Thermal Diffusivity and Quality Deterioration Index of Malaysian Pangasius Sutchi During Cold Storage
The knowledge on thermal properties of food material to be preserved is considered as one of the basic requirements for conducting heat transfer studies and hence to design proper heat transfer equipments such as refrigerators, freezers and cold storages. The local designers obtain those thermoph...
Saved in:
| Main Author: | |
|---|---|
| Format: | Thesis |
| Language: | English English |
| Published: |
2005
|
| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/5977/1/FK_2005_3.pdf |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | The knowledge on thermal properties of food material to be preserved is considered
as one of the basic requirements for conducting heat transfer studies and hence to
design proper heat transfer equipments such as refrigerators, freezers and cold
storages. The local designers obtain those thermophysical properties data from
Europe and America (Ansari et al., 2002).
Experimental measurements have been carried out for the specific heat, mass
density, water content, thermal conductivity and thermal diffusivity of Malaysian
freshwater Pangasius Sutchi fish during precooling process. The mass density was
determined by measuring mass and volume of the fish samples and the water content
was measured gravimetrically through drying of fish samples in oven. The remaining
properties were calculated by empirical formula, which correlated these properties
with water content of fish.
The most significant part in the experimental work was designing and fabrication of
an air blast cooling plant of constant 1 O C air stream temperature. This plant has played the vital role in minimizing the error of the used techniques as well as thermal
diffusivity determination.
A non-dimensionalized mathematical model of temperature variation with time and
spatial coordinates was made and solved by finite difference method. Factors
affecting the solution have been investigated thoroughly to deliver the most accurate
and reliable results with the shortest computational time. The r,alculation procedure
has been developed and proposed for heat transfer and simultaneous heat and mass
transfer model. The proposed scheme showed more superior results when compared
with the results reported in the literature and yielded consistently good agreements
with the measurements.
Three approaches of estimating the surface film conductance (h) during air-blast
cooling process were developed by the present author. Based on the above
mathematical model, a comparison between the developed and five of the existing
literature approaches was made to identify the best one. A thorough investigation
was conducted to establish the most suitable and reliable method of measuring the
thermal diffusivity of Pangasius Sutchi out of important methods reported in the
literature. Due to its superiority, Ansari's method was adapted to calculate the
thermal diffusivity, through the transient temperature measurements at five known
locations in the fish flesh and at the surface. The estimated h was used in this method
to deliver reliable values of a.
Four lots of fish samples were preserved in 4 chillers set at 0, 3, 5 and 10°C for 28
days according to normal practice. During the course of cold preservation, the which comprises overall acceptance (consumer acceptability acc). Secondly,
chemical tests, which included the pH and Thiobarbituric acid (TBA) tests. These
tests play the main role in determining the development of rancidity evolution in the
fish under present investigations. ?he last type of test was the thermal diffusivity
determination through transient temperature measurements across the muscles
orientation, as well as along the n~uscleso rientation.
The above study has revealed that the consumer acceptability (acc), pH and TBA
value were found to be strongly dependent upon temperature and time of cold
preservation. The results of acc and PH led to yield a graphical solution by which the
consumer acceptability and the shelf life of the fish, during cold storage, could be
predicted.
TBA was correlated with thermal diffusivity ratio (a/a) to develop a tool by
which rancidity of fish could be predicted without going through the chemical test,
hence, a new quality deterioration index was developed. When the value of
a 1a ,+sh= 1.0 indicates absolutely fresh sample, and a/a pex>, 1 . O the lesser the
freshness. |
|---|