- The effect of round shrimp post-catch age on the frozen shelf-life
characteristics of processed cooked meat was evaluated. Refrigerated
shrimp, one, three, and five days post-catch, were cooked,
mechanically peeled, frozen at -29°C and held for a period of twelve
months at -18°C. At three month intervals, samples were subjected to
chemical and sensory evaluation. Levels of trimethylamine oxide
(TMAO), trimethylamine (TMA), dimethylamine (DMA), formaldehyde
(FA), inosine monophosphate (IMP) and hypoxanthine (Hx) were determined.
Sensory evaluations included judgements for texture, juiciness,
flavor, and overall desirability.
The degradation of frozen cooked meat quality was directly
related to round shrimp age. Flavor panel scores for meat from one
day old shrimp decreased in a linear manner with regard to texture
(r= -.933, P .005), juiciness (r= -.795, P .005), flavor (r= -.861,
P .005) and overall desirability (r= -.919, P .005). The change in
the quality of the meat from three and five day old shrimp with
respect to storage time was largely non-linear and after an initial
quality reduction during the first three months flavor panel scores
were relatively stable. Scores for frozen meat during the first six
months were equal, but the more rapid deterioration of meat from
one day old shrimp yielded scores inferior to those for meat derived
from three and five day old shrimp after twelve months.
Initial levels of TMAO, TMA, IMP and Hx in cooked meat reflected
the age of round shrimp. Differences in levels were related to chemical
decomposition, drip loss and/or bacterial out growth. DMA and FA
levels were low and not related to round shrimp age. No Hx was detected
in meat from one day old shrimp and only low levels were detected
in meat from three and five day old shrimp.
TMAO decomposed during storage to yield DMA and FA. TMAO levels
decreased in a roughly linear manner. DMA formation was neglegible
during the first six months, but increased during the latter six
months of storage in a manner inversely related to round shrimp age.
The rates of DMA formation did not show a direct inverse proportionality.
Formaldehyde was formed during the first three months of
storage, but determined levels between three and twelve months were
constant, probably reflecting its high reactivity with protein.
Determined IMP and Hx levels were relatively constant. Levels
of TMA were stable for the first nine months, but decreased during
the last three months, concurrent with the rapid formation of DMA.
The degree of quality deterioration during storage was
closely associated with the decomposition of TMAO.
. The regression of TMAO and DMA levels on scores for meat from
one day old shrimp yielded significant positive and negative correlations,
respectively. Levels in meat from three and five day old
shrimp were not correlative with the observed non-linear quality
degradation. Initial levels of TMAO, while not correlative with
initial panel scores, did correlate with scores after twelve months.
The regression of initial TMAO levels in meat from one, three and
five day old shrimp on scores yielded significant negative correlations for texture (r= -.936, P [greater than or equal to] .005), juiciness (r= -.825,P [greater than or equal to] .01) and flavor (r= -.752, P [greater than or equal to] .025). Similarly, texture (r= -.910,
P [greater than or equal to] .005), juiciness (r= -.815, P [greater than or equal to] .01), flavor (r= -.670, P [greater than or equal to] .05) and
overall desirability (r= -.783, P [greater than or equal to] .025) scores correlated in a
significant manner with DMA levels determined for meat stored twelve
The findings of this investigation support the involvement
of TMAO and its decomposition products in mediating the frozen
shelf-life of Pacific shrimp.