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Protein digestibility kinetics in petfood

Dr. Ruben Morawicki and lab technician Delmy Diaz use colorimetric analysis to determine protein content of fermented sorghum samples. Fermentation increases protein content and also makes it more available for digestion in animal feed.
Image Credit: Ark. Agricultural Experiment Station on Flickr (CC BY-SA 2.0)

The search for innovative protein sources is on the rise as a result of increasing global food consumption and consumer concerns about sustainability, animal welfare, and strain on agricultural land.

In line with the humanisation trend, pet owners are likely to select a pet food based on their own dietary preferences. Moreover, the increased awareness of the importance of proper nutrition has led pet owners to become more and more careful when looking at pet food labels. Clean label is amongst the top trends in the pet food market and seems to be driven by the perceived link between health and naturalness. Consequently, innovative protein sources are of great interest in the Pet Industry as a way to meet the growing market demand for pet nutrition.

The importance of absorption kinetics

Protein bioavailability is strongly related to its amino acid composition, size, and mass range. Large proteins, protein associated molecules and nucleic acids have lower digestibility compared to free amino acids and small peptides. Protein digestibility of feed materials is an important information for nutritionists. However, it is not expressing timing of absorption in the gut.

The kinetics of protein absorption should be considered in addition to protein digestibility. It allows nutritionists to properly assess the quality of the protein source. Many properties and functionalities of proteins are related to their absorption kinetics. The kinetics of protein absorption helps categorise the protein fraction according to its speed of absorption. Four categories can be defined as flash, fast, slow and resistant along the digestive tract (Figure 1).

Flash digestibility is important for young animals, especially as their gut is not yet mature and still not able to easily absorb and utilise the protein fraction from the diet. Supplying young animals with a flash digestible protein source that is rich in free amino acids and small peptides will help them easily absorb and use those nutrients.

Hydrolysed yeasts: a source of highly digestible and quickly absorbed proteins

Yeast is an incredible bioengineering factory and a source of valuable nutrients and functional molecules. Yeast experts at Lallemand have worked on the screening of different yeast biomasses and on the optimisation of their production processes, both of which led to the development of a specifically designed hydrolysed yeast, YELA PROSECURE.

YELA PROSECURE’s kinetics of protein absorption has been analysed with the Boisen standard method (Figure 2). YELA PROSECURE’s protein digestibility starts at 77 percent at the beginning of the intestinal phase (right after the stomach) to 94 percent after 48 hours. Moreover, YELA PROSECURE is close to its maximum in vitro digestibility after 3 hours of intestinal digestion, meaning 90.5 percent of the protein content of YELA PROSECURE has flash and fast digestibility kinetics and only 9.5 percent is slow and resistant. The proteins from YELA PROSECURE are, therefore, highly bioavailable for the animals.

kinetics of protein digestibility
Figure 2. YELA PROSECURE: kinetics of protein digestibility

Effect of the yeast process on the protein digestibility kinetic

The protein digestibility kinetic of YELA PROSECURE was compared to a whole-cell inactivated yeast with a focus on the three first hours of the intestinal phase as the process of digestion is already quite complete at that time for young animals.

In whole cell inactivated yeasts, no lysis process is applied, and most nutrients (including the proteins) are in the cytoplasm of the yeast cell making them less accessible. As shown in (Figure 3), their protein digestibility is low right after the stomach (46 percent) and increases slowly, up to 60 percent after 3 hours.

Thanks to the oriented and controlled hydrolysis process used to produce YELA PROSECURE, proteins and nucleic acids are fragmented into small size peptides offering highly digestible nutrients. We can conclude the yeast lysis process strongly benefits protein digestibility and therefore nutrient bioavailability in the gut.

Kinetics of protein digestibility
Figure 3. Kinetics of protein digestibility: YELA PROSECURE vs. a whole-cell inactivated yeast

Hydrolysed yeast protein digestibility compared to five other feed materials

YELA PROSECURE, a yeast-based product, fish meal, soybean meal, and potato protein concentrate were assessed for protein digestibility and kinetics of absorption based on the Boisen method with an adjustment to the gastric pH as previously explained (Figure 4 and Figure 5).

Protein sources are absorbed differently by animals right after the stomach phase:

– YELA PROSECURE’s well controlled hydrolysis process makes the protein highly available and quickly absorbed. With a protein digestibility of 77 percent right after the stomach, we can define YELA PROSECURE as having flash digestibility.

– Fish meal has a digestibility pattern of between 56 to 61 percent.

Soybean meal and whole-cell inactivated yeast have a lower protein digestibility at the beginning of the intestinal phase, with 49 percent and 46 percent respectively, while the potato protein concentrate is around 40 percent digestibility.

– Soybean meal protein digestibility increases up to 70 percent after 3 hours of the intestinal phase.

– The kinetics of protein digestibility for fish meal is between YELA PROSECURE and soybean meal, starting with 56 percent digestibility after the stomach, increasing to 81 percent after 3 hours in the intestine.

 – The potato protein concentrate appears to have a slower protein digestibility kinetic over time (52 percent after 3 hours of the intestinal phase). Being rich in crude protein (77 percent), the potato protein concentrate will contribute to a high amount of non-digested protein in the animal gut.

Compared to these feed materials, YELA PROSECURE shows interesting kinetics of protein digestibility with more than 90 percent of the proteins digested after 3 hours of the intestinal phase.

One direct consequence of that is a negligeable amount of non-digested protein that reaches the lower gut. YELA PROSECURE is, therefore, a valuable protein source that can help reduce the risk of gut dysbiosis associated with non-digested proteins. In addition, a flash and a fast protein digestibility is important in terms of protein functionality with direct and indirect benefits for the animals.

protein digestibility
Figure 4. Raw material protein digestibility after the stomach phase
Kinetics of protein digestibility
Figure 5. Kinetics of protein digestibility of various protein sources

Benefits of a flash and a fast protein digestibility for animals

Free amino acids are known to be beneficial for digestive health at three main levels:

– Free amino acids and especially the branched chain amino acids (BCAAs) — leucine, isoleucine and valine — are involved in the maintenance of the gut mucosa mass and integrity. When they are quickly absorbed, BCAAs play a positive role on the cellular multiplication by supporting the cell proliferation and the amino acids transporters. The direct consequence is a protein synthesis increase and a reduction of the protein degradation mechanism in the intestinal crypts (Duan et al., 2018)

– Glutamic acid, glutamine and glycine help support microbiota growth

– Arginine, glutamine, methionine, tryptophane and threonine help support the gut immune system activity as the gut contains around 70 percent of the total immune cells of the body.

Palatability in Petfood

Some free amino acids are also involved in the mechanism of taste and eating behaviour including feed intake, therefore playing a role in feed appetibility.

In a trial conducted in the Netherlands with 40 adult medium size dogs, the consumption of the diet including YELA PROSECURE was significantly higher by 26 percent (P=0.054) than the control diet.

YELA PROSECURE has shown the potential to enhance petfood appetibility, likely related to the high natural content in specific free amino acids.


To meet growing pet food market demand — and to face the current challenges around global health and digestive care of pets — petfood manufactures and nutritionists are looking for alternative functional protein sources. Hydrolysed yeasts are a promising and innovative functional protein source to consider, mainly due to the free amino acids and the small peptides obtained from the cracking (lysis) process of the protein.

When the hydrolysis process is controlled, yeast has a standardised profile of free amino acids, which plays a positive role in the maintenance of pet gut health, contributing to pet food protein balance and enhancing palatability. This is particularly of interest when applied to the diets of junior animals or in specialty pet food such as Hypoallergenic diets.

by Bruno Bertaud, Technical manager, yeast derivatives and swine solutions, Lallemand animal nutrition, France & Francesca Susca, Global pet product manager, Lallemand animal nutrition, Italy


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