**2.1 Animal-based products**

Meat is a key supply of amino acids, (e.g. cysteine, methionine, glycine, etc.) [9], and vitamins such as linolic acid, taurine, and creatine. By exerting some modifications on meat products, such as reducing the content of sodium chloride and the addition of nutrients like fish oil, natural extracts, and fiber from nuts, meat products can be a precious source of functional food. Moreover, chondroitin sulfate and glucosamine are ingredients that can be extracted from bovine skin and employed in the process of making functional beverages that promote joint health.

Egg also is one of the products that is being used largely in the market and its modification can diminish the risk of ischemic heart diseases. One of the strategies used to produce functional egg is enriching them by omerga-3. For accomplishing this, there are two approaches, in the first one, linseed or flaxseed that contains large amounts of linolic acid would be added to the hen's diet, as a result of which the linolic acid would be incorporated in the egg. However, the health-promoting effects of n-3 are mainly linked to the DHA (docosahexaenoic acid) and the conversion of linolic acid to DHA does not occur sufficiently in the human body. In this case, the second way of enhancing of n-3 level plays a significant role. It carries out via fortifying hen's food with fish oil. Nonetheless, this strategy can lead to an undesirable fishy taste in the egg yolk, which is considered an undesirable characterization [10].
