Nutritional and functional properties of liquid salmon protein in pet food

E.F.S. has recently added S-Pro 37, a hydrolysed liquid salmon protein with a 37% protein content, to its portfolio. The use of S-Pro 37 in pet food has various nutritional and functional benefits.

S-Pro 37 is produced from by-products and trimmings coming from Norwegian Atlantic farmed salmon. A hydrolysis process diminishes the protein chains in fish by-products, such as organs and trimmings, and enhances the nutritional properties of salmon protein. In S-Pro this process occurs with the help of the naturally occurring (digestive) enzymes only.

Salmon hydrolysate can be used in pet food for both its nutritional and its functional properties.

First we will elaborate on the nutritional properties of S-Pro.

Nutritional properties


As a result of the hydrolysis process about 90% of the protein, consisting of small protein molecules and free amino acids, is water-soluble. This fraction can easily be absorbed by the intestinal wall, making S-Pro a highly digestible product. The measured in-vitro ileal digestibility ranges between 98-100%. Due to the short protein chains in S-Pro (80% < 1000 Da) an allergic reaction in the animal is less likely to be induced. Therefore S-Pro can also be used in hypoallergenic feeds.


The hydrolysed proteins and amino acids found in fish hydrolysates, such as S-Pro, enhance the palatability in dog and cat food. The effect can mainly be attributed to the high proportion of the amino acid glutamic acid. E.F.S. has recently completed an acceptance test with cats. The results show that the addition of S-Pro 37 to cat food has a very positive effect on both food consumption and food acceptance.

Immune system

The presence of a combination of nucleotides, the amino acid glutamic acid and omega-3 fatty acids in S-Pro supports the immune system due to its anti-inflammatory effect. S-Pro also reduces the oxidative stress as it contains bioactive proteins with, among others, an antioxidant activity.

Functional properties

In addition to the above-mentioned nutritional benefits, the use of S-Pro in pet food also has technical benefits.

Hardness & durability

Hardness and durability are important quality parameters in pet food. In order to establish the effect of S-Pro 37 on hardness and durability in pet food two diets were produced. In the experimental diet the fish meal (12%) was replaced by 10% of S-Pro 37. In the extruder 18 kg/hour water was added to the control diet and 12 kg/hour to the experimental diet. The Doris test was used to determine the level of durability. Below you will find an overview of the results.

Hardness Doris Doris Doris Doris Process water
(>8.0 mm) (8-5.6 mm) (5.6-2.6 mm) (<2.6 mm)
Unit N % % % % g/kg extrudate
Control diet 159.3 ± 6.8 90.0 ± 2.0 6.0 ± 1.6 1.5 ± 0.3 2.4 ± 0.2 265 ± 3.6
Diet w/ 10% S-Pro 212.2 ± 6.6 97.9 ± 0.3 0.6 ± 0.1 0.2 ± 0.1 1.3 ± 0.1 231 ± 6.1
P-waarde <0.001 0.002 0.004 0.002 <0.001 0.001

Table 1. Quality parameters of the control and experimental diet.

The table above shows that the addition of S-Pro 37 significantly improves the hardness and durability of pet food.

This results in a lower dust fraction in the experimental diet.


In addition to its binding effect S-Pro 37 also has a ‘plasticising effect’. This means that less water needs to be added during the extrusion process, leading to a reduction in energy required during the drying process. The table above shows that the quality parameters are improved by the addition of 10% liquid salmon hydrolysate.

As you can see the use of S-Pro 37 in pet food has many benefits.

Would you like to hear more? Please contact the E.F.S.-team!