Natural ingredients: The case of yucca and sorghum

According to the European Pet Food Industry Federation (FEDIAF), the term ‘natural’ should be used only to describe pet food components (derived from plants, animals, microorganisms or minerals) to which nothing has been added and that have been subjected only to such physical processing to make them suitable for pet food production and maintain their natural composition.

Clearly, this regulatory definition could differ from the consumer perception of ‘natural’. For instance, plant extracts are obtained from the chemical process of extraction, the larger part involving the use of substantial volumes of various organic solvents with chemoselective actions on the plant material. Still, these extracts are being recognized as completely natural by the lay public – justifiably, as their effects stem from active compounds from the plant material and not the chemical solvent.

The case of yucca

Let’s take Yucca schidigera as an example. This is a desert plant whose extract and powder have been used as feed additives and natural ingredients in pet food. The first studies on the ameliorating effect of Y. schidigera extract (YSE) on canine and feline fecal aromas emerged 25 years ago.

At the time, some concerns were raised about the saponins from the extract affecting the gut wall permeability of the treated cats. Indeed, YSE is rich in steroidal saponins, which form complexes with cholesterol in the mucosal cell membranes of the intestines.

These saponins are considered to be toxic by the American Society for the Prevention of Cruelty to Animals (ASPCA). However, several studies have defined safe levels for YSE inclusion in food – levels that reduce fecal ammonia but do not affect the thickness of the intestinal wall or blood parameters.

In contrast to toxic effects, yucca saponins have antiarthritic and antiparasitic activities. YSE is also rich in polyphenols like resveratrol and yuccaols, which could also play a role in antiarthritic activity. An in vitro study demonstrated that supplementation with YSE and chestnut wood tannins could reduce ‘the presence of some potentially toxic volatile metabolites in the animals’ intestine’.

Not a novel natural ingredient

Numerous studies on farm and companion animals demonstrate the safety and efficacy of YSE in various areas, such as growth promotion, improved production, survivability and lower fecal and urine odors.

Since YSE lowers the level of ammonia emissions in farm animals, it can be considered an environmentally friendly ingredient. However, what is missing from these studies is the chemical characterization of the YSE, as the content of bioactive compounds in plant extracts may vary. Furthermore, the sustainability of the use of yucca is an issue that needs to be addressed by the government and industry. Luckily, there are now more sustainable yucca plantations and farms.

Sorghum as an alternative

Sorghum is one of the most sustainable and, thus, widely used animal feed (and food) ingredients. It is a resilient, ‘ancient’ grain that could be used as an alternative to other grains in food formulations. Sorghum is nutritious, as it is rich in proteins, minerals, B vitamins, polyphenols and essential fatty acids.

The phenolic compounds found in sorghum are mostly condensate tannins, believed to have many beneficial health effects. However, these tannins can promote astringency and food refusal, inhibit enzymes, form nutrient complexes and impair digestibility. One of the pioneering evaluations of sorghum as an ingredient in animal diets confirmed that the total tract digestibility of dry matter and organic matter was lowest compared to those of all other starch flours.

A more recent Brazilian study on adult beagles confirmed that sorghum could be used as a source of carbohydrates, but it lowered the digestibility of crude protein and metabolizable energy compared to those of rice.

Another study in dogs found no differences regarding digestibility and energy between sorghum and maize. This could be partly explained by the fact that the amount of polyphenols in sorghum significantly decreased after the extrusion. The loss of phenolic compounds during processing should be considered if sorghum is used as a functional natural ingredient. The same goes for all the natural ingredients, especially fruits and vegetables, that are increasingly incorporated into pet food. These could undoubtedly benefit our companions, but only if their bioactive compounds are well preserved.