Taste preferences and diet palatability in cats

Abstract

The taste of food is an essential characteristic for cats and has been shown to affect food selection. However, understanding of food selection by cats using taste characteristics is far from complete. Therefore, the aim of the present review was to summarize the current knowledge on food preference and the role of taste on this selection in domestic cats. Appetite regulation is one of the determinants of palatability in cats and involves a highly complex interplay between hypothalamus, adipose tissue, and digestive tract. However, knowledge on this interplay is scarce in cats. When evaluating different foods for cats, behavioural responses such as facial expressions involving the movements and positions of ears, tongue, and head can provide increased insight into the effectiveness of formulating a more palatable diet. This paper also reviews food additives currently used in industry for enhancing the palatability of cat foods. In summary, a better understanding of the factors that affect the food preference in cats is essential to produce high-quality foods because cats will not eat a food with a flavour they dislike even though it is complete and nutritionally balanced.

Full text

REVIEW
Taste preferences and diet palatability in cats
Ahmet Yavuz Pekel
a
, Serkan Barış Mülazımoğlu
b
and Nüket Acar
c
a
Department of Animal Nutrition and Nutritional Diseases, Faculty of Veterinary Medicine, Istanbul University-Cerrahpasa, Istanbul, Turkey;
b
Gastrovet,
Inc., Ankara, Turkey;
c
Department of Veterinary and Biomedical Sciences, The Pennsylvania State University, University Park, PA, USA
ABSTRACT
The taste of food is an essential characteristic for cats and has been shown to affect food selection.
However, understanding of food selection by cats using taste characteristics is far from complete.
Therefore, the aim of the present review was to summarize the current knowledge on food preference
and the role of taste on this selection in domestic cats. Appetite regulation is one of the determinants
of palatability in cats and involves a highly complex interplay between hypothalamus, adipose tissue,
and digestive tract. However, knowledge on this interplay is scarce in cats. When evaluating different
foods for cats, behavioural responses such as facial expressions involving the movements and positions
of ears, tongue, and head can provide increased insight into the effectiveness of formulating a more
palatable diet. This paper also reviews food additives currently used in industry for enhancing the
palatability of cat foods. In summary, a better understanding of the factors that affect the food
preference in cats is essential to produce high-quality foods because cats will not eat a food with a
flavour they dislike even though it is complete and nutritionally balanced.
ARTICLE HISTORY
Received 23 May 2019
Accepted 12 June 2020
KEYWORDS
Behaviour; cat; diet; nutrition;
palatability; taste
1. Introduction
There are two hypotheses about the origin of the domestic cats.
The first one presumes that domestic cats originates from Felis
silvestris lybica (the African wildcat) and the second hypothesis
claims that they should be considered to be the subspecies of
Felis silvestris catus which is assumed to have originated from
wild cats living in the Middle East (Clutton-Brock 1999; Randi
and Ragni 1991). Recent evidence shows that feline domesti-
cation approximately occurred 9000 years ago (Vigne et al.
2004). Domestic cat is one of the most popular companion
animals throughout the world (Mameno et al. 2017). According
to a recent report, nearly 35% of the US households own at least
a cat (Pallotto et al. 2018). Approximately 50% of all pet market
is comprised of pet food. The global pet food market size was
nearly 75 billion dollars and the United States was the largest
market which was valued at around 25 billion dollars in 2016
(Phillips-Donaldson 2016).
Although there has been an ongoing debate on whether
dogs are omnivore or strict carnivore, the cat is considered to
be a strict carnivore. Therefore, cats have a relatively higher
protein and essential amino acid requirements than those of
dogs (Salaun et al. 2017). Amylase is not present in cat’s saliva
and their gastrointestinal tract is relatively short compared to
omnivores so they can digest meat much faster than vegetables
(NRC 2006). Cats lack the enzyme called ‘β-carotene 15,15 –
dioxygenase’and therefore, they cannot convert beta carotene
to vitamin A and need to get vitamin A directly from the food of
animal sources (Schweigert et al. 2002). Taurine, an amino acid,
is essential for cats and they need to get it through dietary
animal sources (Knopf et al. 1978). Cats lack the ability to
convert tryptophan into niacin, a vitamin, and therefore it is
required to be taken in through diet (Henderson et al. 1949).
Arachidonic acid, a fatty acid, is also an essential nutrient for
cats since they lack the enzyme necessary to convert linoleic
acid to arachidonic acid and therefore their diet should
contain sufficient amounts of arachidonic acid (Sinclair et al.
1979). The facts mentioned above support the hypothesis
that cats are strict carnivores and therefore their diets need to
be formulated precisely in order to supply all these essential
nutrients (Figure 1).
Different cats have different preferences towards specific
dietary flavours and individual variation in the type of diet
given to kittens contributes to differences in diet/flavour selec-
tion when they reach adulthood. Therefore, a diet must meet
both the nutrients necessary for cats, especially the essential
ones, and also flavours that can encourage feeding to be
counted as complete and palatable. Without palatability,
being complete and balanced diet is not enough for optimal
consumption. Thus, diet palatability, which can be increased
by using dietary additives such as flavours or natural ingredi-
ents, should be high enough to prevent any potential food con-
sumption problems in cats.
2. Eating habits of cats
Despite the domestication process, cats still have the ability to
hunt when it is necessary. Because of cats’innate ability to hunt,
they would live solitarily without any human interference in the
© 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distri-
bution, and reproduction in any medium, provided the original work is properly cited.
CONTACT Ahmet Yavuz Pekel pekel@istanbul.edu.tr Istanbul Universitesi-Cerrahpasa, Veteriner Fakultesi. Hayvan Besleme ve Beslenme HastalıklarıAnabilim
Dalı, Buyukcekmece Yerleskesi. Alkent 2000 Mahallesi. Yigitturk caddesi. A-2 Blok. Buyukcekmece 34500, Istanbul
JOURNAL OF APPLIED ANIMAL RESEARCH
2020, VOL. 48, NO. 1, 281–292
https://doi.org/10.1080/09712119.2020.1786391

wild (Bourgeois et al. 2006). Long canine teeth and shorter inci-
sors and molars make cats very effective at hunting their prey
and stripping the meat from its bones (Van Valkenburgh and
Ruff1987). Cats can hunt preys that are smaller in size several
times daily in the nature. Fitzgerald and Turner (2000) showed
that cats would kill 12 small animals (rodents mostly) on
average in order to meet their daily energy and nutrient
requirements. This instinctive behaviour must have been inher-
ited from its ancestors and probably helps explain the habit of
eating frequent and small meals observed today in domesti-
cated cats (Bradshaw and Thorne 1992). In contrast, dogs are
prone to eat big meals and mostly use this opportunity as a
socialization period like humans. Cats are considered to be a
strict carnivore and their diets mostly consist of muscle and
organ meat of other animals (Lei et al. 2015). Consequently,
the percentage of metabolizable energy that is provided from
proteins and fats are very high (up to 90–95%) and carbo-
hydrates should not contribute to the metabolizable energy
by more than 10%. However, carbohydrate sources are less
expensive and most commercial dry foods contain a lot more
carbohydrate (around 40%) than cats’normal requirement
(Hilton 1987). Cook et al. (1985) reported that a diet with high
palatability and low protein content was preferred over a less
palatable but complete and balanced diet. Therefore, the palat-
ability of diet plays an important role in optimizing energy and
nutrient intake in domestic cats through ensuring enough food
consumption. Odour, taste, texture, and particle size are
additional factors that play role in food intake preferences by
cats (Hullar et al. 2001; Small and Prescott 2005).
3. Appetite
Appetite, by a broad definition, covers a lot of aspects such as
palatability, eating frequency, size of eating episodes, energy
density of foods eaten, and diversity of food consumed by
cats (Arora and Anubhuti 2006;Figure 2). Appetite regulation
is mainly controlled by signals produced both in hypothalamus
and peripheral organs such as adipose tissue and digestive tract
(Erlanson-Albertsson 2005). Hormones or cytokines produced
by adipose tissue have become widely known as adipokines
and they are involved in the regulation of appetite, energy
balance, glucose, and lipid metabolism (Zoran 2010). Leptin is
a protein hormone secreted from adipose tissue that has
been shown to decrease appetite and often referred to as a ‘adi-
postat’in cats (Appleton et al. 2000; Shibata et al. 2003). Since
leptin is secreted from adipose tissue, the higher body fat
levels are associated with higher plasma leptin concentrations
(Appleton et al. 2000). Leptin works as a negative feedback
mechanism in cats to limit food consumption and helps
decrease accumulation of more fat in the body. Therefore, circu-
lating leptin levels has been reported to be positively correlated
to body fat levels in cats (Hoenig and Ferguson 2002). Although
leptin receptors are widely distributed throughout the body,
they are mainly located within the satiety centre of
Figure 1. Some of the features of cats supporting the hypothesis that they are obligate carnivores.
Figure 2. Schematic representation of the main factors involved in appetite and
diet palatability in cats.
282 A. Y. PEKEL ET AL.

hypothalamus (Houseknecht and Portocarrero 1998). The
binding of leptin with the receptors located within the hypo-
thalamus results in the release of two different types of neuro-
transmitters; the first type stimulates anorexigenic neurones,
and the second type suppresses the orexigenic neurones.
Therefore, leptin plays a key role in reducing appetite and
thus controlling food intake in cats (Appleton et al. 2000;
Coppari et al. 2005). Adiponectin is another cytokine and acts
as a food consumption regulator together with leptin in cats
and recently has been shown to be a target molecule for the
treatment of obesity and diabetes in cats (Ishioka et al. 2009).
The same authors found that obese cats had lower plasma adi-
ponectin concentration when compared to non-obese cats.
Tvarijonaviciute et al. (2012) reported a significant increase in
plasma adiponectin concentration after a weight loss in obese
cats. Although there is some evidence to indicate the involve-
ment of adiponectin in fat accumulation in cats, its role on
food intake or appetite remains to be further studied, especially
in obese cats with increased appetite. A schematic figure sum-
marizing the role of leptin and adiponectin is shown in Figure 3.
Ghrelin (a gut hormone) increases appetite and plays a role
in the control of food intake and its plasma concentration has
been shown to be inversely correlated with dietary fat con-
centrations in cats (Backus et al. 2007). Another gut
hormone named cholecystokinin activates peripheral and
central cholecystokinin receptors and causes satiety and acts
as a mechanism to limit food intake in cats (Bado et al.
1991). Neuroendocrine hormones named glucagon-like
peptide-1 and peptide tyrosine are also released from intesti-
nal cells in response to food intake and are involved in the
satiety response but there is a lack of research on their role
in regulation of appetite and therefore on energy expenditure
in cats. The analogues of glucagon-like peptide-1 are used to
decrease body weight through a speculated loss of appetite in
humans, however whether the same effect occurs in cats
remains currently unknown (DeFronzo et al. 2008; Hoelmkjaer
et al. 2016).
An approximately 15% less food intake has been reported in
summer compared to winter in cats during a 4-year cohort
study that was conducted in the south of France where there
is a Mediterranean climate (Serisier et al. 2014). These authors
indicated that the seasonal consumption differences did not
affect the body weights and therefore they speculated that
the change in energy requirement was responsible for the
food intake difference. Therefore, exact detailed mechanism
responsible for these changes is still unclear in cats.
4. Sense of taste in cats
While cats’sense of taste helps them evaluate the nutrient
content of a food, it also protects them from eating toxic,
harmful or indigestible ingredients as much as possible. Chemi-
cal sensors that respond to a variety of chemicals are called
taste buds which are located in tongue, palate, pharynx, and
larynx in cats (Shin et al. 1995). They have relatively small
numbers of taste buds (approximately 470) compared to
dogs, cows, and humans which have around 1700, 20,000,
and 10,000 taste buds, respectively. Therefore, cats have a
weaker taste sensitivity compared to most other animals
(Davies et al. 1979; Ganchrow and Ganchrow 1987; Robinson
and Winkles 1990). Taste buds can detect five basic tastes
which are classified as salty, sour, bitter, sweet, and umami (Li
2013). Although cats have a functional sense of taste like
most mammals; they lack sweet taste receptors and show no
preference for sweet compounds such as sucrose (Li et al.
2005). The reason for the lack of sweet taste perception has
Figure 3. Schematic representation of the role of leptin and adiponectin in appetite control in cats.
JOURNAL OF APPLIED ANIMAL RESEARCH 283

been largely attributed to the deletion of Tas1r gene of sweet
taste receptors found in taste buds (Li et al. 2005,2006).
Results of a recent study indicate that a mutation is responsible
for the deletion of TIR 2 gene very early in the evolution of cats
(Adler 2014). Therefore, they do not show any preference for
glucose, sucrose, and fructose naturally. Cats have been also
reported to reject non-nutritive sweeteners like saccharin and
cyclamate (Bartoshuk et al. 1975). Domestic cats have been
reported to have at least seven different functional bitter
taste receptors but they tend to reject bitter foods where the
opposite is true for dogs and most other mammals (Sandau
et al. 2015). Electrophysiological records showed that water is
not tasteless to cats (Bartoshuk et al. 1971). The very few
number of taste buds found in cats led them to perceive the
taste of food using other complementary senses. Among
these alternative senses, odour appears to be the most impor-
tant one. It is a well-known fact that cat’s sense of smell is 14
times better than humans. The reason for the better sense of
smell was largely attributed to having 2 times more receptors
in the nasal epithelium of cats (Padodara and Jacob 2014). Addi-
tionaly, cats have a vomeronasal organ, which is also called
Jacobson’s organ located in the roof of their mouth which has
a duct that connects it to both nose and mouth. Vomeronasal
organ lying along the base of the nasal cavity, with an
average length of 15 mm, opens into mouth by vomeronasal
duct on the lateral side of incisive teeth through nasal
septum laterally (Chung et al. 2018; Salazar et al. 1995). Vomer-
onasal organ is almost entirely surrounded by a cartilage. This
organ compensate for low taste detection ability of cats since
they have very few numbers of taste buds on their tongue
and cats use his nose, mouth, and vomeronasal organ collec-
tively to arrive at a decision on the taste of food item (Salazar
et al. 1996). When a cat smells food, they open their mouth,
put their chin in lower position, curve the tip of their nose,
then communication starts between the vomeronasal organ
and nasal cavity through the vomeronasal duct, while cat
Figure 4. Parts of cat’s olfactory system and its role in determining the taste of Foods.
284 A. Y. PEKEL ET AL.

rubs its tongue against palate and transfers the smell to the
tongue where taste buds are located. Thus, cats use vomerona-
sal organ, nose, and tongue together to describe the taste of a
compound since its limited capacity for the utilization of taste
by low numbers of taste buds (Papes et al. 2010). The vomero-
nasal organ also functions in determining pheromones and play
a major role in determining sexual behaviour in cats (Doving
and Trotier 1998; Hart and Leedy 1987). Parts of cat’s olfactory
system and its role in determining the taste of foods are sum-
marized in Figure 4.
4.1. Taste preference in cats
Cats were reported to prefer fish and commercial food over rat
in a laboratory setting (Houpt and Smith 1981). Beauchamp
et al. (1977) reported that the increased preference for foods
with large amounts of protein and fat might be considered
proof that cats are obligate carnivores. Cats uses odour infor-
mation generated from food as an effective tool to identify
the source of food to be eaten. If a cat finds an odour of a
food more attractive than another, he will keep eating it
without tasting the other food (Hullar et al. 2001).
4.2. Behavioural responses to different tastes in cats
Measuring just preference and consumption patterns when
concerning the palatability of a diet may not be complete
without assessing behavioural responses of cats. When evaluat-
ing a cat’s behavioural responses to a food item, the facial
expressions should be the very first one to be evaluated.
Facial expressions include the motion of face, tongue, eyes,
and nose. Relationship between these expressions and taste
of a food can be used in the analysis of palatability and
proved to be helpful when combined with preference and con-
sumption data in cats. Behavioural responses related to food
consumption may be classified into three: (a) those related to
the taste of food; (b) those related to consumption; and (c)
those related to satiety (Figure 5). Touching the food with
paws and biting are good behavioural examples related to
the taste of any substance for cats. Behavioural responses
during feeding including eye and face movements can be
indicative of the palatability of the food they consume. Most
house cats are likely to play with their prey when they are not
hungry and they play to practice their hunting skills. Therefore,
playing with food or prey can be given as an example for behav-
ioural responses related to satiety in cats (Levine et al. 2016;
Leyhausen 1979). Hanson et al. (2016) reported an increase in
the duration of ‘half-closed eyes’when they consume a food
they prefer. The same authors also noted that when cats eat
something they like, they tend to do the behavioural responses
such as nose licking, tongue protrusion, smacking lips longer
compared to food they do not prefer. Becques et al. (2014)
investigated the behavioural responses when given highly pala-
table or less palatable dry food to cats during 20 h period a day.
They concluded that feeding the highly palatable diet resulted
in a significant decrease in the length of sniffing the food which
corresponds to less hesitation to consume it when compared to
less palatable diet on the two first visits to feeding station of first
day. After cats eat something they like, they do the licking of the
lip region more frequently. On the other hand, after they
consume a food they dislike; licking their nose, moving their
tail to the right and left, and increased grooming are the behav-
ioural indicators which may be seen at higher frequencies
(Savolainen et al. 2016). Similarly Van den Bos et al. (2000)
reported a significant increase in total duration and frequency
of lip-licking after consuming a more palatable diet compared
to a less palatable diet. The novelty effect or ‘neophilia’is
mostly occurred with cats that have been fed a single food or
diet for a long time. These cats were reported to show a
higher preference for a new diet when they were given a
chance to select between the diet they used to eat and a
new one. This response has been attributed to cats’evolution-
ary habit towards consuming more than one food source to
prevent any nutritional deficiencies (Bradshaw 2006; Stasiak
2002). The duration of preferring the novel food depends on
its palatability. In contrast, some cats show resistant to a new
diet, especially when they were fed one type diet or flavour
for years, this form of behaviour is called ‘neophobia’. This
type of behaviour has been reported to be a strategy of cats
to avoid any toxic or poisonous food item. This type of diet
Figure 5. A schematic of the relationships between food intake and behavioural responses in cats during pre-consumption, consuming, and satiety stages.
JOURNAL OF APPLIED ANIMAL RESEARCH 285

rejection is most commonly reported under physiological,
emotional, or environmental stress in cats. Giving a new type
of food during a visit to veterinarian, or when a cat has a
disease or pain can be good examples of this effect (Bourgeois
et al. 2006; Bradshaw 1991; Bradshaw et al. 1996). Thus, it is
always a good idea to introduce a new food under positive
and usual circumstances to avoid neophobia situation.
5. Palatability
Palatability can be defined as the overall pleasant sensations
related to the hedonic or sensory attributes obtained from
ingested food that contributes with its acceptability in
animals (Hall et al. 2018; Stubbs and Whybrow 2004; Yeomans
et al. 1997). Lists of variables affecting palatability have been
identified in cats in the literature and are discussed below in
this review. However, complex interactions between many
factors related to animal and food have been a major issue
for the pet food industry.
6. Factors affecting food palatability in cats
6.1. Animal-Related factors affecting food palatability
in cats
6.1.1. Preweaning feeding and its influence on feed
preference in adult cats
According to Bradshaw (2006), cats observe their mothers’
feeding practices which can affect their food preferences later
in the adulthood period. Hamper et al. (2012) fed cats with
either raw or canned diet from post weaning 9 weeks to 20
weeks. Then, the same cats were fed with only dry food
between 7 and 23 months of age. Cats demonstrated a
reduced acceptance of canned (moist diet) food after 23
months of age. It was concluded that feeding neither raw nor
canned food earlier affected the transition from dry food to
moist food during adulthood. Stasiak (2001) fed one group of
cats with tuna only while the other group was fed with beef
only during a 3-week-old to 6-month-old period. After feeding
only one type of food, cats were retrained using the alternated
food. Stasiak (2001) demonstrated that both the beef and tuna
cats preferred tuna in stages with alternated food. However,
when cats were nondeprived of a food taste during 6-month
period, no difference in attractiveness of food tastes observed.
Therefore, they concluded that the deprivation of different food
tastes could reveal an inborn food choice. Feeding cats through
a stomach tube during the first 75 days of their lives had a detri-
mental role on sensory system that activates the reward mech-
anism, although they could able to learn to perceive the food
reward as attractive (Stasiak and Zernicki 2000). Bradshaw
et al. (2000). showed that the house cats had an aversion
towards raw beef while the farm cats consumed a little of the
hard-dry food which might have been difficult to ingest. There-
fore, they speculated that the way of life and prior dietary
experiences play a role in food preferences in adult cats.
6.1.2. Hunger level
Physiological state of hunger has been shown to affect feeding
behaviour in cats (Peachey and Harper 2002). Van den Bos et al.
(2000) reported that cats prefer to eat more palatable food
regardless of their hunger level. However, they also showed
that cats consume the less palatable diet depending on their
hunger level.
6.1.3. Age of cat
Aging results in a significant decrease in olfactory receptors and
fibres, thereby reducing the sense of smell. In addition, aging
also has been associated with a concomitant loss of taste in
cats (Boyce and Shone 2006). Despite this, voluntary eating
behaviour of cats has been found to be stable in response to
aging (Taylor et al. 1995). Feeding a more palatable diet, moist-
ening dry food by adding warm water, and feeding fresh food
more frequently have proven to be effective ways of encoura-
ging old cats with appetite problem to consume a satisfactory
Figure 6. (a). Dietary factors which have positive effects on palatability in cats. (b). Dietary factors which have no or negative effects on palatability in cats.
286 A. Y. PEKEL ET AL.

amount of food to maintain a constant nutrient balance
(Laflamme 2005).
6.2. Dietary variables that affect the palatability of
diets for cats
Dietary factors contributing to diet palatability are summarized
in Figure 6(a,b).
6.2.1. Moisture
Although cats can consume dry or semi-moist foods without a
problem, they mostly prefer wet or canned food over dry foods
since the moisture level of canned food is very close to that of
meat (70–85%) (Zaghini and Biagi 2005).
6.2.2. Protein source and content
Kittens were reported to show an impressive regulation of
protein intake and also have an upper limit for carbohydrate
intake which constrains them to deficits in protein and fat
intake on carbohydrate-rich foods (Hewson-Hughes et al.
2011). There is a strong positive correlation between the
protein level of the food and its palatability, especially when
protein sources of animals are used (Zaghini and Biagi 2005).
Diets formulated for cats are known to vary greatly in protein
sources and they can be classified into either vegetable or
animal origin. Soybean and soybean-derived products are the
main vegetable-based protein sources in cat diets, especially
in vegetarian diets; however, they also have low palatability
that limits inclusion in diets for cats (Redmon et al. 2016). One
common industry practice is to use other foods or additives
such as porcine liver or polyphosphates to increase the
overall palatability of the cat diets (Zentek and Schulz 2004).
On the other hand, collagen tissue has been used in relatively
low-priced cat foods as a source of animal protein. However,
it also has a very low palatability compared to muscle meat
sources and again the addition of another high palatability
ingredient is necessary (Paßlack et al. 2017).
6.2.3. Protein/fat ratio
It has been shown that cats are able to regulate and balance
their protein and fat intake regardless of its flavour (fish,
rabbit or orange) even with different protein to fat ratios
(from 10:90 to 70:30) that contribute to the energy density of
the diet (Hewson-Hughes et al. 2016). Therefore, the authors
concluded that macronutrient composition and organoleptic
features of diet mostly play independent roles in diet selection
by cats but these factors might interact in some cases.
6.2.4. Amino acids
The taste buds in cats are innervated by four different cranial
nerves in the mouth (Oliveira et al. 2016). The receptors in
facial nerve mainly react to tastants such as amino acids,
nucleotides, sugar, etc. These reactions may result in either posi-
tive or negative response in the central nervous system of cats.
Cats have been shown to respond positively to amino acids
such as proline, cysteine, ornithine, lysine, histidine, and
alanine which results in sweet taste perception in humans
(Bradshaw et al. 1996). On the other hand, it was confirmed
that ‘bitter’amino acids such as arginine, isoleucine,
phenylalanine, and tryptophan were widely rejected by cats
due to negatively affected receptors in the facial nerve (Oliveira
et al. 2016; Zaghini and Biagi 2005). Another report also showed
that cats rejected L-tryptophan, although they showed a high
preference for L-lysine when given as a pure solution (White
and Boudreau 1975). In contrast, Leucine which has a bitter
taste in humans is a positive flavour in cats (Beauchamp et al.
1977).
6.2.5. Fat
It is a well-known fact that palatability of food increases propor-
tionally as the fat content is increased. Therefore, increasing the
fat content of a diet is a common practice in cats with anorexia.
High-fat diet can help meet cats’energy requirement with
higher palatability even their food consumption is lower than
expected during an anorexic period, except for cats with pan-
creatitis (Delaney 2006). On the other hand, Kane et al. (1987)
did not observe any clear palatability pattern for the low- or
high-fat diet in two diet-choice trials. Dietary salmon oil also
leads to higher palatability and promote food intake in cats
(Filburn and Griffin2005).
6.2.6. Sugar
In a study using electrophysiological recordings, Bartoshuk et al.
(1971) showed that water was not tasteless to cats. Some
authors also reported that although cats were indifferent to
sucrose, with the addition of small amounts of sodium chloride
to suppress the taste of water, cats were able to consume
sucrose. Also, cats were reported to consume sucrose or
lactose when they were offered in diluted milk (Beauchamp
et al. 1977).
6.2.7. Salt and minerals
Cats were reported to be insensitive to salt similar to sugar mor-
phologically and physiologically as opposed to ruminants and
most other herbivores (Bradshaw 2006; Li et al. 2006). Therefore,
they do not have the appetite for salty food that most mammals
have.
Alegría-Morán et al. (2019) reported that mineral com-
ponents including ash and calcium had negative effects on
food preferences in cats by analysing data from a 10-year data-
base of two-feeder food preference tests between 2007 and
2017.
6.2.8. Cellulose
Cats tend to show less preference to foods with kaolin or cellu-
lose (Hirsch et al. 1978). Moreover, Prola et al. (2006) reported
that cats fed on a diet with 6% added cellulose could eat the
same amount of food compared to control diet without
added cellulose; and therefore a significant decrease in
energy intake reported for cellulose fed cats. In this regard,
this phenomenon can be used to limit energy intake in
especially obese cats. Alegría-Morán et al. (2019) indicated
that dietary crude fibre could negatively affect their food prefer-
ences as a result of a significant linear regression analysis
between dietary fibre and diet preference in a 10-year database
food preference study.
JOURNAL OF APPLIED ANIMAL RESEARCH 287

6.2.9. Dilution of food with liquid
Cats usually do not have a high preference for dilution of their
food with a non-caloric liquid (Hirsch et al. 1978; Kanarek 1975).
6.2.10. Warmth and shape of food
Cats prefer to eat dry food at room temperature and they also
likely to have more tendency to prefer ‘easy to grasp’foods in
shape (NRC 2006).
6.2.11. Ph of food
Cats usually show higher preference for acidic (pH = 4.5–5.5)
substances (Thombre 2004).
7. Flavour and palatability enhancers
Substances that increase the overall palatability of a food for
cats are called ‘flavour enhancers’or ‘palatability enhancers’
and this area of research is of considerable interest by pet
food manufacturers.
The palatability of any food item for cats is strongly related to
its high quality attributes such as taste, odour, shape, texture,
and sensation of mouthfeel (Small and Prescott 2005). The
odour perception is very important for cats and plays a key
role in choosing whether to eat a food item or not. Cats will
use odour to define what foods are appropriate for their need
and also will help them perceive toxic substances to their
body. In this regard, cats compensate for their relatively low
ability to taste foods because of having low numbers of taste
buds by using their much more developed olfactory system. It
has previously shown that cats prefer salmon alone over cat
foods mixed with fish, liver, chicken, or beef flavour (Adamec
1976). Cats can be easily attracted to a food by its odour initially,
especially under the conditions when they can smell properly.
Flavour enhancers for cats usually affect food palatability in
cats in two different ways. The first one, called flavours that
affect ‘first choice’which is the first food item tasted by cats
in preference tests and these flavours mostly affect olfactory
perception of cats and improve attractiveness of the food.
The second one, and the most important flavour enhancers
are classified as having a ‘continuous choice effect’in cats
when they are given the same food with the same flavour
again and it reflects actual acceptance of a food item by cats
in the long run (Tobie et al. 2015). In the continuous choice
affect, taste, mouthfeel, texture, etc. have bigger contribution
to the palatability of the specific food item with flavour than
just the odour of the specific food.
Flavour enhancers in pet food are classified as natural or syn-
thetic. Examples of natural flavours given in the US Code of
Federal Regulations are the essential oil, oleoresin, essence or
extractive, protein hydrolysate, distillate or any product of roast-
ing, heating or enzymolysis. The same regulation also describes
the origin of the natural flavours and they could be obtained
from plant materials such as spices, fruits, leafs but also may
be obtained from animal products such as meat, poultry, and
seafoods. However, to be classified as flavour, their major role
must be just for flavouring rather than nutritional (Thombre
2004; Yerger 2003). Flavours do not meet these criteria above
are classified as synthetic flavours under the same regulation.
The efficacy of these flavours depends on multiple factors
including dietary and individual differences. For example, a
flavour that enhancing the palatability in dry foods might not
be as effective in semi-moist or canned foods. Animal proteins,
amino acids, and fat are the most efficacious flavours for cats
compared to the flavours of plant origin.
8. Food additives
A vast number of compounds may be incorporated into cat
foods for nutritional, functional, and also for palatability pur-
poses. Apart from palatability enhancing, food additives can
also be used for purposes such as dental cleaning (eg. phos-
phates), giving colour to food or freshening breath of cats or
even masking unpleasing odour to humans in cat diets (eg.
vanilla scent). Most commonly used food additives for palatabil-
ity purposes are discussed below.
8.1. Hydrolysed proteins
Hydrolysis of proteins (mostly meat) by different methods and
using them dietary to improve animal performance via
different mechanisms (chemical, enzymatic, or microbial) is
being studied by different research groups. Disruption of
protein molecules results in the production of a vast amount
of freely available bioactive peptides which exert a wide
range of activities affecting digestion, immune, and central
nervous systems (Korhonen and Pihlanto 2006). Soy sauce is
one of the earliest and good examples of protein hydrolysates
to improve the palatability of foods for humans (Pasupuleti
and Demain 2010). Protein hydrolysates are also called
‘digest’in animal nutrition and can be in dry or liquid forms
with a common dietary application rate of 1–3% as a coating
(Nagodawithana et al. 2010). Protein hydrolysates are among
the most popular palatability enhancers in commercial cat
diets because of its high short peptide concentration and free
amino acid content (Folador et al. 2006; Martı´nez-Alvarez
et al. 2015). The proteins are broken apart so that the disrupted
whole protein structure cannot be recognized by cats immune
system and this help reduce the allergies related to these pro-
teins in cats and therefore it is a vital part of any hypoallergenic
cat food in the market currently (Cave 2006; Neklyudov et al.
2000).
8.2. Spray-dried plasma
Spray-dried animal plasma is routinely added especially in
canned pet food products due to its high water holding
capacity, and therefore promoting better foaming, gelling,
and emulsifying properties (Rodríguez et al. 2016). Moreover,
Polo et al. (2005) reported higher palatability of diets containing
spray-dried plasma than diet containing wheat gluten in cat
foods.
8.3. Sodium pyrophosphate
Pyrophosphates are chemical compounds that are used as a
raising agent or to improve texture, and flavour of foods
288 A. Y. PEKEL ET AL.

(Terenteva et al. 2017). Oliveira et al. (2016) reported that the
coating cat food with 0.5% sodium pyrophosphate resulted in
a significant increase in food consumption.
8.4. Yeast extract products
Both dried yeast, mostly comes as a byproduct from ethanol
industry, and the brewer’s yeast, are used as a palatability
enhancer in pet food industry worldwide. The palatability
increase with the addition of yeast has been attributed to its
high glutamic acid concentration which gives the umami or
meaty aroma (Nagodawithana 1992). Although Swanson and
Fahey (2004) reported an increase in the palatability of diet
for cats with the addition of 1% yeast, the same authors also
reported a decrease in palatability with the 2% yeast inclusion.
In another study, cats given 0.4% yeast wall dry extract had sig-
nificantly lower diet palatability compared to cats given a diet
without yeast extract (Aquino et al. 2010). Thus, the optimal
inclusion rate of yeast should be achieved by testing it under
different conditions for cat diets.
8.5. Choline
Salt-like taste attributes have been reported for choline chloride
in rats and humans. Therefore, it was recommended as a strat-
egy to replace salt with choline to limit the level of salt con-
sumption in humans (Locke and Fielding 1994). Although,
cats are known to do not possess appetite for salt, according
to Lin et al. (1997) addition of 0.3% choline chloride, which
reported to have a salt-like taste in other animals, was helpful
in increasing the palatability and overall food consumption of
a dry cat food. However, physiological mechanism behind this
relationship is not clear.
8.6. Salt
Studies also demonstrated that kittens lack the ‘salt appetite’
that most omnivorous animals have (Yu et al. 1997). Even
sodium-depleted cats reported to show no preference for
sodium solution or salted water over plain water. Therefore,
cats normally do not show attraction to salty foods and this
attribute makes it unsuitable as a palatability enhancer in cat
diets. Thus, substantial attention needs to be given to protect
cats from any sodium deficiency since they cannot select
foods based on their sodium or salt content (Yu and Morris
1999).
8.7. Prebiotics
A significantly higher palatability was found in cats when given
0.6% dietary mannanoligosaccharide as a prebiotic in dry food
by Aquino et al. (2010). Inulin is another type of prebiotic and
can be used in cat diets (Roberfroid and Delzeene 1998).
Decreased plasma ghrelin levels were achieved through
dietary use of inulin type fructans in human subjects (Harrold
et al. 2013). The same study also revealed that this decrease
in plasma ghrelin levels resulted in a significant increase in
secretion of glucagon-like peptide-1 which lead to a decrease
in hunger and reduced eating highly palatable foods.
However, it remains unknown whether and how dietary inulin
would affect hunger and therefore food intake and palatability
of foods in cats.
9. Conclusion
This review summarized the current knowledge and develop-
ments on the understanding of taste preferences, palatability,
and factors affecting cats’reactions when selecting and con-
suming diets. Overall, studies on leptin, adiponectin, ghrelin,
and cholecystokinin and how they regulate appetite are necess-
ary for understanding the feline food intake and this might be
important in everyday regulation of food palatability in cats. The
use of behavioural responses of cats showing during tasting,
consuming, and after consuming in combination with prefer-
ence and food consumption data may be of benefitasto
provide a more comprehensive and robust data on determining
the palatability of foods for cats. Increasing moisture, protein,
certain amino acids, and fat content of cat foods are effective
and proven methods to improve palatability. However, cats
are insensitive to dietary salt and sugar addition and therefore
these ingredients should not be used as a way to increase the
palatability of a food or diet for cats. Currently spray-dried
plasma, yeast products, choline chloride, and hydrolysed pro-
teins are the commonly used palatability enhancing food addi-
tives in cat diets by the pet food industry. Although protein
hydrolysates are among the most popular palatability enhan-
cers in the cat food industry, there is no specific bioactive
peptide defined as a pure palatability enhancer in cat diets.
Therefore, suggested future research directions on food palat-
ability in cats can include developing easy and economical
ways to produce specific functional molecules (esp. specific bio-
active peptides for different ingredients) which will improve the
acceptability of certain ingredients that are not desirable by
cats. Taken together, the direction of future research should
be towards the promising palatability enhancers with a clear
pattern in cats.
Disclosure statement
No potential conflict of interest was reported by the author(s).
ORCID
Ahmet Yavuz Pekel http://orcid.org/0000-0001-9488-5599
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