Thermal destruction of dried vegetative yeast cells and dried bacterial spores in a convective hot air flow: strong influence of initial water activity

2005 ◽  
Vol 7 (1) ◽  
pp. 40-46 ◽  
Author(s):  
Frederic Fine ◽  
Patrick Gervais
Keyword(s):  
Water Activity ◽  
Strong Influence ◽  
Thermal Destruction ◽  
Air Flow ◽  
Yeast Cells ◽  
Bacterial Spores ◽  
Initial Water ◽  
Hot Air

Heat Resistance of Salmonella weltevreden in Low-Moisture Environments

1998 ◽  
Vol 61 (8) ◽  
pp. 969-973 ◽  
Author(s):  
JULIE ARCHER ◽  
EMMA T. JERVIS ◽  
JON BIRD ◽  
JOY E. GAZE
Keyword(s):  
Heat Resistance ◽  
Water Activity ◽  
Activity Level ◽  
Heat Processing ◽  
Rapid Decline ◽  
Initial Water ◽  
Hot Air ◽  
D Values ◽  
Survivor Curve ◽  
Temperature Water

The heat resistance of Salmonella weltevreden inoculated into flour and heated in hot air was determined for (a) an initial water activity (aw) range of 0.20 to 0.60 prior to heating, (b) a range of storage relative humidities of 6.0 to 35.5% prior to heating, and (c) temperatures of 57 to 77°C. The death curves obtained were biphasic, demonstrating an initial rapid decline in the numbers of survivors (1.0- to 1.5-log reductions) during the first 5 to 10 min of heating for all the temperature-water activity combinations tested. Following this initial rapid decline in the number of cells, a linear survivor curve was obtained where inactivation occurred at a slower rate. The initial decline in survivors coincided with a rapid decrease in the water activity of all the samples tested. Irrespective of the initial water activity level in the samples prior to heating, the aw decreased to <0.2 during the first 5 to 10 min of heating. The D values obtained for these experimental parameters ranged from a D60–62 of 875 min at an initial aw of 0.4 to a D63–65 of 29 min at an initial aw of 0.5. The results demonstrated that, for any temperature, as the initial water activity of the sample prior to heating decreased, the heat resistance of the cells increased. The z values obtained from these data ranged from 15.2 to 53.9°C. The relative humidity during storage prior to heating did not appear to have a significant effect on the heat resistance of S. weltevreden in flour. These results demonstrate that the amount of available water in foods that are considered to be “dry” (i.e., with a water activity less than 0.60) will significantly influence the effectiveness of the heat processing of foods and, in addition to the temperature, the aw prior to heating is a critical controlling factor during these processes.

scholarly journals Unexpected Thermal Destruction of Dried, Glass Bead-Immobilized Microorganisms as a Function of Water Activity

2003 ◽  
Vol 69 (5) ◽  
pp. 3015-3019 ◽  
Author(s):  
C. Laroche ◽  
P. Gervais
Keyword(s):  
Heat Treatment ◽  
Saccharomyces Cerevisiae ◽  
Lactobacillus Plantarum ◽  
Water Activity ◽  
High Temperatures ◽  
Glass Bead ◽  
Thermal Destruction ◽  
Initial Water ◽  
Short Period ◽  
Immobilized Microorganisms

ABSTRACT To help us understand the factors and mechanisms implicated in the death of microorganisms or their resistance to temperature in a low water activity environment, microorganisms were dried on the surface of glass beads before being subjected to high temperatures for a short period followed by rapid cooling. Two microorganisms were studied: the yeast Saccharomyces cerevisiae and the bacterium Lactobacillus plantarum. Experiments were carried out at 150, 200, and 250°C, with four durations of heat treatment and seven levels of initial water activity between 0.10 and 0.70. We observed an unexpected range of water activity, between 0.30 and 0.50, at which microorganisms were more resistant to the various treatments, with maximal viability at 0.35 for L. plantarum and 0.40 for S. cerevisiae.

scholarly journals Enzymatic Synthesis of Isopropyl Acetate by Immobilized   Bacillus cereus Lipase in Organic Medium

2011 ◽  
Vol 2011 ◽  
pp. 1-7 ◽  
Author(s):  
Madan Lal Verma ◽  
Wamik Azmi ◽  
Shamsher Singh Kanwar
Keyword(s):  
Acetic Acid ◽  
Bacillus Cereus ◽  
Water Activity ◽  
Molecular Sieves ◽  
Immobilized Lipase ◽  
Molar Ratio ◽  
Ester Synthesis ◽  
Initial Water ◽  
Isopropyl Acetate ◽  
Mg Addition

Selective production of fragrance fatty acid ester from isopropanol and acetic acid has been achieved using silica-immobilized lipase of Bacillus cereus MTCC 8372. A purified thermoalkalophilic extracellular lipase was immobilized by adsorption onto the silica. The effects of various parameters like molar ratio of substrates (isopropanol and acetic acid; 25 to 100 mM), concentration of biocatalyst (25–125 mg/mL), reaction time, reaction temperature, organic solvents, molecular sieves, and initial water activity were studied for optimal ester synthesis. Under optimized conditions, 66.0 mM of isopropyl acetate was produced when isopropanol and acetic acid were used at 100 mM: 75 mM in 9 h at 55°C in n-heptane under continuous shaking (160 rpm) using bound lipase (25 mg). Addition of molecular sieves (3 Å  × 1.5 mm) resulted in a marked increase in ester synthesis (73.0 mM). Ester synthesis was enhanced by water activity associated with pre-equilibrated saturated salt solution of LiCl. The immobilized lipase retained more than 50% of its activity after the 6th cycle of reuse.

AUS-32 Injector Spray Imaging on Hot Air Flow Bench

2015 ◽  
Author(s):  
Nic van Vuuren ◽  
Gabriele Brizi ◽  
Giacomo Buitoni ◽  
Lucio Postrioti ◽  
Carmine Ungaro
Keyword(s):  
Air Flow ◽  
Hot Air

Temperature Distribution of Hot Air Flow in Heating Zone for Drying Application

2014 ◽  
Vol 627 ◽  
pp. 153-157
Author(s):  
Nawadee Srisiriwat ◽  
Chananchai Wutthithanyawat
Keyword(s):  
Temperature Distribution ◽  
Air Temperature ◽  
Power Supply ◽  
Air Flow ◽  
Heating Zone ◽  
Velocity Control ◽  
Rectangular Duct ◽  
Air Velocity ◽  
Hot Air ◽  
Set Up

The temperature distribution of hot air flow in heating zone of a rectangular duct has been investigated for drying application. The experimental set-up consists of a heater and a fan to generate the hot air flow in the range of temperature from 40 to 100°C and the range of air velocity between 1.20 and 1.57 m/s. An increase of the heater power supply increases the hot air temperature in the heating zone while an increase of air velocity forced by fan decreases the initial temperature at the same power supply provided to generate the hot air flow. The temperature distribution shows that the hot air temperature after transferring through air duct decreases with an increase of the length of the rectangular duct. These results are very important for the air flow temperature and velocity control strategy to apply for heating zone design in the drying process.

scholarly journals Evaluation and Optimisation of Processes Time for the Hot Air Oven Containing Sleeves

2021 ◽  
Vol 9 (11) ◽  
pp. 404-410
Author(s):  
Bandaru Nithin Kumar Varma
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Epoxy Resin ◽  
Latent Heat ◽  
Air Flow ◽  
Whole Process ◽  
Hot Air

Abstract: The Hot air producing Oven is used to heat the sleeves which are used as raiser in casting purpose. The sleeves that are being manufactured are made of epoxy resin which consists of approximately 75% water and 25% mineral mix before heating and once the processes are complete i.e. the sleeves getting heated in the oven the product would turn into 35% water + 65% mix. The whole process would estimate the time around 4.5 hours. The first 2.5 hours the water is being removed from the sleeves in form of latent heat vaporization. The next 2 hours is use as the time for curing the them because of the flow of hot air through the sleeves. The processes time is evaluated keeping in mind that the heat transfer is happening in mixed convection. As they are placed vertically to the direction of air flow. The amount of heat transfer in terms of energy is evaluated for 4.5 hours in actual practise. The energy which is utilised in 4.5 hours is found and the same amount is consumed in 2.5 hours which is a solution solved theoretically by considering datum values. Keywords: epoxy resin, sleeves, latent heat, heat transfer, mixed convection.

IMC-based anti-windup controller for real-time hot air flow and level control loop

2022 ◽  
Vol 16 (2) ◽  
pp. 205
Author(s):  
Rajani K. Mudi ◽  
Ujjwal Manikya Nath ◽  
Chanchal Dey
Keyword(s):  
Real Time ◽  
Air Flow ◽  
Control Loop ◽  
Level Control ◽  
Hot Air

Performance of biomass combustor based drying system for ginger drying

2021 ◽  
Vol 45 (01) ◽  
pp. 19-25
Author(s):  
D. K. Vyas ◽  
N. Seth ◽  
J. J. Chavda
Keyword(s):  
Fuel Consumption ◽  
Flow Rate ◽  
Consumption Rate ◽  
Air Flow ◽  
Air Flow Rate ◽  
Saw Dust ◽  
Fuel Consumption Rate ◽  
Hot Air ◽  
Drying System ◽  
Maize Cobs

A biomass combustor based dryer was evaluated with different biomass for drying of ginger. Biomass combustor based dryer consists of fuel hopper, combustion chamber, heat exchanger, grate for proper combustion of the combustible gas, chimney, ambient air inlet, hot air outlet and drying chamber. The system was evaluated at five fuel consumption rate (1 to 5 kg.h–1) and five air flow rate (100, 150, 200, 300 and 400 m3.h–1) using maize cobs, sized wood and saw dust briquettes for ginger drying. The experimental performances show that the hot air temperature inside the dryer vary between 36 to 81ºC for maize cobs, 53 to 85ºC for sized wood and 49 to 87ºC for biomass briquettes at tested air flow rate and fuel consumption rate in the system. The maximum efficiency of the system was found at the fuel consumption rate of 1 kg.h–1 and 400 m3.h–1 air flow rate using maize cobs, sized wood and saw dust briquettes as fuel respectively. The cost of operation of ginger drying at 1 kg.h–1 fuel consumption rate and 400 m3/h air flow rate was Rs. 32.76, 34.26, 34.76 and 55 per hour using maize cobs, sized wood, saw dust briquettes and mechanical drying system, respectively. Hence, the drying of ginger in biomass combustor based dryer using maize cobs at 1 kg.h–1 fuel consumption rate and 400 m3/h air flow rate resulted in better performance.

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