Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
113~920
This invention relates to a method of reducing curd
formation in a salmon canning process.
The canning of salmon is an important industry in a
number of countries. Canned salmon are particularly important
to the economy of British Columbia. In 1978 the wholesale
value of canned salmon was $116 million dollars which represents
23~ of the wholesale value of fishery products in the province.
That year British Columbia packed 1.1 million 48 lbs cases.
The United States packed 3.3 million cases and Japan 1.7
million.
The production and export of canned salmon has
always been an important economy of British Columbia fish
processing industry. During the past decade its role has
diminished slightly due to the emergence of other markets for
other fishery products, such as herring roe, and an increasing
trend in recent years towards marketing salmon in fresh and
frozen form.
Technological innovations and processing problems
relating to salmon canning have been slight. The basic machinery
used for steaking, filleting, sealing and retorting has remained
virtually unchanged for many decades. One long recognized
problem periodically brought to the attention of researchers
however is the formation of excess curd on the cut surfaces of
canned salmon. The curd, which appears as an offwhite, jelly-
like mass, largely results from the heat coagulation of soluble
proteins exuded from the cut surfaces of salmon flesh. The
curd detracts from the appearance of the canned product.
Attempts have been made to reduce or eliminate this
formation of curd. For example brining the salmon segments
prior to canning is reported to reduce curd formation by
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virtue of the salt solution diluting most of the soluble
proteins from the cut surface of the segments. Similarly the
use of disodium dipicolinate and urea solutions have been
reported to reduce curd formation. As these procedures require
hand filling of individual cans however, the methods are
economically unfeasible and are not acceptable to the established
canning systems employed. Other steps advocated have been
subjecting the surfaces of canned salmon to steam treatment
before the lids are placed on the cans. However, this method
has not proved successful during a fairly large scale trial by
a commercial canning firm in British Columbia.
The present invention has provided a method in which a
substantial reduction of curd formation is possible. The invention
is based on the idea that if the porteinaceous exudate can by hydrolyzed
into small, non-coagulable fragments of polypeptides and peptides then the
amount of curd formed would be appreciably reduced or even eliminated
completely.
Accordingly, the present invention is a method of reducing curd
formation in a salmon canning process. The method comprises application
of proteolytic enzymes or a combination of enzymes to a cut surface
of the salmon prior to the retorting process.
In a preferred aspect the enzyme is natural papaya latex
applied as a water extract. Other proteoloytic enzymes that have
proven useful include pancreatic protease,papainase, trypsin, ficin,
bromelain, prolase, chymopapain and pepsin. Hog pancreatic lipase,
and wheat germ lipase have also proved useful.
Salmon that has been treated includes sockeye salmon, coho
salmon, pink salmon, chum salmon and spring (Chinook) salmon. Steelhead
has also been treated.
In a preferred aspect in the treating of sockeye salmon
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the method comprises applying to a cut surface of the salmon,
while in the can, a water extract from natural papaya latex
powder containing 10 to 15 milligrams of extract protein, or
9.4 to 14.1 units of protease activity, as defined in "Methods
in Enzymology" (1970), Vol. XIX, p 227.
In the treatment of pink salmon the preferred method
is applying to a cut surface of the salmon two to five milligrams
per can of a water extract of natural papaya latex powder
containing two to five milligrams of extract protein, or 1.9
to 4.7 units of protease activity, as defined in "Methods in
Enzymology" (1970), Vol. XIX, p 227.
It has also been observed that the color of the oil
in the can can be improved by adding the water extract of
natural papaya latex powder containing two to 45 mg of extract
protein.
The following experimental information illustrates
the invention:
MATERIALS AND METHODS
A. PRELIMINARY LABORATORY EXPERIMENTS
Proteolytic enzyme products were purchased from Sigma Chemical
Co., St. Louis, Mo, and described by them as:
i. "Crude Powder, Type II - purified from papaya latex",
ii. "Pancreatic Protease, Type I, crude",
iii. "Papainase, twice crystallized".
Other enzymes were obtained from U.S. Biochemical Corp., Cleveland, Ohio.
Preparation of enzyme extract from crude papaya latex powder,
The coarse powder was suspended in 10 volumes of cold de-ionized water,
stirred for 20 minutes and centrifuged for 20 minutes at 15,000 x 9
in a refrigerated centrifuge. The clear amber supernatant fluid
(protein concentration, usually about 45 mg/ml) was further diluted
~13~92~
with water to achieve the required protein concentration for
a given experiment.
Aqueous extracts were similarly prepared from
purified papainase and from crude pancreatic protease
pOwder
Porteolytic activities of the extract were esti-
mated according to Arnon, 1970 Methods in Enzymology, Aca-
demic Press, Vol. XIX, 226. Activity was related to the
increase in optical absorbency at 280 nm by trichloroacetic
acid-soluble digestion products of casein, under stand-
ardized conditions. Protein was measured by the biuret
method according to Gornall, et al, J. siOl. Chem. 177,751
(1949) using commercially prepared serum albumin solution as
reference, and by the Kjeldahl method. Lipids were extrac-
ted with a 3:1 mixture of ethyl alcohol and petroleum ether.Two species of salmon, coho (I. kisutch) and sockeye (0.
nerka) were used in preliminary trials on curd reduction.
Both species were purchased locally in the unfrozen form.
The sockeyes had been transported in a slush ice system from
the fishing grounds to a local fish processing plant. Since
they appeared to be in excellent condition, they were
allowed to "age" from 3 to 7 days in the laboratory cold
room before experimental canning trials were undertaken.
This action was taken on the assumption that a longer post-
mortem period would enhance curd formation. Some sockeyes
were stored at -30C for the same reason.
Salmon were cut into segments, weighed and packed
into cylindrical ("1/2 - lb") cans. The amount of flesh in
each can ranged from about 180 to 220 g. Common salt
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(sodium chloride), 1.5 g, was added to the bottom of each
experimental can.
After the cans were filled, protease-containing
extracts~ usually 1.0 ml, were carefully spread over the
entixe exposed superior surfaces of the flesh with a volu-
metric
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pipet and the cans vacuum-sealed in a Rooney (Trade Mark)
closing machine. Reference control samples were prepared by
applying an equivalent volume of water to the flesh surfaces.
After allowing an interval of 30-45 minutes after applica-
tion of the protease-containing extracts, the sealed cans
were placed in an autoclave, sterilized at 250F (120C) for
75 minutes, then stored overnight at room temperature. The
canned products were usually examined for curd the following
day.
Quantitation of curd on the superior and inferior
surfaces of canned salmon was accomplished by manually
scraping off the curd carefully with a spatula and drying
the collected curd overnight at 103C. The "curd scrapers"
were kept ignorant of the dosage applied to any of the
samples being scraped in order to maintain objectivity.
B. PLANT TRIAL NO. 1
The first trial under commercial canning conditions
was done on sockeye salmon at a commerical cannery in
Vancouver, British Columbia. Aqueous extracts of crude
papaya latex powder were prepared in the laboratory in the
morning of the trial run and transported in ice to the
plant. The dosages applied (per "1/2-lb" can) to the
superior surfaces were 15, 25, 35, and 45 mg of extract
protein in volumes of 1.0 ml. A total of 200 canned salmon
samples were processed, including 40 untreated samples which
served as controls.
The application of the enzyme solutions with
pipets to all samples (randomly chosen from the regular
production line), were completed in about 15 mlnutes, and
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the cans reintroduced into the canning line for vacuum-
closing, rinsing and retorting. About 30 minutes elapsed
between the application of papaya latex extract to the last
experimental sample
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and the introduction of all samples into the retort. Retorting
conditions were according to standard commercial practice;
that is, 30 minutes for "come-up" time, 74 minutes cooking at
245F (116C) and 20 minutes "come-down" time.
The sockeye salmon canned during the first experimental
plant tria1 originated in waters off the north coast of B.C.
and had been kept in ice for 4-5 days.
Collection and estimation of curd formed under
various experimental conditions were performed as described
previously.
C. PLANT TRIAL NO. 2
The second plant trial was carried out at the same
cannery about one month later. The experimental protocol was
the same as for Plant Trial 1, except that (i) the dosages of
water extract of papaya latex applied to each sample were
reduced, (ii) a hand-held sprayer, modified and calibrated to
deliver 0.8 ml of aqueous extract per squeeze of the trigger,
was employed for some of the experimental series, (iii) 10 mg
of ascorbic acid was added to each sample of an experimental
series, in addition to aqueous extracts of papaya latex, (iv)
a series of pink salmon was treated with various doses of
papaya latex extract.
A total of 710 "1/2-lb" cans were obtained, including
40 cans each of untreated sockeyes and pinks which served as
reference controls.
D. EVALUATION
Organoleptic assessment of the experimentally treated
samples was performed. Each sitting consisted of 12 experienced
tasters who were subjected to a standard "Triangle Taste Test"
as described by Roessler et al. 1948 Food Research 13, 503.
1~3~20
Presented with three samples, one of which was different from
the other two, the panelists were asked to identify the two
that were similar. Further, they were asked to indicate which
had an off-flavour or odour. Experimentally treated and
untreated canned salmon, obtained from Plant Trials 1 and 2,
were presented to the taste panels in a mashed form under
subdued light. The entire contents of each can, including the
free liquid, were used to prepare these samples for presentation
to the panelists.
Volumetric measurements of oil and aqueous phases of
canned salmon samples were carried out by allowing the liquid
contents of the cans to drain for at least 10 minutes into
cylindrical graduates. After the aqueous phases were measured
directly from the graduates, the oil phases were carefully
transferred into graduated conical glass centrifuge tubes and
centrifuged for at least 5 minutes. The volume of the oil was
then estimated directly from the graduated tubes.
Aliquots of oil were removed from these tubes,
diluted in appropriate volumes of n-hexane (25-fold dilution
for sockeye salmon oil, 5-fold for coho salmon oil) and read
aga;nst an n-hexane blank in l-cm cells at 470 nm. It had
been previously established that the spectrum of the oil from
canned sockeye salmon showed maximum absorption between 465
and 475 nm, with a peak near 470 nm and that a direct relationship
existed between the amount of coloured oil and absorbance at
470 nm in the range .040 to .270 optical density units. The
spectrum for oil from pink salmon, however, did not possess
the same absorption profile, exhibiting a flat plateau in the
region 420 to 480 nm.
Measurement of the solids in the aqueous phase was
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accomplished by collecting the solids on a Whatman (Trade
Mark) No. 1 filter paper and drying the samples overnight at
103C. Rinsing the filtered residue with 10% w/v sodium
chloride solution, then with water, before drying overnight
in an oven resulted in 50-70% reduction in sediment recovery.
The data for residues given in this report represents the
obsexved weights of unrinsed residues recovered.
The drawings illustrate certain results achieved.
In these drawings:
Figure 1 illustrates the effect of papaya latex
extract on curd recovery from the superior and inferior
surfaces of experimentally canned coho salmon;
Figure 2 illustrates the effect of papaya latex
extract on curd reduction in canned coho salmon, expressed
on the basis of total curd recovered per can and per 100
grams of flesh;
Figure 3 shows the effect of papaya latex extract
on curd recovery from the superior and inferior surfaces of
experimentally canned sockeye salmon; and
Figure 4 shows the effect of papaya latex extract
on curd reduction in canned salmon, expressed on the basis
of total curd recovered per can and per 100 grams of flesh.
In Figure 1 five examples each of control and
experimentally treated cans were prepared from two salmon as
shown. The amounts of curd recovered from the top and
bottom surfaces of untreated samples are represented by the
unmarked bars, the treated samples are indicated by the
cross hatched bars. The total amount of papaya latex
extract (expressed as milligrams of extract protein) applied
~13~920
to each sample and the approximate anatomical source of the
flesh samples are as indicated in the Figures.
In Figure 2 the data obtained and expressed in
Figure 1 were calculated and expressed on a common weight
basis to account
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for variability in sample weights.
In Figure 3 steaks prepared from one side of each fish
served as reference controls for the opposite and corresponding
extract-treated sides. Experimental samples from sockeye I were
treated with 1.0 ml of extract on each surface of the flesh.
Similarly samples from sockeye II and III were treated with 2.5
rnilligrams per side and 5.0 mg per side respectively.
In Figure 4 the data obtained and presented in Figure 3
were calculated and expressed on common weight bases to account
for variability in sample weights.
RESULTS
A. PRELIMINARY LABORATORY EXPERIMENTS
Initial results obtained under carefully controlled
laboratory conditions revealed that the aqueous extract of papaya
latex has a significant effect on curd reduction. Quantitation
of curd collected from both top and bottom surfaces of canned coho
flesh confirmed that the samples treated with the extract contained
much less curd than the control samples treated with water only.
The results with coho salmon, over a range of extract protein
dosages ranging from 10 to 100 mg per sample, are shown in Figure 1,
which also illustrates the anatomical areas of the salmon from which
the samples were derived. Results obtained at higher dosages tend
to be inconsistent with respect to the overall pattern of curd
reduction. This anomaly was attributed to the probability that
excess amounts of proteases applied to the flesh surface hydrolyzed
the flesh itself, resulting in the mixing of much degraded flesh
with the scraped curd samples.
There was slightly more curd recovered from the inferior
surfaces of untreated canned salmon than from the top surfaces
(Figure lB), but the degree of curd reduction was much greater
~L 3t;9 Z O
than that obtained for the top surfaces (Figure lA).
The data from these experiments, expressed in terms of
the total amounts of curd recovered per experimental can, and
curd recovered per 100 9 of flesh, are shown in Figures 2A and 2B,
respectively, to illustrate the consistency of the results regard-
less of the basis on which the data are presented.
These initial results with coho salmon dictated the
need for confirmation using sockeye salmon, a specie which is
canned commercially in much larger quantities than coho. Moreover,
it was decided to examine the possibility that aqueous extracts
prepared from crude pancreatic protease powder, and from highly
purified papainase would prove even more effective than that
prepared from crude papaya latex powder.
Application of papaya latex extracts, in amounts
ranging from 2.5 mg to 7.5 mg of protein, to both top and
bottom sides of sockeye segments resulted in substantial curd
reduction. Figures 3A and 3B illustrate the amount of curd
recovered from the top and bottom surfaces. The same data,
expressed in terms of total curd recovered per can, and curd
recovered per 100 9 flesh, are given in Figures 4A and 4B, respec-
tively and are consistent with those shown in Figure 3.
Results using crude pancreatic protease applied to both
surfaces of sockeye salmon segments were not as visually impressive
as those obtained with extracts of papaya latex. Nevertheless,
analysis of curd weights indicated appreciable reduction in curd
formation, as shown in Table 1. The data also indicates that the
amount of curd recovered from the bottom surfaces of the untreated
samples is consistently less than that recovered from the top
surfaces of the same untreated samples. It is seen also that the
treatment is most effective in reducing curd formation at the
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bottom of canned salmon segments.
Data from the same experiment, calculated on the basis
of curd recovered per 100 g flesh are given in Table 2. The data
are consistent with those presented in Table 1 with respect to
the % reduction achieved. For this reason subsequent calculat;ons
with respect to curd reduction were based on total curd recovered
per canned sample.
Prior to actual plant trials, the final laboratory
experiment performed was to compare the effect of twice-crystallized
papainase with the water extract of crude papaya latex powder that
was used in earlier experiments. It was reasoned that the latter
preparation, being a crude extract, would contain many extraneous
proteins which themselves would coagulate upon heating and con-
tribute towards total curd formed. Use of highly purified papainase
therefore, with its higher specific activity was expected to provide
even better results with respect to curd reduction.
Experimental trials using 1, 2.5 and 5 mg of twice-
crystallized papainase yielded equivocal results. Only the highest
dosage appeared to be effective. Considering the relatively
unimpressive results obtained and the high cost of the purified
papainase, further experiments with this product were terminated.
A number of other enzyme preparations were also tested
for their effect on curd reduction. These included the following
proteases, trypsin (a, Cat. No. 22705) ficin (b, Cat. No. 15770)
bromelain (c, Cat. No. 12380) proteinase (d, Cat. No. 20815)
pronase (e, Cat. No. 20724) pronase ~-chymotrypain (f, Cat. No. 13680)
chymopapain (9, Cat. No. 13675) and pepsin (h, Cat. No. 20010).
All were purchased from U.S. Biochemicals Corp., Cleveland, Ohio,
except for pronase, Type IV, which was purchased from Sigma
Chemical Co., St. Louis, Missouri. Moreover, three lipases
113692~
(Lipase 448, Cat. No. 18480; Lipase, Cat. No. 18416, and wheat
germ Lipase, Cat. No. 18495) all purchased from U.S. Biochemical
Corp. were tried individually and in combination with a number
of proteases. The results of these trials are given in Table 2a.
In addition to its application to coho, sockeye and pink
salmon, water extracts of papaya latex were applied to chum,
spring (chinook), and steelhead. The effect on curd reduction
for these species are given in Table 2b.
In summary, laboratory experiments with extracts of
crude papaya latex powder, crude pancreatic protease, and several
other enzymes including purified papainase revealed that the most
effective and least costly of these protease preparations was the
plain water extract of crude papaya latex.
B. PLANT TRIAL N0. 1
Laboratory experiments, in which 5 to 15 mg of crude
papaya latex protein extract were applied, had demonstrated
clearly that curd formation in canned sockeye salmon was appre-
ciably reduced. For the first plant trial, however, a higher
dosage range of 15 to 45 mg per can was chosen since it was
believed that the ideal conditions employed in a laboratory
setting could not be practised or duplicated in an actual
commercial salmon canning operation. Papaya latex extract was
spread over the randomly selected unsealed cans of sockeye salmon
using 1.0 ml volumetric pipets and the cans re-inserted as soon
as possible into the canning line, vacuum-closed, and placed into
the retort along with that day's commercial production of canned
salmon.
Table 3 shows the effect of added extract upon total
curd recovered for each extract dosage. Large standard deviations
were expected, since no two canned salmon samples are ever identical.
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Moreover, at the high levels of extract protein employed, it is
very difficult to clearly separate the curd from the flesh since
the physical demarcation between the curd and flesh becomes
poorly defined and difficult to discriminate. Nevertheless, the
data for the initial cannery trial revealed a definite reduction
of curd which appeared to show some effects related to the dosages
used.
Of particular interest was the apparent improvement in
the general colour of the extract-treated samples, aside from the
improvement in the general appearance of canned sockeye salmon
as a result of curd reduction.
C. PLANT TRIAL NO. 2
The first plant trial not only confirmed the effective-
ness of the papaya extract when tried under industrial conditions,
but further revealed that trials using a lower range of enzyme
protein concentrations was required in order to establish the
least, yet most effective, amount of extract to be used. In
addition to measuring curd formation in canned sockeye and pink
salmon, other parameters were examined, including volume of free
liquid in the aqueous phase, colour of free oil and the amount of
suspended solids in the aqueous phases. These parameters were
also examined for a set of canned sockeye salmon to which ascorbic
acid (Vitamin C) was included. Previous experiments had indicated
that the colour of extract treated canned salmon was enhanced,
possibly as a result of some natural anti-oxidant present in the
papaya latex extract.
(a) Sockeye Salmon
i. Effect On Curd Formation
Curd formation was appreciably reduced even at the
lowest concentration of extract applied, but the optlmum dosage
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was found to be in the 10 to 15 mg/can range (Table 4), where
about 50-75% reduction of curd was obtained. It is noteworthy
that the mean curd weight of untreated samples from trial #l was
383 + 189 mg (mean + standard deviation), whereas the curd in the
controls from plant trial #2 was 253 + 135 mg. This illustrates
the variance in the amounts of curd found in canned salmon obtained
from plant productions spaced only two weeks apart.
ii Effect of Extract on oil Colour and Volume
Oil recovered from canned sockeye salmon demonstrated
some general irnprovement in colour as a result of treatment with
papaya latex extract. Table 5 shows that the total number of
"colour" units for the oil taken from the experimental samples
were greater than in the untreated controls. The relative intensi-
ties of the oil colours are also provided in Table 5, which more
clearly reveals the increase in the reddish-orange colour of the
oil .
The data obtained for the volume of free oil recovered
appears to suggest a slight increase at the level of 5 to 10 mg of
added extract. However, the large natural variation in the volumes
of oil recorded from sample to sample prohibits a definite con-
clusion to be made in respect of changes in oil volume.
iii Effect of Extract on Volume and Appearance of
Aqueous Phase of Drained Liquid
Incorporation of crude papaya latex extract to canned
salmon resulted in visible increases in the amount of suspended
particulate matter in the aqueous phase of the drained liquid.
The liquid from untreated cans was amber-coloured and quite clear,
whereas those obtained from treated samples demonstrated an
appreciable amount of suspended matter in them. Quantitation of
the solids in the aqueous phase showed that slightly more
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particulate matter was recovered from those samples which had been
treated with extract in the 10 mg range (Table 6), probably as a
result of enzyme action disrupting to some extent the integrity
of the exposed tissues.
A slight increase in the corrected volume of free water
was also noted in experimentally treated samples.
iv Effect of Added Vitamin C
The enrichment in the natural reddish-orange colour of
oil recovered from samples which had been treated with papaya
latex extract suggested that the crude extract possessed some
substance or substances which inhibited, to some extent, the
usual bleaching effect of the retorting process of canned salmon
flesh.
Since the reddish-orange colour of sockeye salmon
flesh is probably derived from one or more of the naturally
occurring carotenoid pigments, the addition of some anti-oxidant
substance to the experimental samples was thought to favour the
retention of the reddish-orange colour in the free oil by
inhibiting the oxidation of the natural pigment. Accordingly, an
independent set of canned sockeye salmon were treated with varying
amounts of papaya latex extract to which were added 10 mg/ml of
ascorbic acid. Table 7 shows that the inclusion of 10 mg of
ascorbic acid to the extract resulted in no enrichment in the
intensity of the oil colour over those samples which were treated
with extract only, as shown in Table 5 earlier.
(b) Pink Salmon
Since pink salmon were also being canned during Plant
Trial 2, a number of samples were treated with various amounts
of papaya latex extract to investigate its effect on curd formation,
oil colour, oil volume, water volume and on suspended solids in
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the water phase.
i. Curd Formation
The amount of curd collected from untreated canned
pink salmon was considerably less than those obtained from sockeye
salmon controls, which probably accounted for the better effect on
curd reduction obtained even at the lowest dosage of extract
employed. For pink salmon, approximately 70-80% reduction in curd
was achieved (Table 8) as compared with 50-75% reduction achieved
for sockeye salmon under similar conditions.
ii Colour and Volume of Oil
As expected, the intensity of the colour of pink salmon
oil was only about 30% of that sockeye salmon oil, and the volumes
of oil recovered to be about 40% less than for sockeye salmon.
Analysis of the intensity of the oil colour of experi-
mentally treated samples revealed a marked improvement over the
controls (Table 9). However, the apparent increase in the total
colour units recovered from the treated samples must be attributed
largely to the increase in the volumes of oil.
iii Residue and Free Water Volume
Treatment with papaya extract resulted in the recovery
of more suspended solids from the aqueous phase and a very pro-
nounced increase in the corrected volume of the free aqueous
phase as shown in Table lO. Compared to canned sockeye salmon
(Table 6), pink salmon flesh released about lO% more water after
being canned and retorted.
D. TASTE PANEL
Three independent organoleptic trials were conducted
on experimentally canned salmon to determine whether taste
panelists could differentiate between the untreated and treated
samples. They were also asked to identify the treated sample.
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The test samples included sockeye salmon canned in Plant Trial 1,
containing 15 to 45 mg of extract per can, and those obtained
from Plant Trial 2, treated with 17.4 mg of extract.
The results of the three taste tes~ are summarized in
Table 11. The triangle test employed dictates that by chance alone,
three correct answers are to be expected from 12 testers, and a mini-
mum of eight correct answers are necessary to establish, at the 95%
confidence level, the ability of the tasters to discriminate between
the treated and untreated samples. The results given in Table 11
clearly show that the panelists experienced considerable difficulty
in differentiating between the treated and untreated samples of
salmon, and encountered even more difficulty in correctly identi-
fying the treated sample, even for those cans in which 45 mg of
papaya latex extract was incorporated.
It is worth noting, however, that of those panelists
who correctly distinguished between the 45 mg treated and
untreated samples, all three correctly identified the sample
(or samples) that had been treated, whereas such was not the
case in which 15 and 17.4 mg extract had been used.
E. OTHER RESULTS
i Application of Extract by Spraying
In all preliminary work leading to plant trials, known
volumes of enzyme extract were spread manually and laboriously
over the surfaces of canned salmon with p;pets. However, it was
recognized that if the use of papaya latex extract in the
commercial canning of salmon should ever be realized, the extract
would have to be applied by another method, likely by spraying
at rates exceeding 250 cans per minute.
For this reason, trials were performed in which
extracts were applied to the exposed top surfaces of a series of
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canned salmon using a hand-held sprayer, modified to deliver 0.8 ml
of extract with each squeeze of the plunger. The efficacy of this
technique on curd reduction and on other parameters was examined,
and subsequent analyses showed that the spray method of application
was as effective as pipetting. The data in support of this con-
clusion are given in Table 12 (for curd reduction) and in
Table 13 (for oil colour oil and water volumes and quantity of
residue recovered from the aqueous phase). Although the dosages
applied by spraying differ somewhat for the pipetted series,
the data in Table 12 can be compared with those given in Table 4
(for the pipetted series). The data given in Table 13 can be
compared with those given in Tables 5 and 6. These comparisons
clearly show that the application of the extract by spraying
was as effective as pipetting.
ii Composition of Curd
Curd collected from a number of untreated canned sock-
eye salmon were subjected to routine chemical analysis for fat,
protein and water content. The results, shown in Table 14,
illustrate the lipoprotein nature of curd which forms in canned
sockeye salmon.
CONCLUSION AND COMMENTS
It was unequivocally demonstrated in laboratory and
plant trials that the application of a water extract of natural
papaya latex powder to the surfaces of canned salmon effectively
reduced the amount of curd formed. Under the conditions
employed, the optimum amount of extract recommended is in the
10-15 mg~can range for sockeye salmon (to achieve approximately
50-75% reductjon), and 2-5 mg for pink salmon (to achieve approxi-
mately 70-80% reduction), provided (a) an interval of at least
30 min at ordinary room temperature is allowed between the
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application of the extract and the heat sterilization
process, and (b) the specific activity of the extract is
0.94 optical density units per minute per mg. of protein.
The use of excess papaya latex extract gives canned salmon a
"dryish" look and should be avoided.
Concerning proteolytic activity individual proteol-
ytic preparations will have a range of specific activities,
based upon their state of purity. The relatively impure
preparations will have a lower specific activity than the
more highly purified preparations. For example, typical
specific proteolytic activity values for crystalline papain
(highly purified) are about four times greater than those
for crude papaya extracts (latex). Under conditions where
time and temperature are approximately constant, as in a
fish canning line, the desired result according to the
invention is brought about by the total amount of proteoly-
tic activity which is added. The total activity is repre-
sented by the product of the protein concentration (milli-
grams per liter) multiplied by the specific activity (rate
of protein hydrolysis per milligram of protein). Thus with
2 to 40 milligrams of protein multiplied by a specific
activity of 0.94 the range of total activity is from 1.8 to
37.6. This is satisfactory according to the invention, that
is the range of total activity may be about 1 to about 38.
This range can be made up from proteolytic preparations
having specific activity values other than 0.94. For
example, assume that the preparation had a specific activity
of 1.88, then the milligrams of protein required would be 1
to 20. It is unlikely that even crude extracts, which have
--19--
1~3~
been shown to be the most useful, will have a specific
activity of exactly 0.94. They could be 0.82, 1.11 or any
variety of numbers in the environs of 0.94.
Apart from the general improvement in the appear-
ance of canned salmon as a result of curd reduction, improve-
ment in the colour of the canned product was also achieved.
Examination of the free oils revealed an increase of approxi-
mately 1.5-fold in the intensity of the natural reddish-orange
colour of sockeye oil. Similar increases were observed for
oils recovered from canned pink salmon. No marked improve-
ment, however, was noted in the colour of the flesh intself.
The choice of ascorbic acid (vitamin C) as the
antioxidant was predicated largely upon its high acceptance
as an additive in many food preparations. Our experiences
showed that no improvement in the colour of sockeye salmon
oil results beyond that already achieved by the addition of
papaya latex extract only.
Unlike many enzyme preparations, the proteolytic
activity of the dilute water extracts of papaya latex was
stable for at least 8 hours at ordinary room temperature.
This particular property is extremely important from a
practical standpoint, since the water extract can be
prepared at the beginning of a canning shift and be used
for the entire day's canning operation or longer with no
need for refrigeration.
-19a-
j ~.~
920
I~ELE I
EFFECT ON NON~Pln~n~rED PA:3o~FIC PF~n~5~5E E~lWCT oN CURD
FCRM~I~oN IN C~D~aD ~ SALMoN
. Total Wbights of Cbra
P~ed E~
Fish Nb. No. Cans Tbtal Reduction
Tbp Surface 80tbom Surface ~ng dried wt) Achieved
(~ dr~ wt) (T~ dried wt)
. , . , ._
. 1 Cbntrol (4) 1951 562 2513
Exptl (4) 1710 286 1996 21%
: _ .
2 Ckntrol ~4) 1862 489 2351
~Xpkl (4) 1671 198 1869 21%
. . _ _
3 oontLvl (4) 1780 736 2516
Expkl (4) 1257 385 1642 35%
, . .......................... . . , -,-
Sesment~ oktained fron one side of e æ h sa~non were tL~ated with protease pre$ar-
ation with the cpposite and correspond~ng ~egment~ serviing as oontrol~. The
enzyme was applied to both Lut~ and top surfaces of salmon ses~ents with a
hand-held sprayer. Ihe follcwing dosages were applied: Fish #1, 1.0
mg/siae; Fi~h #2,-2.5 n~wide; Fish #3, 5.0 mg/side.
~13~9;~0
~2
- 100 g E~ USED
. _ ~ . ._
Curd P~ Per 100 g fle~h
Fi~;h ~. Sa~ple Total Red~cti~
Ibp Surfaoe Bott~ S~faoe ~ dFied wt) A~hieved
(n~ dried wt) (mg dried wt)
1 (~1 231 300
Exptl 200 32 232 23
2 C;~ntrol 230 60 2gO
_ _ E~ 193 24 217 25%
3 (~1~1 245 101 346
E~ 177 53 230 3496
. ._ . _ ._ __ ._
tal pr~ocol as descri~ed far Table 1.
113~'~ZO
IA~LE 2a
EFFECT QF SEVER~L PRCr~LYIIC AND LIPOLY~IC ENZYME
PKEPARA~ICNS CN FCRM~IICN CF CURD IN CANMED SCC~YE SiUllo~
_ _ Curd Reocvered ~mg dried weight)
Enzymemg Applied/Can Control^ E~qperiment~l~ ~ Reduction
_ _ __
Trypsin 12 2887 2198 24
Ficin 14 2763 1703 38
8rcnelain 30 2976 1804 39
Proteinase 14 2537 2093 18
Prolase 4.5 2129 1977 7
Pronase 5.5 2386 2384 O
~-Chymftrypsin 10 2775 2959 O
Chymcpapain23 2476 1449 42
Pepsin 16 2087 1665 20
Lipase 448 3.5 2807 2503 11
Lipase ~12 x NF~ 15 2008 1733 14
Lipase (wheat germ) 40 2789 2565 8
Papaya Latex Extract 35 2638 1004 62
Ficin7 ~ combined 2556 1736 32
Lipase "12 x N F 7 )
Chymopapain11.5~ combined 2556 1496 42
Lipase ~12 x NF- 7
Trypsin6 ~ cc~'oined 2556 2177 15
Lipase ~12 x NF" 7 ~
Papaya Latex Extract 17 ~ csmbined 2556 1787 30
Lipase ~12 x NF~ 7 J
Samples were prepal~d in such a way that seg~ents taken fro~ one side of the fish
served as ccntrols for the experi~antal sesments taken fnon the c~x~sita and
correspcnding side. Each figure in the control and expe~inl~tal columns represents
the average of three samples.
22
113~5~ZO
TABLE 2b
EFPECT OF PAPAYA LATEX EXTRACT CN CURD FORMATION
IN CHUM, SPRING (CHINOOK) AND STEELHEAD
.. _ ,
mg Papaya Latex
SpeciesExtract Protein Added mg Dr ed Weight % ~eduction
Control* Exptl.*
_ _
Chum 2 640a 252a 61
808b 396b 51
949b 395b 58
Spring 5 ll87a 437a 63
l079c 509c 53
Steelhead 5 264a llla 58
333a 44a 87
* Samples were taken from fish and canned as described in Table 2a
a Average from two sa~ples
b ~verage from five sa~ples
c Average frcm three samples
113ti920
~LE 3
.. __ ,
~o~age Curd ~ Redlticn
., ~ ~ ~ ~ ) per can ~q dried wt) A ~ieved
.. _ .
O (canl~v11 383 + 189 ~11)
._ .. _
152 + 134 (11) 60%
128 + 113 (11) 67%
. .__
141 + 109 tll) 63%
. _
46+ 27 (11) 88%
nunber of ~le~ given in par~ehes~. App~tc~stian of Dunnet's
24
11369ZO
T~BLE 4
ON ~RD REDCC:~ IJ~
. _ . ..
Dosage C~d ~ P~icn
~g extract prctein) per can ~ng dried wt) Achieved
. ._
O (control) 253 + 135 (12) _
.
2.9 179 + 128 tl2) 29%
. _ 178 ~ 131 (12) 29%
; 5.8 135 + 88-(12)- 47%
. __
11.6 60 + 43 ~12) 7S%
- _ _ . ~
17.4 99 + 113 (12) 61%
l~e papa ~ late~c e~act8 were aE~ lg 1.01~ VOlUll~iC
pipets. Cord rex~rnrred is expressed a~ nn3 ~ standard devia-
tion, with the nu~ r of samples given in p2rentheses.
113~i9Z~)
I~BIE 5
5ECCND PL~NT TRIALs ~w ~L~l~ oF P~PAY~ IAIEX EXTRACT ON Ct~XJR
.__
Dosage 0~1 Volume Cblcur Intensity Col Uhit~
(mg e~tract prokein) ~1) (O.D. 470 units)
. .. . _ ___ . __ _ _ . _ _
O (oontrol) 4.6 + 1.7 (18) 2.3 + 0.4 10.6 ~ 0.7
2.9 4.7 + 2.1 (6) 3.4 + 0.6 16.0 + 1.3
..... ._ . _.
4.6 5.6 + 2.6 (6) 3.1 + 0.5 17.4 + 1.3
5.8 5.9 + 3.8 (5) 3.4 + 0.4 20.1 + 1.5
11.6 4.3 + 1.3 (6) 4.1 + 0.4 17.6 + 0.5
.
- 17.4 3.9 + 1.4 (6) 3.1 + 0.6 12.1 + 0.8
nC~l in Pncity" is def~n4~ as the number of cçti~l density (O.D) units
for a given canned sa~mon oil whe~ read at 470 nm in a lOl cm cell at
20-23C. "Col units" is the product of ccl intensity and volume.
Extracts were applied to sa~on surface~ with Pipets.
26
~369ZO
2~E 6
r~ ~ AND E~;~LS
Dosage Free Wa~Pr Vol~me Residue
(n~ extract Fr~tein) (ml) ~ dried wt)
O (con-L~11 36.5 + 4.3 (12) 968 + 144 (12)
.. .... _ . .
2.9 37.7 + 4.1 (12) 728 + 174 (12)
4.6 36.3 + 5.2 (12) 1092 + 235 (12)
5.8 37.3 + 4.9 tll) n 8 + 155 (11)
11.6 38.3 + 3.4 ~12) 1192 + 333 (12)
17.4 44.1 + 5.2 (12) 813 + 200 (12)
Extracts were applied with pipet~.
Except for the control group, free water volumes are crl~Y~bDd
bo a ~ t Lor the l.0 nl of a ~ s extract added.
Data e~pressed as T##ms + standard deviation, wit~ number of
samples shown in parentheses.
27
~131~9ZO
5ECCND PL~NT TRI~L: EFFECT CF AS~w IC AC m oN
.. .. _ ..
Dosage O~l Volume Colour IntensityColour Units
(mg extract protein)(ml) (O.D. 470 units)
. __
O (control) 4.6 + 1.7 (18) 2.3 ~ 0.4 10.6 + 0.7
. _ .. ..
4.6 5.7 + 2.5 (6) 3.0 + 0.7 17.1 + 1.7
9.3 5.7 + 1.8 (6) 3.2 + 0.4 18.2 + 0.7
_ ._
___ 6.0 + 2.2 (6) 3.7 1 0.4 22.2 + 0.9
16.0 5.3 + 2.0 (6) 2.9 + 0.1 15.4 + 0.2
. .
"Cblour mtensity" and "oolour unit" as def m ed in Table 5.
All exper~mental s ~ e~ were treated with 10 mg asccrbic acid. m e data
gi~en in this table should be compared with those gi~en in lable 5,
althcugh the dosages di ff OE slishtly.
Extracts were applied by spraying.
28
~136gZO
l~eLE 8
Dosage Curd FbYIJnerod Reducti3n
~ng e~tract Frotein) per can (~g dried w~) Achieved
95 + 69 (1~) _
4.6 20 + 17 (12) 79%
9.3 17 + 31 (12) 82%
13.9- 30 + 41 (12) 68%
16.0 20 + 22 (12) 79
. . _.
Curd reo~very ~ e~p~essed as nY~ms I standard deviation.
- ' .
113~i~ZO
~[E 9
CN ~ P~ VaU~ E~ OIL ~N CP~NED P~ SPIM~
. . _
DosageO~l VolumeCblcur ~ntensity Cblour Uhits
(mg extract protein) ~nl) (O.D. 470 units)
0 2.6 + 1.0 (6) 0.9 + ~.3 2.3 + 0.3
. . .
4.6 3.4 + 1.4 (6) 1.2 + 0.3 4.1 + 0.4
. ,
9.3 3.5 1 1.0 (6) 1.2 + 0.2 4.2 + 0.2
~ . .
13.g 3.9 ~ 2.4 (6) 1.2 + 0.3 4.7 + 0.7
... .... . . _
16.n 5.8 + 3.5 ~6) 1.3 + 0.17.5 + 0.3
"Cblour Inten~ity" ~nd nCOaOUr uni~qn aq defined in Table 5.
Papaya latex e~Lr~ct applied by spraying.
Data expressed a_ neans + ~tandard deviation, with nn~ber o~ 5amples shown
in parentheses.
11~69ZO
~E 10
l . . _ __
DbsageFree Water Volu~eResidue
~n~ e~tract protein) ~nl) (mg dried wt)
O (control)42.5 _ 2.8 (6) 881 + 211 ~9)
4.6 46.2+1.9 (6)1094~345 (9)
9.3 49.3 + 3.7 (6)1300 _ 221 (4)
13.9 49.0 _ 1.8 (6)1132 _ 121 (4)
16.0 51.8 _ 2.8 ~6)1485 + 348 (4)
Data shown as-~eans + stanaard deviation, with n~lL~ of samples
- in p2rentheses.
Excepk for the c~A,trol group, free water vDl~ne~ were ccn~lx:bel
bo acccunt for the water added.
31
1136~9~0
q3~LE 11
O~C = ~ CE ~rWED SO~E
q~ w~ Ppæ~ ~c ~
~ ----- --
si~ng N~ 1 2 3
.
Dosage/ex~i~,~,tal can ~) 17.4 15 45
... . _
ND. of tasters participating 12 12 12
.
No of tasters ~rrectly picldng out ~e "odd". sample* 6 6 3
~ . l
~;b. of ta~ters correctly identi~i3lg treat~ s~mple 2 4 3
~. oE carrect-arlswers needed to e ~ bli~h significa~rt
difference between treated and untreated sample~ at
95% ccnfid~nce level ~8) 8 8 3
* S3mples were presented ae: C-C-E, C-E-C, E-C-C, E-E-C, E-C-E, C-~-E,
where C = untreated, and E = treated sa~ples. One of the three ~amples
in a triangular taste test represent~ the "odd" sample, whlch could
he either treated or untreated.
32
~13~i9ZO
~2
S = S~
..
Dosage Curd Re~ered P~
P~:~) p~r can (~ drl~ed wt) A~
....
O (oontrol) 253 _ 135 ~18)
. .
4.6 162 1 172 (12) 36%
9.3 114 _ 80 (12) 5s%
13.9 73 + 66 ~12~ 74%
...... .
16.0 67 + 78 (12) 73%
Mbthod of spraying and volumes dirç~sliod are described ~n
the text.
Cord recovered is exçregced A~ n~#~n~ + standard deviation,
with nuTber of sa~ples in pYcls~ibeses.
113~920
~-- ~1 _ _ _~ D
.. ~ ~ ~r ~ _~ ~ ~Y
~ +l +l +l +l +l
~ CD g O _I
~ ~ o ,~ ~ ~ ~ _, ~0 ~ 3
~ ~ ~3 U~ o i C o
# ~ ~ +l +l +l +l +l .
~ d l ~ .~. o o~ ~ o ~ ~
~3 ~ ~ o _, _, ~ ~ ~
~1 ~
~ ¦ ~ D ~o I ~} g
+l +l +l ~ol +l 1
o ~ a~ _1 -1 q~
l ~ _ l _ l ~ ~ '
34
11369ZO
q~l3LE 14
%~t~
~at 3.5
Pr~n 17.4
~te~ 79.8
100.7
;
..
