Readers' Rating:

(See details)  Rate this article

Send to a friend

Several strains of the yeast Saccharomyces cerevisiae are used in the baking, brewing, distilling, and wine production industries (Sumner and Avery, 2002).

Although these strains share common features such as efficient sugar utilization, high ethanol tolerance and production, high yield and fermentation rate, and genetic stability, they also possess properties specific to each group (Trivedi et al., 1986; Benítez et al., 1996).

Eight official and one ‘tentative’ yeast products are currently defined by the Association of American Feed Control Officials (2003) and are differentiated by source of yeast and characteristics such as moisture and crude protein concentrations, and fermentative activity. Brewer's dried yeast is the dried, nonfermentative, non-extracted yeast of the botanical classification Saccharomyces resulting as a by-product from the brewing of beer and ale. It must contain not less than 35% crude protein and be labeled according to its crude protein content (AAFCO, 2003). As defined, brewer's dried yeast must originate from a brewery and the brewing of beverages, beer or ale for human consumption, and should not be confused with corn wet milling yeast that is used in industrial ethanol production.

Brewer's dried yeast and corn wet milling yeast are different in terms of chemical composition and organoleptic properties, which is likely due to differences in the fermentation processes and in the substrates used (Table 1). In the brewing industry, wort derived mostly from malted barley is fermented slowly at temperatures of 10 to 20°C using a batch fermentation process that yields a beer with an alcohol content of approximately 6%. In contrast, during wet milling ethanol fermentation, distillers commonly grind and cook corn using enzymes to convert starch to sugar. A rapid continuous fermentation process at temperatures between 35 and 38°C then is employed to maximize substrate utilization and ethanol production yielding 9-12% alcohol. Although not fully researched, many of the differences in brewer's dried yeast and yeast from corn wet milling ethanol production [e.g., fat content, hops products (caryophyllene, humulene), and sugar profiles] are likely factors that affect palatability.

Table 1. Chemical composition of brewer's yeast and corn wet milling yeast

1Not detected

COMPOSITION OF BREWER'S YEAST

Commercially available brewer's yeast is typically dried from a yeast slurry to a dry powder of less than 10% moisture to facilitate handling, storage, and transport. Brewer's yeast is relatively high in crude protein and carbohydrate concentrations, while the concentrations of fat and ash are relatively low. This is not surprising because yeast synthesizes protein and vitamins while absorbing minerals from the beer wort during the fermentation process. The relatively low fat content of brewer's yeast compared to yeast from commercial wet milling ethanol fermentation likely is due to substrate differences (the low fat concentration of barley compared to corn) and differences in the fermentation processes.

Fiber concentration of yeast depends greatly on the method used (Table 2). Although the method of measuring crude fiber (AOAC, 1980) is used for regulatory purposes, results are misleading as several fibrous compounds are solubilized with this procedure, resulting in a large underestimation of fiber content. The neutral detergent fiber (NDF) method of Robertson and Van Soest (1977) results in solubilization of viscous fiber components and recovery of cell wall constituents. Because brewer's yeast contains a considerable amount of protein that becomes viscous when partially hydrolyzed during the NDF procedure, filtration problems and inflated recoveries result in overestimated fiber concentrations (Merchen et al., 1990). For proteinaceous feeds such as brewer's yeast, the method of Prosky et al. (1992) used to measure total dietary fiber (TDF) is most accurate.

Table 2. Fiber composition of brewer's yeast1

1Merchen et al., 1990.

YEAST CELL WALL COMPOSITION

The cell wall of Saccharomyces cerevisiae constitutes approximately 15-30% of the dry weight of the cell and consists primarily of mannosylated proteins, ßglucans, and chitin (N-acetylglucosamine), which are covalently linked. The glucan portion consists ofß(1,3)- and ß(1,6)-chains. Beta (1,3)-glucans, which form the internal skeletal framework of the cell, are the major structural components and are largely responsible for its mechanical strength. This form of glucan is highly branched and possesses multiple nonreducing ends that function as attachment sites for other components of the cell wall (Kollár et al., 1997).

Beta (1,6)-glucans are found primarily outside the skeletal framework and often are linked to cell wall proteins.

Mannose polysaccharides are linked to proteins to form a mannoprotein layer localized at the external surface of the yeast cell wall. Two classes of covalently linked cell wall proteins have been identified. The first class consists of glycosyl phosphatidylinositol proteins that form a complex with ß(1,3)- and ß(1,6)-chains (Kollár et al., 1997).

The second class of cell wall proteins, the protein with internal repeats, are linked directly to ß(1,3) glucans. Mannoproteins are strictly regulated in response to changes in external conditions (e.g., heat shock, hypo-osmotic shock, carbon source) and internal changes during the cell division cycle (Horie and Isono, 2001).

While glucans and mannoproteins are main components of the cell wall and found in approximately equal amounts, chitin constitutes only ~1-3% of the cell wall. Although present in small quantities, it is a major component of the primary septum and is involved in the separation of mother and daughter cells, making it essential for cell division (Shaw et al., 1991). The remaining components of yeast, excluding the cell wall, are collectively referred to as yeast cell extract and contain numerous nucleotides, enzymes, vitamins, and minerals.


SELENIUM YEAST

The essential trace element, selenium (Se), has been heavily studied recently as it is thought to play a role in cancer prevention. Selenium is an integral part of the enzyme glutathione peroxidase, which functions to prevent oxidative damage. In the past, sodium selenite (inorganic form) was commonly used as the Se supplement for livestock feeds.

However, recent studies have identified organic sources (e.g., selenomethionine) present in plants and selenized yeast as highly digestible alternatives (Yoshida et al., 2002; Gunter et al., 2003). Although growth conditions and yeast strain may influence the proportion of selenocompounds present in selenized yeast, the bulk of the Se is in the form of selenomethionine (Ip et al., 2000; Zheng et al., 2000; Yoshida et al., 2002). Other Se forms present in selenized yeast include selenite and selenoamino acids (selenocystine, selenolanthionine, selenocystathionine, Se-methylselenocysteine, Se-adenosyl selenohomocysteine, and γ-glutamyl-Se-methylselenocysteine (Ip et al., 2000). The presence of these highly digestible forms of Se may be partly responsible for the beneficial effects often observed with selenoyeast supplementation.


Use of yeasts in companion animals

Brewer's yeast is used in companion animal foods because it is a high quality protein source rich in Bvitamins, amino acids, and minerals. Inclusion of brewer's yeast (included at 1% of diet) in companion animal diets has been shown to increase (P<0.05) palatability in both dogs (Figure 1; Kennelwood Inc., unpublished data; Ontario Nutri Lab Inc., unpublished data) and cats (Figure 2; Kennelwood Inc., unpublished data) compared to diets containing corn wet milling yeast (included at 1% of diet). In these experiments, consumption ratios of brewer's yeast were 1.9:1 – 2.1:1 compared to corn wet milling yeast. In each experiment, a panel of 20 dogs or cats was used to test food preference with a standard 4- day palatability test. Each day on test, both diets were offered simultaneously for a period of 1 hr. To account for right-left bias, the placement of diets was alternated each day. After the 1 hr feeding period, both diets were removed simultaneously and weighed to calculate intake.

Although few have studied the effects of selenized yeast on companion animal health, one recent experiment reported its beneficial effects on prostate health in aged dogs (Waters et al., 2003). In that study, 49 elderly (8.5 to 10.5 yr) sexually intact males were randomly assigned to one of five treatments and fed for 7 months: 1) control diet containing 0.3 ppm Se; 2) control diet + 3 μg/kg/d selenomethionine; 3) control diet + 6 μg/kg/d selenomethionine; 4) control diet + 3 μg/kg/d high-Se yeast; or 5) control diet + 6 μg/kg/d high-Se yeast. Although no carcinomas were observed during histopathologic examination, Se supplementation decreased (P<0.001) DNA damage and increased (P=0.04) number of apoptotic cells in prostate epithelia.

Because DNA damage and apoptosis may be Seresponsive events that are important regulatory points in prostate carcinogenesis, selenized yeast supplementation may prove to be protective against its development.

Figure 1. Four-day canine palatability tests. Consumption of dog food including brewer's yeast was greater (P<0.05) than that of a food including corn wet milling yeast (n = 20 dogs in each experiment).

Figure 2. Four-day feline palatability test. Consumption of cat food including brewer's yeast was greater (P<0.05) than that of a food including wet milling yeast (n = 20 cats).

Use of yeast components in companion animal foods‘Functional foods’, ‘nutraceuticals’, and ‘phytochemicals’ are terms commonly used to refer to foods or compounds in foods that possess properties that may benefit the human in ways other than providing nutritive value. Although use of these ingredients began in the human food industry, there is interest in including them in pet foods as well.

Many functional ingredients are thought to decrease the incidence of certain disease states or extend the lifespan of pets by possessing antioxidant activity, antimicrobial action, or immuno-enhancing properties. Several components present in yeast may be classified as being functional, including glucomannans, mannans, mannoproteins, ß-glucans, and nucleotides.


GLUCOMANNANS

Glucomannans, extracted from the inner cell wall of yeast, may prove to be beneficial in animal foods because of their ability to bind mycotoxins.

Mycotoxins are naturally occurring toxic chemicals produced by molds under certain environmental conditions. Sharma and Márquez (2001) tested 12 pet foods commercially available in Mexico for frequency and concentration of aflatoxins. In that experiment, seven aflatoxins and aflatoxicol were detected in most samples, with aflatoxin B1 being present in the highest frequency and concentration.

In all contaminated samples, maize was the main ingredient. Research is needed to measure incidence and concentration of mycotoxins in pet foods commercially available in the US, and to determine whether these concentrations are cause for concern.

If that is the case, inclusion of glucomannans in pet foods, especially those containing high concentrations of grain, may be prudent. Glucomannans may also play a role in colon cancer prevention because of their antimutagenic and antioxidative activity (Chorvatovicová et al., 1999; Krizková et al., 2001).


MANNANS

Mannans, also referred to as mannan oligosaccharides (MOS), are composed of short chains (attached mainly by α(1,2) and α(1,3) bonds) and long chains (attached mainly by α(1,6) linkages with branches linked by α(1,2) and α(1,3) bonds) (Spring and Dawson, 2000). Mannans have been studied for their ability to agglutinate and interfere with intestinal binding and colonization of harmful microbial species. Numerous E. coli and Salmonella strains possess mannose-specific fimbriae, agglutinate mannans in vitro, and colonize in lower concentrations in animals supplemented with mannans. Fimbrial adhesins specific for mannan residues are referred to as Type-1 adhesins. Mannans aid in the resistance of pathogenic colonization by acting as receptor analogues for Type-1 fimbriae and decrease the number of available binding sites (Oyofo et al., 1989).

Mannans are capable of modulating the immune system and influencing microbial populations in the gut. Mannans (Bio-Mos®) have been reported to increase (P=0.14) serum IgA concentrations in dogs (2.33 vs 1.93 g/L, Swanson et al., 2002a). In adult dogs, mannan oligosaccharides as Bio-Mos® beneficially altered microbial ecology by increasing (P=0.13) lactobacilli populations (9.16 vs 8.48 log₁₀ CFU/g fecal dry matter) and decreasing (P=0.05) total aerobe populations (7.68 vs 8.67 log₁₀ CFU/g fecal dry matter, Swanson et al., 2002a).


MANNOPROTEINS

Recent experiments have suggested that mannoproteins could be promising vaccine candidates for individuals with compromised T-cell function (e.g., AIDS, lymphoma). Mansour et al. (2002) determined that mannoproteins are ligands for the macrophage mannose receptor, which serves as a link between innate and adaptive immunity (Sallusto et al., 1995).

Mannoproteins also have been shown to elicit delayedtype hypersensitivity reactions and induce production of cytokines important in decreasing fungal pathogens (Chaka et al., 1997; Pietrella et al., 2001).


ß-GLUCANS

Although much of the ß-glucan research has focused on oat bran, experiments using ß-glucans derived from yeast have resulted in similar findings. Of all the beneficial properties that have been reported, the lipid-lowering effect of ß-glucans probably has been the most popular. An experiment using free-living, obese, hypercholesterolemic men demonstrated that yeast-derived ß-glucans were well tolerated and decreased (P<0.05) blood total cholesterol concentrations similar to the effect of oat products (Nicolosi et al., 1999). Yeast-derived ß-glucans also appear to possess antimicrobial and antitumor properties by enhancing immune function. The binding of ß-glucan to its receptor present on macrophages results in phagocytosis, respiratory bursts, and secretion of TNF-α (Chen and Hasumi, 1993; Lee et al., 2001). Finally, ß-glucans are readily fermented in the large bowel and serve as a fuel source for microbial populations.


NUCLEOTIDES

In contrast to the components listed above, nucleotides are present in yeast extract rather than cell wall.

Although endogenously produced by the body, dietary nucleotides may be essential in certain life stages or in certain health conditions (e.g., neonates, immunecompromised) (Sánchez-Pozo and Gil, 2002). In addition to stimulating the development of the small intestine (Bueno et al., 1994) and liver (Sánchez- Pozo et al., 1998), exogenous nucleotides have been shown to enhance immune function by increasing production of immunoglobulins, improving response to vaccines, and increasing tolerance to dietary antigens (Maldonado et al., 2001). Because of their importance in neonatal nutrition, the inclusion of nucleotides in human infant formulas is under investigation (Cordle et al., 2002; Ostrom et al., 2002).


IN VITRO RESEARCH ON YEAST COMPOUNDS

Limited research has been performed testing the effects of yeast or yeast fractions on dog and cat health, with mannans being the only fraction studied to any extent. Vickers et al. (2001) used canine fecal inoculum to determine the fermentability characteristics of mannan oligosaccharides. In that experiment, moderate concentrations of total shortchain fatty acids were produced after 6 (0.49 mmol/ g of organic matter), 12 (1.45 mmol), and 24 hrs (2.40 mmol/g) of in vitro fermentation. The microbial species responsible for mannan oligosaccharide breakdown were not determined in this experiment.

Hussein and Healy (2001) also performed an in vitro experiment using canine and feline fecal inoculum to determine fermentability of mannan oligosaccharide in Bio-Mos® (Alltech Inc.).

Differences were not observed in fermentability between dog and cat fecal inoculum. By examining dry matter and organic matter disappearance, it appeared that mannan oligosaccharide was highly fermented. Dry matter disappearance after 6, 12, 18, and 24 hrs of in vitro fermentation was 54.3, 57.9, 60.7, and 61.3%, respectively. Organic matter disappearance was similar to that of dry matter (56.8, 60.7, 63.7, and 64.1% after 6, 12, 18, and 24 hrs of fermentation). Dry matter and organic matter disappearance do not always reflect microbial fermentation due to the disappearance of soluble carbohydrates present in the substrates that are not retained during filtering. Although soluble carbohydrates are available for fermentation, gravimetric methods cannot determine the proportion used by the microbes as an energy source.

Therefore, the measurement of dry matter and organic matter disappearance is not as accurate as the measurement of the fermentation end-products (i.e., short-chain fatty acids and gas), which is a direct measurement of fermentation. Concentrations of total short-chain fatty acids, acetate, and propionate increased linearly over time. Moderate concentrations of total shortchain fatty acids (10.1, 26.8, 36.7, and 49.7 mM) were produced after 6, 12, 18, and 24 hrs. In comparison to total short-chain fatty acids, lactate concentrations were fairly high (7.7, 8.7, 7.6, and 5.9 mM), suggesting fermentation by a lactateproducing species (e.g., lactobacilli, bifidobacteria).

In agreement with the work of Vickers et al. (2001), these data suggest that mannan oligosaccharide is moderately fermentable by canine and feline microflora. The lactate produced during fermentation suggests that lactate-producing species are able to utilize mannan oligosaccharide, possibly by acting as a prebiotic for these species. In vitro data from our laboratory indicated that mannan oligosaccharide was highly fermentable by canine fecal inoculum (Swanson, unpublished data).

After 0, 4, 12, and 24 hr of in vitro fermentation, organic matter disappearance was 38.1, 40.5, 41.5, and 60.4%, respectively. The relatively high organic matter disappearance at 0 hrs was not due to microbial fermentation, but rather to the soluble carbohydrates present in mannan oligosaccharide not being retained during filtering. After 4, 12, and 24 hrs of fermentation, corrected total short-chain fatty acid concentrations were 1.18, 2.71, and 4.60 mmol/g organic matter, respectively. These short-chain fatty acid concentrations were approximately twice as high as those reported by Vickers et al. (2001) at the 12 and 24 hr time points. In agreement with short-chain fatty acid data, gas was produced in relatively high amounts (corrected gas values were 17.4, 58.3, and 100.9 mL/g organic matter after 4, 12, and 24 hrs of fermentation).


CANINE RESEARCH ON YEAST COMPONENTS

O’Carra (1997) performed two experiments examining mannan oligosaccharide in Bio-Mos® (Alltech Inc.) and its effects on immune function in dogs. In the first experiment, adult beagles were fed diets containing 0, 1, 2, or 4 g Bio-Mos®/kg diet.

Changes in plasma protein and IgG measurements were not observed after 15 or 31 days of supplementation.

In the second experiment, Border collie pups were fed diets containing 0 or 2 g Bio-Mos®/ kg. After a 7-day adaptation period, a vaccination protocol was initiated. All dogs were vaccinated against parvovirus, leptospirosis, adenovirus, and distemper. Vaccine boosters were applied on day 21 for leptospirosis and on day 35 for parvovirus. Blood characteristics were measured over a 9-wk period.

No changes were observed in weight gain, lysozyme activity, plasma protein concentration, or plasma IgG concentration. Neutrophil activity was numerically increased in pups fed the diet containing Bio-Mos® after vaccination [approximately 18 vs 14 Nitroblue tetrazolium (NBT)+ cells/slide]. However, due to low animal numbers (n = 3/group), statistical significance was not reached.

Using adult ileal cannulated dogs, Strickling et al. (2000) compared a control diet to those containing 5 g oligosaccharide/kg diet, one of which was Bio- Mos®. Researchers measured ileal and total tract nutrient digestibilities, microbial populations, ileal pH, ammonia and short-chain fatty acid concentrations, blood glucose, and fecal consistency.

Besides minor changes in short-chain fatty acid concentrations, the only relevant finding was a decrease (P = 0.07) in Clostridium perfringens populations in dogs fed Bio-Mos® (4.48 log₁₀ CFU/ g) vs dogs fed xylooligosaccharides (5.16 log₁₀ CFU/ g) or oligofructose (4.74 log₁₀ CFU/g). Because clostridia species do not possess mannose-specific fimbriae, another mechanism is likely occurring. The lack of any significant findings may be due to the low dose of prebiotics consumed (only ~1.3 g/d) or to the use of soybean meal in the control diet, which supplied an estimated 10 g/kg of naturally occurring oligosaccharides, mainly galactooligosaccharides.

Any beneficial effects resulting from Bio-Mos® consumption may have been masked by the presence of these naturally occurring oligosaccharides.

Zentek et al. (2002) used 4 dogs in a 4 x 4 Latin square design to determine the effects of mannan oligosaccharide (Bio-Mos®), transgalactosylated oligosaccharides, lactose, and lactulose on fecal characteristics, total tract digestibility, and concentrations of microbial end-products in feces and urine.

Carbohydrate supplements were administered at a rate of 1 g/kg BW/d. Mannan oligosaccharide supplementation decreased (P<0.05) fecal pH (6.6 vs 6.9), fecal ammonia excretion (78.4 vs 116 μmol/ g feces), and apparent dry matter (81.9 vs 85.0%), crude protein (79.8 vs 82.5%), and nitrogen-free extract (83.1 vs 94.8%) digestibilities. By decreasing fecal pH and ammonia, mannan oligosaccharide supplementation appeared to improve indices of colonic health. However, the decreases observed in apparent nutrient digestibilities resulting from mannan oligosaccharide supplementation would increase fecal quantity and the cost of feeding the animal. The dose of carbohydrate supplements fed in this experiment (1 g/kg BW/d) was very high. Smaller doses of mannan oligosaccharide may not have such negative effects on nutrient digestibility.

Using ileal cannulated adult dogs, Swanson et al. (2002a) examined the effects of supplemental mannan oligosaccharide (Bio-Mos®) and (or) fructooligosaccharides (FOS) on colonic microbial populations, local and systemic immune function, fecal protein catabolite concentrations, and ileal and total tract nutrient digestibilities. A 4 x 4 Latin square design with 14-day periods was used. Twice daily, dogs were offered 200 g of dry, extruded, kibble diet and given the following treatments orally via gelatin capsules: 1) control (no supplemental MOS or FOS), 2) 1 g FOS, 3) 1 g MOS, or 4) 1 g FOS + 1 g MOS. Mannan oligosaccharide supplementation beneficially influenced microbial populations, decreasing (P=0.05) total aerobe (7.68 vs 8.67 log₁₀ CFU/g fecal dry matter) and tending to increase (P=0.13) Lactobacillus populations (9.16 vs 8.48 log₁₀ CFU/g fecal dry matter). Mannan oligosaccharide also increased serum IgA concentrations (2.33 vs 1.93 g/L, P=0.14) and lymphocyte numbers (20.4 vs 15.6% of total white blood cells, P<0.05). A tendency for decreased ileal dry matter (55.0 vs 67.7 %, P=0.15) and organic matter (63.6 vs 74.1%, P=0.15) digestibility also was observed from Bio-Mos® supplementation.

The combination of FOS and MOS supplementation enhanced immune characteristics, increasing ileal IgA concentrations on a dry matter basis (4.90 vs 3.40 mg/g ileal dry matter, P=0.06) and crude protein basis (12.22 vs 8.22 mg/g ileal crude protein, P=0.05). Supplementation of FOS + MOS also decreased (P<0.05) total fecal indole and phenol concentrations (1.54 vs 3.03 μmol/g fecal dry matter), compounds partially responsible for fecal odor and detrimental to intestinal health. This experiment was performed using healthy adult dogs, which would not be at the highest risk for intestinal irregularities. It is likely that the health benefits of feeding mannan oligosaccharide alone, or in combination with FOS, would be more beneficial to populations of elderly dogs, young weanling puppies, or stressed animals.

In a follow-up study, Swanson et al. (2002b) supplemented ileal cannulated dogs with either 1 g sucrose (placebo) or 2 g FOS plus 1 g Bio-Mos®.

Fecal, ileal, and blood samples were collected at the end of each 14-day period to measure microbial populations and immune characteristics.

Supplementation of FOS plus MOS increased (P<0.05) fecal bifidobacteria (10.04 vs 9.42 log₁₀ CFU/g fecal dry matter) and lactobacilli concentrations in feces (9.75 vs 8.24 log₁₀ CFU/g fecal dry matter) and ileal effluent (8.66 vs 7.55 log10 CFU/ g ileal dry matter). Dogs fed FOS plus MOS also tended to have lower (P=0.08) blood neutrophils (62.99 vs 66.13 % of total white blood cells; 6.40 vs 7.22 x 103 cells/μL) and greater (P=0.06) blood lymphocytes (19.95 vs 17.29 % of total white blood cells) vs placebo. Serum, fecal, and ileal immunoglobulin concentrations were unchanged (P>0.05) by treatment. Supplementation of FOS plus MOS beneficially influenced indices of gut health by improving ileal and fecal microbial ecology and altered immune function by causing a shift in blood immune cells.

Grieshop et al. (2004) tested the effects of chicory and (or) mannan oligosaccharide on nutritional and immunological characteristics of geriatric dogs. After a 4-wk baseline period, 34 senior dogs (beagles: 9- 11 yr old; pointers: 8-11 yr old) were randomly allotted to one of four treatments: 1) control (no chicory or Bio-Mos®); 2) 1% chicory; 3) 1% Bio- Mos®; or 4) 1% chicory + 1% Bio-Mos®. Dogs remained on treatment for 4 wks. Increased (P=0.07) food intake by dogs fed chicory + MOS and MOS alone resulted in increased (P<0.05) wet fecal output.

Dry matter, organic matter, and crude protein digestibilities were unchanged due to treatment.

Supplementation of Bio-Mos® increased (P<0.05) fecal bifidobacteria populations and decreased (P<0.05) fecal E. coli populations compared to control. Supplementation of chicory + Bio-Mos® tended to increase (P<0.10) neutrophil concentrations, while Bio-Mos® (P = 0.06) and chicory + Bio-Mos® (P<0.05) decreased lymphocyte concentrations.

Finally, prebiotic supplementation altered proportions of lymphocytes expressing CD4 and CD8 cell surface markers. Chicory + Bio-Mos® supplementation decreased (P=0.07) CD8-specific lymphocytes.

Results of this experiment support findings from previous experiments that in addition to altering gut microbial ecology, Bio-Mos® supplem entation may affect immune status.


ACTIVE COMPONENTS IN YEAST COMPONENTS

Our laboratory has analyzed several commercially available sources of mannan oligosaccharides and found considerable differences in crude protein, fat, total dietary fiber, and monosaccharide concentrations (Table 3). Most of the monosaccharides are present as part of polysaccharides rather than as free sugars.

Source B was unique in that it contained a considerable amount of galactose in addition to glucose and mannose. The presence of galactose in that source may suggest that guar gum or locust bean gum, which contain galactomannans, are also present in this source of MOS. Although marketed as a source of MOS, these products are very complex and also contain glucans, mannoproteins, phosphate, and several other compounds that apparently are not excluded in the crude extraction process.

Because the composition of MOS is complex, the components that result in beneficial effects are not known. Although the mannan portion of MOS is generally thought to be responsible for the pathogenic resistance effect by acting as a receptor analog for Type-1 fimbrial adhesions present on species such as E. coli and Salmonella, it is possible that a different fraction present in MOS is responsible for its effects on immune function. For example, mannoproteins andß-glucans taken from yeast cell walls have been reported to enhance immunity. Therefore, more research is needed in order to determine whether bioactive peptides, ß-glucans, mannans, or unknown factors present in MOS are responsible for the immune responses observed as a result of their supplementation.

Table 3. Chemical composition of several mannan oligosaccharide sources

1% of dry matter; 2ND = not detected. 3TR = trace. 4NA = not analyzed.

References

Association of American Feed Control Officials: Official Publication. 2003. Association of American Feed Control Officials, West Lafayette, IN.

AOAC. 1980. Official Methods of Analysis. (13th Ed). Association of Official Analytical Chemists, Washington, DC.

Benítez, T., J.M. Gasent-Ramírez, F. Castrejón and A.C. Codón. 1996. Development of new strains for the food industry. Biotechnol. Prog. 12:149- 163.

Bueno, J., M. Torres, A. Almendros, R. Carmona, M.C. Nunez, A. Rios and A. Gil. 1994. Effect of dietary nucleotides on small intestinal repair after diarrhoea. Histological and ultrastructural changes. Gut 35:926-933.

Chaka, W., A.F. Verheul, V.V. Vaishnav, R. Cherniak, J. Scharringa, J. Verhoef, H. Snippe and A.I. Hoepelman. 1997. Induction of TNF-α in human peripheral blood mononuclear cells by the mannoprotein of Cryptococcus neoformans involves human mannose binding protein. J. Immunol. 159:2979-2985.

Chen, J.T. and K. Hasumi. 1993. Activation of peritoneal macrophages in patients with gynecological malignancies by sizofiran and recombinant interferon-gamma. Biotherapy 6:189- 194.

Chorvatovicová, D., E. Machová, J. Šandula and G. Kogan. 1999. Protective effect of the yeast glucomannan against cyclophosphamide-induced mutagenicity. Mutat. Res. 444:117-122.

Cordle, C.T., T.R. Winship, J.P. Schaller, D.J. Thomas, R.H. Buck, K.M. Ostrom, J.R. Jacobs, M.M. Blatter, S. Cho, W.M. Gooch III and L.K. Pickering. 2002. Immune status of infants fed soybased formulas with or without added nucleotides for 1 year: Part 2: Immune cell populations. J. Ped. Gastroenterol. Nutr. 34:145-153.

Grieshop, C.M., E.A. Flickinger, K.J. Bruce, A.R. Patil, G.L. Czarnecki-Maulden and G.C. Fahey, Jr. 2004. Gastrointestinal and immunological responses of senior dogs to chicory and mannanoligosaccharides. Arch. Anim. Nutr. (in press).

Gunter, S.A., P.A. Beck and J.M. Phillips. 2003. Effects of supplementary selenium source on the performance and blood measurements in beef cows and their calves. J. Anim. Sci. 81:856-864.

Horie, T. and K. Isono. 2001. Cooperative functions of the mannoprotein-encoding genes in the biogenesis and maintenance of the cell wall in Saccharomyces cerevisiae. Yeast 18:1493-1503.

Hussein, H.S. and H.P. Healy. 2001. In vitro fermentation characteristics of mannanoligosaccharides by dogs and cats. In: The Waltham International Symposium Abstracts, p. 80.

Ip, C., M. Birringer, E. Block, M. Kotrebai, J.F. Tyson, P.C. Uden and D.J. Lisk. 2000. Chemical speciation influences comparative activity of selenium-enriched garlic and yeast in mammary cancer prevention. J. Agric. Food Chem. 48:2062- 2070.

Kollár, R., B.B. Reinhold, E. Petráková, H.J.C. Yeh, G. Ashwell, J. Drgonová, J.C. Kapteyn, F.M. Klis and E. Cabib. 1997. Architecture of the yeast cell wall: Beta(1—>6)-glucan interconnects mannoprotein, Beta(1—>3)-glucan and chitin. J. Biol. Chem. 272:17762-17788.

Krizková, L., Z. Duracková, J. Sandula, V. Sasinková and J. Krajcovic. 2001. Antioxidative and antimutagenic activity of yeast cell wall mannans in vitro. Mutat. Res. 497:213-222.

Lee, J-N., D-Y. Lee, I-H. Ji, G-E. Kim, H.N. Kim, J. Sohn, S. Kim and C-W. Kim. 2001. Purification of soluble beta-glucan with immune-enhancing activity from the cell wall of yeast. Biosci. Biotechnol. Biochem. 65:837-841.

Maldonado, J., J. Navarro, E. Narbona and A. Gil. 2001. The influence of dietary nucleotides on humoral and cell immunity in the neonate and lactating infant. Early Human Dev. 65:S69-S74.

Mansour, M.K., L.S. Schlesinger and S.M. Levitz. 2002. Optimal T cell responses to Cryptococcus neoformans mannoprotein are dependent on recognition of conjugated carbohydrates by mannose receptors. J. Immunol. 168:2872-2879.

Merchen, N.R., G.C. Fahey, Jr., J.E. Corbin and D.A. Hirakawa. 1990. Researchers seek best way to assess fiber in dog food. Feedstuffs, May 14, 1990 issue, pp. 49-51.

Nicolosi, R., S.J. Bell, B.R. Bistrian, I. Greenberg, R.A. Forse and G.L. Blackburn. 1999. Plasma lipid changes after supplementation with beta-glucan fiber from yeast. Am. J. Clin. Nutr. 70:208-212.

O’Carra, R. 1997. An assessment of the potential of mannan oligosaccharides as immunostimulants. M.S. thesis. Nat’l Univ. of Ireland, Galway.

Ostrom, K.M., C.T. Cordle, J.P. Schaller, T.R. Winship, D.J. Thomas, J.R. Jacobs, M.M. Blatter, S. Cho, W.M. Gooch III, D.M. Granoff, H. Faden and L.K. Pickering. 2002. Immune status of infants fed soy-based formulas with or without added nucleotides for 1 year: Part 1: Vaccine responses and morbidity. J. Ped. Gastroenterol. Nutr. 34:137- 144.

Oyofo, B.A., R.E. Droleskey, J.O. Norman, H.H. Mollenhauer, R.L. Ziprin, D.E. Corrier and J.R. DeLoach. 1989. Inhibition by mannose of in vitro colonization of chicken small intestine by Salmonella typhimurium. Poult. Sci. 68:1351-1356.

Pietrella, D., R. Cherniak, C. Strappini, S. Perito, P. Mosci, F. Bistoni and A. Vecchiarelli. 2001. Role of mannoprotein in induction and regulation of immunity to Cryptococcus neoformans. Infect. Immun. 69:2808-2814

Prosky, L., N.G. Asp, T.F. Schweizer, J.W. de Vries and I. Furda. 1992. Determination of insoluble and soluble fiber in foods and food products: Collaborative study. J. Assoc. Off. Anal. Chem. 75:360-366.

Robertson, J.B. and P.J. Van Soest. 1977. Dietary fiber estimation in concentrate feedstuffs. J. Anim. Sci. 45(Suppl.1):254.

Sallusto, F., M. Cella, C. Danieli and A. Lanzavecchia. 1995. Dendritic cells use macropinocytosis and the mannose receptor to concentrate macromolecules in the major histocompatability complex class II compartment: Downregulation by cytokines and bacterial products. J. Exp. Med. 182:389-400.

Sánchez-Pozo, A. and A. Gil. 2002. Nucleotides as semi-essential nutritional components. Brit. J. Nutr. 87:S135-S137.

Sánchez-Pozo, A., R. Rueda, L. Fontana and A. Gil. 1998. Dietary nucleotides and cell growth. Trends Comp. Biochem. Physiol. 5:99-111.

Sharma, M. and C. Márquez. 2001. Determination of aflatoxins in domestic pet foods (dog and cat) using immunoaffinity column and HPLC. Anim. Feed Sci. Technol. 93:109-114.

Shaw, J.A., P.C. Mol, B. Bowers, S.J. Silverman, M.H. Valdivieso, A. Duran and E. Cabib. 1991. The function of chitin synthases 2 and 3 in the Saccharomyces cerevisiae cell cycle. J. Cell Biol. 114:111-123.

Spring, P. and K. Dawson. 2000. Utilizing biotechnology to improve pet food quality. Proc. Petfood Forum 2000, Watt Publishing Co., Mt. Morris, IL, pp. 123-136.

Strickling, J.A., D.L. Harmon, K.A. Dawson and K.L. Gross. 2000. Evaluation of oligosaccharide addition to dog diets: Influences on nutrient digestion and microbial populations. Anim. Feed Sci. Technol. 86:205-219.

Sumner, E.R. and S.V. Avery. 2002. Phenotypic heterogeneity: Differential stress resistance among individual cells of the yeast Saccharomyces cerevisiae. Microbiol. 148:345-351.

Swanson, K.S., C.M. Grieshop, E.A. Flickinger, L.L. Bauer, H.P. Healy, K.A. Dawson, N.R. Merchen and G.C. Fahey, Jr. 2002a. Supplemental fructooligosaccharides and mannanoligosaccharides influence immune function, ileal and total tract nutrient digestibilities, microbial populations and concentrations of protein catabolites in the large bowel of dogs. J. Nutr. 132:980-989.

Swanson, K.S., C.M. Grieshop, E.A. Flickinger, H.P. Healy, K.A. Dawson, N.R. Merchen and G.C. Fahey, Jr. 2002b. Effects of supplemental fructooligosaccharides plus mannanoligosaccharides on immune function and ileal and fecal microbial populations in adult dogs. Arch. Anim. Nutr. 56:309-318.

Trivedi, N.B., G.K. Jacobson and W. Tesch. 1986. Baker’s yeast. CRC Crit. Rev. Biotechnol. 24:75- 109.

Vickers, R.J., G.D. Sunvold, R.L. Kelley and G.A. Reinhart. 2001. Comparison of fermentation of selected fructooligosaccharides and other fiber substrates by canine colonic microflora. Am. J. Vet. Res. 62:609-615.

Waters, D.J., S. Shen, D.M. Cooley, D.G. Bostwick, J. Qian, G.F. Combs, Jr., L.T. Glickman, C. Oteham, D. Schlittler and J.S. Morris. 2003. Effects of dietary selenium supplementation on DNA damage and apoptosis in canine prostate. J. Nat’l. Cancer Inst. 95:237-241.

Yoshida, M., S. Sugihara, T. Suenaga, C. Naito, K. Fukunaga and H. Tsuchita. 2002. Digestibility and chemical species of selenium contained in highselenium yeast. J. Nutr. Sci. Vitaminol. 48:401- 404.

Zentek, J., B. Marquart and T. Pietrzak. 2002. Intestinal effects of mannanoligosaccharides, transgalactooligosaccharides, lactose and lactulose in dogs. J. Nutr. 132:1682S-1684S.

Zheng, J., M. Ohata, N. Furuta and W. Kosmus. 2000. Speciation of selenium compounds with ion-pair reversed phase liquid chromatography using inductively coupled plasma mass spectrometry as element-specific detection. J. Chromatogr. 874:55- 64.

Readers' Rating:

(See details)  Rate this article

Send to a friend