Analysis of Physical Pellet Quality of Diets Containing Different SPC Sources

The continuous growth of aquaculture production based on fishmeal (FM) is fundamentally unsustainable, since most wild fisheries stocks are already beyond their catch limits (FAO, 2018). Plant-based ingredients, such as soy protein concentrate (SPC), are sustainable products widely used by the aquaculture industry as an important source of protein (ABDUL KADER et al., 2012). Fermented SPC is an innovative product, based on aerobic SPC fermentation using the bacteria Bacillus spp. to improve highly active of proteolytic and carbohydrases, responsible for decomposing complex compounds, minimizing anti-nutritional and soluble carbohydrate factors, improving higher nutritional quality. The SPC fermentation process increases higher digestibility of proteins and short chain peptides, improving beneficial effects on the growth performance and immune response in animals.

The aim of the present study was to evaluate the effects of two sources of SPC on the physical quality of pellets in the Atlantic salmon diet (Salmo salar).

Two practical-type commercial extruded diets were designed to satisfy the nutritional requirements of Atlantic Salmon (Salmo salar) (Nofima Feed Technology Center - Bergen, Norway) for analysis of pellet quality. A basal diet (reference diet, Dbasal) was replaced about 30% by the respective test ingredients: conventional soy protein concentrate (SPCconv) and fermented soy protein concentrate (SPCferm).

Ingredient and chemical composition of the diets are reported in Table 1. Pellet breaking force (hardness) was measured in the pellets by means of a texture analyzer (TA-HDi®, Stable Micro Systems Ltd, Surrey, United Kingdom). The major break of the pellet (the peak force) was measured and presented in Newton (N).

Bulk density was measured by loosely pouring the feed into a 1,000 ml measuring cylinder. The water stability index was measured according to BAEVERFJORD et al. (2006), by placing the feed (20 g) in a beaker with water under constant agitation (170 shaking/minute) for 120 minutes at 23°C, and the remaining dry matter was recorded (%). The ration (20g) was placed in plastic box with absorbent paper and incubated at 40°C for 24 h, to evaluate the percentage of pellet Fat leakage (%). A pre-sieved diet sample (350g) was placed in the AkvaMarina DORIS Feed Tester (Aquasmart ASA, Bryne, Norway), and then stirred and separated in sieves of different aperture sizes, and the fraction (%) of each particle size was measured in each category (sieve).

Practical diets using SPC or SPCferm as fishmeal replacement, do not affect the physical pellet quality. No significant differences were found between the treatments analyzed. The pellets of the SPCferm feed had the hardest pellets (69.3 N), the lowest water stability index (75.0%) and lowest fat leakage (0.77%), however, it had the highest density value apparent when compared to the other diets. All diets had low breakage in the DORIS test, with slightly more production of small particles from the SPCconv feed than the SPCferm and Dbasal (Table 2). Our results indicate that the pellet quality of all ingredient tests was considered within the normal range for all measured parameters.

According to ABDUL KADER et al. (2012), FM can be partial replaced by fermented soybean meal without any negative effects on performance, feed utilization, body composition, nutrient retention and health/welfare of fish. Therefore, SPC fermentation may be a sustainable alternative for the partial use of FM in animal feeds (ABDUL KADER et al., 2012).

In conclusion, this study shows that the different types of SPC analyzed can be used as protein ingredient in the extruded feeds without affecting the integrity and quality in the salmonids pellets diets and possibly other fish species. In addition, SPCferm is a promising new ingredient, which may contribute to the possibility of application in practical diets.