Ficus carica Fruits, By-Products and Based Products as Potential Sources of Bioactive Compounds: A Review

: In this review, studies ( n = 41) were searched in which the compounds and contents were determined for whole ﬁg fruit, peel, leaves and pulp, the types of ﬁg-based products were identiﬁed and their total phenols and antioxidant capacity as well as the potential uses of different extracts of ﬁg parts were analyzed. There is a need to reduce the fruit’s environmental impacts (zero waste), and bioactive compounds from ﬁg fruits present a high added value as functional ingredients. Focusing on ﬁg by-products (peel, seeds, no-optimal fruits and leaves), individual compounds and/or extracts can increase the functional, nutritional and techno-functional properties of food products such as additives. A high number of phenolic compounds was found in whole fruit ( n = 19), peel ( n = 26), pulp ( n = 24) and leaves ( n = 42). Quercetin-3-O-rutioside was reported as the major individual phenolic compound in whole ﬁgs, while cyanidin-3-rutinoside, epicatechin and caftaric acid were the highest compounds in peel, pulp and leaves, respectively. A potential strategy could be the development of novel additives and/or ingredients for food industry from ﬁg by-products. Therefore, the use and valorization of the waste material produced during ﬁg processing should be further investigated.


Introduction
. The fleshy and sweet part of the fig corresponds to the flower receptacles that, after fertilization, become swollen and fleshy [3]. It is worth mentioning that it is one of the oldest species domesticated by humanity [4]. In the Middle East and the Mediterranean region, the fig has been included in the diet since ancient times and is considered a symbol of health [5]. It has been suggested that the cultivation of the fig originated in the East Mediterranean region, which was later expanded into the West Mediterranean area [6].
According to the Food and Agriculture Organization (FAO) of the United Nations, the world production of fig fruit is stable. Worldwide, the area under cultivation of fig trees exceeds 289,818 ha, with an estimated production of 1,315,588 t [7]. Turkey is the biggest world producer, with 310,000 t in 2019, followed by Egypt, Morocco, Iran, Algeria and Spain. Therefore, of utmost importance for fig production is still the Mediterranean basin and the Near East [7]. Spain is the main source of figs in Europe (51,600 t), followed by Greece (19,730 t) and Italy (11,830 t) [7]. In Spain, the main producer is Extremadura (37,382 t), followed by Cataluña (5834 t) and the Comunidad Valenciana (2932 t) [8]. Because the fig tree is highly resistant to salinity and active calcium, it is quite suitable for marginal areas, such as southeastern Spain [9]. Taking production, yield and size of the cultivars cultivated The main focus has been given to studies published in journals included in the Journal Citation Reports. Only research papers that included the experimental design and data treatment were selected. The structure of the review allows a dissection of (i) which com-   Table 1 shows the individual phenolic compounds found in different part of fig parts: whole fruit (n = 19), peel (n = 21), pulp (n = 22) and leaves (n = 40). Identified compounds belong to different chemical families, such as phenolic acids (caffeic acid, chlorogenic acid, ferulic acid, coumaric acid, syringic acid, quinol and gallic acid) and flavonoids (catechin, kaempferol, quercitin and myricetin). The chemical structure of the main compounds found in fig fruits and derivatives are shown in recent studies related to chemical composition [14,16]. It is important to highlight that the results in the literature are not always reported in a unified manner, which makes it difficult to compare research findings. Data are expressed as dried matter/weight (dw) and fresh matter/weight (fw). Depending on the part of the fruit, maturity index, variety and region, the type of compounds varies. Quercetin-3-O-rutioside was reported as the major individual phenolic compound in whole figs (Table 1), followed by polymeric procyanidins, quercentin-3-glucoside, chlorogenic acid and cyanidin-3-0-rutinoside. As for the peel's bioactive compounds, cyanidin-3-rutinoside was the most abundant, followed by cyanidin-3,5-diglucoside, cyanidin-3-Odiglucoside, epitecatechin, catechin and quercetin-rutinoside. Epicatechin and cyanidin-3-rutinoside were the main compounds found in fig pulp, while caftaric acid, in the form of kaempferol 3-O-glucoside, was the main compound reported in fig leaves. On the other hand, Badgujar et al. [15] and Li et al. [14] reviewed the phytochemical composition of Ficus carica fruits and their derivatives. This study only indicated the profile of the bioactive compounds (isolation of phytosterols, anthocyanins, phenolic components and a few other classes of secondary metabolites), not the quantification. Therefore, these manuscripts were not added to Table 1. Most of these phytochemicals were found in latex,  Table 1 shows the individual phenolic compounds found in different part of fig parts: whole fruit (n = 19), peel (n = 21), pulp (n = 22) and leaves (n = 40). Identified compounds belong to different chemical families, such as phenolic acids (caffeic acid, chlorogenic acid, ferulic acid, coumaric acid, syringic acid, quinol and gallic acid) and flavonoids (catechin, kaempferol, quercitin and myricetin). The chemical structure of the main compounds found in fig fruits and derivatives are shown in recent studies related to chemical composition [14,16]. It is important to highlight that the results in the literature are not always reported in a unified manner, which makes it difficult to compare research findings. Data are expressed as dried matter/weight (dw) and fresh matter/weight (fw). Depending on the part of the fruit, maturity index, variety and region, the type of compounds varies. Quercetin-3-O-rutioside was reported as the major individual phenolic compound in whole figs (Table 1), followed by polymeric procyanidins, quercentin-3-glucoside, chlorogenic acid and cyanidin-3-0-rutinoside. As for the peel's bioactive compounds, cyanidin-3-rutinoside was the most abundant, followed by cyanidin-3,5-diglucoside, cyanidin-3-O-diglucoside, epitecatechin, catechin and quercetin-rutinoside. Epicatechin and cyanidin-3-rutinoside were the main compounds found in fig pulp, while caftaric acid, in the form of kaempferol 3-O-glucoside, was the main compound reported in fig leaves. On the other hand, Badgujar et al. [15] and Li et al. [14] reviewed the phytochemical composition of Ficus carica fruits and their derivatives. This study only indicated the profile of the bioactive compounds (isolation of phytosterols, anthocyanins, phenolic components and a few other classes of secondary metabolites), not the quantification. Therefore, these manuscripts were not added to Table 1. Most of these phytochemicals were found in latex, followed by leaves, fruit and root. Additionally, Li et al. [14] collected data of the phytochemical composition related to health properties, indicating that conventional and modern isolation and characterization techniques were used for the identification of about 126 chemical constituents, which were divided into eight categories: hydroxybenzoic acids, hydroxycinnamic acids, flavonoids, coumarins, furanocoumarins, volatile constituents, triterpenoids and miscellaneous [14]. Chlorogenic acid 0.0880 1.2450

Bioactive Content of Fig-Based Products and Their Antioxidant Activity
In general, fig fruits have mainly been consumed fresh and dried, but they have also traditionally been preserved and processed into jams [21]. Nowadays, consumer trends have changed and there is an increase in the range of other products based on figs [4]. Table 2 shows important information (type, cultivar and treatment) and bioactive compounds (total phenols, total flavonoids and total anthocyanins) as well as the antioxidant capacity of products based on fig fruits and their by-products. Additionally, the following lines include more information on the main reported fig-based products.   The bioactive compound content and antioxidant activity strongly depend on the cultivar type in both fresh and processed fruits [48]. Khadhraou et al. [36] studied the main phenolic compounds, as well as the phenolic profiles and antioxidant activity, in nine sun-dried fig cultivars with different skin colors, originating from South-Eastern and Middle Eastern Tunisia [36]. For all evaluated parameters, a considerable variability with high significant differences was observed among the cultivars studied and the principal component analysis showed three groups of cultivars based on their similarity level. Dark cultivars contained the highest levels of flavonoids and phenolics and exhibited a high antioxidant capacity, while light-skinned cultivars contained the lowest levels. A recent study suggest that the preparation of fig jam preserves some bioactive compounds, especially carotenoids and phenolic compounds during storage [49]. On the other hand, Rababah et al. [33] studied the total phenolics and anthocyanins of fig jam after five months of storage and concluded that jam processing decreased the total phenolics (by 68.6%) and anthocyanins (by 60.2%). The minimum value to total phenolics and anthocyanins was 130.97 mg GAE kg −1 and 11.20 mg kg −1 of cyanidin-3-glucoside, respectively ( Table 2).
As for dried figs, Slatnar et al. [34] showed results of total phenolics after a drying treatment. The drying process affected the degradation of phenolic compounds, the content of phenolic compounds being higher in fresh figs, followed by oven-dried figs and sundried figs. For example, Vallejo et al. [5] showed that around 15% of the total phenolics were lost in the drying processes in figs "Cuello Dama". Not only is the quality important, but safety is essential to be maintained. Mycotoxins have been found in quantities above the recommended limit in commercial samples of dry figs [50]. Therefore, a controlled drying process helps to reach a safety level. Alternatives to traditional sun drying is necessary for improving the protection of public health [51].
Nowadays, there is an increase on developing nutrient-rich value-added products by partially replacing its ingredients by others, such as underutilized fruits and added value by-products (pectins, colorants, emulsifier and antioxidants) from leaves and peels. As for fig by-products, Table 2 shows the reported inclusion alternatives; for example, fig powder as a colorant in the production of buns and muffins [52]. The authors also reported how the addition of fig seed powder to the formulation of a cookie improved its fiber content and also increased the total phenolic content and antioxidant activity [39]. Additionally, fig by-products' sweet extracts have been used for making traditional desserts without adding sugar, for example "Shir Anjir", an Iranian dessert [40]. Minimally processed fruits, such as smoothies, retain a large number of phytochemicals and they could in fact be considered a valid alternative to eating fresh fruits. Moreover, De Pilli et al. [53] found that the polyphenol content and antioxidant activity are strongly correlated in both fresh fruits and smoothies. In the same way, fig and pomegranate smoothies also showed a correlation between anthocyanins content and antioxidant capacity; smoothies with 60% of wonderful pomegranate juice showed a higher anthocyanin and antioxidant capacity ( Table 2)  Recent studies suggested that by-products/co-products obtained from peel and fig pulp showed potential properties to be used as ingredient in food products/additives (Tables 1-3). Table 3 shows the reported research about different raw fig by-product materials (different plant parts, peel, leaves and whole figs) and the extraction method used to obtain the desired ingredients/additives and their uses. For instance, peel extract could be used as a colorant due to its potential source of anthocyanin. Consequently, fig peel extract has great potential to be used as a natural food dye, where in addition to its ability to add natural purple colors, it also presents interesting antioxidant and antimicrobial activities. Table 3 also shows the extraction and uses of pectin from fig peel and pulp [55].  Clotting ability in goat's fresh cheese production [62] Powdered Surfactant (PEG8000)-based microwave-assisted extraction method Source of bioactive compounds [63] Powdered 0.1 g of sample and 10 mL aqueous 50% acetone, centrifuged using Eppendorf centrifuge and filtered with a 0.22 µm PTFE syringe filter.
Source of bioactive compounds [54] Whole figs Syrup 100 g of low-quality dried fig fruits were soaked in 500 mL distilled water, mixed and then centrifuged to remove solids.
Pullulan gum production from low-quality fig syrup using Aureobasidium pullulans [64] Powdered Samples (1 g) were mixed with ethanol (50 mL) and left macerating for 24 h; then, solutions were centrifuged (6800× g/20 min) and extraction was repeated three times.
Source of bioactive compounds [65] Dry fig and stevia extract Microwave-assisted extraction of stevia Sugar replacement in ice cream [66] Regarding leaf extracts, El Dessouky Abdel-Aziz et al. [31] suggested that they can be used to extend the shelf life of pasteurized milk from 5 to 16 days without altering organoleptic properties. Moreover, other authors have reported that leaf extracts or fig powder can be a potential product for manufacturing functional foods [46] (Table 3). Fermentation is also known to promote the concentration of bioactive compounds of fruits and vegetables [55].

Conclusions
Although there has been an increase in research focused on the bioactive compounds of fig fruits and their by-products, more scientific evidence (combined with a unified way of publishing data on bioactive compound content) is needed to establish the potential health properties. Future investigations should be focused on in vitro and in vivo studies to reveal their beneficial properties. There is scientific research about the potential use of underutilized fig fruit and figs by-products and its bioactive compounds as nutritional, functional and techno-functional properties. The use and valorization of the waste material (leaves, peel and pulp) produced during fig processing should be further investigated, since this could offer financial benefits to farmers and solve environmental issues by ensuring the sustainable management of these materials and, furthermore, bringing benefits to consumers' health and well-being. In addition, an economic estimation of the bioactive compounds of fig by-products could be essential to gain more knowledge and obtain added value.