In the search for new, high quality, raw material sources with consumer appeal and a solid nutritional pedigree, pulses are one class of ingredient that the petfood industry has all but completely overlooked. Is that because of limited availability, poor acceptability by the pet, misperceptions about acceptable ingredients for pets or some other intrinsic nutritional or health issue?
Direct answers may be hard to find. But given that we are facing issues regarding the availability of quality ingredients and a shrinking list of alternatives, maybe it is time we explored this class of ingredients to see if they provide options worth considering.
Pulses are the dried seeds found in pods of leguminous plants. These legume seeds include various dry beans from the Phaseolus and Vigna genus (e.g., pinto beans, navy beans, kidney beans, black beans) along with lentils, peas, chickpeas (also known as garbanzo beans), field beans, cow peas and several minor families. Pulses do not include seeds grown for oil production such as peanuts and soybeans, "greens" such as fresh or succulent peas and green beans or leguminous forage seeds such as clover and alfalfa.
Pulses are grown on each of the continents with arable land and in about every type of climate and soil. There are at least 11 primary pulses recognized and a multitude of varieties or accessions within each group. Global production exceeds 40 million metric ton annually, with India, Canada, Brazil and China being the largest producers. The dry beans make up nearly half the annual production, peas about 25% of the mix, chickpeas around 20% and lentils less than 10% (FAO, 2006).
These ingredients contain about twice as much protein as grains (approximately 20-25%) and have been described by some as "the poor man's meat" because of their quality amino acid profile. As it relates to cat and dog nutrition, the sulfur amino acids, methionine and (or) cysteine, are the first-limiting amino acids.
With the exception of chickpeas, most pulses are low fat. However, the fat is rich in the nutritionally important linoleic (C18:2n6) acid with small amounts of omega-3 linolenic (C18:3n3) acid as well. The ash (mineral) content of pulses is two to three times that of common grains like wheat and corn, but relative to protein level, pulses carry half to a third of the "ash penalty" compared to rendered animal protein meals.
Regarding minerals, pulses are rich in potassium and phosphorus, but bioavailability can be an issue. Pulses are also a rich source of fiber, ranging from 10-25% total dietary fiber. The starch content ranges from 30-60% depending on the variety. The starch found in pulses has been characterized as slowly digested (Bednar et al., 2001), which may benefit glucose-insulin metabolism in both dogs and cats (de-Oliveira et al., 2008; Carciofi et al., 2008).
Like other plant-based ingredients, pulses are known to possess a number of compounds that can affect their utilization. For the most part, these are active plant defenses against predation by microbes and insects. In large doses, they can negatively affect nutrient usage in mammals, but some have the potential to be beneficial under the right circumstances (Champ, 2002).
The list includes digestive enzyme inhibitors such as trypsin inhibitors and amylase inhibitors, lectins (phytohaemagglutinnins) that can agglutinate red blood cells, phytates and oxalates that impede mineral utilization, various phenolic compounds with flavor, digestive, antioxidant and physiological effects (e.g., tannins, lignins, isoflavones, lignans) and saponins with emulsifying properties. These may sound unhealthy; however, to put this in perspective, these compounds are found in many other common food and petfood ingredients.
Further, the protease inhibitors and lectins are denatured by heat treatment so they aren't an animal health issue in processed petfoods. For diets with a large amount of pulses, accounting for available phosphorus and supplementing accordingly is the most direct work-around to the phytate issue. Conversely, phytate-bound phosphorus could be a route to restrict phosphorus in kidney diets.
Oxalate content of pulses is around one-fiftieth of that found in spinach, so it is not a real issue outside of an oxalate-urinary tract health diet for cats. The phenolics like tannins are a tenth of that found in sorghum and isoflavones a hundredth of that found in soy, so the dose is inconsequential even if a physiological effect were desired.
While these are certainly things to keep in mind from a customer relations and education perspective, the biggest hurdle to using pulses in petfoods is likely the sub-fraction of fiber that gets blamed for flatulence-specifically the oligosaccharides raffinose, stachyose and verbescose. The sum of these oligosaccharides is in the order of 2.5-5% of the dry matter (Canadian Grain Commission, 2004). They have been linked in the veterinary literature with gas production (mostly hydrogen sulfide) via fermentation in the colon (Roudebush, 2001).
The content varies with type of pulse, variety and growing conditions, and animal response varies with individual. But less is better, so selecting the right pulses, along with adequate evaluation, are key to successfully managing this hurdle.
Pulses are known to mill and mix well with other ingredients. Plus, the starch and protein possess functionality that can be effectively exploited in extrusion. By European rules, pulses require thermal processing for use.
From a regulatory and labeling perspective, pulses are a bit ill-defined, with dried beans and sweet lupin meal being described but no direct definition for peas, lentils or chickpeas available (AAFCO, 2009). Of the pulses, peas are currently the more common in petfoods, with beans, such as pintos, finding their way into vegetarian and elimination diets. This suggests that with proper oversight of the oligosaccharide hurdle, other pulses might be a nice fit in petfoods, too.
Click here for a list of recognized primary pulses and their nutrient analyses.
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