Radio Frequency-Vacuum Drying of Kiwifruits: Kinetics,Uniformity, and Product Quality

To overcome long drying time, low energy efficiency and poor product quality associated with conventional drying, a radio frequency (RF) vacuum technology is proposed for drying kiwifruit slices using a 27.12 MHz, 3 kW RF-vacuum drying system. The results demonstrated that the process variables, electrode gap, vacuum pressure, and sample thickness, had major effects on the RF-vacuum drying. The RF-vacuum drying was associated with internal heating and rapid drying resulting in 65% reduction of hot air drying (60 °C) time. Moreover, kiwifruits dehydrated by RF-vacuum drying were associated with better color stability, higher vitamin C retention, and higher rehydration capacity (p?<?0.05) as compared with hot-air-dried samples. Based on acceptable drying rate, stable temperature and avoiding arcing, a RF-vacuum drying protocol with the electrode gap of 60 mm, vacuum pressure of 0.02 MPa, and sample thickness of 8 mm was identified. Despite some differences observed in individual fruit slices, the RF-vacuum drying technique achieved better and more uniform drying patterns among the samples. Overall, the RF-vacuum drying process may provide a more effective and practical method for high-quality dehydration of kiwifruits.     

Impact of genotype,seasons and manufacturing process on the activities of peptidase and lipoxygenase in tea

Tea flush shoots comprising three leaves and a bud were harvested from five different cultivars planted in a single area of UPASI Tea Research Farm and analysed for lipoxygenase (LOX) and peptidase activities. Among the cultivars, UPASI-3 recorded high peptidase activity, while UPASI-9 registered significantly higher lipoxygenase activity. This study suggested the influence of genotype on these enzymes. Green leaves sampled during mid-April to May (Premonsoon) exhibited higher peptidase activities, while LOX activity was predominant during monsoon period (June to August). Peptidase activity was higher in actively growing tea tissues (bud) and decreased with shoot maturity, whereas LOX activity significantly increased with the maturity of shoot from bud to third leaf and rapid decline in the internodes. During manufacturing process, the activity of both the enzymes varied widely and maximum peptidase activity was observed in withered leaves and cut dhool had maximum LOX activity. The flavour analysis was carried out in green leaf, withered leaf, cut dhool, fermented dhool and black tea which indicated that the value of flavour index was higher in final black tea and lowest in green leaf. This provides significant information that most of the aroma compounds are formed during processing (after harvesting only).     

High-pressure destruction kinetics of Clostridium sporogenes ATCC 11437 spores in milk at elevated quasi-isothermal conditions

The high-pressure sterilization establishment requires data on isobaric and isothermal destruction kinetics of baro-resistant pathogenic and spoilage bacterial spores. In this study, Clostridium sporogenes 11437 spores (10⁷ CFU/ml) inoculated in milk were subjected to different pressure, temperature and time (P, T, t) combination treatments (700–900 MPa; 80–100 °C; 0–32 min). An insulated chamber was used to enclose the test samples during the treatment for maintaining isobaric and quasi-isothermal processing conditions. Decimal reduction times (D values) and pressure and temperature sensitivity parameters, Z_T (pressure constant) and Z_P (temperature constant) were evaluated using a 3 × 3 full factorial experimental design. HP treatments generally demonstrated a minor pressure pulse effect (PE) (no holding time) and the pressure hold time effect was well described by the first order model (R² > 0.90). Higher pressures and higher temperatures resulted in a higher destruction rate and a higher microbial count reduction. At 900 MPa, the temperature corrected D values were 9.1, 3.8, 0.73 min at 80, 90, 100 °C, respectively. The thermal treatment at 0.1 MPa resulted in D values 833, 65.8, 26.3, 6.0 min at 80, 90, 95, 100 °C respectively. By comparison, HP processing resulted in a strong enhancement of spore destruction at all temperatures. Temperature corrected Z_T values were 16.5, 16.9, 18.2 °C at 700, 800, 900 MPa, respectively, which were higher than the thermal z value 9.6 °C. Hence, the spores had lower temperature sensitivity at elevated pressures. Similarly, corrected Z_P values were 714, 588, 1250 MPa at 80, 90, 100 °C, respectively, which illustrated lower pressure sensitivity at higher temperatures. By general comparison, it was concluded that within the range operating conditions employed, the spores were relatively more sensitive to temperature than to pressure.     

Characterization of Ice Crystals in Pork Muscle Formed by Pressure-shift Freezing as Compared with Classical Freezing Methods

ABSTRACT: Cylindrical specimens of fresh pork muscle packed in plastic bags were frozen by air blaster freezing (ABF), liquid immersion freezing (LIF), and pressure-shift freezing (PSF) (100 to 200 MPa). Sample internal temperature and phase transformations were monitored at center, midway, and surface locations. ABF and LIF resulted in large irregular ice crystals, causing serious muscle structure deformation. PSF ice crystals were generally small and regular, but differed along the radial direction. Near the surface, there were many fine and regular intracellular ice crystals with well-preserved muscle tissue. From midway to the center, ice crystals were larger in size and located extracellularly. Ice crystal formation was affected by super-cooling during/after depressurization and subsequent freezing.     

Enhanced destruction of spoilage microorganisms in apple juice during continuous flow microwave heating

Destruction kinetics of two selected spoilage microorganisms, Saccharomyces cerevisiae and Lactobacillus plantarum in apple juice were evaluated under continuous flow microwave heating conditions and compared with conventional batch heating in a water bath. Inoculated apple juice was heated in a microwave oven (700 W, 2450 MHz) under continuous-flow conditions to selected exit temperatures (52.5–65°C). Aliquots of inoculated juice were also subjected to batch thermal treatments (50–80°C) in a well-stirred water bath. Time-temperature profiles obtained both during heating and cooling of test samples were used to correct both come-up and come-down times. The time-corrected D-values under microwave heating were 4.8, 2.1 and 1.1 s at 52.5, 55 and 57.5°C, respectively, for S. cerevisiae and 14, 3.8 and 0.79 s at 57.5, 60 and 62.5°C, respectively, for L. plantarum with corresponding z-values of 7 and 4.5°C. D-values under batch thermal heating were 58, 25, 10 and 1.9 s at 50, 55, 60 and 70°C, respectively, for S. cerevisiae and 52, 22, 8.4 and 1.2 s at 55, 60, 70 and 80°C, respectively, for L. plantarum with corresponding z-values of 13.4 and 15.9°C. Microbial destruction thus occurred much faster under microwave heating than under thermal heating suggesting some contributory enhanced effects to be associated with microwave heating.     

Effect of High Pressure Treatment and Degree of Milling on Gelatinization and Structural Properties of Brown Rice

Brown rice (BR), medium-milled rice (MR), and fully milled white rice (WR), with different degrees of milling (DOM), 0, 6.6, and 10.4 %, respectively, were high pressure (HP) treated at 200 to 500 MPa for 5 to 15 min. Water absorption, swelling, and gelatinization properties, and microstructural changes were investigated. HP treatment (≥200 MPa) or partial milling (DOM 6.6 %) resulted in water absorption comparable with that of white rice. Swelling behavior was affected by milling and processing temperature. Both HP treatment and milling promoted gelatinization properties. In addition, partial milling reduced the pressure resistance of rice grain, while differences in water absorption, swelling behavior, and gelatinization properties due to milling were reduced by HP treatment. Further, the degree of gelatinization (DG) increased with HP treatment with 400 MPa and 10 min defined as the threshold values for pressure and holding time, respectively. DG values, observed with 400 MPa-10 min treatments, were 41.2, 50.2, and 39.9 %, respectively for BR, MR, and WR. Results demonstrated that HP treatment, combined with milling, is technically feasible and produces rice and rice flour with enhanced DG and swelling behavior. These basic data can be used to improve the processing efficiency and quality of brown rice-based product.     

Clostridium sporogenes-ATCC 7955 Spore Destruction Kinetics in Milk Under High Pressure and Elevated Temperature Treatment Conditions

Clostridium sporogenes (ATCC 7955) spores inoculated in milk (2% fat) were subjected to high-pressure (HP) treatments (700–900 MPa) and at elevated temperatures (80–100 °C) for selected times up to 32 min. Samples were sealed in 1-mL plastic vials and placed in a specially constructed insulated chamber to prevent temperature drop during the treatment. Both pressure pulse (with no hold time) and pressure hold techniques were employed for treatment. Pressure pulse resulted in a small, but consistent, destruction (up to 0.5 log kill) of spores. During the pressure hold treatment, the destruction followed a first-order model (R ² > 0.90). The kinetic data were compensated for the small variations in temperature during the treatment. As expected, higher pressures and higher temperatures resulted in a faster rate of spore destruction. Temperature-corrected D values ranged from 13.6 to 2.4 min at 700 MPa and 7.0 to 1.3 min at 900 MPa, respectively, with process temperatures set at 90 and 100 °C. In comparison, thermal treatments gave D values ranging from 156 min at 90 °C to 12.1 min at 100 °C. The temperature sensitivity Z _P values (16.5 to 20.3 °C) under high pressure (700–900 MPa) were higher than under conventional thermal processing (9.0 °C), indicating the spore’s thermal resistance to increase at HP processing conditions. The pressure sensitivity Z _T values varied between 450 and 680 MPa under the elevated temperature (80–100 °C) processing conditions. Overall, C. sporogenes 7955 spores were relatively more sensitive to temperature than pressure.     

Heat-Resistant,Robust, and Hydrophilic Separators Based on Regenerated Cellulose for Advanced Supercapacitors

Separators in supercapacitors (SCs) typically suffer from defects of low mechanical property, limited ion transport, and electrolyte wettability, and poor thermal stability, impeding the development of SCs. Herein, high-performance regenerated cellulose (RC) based separators are designed that are fabricated by effective hydrolytic etching of inorganic CaCO₃ nanoparticles from a filled RC membrane. The as-prepared RC separator displays excellent comprehensive performances such as higher tensile strength (75.83 MPa) and thermal stability (200 °C), which is superior to commercial polypropylene-based separator (Celgard 2500) and sufficient to maintain their structural integrity even at temperatures in excess of 200 °C. Benefiting from its hydrophilicity, high porosity, and outstanding electrolyte uptake rate (208.5%), the RC separator exhibits rapid transport and permeability of ions, which is 2.5× higher than that of the commercial nonwoven polypropylene separator (NKK -MPF30AC-100) validated by electrochemical tests in the 1.0 m Na₂SO₄ electrolyte. Results show that porous RC separator with unique advantages of superior electrolyte wettability, mechanical robustness, and high thermal stability, is a promising separator for SCs with high-performance and safety.     

Effect of Partial Replacement of Retort with an Insulation Material on Mc-Silicon Grown in Directional Solidification Furnace: Numerical Modeling

Silicon - In this paper, the transient global numerical simulation was used in order to study the four types of insulation surrounding the retort within directional solidification furnace which are...