| Summary: | 碩士 === 國立中興大學 === 畜牧學系 === 84 === Studies on quality characteristics and thermal
properties of pork postmortem
Lieh-Chin Lin
Abstract
The functional properties of raw meat influences the
quality of meat products and they are the major topic to
meat scientists and are also what meat processer most
concerned.
Differential scanning calorimetry(DSC) can detect the
thermal properties of protein in the complex food system.
The technique of DSC applied in meat products, egg
procucts and soybean protein...etc, is gradually popular,
and it also can be applied to observe the change and
denaturation of the thermal properties of protein and to
determine the freshness and properties of meat and what
kind of non-meat protein additives exists. So, we can use
DSC to determine the thermal properties of protein, their
interrelation, and to compare with other functional
properties. The purpose of this study was to determine the
relation of the thermal properties of pork chilled at -2℃
for 24hrs based on DSC and the functional properties of
muscle protein and then to find the changes of meat quality
during 24 hrs after slaughtering. We also investigated the
change of pork during storage at -2℃ and 25℃,
respectively. DSC thermal properties, K-value,Volatile
Bacic Nitrogen(VBN) and the change of ATP-related
compounds are determined to find the relationship between
freshness and quality of meat.
In experiment Ⅰ, the M. longissimus dorsi of pork was
chilled at -2℃ and sampled at 0, 2, 6, 12 ,24 hrs to
detect internal temperature, pH value, sarcomere length,
water holding capacity, emulsifying capacity, gelation
characteristics, hardness, DSC thermal porperties, salt
soluble protein estractability, electrophoretic behavior and
scanning electron micrograph(SEM) of pork.In experiment
Ⅱ ,the same samples were stored at -2 and 25
℃,respectively,and sampled at 0, 12, 24, 36, 48, 96 hrs to
detect pH value, total plate counts,ATP-related compounds,
K-value, VBN, NMR-spectra and electrophretic
behavior(SDS-PAGE).The result were as follows:
In experiment Ⅰ :the pH value declined slightly ,
sarcomere length changed few after slaughtering
immediately to 24 hrs , water holding capacity , emulsifying
capacity and salt soluble protein extractibility were slightly
higher after slaughtering immediately but then remained
stable during 24 hrs postmortem . Gel strength and hardness
declined with the storage time increased, significantly.A
exothermic peak and three endothermic peaks including
myosin , sarcoplasmic protein and actin appeared on DSC
thermogram within 6 hrs postmortem,then the transition
temperature(Tmax) of myosin and sarcoplasmic protein
declined with the storage time increased,but Tmax of actin
was more stable, and the △H value also declined with the
storage time increased.
In experiment Ⅱ: the pH value decreased initially then
increased, and pH of the samples stored at -2℃ were more
stable than pH of the samples stored at 25℃.ATP-
related compounds of the samples stored at -2℃ also
remained more stable than that stored at 25℃.And ATP-
related compounds of the samples stored at -2℃ degraded
slower in 24hrs.IMP concentrates almost reached the
highest level; ATP and IMP concentrations of the sample
stored at 25℃ degraded quickly. K-value and VBN value,
the sample stored at -2℃ had few change and those of the
sample stored at 25℃ changed remarkably as the storage
time increased. DSC thermal properties of the samples
stored at both -2℃ and 25℃, could find a exothermic peak
at 0 hr then Tmax of myosin and sarcoplasmic protein
decreased as the pH value declined. The Tmax of actin
changed more less.However, two endothermic peaks existed
in the sample stored at25℃ for 96 hrs. The NMR-spectra of
ATP-related compounds had sugar phosphate and
inorganic phosphate only. Electrophoretogram of the
samples stored at -2℃ did not change remarkably before
48 hrs storage, but myosin heavy chain and G-actin tended
to decrease for the samples stored at 25℃ for 96 hrs. In all
time interval, we can observe the 30K daltons component
appearing on the electrophoretogram.
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