Rajat Chakraborty

Infrared-Assisted Freeze Drying of Tiger Prawn: Parameter Optimization and Quality Assessment

This article presents an extensive experimental study coupled with statistical analysis on infrared (IR)-assisted freeze drying of tiger prawn (Penaeus monodon) in cuboidal geometry. The work aims to estimate quality attributes of freeze-dried prawn in terms of final product temperature (below protein denaturation temperature), rehydration ratio, and final moisture content as a function of process parameters, viz. IR temperature (55–65°C), distance between sample and IR heater (30–60 mm), sample thickness (10–25 mm) and freeze-drying time (5.5–6.5 h). Response surface methodology (RSM) has been employed using a three-parameter, three-level face-centered central composite design (FCCD) to develop multivariate regression models in order to evaluate the influence of process parameters on the quality of the freeze-dried prawn. Optimal drying conditions of 10-mm sample thickness, 60-mm sample distance from the IR heater, 65°C IR temperature, and freeze-drying time of 6.37 h have been established. Separate validation experiments at the derived optimal conditions ascertained the predictive ability of the developed model equations. The outcome of this study would contribute to the development of technical capabilities for the design of freeze dryers applicable to such high-valued foodstuffs.

Intensification of Freeze-Drying Rate of Bacillus subtilis MTCC 2396 Using Tungsten Halogen Radiation: Optimization of Moisture Content and α-Amylase Activity

A novel freeze-drying protocol has been explored to render fast and cost-effective freeze drying of hyperamylase producing Bacillus subtilis MTCC2396 employing a tungsten halogen lamp radiator (THLR) as a heat source. Response surface methodology assessed the maximum reduction in moisture content (96.07%) and minimum reduction in α-amylase (EC 3.2.1.1) activity (1.02%) in 4 h drying time at 42.5°C radiation temperature. α-amylase activity (0.046 U) and final moisture content (3.93%) of the optimally freeze-dried bacterial strain appeared satisfactory. The freeze-drying time using THLR (4 h) is remarkably lower compared to that under a conventional conductive plate heater (CPH) (10 h) at otherwise identical conditions. The higher effective moisture diffusivity of 0.0052 to 0.0078 m 2/s under THLR compared to 0.00084 to 0.0015 m 2/s under CPH (corresponding to 20–50°C) advocated the superiority of the THLR heating protocol. The higher efficacy of THLR was also evidenced through lower activation energy (8.42 kJ/mol) of moisture diffusion compared to that (12.051 kJ/mol) of CPH. The optimally freeze-dried bacteria demonstrated the same growth rate in addition to exhibiting excellent retention of bioremedial (Hg2+ removal) activity to that of the control.

Optimization of Intensification of Freeze-Drying Rate of Banana: Combined Applications of IR Radiation and Cryogenic Freezing

A programmed experimental study on infrared (IR) aided freeze-drying of cryogenically (LN2) frozen heat sensitive material viz. banana (Musa acuminata) rendered faster moisture separation rate compared to the conventionally frozen samples. Response surface methodology (RSM) could determine the simultaneous optimal freeze-drying conditions of 59.78°C IR temperature, 10 mm sample thickness, and 5 h drying time corresponding to the minimum moisture content of 4.11%, lowest final product temperature of 22.799°C, and maximum rehydration ratio of 1.72. Color difference, shrinkage, microstructure, pH, wettability, polysaccharide, and mineral contents of the cryogenically frozen freeze-dried banana at the optimal conditions have been determined coupled with Fourier Transform Infrared Spectroscopy (FTIR) and Carbon Hydrogen Nitrogen Sulfur (CHNS) analyses. Freeze-drying kinetics at optimal conditions have been evaluated and compared with literature published models and the “Handerson and Pabis” model was found to characterize the present case most closely among all drying models. A novel method for intensification of moisture separation rate leading to freeze-dried banana with high quality could thus be explored.

Far infrared radiated energy-proficient rapid one-pot green hydrolysis of waste watermelon peel: optimization and heterogeneous kinetics of glucose synthesis

For the first time, a one-pot green hydrolysis of waste watermelon (Citrullus lanatus) peel (WWP) was optimized for a maximum glucose yield employing a heterogeneous Amberlyst-15 catalyst. The effects of energy-proficient far infrared radiation (FIRR) on intensification of pretreatment and subsequent solvent-free hydrolysis reactions in the one-pot system have been maximized. The optimal process variables for pretreatment and consequent hydrolysis were 20 min and 10 min batch times, 70 °C and 60 °C reactor temperatures, and 5 and 10 (w/w) water to WWP ratios, respectively. Optimal 2.5 (w/w) NH4OH loading and 2.5 wt% catalyst concentration for pretreatment and hydrolysis under FIRR resulted in a maximum glucose yield (89.87 mol%), which was superior to that obtained (59.86 mol%) using a conventional thermal source. In comparison with pseudo-homogeneous and Langmuir–Hinshelwood models, the Eley–Rideal model described the hydrolysis kinetics more accurately. Significantly, a higher hydrolysis activation energy (92.02 kJ mol−1) in the conventional system compared to the FIRR mode (activation energy, 59.69 kJ mol−1) clearly demonstrated the superior energy-efficiency of the FIRR system. The energy-proficient fast hydrolysis process is expected to be sustainable and applicable to similar lignocellulosic biomasses.

Biofilm Reactor for Hg2+ Removal: Review with Challenges and A Study with Freeze Dried Bacteria

AbstractThe present article intends to make a state-of-the review of removal of Hg2+ ions from wastewater using biofilm reactor. Preservation of mercury resistant bacteria has been identified as one of the challenges regarding commercialization of biofilm reactors for this purpose. Finally, a case study on biofilm reactor using freeze-dried Bacillus cereus (JUBT1) has been incorporated. A novel, cost-effective, and economically feasible freeze-drying protocol has been designed and optimized for JUBT1. The freeze-dried strain renders the same characteristics as that of the native strain after revival. The mercury removal efficiency of the biofilm of revived freeze-dried cells is comparable to that of the native cells with a negligible deviation (absolute) of 0.16%. Thus, the present study could prove itself sufficient to throw some light on the future prospects on demercurization of wastewater using bacterial biofilm.

Recent Trends in Catalytic Hydrolysis of Waste Lignocellulosic Biomass for Production of Fermentable Sugars

This article presents a comprehensive comparative assessment of the reaction conditions employed in the heterogeneous and homogeneous catalytic hydrolysis of waste lignocellulosic biomass (WLB) for the production of fermentable sugar (FS) for its subsequent conversion to renewable bioethanol. The effects of catalyst type and reaction conditions on the selectivity of FS in catalytic hydrolysis of low-cost WLB have been meticulously assessed. Moreover, representative radar plots demonstrating FS (substrate for bioethanol) yield in both homogeneous and heterogeneous catalytic protocols have been elucidated. An intensive global attention has recently been paid for the improvement of catalytic technologies pertaining to efficient pretreatment and hydrolysis for conversion of WLB to FS. Cellulose [(C6H10O5) n ], the foremost component in WLB materials, is a biodegradable polymer of simple carbohydrates, consisting of β (1, 4)-linkage of d-glucose units, which can be depolymerized to FS for the subsequent sustainable synthesis of renewable biofuels. In this article, a critical assessment of the production of FS through catalytic pretreatment and subsequent hydrolysis of WLB resources has been elucidated. The abundant presence of low-cost WLB and their potential application for synthesis of FS (d-glucose) and other derivatives (xylose) for subsequent bioethanol, biobutanol, bio-H2 production can provide an economically sustainable and environmentally benign avenue to mitigate energy crisis and global climate change.

Effects of intermittent CO2 convection under far infrared radiation on vacuum‐drying of pre‐osmodehydrated watermelon

BACKGROUND Watermelon, a tropical seasonal fruit with high nutrient content, requires preservation through drying due to its perishable nature. Nevertheless, drying of watermelon through conventional processes has a negative impact either on the drying time or on the final product quality. In this work, osmotic dehydration of watermelon followed by far-infrared radiation-assisted vacuum drying (FIRRAVD) was optimized to develop dehydrated watermelon with minimum moisture content. Significantly, during FIRRAVD, an attempt was made to further intensify the drying rate by forced convection through intermittent CO2 injection. Drying kinetics of each operation and physicochemical qualities of dried products were evaluated. RESULTS FIRRAVD was a viable method of watermelon drying with appreciably high moisture diffusivity (Deff,m ) of 4.97 × 10-10 to 1.49 × 10-9 m2 s-1 compared to conventional tray drying. Moreover, intermittent CO2 convection during FIRRAVD (ICFIRRAVD) resulted in appreciable intensification of drying rate, with enhanced Deff,m (9.93 × 10-10 to 1.99 × 10-9 m2 s-1 ). Significantly, ICFIRRAVD required less energy and approximately 16% less time compared to FIRRAVD. The quality of the final dehydrated watermelon was superior compared to conventional drying protocols. CONCLUSIONS The novel CO2 convective drying of watermelon in the presence of far-infrared radiation demonstrated an energy-efficient and time-saving operation rendering a dehydrated watermelon with acceptable quality parameters.