## 1 Introduction  
Antioxidants and antiradicals compounds can preserve the quality and can contribute to the stability of foods, drugs and chemical products towards oxidation reactions, which can occur during exposure to air (oxygen), heat or light, and during their production, storage and transportation. As such, antioxidant and antiradical molecules continue to be demanded in many fields [1]. In body cells, the oxidative stress has been related to the appearance of diseases such as diabetes, hypertensions, obesity, cardiovascular issues, dyslipidemia, etc. [1, 2], hence, the incorporation of antioxidant compounds in food can contribute to increase its healthy value apart to preserve the nutritional one. Until now, synthetic antioxidants have been more utilized than the natural analogues because they often show higher stability and performance, wide availability and lower costs. However, products of natural origin are increasingly demanded either by consumers or by industry, which are concerned about the presence of synthetic compounds in food [3] and also because some synthetic antioxidants have been associated to health issues such as allergies, gastrointestinal problems, premature senescence, adverse effects on liver and increased risk of cancer [4]. Collagen peptides from animal and marine tissues, such as skin, scales, cartilages, bone, etc., have received attention since they showed a significant potential in multiplesfields such as food, nutrition, health, cosmetics and biomaterials [5; 6; 7; 8; 9; 10; 11]. A significant range of bioactivities has been observed, such as antihypertensive, antioxidant, antidiabetic, immunomododulatory, anti-inflammatory, opioid agonist, wound healing, mineral binding, drug carrier, contribution to the synthesis of native collagen, etc. [5; 6; 7; 8; 9; 10; 11]. Most used enzymes for the hydrolysis of collagen to bioactive peptides (<3000 Da molecular weight) have been the digestive enzymes pepsin and trypsin, the specific collagen enzyme collagenase, and alcalase since and it has showed to be effective in the release of bioactive peptides from different protein sources and it is easily available at a commercial scale [7; 8; 9; 11; 12]. However, few studies have focused on other enzymes and on the effect on bioactivity of processing parameters such as the enzyme: collagen ratio, sterilisation, heating, and also possible synergies between peptides obtained by several enzymes. Moreover, the antioxidant activity has mainly been addressed by the use of synthetic radicals and very few studies are available on the antioxidant effect on food matrix [13; 14]. Besides, among all animal tissues, the mineralised ones, such as bone (and fish scales), have been considered at a lower extent than the non-mineralised tissues (such as skin, tendons and cartilages) and in particular if of bovine origin [7; 14]. The animal and fish bone are composed by 60% \(w/w\) of mineral matter, mainly calcium and phosphorous and in a lower amount magnesium, by 30% \(w/w\) of collagen, mainly of type I, and by 10% of water. In particular, the bone stores 99% of calcium, 85% of phosphorous and almost 60% of all the magnesium of the animal and human body [6]. Animal bone is one of the most abundant by-products, in terms of volume and weight, of meat and milk production. The European regulation allows the valorisation of food-grade bones in several fields, including food, medicine and agriculture (article 33 of the EC 1069/2009, and EC 2019/1009). Nonetheless, for food applications, bones continue to be mainly converted into gelatine albeit at a low degree (ca. 20%) due to presence of the mineral phase; although gelatine, from several animal tissues, has showed a significant antioxidant power, it is not used for this purpose since it significantly affects the texture of the products where it is incorporated [5] besides, it has a moderate commercial value.