## 5 Applications in Food Products and Nutraceuticals  
### Food Industry  
#### 5.1.1 Food Packaging  
_Citrus_ seed wastes cover a variety of bioactive components (e.g., polyphenols, limonoids, carotenoids, and tocopherols) with antioxidant and antimicrobial activities, as well as suitable compatibility with biopolymeric matrices that make them well-suited for formulating food packaging films [4; 65]. This allows for the waste collected after the extraction of high-value components from _Citrus_ fruits to be molded and turned into biodegradable packaging material, thus boosting the reuse of waste [85]. In this context, numerous investigations have been conducted on the development of packaging films from _Citrus_ by-products [86]. A recent study evidenced that the incorporation of lemon peel extract-loaded nanogels in active food packaging films based on casein and basil seed gum enhanced the film properties; mechanical, thermal stability, hydrophobicity, water vapor permeability, biocompatibility, and water solubility, among others. Moreover, satisfactory results were also achieved in the evaluation of the antioxidant and antimicrobial activities of the films [87].  
As in the previous example, lines of research in this field have focused mainly on the recovery of value-added products from _Citrus_ pulp and peel. Seeds are underexploited de spite the value and potential reserve of their phytochemical composition. Moreover, scarce information is available about their recycling and valorization [1]. Nevertheless, certain _Citrus_ fruits, such as mandarin, are especially rich in secondary compounds, contained mostly in the seeds, which are a source of antioxidants.  
[PERSON] et al. analyzed the impact of gelatine films enriched with 2% lemon and sweet orange seed extracts on the quality of sea bass fillets during 15 days of chilled storage (4 \(\pm\)\({}^{\circ}\)C). Findings revealed that the inclusion of the seeds of both _Citrus_ fruits made a significant sensory and microbiological contribution to their shelf life, as well as increasing the effectiveness of the packaging, resulting in a potent natural antioxidant additive, which could greatly enhance consumer acceptance [88].  
Currently, grapefruit _Citrus_ seed extracts (GSE) have been actively immobilized in different natural biopolymeric matrices to manufacture functional composite films and are commercially available [4,89]. [PERSON] et al., 2021, prepared multifunctional pectin/agar composite films reinforced with melanin nanoparticles (MNP) and GSE. The pectin/agar/MNP/GSE composite film showed significant enhancement of physical and functional properties, as well as excellent antioxidant and antibacterial activity [89]. [PERSON] et al., 2021, proved in the fabrication of a halochromic functional film based on carboxymethyl cellulose/agar by adding alizarin and GSE that the antioxidant and antimicrobial properties were strongly enhanced with the incorporation of GSE [90]. [PERSON] et al. elaborated multifunctional carboxymethylcellulose (CMC) composite films by adding chitin nanocrystals from shrimp shell powder by acid hydrolysis. The results revealed that the addition of GSE reduced the strength and stiffness of the films by 10.4% and 30.3%, whereas the flexibility increased by 17.7%. Further, the films with GSE also exhibit strong antibacterial activity and UV barrier properties, so they are highly applicable as active food packaging materials [91].  
As mentioned above, seed-based studies are not plentiful compared to those available on the _Citrus_ peel. Nonetheless, those conducted with seeds have encouraging results. This may be because occasionally the direct use of _Citrus_ seeds may lead to sensory issues in the product such as woody texture or astringent and bitter taste disorders resulting from metabolites such as limonin present in the seeds [88,92,93] (Figure 1).  
Figure 1: Examples of _Citrus_ seeds waste applications in food and non-food industry. Created with BioRender.com.