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Functional properties of spray-dried animal plasma in canned petfood

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Over the last 15 years, spray-dried animal plasma (SDAP) has become a commonly used gelling ingredient in canned petfood diets. However, little is known about the functional properties of this product in this application.SDAP is a concentrate of proteins with the property of producing a very stable and compact gel when submitted to high temperatures. High gel strength capacities are obtained at temperatures above 90°C, with peak strength at 121°C (force needed to break a 100g/kg gel was 5.29N). The water retention capacity of the gel formed is stable at temperatures above 80°C. When compared with other gelling and binding agents, SDAP is a soluble product with better gelling properties than egg albumin (EA), wheat gluten (WG), and porcine products (PP), but less than carrageenan (CM) (force needed to break 100g/kg water gels were 7.02, 3.45, 2.11, 0 and 10.20N, respectively). When used in a complete loaf type of canned petfood, SDAP maintains a more compact texture compared with the other binding agents at the same inclusion level, and reduces the exudation associated with these products. This exudation was significantly reduced compared with WG and CM, which gave 156 and 125%, respectively, more exudation than SDAP in the same loaf recipe.According with the results obtained, SDAP can replace other binding or gelling agents at the same formula cost, helping in the reduction of exudation from the meat block and maintaining or increasing the texture of the final canned petfood.The addition of plasma contributed to enhancing the palatability, particularly in cats, over the standard diet in which it replaced wheat gluten. The total intake in cats after 2 consecutive days comparing loaf containing SDAP or WG at the same inclusion (20g/kg) was statistically improved with the inclusion of SDAP (141 and 78g, P
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Animal Feed Science and Technology
122 (2005) 331–343
Functional properties of spray-dried animal
plasma in canned petfood
Javier Polo, Carmen Rodr´
ıguez, Neus Saborido, Jes´
us R´
odenas
APC EUROPE, S.A., R&D Department, Avda. Sant Juli`a 246-258, Pol. Ind. El Congost,
E-08400 Granollers, Barcelona, Spain
Received 27 October 2004; received in revised form 10 March 2005; accepted 13 March 2005
Abstract
Over the last 15 years, spray-dried animal plasma (SDAP) has become a commonly used gelling
ingredient in canned petfood diets. However, little is known about the functional properties of this
product in this application.
SDAP is a concentrate of proteins with the property of producing a very stable and compact gel
when submitted to high temperatures. High gel strength capacities are obtained at temperatures above
90C, with peak strength at 121C (force needed to break a 100 g/kg gel was 5.29 N). The water
retention capacity of the gel formed is stable at temperatures above 80C. When compared with
other gelling and binding agents, SDAP is a soluble product with better gelling properties than egg
albumin (EA), wheat gluten (WG), and porcine products (PP), but less than carrageenan (CM) (force
needed to break 100g/kg water gels were 7.02, 3.45, 2.11, 0 and 10.20N, respectively). When used
in a complete loaf type of canned petfood, SDAP maintains a more compact texture compared with
the other binding agents at the same inclusion level, and reduces the exudation associated with these
products. This exudation was significantly reduced compared with WG and CM, which gave 156 and
125%, respectively, more exudation than SDAP in the same loaf recipe.
According with the results obtained, SDAP can replace other binding or gelling agents at the same
formula cost, helping in the reduction of exudation from the meat block and maintaining or increasing
the texture of the final canned petfood.
Abbreviations: SDAP, spray-dried animal plasma; WG, wheat gluten; EA, egg albumin; CM, carrageenan mix
for petfood; PP, pork protein; GSC, gel strength capacity; WHC, water holding capacity; FEC, fat emulsifying
capacity
Corresponding author. Tel.: +34 93 861 50 60; fax: +34 93 849 59 83.
E-mail address: javier.polo@ampc-europe.com (J. Polo).
0377-8401/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.anifeedsci.2005.03.002
332 J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343
The addition of plasma contributed to enhancing the palatability, particularly in cats, over the
standard diet in which it replaced wheat gluten. The total intake in cats after 2 consecutive days
comparing loaf containing SDAP or WG at the same inclusion (20g/kg) was statistically improved
with the inclusion of SDAP (141 and 78g, P<0.001). Similar results were obtained for first choice
and in another study comparing loaf containing SDAP at 10g/kg or WG at 30g/kg (total intake 151
and 61 g, P<0.001, respectively).
© 2005 Elsevier B.V. All rights reserved.
Keywords: Spray-dried animal plasma; Canned petfood; Gel strength capacity; Water retention capacity; Fat
emulsifying capacity; Texture; Palatability
1. Introduction
The use of spray-dried animal plasma (SDAP) in wet petfood recipes is not new. On the
contrary,ithasbeen a commonlyused ingredient forthe last 15years. The main applications
of SDAP are in chunks and pouch-type of products and in cat food. The use of SDAP not
only contributes effectively to enhance the texture of the chunk, but also to maintain a high
degree of cohesion between the different ingredients of the recipe due to its high water
retention and fat emulsifying capacities.
According to the generalized opinion of the petfood manufacturers, SDAP is a unique
product in their wet diets, because it allows them to standardize the quality of their final
product, irrespective of their raw material quality.
The porcine or bovine blood used to produce SDAP is collected hygienically from
authorizedslaughterhouses afterinspection and approvalby government veterinarians. This
blood is kept in liquid state by adding anticoagulants (sodium citrate or sodium phosphate)
at the time of bleeding. The blood collected is kept refrigerated until processing in a plate
centrifuge where two main fractions, red blood cells and plasma, are separated. The liquid
plasma is concentrated using reverse osmosis membranes or a vacuum evaporator. Finally,
the concentrated plasma is spray-dried, obtaining a very fine powder (particle size lower
than 0.4mm) that preserves all the functional properties of the liquid plasma such as the
capacity of producing a thermoplastic gel when it is diluted in water and submitted to
high temperature or extreme pH, or its high water retention and emulsifying capacities to
cite some of the physical properties of plasma protein. SDAP maintain also the biological
functionality of some of the proteins that contain, like immunoglobulin, transferrin and
albumin (Par´
es et al., 1998b).
Typically, SDAP showed a water content lower than 100g/kg, 150–170 g/kg of ash and
700–780g/kgof protein. When the plasma isheated,anirreversibleandstablegelisobtained
by protein denaturation (Harper et al., 1978; Howell and Lawrie, 1984; Cheftel et al., 1989;
Par´
es et al., 1998a). Blood plasma is widely used in several common meat products in
Europe. A heat-induced gelling capacity offers a potential interest for food applications
since gels give texture and consistency, improve water holding capacity, retain flavors and
nutrients and reduce fat losses. Plasma albumin has also excellent emulsifying (Tybor et al.,
1973, 1975; Caldironi and Ockerman, 1982; Nakamura et al., 1984) and foaming properties
(Tybor et al., 1975; De Vuono et al., 1979; Etheridge et al., 1981).
J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343 333
Despite the common use of SDAP in petfood products, the literature available on this
application is very limited. The purpose of this manuscript is to explain the main properties
ofSDAPandhowthese functional properties canbe evaluatedin isolated conditions (diluted
in water) or in a complete petfood product (loaf), compared with other binding ingredients
commonly used in this industry.
2. Material and methods
2.1. Tested products
The products used in isolated environment or in the complete recipe of a canned loaf
format were SDAP (AP-820), obtained from APC-Europe (Spain), wheat gluten (WG)
obtainedfromMidwest Grain Products, Inc.(US),eggalbumin(EA),obtained from Primera
Foods, Inc. (US), carrageenan mix for petfood (CM), a mixture containing 500g Kappa-
carrageenan/kg, 200g KCl/kg and 300 g locust bean gum/kg, obtained from G3 Aliments
(Spain), and Scanpro T95 (PP) as pork protein, obtained from Danexport (Denmark).
2.2. Physicochemical analysis
The water content was analyzed in accordance with AOAC (1999) procedure 930.15,
and ash content in accordance with the Journal Officiel des Communit´
es Europ´
eennes,
no. L155/20. Protein content was measured by the combustion method in accordance with
AOAC (1999) procedure 990.03. Water solubility was determined by measuring the insol-
uble particles present in a 100g/kg (w/w) solution of the products in water. Briefly, 0.5 g
of powder were dissolved in 5ml of water. The tubes containing the solution were cen-
trifuged in an angular centrifuge at 3000rpm for 15 min. After centrifugation, the liquid
was discarded and the pellet remaining at the bottom of the tubes was measured after drying
at 105C for 24 h. Thus, the solubility of the powder was calculated by determining the
percentage of insoluble material with respect to the initial quantity dissolved.
2.3. Gel strength capacity (GSC)
Thegellingcapacityisthepropertyofaproductdissolvedinwatertoformathermoplastic
gel when it is submitted to high temperatures or other denaturing conditions (pH, salt
concentration). The gel strength capacity is measured by quantifying the force needed to
break a gel obtained after heat treatment. Briefly, a 100g/kg (w/w) solution in water was
obtained by dissolving completely 33g of the tested product in 300 ml of tap water and
one drop of antifoam agent while stirring vigorously for 30min. Once fully dissolved, one
aluminum can (diameter 75 mm, height 110mm, 400g capacity) was filled and autoclaved
at 121 C for 1h. After sterilizing, the cans were left cooling overnight inside the autoclave
(it is important to not analyze hot cans immediately after autoclaving because rapidly
cooling cans could cause cracks (fissures) and introduce errors into the measurements). The
texture was analyzed by subjecting the gels to a single compression test using the TA-XT2i
texturometer analyzer (Stable Micro System, Surrey, UK). The hardness, defined as the
maximum force attained during the first compression cycle, is expressed in Newton. For
334 J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343
Table 1
Standard loaf recipe for the canned petfood used in the studies
Inclusion (g/kg)
Ingredients
Kidneys 50
Lungs 210
Poultry carcasses 150
Textured wheat 20
Rice 20
Wheat flour 50
Tested product 20
Water 480
Additives
Common salt 10
Sodium nitrite 0.1
Sodium polyphosphate 3
the penetration test, a cylindrical ebonite probe (diameter 12.7mm) was driven 30mm into
the gel at a velocity of 0.5mm/s. These conditions were also used to analyze the texture in
the canned loaf-format petfood produced in accordance with the recipes given in Table 1.
2.4. Water holding capacity (WHC)
This method evaluates the capacity of a powder (plasma, gelatin) to absorb and retain
water after gelling. The method used was based on the proposed by Kocher and Foegeding
(13) with slight modifications. Briefly, a solution of the product to be analyzed was prepared
at different concentrations (w/w) in a phosphate buffer saline (PBS) at pH 6.8. Centrifuge
tubes (40–50ml capacity) were filled with these solutions, covered and weighed. The cen-
trifuge tubes were placed in a water bath and heated at 90C (or any other temperature
interested to test as 70, 80 or 121C) for 15 min. After gelling, the tubes were left at 4 C
for 30min to allow the contraction of the gel. Tubes were centrifuged at 15,000rpm for
30min (Sorvall RC 5B, DuPont Co., Newtown, Ct). The supernatant was removed and
weighed. Results are reported as the percentage (w/w) of water released after centrifuging
the gel.
2.5. Fat emulsifying capacity (FEC)
This is the capacity of one product to maintain a homogeneous mixture of water and fat
(oil). The method determines, in specific conditions, the maximum quantity of oil that
can be added to an aqueous solution before the emulsion breaks down. Briefly, 100 g
of a 100g/kg (w/w) sample solution in PBS (pH 6.8) were stirred vigorously (for ex-
ample, using a IKA R1381 helix stick at 500rpm) while adding dropwise colored Soya
oil (prepared by adding a few grains of Oil red O (Merck 5230) to Soya oil (Fluka
85471)). The addition of oil was stopped when the emulsion brokes down (the oil is
no longer incorporated in the mixture). The emulsifying capacity is expressed as goil/g
product.
J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343 335
2.6. Losses
The losses concept refers to all of the material that is outside of the main “meat block”
after opening the can and the removal of the loaf from the tin. Losses are expressed as a
percentage (g of losses/100g of total product).
2.7. Loaf recipe and processing conditions
The standard formula used to produce loaf-format canned petfood is given in Table 1.
This formula has been used to test all of the products at the same inclusion (20g/kg), or at
inclusion of 30g/kg and 50 g/kg in the specific study comparing SDAP and WG.
The processing conditions used to produce a loaf of canned petfood were as follows:
the offals (kidneys, lungs and poultry carcasses) were cut in a pilot plant meat cutter (Cato
SA, Spain) until a mincedand homogeneous mixture was obtained. The textured wheat
was hydrated in water to a ratio of 1:3. The rice was boiled in water and re-hydrated after
cooling to a final ratio of 1:3. The offals were mixed thoroughly with the hydrated wheat,
the re-hydrated rice and the rest of ingredients (wheat flour and tested products), additives
and water in the cutter at a low speed for 3min. The 400-g capacity aluminum cans were
then filled and sealed. The cans were sterilized in a laboratory autoclave at 121C for 1h
and left cooling to room temperature for 2 days before performing the analyses.
2.8. Palatability studies
A two consecutive days preference study was performed in two different experiments
in dogs (n=20) and cats (n= 20) of different breeds in a Commercial Facility (Kennel
De Morgenstond, Holland). The dogs used were from different breeds from small size
Badgerdogs to big size as Labrador retrievers but most of the dogs were medium size dogs
like Beagel, Cocker spaniel and Fox terrier. The weight range was between 5 and 25 kg and
the age range was between 3 and 11 years old. The cats used in both studies were European
shorthair cats, with body weight range between 3 and 8 kg and age range between 1 and 10
years old.
Each day the same quantity of both diets tested were offered at the same time to animals
and first choice and daily consumption were recorded on both days. The first experiment
compared loaf recipes containing an inclusion of 20g/kg of SDAP or WG; the second
experiment include SDAP at the appropriate percentage to maintain the same basic cost
as the recipe containing 30g/kg (10 g/kg in the case of SDAP). The rest of ingredients
used in both recipes of each experiment were from the same batch, and the manufacturing
conditions were similar in all the cases.
2.8.1. Statistical analysis
Statistical analysis of the data were performed with the aid of Statgraphics statistical
software, version 5 Plus from Manugistics, Inc. (USA). When comparisons were made
between two groups Student’s t-test was used and the level of significance was indicated
by * when P<0.05, ** when P< 0.01 and *** when P<0.001. Comparisons among three
or more groups were done by one-way ANOVA using L.S.D. as a all pairwise multiple
336 J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343
comparison procedure. Differences were considered significant when P<0.05. The effect
oftwoormore factors on several variableswas assessed by factorial ANOVA,whichallowed
also the study of their interactions.
Results of preference in studies of palatability were analyzed using the Chi-square test
(P<0.05).
3. Results and discussion
3.1. Functional properties of SDAP in isolated conditions
According to the results shown in Fig. 1, the gelling capacity of SDAP is related to the
heatingtemperature and the percentage ofinclusion of plasma.The results obtained at 80C
are consistent with the results described previously for SDAP in similar conditions (Par´
es
et al., 1998a,b, 2001; Par´
es and Ledward, 2001).
Although the exact mechanism involved in gel formation is unknown, the most likely
mode of action will be according to the following sequence of events: protein denaturation
and unfolding followed by protein interactions and aggregation to form a three-dimensional
protein net. At original pH, the plasma proteins are completely denaturized at temperatures
higher than 75C(Par´
es et al., 2000).
The interactions between protein and water, and the attracting and repelling forces be-
tween peptide chains, lead to the formation of the gel. Some of the attraction forces which
may contribute to gel formation arise from hydrophobic and electrostatic interactions, hy-
drogen, covalent and disulfide bridges. Given the important role played by intermolecular
Fig. 1. Gel strength of SDAP (mean ±S.D.) diluted in water at different cooking temperatures and concentrations.
Results obtained from the analysis of 10 different batches of SDAP. The multivariate analysis showed a significant
effect (P<0.001) of both factors (temperature and percentage of inclusion) and its interaction on gel strength.
J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343 337
Fig. 2. Water retention capacity of SDAP (mean ±S.D.) in isolated conditions at different temperatures and solu-
tion concentrations. The multivariate analysis showed a significant effect (P< 0.001) of both factors (temperature
and percentage of inclusion) and its interaction on water retention capacity.
protein interactions in gelling, better results are obtained when high protein concentrations
are used, since increases the chances of intermolecular contact.
Gelling capacity shows a parabolic curve, with peak values at 121C. The albumin
fraction represents about 45–55% of total protein in SDAP (Gras, 1983). This majority
protein is also the most heat-resistant (data not showed), therefore it is probably the main
protein responsible for the texture obtained when plasma is submitted at high temperatures.
The aggregation phase is slower than the denaturation; it allows the unfolded proteins
to arrange themselves and form an irreversible gel which is homogeneous, very elastic and
stable against syneresis and sweating.
The WHC of SDAP shows a different pattern when analyzed in isolated conditions
compared with GSC. At the different temperatures tested, the minimum value for WHC,
measured as water released from the gel, was obtained at 80C. As it was found in the
texture analysis, at higher SDAP concentration, lower water released from the gel was
obtained at any temperature, perhaps due to the higher probability of intermolecular contact
(Fig. 2).
The values obtained with a 100g/kg solution are consistent with other results published
previously obtained at 80C and original pH (Par´
es et al., 1998b; Par´
es and Ledward,
2001).
At 80C, plasma proteins are denaturized. Therefore, during molecule reorganization
after heat treatment to produce the three-dimensional gel structure, a higher degree of water
absorption and retention takes place inside the gel structure. The increased tendency of
denaturated proteins to undergo protein–protein interactions probably gives rise to stronger
gelsat 121 Cbutwith a reducedWHC because ofa partial disruptionof the proteinnetwork
due to local aggregation phenomena. This has also been observed in plasma gels at different
pH values (Par´
es et al., 1998b; Par´
es and Ledward, 2001).
338 J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343
Table 2
Physicochemical and functional properties of different ingredients that can be used in canned petfood as binding
or gelling agents
Dry protein
(g/kg) Dry ash
(g/kg) Solubility
(g/kg) GSCa(force, N) WHC (g water
released/100 g 10% gel) FEC (g oil/g)
SDAPb820 157.0 965 7.0±0.10 c 41.7 ±0.64 a 428 ±11.7 b
WGc860 6.0 247 2.1 ±0.82 a 78.0 ±0.18 b 248±14.8 a
EAc920 69.0 985 3.5 ±0.08 b 42.4±0.53 a 418 ±8.0 b
PPc990 10.00 –
ddd
CMc26.0 451.0 nd 27.9±1.0 d 0 nd
Results of GSC, WHC and FEC are expressed as mean±S.E.M. A different letter in the same column means a
significant difference, P<0.05. nd=not determined, CM is completely insoluble in cold water.
aThe GSC was analyzed at the concentration of 100 g/kg and heated at 121C during 1 h.
bThe results given for SDAP correspond to the average of more than 200 batches of SDAP (AP-820) produced
at the APC EUROPE plant during 2003.
cAnalytical specifications for dry protein, dry ash and solubility from the technical sheet of each product.
dPP does not produce a gel after heat treatment; therefore, the GSC and WHC of the gel can not be analyzed.
3.2. Functional properties of different binding agents compared with SDAP in isolated
conditions
The analyses performed on different binding or gelling agents to determine their physic-
ochemical and functional properties showed major differences among them in both charac-
teristics (Table 2).
Allof the productstestedhad higher proteinconcentration than SDAP,with the exception
of CM. Thus, the inclusion of most of these products not only contributes to improve the
gelling and other functional characteristics of the recipe, but also to increase the protein
concentration. The highest protein concentration were obtained for PP and EA. WG and PP
showedlowashconcentration comparing with EAand SDAP. CMshowedthe highest value.
The ash concentration of SDAP is a natural characteristic of the ash concentration in blood
plasma to maintain the body osmotic pressure and also due to the addition of anticoagulant
at the time of bleeding. The amount of ash inclusion in the final canned formula can be
re-calculated to take into account these values.
Thedegree of water solubilityvariesconsiderably among theproducts tested andthis fact
could be related with their functional properties and the manufacturing procedures used to
obtain them. For soluble proteins, the degree of insolubility is a useful index for measuring
the level of protein denaturing-aggregation and could also be related with the conditions of
protein processing and storage (Par´
es et al., 1998b). SDAP and EA had very high solubility,
while WG and PP showed a very low degree of water solubility. The solubility of SDAP is
consistent with previously published results (Par´
es et al., 2000).
PP did not show any of the functional properties studied (GSC, WHC and FEC). There-
fore, this product could be used as a protein supplement but not as a binding or gelling
agent.
Out of all the ingredients tested, except CM, SDAP showed the highest GSC value, with
about three times more gelling capacity than WG and double that of EA. The results for
WHC and FEC were very similar for EA and SDAP, and both products showed higher
values of FEC and lower of WHC than WG.
J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343 339
Table 3
Characteristics of loaf-format product obtained with 20g/kg inclusion of the different binding agent
(mean±S.E.M.)
Solids (g/kg) Proteina(g/kg) Asha(g/kg) GSCb(force, N) Losses (g/100 g)
SDAP 244±3.0 83±1.8 22±08 2.6±0.05 d 9.3 ±1.1 a
WG 245±2.0 84±1.4 20±06 2.0±0.04 b 21.4 ±1.0 c
EA 245±5.0 87±1.6 20±1.0 2.3±0.10 c 9.1 ±1.3 a
PP 248±30 87±1.9 21±06 1.4±0.02 a 24.4 ±0.7 d
CM 243±5.0 69±1.2 28±08 2.5±0.12 cd 18.2 ±1.0 b
Results are expressed as mean±S.E.M. A different letter in the same column means a significant difference,
P<0.05.
aProtein and ash are expressed as feed material.
bThe GSC was analyzed at the concentration of 100 g/kg and heated at 121C during 1 h.
The most important aspect involved in the emulsifying properties of a soluble protein
such as SDAP is its ability to unfold towards the oil/water interface and be absorbed. When
the protein comes into contact with the interface, the non-polar domains of amino acids
are reoriented towards the non-aqueous phase and the rest of the molecule is absorbed
spontaneously. During absorption, most of the protein unfolds itself completely, increasing
the surface available and improving emulsifying properties. In general, it can be said that
moredissociated protein structures and highernet separations betweenvery hydrophilic and
lipophilic zones in the polypeptide chain will give better emulsifying properties. According
to De Vuono et al. (1979), the globulin fraction, which accounts for about 40–45% of total
plasma protein, has the best emulsifying properties.
3.3. Functional properties in a complete canned recipe
In these trials, the functional properties of the different products tested as binding agents
using the same inclusion (20g/kg) in the canned petfood formula defined in Table 1 were
analyzed. The processing conditions for this loaf-type canned petfood have been explained
previously.
There were small differences in solids content between the final loaf products. However,
only CM had lower protein concentration than the other binding agents. In contrast, the loaf
containing CM also had the highest ash concentration compared with the other products
tested. These differences in protein and ash content were expected and reflect differences
in these indexes between the binding products tested (Table 3).
When we analyzed the GSC of the final loaf products obtained, we observed that CM,
SDAP and EA gave better values and therefore textures in the cooked product compared
with WG and PP which gave the lowest result (Table 3). Nevertheless, the results for losses
(Table 3) showed that SDAP retained most of the water inside the loaf petfood, while WG,
CM and PP lost more than 150g/kg of the product. These results are consistent with the
low WHC showed but these products, and reflected the differences observed among them
in the tests performed in isolated conditions, indicating that this kind of analysis are useful
predicting the products behavior in the final recipes.
In a more extensive and specific study designed to compare the functional properties
of loaf-format canned petfoods obtained with SDAP or WG at different inclusion (20, 30
340 J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343
Table 4
Functional properties of loaf-format canned petfoods obtained at different inclusion levels of SDAP or WG
Binding agent Protein (g/kg) GSC (force, N) Losses (g/100 g)
Formula at 20g/kg inclusion level
SDAP 83±1.6a 2.7±0.06 c 9.3±1.1 b
WG 84±0.7a 2.1±0.03 a 21.4±1.0 d
Formula at 30g/kg inclusion level
SDAP 89±1.0b 3.9±0.07 d 3.9±0.5 a
WG 91±07 b 2.0±0.03 a 19.5±0.9 d
Formula at 50g/kg inclusion level
SDAP 106±1.2c 7.1±0.06 e 1.9±0.3 a
WG 106±0.6c 2.4±0.04 b 14.0±0.8 c
Multivariate analysisa
Effect of
Binding agent 0.2707 <0.001 <0.001
Inclusion (%) <0.001 <0.001 <0.001
Binding agent ×inclusion 0.5013 <0.001 0.4581
Results are expressed as mean±S.E.M. of 240 values for WG and 120 values for SDAP. A different letter in the
same column for each condition tested means a significant difference, P<0.05.
aValues in the multivariate analysis table refer to Pvalues. A P> 0.05 denotes not significant effect.
and 50g/kg), we observed that, irrespective of the inclusion tested, the GSC was always
significantly higher for the recipe including SDAP. In addition, the losses were also always
lowerinformulas containing SDAP.At SDAP inclusion of 30or 50 g/kg,there was amarked
reduction in the water released from the final cooked product. At a 50g/kg inclusion, the
formula containing SDAP had a hard gel (Table 4). Consequently, the correct inclusion
concentration in order to take advantage of all the functional properties of SDAP would be
30g/kg or lower. An interesting observation was that the GSC and losses obtained in the
formulacontaining 50g/kg were evenworsethan the formula containing 20g/kg, indicating
the better functional properties offered by SDAP, as observed in the tests performed in
isolated conditions.
3.4. Palatability studies
In the palatability studies, we compared SDAP versus WG included at 20g/kg (iso-
product inclusion) in the standard loaf-format canned petfood and using a formula where
SDAPwasincludedatasimilarcostas the inclusion ofWGat30 g/kg in theformula(10 g/kg
inclusion for SDAP). The other ingredients and processing conditions were similar for all
of the products obtained.
Table 5 shows the different characteristics of the products used in the palatability
comparison. As was expected, the inclusion of SDAP at 10g/kg showed differences in
protein concentration compared with the formula containing 30g. However, these dif-
ferences were not observed for GSC and, in fact, the formula containing SDAP had
lower losses than the formula with WG. These results may indicate that SDAP could
replace WG or other binding agents used at a similar cost in the formula without caus-
J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343 341
Table 5
Products used in the palatability study performed with dogs and cats
Solida(g/kg) Proteina(g/kg) Asha(g/kg) GSC (force, N) Losses (g/100 g)
Iso-product formula at 20 g/kg inclusion level
SDAP 240 84 21 3.3±0.07 b 0.5±0.21 a
WG 233 85 19 2.1±0.06 a 6.9±1.91 b
Iso-cost formula at 30 g/kg inclusion level of WG
SDAP (10.4g/kg) 230 75 19 2.0±0.08 a 1.7±0.22 a
WG 247 92 21 2.2±0.07 a 13.1±1.06 c
Multivariate analysisb
Effect of
Binding agent <0.001 <0.001
Inclusion (%) <0.001 <0.001
Results are expressed as mean ±S.E.M. of 24 values for GSC and six values for losses. A different superscript in
the same column for each condition tested means a significant difference, P<0.05.
aAnalysis were done using an integrated sample of cans, as a consequence not statistics could be performed.
bValues in the multivariate analysis table refer to Pvalues. A P> 0.05 denotes not significant effect.
ing significant differences in texture but with a potential improvement in water reten-
tion. Specific studies could be performed for each application. Results obtained with
a 20g/kg inclusion (differences in GSC and losses) were similar to those observed
previously.
Fig. 3. Daily and total intake in cats for each diet used in the two palatability studies. Statistics were performed
by trials (iso-product [1] or iso-cost [2]) using Student’s t-test.
342 J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343
Table 6
First choice for each diet in the two palatability studies performed in cats
First choice Day 1 (%) Day 2 (%) Total (%)
Iso-product formula
WG-1 (20 g/kg) 10 44 21
SDAP-1 (20g/kg) 90a66 79a
Iso-cost formula
WG-2 (30 g/kg) 25 20 22
SDAP-2 (10g/kg) 75a80a78a
aThe symbol denotes a significant preference (P<0.05) for the diet containing SDAP in the first choice made
for the animal. Data were analyzed with the Chi-square test.
The palatability or first choice results with dogs were similar in both trials (iso-product
at 20g/kg or iso-cost inclusion), indicating that dogs cannot differentiate between the two
products (data not shown). In addition, some dogs were able to eat the total amount of food
given (1kg for each formula). The use of flavors was not allowed in any case in order to no
mask the effect of SDAP or WG by their selves in the palatability of the loaf petfood.
In the case of cats, in the two recipes tested, there was a clear preference in palatability
for the formula containing plasma (Fig. 3). In both trials, there was a higher intake over the
entire test period (P<0.001) and, in the case of the iso-cost study, this difference was also
observed on each day. These results show that the taste of SDAP is appreciated by cats and
that these animals are able to differentiate and positively select the inclusion of SDAP in
the formula, even when SDAP is included at low rates (about 10g/kg).
These differences in intake were also observed for the first choice of each diet, as shown
in Table 6. There was a preference for the diets containing SDAP in both studies.
4. Conclusions
In summary, SDAP is a soluble concentrated protein product that is used as a binding
agent in canned petfoods due to its high functional properties (texture, water retention
and emulsifying capacity). The better functional properties of SDAP observed in isolated
conditionswere also obtained incanned loaf recipes. Oneof the most significantobservation
has been that SDAP could replace most of the binding agents used for this application at a
similar cost, or at an inclusion which does not impair the functional aspects and which may
increase water retention.
In addition, SDAP is a palatable product for cats, which could explain, at least in part,
why it is extensively used in cat diets.
Althoughtheresults obtained in loaf-format cannedproductscannot be fully extrapolated
to other types of wet product, such as pouches or chunks, some of the properties observed
could be expected in these applications.
Future studies using SDAP are required to explore the effects of its inclusion in other
kinds of products such as chunks or pouches and looking for other important index like the
impact of the excess of animal fat or water in the quality aspects of canned petfood, the
viscosity of raw recipe before cooking, etc.
J. Polo et al. / Animal Feed Science and Technology 122 (2005) 331–343 343
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... The measurements were taken at a rate of 200 measurement points per second (PPS 200) with a trigger force of 0.05 N. Then, the maximum force obtained during the first compression cycle was expressed in N × cm −2 of the probe area [26]. ...
... The emulsifying capacity value was determined at the inversion point at which an oil-in-water emulsion turns into a water-inoil emulsion, as indicated by a sudden drop in conductivity. The emulsifying capacity is expressed as ml of oil per 1 g of product [26,27]. ...
... The analyses performed in this study also included a description of solubility, gelling, and emulsifying abilities, as suggested and reported by many authors studying the quality attributes of various animal and plant origin preparations [17,26,27]. ...
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... The measurements were taken at a rate of 200 measurement points per second (PPS 200) with a trigger force of 0.05 N. Then, the maximum force obtained during the first compression cycle was expressed in N × cm −2 of the probe area [26]. ...
... The emulsifying capacity value was determined at the inversion point at which an oil-in-water emulsion turns into a water-inoil emulsion, as indicated by a sudden drop in conductivity. The emulsifying capacity is expressed as ml of oil per 1 g of product [26,27]. ...
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