摘要:

A microcomputer was interfaced with a batch retort for digital PI control of the retort temperature. Six retort temperature profiles (three isothermal, sinusoidal, step, and ramp) were examined for processing pea puree to nearly the same lethality values in 211 × 400 cans. Thiamine content and steam consumption were measured. Thiamine retentions in non‐isothermal processes were greater than in the isothermal processes, but there was no significant difference in the steam consumption.Lethality and thiamine retention were also simulated using a finite difference model for the same heating profiles, with good agreement with experimental results. the simulation suggests that differences in thiamine retention due to differing heating regimes are significant only for large lethality values and smaller cans. For F0values smaller than 10 min, the simulation suggests that the sinusoidal heating regime will provide better thiamine retention. Limitations of the model and suggestions for future improvement are also discuss

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1996.tb00377.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The effects of different dipping pretreatments on microwave drying of grapes was studied in a multimode cavity. Grapes pretreated with 2% ethyl oleate in 0.5% sodium hydroxide (NaOH) solution resulted in comparatively good quality raisins with lowest drying times. Pretreatment with 3% ethyl oleate in 0.5% NaOH solution led to similar product without any major advantage over the former. Grapes treated with 3% ethyl oleate in 2.5% potassium carbonate solution took longer time to dry. Grapes treated with only NaOH solution resulted in raisins of inferior quality in terms of color and appearance. the interphase mass transfer coefficients also described the effect of these chemical pretreatments. Studies conducted on the effect of washing and time of holding after the pretreatment indicated that both of these factors had no influence on drying time.

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1996.tb00378.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The study of the simultaneous diffusion of chemical preservatives in vegetable tissues permits the determination of the time required to complete this process and the concentration distributions of the preservatives.The individual or simultaneous diffusion of citric and ascorbic acids in pre‐peeled potatoes was analyzed; the effect of pH decrease on the diffusive flux of ascorbic acid and the interaction between both acids was considered as the multicomponent diffusion problem.Potato spheres of different radii were immersed in individual solutions or mixtures of citric and ascorbic acids in concentration ranging from 0.5% to 2% W/V for different immersion times and agitation conditions. the residual concentration of citric acid was determined by titrable acidity (22058 AOAC method) and that of ascorbic acid by 2–6 dichlorophenol‐indophenol method.Experimental data were fitted to the mathematical models and the effective diffusion coefficients were determined for citric (De= 4.3 ± 0.2 × 10−10m2/s) and ascorbic acids (De= 5.45 ± 0.4 × 10−10m2/s) diffusing individually. When mixtures of two acids were used, multicomponent analysis was adopted and interaction coefficients were evaluated (D12= 6.67 ± 0.8 × 10−11m2/s and D21= 8.33 ± 0.8 × 10−11m2/s); they were an order of magnitude lower than binary diffusion values.The pH effect on the diffusive flux of ascorbic acid was decoupled from the interaction of both acids during simultaneous diffusion by studying the diffusion of the first acid in potatoes preacidified

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1996.tb00379.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Through a simple application, this research demonstrates the potential and procedure of applying computer vision and control techniques in developing automated real‐time statistical process controllers (SPC). A computer vision system was developed to sample and measure quality variables (area, length, and width) of an extruded food product. Shewhart control charts were used to monitor the state of statistical control. Corrective actions were determined by using a PI control algorithm to minimize the product size variation caused by material inconsistency in moisture content. the system was implemented and tested. Considerable improvement was achieved in product size uniformit

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1996.tb00380.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

A nondestructive method of determining milk coagulation cut‐time was investigated. Velocity and attenuation of ultrasonic waves through coagulating skim milk were measured after rennet addition. the ultrasonic attenuation measurements were found suitable for distinguishing the effect of different experimental variables (three levels of temperature, rennet and CaCl2). Based on the rate of change of attenuation during coagulation, a turning point was defined at which the attenuation rate change was ‐0.1 neper/m/min. the cut‐time was proposed to be 20 min from the time the turning point was observed. the cut‐times predicted by this criterion were statistically similar to those predicted by the manual method currently used in the i

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1996.tb00381.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Liquid‐to‐particle convective heat transfer coefficient (hfp) between fluid and particle was investigated in continuous flow through a horizontal scraped surface heat exchanger. the relative velocities between fluid and particle were measured, and hfpcalculated from well known correlations. Heat transfer coefficients increased with increasing flow rate, rotational speed, and decreased with increasing carrier medium viscosity and particle size. the measured relative velocities during flow visualization studies ranged from 0.04 to 0.29 m/s with corresponding hfpvalues of 597 W/m2°K and 1975 W/m2°K, respectively. Even with the most conservative correlation, Nusselt numbers ranged from 12.1 to 49.7; significantly greater than the value of 2.0 for a sphere in a stagnant

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1996.tb00382.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

A mathematical model for microwave cooking of cocktail shrimp was developed. the model included heat and mass transfer and microbial inactivation kinetics. A simple 2 dimensional cylindrical slab geometry was used and model equations were solved using the finite difference method. the model predictions on temperature and mass loss were in good agreement with the observed data. Temperature predictions were within ± 6C and mass predictions were within ± 2 g of the observed dat

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1996.tb00383.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

An important factor in the design of the sheeting operation used in the snack food and bakery industries are the forces exerted on the rolls as a result of the pressure developed between the rolls. These forces can cause significant mechanical deflections that result in nonuniform products being produced across the width of the rolls. Unfortunately, measurements of closing forces on operating sheeting systems can be difficult to obtain. This note illustrates a simple method for estimating the difficult to obtain sheeter closing forces from more easily obtained power measurements. A limited quantity of data confirms the accuracy of the procedure.

ISSN:0145-8876    

DOI:10.1111/j.1745-4530.1996.tb00384.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY