Optimisation of surface quality
retention during the thermal processing of conduction heating foods using
variable temperature retort profiles.
Noronha, J.; Hendrickx, M.; Suys, J. and Tobback, P.
Optimal variable retort
temperature profiles (VRT) for the sterilisation of conduction heated foods
were calculated using a quasi-Newton multi-variable optimisation algorithm
considering both the maximisation of surface quality and the minimisation of
total process time. When the maximisation of surface quality was the objective
an increase up to 20% in quality retention was predicted for optimal VRT
profiles as compared to optimal constant retort temperature profiles (CRT).
When considering the minimisation of total process time the use of VRT profiles
allowed to reduce the total process time up to 45% still providing the same
surface quality as optimal CRT. Since the results could not be generalised, it
was concluded that optimal VRT profiles should be calculated on a case by case
basis.
Simultaneous Optimisation of Surface Quality for Three Components during
the Sterilisation of Conductive Heating Foods using Constant and Variable
Retort Temperature Profiles.
Noronha, J.; Van Loey, A.; Hendrickx, M. and Tobback, P.
The feasibility of the
simultaneous optimisation of surface quality of three quality factors
presenting different activation energies was investigated for the sterilisation
of conduction heating foods using a computer simulation approach.
Optimal constant and
variable retort temperature profiles were calculated considering the
maximisation of surface retention for each of the individual quality factors
and considering the simultaneous maximisation of the retention of the three
components. Optimal variable retort profiles that allow the minimisation of the
process time still providing overall final surface retention similar to the
optimum constant retort temperature where also calculated.
It was found that the use
of optimum variable retort profiles allows the simultaneous optimisation of
three quality factors, where the final surface retention of each quality
attribute is higher than those calculated based on optimum constant temperature
profiles. Moreover it was found that the use of variable retort temperature
profiles allows substantial reductions in process time still providing final
surface retention of the individual quality factors comparable to those
obtained using the more time consuming constant temperature profiles.
Determination of Appropriate Heat Penetration Parameters for the
Evaluation of Process Deviations During In-Pack Sterilisation of Foods
Noronha, J., Van Loey, A., Stoforos, N.G. Hendrickx, M. and Tobback, P.
Methods for the
determination of appropriate heat penetration parameters to be used with
semi-empirical methods for the determination of product temperature evolution
during the sterilisation of packed foods in batch type retorts are presented.
The heat penetration parameters determined are used with semi-empirical methods
for the determination of the temperature evolution for the evaluation of
process deviations consisting on temperature drops on the scheduled processing
temperature.
The proposed methods for
the determination of appropriate heat penetration parameters were able to
calculate heat penetration parameters independent of the duration and shape of
the retort come-up-time. The use of the determined heat parameters allowed an
accurate evaluation of process deviations in a retort simulator during the
thermal processing of food simulants. A good agreement between experimental and
predicted product temperatures could be achieved. A good agreament between
processing values calculated from experimental measured temperature profiles
and from predicted temperature profiles could be found.
Experimental Validation of
Mathematical Procedures for the Evaluation of Thermal Processes and Process
Deviations During the Sterilisation of Canned Foods
Tucker, Gary S.; Noronha, João F. and Heydon, Camilla J.
In this article
mathematical models for the design and evaluation of in-pack sterilisation
processes including the evaluation of process deviations consisting of drops in
the ambient temperature are discussed. Models for simulating conduction
heating, broken heating and convection heating are considered. The
methodologies used in the determination of the empirical parameters associated
with the proposed methods are briefly discussed.
The methods are validated
against experimental data obtained by processing real foods in a retort
simulator. Results for beans in tomato sauce, chicken cream soup and peas in
brine, processed in A1 metal cans (
[artigo]
Alternative algorithms for
evaluation of process deviations in batch-type sterilisation processes.
Noronha, J .; Van Loey, A.; Hendrickx, M. and Tobback, P.
Process deviations during the
thermal processing of non-conductive heating foods are difficult to handle. The
commonly used formula methods (Ball, Hayakawa) are restricted to processing
conditions existing of a come-up time, a holding period at constant heating
medium temperature followed by cooling, leading to log-linear heating of the
container. Numerical equations for the Fourier heat equations are available but
not directly useful to non-conduction problems. An approach using an apparent
thermal diffusivity to simulate the heating rate of the product (fh) and a time
correction factor to allow changes in the lag-factor (j-value) has recently
been proposed by Teixeira et al. (1992).
This paper discusses
alternative empirical, analytical and numerical approaches to handle process deviations.
Empirical equations (Hayakawa) and analytical solutions are used together with
the Duhamel theorem to handle variable boundary conditions. In the context of
these methods, a new procedure for determination of heating parameters fh and j
is described. The performance of these methods for determination of heating
characteristics and evaluation of process deviations is tested against
theoretically generated case studies and experimental data obtained on food
(model) systems in a pilot retort.
New semi-empirical approach to
handle time-variable boundary conditions during sterilisation of non-conductive
heating foods.
Noronha, J.; Hendrickx, M.; Van Loey, A. and Tobback, P.
Semi-empirical methods for
the prediction of time temperature histories in conductive and non conductive
(convective and mixed mode) heating foods subjected to a time variable
processing temperature are proposed. Four alternatives are considered: (i)
Hayakawa's method (Duhamel's theorem with Hayakawa's formulas) (ii) Duhamel's
theorem with analytical solution (iii) Numerical solution with apparent time
(time shift) (iv) Numerical solution with apparent position. The incorporation
of the empirical heating characteristics f and j in conductive models was
accomplished by evaluating the existing analogies with thermophysical
properties in the solutions of the Fourier equation. Approaches using Duhamel's
theorem or finite difference solutions were used to handle variable boundary
conditions. The application of the models in the calculation of processing
values for thermal processes with different come up times and different
boundary conditions during come up time and thermal processes with process
deviations is discussed. The numerical solution with apparent position was
preferred because it combines accuracy and flexibility.
[artigo]
Simultaneous optimisation of surface
quality during the sterilisation of packed foods using constant and variable
retort temperature profiles
Noronha, J.; Hendrickx, M. and Tobback, P.
The differences in
temperature dependence between spore inactivation and degradation of quality
factors allow the optimisation of thermal processes in terms of maximisation of
quality retention by choosing an optimum heating profile. While the
maximisation of the retention for a single quality factor has received
considerable attention in research, the possibilities of simultaneously
maximising the retention of different quality factors has up to now not been
addressed.
In this article the
possibilities of the simultaneous optimisation for more than one quality
factors were theoretically assessed. Both the use of constant and variable
retort temperature profiles were considered. A special emphasis was given to
the formulation of appropriate objective functions for the simultaneous optimisation
of the surface retention of quality factors.
For the simultaneous
optimisation of quality factors the objective functions should be formulated in
terms of maximising final retention and not, as in the case of single component
optimisation, in terms of minimisation of cook values. The use of variable
retort temperature profiles was shown to be particularly interesting for the
simultaneous optimisation of more than one quality factor, as the final
retention calculated compared well with the maximum retention achieved using
individual calculated optimum constant retort temperature control for each of
the components.
[artigo]
An empirical equation for the
description of the optimum profiles that maximise surface quality retention of
thermally processed foods
Noronha, João Freire de; Hendrickx, Marc and Tobback, Paul
It has been previously
shown that, when compared with the traditional constant retort temperature
profiles, variable retort temperature profiles allow a substantial increase in
quality retention during the sterilisation of packed foods. When the
minimisation of the process time with a constraint on the minimum surface
quality is considered, variable retort policies show significant reductions on
process times when compared to equivalent optimum constant retort temperature
profiles. However the results were presented on a case by case basis and no
effort was done to try to generalise this principle.
In order to allow the
generalisation of the use of variable profiles we present in this article an
empirical formula, developed based on the analysis of calculated optimum
variable retort temperature profiles, that allows an accurate description of
optimum variable temperature profiles. The use of the proposed equation allows
a substantial reduction on the calculation effort necessary for the calculation
of optimum variable retort temperature profiles.
Optimizing thermal process for
canned white beans in water cascading retorts.
Van Loey, A.; Fransis, A.; Hendrickx, M.; Maesmans, G.; Noronha, J. and
Tobback, P.
Based on thermal
degradation kinetics and heat transfer expressed as the Ball formula method, a
simplified approach was used to optimize sterilization processes for thermal
softening of white beans (Phaseolus vulgaris, subsp. nanus Metz., variety
Manteca de Leon). Constant retort profiles in a still and end-over-end rotary
water cascading retort (Barriquand Steriflow) were used. Quality attributes of
beans processed at the optimum were evaluated by a trained taste panel and by a
tenderometer. Both approaches could distinguish (P < 0.01) between
attributes of products from optimal rotary and still processes. End-over-end
rotation resulted in faster heat penetration and better quality retention of
beans. Texture of white beans processed at 4 degrees or 8 degrees C from the
optimal temperature could be distinguished (P < 0.01) by the sensory panel
and by the tenderometer.
Evaluation of the integrated
time-temperature effect in thermal processing of foods.
Hendrickx, M., Maesmans, G., De Cordt, S., Noronha, J., Van Loey, A. and
Tobback, P.
In this review,
current methods used to evaluate the integrated impact of time and temperature
upon preserving a food product by a heat treatment are considered. After
identifying the basic premise any preservation scheme shall meet, the central
role of a feasible description for the heat activation kinetics of
microorganisms, their spores, and other quality attributes are stressed. Common
concepts to quantify a thermal process are presented. Shortcomings of the
prevalent evaluation methods are highlighted and attention is given to the
development, restrictions, and possibilities of time-temperature-integrators as
"new" evaluation tools to measure the impact of a
"classical" in-pack heat treatment and more modern heating techniques
such as continuous processing of solid, liquid mixtures on foods.
Evaluation of Process deviations,
consisting of drops in rotational speed during thermal processing of foods in
rotary water cascading retorts
Denys, S.; Noronha, J.; Stoforos, N.G.; Hendrickx, M. and Tobback, P.,
Taking into account
the similarities of broken-line heating curves and heat-penetration curves
obtained when a product undergoes a drop in rotational speed during thermal
processing in a rotary water cascading retort, a semiempirical method used for
handling broken-line heating behaviour is suggested as a method of dealing with
this type of process deviation. For this purpose, the possibility of extrapolating
the empirical heating rate parameter fh, determined on the heat-penetration
curve of white beans in brine processed in a still retort, to the 'still'
conditions associated with a rotational speed drop in a rotary water cascading
retort, was investigated. Following this approach, safe product temperature
predictions were obtained. The main criterion influencing the quality of the
evaluation was the determination of the correct empirical parametric value to
be used. This means, when determining this parametric value, care is required
when selecting the correct temperature interval on the heat-penetration curve.
[artigo]
Inverse superposition for
calculating food product temperatures during in-container thermal processing.
Stoforos, N.G, Noronha, J., Hendrickx, M. and Tobback, P.
A procedure was
developed for theoretical calculation of internal product temperatures during
in-container sterilization of foods. Experimental product temperatures were
determined through traditional heat penetration tests (processing in a retort
with come-up time of increasing temperature and holding time at constant
temperature). These were used to produce, through a proposed inverse
superposition solution, a "standardized," normalized, dimensionless
product temperature curve corresponding to the response of product temperature
to a constant retort temperature profile. This "standardized" curve
was then used, through Duhamel's superposition theorem, to calculate product
temperatures for time-varying retort temperature profiles. Limitations
associated with the application of Duhamel's theorem were also transferred to
the proposed methodology. Theoretical, for perfect mixing, and experimental,
for conduction heating, data were used in example calculations.
A semi-empirical approach to handle
broken-line heating: Determination of empirical parameters and evaluation of
process deviations.
Denys, S.; Noronha, J.; Stoforos, N.G.; Hendrickx, M. and Tobback, P.
An existing
semi-empirical model for simulating product temperature profiles during thermal
processing of conduction or convection heating foods under time varying
boundary conditions (variable retort temperatures) was extended for the case of
broken-line heating products. The use of the method for determination of the
empirical heat penetration parameters for broken-line heating curves as defined
by Ball (jh, fhl, fh2, xbh) was evaluated. Starch solutions, showing
broken-line heating behavior, were used as a food simulant. To investigate the
consistency of the determined broken-line heating parameters, and to test the
applicability of the method when boundary conditions are time dependent,
process deviations consisting of drops on the heating medium temperature during
the holding phase of a process were evaluated. The model is a promising
approach, if the correct empirical parameters are used.
A critical analysis of mathematical
procedures for the evaluation and design of in-container thermal processes for
foods.
Stoforos, N.G., Noronha, J., Hendrickx, M. and Tobback, P.
Kinetic data on thermal
destruction of spoilage and quality factors coupled with the temperature history
of a product during a heat sterilization cycle are the basic information needed
for the evaluation and the design of thermal processes through a
physical-mathematical approach. A critical review on the available physical-
mathematical procedures used for thermal process calculations of in-container
processed foods is presented. The origin and the limitations of each method are
discussed. The equations associated with each method, for internal product
temperature predictions, are explicitly given. The relative performance of
selected methods under identical processing conditions is illustrated. Several
problems associated with thermal process calculations are discussed.
AGRO44- Development of a common
understanding of HACCP in traditional cheese-dairies
Food Science and Techonology
Department, Escola Superior Agraria de Coimbra. Bencanta - 3040-116
In this poster we will
introduce an ongoing project (AGRO 44, started in March 2002) aimed at the
dissemination of GMP/GHP/SOP and HACCP in the manufacturing of DOP cheeses
produced in the central region of
The project is being
developed in five main areas: (i) Development of a GMP/GHP Manual for milk
production (farm); (ii) Development of a GMP/GHP/SOP Manual for small (micro)
traditional cheese-dairies; (iii) Implementation of HACCP in selected cheese-dairies
(demonstration plants) (iv) Development of Generic HACCP Plans for the
production of cheese; and (v) Development of an Internet site for the
dissemination of all the produced material.
The participant
institutions (academia, regulatory/inspection authorities, producer
associations and a local rural development agency) will promote various actions
in order to make the collected information available to the final users (milk
and cheese producers).
AGRO44 is funded by the
AGRO Program (Measure 8, Action 8.1) from the Portuguese Ministry of
Agriculture.
Elaboração de uma
lista de descritores para queijos tradicionais portugueses
Departamento de Ciência e Tecnologia Alimentares. Escola Superior Agrária de Coimbra. Bencanta. 3040-116 Coimbra. noronha@mail.esac.pt Tel. 239 802 276
Neste trabalho descreve-se a elaboração de uma lista de descritores para a análise sensorial descritiva de queijos tradicionais portugueses. Este trabalho foi realizado no âmbito do projecto “AGRO 243 - Caracterização sensorial de queijo e requeijão elaborados a partir do leite de ovinos e caprinos da região centro. Aplicação ao queijo da Serra Velho e Requeijão”.
Para a elaboração da lista de descritores foi seleccionado um painel inicial
de 50 elementos com experiência diversificada na participação
Este trabalho foi apoiado pelo Programa AGRO, Medida 8 - Desenvolvimento Tecnológico e Demonstração,Acção 8.1 - Desenvolvimento Experimental e Demonstração (DE&D).