromosuccinimide (NBS), 1-ethyl-3-(3-dimethyl-amino-propyl)-carbodiimide (EDC), phenylmethanesulfonyl fluoride (PMSF), and sodium dodecyl sulfate (SDS). The β-mannanase was highly active towards glucomannan, and showed endo-activity by producing a mixture of oligosaccharides. Moreover, the enzyme displayed a classical endo-type mode on mannooligosaccharides. The β-mannanase coupled with xylanase significantly improved the brightness of kraft pulp, whereas it has no remarkable effect on the tensile strength of the pulp. Our functional studies of the purified β-mannanase indicate that the enzyme is beneficial to industrial applications, in particular, biotechnological processes, such as food, feed and pulp industry.

BACKGROUND: Xylanase is the key enzyme involved in the conversion of lignocelluloses.RESULTS: An extracellular xylanase from Streptomyces althioticus LMZM submerged culture medium using corncob was purified and characterized. The enzyme was purified 12.65‐fold through ammonium sulphate precipitation, Sephadex G‐25, DEAE cellulose chromatography, followed by gel filtration through a Sephadex G–100 column. The molecular mass of purified xylanase was about 31.75 kDa. The enzyme was an endo‐xylanase, as it degraded xylan to xylooligosaccharide with non‐xylose after 24 h. The purified enzyme showed optimum activity at 60 °C and at pH 8.0 but remained active over a wide range of pH (6.0–11.0) and temperature (40–80 °C). The enzyme retained 98.72% and 69.50% residual enzyme activity at pH 8.0 and at 60 °C after 1 h. The K_m and V_max values were found to be 43.03 mg mL⁻¹ and 312.5 µmol (min mg⁻¹), respectively. The enzyme was remarkably activated by cysteine and Cu²⁺, and its activity was strongly inhibited by Hg²⁺. The brightness of kraft pulp was improved by this xylanase.CONCLUSION: Since the enzyme was active over a wide range of pH, and remained active at high temperature, it could find potential uses in biobleaching processes in pulp paper industries and in the production of xylooligosacaharides. © 2015 Society of Chemical Industry