## 1 Introduction  
Lipid oxidation is considered to be the main factor limiting the shelf-life and quality of almonds due to their high content in polyunsaturated fatty acids, mainly linoleic acid [1]. The primary and secondary products such as hydroperoxides, aldehydes and ketones, among others formed during the oxidation process are responsible for the rancid flavour present in the oxidized almonds [2]. The aforementioned degradation is also favoured by cooking processes such as frying in which high temperatures impact directly in the quality of almonds. In addition, the initial linoleic acid content in almonds subjected to frying processes has been reported to be higher than in raw ones, due to oil frying medium migration to the sample, causing a more severe food degradation [3]. To overcome this problem, special attention has been paid in recent years to the use of agri-food by-products as new sources of natural antioxidant agents [4]. This new strategy is aligned with the circular economy action plan to reduce food waste implemented by the European Union since around 1/3 of the total food produced worldwide is estimated to be lost or wasted [5]. Natural antioxidants from food wastes have been incorporated in food packaging, avoiding the direct addition of preservatives into the food and reducing the final price of the packaging materials [6]. The use of agri-food by-products as natural additives for the development of active packaging systems has several advantages; such as availability, recyclability, low-cost, environmentally friendly properties, no toxicity and biodegradability [7]. Several reviews [6; 8; 9] and research works can be found in the recent literature related to the use of natural antioxidants extracted from food waste or by-products such as orange [10; 11], potato [12], olive leaf [13] and mango peels [14] for the development of antioxidant food packaging materials. Among the compounds naturally found in these by-products, antioxidants such as \(\alpha\)-tocopherol [15], thymol, carvacrol [16], hydroxytyrosol [17], curcumin [18] and hydrolys cottonseed proteins [19] have also been incorporated into packaging materials to reduce the problems associated with the lipid oxidation of fatty foods. In addition, oxygen scavengers have been considered as active systems to prevent food oxidation processes. In particular, iron-based [20], organic- [21] and inorganic [22]-based, polymer-based [23] and enzyme-based [24] scavenging systems, among others, have been widely used by the food industry with a residual oxygen reduction to less than 0.1% into the food packaging [25]. However, unlike antioxidants coming from food wastes, these substances are not always in line with the new circular economy concept. In this context, almond skin (AS) comprises the 4.0-8.0 wt.% of the total shelled almond fresh weight [26] which contains up to 50-75% of the total phenols present in the nut, being rich in hydroxybenzoic acids and aldehydes, phenolic acids, flavan-3-ols, flavonoid glycosides, flavonoid aglycones, flavanones, flavonone glycosides, flavonone aglycones, isoflavenes and lignans [27]. In addition, in a previous work, it was confirmed that AS is a potential natural antioxidant that can reduce the lipid oxidation of food [28]. Then, the incorporation of AS extracts with antioxidant compounds into polymer matrices could be an interesting approach to revalorise AS by-products and to avoid lipid oxidation of fatty foods, such as fried almonds. Poly(\(\varepsilon\)-caprolactone) (PCL) is a chemically synthesized polymer which is fully biodegradable and can be processed using conventional plastics machinery [29]. Moreover, it has good properties and is also compatible with other materials [30]. Regarding the use of PCL for active packaging applications, [PERSON] et al. [31] developed biodegradable antimicrobial packaging films based on PCL, starch and pomeranate rind hybrids showing a strong antimicrobial efficiency at higher concentrations of the active compound.