Papaya is one of the healthiest fruits, rich in antioxidants, polyphenols, and vitamins C and A. On the other hand, papayas are larger fruits that are more difficult to transport and are more perishable because of their high free water content and potential for microbial infection. To overcome this problem, various studies have been undertaken on different papaya drying processes. Therefore, this review aims to assess the research that has been conducted on drying methods and identify the best nutrient retention methods among driers. Drying methods such as solar (direct and indirect), oven (hot air), microwave, refraction window, and freeze dryers are the most common. Moreover, the nutritional quality of papaya depends not only on the drying methods but also on the thickness of the papaya slice or purée, the drying temperature, and the time. The most valuable nutrients of papaya, beta-carotene/provitamin A, lycopene, and vitamin C are better retained by a freeze dryer followed by a refractance window; hence, the nutrients are heatliable. Instead, phenols and flavonoid nutrients are more retained by heat-driven dryers through the release of polyphenolic compounds from the food matrix during drying; hence, heat breaks down covalent bonds and facilitates the liberation of bio-compounds. The refractance window dryer is the most promising papaya drying technology over the freeze dryer because it uses less energy, is easier to use, is more environmentally friendly, and retains more nutrients than previous drying methods.

• Nutritional content

• Ripening stage

• Drying methods

• Nutrient retention

Minuye M (2024) Papaya Processing Methods and its Nutritional Value. J Hum Nutr Food Sci 12(1): 1182.

Fruits and vegetables are among the best food crops, and because of their high nutritional value and therapeutic characteristics, eating them is strongly associated with several health benefits [1]. Low fruit and vegetable consumption is listed as one of the 20 risk factors for world mortality, immediately after the most well-known killers like smoking and high cholesterol levels [2]. Therefore, increasing fruit and vegetable consumption is necessary to improve human health [3]. These advantages of fruits and vegetables have generally been attributed to their antioxidant properties. Carotenoids (provitamin A), which are antioxidants, are the most intriguing and have received special attention in addition to their antioxidant characteristics because of their use as provitamin A (a source of vitamin A). According to a recent assessment, only 2.4% of adults consume the recommended five servings of fruits and/or vegetables daily, which increases their risk of developing chronic diseases and nutrient deficiencies (such as a lack of vitamin A). The highest number of years of life lost (YLLs) and disability-adjusted life years (DALYs) (11–12%) were associated with poor fruit consumption [4].

People in regions with widespread vitamin A deficiency consume provitamin A (carotenoids) almost exclusively [5]. Provitamin A and preformed vitamin A both contribute 30% and 70% of the daily vitamin A requirements in developed nations, respectively. In contrast, provitamin A carotenoids constitute 70% of the daily vitamin A intake in underdeveloped countries [6]. The introduction of affordable, food-rich beta-carotene to combat widespread vitamin A deficiency is essential. Carotenoids, a type of provitamin A, are highly intriguing because they serve as both vitamin A and antioxidant sources. Furthermore, because they are only converted to vitamin A when the body requires them, it is crucial to avoid exposure to vitamin A toxicity [7]. Therefore, besides health and nutritional benefits, the consumption of fruits and vegetables helps to prevent the prevalence of vitamin A deficiency, which plays a critical role, especially in developing countries because of the inaccessibility of livestock products.

Because of its high carotenoid content and pro-vitamin A-rich fruit, papaya fruit (Carica Papaya L.) is a targeted crop for nutrient enrichment to be utilized in sustainable programs to combat vitamin A insufficiency in underdeveloped countries [8]. According to Souza et al., [9], it is regarded as a source of vitamin A, calcium, and vitamin C (ascorbic acid), which is frequently utilized in diets. Therefore, consuming papaya fruit can be a useful alternative strategy to lower the prevalence of vitamin A deficiency in underdeveloped nations. Papaya fruit (Carica Papaya L.) is thought to be the most effective alternative way to reduce the prevalence of vitamin A deficiency [8] because (1) it is important as an economical and highly nutritious foodstuff, (2) it has a high content of beta carotenoid, (3) it is available all year (in the growing potential area), and (4) it is less expensive than other fruits with a higher beta-carotenoid source. However, (1) papaya fruit is highly perishable, with > 80% moisture content [10], (2) it is difficult to transport because of its enormous size (resulting in high transportation costs), (3) it is subject to substantial postharvest loss, and (4) it is not available in the requisite quantity for purchase. Therefore, to solve such problems, researchers have been trying to dry fruits using different drying technologies, and this review aims to assess the best papaya fruit drying method with minimal loss of nutrients.

Drying is the process of removing moisture from fruits to limit microbial activity and produce shelf-stable and easily handled products [11]. Along with papaya preservation, dried items have lower weight and volume, as well as lower packing, handling, shipping expenses, and storage space [12]. Inadequate work has been recorded on the drying of papaya fruit using a different drying process, which is likely to be prohibitively expensive and inaccessible to LMICs. However, a complete comparison of sun drying technologies to more typical drying methods, such as oven and freeze-drying, is lacking, and this research study includes another locally adapted eco-friendly drying technology (refractance window).

Papaya Fruit Description

The fruit is prized for its sweetness and delicate pulp [13], and is frequently enjoyed when ripe. Although its origin is unknown, evidence shows that it originated in the American tropics [14]. Papaya is a year-round climacteric fruit with elongated berries of varying sizes, smooth thin skin, and a greenish-yellow tint [15]. It is typically 15–50 cm long, 10–20 cm wide, and weighs up to 9 kg [16]. Papaya trees bear fruits for 5 months and can live for 4-5 years, the seeds are abundant, tiny, black, and covered in gelatinous aril [17]. It has a high concentration of orange pulp and frequently has orange-red, yellow-green, and yellow-orange colors. Its flesh is thick and yellow to red in hue, with a pleasant, sweet, mellow flavor. The varied flesh colors of papaya are caused by carotenoids accumulating in fruit cell chromoplasts, primary lycopene in red flesh, and b-carotenoids in yellow flesh, which provide antioxidant activity and vitamin A nutrition, respectively. The climatic parameters for papaya growth in both tropical and subtropical climates are between 21 °C and 33 °C. It cannot handle cold temperatures below 15 °C; however, at an ideal storage temperature (°C) of 8-12, it has a maximum postharvest life (days)/shelf life of 7-21 days [18].

Papaya (Carica Papaya L.) Nutritional Value

The nutritional value of papaya was rated as one of the highest among 38 common fruits, and each portion of the fruit had a different medical purpose [19]. It is a tropical and subtropical crop fruit recognized for its strong nutritional benefits, as well as its appeal due to its low-calorie content and high antioxidant content [20] [Table 1].

Table 1: Papaya major nutrient values

The major carbohydrates present in the papaya fruit are glucose, sucrose, and fructose, with glucose being the most abundant carbohydrate present in the initial phases of development [21]; however, the sucrose content increases during ripening and can reach up to 80% of the total sugars, when the percentage of sugars varies between 10 and 13% [22].

In general, the nutritional value of a fruit is determined by its variety, growing conditions, and ripeness at the time of eating, but the nutritional content of papaya fruit is highly associated with ripening [23]. The ripening process is aided by respiration and is linked to the generation of ethylene. According to Zuhair et al., [24], when papaya fruit ripens, it becomes more nutritious. It boosts physicochemical properties, antioxidant activity, and total phenolic and flavonoid content. There are five stages of papaya maturity based on peel color when stored at room temperature (24 ± 1 °C, 75 ± 5% RH) [Table 2].

Table 2: Papaya maturity stage at room temperature storage

Source: Export program for Brazilian papaya. Ministry of Agriculture, Livestock, and Environment.

Furthermore, more ripe papaya fruits had higher redness and yellowness. Aside from nutritional benefits, fruit hardness rapidly declines following separation from the tree during papaya ripening [23], indicating accelerated respiration/ deterioration. Different physicochemical parameters of papaya fruit, including pH, titratable acidity, total soluble solids, moisture, and fruit color, were affected by ripening phases. Furthermore, sensory quality improves with ripening; therefore, it is dependent on color, flavor, sweetness, and sourness. Volatile chemicals (benzyl isothiocyanate, terpenes, hydrocarbons, esters, aldehydes, ketones, alcohols, and organic acids) [15] contribute to papaya sensory properties (mostly taste and scent). Linalool is the most abundant volatile component in papaya and is responsible for its taste and scent [25].

Research studies conducted by Martins et al. [26], on Golden’ and Sunrise Solo papaya varieties at two different ripening stages found that Carotenoid levels increased with all-trans-lycopene varying from 0.73 to 1.58 μg/g in the ‘Golden’ and from 0.68 to 1.67 μg/g in the ‘Sunrise Solo’, and All-trans-β- cryptoxanthin content from 1.29 - 3.0 μg/g in the ‘Golden’ and 0.28 -5.13 μg/g in the Sunrise Solo’. Moreover, accordingly, Bhaskarachary et al. [27], in the study of papaya (Honey Dew) varieties at different ripening stages of light yellow and deep yellow, results of betacarotenoid content (mg/100g) found 1.25 and 3.71 respectively. Furthermore, he also tried to see the differences after storing deep yellow ripe papaya fruits for 24 h and 72 h, and the result showed statistical variation. Fruit maturity studies stated that total carotenoid content was nearly doubled (22 mg/100 g), while β- -carotene content showed an increment of about three fold through ripening when compared to contents of light-yellow ripe fruit. In 24-hour storage, the total carotenoid content did not change significantly (p<0.001). After 72 h, these two carotenoids, as well as the total carotenoid content of the fruit, diminished. Vitamin A activity was reduced as the storage time was extended from 24 to 72 hours [28].

Papaya is a rich source of antioxidants, such as vitamin A, E, and B complex and ascorbic acid, compared to carrots and oranges [29]. It is also the cheapest source of carotenoids, thiamine, riboflavin, niacin, vitamin B-6, and vitamin K [30]. Antioxidants, such as vitamins C, A, and E, as well as phenolics and carotenoids, diminish the oxidative stress caused by free radicals [31]. They are thought to control or reduce oxidative impairment in foods and biomolecules by suspending or inhibiting the oxidation process caused by reactive oxygen species, thereby improving product shelf-life and protecting biological systems [28]. Antioxidant chemicals such as (B-carotene, ascorbic acid, and phenolics) are therapeutic and preventive against a variety of disorders, including aging, inflammation, and some malignancies [32]. Carotenoids are the most fascinating antioxidants and have received special attention in addition to their antioxidant capabilities owing to their use as provitamin A (used as a source of Vitamin A) [33]. Provitamin A carotenoids are extremely beneficial to our bodies in controlling Vitamin A toxicity since provitamins are converted to vitamin A when only the body is required. 

Papaya Varieties and Their Properties

There are two types of papaya based on their flesh color: red and yellow, which result from carotenoids accumulating in fruit cell chromoplasts. Red flesh papaya primarily contains lycopene, whereas yellow contains beta-carotenoids and -cryptoxanthin, which provide antioxidant activity and pro-vitamin A activity, respectively [34]. Lycopene is responsible for the red flesh whereas β- carotene is responsible for the orange/yellow color [35]. Red flesh papaya softens faster and has a shorter shelf life; however, some consumers prefer it, which is commonly referred to as “strawberry papaya” on the market. The carotenoid alignments of red- and yellow-fleshed Hawaiian Solo papayas revealed a significant concentration of lycopene (about 63% of the total carotenoid content) in red-fleshed fruit but none in yellow-fleshed fruit [36]. Yellow-fleshed fruit carried up to 75% of the total carotenoid content in the form of β-cryptoxanthin and β-carotene derivatives, whereas red-fleshed fruit contained around half that proportion. During ripening, lycopene is rapidly transformed into β-carotene by the action of lycopene beta cyclase, which is then turned into xanthophylls by β-carotene hydroxylase [35]. In cultivars with red pulp, lycopene conversion to cyclic carotenoids is slowed or even blocked, resulting in lycopene build-up [37]. β-carotene can be found in green leafy vegetables and yellow-orange fruits and vegetables. Growing conditions, maturity index, post-harvest handling conditions, and variety or cultivar can all influence the β-carotene concentration of fruits (peach, papaya, apricot, and tangerine) [38].

Papaya Drying

Drying is a traditional food preservation method that increases product shelf life at room temperature [39] and reduces weight, volume, packaging material, storage, and transportation costs [40]. According to Kaleem et al., [41], drying can remove between 80 and 90 percent of water from a fresh product while retaining a significant amount of nutrients. Although the drying of food products can be performed using different technologies, their dried food product quality is significantly different. Fruits that have been dried should be of the highest quality possible, so it is important to optimize new drying technologies that include proper pre-treatments and dehydration methods. Likewise, it is important to determine the appropriateness of a dryer in the drying of fruits as the physical properties of fruits may change when various drying practices are applied. If the correct drying technique cannot be used, the dried product may not be satisfactory in terms of acceptability and nutrient value for the consumer. Therefore, choosing appropriate/innovative drying technologies for fruits and vegetables should be a big priority. To maximize the marketability of the dried product, cutting-edge drier technology must be able to reduce changes in the physical characteristics of the fruit.

Papaya Drying Technology

Papaya nutrient retention is affected by different drying techniques. In addition, a few other variables affect the nutritional content and quality of dried papaya.

• Papaya slice thickness or puree: The drying rate and moisture content decreased with the thickness of the slices or purée. However, thin slices or puree can also lead to more flavor, color, and vitamin C losses [42,43].

• Pre-treatment prior to drying: pre-treatment of papaya might be applied by edible coating or ascorbic/ citric acid treatment. Dried papaya can benefit from edible coverings and ascorbic acid pretreatment that increase retentions of carotenoid, beta-carotene, vitamin C , and anti-oxidants , stop oxidation, and enhance sensory aspects [43].

• Drying temperature and time: Higher temperatures and longer drying times can reduce the drying time and energy consumption, but they can also cause more degradation of bioactive compounds, such as carotenoids, phenolics, and flavonoids [44].

• Drying method: Different drying methods have different effects on the quality and nutritional value of dried papaya. Some of the common drying methods are hot air drying, freeze drying, vacuum drying, microwave drying, and solar drying. Each method has advantages and disadvantages in terms of efficiency, cost, environmental impact, and product quality.

Solar, oven, refractance window, freeze, and microwave drying of papaya pulp have been studied for their effects on the retention of nutritional compounds. These drying technologies display different drying rate patterns owing to differences in dryer designs, mechanisms of heat input, operating temperatures, and pressure conditions, among others. Solar drying can be carried out in various ways, including direct sun drying and indirect sun/solar drying (tray and glass hose dryer); however, they showed a different dried papaya quality even though they used the same solar energy. Direct sun exposure might lead to the loss of a major nutrient as it is in direct contact with the sun and the oxidation reaction is higher, but some methods of drying are better. Nevertheless, among the solar drying methods, glasshouse drying mechanisms are the most preferable and maintain the quality of dried papaya products [45]. The time was longer for sun/solar drying owing to the fluctuation of sunlight (ambient temperature) and laminar airflow over the product during the drying period [46]. However, the drying time for convective drying was considerably shorter when compared with the other drying technologies of solar and freeze drying. The continuous hot air circulation inside the oven rapidly removed the surface water from the product exposed with a large transfer area to hot dry air. This effect causes a rapid drying rate period, followed by a short falling rate period. A comparable activity was also noted by Lemus-Mondaca et al., [47] in papaya slices dried by convective drying under similar conditions. Nonetheless, VegaGálvez et al., [48] discovered that papaya slices were dried with ultrasound or vacuum at a higher rate than convective drying. On the other hand, refractance window drying technology is the most suitable drying technology for fruit and vegetables. Drying principles are based on heat transmittance from boiling water, and it is a modern nonthermal method for drying products [49]. The refractance window drying technology drying rate depends on slicing, load, and design; as a result, the drying time varies but is not longer than 2 h.

Nutrients found in fruits and vegetables are critical for human health, but they are sensitive to heat, and their retention during drying is determined by the type of pretreatment, drying time, and drying technology [45]. Osmotic dehydration with ultrasound pretreatment followed by vacuum drying showed the highest retention of phenols and antioxidants compared to other drying techniques [50]. Tray drying at 70 °C resulted in decreased moisture content, water activity, and shrinkage of the dried papaya, while higher osmotic solution concentration and lower process temperature retained maximum bioactive compounds [51]. Furthermore, both freeze and spray drying are viable options for drying papaya pulp, with spray drying showing higher retention of phenolic and flavonoid compounds [52]. Osmotic pretreatment combined with freeze-drying at different working pressures affects the microstructure, color, and functional properties of papayas, with higher working pressures conserving bioactive compounds and minimizing structural deformation [53]. Solar drying, which includes openair, tray drying, and glasshouse methods, has been found to result in lower retention of total polyphenol content, total carotenoids, and beta-carotene, especially when compared to freeze-drying [54]. Refractance window drying and freeze-drying were found to retain high levels of bioactive compounds, and ascorbic acid, as well as preserve quality attributes color, and flavor [55].

Here are some of the research findings of dried papaya that are dried under different drying methods as shown in [Table 3].

Table 3: Papaya nutrient retentions at different drying methods

The nutritional value, variety type, ripening stage, and effects of different drying techniques on nutrient retention of papayas were evaluated in the current review. Papayas with yellow pulp have more provitamin/beta-carotene than those with red pulp, however, both types of pulp can help lower the prevalence of vitamin A insufficiency. The nutritional value of papaya increased significantly as the ripening stage increased. Various drying methods have their effect on papaya nutrient retention; however, other important elements that affect nutrient retention include temperature, slice/pure load, pretreatment before drying, and drying duration. Carotenoids, provitamins, and vitamin C are heat-sensitive components found in papayas that are better preserved in freeze and spray dryers than in other drying methods; moreover; refractance window driers also maintain these nutrients better. Instead, due to the release of polyphenolic compounds from the food matrix during drying, which results in increased quantification of flavonoids and phenolic, the phenolic and flavonoid contents are higher for heat induced dryers. In general, following freeze drying, refractance window is a prominent promising drying method for papaya. Promoting drying of papaya using eco-friendly techniques such as solar-glass houses and refractance windows can prolong the fruit’s shelf life and preserve its nutrients, perhaps leading to an increase in fruit supply and accessibility. Products made from dried papaya may easily be included in meals and significantly help fulfill vitamin A needs.

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