Preparation, characterization and stability of cross linked nitrilase aggregates (nitrilase-CLEAs) for hydroxylation of 2-chloroisonicotinonitrile to 2-chloroisonicotinic acid

Nitrilases capable of performing hydroxylation of 2-chloroisonicotinonitrile to 2-chloroisonicotinic acid were screened, and ES-NIT-102 was the best nitrilase for said biotransformation. Nitrilase was immobilized as cross linked enzyme aggregates (nitrilase-CLEAs) by fractional precipitation with iso-propanol, and cross linked with glutaraldehyde. The nitrilase-CLEAs prepared with optimized 35 mM glutaraldehyde for 120 min cross linking time had 82.36 ± 4.45% residual activity, and displayed type-II structural CLEAs formation as confirmed by particle size, SEM, FTIR, and SDS-PAGE analysis. Nitrilase-CLEAs had superior pH and temperature stability, showed a shift in optimal temperature by 5 °C, and retained nearly 1.5 to 1.7 folds activity over free nitrilase at 50 °C and 55 °C after more than 9 h incubation. Nitrilase-CLEAs showed reduced affinity and decreased conversion of substrate as indicated by slightly higher K_m values by 5.19% and reduced V_max by 17%. Furthermore, these nitrilase-CLEAs showed 98% conversion, 94.72 g/L product formation, and 83.30% recovery after 24 h when used for hydroxylation of 2-chloroisonicotinonitrile to 2-chloroisonicotinic acid. Nitrilase-CLEAs were catalytically active for 3 cycles showcasing 81% conversion, 75.53 g/L product formation and 66.42% yield. The recovered product was confirmed by HPLC, FTIR, LC-MS, and ¹H NMR, and displayed > 99% purity.

Preparation of cross-linked enzyme aggregates of lipase from Aspergillus niger: process optimization, characterization, stability, and application for epoxidation of lemongrass oil

Cross-linked enzyme aggregates (CLEAs) of lipase were prepared after fractional precipitation with 40-50% ammonium sulfate and then cross-linking with glutaraldehyde. The process variables for the preparation of lipase-CLEAs such as glutaraldehyde concentration, cross-linking period, and initial pH of medium were optimized. The optimized conditions for the preparation of lipase-CLEAs were 25 mM/80 min/pH 7.0, and 31.62 mM/90 min/pH 6.0 with one factor at a time approach and numerical optimization with central composite design, respectively. Lipase-CLEAs were characterized by particle size analysis, SEM, and FTIR. Cross-linking not only shifted the optimal pH and temperature from 7.0 to 7.5 and 40-45 to 45-50 °C, but also altered the secondary structure. Lipase-CLEAs showed an increase in K_m by 7.70%, and a decrease in V_max by 16.63%. Lipase-CLEAs presented better thermostability than free lipase as evident from thermal inactivation constants (t_1/2, D and E_d value), and thermodynamic parameters (E_d, ΔH°, ΔG°, and ΔS°) in the range of 50-70 °C. Lipase-CLEAs retained more than 65% activity up to four cycles and showed good storage stability for 12 days when stored at 4 ± 2 °C. They were successfully utilized for the epoxidation of lemongrass oil which was confirmed by changes in iodine value, epoxide value, and FTIR spectra.

Production of biologically active peptides by hydrolysis of whey protein isolates using hydrodynamic cavitation

Whey protein isolate (WPI) hydrolysates have higher solubility in aqueous phase and enhanced biological properties. Hydrolysis of WPI was optimized using operating pressure (ΔP, bar), number of passes (N), and WPI concentration (C, %) as deciding parameters in hydrodynamic cavitation treatment. The optimum conditions for generation of WPI hydrolysate with full factorial design were 8 bar, 28 passes, and 4.5% WPI concentration yielding 32.69 ± 1.22 mg/mL soluble proteins. WPI hydrolysate showed alterations in binding capacity over WPI. SDS-PAGE and particle size analysis confirmed the hydrolysis of WPI. Spectroscopic, thermal and crystallinity analyses showed typical properties of proteins with slight variations after hydrodynamic cavitation treatment. ABTS, DPPH and FRAP assays of WPI hydrolysate showed 7-66, 9-149, and 0.038-0.272 µmol/mL GAE at 1-10, 0.25-4, and 3-30 mg/mL concentration, respectively. Further, a considerable enhancement in fresh weight, chlorophyll, carotenoids, reducing sugars, total soluble sugars, soluble proteins content and total phenolics content was noticed during in vitro growth of sugarcane in WPI hydrolysate supplemented medium at 50-200 mg/L concentration over the control. The process cost (INR/kg) to hydrolyze WPI was also calculated.

Extension of postharvest shelf life of strawberries (Fragaria ananassa) using a coating of chitosan-whey protein isolate conjugate

Chitosan and whey protein isolate (WPI) conjugate films were prepared as a novel matrix for encapsulating and extending the postharvest shelf life of strawberries. Film forming solutions of chitosan, WPI, and chitosan-WPI conjugate were mixed with glycerol, casted for films at 60 ± 2 °C and assessed for their colour, water vapour and oxygen transfer rate, textural, functional groups and secondary structure, thermal, crystallinity, and antioxidant properties. Chitosan-WPI conjugate films were applied as an edible coating on strawberries, and studied for storage stability at 5 °C and 20 °C by assessing physical and biochemical parameters. A considerable reduction in colour indices, weight loss, pH and titratable acidity, reducing sugars, ascorbic acid, total phenolics, DPPH and ABTS assay was noted in the coated strawberries over the control at both the studied temperatures. The control strawberries had a shelf life of 5 and 3 days, whereas coating enhanced the shelf life of strawberries to 8 and 5 days when stored at 5 °C and 20 °C, respectively.

Isolation and functional validation of stress tolerant EaMYB18 gene and its comparative physio-biochemical analysis with transgenic tobacco plants overexpressing SoMYB18 and SsMYB18

MYB transcription factors are one of the most important mediators for the survival of plants under multiple stress responses. In the present study, EaMYB18, encoding a single R3 repeat MYB DNA binding domain was isolated from stress-tolerant wild relative species of sugarcane Erianthus arundinaceus. In silico analysis of 948 bp coding mRNA sequence of EaMYB18 exhibited the presence of four exons and three introns. Further, the EaMYB18 gene was transformed in tobacco and its stable inheritance was confirmed through antibiotic resistance screening, PCR amplification and Southern hybridization blotting. Results of the estimation of MDA, proline, total chlorophyll and antioxidant activities of EaMYB18 transgenic tobacco lines exhibited least oxidative damage under drought and cold stress over the untransformed ones, the over-expression of EaMYB18 has improved drought and cold stress tolerance ability in tobacco. The comparative physiological and biochemical analysis of transgenic tobacco plants overexpressing SoMYB18, SsMYB18 and EaMYB18, revealed that the EaMYB18 and SsMYB18 transgenic plants demonstrated effective tolerance to drought and cold stresses, while SoMYB18 showed improved tolerance to salt stress alone. Amongst these three genes, EaMYB18 displayed the highest potential for drought and cold stress tolerances as compared to SoMYB18 and SsMYB18 genes.