**5. Nutraceuticals**

Fruits, leaves, and seeds of papaya have a long history of human consumption and use. Fruit pulp is widely known for its nutritional value while the leaves and seeds are used in cooking in many cultures. Papaya pulp consists of macronutrients (protein, carbohydrate, lipid), fiber, minerals, carotenoids, and vitamins A, B, and C. Carotenoids from papaya are more bioavailable for human nutrition than those from tomato and carrot [64]. Other papaya tissues including leaves and seeds are of high nutrition, although with reduced levels of vitamins. Phytochemical analysis of papaya pulp reveals significant levels of phenols, terpenols, alkaloids, flavonoids, and saponins. Papaya leaves contain alkaloids, carpain, pseudocarpain and dehyrocarpaine, choline, carposide, saponins, pro-anthocyanin, benzyl isothiocyanate, while papaya seeds contain papaya oil, carpaine, benzyl isothiocyanate, benzyl glucosinolate, glucotropacolin, benzylthiourea,

hentriacontane, and β-sitostrol. Papaya oil contains oleic acid (72.5%) and palmitic acid (12.5%) [49, 65]. Caffeic acid, myricetin, rutin, quercetin, α-tocopherol, benzyl isothiocyanate (BiTC), and kaempferol have been identified in papaya, all of which have antioxidant activities and in the plant either promote antioxidant enzyme expression or reduce reactive oxygen species (ROS) production [66]. Alkaloids, flavonoids, saponins, and oleic acid all poses anti-inflammatory activities [12, 67, 68]. Alkaloids, flavonoids, and saponins in papaya have been shown to inhibit the bacterial growth of *Enterobacter cloacae*, *Pseudomonas aeruginosa*, *Proteus vulgaris*, *Klebsiella pneumoniae*, and *Bacillus subtilis* [69–71]. Finally, papaya latex, often considered a nuisance and irritatant, has been shown to actively inhibits the growth of gram-negative bacteria [72].

#### **6. Conclusions**

Lifestyles in the twenty-first century (and beyond) are setting strikingly different needs and demands from those of earlier periods. Twenty-first century consumers have higher expectations with respect to fruit type and quality; more flavorful, of higher nutritional value with additional benefits to both health and to the environment. Growers are constantly under pressure in meeting not just the demand for quantity but, more importantly, quality and overall consumer satisfaction. With the ready availability of papaya genomics and transcriptome databases, desired agronomic characters associated with fruit quality, yield, and plant adaptation can be identified in germplasm and incorporated into breeding programs [73, 74]. Papaya can be produced "for all seasons" using open field cultivation under favorable conditions and in protected cultivation systems and climate-controlled greenhouses regardless of climate and region.

Papaya cultivation under open field conditions offers large-scale production with low to medium capital inputs and low operating expenses, offsetting the issues of inconsistent quality and quantity due to seasonal changes, disease, and abnormal weather events. Protected cultivation and greenhouses with controlled environments provide more expensive papaya fruit year-round, but in higher yields and into markets demanding higher quality and capable of absorbing the additional costs. These conditions provide flexibility for papaya production under varying conditions and locations.

Metabolites with nutritional values such as vitamin C and carotenoids in papaya can be consumed directly because of their high concentration in papaya flesh. Metabolites extracted from papaya fruit, including Papain, an enzyme widely known and used in the food industry and cosmetics, offer additional markets for the fruit. Other metabolites including antioxidants can be purified from papaya seed, flesh, and leaves and there are other active constituent molecules that are the subject of evaluation and many no doubt many others yet to be explored. With multiple applications and the potential for the increased demand for papaya fruit and products, papaya is undoubtedly the fruit for the future.
