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Article

Chemical Composition and Palatability of Nutraceutical Dog Snacks

by
Jagoda Kępińska-Pacelik
1,
Wioletta Biel
1,*,
Małgorzata Mizielińska
2 and
Robert Iwański
3
1
Department of Monogastric Animal Sciences, Division of Animal Nutrition and Food, West Pomeranian University of Technology in Szczecin, Klemensa Janickiego 29, 71-270 Szczecin, Poland
2
Center of Bioimmobilisation and Innovative Packaging Materials, Faculty of Food Sciences and Fisheries, West Pomeranian University of Technology in Szczecin, Klemensa Janickiego 35, 71-270 Szczecin, Poland
3
Department of Fish, Plant and Gastronomy Technology, Faculty of Food Sciences and Fisheries, West Pomeranian University of Technology in Szczecin, Papieża Pawła VI 3, 71-459 Szczecin, Poland
*
Author to whom correspondence should be addressed.
Appl. Sci. 2023, 13(5), 2806; https://doi.org/10.3390/app13052806
Submission received: 25 January 2023 / Revised: 19 February 2023 / Accepted: 20 February 2023 / Published: 22 February 2023
(This article belongs to the Special Issue Advances in Food Flavor Analysis II)
Browse Figures
Review Reports Versions Notes

Abstract

:
The aim of this study was to evaluate self-produced nutraceutical treats, taking into account the nutritional preferences of dogs, and to analyze the proximate composition, macrominerals and trace elements content. Four variants of snacks were prepared—two extruded and two baked. The snacks consisted of wholegrain buckwheat flour, wholegrain spelt flour, banded cricket meal, dried hemp inflorescences, dry spirulina biomass, linseed (in the case of baked snacks) and guar gum (in the case of extruded snacks). The proximate composition was determined according to the Association of Official Analytical Chemists methods. Mineral and heavy metal content was analyzed by colorimetry and mass spectrometry. The extruded and baked snacks were analyzed with a scanning electron microscope. The two-bowl test was used as the palatability test. It should be mentioned that when comparing baked snacks to the extruded ones, spaces between starch granules and protein were less visible in the baked snacks but air bubbles were observed suggesting a higher expansion. The mean level of crude fat was twice as high in the baked snacks compared to the extruded snacks. In the case of total carbohydrates, the extruded snacks had a higher content compared to the baked. The analyses showed differences in terms of magnesium content. The average content of trace elements was significantly higher in baked snacks than in the extruded snacks. Dogs preferred the baked variant and the difference between the buckwheat flour content also influenced their preferences—variants richer in buckwheat were chosen less often. This could probably be related to the bitterness in the variant with a higher content of buckwheat flour, which translated into less frequent selection of this variant by dogs. Treats containing insect meal and spirulina can be used in dog nutrition due to their good nutritional value and potential health benefits.

1. Introduction

It is expected that the global population growth will reach 10 billion by 2050, causing enormous challenges to all sectors involved in food production [1]. Additionally, the number of pets kept in households is significant, i.e., 703.3 million globally. Conventional animal production that provides humans and their pets with the main amount of protein containing the necessary amino acids may turn out to be insufficient. Breeding of poultry, pigs and cattle requires a lot of energy, water and space. It should be underlined that it causes environmental problems, such as greenhouse gas emissions. Furthermore, the production of commercial pet food generates up to 30% of the negative impact on the environment [2]. The usage of insects as the main source of protein in the diets of pets, such as dogs, has not only a nutritional effect but also a beneficial influence on the environment. Moreover, insects have a fast growth and development cycle, which greatly facilitates their production [3]. The possible implementation of products derived from insects, i.e., insect-based dog treats, allows to expand the branch of dog diets including hypoallergenic diets. However, in the available literature, there are little data in terms of experimentation carried out on dog food to evaluate the potential effect of insect-based diets on nutritional preferences of dogs [2,3]. Currently, the vast majority of animal caregivers use commercial ready-made foods purchased in pet stores [4]. In addition to foods that meet the basic needs of animals, the pet treats market is increasingly growing. Treats are commonly given to dogs to strengthen the pet and caregiver relationship. Most treats on the market are baked and wheat based as this cereal contains gluten, which provides proper texture attributes and facilitates production. Production of baked treats with gluten-free or low-gluten pseudocereals is challenging as they lack the same functional proteins [5]. Treats are a complementary food; they cannot be used as a complete food. In legal terms, complementary pet food is defined as pet food which has a high content of certain substances but which, by reason of its composition, is sufficient for a daily ration only when used in combination with other pet foods [6].
According to the information in Figure 1, there are no strict or clear guidelines outlining recommendations for balancing dog snack’s composition. It should be kept in mind that they should not constitute more than 10% of the daily food ration of the animal. Additionally, little is known about the nutritional value of treats and their impact on the dog’s diet, health and wellness despite the increasing popularity of these products. Moreover, treats are not intended to significantly supplement the daily ration but may be given in amounts that impact total energy intake. Therefore, feeding instructions should provide clear recommendations on how not to overfeed dogs as suggested by European Pet Food Industry Federation (FEDIAF) Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs [7,8].
An important aspect is the palatability of the snacks, as they are often used in training to motivate a dog to perform a specific task and/or reward them. Before a product reaches the market, its palatability can be tested in several ways. There are mainly two methods–the one-bowl test and the two-bowl test. The one-bowl test is used to assess the acceptability of a product and measures the food consumption of pets, while the two-bowl test is used to determine preferences of one product over another and also to measure food consumption. The types of pet panels that can be used to perform palatability tests may consist of animals trained by “experts” at pet centers or untrained animals fed at home [9]. Variables, such as a dog’s breed, age, body condition, weight or gender, can influence their eating behavior [10].
It is known that fats are the carriers of flavor; therefore, the palatability of a product will be influenced by the components that constitute the majority of the fat. In the case of dog food and treats, these will be primarily animal components. An example of an animal component that is gaining popularity is insects, which is a new source of protein in the pet food industry despite the fact that they have been consumed by predators in the natural environment for thousands of years [3]. In addition, they are a very good source of fat, the content of which positively affects the palatability of the product [11]. However, despite their nutritional value, entomophagy is still common [12,13].
Currently, an alternative to the most popular cereal, i.e., common wheat, is also being sought. They are so-called ancient grains (i.e., spelt) or pseudocereals (such as buckwheat). Ancient grains are richer in protein, fats, crude fiber and crude ash than common wheat grains. Furthermore, spelt flour dough is characterized by better functional properties [14]. Interestingly, buckwheat flour is rich in essential trace metal elements and can be used as a source of dietary nutrients for Mg and Mo [15]. There is also a growing interest in the use of ingredients with health-promoting properties, such as hemp or spirulina.
There are two main categories of maintenance foods and treats based on the way they are made–extruded and baked. They differ in the parameters of the technological process and additional components responsible for the appropriate combination of all ingredients, as well as texture. It is supposed that the palatability is influenced by the above-mentioned texture in addition to its sensory value. The hypothesis of our study is that snacks based on an insect protein source containing more buckwheat flour will be a better source of nutrients but will be less tasty. Therefore, the aim of the study was to evaluate self-produced nutraceutical treats based on an insect protein source (extruded and baked), taking into account the nutritional preferences of dogs and to analyze their chemical composition and mineral content.

2. Materials and Methods

Four variants of snacks were prepared–two extruded and two baked. The composition of the snacks was developed based on the analyzed chemical composition of the components (Table 1), which was determined according to AOAC [16].
The snacks consisted of wholegrain buckwheat flour, wholegrain spelt flour, banded cricket meal, dried hemp inflorescences, dry spirulina biomass, linseed (in the case of baked snacks) and guar gum (in the case of extruded snacks). The dry ingredients were supplemented with reverse osmosis (RO) water to combine the ingredients and make the mass elastic. The prepared variants differed in the content of buckwheat flour:
  • S1—extruded variant, containing buckwheat and spelt flour in a ratio of 1:1;
  • S2—extruded variant, containing buckwheat and spelt flour in a ratio of 7:3;
  • S3—baked variant, containing buckwheat and spelt flour in a ratio of 1:1;
  • S4—baked variant, containing buckwheat and spelt flour in a ratio of 7:3.
The components for the extruded treats were mixed together, combined with RO water and then passed through a three section heating extruder (85 °C, 93 °C and 95 °C) (Brabender, Duisburg, Germany). The final under expansion degree and forming pressure was 15 MPa. The obtained extrudates were cut into strips with average dimensions of 2 × 3 cm then left to dry for seven days at the laboratory temperature (18–22 °C). Then, they were placed in packaging with a zipper closure.
In the case of baked treats, the dry ingredients were combined with RO water and the dough was kneaded by hand, then it was rolled out and medium sized cookies 2 × 3 cm were cut using casts. The treats were baked in a laboratory oven (type UM300, Memmert, Schwabach, Germany) at 180 °C for 20 min. After taking it out of the laboratory oven, it was allowed to cool down at the laboratory temperature overnight. Then they were placed in packaging with a zipper closure.

2.1. Proximate Composition

The snacks were ground in a laboratory mill (KNIFETEC 1095, Foss Tecator, Höganäs, Sweden). The proximate composition (dry matter, crude protein, crude fat, crude fiber, crude ash and total carbohydrates) was determined according to AOAC [16]. Chemical reagents for analyses were obtained from Avantor Performance Materials Poland S.A., Gliwice, Poland. To determine the dry matter, the samples were dried at 105 °C until constant weight. Crude fat was determined by the Soxhlet extraction method with diethyl ether as the solvent; crude ash by burning in a muffle furnace at 580 °C for 8 h; total protein by the Kjeldahl method on a Büchi B-324 distillation unit (Büchi Labortechnik AG, Flawil, Switzerland); and crude fiber was determined with an ANKOM220 analyzer (ANKOM Technology, New York, NY, USA). Total carbohydrates (TC) were calculated according to Equation (1) based on the results of other proximate components determined according to AOAC [16].
TC (%) = 100 − (%moisture + %crude protein + %crude fat + %crude ash + %crude fiber)

2.2. Metabolizable Energy

The metabolizable energy value was calculated using a four-step calculation according to NRC [15] and FEDIAF [7] (Table 2).

2.3. Minerals

The total content of potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) was determined by wet mineralization in a mixture of nitric acid (V) and perchloric acid (VII) [18]. The analyses were performed with an atomic absorption spectrometer (Thermo Fisher Scientific iCE 3000 Series, Waltham, MA, USA). For the determination of Ca, K, Mg and Na content, the wavelengths were: K—766.5 nm; Ca—422.7 nm; Mg—285.2 nm; and Na—589.0 nm. For the determination of Fe, Mn, Zn, Cu content, the wavelengths were: Fe—248.3 nm; Mn—279.5 nm; Zn—213.9 nm; and Cu—324.8 nm. The calculation of the content of the individual elements K, Ca, Mg, Na, Fe, Mn, Zn and Cu was started with a standard curve taking into account the weight of the test portion and the dilutions used. The phosphorus content was determined by the Egner–Riehm colorimetric method, with ammonium molybdate on a Specol 221 apparatus spectrophotometer (Carl Zeiss, Jena, Germany) [19]. The material for P concentration analyses was subjected to mineralization in concentrated sulfuric acid (H2SO4) and perchloric acid (HClO4). The absorbance value of the sample, determined spectrophotometrically from P2O5 to total phosphorus, was calculated according to the chemical equivalent (0.436). The credibility of the method used has been confirmed by comparative studies, including the calibration curve, using the calibration series method. All chemical determinations were performed in triplicate and presented as mean values. The accuracy of the analytical methods was verified based on certified reference material—skimmed milk powder (ERM®-BD151), which was obtained from the Institute for Reference Materials and Measurements (IRMM, Geel, Belgium).

2.4. Scanning Electron Microscopy

The extruded and baked snacks were analyzed using a scanning electron microscope (SEM). A microscopic analysis was performed using a Vega 3 LMU microscope (Tescan, Brno-Kohoutovice, Czech Republic). The experiments were important to determine if the surface of snacks was homogeneous or not. The presence of the additive granules, which were introduced into the snack matrix was also analyzed. A test was carried out at 25 °C with a tungsten filament and an accelerating voltage of 10 kV was used to capture SEM images for both the extruded and baked snack samples. All specimens were viewed from above.

2.5. Palatability Test

In order to determine the correct number of treats that were later fed to the dogs, it was necessary to establish the daily energy requirements of the dogs participating in the study. For this purpose, the formula for daily energy requirement (DER) for dogs with moderate activity [7] was used: DER = 110 kcal metabolizable energy/kg of body weight0.75.
Knowing the calorific value in 100 g of the produced snacks, the proportion was used to calculate the number of snacks (g) that the dog could take. We assumed that treats should constitute no more than 10% of the daily ration.
The palatability test was based on the research of Smith et al. [20], Araujo and Milgram [21] and Aldrich and Koppel [22]. The two-bowl method was used for the palatability test. In this method, two foods are placed in bowls and served simultaneously to the dog. Therefore, unlike the single-bowl test, there is a choice. Before proceeding to the test, the animals were assessed in a blank test where the same food was given in each bowl. This was done to see if the animal had a bias (preferring the left or right bowl). The dogs involved for the palatability test were qualified before being involved in the tests. Healthy dogs with no predisposing disease or behavioral problems that prevent objective and balanced results from being obtained were selected. Ten adult dogs, including females and males, were selected.
The dogs were allowed to smell the food and the bowls were then placed simultaneously in front of the animal for consumption. The test was performed in the morning after an overnight fast, for 2 days. The “technician” monitored which of the two foods the animal approached first and from which bowl the first bite was taken. It is commonly accepted that this “first bite” is related to the aromatic properties of the food. The bowls were left with the dogs for 15 min. After this time, leftovers from both bowls were weighed to determine the preferences of the dogs. Treats consumed in larger quantities indicated that dogs preferred this type of snacks.
All tests were performed according to the European directive [23] and Polish regulations regarding experiments in animals, in accordance with the Journal of Laws [24], as amended by the Journal of Laws [25]. There was no need for the approval of an Ethical Committee for the described procedures as they qualified as non-experimental clinical veterinary practices, which are excluded from the directive.

2.6. Statistical Analyses

Statistical analyses were performed using the Statistica 13.1 package, with a significance level of p = 0.05, using the post-hoc test of Tukey’s significant difference [26].

3. Results

3.1. Proximate Composition and Minerals

All results for the proximate composition were significantly different from each other. Particular attention is paid to the content of crude fat and total carbohydrates. The mean level of crude fat was twice as high in the baked snacks (5.74 g/100 g DM) compared to the extruded snacks (2.35 g/100 g DM). In the case of total carbohydrates, the extruded snacks had a higher content (73.54 g/100 g DM) compared to the baked snacks (69.41 g/100 g). Table 3 summarizes the proximate composition results of the produced dog snacks.
The analyses showed that snacks differed significantly only in terms of magnesium content—its average content was statistically significantly higher in baked snacks (Table 4). The average content of trace elements was statistically significantly higher in baked snacks than in extruded ones, apart from the molybdenum content (Table 5). Particular attention is paid to the average iron content, which was twice as high in baked snacks. The content of cobalt, cadmium, lead, chromium and nickel was not detected (nd).

3.2. Texture of Snacks

Scanning electron microscopy images of the extruded and baked snacks are shown in Figure 2, Figure 3, Figure 4 and Figure 5.
The SEM analysis determined that the surface and cross-section of the extruded snacks (S1, S2) was relatively smooth but not homogenous. The pores were slightly visible, meaning a lack of expansion of the snacks (Figure 2a,b and Figure 3a,b). Additionally, deeply embedded starch granules were visible on the cross-section of the samples. It may be concluded that the addition of banded cricket protein into the starch caused the increase of the protein network around the starch granules, which resulted in a decrease of the extruded snack expansion. Moreover, little cracks were visible on the surface of both samples (Figure 2a and Figure 3a). Analyzing the cross-section of the S1 and S2 snacks (Figure 2b and Figure 3b), it was concluded that the S1 sample was compact. Contrary to S1, the S2 sample consisted of two visible layers that were not compact and homogenous. Starch granules were visible as well as the protein network. Comparing the S1 and S2 surface (Figure 2a and Figure 3b), it should be noticed that the differences between starch particles size were higher for the S1 snack than for the S2 snack.
The SEM analysis demonstrated that the surface of the baked snacks (S3, S4) was smooth, dense and compact with swollen and gelatinized starch granules (Figure 4a,b and Figure 5a,b). It was indicated that the starch granules were embedded in a protein matrix. Moreover, little cracks were visible on the surface of both samples. Additionally, the differences between the granules size were noticed meaning that their swelling was insufficient. It should be underlined (Figure 4b and Figure 5b) that air bubbles (holes) were visible on the cross-section of S3 and S4 snacks, confirming the expansion of the baked snacks. The structure of the S4 cross-section was less compact than the S3 structure. It should be mentioned that the S4 sample was similar to closed-cell foam in which gas formed little pockets surrounded by the protein network containing starch granules.
In summary, the SEM analysis demonstrated that all the snacks were a heterogeneous system. Additionally, the SEM images revealed that baked snacks contained large-sized starch granules with slightly visible spaces between starch granules and protein, suggesting the dominance of starch over the protein network. Additionally, air bubbles were observed on the cross-section of the S3 and S4 samples confirming a higher expansion of the baked snacks compared to the extruded samples.

3.3. Palatability Test

In our study, the palatability test was divided into four stages (Table 6, Figure 6). Test 1 consisted of checking the preferences of the dogs between the extruded variants that differed in the content of buckwheat flour (S1 and S2). Our research showed that dogs chose the S1 variant as often as the S2 variant. Another test (Test 2) consisted of checking the dogs’ preferences for baked variants (S3 and S4). The results showed that dogs chose the 50:50 buckwheat to spelt version more often than the one with higher buckwheat flour content. Test 3 analyzed whether the production of the snack (extrusion and baking) influenced the dogs’ preferences despite the same component content of the treats (S1 and S3). The results indicated that the overwhelming majority of dogs chose the baked variant. Test 4, similar to the previous one, was used to check the dogs’ preferences in relation to the production of treats (S2 and S4). In this test, the results also indicate that dogs prefer the baked variant more frequently to the extruded one, which may be related to the improved sensory qualities of the baked snacks compared to the extruded variants.

4. Discussion

4.1. Proximate Composition and Mineral Content

In our research, we focused on the production of treats that contain ingredients that can bring health benefits to pets if consumed on a regular basis. In order for both the extrusion process and the baking process to run properly, it was necessary to use carbohydrate sources. In this case, they were buckwheat flour and spelt flour. Cereals and cereal products have been used for years in the case of dry pet food as a source of energy, but most of all they are a structure-forming raw material that determines the viscosity, brittleness, moisture and strength of the kibble. Its presence in food is necessary to ensure the right texture of the final product; it also determines the taste. It is not possible to produce dry food without such ingredients, which is the problem when choosing the type of carbohydrate sources in dry food. For some time, grain-free ingredients (such as legumes seeds) have been used. As demonstrated by Quilliam et al. [27], grain-free dog food has favorable low glycemic properties, but their use after 7 days reduces the digestibility of macronutrients and amino acids. According to the authors of that study, it is likely that this phenomenon may be related in part to the lower animal protein content, but in the long run it could put dogs at risk of developing low taurine and dilated cardiomyopathy. That is why it is suggested that grains should be present in a dog’s diet, especially since they are a relative carnivore, meaning their diet should not consist only of meat [27].
Buckwheat flour does not contain gluten. “Non-celiac gluten sensitivity” is a human disorder characterized by gut and parenteral symptoms associated with the consumption of foods containing gluten but without the development of antibodies specific to celiac disease and villous atrophy [28,29]. It is possible that gluten-containing foods can cause intestinal and parenteral disorders in susceptible dogs and in a similar way, but this has not yet been documented [30]. Gluten sensitivity has been reported as a genetic trait in Irish Setters [31], and avoiding gluten was described to be beneficial for Border Terriers with canine epileptoid cramping syndrome [32]. Due to the difficulty of diagnosis, it is unclear whether gluten allergy or intolerance occurs in the general dog population [33]. Still, consumer preferences need to be considered when formulating pet food [34].
Doubts regarding the choice of cereal or grain-free food are also associated with the increasing incidence of food allergies in dogs. More and more foods with limited or alternative protein sources are available at pet stores. Currently, the number of potential food allergens is large [35]. The risk of giving a pet a commercial food is possible contamination with foreign protein; therefore, food containing hydrolyzed protein is not always appropriate [36]. That is why, in the case of dogs with food allergies, it is worth introducing insect food into the diet [37]. It is worth noting that insects are invertebrates; therefore, the risk of a dog food allergy to insect protein is low [37,38]. That is why insect-based foods are more and more used in the nutrition of dogs, which are suffering from food allergies to proteins, such as poultry and beef [39]. Insects are characterized by a rich nutritional value. They contain higher amounts of protein and fat compared to chicken meat [40]. Their protein is a rich source of essential amino acids and substances, which are necessary in the processes of amino acid synthesis, energy transformations and gluconeogenesis. Moreover, insects are a source of antimicrobial peptides (AMP), lauric acid and chitin, which may be factors improving the immune response (a favorable impact on immunity–tumor necrosis factor-a [TNF-a]), antioxidative status (glutathione peroxidase) and positively influencing the composition of the gastrointestinal microbiome [2,41,42,43]. The use of insects in pet food is allowed in accordance with Commission Regulation No 893 [44].
In our study, we used sub-imago banded crickets to minimize the amount of chitin affecting the crude fiber content of the product. Banded cricket contains more protein but less fat (Table 1) compared to the popular mealworm, which is more commonly used in the pet food industry [45]. The inclusion of cricket meal in a dog’s diet may serve as an acceptable protein source compared to the control diet with chicken meal as a protein source. As demonstrated by Kilburn et al. [46], the maintenance of acceptable stool characteristics and blood parameters throughout the study period indicates that no adverse health effects occurred when animals were fed a diet containing crickets. Differences in apparent digestibility, possibly due to an increase in total dietary fiber content, may determine the optimal level of incorporation of cricket meal fed to adult dogs. More research is needed to investigate the potential functionality of the chitin component in cricket meal. Moreover, Areerat et al. [47] also investigated the possibility of replacing poultry meal with the pupae of domestic crickets (Acheta domesticus, AD) or mulberry silkworms (Bombyx mori, BM). The results of this study suggested that both insect species could replace poultry meal without negative side effects. Therefore, an AD of 20% or a BM of 14% can be used in products intended for feeding dogs. Higa et al. [48] indicated that people were most willing to feed their dog treats made with cricket flour, followed by black soldier fly larvae, followed by both mealworms and ants. Moreover, Higa et al. [48] indicated that people were most willing to feed their dog a bowl of dried crickets or black soldier fly larvae than either mealworms or ants.
Some components of the diets, covering the basic nutritional needs of the body, support it in the fight against many diseases or are an element of prevention. It is noticed in the diet of people but also pet food producers have noticed this trend by enriching their products with numerous natural supplements with pro-health (and nutraceutical) effects. Spirulina is more and more often used by producers of food and dietary supplements for companion animals. It is also called commonly “green meat” due to its high protein content (Table 1) of high quality, resulting from good amino acid composition with high digestibility [49]. It is also a good source of high-quality fat. Spirulina biomass is an excellent source of polyunsaturated fatty acids (including EPA and DHA) [50]. It is used in food recipes not only because of the protein level, but also because its addition to the food can significantly delay the lipid oxidation process and reduce the number of harmful microorganisms. Supplementing the diet with spirulina results in a significantly increased stability of the intestinal microflora in dogs, which translates into an improvement in the immune response [51]. The inclusion of microalgae (including spirulina) in dry food increases the apparent protein digestibility and palatability of the dog food [52].
Hemp has a fairly wide range of uses, ranging from cosmetology to the food and pet food industry. The cannabidiol (CBD) present in their inflorescences has many pharmacological effects, including anxiolytic, sedative, anti-epileptic, anti-inflammatory, analgesic, anti-emetic, anti-diabetic and anti-ischemic effects [53,54,55]. All these effects can be convincingly explained by observations about the mechanism of action of CBD. However, it is not known in what dose cannabis would produce the above-mentioned effects. While CBD may have therapeutic potential, scientific evidence for its use in animals is currently limited [56]. Evidence of the beneficial behavioral and health effects of CBD in companion animals has reinforced the need to clarify the safety and potential effects of CBD. Morris [57] aimed to determine the effects of industrial administration of cannabis-derived CBD on the health and well-being of dogs. They hypothesized that CBD would have a beneficial effect on the behavior of dogs without adversely affecting the health of the animals. Dog treats were formulated to be CBD-rich and found palatable at various levels of CBD incorporation. The test treats were quite different from the commercial treats in smell, texture and taste and were extremely palatable [57]. During the adaptation phase, consumption of commercial treats was lower than consumption of test treats during the treatment period due to differences in treats. Therefore, it can be concluded that the palatability of CBD-containing treats is comparable to non-CBD treats, and the presence of CBD does not affect food intake when supplemented with up to 25 mg of CBD per day [57]. In the studies of Almeida et al. [5], the nutritional value of different snack variants was analyzed. The crude protein fluctuated from 8.36 to 19.84% and was a main effect of cereal and protein sources. The crude fat ranged between 6.38 and 7.27%. The results differed by the cereal and protein source added. In the studies of Morelli et al. [8], a similar analysis showed that biscuits are the most caloric type of treats with 390.77 kcal ME/100 g DM. All categories showed a DM of over 80 percent with the biscuits having the highest. In our research, iron content was noticed, which was higher in the baked product. In the studies of Yusuf et al. [58], iron content in the extruded product was higher (1.90 g/100 g DM) than in the non-extruded (1.34 g/100 g DM) product.

4.2. Texture

Texture is one of the main quality factors of fresh and processed foods in terms of appearance, flavor and nutritional properties. Texture can correlate not only with processing conditions, but also with product stability and shelf life for processed foods [59]. Fat in the diets for companion animals plays a role in contributing not only to the palatability, but also to the texture of food [60]. More than 60% of pet food products are processed using extrusion, and a significant proportion are produced by baking. However, research is lacking on fundamental process and product differences between extrusion and baking [61]. As shown in the research of Gibson [61], the course of the production process depends mainly on the process parameters and the raw materials used. Moreover, the modifications in extrusion processing mechanical energy have an impact on kibble characteristics and starch transformation [62].
The use of flour from buckwheat, which belongs to the pseudo-cereals with a high level of fat, up to 2.75 g/100 g (Table 1), reduces the need to add fat when pseudo-cereal flours are used as an ingredient in products where fat plays an important role in texture and flavor [63]. It was suspected that a greater or lesser presence of buckwheat flour may result in better plasticity of the mass from which the snacks are made. In our study, we investigated whether it affects the technological process, but it does not have a significant effect; there was no significant differences in kneading the dough and during the technological process depending on the variant of treats. In a study by Gibson [61], the expansion coefficient (4.1–3.5) decreased independently of extrusion when the proportion of fresh meat increased (0–15%). Expansion was not evident in the baked croquettes and the bulk and chunk density was up to 56% higher for the baked croquettes compared to the extruded ones. The baked products had a “smooth” deformation response with a higher peak hardness than the extruded products [61]. In our research, the process parameters had the opposite effect on the expansion of the products; the baked treats were better developed than the extruded ones.
While there are obvious fundamental differences between the extrusion and the baking process to prepare dry pet food, there is little scientific evidence in the literature that quantifies these differences or contrasts the transformation and properties of end products [64]. Extrusion is a process that has been used in the production of pet food since 1954. Plant-derived ingredients are still included in recipes to this day to ensure the starch content, which in the right amounts is necessary for the proper processing and formation of kibbles. In addition to starch, the foods also contain fiber. Despite not being recognized by FEDIAF [7] as an essential nutrient for dogs and cats, supplementing with fiber may provide benefits [65]. Fibrous components affect the extrusion process. The best-known effect is increased density or, conversely, reduced kibble expansion [66]. This reduced expansion affects the texture of the product, which in turn can affect palatability [67,68]. Fiber sources can be different depending on the manufacturer’s will. Recently, even citrus pulp granules (CPP) and orange fiber (OF), which are co-products of the citrus juice industry, have been studied. In study by Pacheco et al. [69], dogs preferred the OF diet (65%) to the CO diet (35%). CPP and OF were fermentable sources of fiber, increasing the concentration of SCFA and butyric acid in the stool. OF was more fermentable than CPP, with limited effects on croquette formation, starch cooking and was well accepted in the diet of dogs [69].
Starch constitutes up to 11–43% of dogs’ dry diet and represents an important source of digestible energy due to the release of glucose after its digestion [70]. Moreover, from a technological point of view, its presence is necessary to obtain the specific structure of kibbles.
Nawaz et al. [71] mentioned that large-sized starch granules of snacks may signify the proper starch gelatinization of the sample compared to the snack sample with smaller size of granules. The authors suggested that the proper gelatinization was supported by the high expansion of the snack sample. Additionally, Nawaz et al. [72] demonstrated that less starch swelling (insufficient gelatinization) might be caused by the replacement of wheat flour with red fish meat. As was confirmed by the Nawaz et al. [73], the addition of fish bones to the wheat flour with potato powder may also influence the snack’s structure resulting in a compact structure with improper gelatinization.
Properly conducted extrusion has its advantages—the conditions occurring in this process are conducive to greater retention of amino acids and vitamins, less lipid oxidation and high digestibility of protein and starch. Moreover, the extrusion process denatures unwanted enzymes, such as anti-nutrients (trypsin inhibitors, hemagglutinins, tannins and phytates), and sterilizes the finished product [74]. The relatively high moisture content, the use of moderate temperatures and the short cooking time help maintain the nutritional quality of extruded foods [75,76].

4.3. Palatability

Despite many years of evolution, dogs still share many of their ancestral eating habits. For example, they rely heavily on their sense of smell when given any kind of food. Dogs usually do not invest much time masticating and savoring, instead they eat in a gluttonous manner [22]. Dogs have few taste buds compared to humans. Nevertheless, dogs can distinguish sour, bitter, salty, sweet and umami flavors when these chemoreceptors are stimulated. Dogs have different bite forces that increase with greater body weight and skull size, which may also be affected by chewing enthusiasm, personality and breed of dog [77]. Dogs choose food based on its palatability [78]. Their food preferences may also be determined by genetics and early life experiences [5,79]. The sensory properties, and hence palatability of pet food products, can be influenced by the types of ingredients used in the formulation, the treats added and the processing factors used. Protein, fat and fiber sources can affect the appearance, aroma, taste and texture of extruded dog food [80].
In the studies by Kierończyk et al. [11], the preferences of a wide population of different breeds of dogs in order to generally verify the suitability of insect attractants were analyzed. As shown in that study, insects can be as effective in influencing dogs as commercial fodder containing flavor, while providing an additional source of high-quality crude protein and fat [11]. The palatability of meat-based pet food was found to be better than that of a vegetarian diet [81]. Interestingly, it has been shown that dogs fed with food with similar palatability values consume different macronutrient compositions. Dogs, on average, chose to consume most of their calories from fat rather than from carbohydrates [78]. The addition of fiber has been shown to reduce palatability. This is not a surprising result given the negative traits associated with fiber in general, including hardness and bitterness. Most dogs do not chew their food very intensively, but the fibrous consistency likely influences the mouthfeel of the food [67].
However, there is little information about how all of these variables can influence food choices in domestic dogs. Knowing the impact of these variables allows to better understand their food selection and food acceptability. Research by Alegría-Morán et al. [10] provides information on the relationship between the composition of the food and the nutritional preferences of dogs. The choice of diet can reflect the internal needs of the animal, helping it to achieve homeostasis. High dry matter and crude fiber content have been shown to negatively affect dog preferences. As noted in this study, dogs, similar to other mammals, prefer wet and semi-moist food over dry food [10]. In the studies by Koppel et al. [80], grain-free dry dog food was compared to dry dog food made from cereals but also to different protein sources due to their aromatic volatile components. The results of that study showed that dry dog foods are products with complex odor characteristics, and grain-free products are less aromatic. Particle size, shape, density, hardness and moisture content of the food affect the palatability of a dog food. In addition, the density affects the contact surface and the degree of fat absorption and the flavor coating on the granules, influencing the perception of food by dogs [82]. Some argue that vegan diets may be less palatable or may endanger animal welfare. Based on caregiver-reported behavior, Knight and Satchell [83] found that vegan pet food is generally at least as tasty for dogs and cats as conventional meat or raw meat diets and does not compromise their welfare when other determinants of welfare, such as nutritional requirements, are adequately covered. The effect of the addition of algae on the palatability of food was investigated. A study by Isidori et al. [84] investigated the effect of A. nodosum on extruded dog food palatability using the split-plate test. The results suggest that A. nodosum has a negative effect on the palatability of the food. Interestingly, it is associated primarily with taste factors, not olfactory factors [84].

5. Conclusions

In our study, we evaluate the self-produced nutraceutical treats (extruded and baked) taking into account the nutritional preferences of dogs and analyzed the proximate composition and mineral content of the snacks. The mean level of crude fat was twice as high in the baked snacks compared to the extruded snacks. In the case of total carbohydrates, the extruded snacks had a higher content compared to the baked. The analyses showed differences in terms of magnesium content. The average content of trace elements was statistically significantly higher in baked snacks than in extruded ones. Comparing baked snacks to the extruded samples, it should be mentioned that in the case of baked treats, spaces between starch granules and protein were less visible, but air bubbles were observed suggesting a higher expansion of the baked snacks. The difference between the content of buckwheat flour influenced the preferences of dogs—variants richer in buckwheat flour were chosen less often, which could be related to the aftertaste of bitterness. The dogs chose the baked variant more willingly than the extruded one. Treats containing insect meal and spirulina can be used in dog nutrition due to their good nutritional value and potential health benefits.

Author Contributions

Conceptualization, J.K.-P. and W.B.; methodology, J.K.-P., M.M. and R.I.; validation, R.I.; formal analysis, J.K.-P.; investigation, J.K.-P., M.M. and R.I.; writing—original draft preparation, J.K.-P., W.B. and M.M.; writing—review and editing, J.K.-P., W.B. and M.M.; visualization, J.K-P. and M.M.; supervision, J.K.-P., W.B. and M.M.; project administration, J.K.-P. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data sharing is not applicable to this article.

Acknowledgments

The authors gratefully acknowledge R. Stuart from the West Pomeranian University of Technology in Szczecin (Poland) for instructions and help in performing analyses of mineral content. The authors thank the cynology students for their involvement in the production of snacks analyzed in this research. The authors would also like to thank the caregivers and their dogs for their willingness to participate in the palatability test.

Conflicts of Interest

The authors declare no conflict of interest.

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Applsci 13 02806 g001 550
Figure 1. Range of complementary pet food products. Adapted from [7].
Figure 1. Range of complementary pet food products. Adapted from [7].
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Figure 2. (a) The surface of the snack S1; (b) the cross-section of the snack S1.
Figure 2. (a) The surface of the snack S1; (b) the cross-section of the snack S1.
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Figure 3. (a) The surface of the snack S2; (b) the cross-section of the snack S2.
Figure 3. (a) The surface of the snack S2; (b) the cross-section of the snack S2.
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Figure 4. (a) The surface of the snack S3; (b) the cross-section of the snack S3.
Figure 4. (a) The surface of the snack S3; (b) the cross-section of the snack S3.
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Figure 5. (a) The surface of the snack S4.; (b) the cross-section of the snack S4.
Figure 5. (a) The surface of the snack S4.; (b) the cross-section of the snack S4.
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Figure 6. Dog preferences in four palatability tests.
Figure 6. Dog preferences in four palatability tests.
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Table
Table 1. Proximate composition of ingredients (g/100 g) used in the production of snacks.
Table 1. Proximate composition of ingredients (g/100 g) used in the production of snacks.
ItemDry MatterCrude ProteinCrude FatCrude AshCrude FibreTotal Carbohydrates
Banded cricket (meal)98.0565.6621.514.857.360.62
Wholegrain spelt flour90.1515.412.301.581.8478.88
Wholegrain buckwheat flour89.0512.943.092.212.0379.73
Dry spirulina biomass94.9376.582.006.440.0014.98
Dried hemp inflorescenes91.8814.069.4721.2624.4930.72
Linseed (meal)93.3524.3312.633.2620.1639.62
Guar gum92.435.050.520.9317.8775.63
Table
Table 2. Calculation of the metabolizable energy (ME, kcal) in dog foods. Adapted from [7,17].
Table 2. Calculation of the metabolizable energy (ME, kcal) in dog foods. Adapted from [7,17].
1.Calculate gross energy (GE):
GE (kcal)=(5.7 × %CP) + (9.4 × %CFAT) + [4.1 × (%TC + %CF)]
2.Calculate energy digestibility (ED)(%):
ED (%)=91.2 − (1.43 × %CF in DM)
3.Calculate digestible energy (DE):
DE (kcal)=(kcal GE × ED)/100
4.Calculate metabolizable energy (ME):
ME (kcal)=DE − (1.04 × %CP)
CP, crude protein; CFAT, crude fat; TC, total carbohydrates; CF, crude fiber; DM, dry matter.
Table
Table 3. Proximate composition (g/100 g DM) and metabolizable energy (kcal/100 g) of extruded (S1, S2) and baked (S3, S4) dog snacks.
Table 3. Proximate composition (g/100 g DM) and metabolizable energy (kcal/100 g) of extruded (S1, S2) and baked (S3, S4) dog snacks.
ItemDry Matter
(g/100 g)		Crude ProteinCrude FatCrude AshCrude FibreTotal CarbohydratesMetabolizable Energy
S192.2919.852.572.751.1673.68347.97
S292.0920.432.132.861.1873.39344.98
Mean92.19 a20.14 a2.35 a2.81 a1.17 a73.54 b346.23 a
SD0.140.410.310.080.010.212.11
S392.8320.926.032.891.7369.68365.84
S493.7621.085.443.141.8169.14363.43
Mean93.30 b21.00 b5.74 b3.02 b1.77 b69.41 a364.64 b
SD0.660.110.420.180.060.381.70
Means with the same letter in the superscript (a, b) did not differ statistically at p = 0.05 (for all columns separately); SD, standard deviation.
Table
Table 4. Macromineral (g/100 g DM) content of extruded (S1, S2) and baked (S3, S4) dog snacks.
Table 4. Macromineral (g/100 g DM) content of extruded (S1, S2) and baked (S3, S4) dog snacks.
ItemCaPKNaMg
S10.1050.6700.7020.0590.242
S20.0790.5490.7170.0610.269
Mean0.09 a0.61 a0.71 a0.06 a0.26 b
SD0.0180.0860.0110.0010.019
S30.0820.6070.6870.0590.255
S40.0790.6170.7000.0700.317
Mean0.08 a0.61 a0.69 a0.06 a0.29 a
SD0.0020.0070.0090.0080.044
Means with the same letter in the superscript (a, b) did not differ statistically at p = 0.05 (for all columns separately); SD, standard deviation.
Table
Table 5. Trace elements (mg/100 g DM) content of extruded (S1, S2) and baked (S3, S4) dog snacks.
Table 5. Trace elements (mg/100 g DM) content of extruded (S1, S2) and baked (S3, S4) dog snacks.
ItemCuFeMnZnCoCdPbMoCrNi
S10.4853.2181.4432.265ndndnd0.136ndnd
S20.5333.7031.2992.334ndndnd0.120ndnd
Mean0.51 a3.46 a1.37 a2.30 andndnd0.13 andnd
SD0.0340.3430.1020.049---0.011--
S30.5584.8751.5642.420ndndnd0.130ndnd
S40.6796.1151.4812.594ndndnd0.105ndnd
Mean0.62 b5.50 b1.52 b2.51 bndndnd0.12 andnd
SD0.0860.8770.0590.123---0.018--
Means with the same letter in the superscript (a, b) did not differ statistically at p = 0.05 (for all columns separately); SD, standard deviation; nd, not detected.
Table
Table 6. Dog preferences in four palatability tests.
Table 6. Dog preferences in four palatability tests.
DogSex (F/M)Age (Years)Test 1Test 2Test 3Test 4
S1S2S3S4S1S3S2S4
1F1x x x x
2F3 x x x x
3F6 xx x x
4F8x xx x
5F9x x x x
6M2x x x x
7M3 xx xx
8M5 xx x x
9M6x xx x
10M8 xx x x
%50 a50 a60 b40 a20 a80 b30 a70 b
Means with the same letter in the superscript (a, b) did not differ statistically at p = 0.05 (for all columns separately); F, female dogs; M, male dogs.
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Kępińska-Pacelik, J.; Biel, W.; Mizielińska, M.; Iwański, R. Chemical Composition and Palatability of Nutraceutical Dog Snacks. Appl. Sci. 2023, 13, 2806. https://doi.org/10.3390/app13052806

AMA Style

Kępińska-Pacelik J, Biel W, Mizielińska M, Iwański R. Chemical Composition and Palatability of Nutraceutical Dog Snacks. Applied Sciences. 2023; 13(5):2806. https://doi.org/10.3390/app13052806

Chicago/Turabian Style

Kępińska-Pacelik, Jagoda, Wioletta Biel, Małgorzata Mizielińska, and Robert Iwański. 2023. "Chemical Composition and Palatability of Nutraceutical Dog Snacks" Applied Sciences 13, no. 5: 2806. https://doi.org/10.3390/app13052806

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