Utilization of stevioside, a new natural, non-caloric feed sweetener, in feeds for dogs.

E. De Muylder ¹, P. Naudts ², J. Geuns ³, S. Simoens ¹ and L. Vanhoudt ¹.

¹ : VDS bvba,
² : STEPAJA bvba,
³ : Laboratory of Plant Physiology, Catholic University of Leuven.

Abstract

Stevia rebaudiana Bertoni, a plant originated from Paraguay, contains the natural sweeteners, Stevioside and Rebaudioside A. Stevioside is 300 times sweeter than sugar. The Laboratory of Plant Physiology of Dr. Jan Geuns has selected a strain of this plant which contains up to 15 % sweetener in the leaves. The strain is patented under the name STEPA®. It is now marketed for human nutrition and licenses to use stevioside as a non-caloric sweetener in human foods have been applied for (May 1998).
Sugar is often used as a preservative and for palatability in dog foods. Although sugar, corn syrup, and other simple carbohydrates can supply calories, they are "empty calories" devoid of any nutrient. Health considerations limit the utilization of sugar in dog diets to a maximum of 8 %. For older and obese dogs, it is even preferable not to use any sugar at all in the feeds. To be able to give our dogs their preferred taste without compromising on their health, STEPA® offers the solution. An inclusion rate of only 0.3 kg Stevioside per ton or 2 kg of dried STEPA® leaves will have the same effect on palatability, without compromising on the nutritional requirements of dogs.
Nutrition studies on rats, have proven that stevioside does not pose any health treat, even when used in high concentrations during long periods (Yamada et al, 1985).

Palatability of dog foods

Palatability is used to describe how an animal likes the taste, smell and texture of a particular feed. A pet food, formulated to contain all essential nutrients is useless if the dog or cat doesn't like it. The palatability of the food is not only important for the dog, but also for the pet owner, who will tend to choose the food his pet likes. After all, it is the pet owner who buys the food. Dogs generally find sugars palatable but other pets, such as the cat, do not respond to the taste of sugar.
The sense of taste is confined to the tongue, the palate and the epiglottis, and is therefore only sensitive to substances brought to the mouth. In dogs, the most abundant taste buds are those that respond to sugars or sweet tastes. Both sugars, including mono- and disaccharides (such as fructose and sucrose), artificial sweeteners but also "sweet" amino acids can trigger these receptors.

Sugar in dog foods and their consequences on health

Sugars are also economical and easily digested sources of energy. Short chained sugars are to be avoided in dog foods as much as possible. Although they are a source of fast energy, they are considered as empty calories, because they are not adding any nutrient to the dogs diet. They quickly appear as glucose in the blood and will be converted to lipids and accumulate in the body, if the dog does not use them for energy.

Sugars can also play a role in the dog food as humectant. Products such as hydrogenated corn syrup are often used in moist dog foods as humectant and plasticizer, to give the food a certain flexibility. The sugar also acts as a preservative against spoilage.

The excessive use of sugar in feeds for dogs can create a series of problems starting with obesity, especially in older dogs who's activity has slowed down over the years but their appetite didn't. Mostly the problem is only identified when the dogs are already seriously overweight. Putting them on a diet is the only solution at that time and most pet owners are not really tempted by the idea. After all, it is their pet and they are supposed to "spoil" it. Interesting is the study of Mason (1970) who showed a correlation between the condition of the dogs and those of their owners. While 25 % of the dogs were obese from "normal" owners, this was 44 % for obese owners.


An additional complication in putting the dog on a diet is his addiction to the sweet taste, which could prevent him from switching to another, light diet. The inclusion of natural or artificial, non-caloric sweeteners is in this case the only solution.
The obesity has a number of consequences to the dog's health :

• Orthopaedic problems caused by the stress imposed by excess weight on the stifles and elbows.
• Respiratory difficulties due to narrowing of the airway by fatty deposits in the tissues surrounding the larynx and pharynx
• Higher risk of infectuous diseases (Williams and Newberne, 1971)

Another problem occuring is diabetes mellitus. It is characterized by clinically significant glucose intolerance and an absolute or relative lack on insulin. Insulin has to be administered artificially to match the glucose produced by digesting the diet. It is clear that monosaccharides and disaccharides are to be banned completely from the diet, since they will raise the glucose level suddenly (hyperglycaemia).
Another consequence of administrating insulin is the importance of palatability. Palatability is particularly important when using relatively short duration insulins. With these insulins in particular, it is vital that all the offered food is consumed within a short time.

Stevia rebaudiana Bertoni and STEPA®

Stevia rebaudiana Bertoni, a plant originating from Paraguay, contains the natural sweeteners, Stevioside and Rebaudioside A.

STEPA is an incredibly sweet herb, obtained by a natural selective breeding process of the sweetest Stevia parent plants. Prof. Dr. Jan M.C. Geuns of the Catholic University of Leuven (KULeuven) is responsible for the scientific research and the optimising of the growth conditions of this plant. The sweetener, stevioside, extracted from the plants, is 300 times sweeter than sugar. The fresh leaves have a nice liquorice taste. The Laboratory of Plant Physiology of Dr. Jan Geuns has selected a strain of this plant which contains up to 20 % sweetener in the leaves.
The strain is patented under the name STEPA®. It is now marketed for human nutrition and licenses to use stevioside as a non-caloric sweetener in human foods have been applied for (May 1998). What makes the Stevia plant so special is that it can be used to replace sugar (sucrose). Indeed, the leaves contain diterpene glucosides with a sweet taste but which are not metabolised and contain no calories. The biggest part of the glucosides consists of the stevioside molecule.
The principal advantages of Stevia are the following:

• It is a completely natural non-synthetic product;
• Stevioside (the sweetener) contains absolutely no calories;
• The leaves can be used in their natural state;
• Thanks to its enormous sweetening power, only small quantities need to be used;
• The plant is non-toxic;
• The leaves as well as the pure stevioside extract can be cooked;
• No aftertaste or bitterness;
• Stable when heated up to 200 degrees;
• Non fermentative;
• Flavour enhancing;
• Anti-caries, bactericidal activity (Tomita et al, 1997);
• Clinically tested in animals and frequently used by humans without negative effect;
• Non-addictive sweetener.

Small Stevia rebaudiana plants.

Safety of using stevioside

Although stevioside has no mutagenic effect (Pezzuto et al, 1986), (Suttajit et al, 1993), its aglycone, steviol (13-hydroxy-ent-kaurenoic acid) has been shown to be mutagenic in some tests with Salmonella typhimurium strains (Pezzuto et al, 1986), (Matsui et al, 1989). 15-oxosteviol and Ent-kaurenoic acid itself is not mutagenic and acetylation of steviol at the hydroxy position negates mutagenicity. Matsui et al (1996) examined the genetic toxicity of stevioside and steviol with 7 mutagenicity tests using bacteria, cultured mammalian cells and mice. Stevioside was not mutagenic in any of the assays examined. Steviol however, produced dose-related positive responses in some mutagenicity tests. Nutrition studies on rats, have proven that stevioside does not pose any health treat, even when used in high concentrations during long periods. Yamada et al(1985) administered stevioside and rebaudioside A to rats for 2 years at a rate of 0.3-1 % of the diet. Even at the highest dose, no differences were observed in biochemical, anatomic, pathological and carcinogenic tests on 41 organs following autopsy. Toskulkao et al (1997) found that stevioside at a dose of 15 g/kg BW was not lethal to either mice, rats or hamsters. This corresponds with the sweet equivalent of eating almost half its body weight of sugar daily.

Stability of stevioside during processing

Chang and Cook (1983) investigated the stability of stevioside in carbonated beverages. Prolonged heating of a stevioside solution resulted in a decrease of the stevioside in the solution by 16.7 % after 12 hours at 100 °C in a neutral solution and 46.0 to 53.8 % after 4 hours in acidic solutions.

Palatability of stevioside for dogs

To test the suitability of stevioside as a palatability enhancer for dogs, the following trial was done.
A commercial diet was used as the basis. Dried STEPA leaves were cooked and the liquid was sprayed on the feed and the feed was dried afterwards. The concentration of stevioside in the feed was 90 mg per kg feed, which corresponds with 2.7 % of sugar added to the diet.
5 dogs were fed a little less than their normal daily ration. After finishing their food, two bowls with a small quantity of food were provided. This was done during 5 days and the food was always supplied in the same bowl. After 5 days, the bowls were switched to confuse the dogs. The behavior of the dogs was observed. Observations were defined as following :

• Exclusive consumption : The dog only feeds on 1 diet, leaving the other untouched.
• First choice preference : The dog consumes both diets, but consumes one diet first.
• Difference in amount of feed consumed : The dog consume part of the feed given, but consumes more from one of them.
• No preference : The dog don't show any preference, nor in amount of feed consumed, nor in his first choice.

The result of the trial is shown in Table 1.

Table 1 : Palatability of stevioside for dogs
	nr of dogs
Dog behaviour	Commercial diet + STEPA	Commercial diet
Exclusive consumption	2	0
First choice preference	1	0
Difference in amount of feed consumed	2	0
No preference	0	0
Total nr with preference	5	0

(This study is still in progres at this moment)

Conclusion

The utilization of stevia or stevioside in feeds for dogs has the following advantages :

• Increased palatability of the feed
• No addition of empty calories in the feed
• Possibility to produce sweet tasting feeds for diabetic and obese dogs
• Because its strong sweetness, limited doses have to be added, leaving more space in the formulation for other ingredients and nutrients
• Heat stable (important for extruded feeds)
• Safety of utilization

References

S.S. Chang and J.M. Cook, 1983.
Stability studies of stevioside and rebaudioside A in carbonated beverages.
J. Agric. Food Chem. 31 : 401-412.

M.E. Krejci and D.A. Koechel, 1992.
Acute effects of carboxyatractyloside and stevioside, inhibitors of mitochondrial ADP/ATP translocation, on renal function and ultrastructure in pentobarbital-anesthetized dogs.
Toxicology 72 : 299-313.

E. Mason, 1970.
Obesity in pet dogs.
Vet. Rec., 86:612-616.

M. Matsui, K. Matsui, T. Nohmi, H. Mizusawa and M. Ishidate, 1989.
Mutagenicy of steviol : an analytical approach using the Southern blotting system.
Eisei Shikenjo Hokoku 300 : 83-7.

M. Matsui, K. Matsui, Y. Kawasaki, Y. Oda, T. Nogushi, Y. Kitagawa, M. Sawada, M. Hayashi, T. Nohmi, K. Yoshihira, M.Jr. Ishidate and T. Sofuni, 1996.
Evaluation of the genotoxicity of stevioside and steviol using six in vitro and one in vivo mutagenicity assays.
Mutagenesis 1996 Nov; 11(6):573-579.

J.M. Pezzuto, N.P. Nanayakkara, C.M. Compadre, S.M. Swanson, A.D. Kinghorn, T.M. Guenthner, V.L. Sparnins and L.K. Lam, 1986.
Characterisation of bacterial mutagenicity mediated by 13-hydroxy-ent-kaurenoic acid (steviol) and several structurally-related derivates and evaluation of potential to induce gluthathione S-transferase in mice.
Mutat Res. 169 : 93-103.

M. Suttajit, U. Vinitketkaumnuen, U. Meevate and D. Buddhasukh, 1993.
Mutagenicity and human chromosomal effect of stevioside, a sweetener from Stevia rebaudiana Bertoni.
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T. Tomita, N. Sato, T. Arai, H. Shiraishi, M. Sato, M. Takeuchi and Y. Kamoi, 1997.
Bactericidal activity of a fermented hot-water extract from Stevia rebaudiana Bertoni towards enterohemorraghic Escherichia coli 0157:H7 and other foodborne pathogenic bacteria.
Microbiology and Immunology, 41(12) : 1005-1009.

C. Toskulkao, L. Chaturat, P. Temcharoen and T. Glinsukon, 1997.
Acute toxicity of stevioside a natural sweetener, and its metabolite, in several animal species.
Drug and Chemical Toxicology, 20(1-2) : 31-44.

K. Toyoda, H. Matsui, T. Shoda, C. Uneyama, K. Takada and M. Takahashi, 1997.
Assessmentof the carcinogenicity of stevioside in F344 rats.
Drug and Chemical Toxicology, 35(6) : 597-603.

G.D. Williams and P.M. Newberne, 1971.
Decreased resistance to Salmonella infection in obese dogs.
Fed. Proc., 30 : 572.

Yamada et al, 1985.
Chronic Toxicity study of dietary Stevia extracts in F344 rats.
J. Food Hyg. Soc. Japan Vol 26(2) : 169-183.



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