The third step in food selection occurs when the pet takes the food into his mouth. At this time, the food's taste, shape, feel and texture can all be assessed by the pet. Of these factors, taste is arguably the most critical, but the importance of kibble shape and texture should not be under-estimated.
|
Taste assessment of food
Taste is one of the most complex senses. A Medline search using the keyword "taste" yields over 15,000 references (for humans and animals).
|
The growing incidence of obesity in humans, apparently linked to dietary preferences for sweet and fat (Levine et al., 2003), has driven scientific interest in taste. These studies have evaluated the physiological and psychological (or behavioral) aspects of taste.
|
• The physiology of taste
|
Our knowledge of taste has evolved through the study of neurological signals in cranial nerves following the stimulation of the taste buds by different substances.
|
Three cranial nerves are involved in taste. The facial nerves, in particular the chorda tympani, have undergone the most observations.
|
This research has given rise to many theories, particularly in animals. For example, Boudreau (1973, 1977 & 1989) presented a theory suggesting acid, amino acid and nucleotide taste systems specific to cats. This theory has not been confirmed by other authors. Other studies have shown that dogs, like humans, respond to the umami taste (Kumazawa et al., 1991).
|
Today, molecular biology helps select rodent strains for their taste receptors. As strange as it may seem, at the start of the third millennium, there remains considerable controversy over the properties of these receptors (Amrein & Bray, 2003).
|
Of the five universally recognized tastes, two involve "simple" receptors - acid and salty. The three others – bitter, sweet and unami – involve more complex mechanisms. Several of the receptors involved in recognizing these tastes – T1R1, T1R2, T1R3 – are the subject of in-depth studies (Damak et al., 2003). The latest research (Zhang et al., 2003) seems to suggest that individual taste cells are dedicated to the perception of only one of these three tastes (sweet, bitter or umami). The receptors' capacity to recognize amino acids is being investigated (Nelson et al., 2002).
|
5 types of taste receptors
|
There are 5 types of taste receptors. Two works on ions channels (salt and sour) and three with coupled proteins (sweet, bitter and umami). Latest studies indicate that tastes cells only have one type of receptor.
|
Umami
Umami taste, perceived by dogs and cats, involves the recognition of a non-essential amino acid glutamate, and certain nucleotides like inosine or guanosine. Discovered early in the 20th century by a Japanese researcher (Yamaguchi & Ninomiya, 2000), it is still being extensively studied (Jingami et al., 2003).
|
Bitter
Cats are particularly sensitive to bitter taste. They can detect concentrations of bitter taste four hundred times smaller than levels detected by hamsters (Carpenter, 1956; Houpt, 1991). Bitter taste is due to a wide variety of components (tannins, alkaloids, etc). The perception of this taste is localized toward the back of the tongue. Cats are more sensitive than dogs to bitterness and detect it at lower concentrations. This perception enables them to avoid many toxic substances (for example strychnine), which are often very bitter.
|
Sweet
Cats do not respond to sweet taste and even tend to reject synthetic sweeteners like saccharine or cyclamate, since they are perceived as bitter (Bartoshuk et al., 1975). Dogs' preference for sweet taste is often a result of conditioning, when owners use sweet foods as a reward (i.e. human foods). The dog's attraction to sweet taste is often the basis for ethylene glycol poisoning in dogs. The sweet taste of antifreeze appeals to dogs but not to cats. Rather, cats are typically poisoned by cleaning their paws after walking through antifreeze.
|
Acid
The recent identification of genes coding for acid receptors (Ugawa, 2003) should help improve our understanding of the mechanisms involved (DeSimone et al., 2001). The perception of acid taste is dispersed over the entire surface of the tongue. The longer the molecular chain of the acid, the stronger the perception of the acid taste.
Cats are particularly attracted to strong acid taste. This perceptiveness is widely used by petfood companies.The cat's strong preference for acid presents significant challenges in the formulation of food for cats with renal disease. Excessive acid and phosphorus intakes must be avoided in cats with impaired renal function yet most commercially available cat food digests contain phosphoric acid. Considerable proprietary research at Royal Canin has been invested in the development of highly palatable alternatives for cats with renal disease.
|
Salty
In humans, the perception of sodium chloride is complex: at low concentrations, salt tastes sweet. At medium concentrations, it tastes acid (Smith & van der Klaauw, 1995). Considerable progress in the understanding of salty taste has been possible thanks to the use of amiloride, a substance which attenuates the gustatory response to NaCl (Halpern, 1998).
|
Taste cells are grouped in taste buds. They have a limited life of only 10 days (Shimatani et al., 2003)
|
Gustatory modulations
The most important factors modulating taste perception include sex, age, health and the administration of drugs.
- Sex: female dogs are more receptive than males to sweet taste (Houpt et al., 1979).
- Age: taste sensitivity declines with age. In humans, some observations have shown that salty and bitter tastes decline more rapidly than sweet and acid (Winkler et al., 1999). For other authors, the decline affects all tastes equally (Mojet et al., 2001).
- State of health: some diseases affect taste, in particular thyroid dysfunction, chronic renal insufficiency, diabetes mellitus, and cranial trauma.
- Drugs: tetracycline, a broad-spectrum antibiotic often used in veterinary medicine, alters taste perception.
|
• The psychology of taste
|
The psychological dimension is essential in olfactory and taste perception. The psychological consequences of a particular smell or taste depend greatly on the animal's dietary history and are subject to great individual variability. In fact, while eating, both humans and animals taste not so much their food, as their memories.
|
Modified atmosphere packaging
 The technique of modified atmosphere packaging adds the inert gas nitrogen (depicted in blue) into the package. The nitrogen particles flush out, and replace most of the oxygen gas (depicted in pink). Reducing the amount of oxygen gas in the sealed package minimizes the potential for the oxygen to oxidize the food, substantially enhancing the palatability of the diet.
|
Maximizing the taste appeal of a pet food
There are many factors involved in maximizing the taste appeal of a pet food. These include ingredients selected, ingredient sourcing, quality assurance practices, manufacturing practices, pet food preservation systems, palatability enhancers, storage, and handling systems. While much of this work is proprietary, clearly ingredient quality, manufacturing standards and diet formulation all play critical roles in the development of diets with superior taste appeal for pets.
|
By-products of fat oxidation, e.g. peroxides, aldehydes (i.e. hexanal) and ketones, all reduce a food's palatability by producing rancid off-odors. Royal Canin has taken several steps to ensure the lasting taste appeal of their foods. These include :
|
The use of high quality, fresh raw materials.
- Early incorporation of natural antioxidants that limit oxidation reactions and stabilize the food's quality.
- The use of chelated trace elements that remain bioavailable but are incapable of catalyzing oxidation reactions in food.
- Packaging using the "nitrogen-flushing" (modified atmosphere packaging) process in which oxygen-containing air is replaced by a non-oxygen-containing gas (nitrogen) at the time of packaging, to limit oxidation after packaging (see figure for more information).
- The use of high quality airtight bags for packaging.
- Packaging the food as soon as possible after manufacture.
|
Main degradation products resulting from the oxidation of food
|
In the presence of oxygen, fat (unsaturated fatty acids in particular), are transformed into peroxides, unstable compounds that gradually give way to aldehydes (hexanal, propanal...) and ketones (Shahidi, 2001).
|
Level of hexanal in diets over time using two different preservation systems
|
Physical assessment of food
The physical aspects of food which may have an impact on food selection and preference include kibble shape, size and texture. Texture parameters include maximum force for rupture, the work at maximum force (an indication of the amount of work required to chew the kibble), distance of tooth penetration before rupture, and food rigidity.
|
No company has as much expertise on physical properties of dry pet food as Royal Canin. This is evidenced by the company's wide variety of kibble shapes and sizes, by the patents the company holds on kibble design, and by the unique research tools developed by Royal Canin to assess kibble parameters.
|
While kibble size and shape do not affect the taste or aroma of a food, they do affect how easy it is for the pet to pick up the food and eat it. Having the kibble size and shape appropriate for the pet therefore encourages ready consumption of the diet. Kibble that is too small may be inhaled by dogs as they gulp it down. Kibbles, which are appropriate in size for the dog are chewed and the speed of ingestion is slowed. Slowing ingestion may affect food satisfaction since a prolonged mealtime helps to promote satiety.
|
Growth of carnassials in dogs of large breeds
|
Royal Canin has documented tooth size for the main canine breeds as adults and during their growth as puppies. These studies have made it possible to target specific kibble size and shapes to the relevant breeds and ages.
|
Kibble texture is evaluated using a texturometer. This machine has interchangeable heads, which simulate the tooth dimensions of different sized cats and dogs. Using this equipment, it is possible to adapt kibble texture so that the force necessary to rupture the kibble matches the jaw strength of the targeted pet. In the Royal Canin diet range, the force to rupture kibble can vary from 13 Newtons for a kitten food to 165 Newtons for giant dog food.
|
The texturometer also measures the distance of penetration of teeth into kibble. A specific mode of extrusion triples this penetration. While this measurement does not have a direct effect on palatability, it does provide other benefits. Deeper tooth penetration provides a scrubbing effect on teeth. This principle is used for foods claiming dental benefits.
|
 A texturometer measures not only the force necessary to break a kibble, but also the depth of tooth penetration before the kibble breaks. Various interchangeable heads mimic the teeth of dogs and cats of different sizes and ages.
|
Force for kibble rupture vs tooth penetration as measured by a texturometer
|
Kibble with a tubular shape increases tooth penetration without increasing the force needed to chew
|
Maximizing the physical appeal of a pet food
Clearly, the size, shape and texture of the kibble will affect the overall appeal of a pet food. Much Royal Canin research has gone into the development of kibbles which are specifically designed for pets of various breeds, sizes and ages. No other company offers as much diversity in kibble design. These parameters have an obvious impact on food acceptance and eating enjoyment.
|
|
