- The effects of ambient temperature storage on the chemical
and nutritional characteristics of phosphoric and sorbic acid-stabilized
fish autolysates were determined. Variations in sample
composition due to autolysis, deboning, and acidification were also
Autolysates of English sole (Parophrys vetulus), true cod
(Gadus macrocephalus), Dover sole (Microstomus pacificus), and
orange rockfish (Sebastodes pinniger) carcass wastes, whole Pacific
hake (Merluccius productus) and dogfish shark (Squalis acanthias),
and a hake/tuna viscera (70/30 wt/wt) mixture were utilized in the
investigation. Samples were acidified to ca. pH 3.25 with phosphoric
acid (85% w/v) and contained potassium sorbate at the 0.2% (wt/wt)
Screen separation of bone reduced the ash levels of samples,
with the exception of dogfish shark. Loss of bone minerals, specifically
calcium and phosphorus, was responsible. Phosphoric acid addition elevated ash and phosphorus contents to higher levels than
for raw materials.
Acid-stabilized autolysates were stable to microbial outgrowth
throughout 8 months of ambient temperature storage. Slight increases
in pH levels were generally observed. Sorbate levels decreased
at an apparently exponential rate with respect to time
(r=-.9146, P [greater than or equal to] .005).
Hydrolytic rancidity did not proceed during storage. Stability
towards microbial outgrowth, inactivation of endogenous lipases
during pasteurization, and maintenance of acidic environmental conditions
enhanced fat stability. Oxidative rancidity, as measured by
2-thiobarbituric acid (TBA) numbers, progressed during storage.
Carcass wastes showed higher rates and overall levels of oxidation.
Initial free fatty acid levels correlated in a linear manner with 0 and
4 month TBA numbers (r=.9548, P [greater than or equal to] .005; r=.9187, P [greater than or equal to] .005, respectively).
The regression of TBA numbers at 4 months on zero time
values increased in a linear manner (r=.9346, P [greater than or equal to] .005).
Proteolysis during storage, as monitored by free amino groups,
was not detected. Inactivation of native proteases during processing
and the microbial stability of samples were responsible. Levels of
available e-amino lysine and tryptophan were stable throughout storage.
The protein quality of acidified hake, dogfish shark, orange rockfish, and English sole autolysates, stored for 0, 4, and 8 months,
was evaluated using protein efficiency ratio (PER) determinations.
Protein quality was not affected by storage in samples of acidified
hake, English sole, and orange rockfish (P=.05). Ratios for all
samples of hake and the 0 and 8 month samples of dogfish shark did
not vary significantly (P=.05) from the casein control. English sole
and orange rockfish samples yielded PER values that were inferior
to casein and round fish samples (P=.05). The regression of feed
consumption and PER values on TBA numbers decreased in a linear
manner (r=-.7999, P [greater than or equal to] .005; r=-.8424, P [greater than or equal to] .005, respectively).
Higher contents of nutritionally inferior visceral proteins and increased
rates of oxidative rancidity in the carcass waste samples
probably were responsible for their reduced protein qualities.