Potential Functional Food Products and Molecular Mechanisms of Portulaca Oleracea L. on Anticancer Activity: A Review

Portulaca oleracea Linn. (P. oleracea L.) has recently gained attention as a functional food due to the chemical composition of this plant regarding bioactive compounds. The special attention to the use of P. oleracea as an ingredient in functional food products is also due to the promotion of sustainable food. It is an unconventional food plant, and its consumption may contribute to preserving biodiversity due to its cultivation in a polyculture system. Food sovereignty may be achieved, among other strategies, with the consumption of unconventional food plants that are more resistant in nature and easily cultivated in small places. P. oleracea grows spontaneously and may be found in streets and sidewalks, or it may be cultivated with seeds and cuttings propagation. The culinary versatility of P. oleracea opens up opportunities to explore the development of sustainable, functional food products. This mini-review shows that functional food products developed from P. oleracea are already available at the research level, but it is expected that more scientific literature focusing on the development of P. oleracea functional products with proven anticancer activities may be released in the near future. Polysaccharides, some phenolic compounds, alkaloids, and cerebrosides are associated with the inhibition and prevention of carcinogenesis through in vitro and in vivo investigations. The anticancer activities of P. oleracea, its bioactive compounds, and the involved molecular mechanisms have been reported in the literature. The importance of further elucidating the cancer inhibition mechanisms is in the interest of forthcoming applications in the development of food products with anticancer properties for implementation in the human diet.


Introduction
The common purslane (P. oleracea L) is a herbaceous succulent annual plant from the Portulacaceae family, native to the Middle East and India [1,2]. It may be found on roadsides, gardens, and cultivated areas in the tropical and subtropical regions [3,4]. There are various cultivars of P. oleracea distributed worldwide, mainly with morphological differences, with the common purslane having green-red stems, obovate leaves, yellow flowers, and single-layered petals, while the ornamental purslane produces flowers of different colors [1]. The stems and leaves have a slightly acid and salty taste and are usually consumed in salads, soups, and stews [5,6]. It is an edible plant in regions of European, Mediterranean, African, and Asia countries and Australia [6]. In Brazil, P. oleracea is known as an "unconventional food plant", a term referring to plants that are not part of the usual consumption of most of the population in a particular region, country, or even the planet because basic food is very homogeneous, with the use of few food species [7].
Thus, this mini-review aimed to assemble the anticancer effects of bioactive compounds of P. oleracea, demonstrating the molecular mechanisms and the potential for the development of functional food products with anticancer properties.
High concentrations of oxalic acid have also been detected in P. oleracea. The intake of oxalic acid provided by the diet with P. oleracea may form complexes with minerals such as calcium and iron (insoluble salts) or sodium, magnesium, and potassium (soluble salts), reducing their bioavailability and possibly leading to the development of kidney stones through the formation of calcium oxalate crystals [35]. Thus, consumption of P. oleracea should be moderated by individuals with a propensity to develop kidney stones. Amounts of 23:45 ± 0:45 g,5:58 ± 0:18 g, and 9:09 ± 0:12 g of total oxalates per kilogram of fresh weight oxalates were obtained in fresh leaves, stems, and buds, respectively, with 75.0% being soluble oxalates in the stems and buds, and only 27.5% in the leaves [36]. The authors reported a 66.7% reduction (p < 0:001) of soluble oxalates after cooking the leaves for a short time, discarding the water, and pickling them with white vinegar [36]. Some other bioactive compounds from secondary metabolism of P. oleracea such as flavonoids, alkaloids, terpenoids and their pharmacological activity can be seen in Table 1.
Other bioactive compounds with pharmacological importance in P. oleracea are alkaloids and terpenes. Anticancer, anti-inflamatory and antioxidant effects were described for alkaloids found in this plant while hepatoprotective, antibacterial, antifungal and anti-hypoxia effects were described for terpenes of P. oleracea [44][45][46][47][48].
The dry weights of the samples (leaves, flowers, and stems) from two different locations were investigated for potential antioxidant activity by Silva and Carvalho [41], who found that stems had a higher total phenolic content and total antioxidant activity than the flowers and leaves. The oil from seeds, leaves, and stems of P. oleracea were analyzed and found that the peroxide value was significantly higher for seed oil and the lowest for stem oil [51]. Furthermore, the highest ascorbic acid content was found for P. oleracea seed oil (41.67%), followed by leaf oil (32.29%), and the highest DPPH was obtained for leaf oil (12.55%), followed by seed oil (2.05%). Values for lettuce (IC50 = 17:07 mg/ml), artichoke (IC50 = 18:14 mg/ml), turmeric (IC50 = 21:14 mg/ml), spinach (IC50 = 22:87 mg/ml), and escarole (IC50 = 32:2 mg/ml) were reported by Tiveron et al. [52], showing that P. oleracea presents the lowest IC50 necessary to reduce 50% of DPPH free radicals.

Functional Food Products and P. Oleracea
The P. oleracea plant may be used as an ingredient in functional food products due to its nutritional value and bioactive compounds that will be incorporated into the formulations.
The use of the P. oleracea plant as food may not only enhance the nutrients and bioactive composition of functional products but also influence their sensory and technological characteristics. Although it is well-known that sensory acceptance by consumers is essential for a product's commercial success on the market, few studies in the literature have reported the application of P. oleracea in products and its performance or the sensory profile of such products.
Regarding the technological aspect, the incorporation of the durum wheat flour with 5% of P. oleracea to bread resulted in the improvement of the rheological characteristics, an increase in antioxidant properties, and a decrease in the Omega-6-to-Omega-3 ratio, which is beneficial for human health, in addition to improving the sensorial quality [53].
The durum wheat spaghetti fortified with 10% of P. oleracea, a potential functional food, was appreciated by consumers. It showed a high concentration of α-linolenic acids (Omega-3), total phenolic compounds, and antioxidant properties, so that, considering 100 g of pasta per day, it is possible to obtain 75 mg of essential linoleic acid and 9 mg of linolenic acid, along with a four-fold increase in total phenolic compounds [54]. The Omega-3 fatty acids can also inhibit carcinogenesis and slow tumor growth, as demonstrated by in vitro, in vivo, and clinical investigations [55].
The analysis of bread incorporated with four different concentrations of P. oleracea powder (0%, 5%, 10%, and 15%) showed increasing water absorption capacity, stability under the mixer, and softening levels as the P. oleracea powder concentration in the samples increased. The protein, fat, total ash, moisture, and fiber contents also increased along with the P. oleracea concentrations [56]. However, the bread with 15% of P. oleracea powder showed a decreased farinograph quality number and presented the lowest scores for sensory properties and color, taste, texture, and overall liking. The optimized formulation containing 10% of P. oleracea powder had the highest acceptance.
P. oleracea has also been used to produce powder mixtures with two other plant species, Amaranthus hybridus L. and Chenopodium berlandieri L. The powder mixtures containing P. oleracea showed more significant contents of phenolic compounds, with an increase in the antioxidant activity [57].
Another innovative functional product assessed was a fermented P. oleracea juice added with a selected lactic acid bacteria. Results demonstrated an increase in total antioxidants, preserved vitamin C, A, and E levels, and increased contents of vitamin B2 and phenolic compounds. In addition, decreased levels of pro-inflammatory mediators and 3 Oxidative Medicine and Cellular Longevity  Anti-NF-κB activity along with two upstream ROS and NO mechanisms [17] 5 Oxidative Medicine and Cellular Longevity reactive oxygen species were observed, with a consequent increase in the restorative characteristics of the use of P. oleracea juice for intestinal inflammation and epithelial injury [58].
The combination of yogurt or coconut plant extract or coconut cream with fresh leaves of P. oleracea reduced the overall oxalate content by simple dilution. The soluble oxalate content decreased from 53.0% to 10.7% when P. oleracea leaves were added to yogurt. However, the coconut plant extract and coconut cream had no effect on the percentage of soluble oxalate content but provided the mixture with an acceptable flavor [59].
The addition of fresh purslane leaves (ranging from 1% to 10%, w/w) to tomato sauces resulted in a decrease of total soluble solids from 9.57°Bx to 9.20°Bx, beneficially impacting sugar reduction. On the other hand, the amount of protein significantly increased from 0.12% to 1.83% from the lowest to the highest concentrations, respectively [60].

Bioactive Compounds of P. Oleracea on
Anticancer Activity P. oleracea presents phytochemicals and nutrients associated with anticarcinogenic properties. The 12% reduction in the activity of the mutagenic nitrosation mixture may be attributed to the ascorbic acid (vitamin C), α and β-carotene, chlorophyll, and polyphenols of the P. oleracea extract obtained through a standard juice extractor [42]. Phenolic compounds such as kaempferol and apigenin from a hydroethanolic extract of P. oleracea have effects in vitro against human glioma cells, and homoisoflavonoids showed in vitro selective cytotoxic activity for SF-268, NCI-H460, and SGC-7901 cell lines, as shown Table 2 [18,61].
Polysaccharides from P. oleracea act on free radicals through the antioxidant mechanism, modulating the immune system, which may be preventive and therapeutic  Oxidative Medicine and Cellular Longevity in rat ovarian and gastric cancer and mouse cervical cancer and sarcomas, as shown Table 2 [19][20][21][22]62]. Another bioactivity from P. oleracea is portulacacerebrosie A, a cerebroside compound that suppresses the invasion and metastasis of liver cancer HCCLM3 cells and acts in leucocythemia treatment are show in Table 2 [24,63].
In gastric cancer, interleukins (IL-2 and IL-4) and TNFα were enhanced by polysaccharides that also provide dosedependent protection against N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) induced oxidative injury by enhancing Superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH-Px) [22]. In addition to acting against ovarian, gastric, and cervical cancer, polysaccharides also work against intestinal cancer by stimulating the TLR4-PI3K/ AKT-NF-κB signaling pathway and Anti-NF-κB activity along with two upstream ROS and NO mechanisms [18,62], showing the importance of studying these molecules in P. oleracea matrices.
Alkaloids inhibited lung and breast cancer through moderate cytotoxic activities against A549, weak cytotoxic activities against K562, and low cytotoxic activity against MCF-7 and MDA-MB-435 cells.
Some possible mechanisms of P. oleracea for anticancer activity are represented in Figure 1. The bioactivity of P. oleracea and the potential to develop new products from this underused plant in some regions deserve attention regarding its valorization as a functional food and its pharmacological properties. Different anticancer mechanisms of P. oleracea were explored and reported in this review. Aqueous extracts, seed oil, and hydroethanolic extracts present cytotoxicity to cancer cell lines while chloroform extract does not have cytotoxic activity [67]. Further studies will be needed to determine anticancer activity in particular food matrices and beverages.

Conclusion
The P. oleracea plant may be promising for developing and innovating potential functional food products. The high levels of antioxidants such as phenolic compounds, carotenoids, and other nutrients such as minerals and Omega-3 fatty acids are supported by functional food studies. Research has indicated the anticancer activity of P. oleracea extracts. Polysaccharides, some phenolic compounds, alkaloids, and cerebrosides detected in P. oleracea and contained in aqueous extracts, seed oil, and hydroethanolic extracts are associated with inhibition and prevention of carcinogenesis. However, more studies are needed to prove the anticancer activity of food products containing P. oleracea as an ingredient to promote health benefits to the consumers.

Data Availability
The data used to support the findings of this study are included within the article.

Conflicts of Interest
The authors declare that there is no conflict of interest.