Protein quality has relied on methods such as PDCAAS. However, the Food and Agriculture Organization has proposed a new method called DIAAS to better assess protein quality in human foods using the pig as a model. This shift is crucial, not only for optimizing diets, but also for understanding the nutritional value of protein-rich foods. According to the DIAAS method, protein claims can only be made for foods with a score above 75. In general, animal-based foods are considered high quality proteins with score above 75 or 100, being, in most cases, complete proteins that can complement lower quality proteins such as plant-based proteins. Meats, eggs, and fish are examples of high quality proteins, however, salmon proteins are also available, and use of by-products in human consumption has been increasing due to their nutritional value and versatility. Novel sources of salmon proteins such as salmon hydrolysate that may be used in human nutrition have been developed. Salmon hydrolysate proteins contain more than 68% crude protein (CP) and are highly digestible food ingredients, but limited information demonstrating the protein quality of these products is available. Therefore, the objectives of this study were to determine the standardized ileal digestibility (SID) of amino acids (AA) and the digestible indispensable amino acid score (DIAAS) for salmon proteins when fed to growing pigs.

Experimental Procedure

Three different salmon hydrolysate proteins (i.e., Salmigo Active^®, Salmigo Protect SD^®, and SalMe Peptides^®) were used. Each of these proteins was included in one diet as the only source of CP and AA in the diet. A nitrogen-free diet was also used to measure basal endogenous losses of CP and AA. Therefore, a total of four diets were formulated. All diets included vitamins and minerals to meet or exceed current nutrient requirement estimates for swine. In addition, titanium dioxide was used as an indigestible marker. Twelve growing gilts with a T-cannula in the distal ileum were randomly allotted to a quadruplicate 3 × 2 Youden square design with three salmon protein diets and two 7-day periods in each square. There were therefore, eight replicate pigs per treatment. All pigs were fed a nitrogen-free diet in the third period and each pig was its own control. Pig weights were recorded at the end of each experimental period to calculate feed allowance for the following period. Each experimental period lasted 7 days with the initial 5 days being considered an adaptation period to the diet and the last two days being used for digesta collection. Chemical analysis was performed in all ingredients, diets, and digesta samples. Values for digestibility of CP and each AA were calculated. Protein quality was measured using the DIAAS method for different ages including children between 6 months and 3 years old and individuals older than 3 years. If the DIAAS cut-off value was between 75 and 99, it was termed "good" protein quality. Protein quality was considered "excellent" if it had a value of 100 or greater.

Results

The SID of CP, His, Met, and Trp were greater (P < 0.05) in Salmigo Active and Salmigo Protect SD compared with SalMe Peptides (Table 5). The SID of Thr, Cys, and Ser were greater (P < 0.05) in Salmigo Active than in Salmigo Protect SD and SalMe Peptides, with the expection that for SID of Asp, no difference was observed between Salmigo Active and Salmigo Protect SD. In addition, no statistical differences were observed for the SID of the remaining AA among all salmon proteins (Table 1). For children and individuals older than 3 years, Salmigo Active had greater (P < 0.05) DIAAS compared with Salmigo Protect SD and SalMe Peptides (Table 2). The SalMe Peptides had greater (P < 0.05) DIAAS than Salmigo Protect SD. For children, Leu was the first limiting AA for Salmigo Active and Trp was the first limiting AA for Salmigo Protect SD and SalMe Peptides. For individuals older than 3 years, there was no limiting AA (DIAAS ≥ 100) for Salmigo Active, but for Salmigo Protect SD and SalMe Peptides, Leu was the first limiting AA. No claims regarding protein quality (DIAAS < 75) can be made for Salmigo Protect SD and SalMe Peptides for children. However, SalMe Peptides can be considered a “good” protein quality ingredient for individuals older than 3 years. In addition, Salmigo Active can be considered a “good” protein quality ingredient for children and an “excellent” protein quality source for individuals older than 3 years.

Key points

• All tested proteins have high digestibility of protein and AA.
• Salmigo Active have “excellent” protein quality for individuals older than 3 years and can be used to complement lower quality proteins.
• No claims regarding protein quality can be made for Salmigo Protect SD regardless of age.
• SalMe Peptides have “good” protein quality for individuals older than 3 years.
• Different procedures used to make salmon protein hydrolysate can affect DIAAS.
• Salmon hydrolysate can be incorporated into powders, capsules, and functional foods to provide targeted nutrition and potential health benefits.

Table 1. Standardized ileal digestibility (SID) of crude protein and amino acids in salmon proteins¹

^a-cMean values within a row with unlike superscript letters are significantly different (P < 0.05).

¹Data are means of 8 observations per treatment, except for the Salmigo Protect SD that had 6 observations per treatment due to statistical outliers.

²The SID values were calculated by correcting values for basal ileal endogenous losses for each pig as its own control.

Table 2. Digestible indispensable amino acid scores (DIAAS) in salmon proteins¹

^a-cMean values within a row with unlike superscript letters are significantly different (P < 0.05).

¹First limiting AA in parenthesis. AAA, aromatic amino acids (Phe + Tyr); SAA, sulfur amino acids (Met + Cys).

²The DIAA reference ratios and DIAAS values were calculated using the recommended AA scoring pattern for a child (from 6 months to 3 years). The DIAA reference patterns are expressed as mg AA/g protein: His, 20; Ile, 32; Leu, 66; Lys, 57; SAA, 27; AAA, 52; Thr, 31; Trp, 8.5; Val, 43.

³The DIAA reference ratios and DIAAS values were calculated using the recommended AA scoring pattern for an older child, adolescent, and adult. The DIAA reference patterns are expressed as mg AA/g protein: His, 16; Ile, 30; Leu, 61; Lys, 48; SAA, 23; AAA, 41; Thr, 25; Trp, 6.6; Val, 40.