| Summary: | 碩士 === 國立海洋大學 === 食品科學系 === 88 === Abstract
Changes of meat texture quality of tilapia dorsal muscle as effected by the competitional occurrences of rigor mortis and tenderization during postmortem storagings at 4oC and 20oC were investigated.
In order to evaluate the rigor mortis development more accurately, different rigor parameters or indices were studied and compared. A home-made new instrument, being named as meat thermal rigorometer (MTRM) which was a modified version of traditional rigorometer (RM), was designed and constructed to monitor postmortem muscle tensional and shortening (S%) (alternatively being expressed as RIfiber) changes, to see if they could be successfully adopted for use as new rigor indices. Traditional rigor indices, including fish body stiffness index RIbody, pH, ATP content, and ATP plus ADP content were studied. In addition, a newly developed rigor index, Ts value studied by DSC was also performed. It was found that, except pH and MTRM tensional change which did not correlate well to other indices, all other indices could be correlated into two groups to reveal that two extents of rigor development could be resolved by them. Among the first group indices, while RIbody and RIfiber were changing simultaneously from 0 % to 100 %, muscle ATP content was changing from ~4.5μmole/g-meat to its ultimate value 0.1~0.2μmole/g-meat in response. This revealed that 12hr and 24hr aging were sufficient to bring tilapia body and muscle apparently to its onset of full rigor at 4oC and 20oC, respectively. Whereas, a slight extended aging period at each aging temperature was required to allow a small extent of rigor mortis remained to go complete while ATP plus
ADP content falling from 5.0μmole/g-meat to its ultimate value 0.1~0.2μmole/g-meat and DSC Ts value which would change from 49oC to its ultimate value 28oC in response.
A modified〝extractability method 〞was adopted to evaluate the progressing of postmortem tenderization quantitatively. It was based on that the postmortem tenderization could cause graduate damage of muscle fiber cell membrane, whereas the extent of damage could be reflected in terms of intracellular salt soluble protein extractability under a limited but fixed homogenation force. Three phases of tenderization developing were observed, including slow-developing stage, rapid-developing stage and terminating stage. The onset time of rapid-developing stage and terminating stage were 13hr and 25hr as were as 6hr and 18hr for agings at 4oC and 20oC, respectively. In contrary to rigor mortis, tenderization was promoted by increasing of aging temperature.
Penetration forces were determined from share-stress curves of aged muscle measured by a food texture meter with 50.9o corn-shape probe. Penetration force-aging time plots and were thus obtained and used to reflect the postmortem aged muscle texture change. These texture profiles, consisting a raising phase leading to a maximum followed by a falling phase lading to an ultimate low value, were highly related to their postmortem rigor and tenderization. At 4oC , penetration force raising phase lasting over a period of 12hr was correlated well to the span of rigor mortis development, whereas the followed declaring phase was compared by late-occurring tenderization such that the ultimate values of both penetration force and tenderization were reached at a same aging
time, 25hr. At 20oC, rapid developing of tenderization taking place at 6hr of aging which was far ahead of significant rigor mortis development, thus rigor mortis promoting penetration force raising phase was interrupted at 6hr of aging by tenderization, and the span of texture softening period was again controlled by tenderization and to terminate at a same time, 18hr of aging.
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