THERE IS BETTER THAN JUST A MEAL
The fish processing industry produces more than 60% by-products as waste, which includes skin, head, viscera, trimmings, liver, frames, bones, and roes. These by-product wastes contain good amount of protein rich material that are normally processed into fish meal, fish solubles or fish hydrolysate. The differences between these 3 ingredients are not always clear and deserve to be explained.
Fishmeal production process goes through grinding, pressing, cooking and drying (100-130 C°) of fish or fish waste into a solid. During the pressing, we get rid of oil and water. That water called stick water will be further concentrated at high temperature for long time to become fish soluble. Fish soluble is actually already a by-product of the fish meal process.
Fish protein hydrolysates (FPH) is coming from a very different manufacturing process. It consists in grinding, and cooking the fish materials by the method of protein hydrolyzation which happen at much lower temperature (50-60 C°).
Standard fishmeal processing technology, which are mostly used in the by-product industry especially in Asia, does not maximise the potential of this valuable raw material. Fish meal undergoes harsh processing conditions, whereby the native proteins are partly denatured, polyunsaturated fatty acids (PUFA’s) oxidised, thereby limiting their uptake and assimilation. Soluble fraction is often removed and concentrated into fish soluble, squid paste during long and high temperature process.
There are great abondance of fish meals and solubles in Asia, especially from Tuna or sardine species. The important drawback of using these products is the huge variability observed from one source or batch to another. There is great variability of compositions (dry matter, protein content) but also protein profile (peptides size) and freshness quality (biogenic amines content).
In addition, fish/squid solubles often show high viscosity (stickiness), high salt and high heavy metal content especially in Cadmium. Vietnam authorities have recently reduced their maximum limit at 2ppm of Cadmium to follow EU standards.
The standard process for producing fish meal is creating a major stress to the proteins through the increase of temperature between 100 to 120 degrees Celsius with a reduced moisture. These conditions create irreversible “maillard” complexes affecting negatively the bioavailability of these proteins. High temperature leads to oxidization of the fat affecting as well their nutritional value.
In order to improve the nutritional value of these by-products, it is important to reduce the temperature of processing and to use instead a hydrolysis. We will then a product called fish hydrolysate that is significantly different from fish meal and fish soluble. Prior to the hydrolysis process, we normally filter the materials to remove fish bones and keep only the highly digestible contents. As a result, the fish hydrolysate obtained will have lower ashes content and will be easier to incorporate in diets where level of ashes is an issue.
Finally, the fish hydrolysate will present a different profile of peptides than fish meal and fish soluble. The hydrolysis enables indeed to reduce the size of the peptides from polypeptides for fish meal to tri or di-peptides or even single amino-acids.
Importance of Peptides in animal nutrition
From a traditional point of view, it was believed that the protein can only be absorbed in the form of free amino acids.
In 1953, for the first time, it was found that the dipeptide can completely, without splitting into individual amino acids, pass through the wall of the intestinal epithelium. Further scientific researches have shown that the absorption of small peptides (di- and tripeptides) is accomplished by a specific mechanism (PEPT1). And, most importantly, this specific process of absorption is even more efficient than the absorption of the corresponding amino acids.
Thus, 2 or 3 amino acids are transported to the cell by means of PepT1 with the same energy inputs as one free amino acid, energy required for peptide uptake is 2-3 times lesser than for amino acids.
The number of amino acid residues distinguishes di-, tri-, tetra-peptides, etc., as well as polypeptides. These peptides are constantly synthesized in all living organisms to regulate physiological processes. They are defined as ‘bio-active’ peptides with antioxidant, anti-hypertensive, immunomodulatory and antimicrobial activities. Their biological importance is still currently undervalued but more and more researchers are doing on these mechanisms to underline their mode of action.
Glutathione, due to intensive scientific research, is the most famous bioactive peptide. It is considered almost the main antioxidant in the body. The only problem is that the animal's organism produces glutathione in small amounts, which are quickly consumed to protect against oxidative stress. Small peptides, performing a number of important biological functions in the body, are not just an alternative to highly digestible protein sources, but also allows achieving a number of additional effects on the productivity, safety, digestibility of other nutrients.
Hydrolysate is often seen as a possible alternative to fish meal but it is actually a complement. Fish hydrolysate is often mistaken with fish soluble although they are both resulting from very different manufacturing process given then different characteristics. The table below underlines the differences between the 3 by-products coming from fish.
Each product has its own benefits. The level of crude protein alone is not sufficient to differentiate them. Nutritionist needs to look deeper into the product specifications to select the source he requires depending on his constraints on bio-active peptides profile but as well salt content, ashes, Total Volatile Nitrogen.