Introduction

Persimmon (Diospyros kaki) is a premium fruit native to China (Matheus et al., 2022). The fruit belongs to the Ebenaceae family and is mainly grown in China and other countries, such as Spain, Republic of Korea (since the 14th century), Japan (since the 7th century), Brazil, Italy, and Iran (Hanif et al., 2015). During the 20th century, fruit production rapidly spread in countries such as Australia and New Zealand (Matheus et al., 2022). In 2021, the fruit was cultivated over 1.032 billion hectares, yielding 4.332 billion tons of fresh produce. In 2021, China was the leading producer of persimmon, followed by the Republic of Korea, Azerbaijan, and Japan (Food and Agriculture Organization [FAO], 2023).

As fruit cultivation is limited to particular regions, persimmon is not grown globally, although the fruit is gaining popularity because of its attractive color, appearance, sweet taste, astringency, and unique chewiness (Yang et al., 2022). Persimmon is an underutilized tree fruit with an orange-red color, fibrous flesh that is sweet in taste, and a round shape. Depending on its tannin content and organoleptic properties, it is further categorized into two types: astringent and non-astringent fruit (Jung et al., 2005).

In today’s modern era, the demand for foods with additional health benefits is increasing. Most foods provide nutritional benefits to the consumer whereas functional foods offer nutritional value and other health benefits. They help to reduce the risk of chronic diseases. Persimmon is one of the fruits that can satisfy some of these functional food demands. The fruit is fully loaded with nutrition and many bioactive components, such as soluble tannins (vary from 0 to 4% fresh weight), polyphenols, ascorbic acid (approximately 50 mg/100 g fresh pulp; immature fruit contains relatively more vitamin C), carotenoids and vitamins A, B₆, B₁₂, D, and E, and amino acids (19 amino acids are identified in the flesh). Minerals such as potassium, sodium, iron, and calcium, high levels of sugars (mainly fructose and glucose together share 90% of the total sugars present with a ratio of 1:1), pectic substances (varying from 0.7% to 1% of fresh weight) are also present (Testoni, 2002). The main organic acids in the fruit are citric, ascorbic, malic, and succinic acids. Both sugars and organic acids contribute to flavor and sensory properties. The total fiber and protein contents in fruit are 3.86% and 0.54%, respectively. Tannins, carotenoids, and phenolic compounds contribute to the fruit’s antioxidant activity (Matheus et al., 2022). Owing to its abundant bioactive components, this fruit is anti-carcinogenic, anti-inflammatory, cardioprotective, and anti-hypercholesterolemic and has antioxidant effects on regular consumption (Yang et al., 2022). Several studies have reported that fruit flesh is more nutritious than its pulp (Direito et al., 2021).

Persimmon can be found in Europe from September to early December (Direito et al., 2021). In India, fruit harvesting is done from late autumn to early winter, from October to December (Anjum et al., 2021). Owing to the presence of moisture (82–83%), nutrients, and climacteric properties, the microbes can quickly thrive over the fruit, resulting in spoilage and deterioration. The fruit has a limited shelf life and harvesting time; hence, it is inaccessible around the whole year. Therefore, there is a massive demand for the processing of this fruit to make it available to consumers aound the year. Furthermore, the fruit must be processed into various products to maintain its bioactivity and nutritional and sensorial characteristics (Anjum et al., 2021).

Drying is one of the methods by which food or fresh produce could be preserved for a long period. Drying inhibits or prevents microbial growth and increases food stability, facilitate storage, and reduce transportation costs by removing excess moisture (Yang et al., 2022). Dried persimmon has many applications in the food industry as it can be incorporated into snacks, cakes, breakfast cereals, and muesli. Dried persimmon slices can also be consumed as a snack. Besides, the drying of persimmon opens a window for utilizing this underutilized fruit in the form of different dried products, such as persimmon dried slices, partially dehydrated fruits, powder, and many more forms. Studies are conducted on the drying of persimmon in different forms. The present article reviews the studies conducted on the drying of persimmon and its effect on various quality characteristics of its dried form.

Drying of Persimmon

Persimmon contains abundant water in the form of moisture (approximately 81% on wet basis), which restricts its shelf life (Karaman et al., 2014). Moreover, it is available only in a particular season, which limits its consumption and usage. Drying can help to store it for a longer period with less risk of microbial contamination because of lessening of free water. Luo (2006) reported maximum ethylene and carbon dioxide production after four days in ‘Qiandaowuhe’ persimmon fruit. Harima et al. (2003) observed that persimmon fruit becomes soft and degrades to an unacceptable quality after 5 days of harvesting. With the help of drying and packaging techniques, the shelf life of dried persimmon could be extended from 1 month by storing in polythene to 8 months if stored in aluminum or polypropylene, with carbon dioxide and nitrogen flushed inside the package (Park et al., 2006). Limited shelf life and immediate deterioration after harvesting necessitate its drying as a processing method. Moreover, drying also decreases fruit’s volume or weight, which helps to reduce economic cost of shipping or transportation.

Persimmon is dried in various forms, such as slices, slabs, pulp, peels, and complete fruit. Multiple methods are used for drying, such as hot air drying (HAD), which consists of various drying methods, such as tray dryers, conventional oven dryers, sun drying, flat plate solar collectors, pulsed vacuum osmotic dehydration (PVOD), ultrasound-assisted osmotic dehydration (USOD), commercial dehydration, ultrasound-assisted vacuum drying (USV), pulsed vacuum drying, vacuum oven drying (VOD), vacuum freeze-drying (VFD), and combined hot air-microwave (MW) drying. A hot air oven drier is the preferred one. Figure 1 enlists various drying methods employed for drying of persimmon.

Figure 1. Drying of persimmon: different pretreatemts and methods.

Numerous factors affect the drying of fruit that can be classified as intrinsic to the fruit, such as the variety, shape, size, and form of the fruit (slice or pulp). The maturity of the fruit also plays a crucial role in drying, as Vilhena et al. (2020) observed when fruits of two different maturities were dried. The authors observed a considerable difference in the drying time and evaluated the physicochemical and microstructural changes of two maturity stages (S₁ and S₂) of ‘RojoBrillante’ persimmons. Different maturity levels have different microstructures, affecting rate and time of fruit drying. Owing to structural differences, the moisture loss was faster in S₁ than in S₂; 0.5-g H₂O/g was observed in S₁ and S₂ after 21 days and 28 days, respectively. The authors also observed a different effect on the color concerning the maturity stage, a decrease in L* values of S₁ and S₂ at the end of the drying period as against the initial average values, with a slight increase in the initial days of drying. L* values for S₁ were more, compared to S₂. The same trend was observed for chroma (C*) and hue angle (h*).

Another study showed that as the fruit matured, carotenoids increased with increase in the maturity of the fruit (M₃ > M₂ > M₁). In contrast, the antioxidant activity (AA) discovered by 2,2-diphenyl-1-picrylhydrazyl (DPPH) showed that AA was maximum in M₂ than in M₃ and M₁ (González et al., 2021). Thus, it was concluded that drying was affected by different factors. Thus, it can be interpreted from the above two cases that maturity index is a crucial factor that governs drying rate and quality of the dried product. Other critical factors could be the variety of fruit, type of feed (form, size, and shape), dryer, drying conditions, pretreatment, and environmental conditions. Drying period for persimmon slices was reduced by 220 min when the drying temperature was increased from 45°C to 65°C (Senadeera et al., 2020). Karaman et al. (2014) observed that the total dry matter of dried persimmon was maximum in the case of oven-dried samples, compared to vacuum oven-dried and freeze-dried samples. It intends that an oven-dried sample retained less moisture, and removal of more free water was evident.

The drying of fruit requires various preceding unit operations. After harvesting, the fruits are usually washed to remove adhering dirt and foreign particles. The fruits are sorted and graded based on the size, color, and degree of firmness to get the desired characteristics and uniformly dried forms. Based on the desired product and the drying method, the fruits are cut into different shapes or slices of the required thickness or pureed to have the dried form, such as powder or flakes. Different pretreatments, as explored in the literature, are rendered for persimmon fruits, similar to other fruits. The effect of different pretreatments and changes in the nutritional and functional properties of dried fruits are reported in the literature.

Effect of Pretreatments

It is worth noting that different pretreatments have different effects on the drying time and quality of the dried persimmon. For instance, Demiray and Tulek (2017b) concluded that dipping in water at 70°C as a blanched pretreatment, followed by HAD, provided better color retention than immersing in 20% sucrose solution as a pretreatment. Generally, drying by hot air usually takes longer time, but with the help of pretreatments, the drying time could be decreased, compared to conventional drying. The same authors observed that drying time for the fruit sample immersed in sugar syrup (20%) was 5 h less at 55°C, 6 h less at 65°C, and 4 h less when drying was carried out at 75°C because of osmotic dehydration (Demiray and Tulek, 2017b).

It was also observed that the effective diffusivity values vary more with pretreatment than with drying temperatures. Igual et al. (2011) reported 3.05 × 10^-10 m²/s diffusivity of water for the pretreated sample before drying and 3.43 × 10^-10 m²/s for the control dried sample, which indicated lower moisture content in the pretreated sample, resulting in a lower driving force. Pretreatment with an ultrasonication bath decreased the drying period of persimmon by 46%, compared to the control samples. Drying period and ultrasonication treatment are inversely proportional to each other; as the ultrasound treatment increases, the cell disruption increases, resulting in easy moisture loss. Average drying proportions increase with increase in the frequency of ultrasound. Doymaz (2012) observed a 21–42.8% decrease in the drying time of persimmon slices when blanching was done prior to drying.

For osmotic dehydration, 24% and 34% moisture were reduced when dipped in 30 °Brix and 45 °Brix fructose solutions, respectively. Interestingly, applying edible coatings of guar gum, gum Arabic, and xanthan gum was also explored as a pretreatment for persimmon slices. Using these coating not only accelerated the drying process but also preserved the color (Or et al., 2024).

Similarly, a combination of pretreatments, such as blanching followed by osmotic treatment, was also carried out; this was found to be quite promising for retention of color, along with the observation that blanching pretreatment resulted in better retention of antioxidant activity whereas osmotic pretreatment affected the phenolic content of the fruit (Yildiz et al., 2024). Similarly, some pretreatments adversely affect the quality of the fruit. The dried product, as observed for the drying of persimmon control samples, showed a better rehydration ratio (RR) than carbon dioxide-treated slices (Khademi et al., 2019). Various pretreatments executed before drying are reported to affect product quality (nutritional, functional, and nutritional properties) and drying coefficients as summarized in Table 1. Figure 2 shows the schematic for effects of pretreatment.

Figure 2. Effects of pretreatment on persimmon.

Different Methods of Drying

The drying of any product depends on various factors, such as the product’s shape and size, initial and final moisture content, bulk density, feed thickness, air velocity, temperature and humidity, and other environmental factors (Tiwari, 2016). Apart from this, the drying method dominates the product’s characteristics. In literature, sun drying, solar drying, tray drying, infrared drying (IRD), microwave drying (MWD), vacuum drying, and spray drying (SD) are used for persimmon drying. Table 2 highlights different forms of persimmon used for hot air and sun drying with different drying conditions. Similarly, Table 3 shows vacuum, spray, and radiation-based methods for drying.

Sun drying

Sun drying happens to be the oldest drying method employed by farmers on a large scale to preserve fruits and vegetables; however, it has limitations and drawbacks, such as longer drying periods, poor drying rate, and contamination of the product by dirt and microbes (Sontakke and Salve, 2015). These drawbacks have restricted the use of sun drying. Period of the year, area’s geographical location, and weather conditions affect the duration and intensity of sunlight (Tiwari, 2016). These factors lead to varying diffusion and drying rates and product quality. The drying of a product is highly dependent on environmental conditions and usually takes a longer time than other drying methods. The product’s characteristics are a function of surrounding conditions, such as weather, amount of oxygen in the atmosphere, and relative humidity. Hence, variable characteristics of the final product are expected from the sun drying of persimmon. In addition, it is worth noting that different pretreatments could be used to have the desired characteristics of the final product. The sucrose-pretreated persimmon slices showed better retention of color, rehydration ratio, and antioxidant activity, compared with the control and astringency-reduced persimmon sun-dried slices. This could be attributed to the de-astringent process leading to reduced tannin content, which ultimately affected antioxidant activity (Khademi et al., 2019).

The use of newly designed techniques, such as solar drying or sun drying with some modifications, is now in the trend. Drying temperature is important for the retention of bioactives. As sun drying is carried out at a lower temperature, it provides a product of greater preeminence than conventional drying. Vitamin C retention is better in sun-dried samples (Khademi et al., 2019) or solar-dried samples (Karakasova et al., 2013). Park et al. (2006) reported better retention of polyphenols, antioxidant activity, trace elements (such as manganese and copper), and fibers in sun-dried persimmon than in cabinet-dried persimmon. As drying time increases, antioxidant activity and retention of polyphenol content decrease (Park et al., 2006). Temperature also affects quality of the dried product. Concentration of vitamin C is reduced by approximately 20% when the drying temperature of flat plate solar collector increases from 45°C to 65°C (Hanif et al., 2015).

Hot air drying

Hot air drying is the most commonly used method for drying fruits and vegetables; in this method, hot air is passed over the products to be dried. The effect of pretreatment (Bozkir and Ergün, 2020; Demiray and Tulek, 2017b; Doymaz, 2012; Igual et al., 2011), varying temperatures (Demiray and Tulek, 2017b), varying thickness (Mosavi Baygi et al., 2015) with drying rate, effective diffusivity, activation energy, sensory characteristics, rehydration ratio, and quality characteristics are studied in the literature. The drying of persimmon occurs mostly in a falling rate period, where the moisture from the food sample travels from the interior to the surface and thus the drying rate continuously decreases (Doymaz, 2012; Igual et al., 2011; Khaled et al., 2020). Air temperature and drying period are more important for the quality of dried product than air velocity, as observed by Vivek et al. (2021). The authors also reported that the thickness of slices affects the drying time, ascorbic acid, browning index, and rehydration ratio. Increasing hot air velocity can lead to more loss of vitamin C in persimmon (Nicoleti et al., 2007). Senadeera et al. (2020) concluded that drying time of the product decreases if temperature increases. It is interpreted that drying time and temperature are inversely proportional; if drying temperature increases from 45°C to 55°C, then drying time decreases by 120 min (Senadeera et al., 2020).

Effective diffusivity also increases with an increase in drying temperature. Better color retention and lower shrinkage were observed when the fruit was dried quickly at higher temperatures (Senadeera et al., 2020). Color is one of the main factors influencing consumer acceptability; hence, a drying method with better color retention is preferable. Coefficient of diffusivity of 6.45 × 10^–7, 7.48 × 10^–7, and 9.08 × 10^–7 m²/s were reported for drying temperatures of 50°C, 60°C, and 70°C, respectively (Zhao et al., 2021). Nutritional parameters, such as phenolic compounds, flavonoids, β-carotene, proanthocyanidin, and ascorbic acid concentration vary with drying temperature. Jia et al. (2019) and Zhao et al. (2021) observed that increased drying temperature decreases phenolic content, flavonoids, β-carotene, ascorbic acid, and total proanthocyanidin values.

The effect of pretreatment on drying time cannot be overlooked, as observed in the previous section. HAD is now mostly used with techniques such as pulsed vacuum, ultrasonication treatment, etc. Osmotic dehydration reduces the moisture content of persimmon by 24% and 34% when dipped in 30 °Brix and 45 °Brix fructose solution, respectively. However, 35% and 43% decrease in moisture was observed in PVOD. In contrast, only 23% and 31% decrease was observed in USOD. In USOD, prolonged treatment period leads to a loss in cell rigidity, thus hindering mass transfer during dehydration. The formation of channels by cavitation during treatment with mass transfer takes place.

In pulsed vacuum, syrup penetrates due to macroscopic pressure gradients and capillary action. However, a longer run time in PVOD (structure of the sample disintegrates) can also hinder mass transfer (Corrêa et al., 2021). Sucrose-pretreated hot air-dried slices showed better rehydration ratio, antioxidant activity, and vitamin C retention, compared to control (Khademi et al., 2019); it also reduced drying period and lowered activation energy (Demiray and Tulek, 2017b). Ultrasonication-assisted HAD results in faster drying kinetics, and the increased value of effective diffusivity at lower air velocity was observed, compared to normal HAD (Cárcel et al., 2007). Pretreatment with dipping persimmon slices in sodium metabisulphite before dehydration leads to better color and phenolic content retention than the control dried samples (Akyıldız et al., 2004). Blanched persimmon showed a higher value of effective diffusivity (Demiray and Tulek, 2017b) and improved the drying rate (reduced drying time), reduced activation energy, and showed better rehydration ratio (Doymaz, 2012).

Vacuum drying

The vacuum drying of fruits and vegetables helps to accomplish drying at lower temperatures, thus offering better retention of bioactive and quality aspects, similar to the fresh ones. Vacuum drying operates by removing moisture under reduced pressure. By lowering the pressure, the boiling point of water is reduced, which allows drying at a lower temperature than HAD (Coşkun et al., 2024; Lekjing et al., 2024). This lower temperature minimizes the degradation of heat-sensitive bioactive components, resulting in better retention than HAD (Papoutsis et al., 2017; Yang et al., 2024). Reduced pressure also prevents oxidation and enzymatic reactions, which can degrade bioactive components (Jiang et al., 2013; Papoutsis et al., 2017; Yang et al., 2024). However, limited studies are conducted on the vacuum drying of persimmon, with more studies accomplished on the application of pulsed vacuum drying or ultrasonication treatment.

Compared to HAD, VOD showed better retention of total phenolic content (TPC), condensed tannins, total flavonoids (Karaman et al., 2014), and total sugars (Khademi et al., 2019). Sample dried in VOD showed lesser L*, a*, b*, and h* values than HAD samples. However, Khaled et al. (2020) reported more color change in vacuum-dried samples, compared to HAD samples, and a lesser activation energy for vacuum drying of 8-mm samples whereas effective diffusivity was reported to be lower.

The effectiveness of the treatment was more with the application of pulsation and ultrasonication. Yang et al. (2022) achieved the drying of persimmon slices with vacuum pulsation. With decreased drying temperature, the L* value decreased and a* and b* values increased. Vacuum pulsation increased color change and improved rehydration ratio. At the same time, ultrasonication decreased total color change and drying time (Kayacan et al., 2020). Ultrasonication and pulsation help in a better retention of tannin content, TPC, and antioxidant activity (Kayacan et al., 2020; Yang et al., 2022).

Infrared drying

Infrared drying has been used in food processing for the past few decades. IRD serves the heating purpose and replaces the old heating instruments driven by fuels because of its simple and compact designs and energy saving. IRD is applied for pasteurization, blanching, sterilization, baking, roasting, and drying (Krishnamurthy et al., 2008). It enables a faster drying rate, uniform distribution of temperature, better quality of dried product, and saving of space.

Infrared radiation is essential for interaction between water and energy. The presence of O-H bonds results in the absorption of IR radiation. Owing to these linkages, water molecules vibrate at the same frequency as the incoming IR light, facilitating its efficient absorption. Water’s temperature rises when it absorbs IR radiation, causing increased molecular mobility, resulting in evaporation (Aboud et al., 2019). The frequency of electromagnetic waves was 60,000–150,000 MHz, resulting in internal heating. IRD depends on IR power density, distance between lamp and sample, and lamp intensity.

The drying time reduces with increased lamp power (El-Mesery et al., 2024; Fadaie et al., 2020). The drying time is reduced by approximately 2½ times for IRD persimmon, and the retention of bioactive components and the color is better, compared to HAD persimmon (Kayacan et al., 2020). This could be attributed to the direct transfer of IR energy from lamp to food without high-efficiency losses, which hastens the drying process. Moreover, it has been found that the drying time decreases by 63.04% if the distance is decreased from 150 mm to 50 mm. The total color change increases with an increase in lamp distance, as it increases the drying time, and the same trend was observed if lamp with lesser power was used (Fadaie et al., 2020).

Freeze-drying

Freeze-drying removes water or moisture from the product with the help of sublimation process. Water is present in ice, which is carried at low pressure. The three main drying stages are freezing, primary, and secondary (Nowak and Jakubczyk, 2020). Drying at low temperatures (temperatures lower than the freezing point of water) maintains the quality parameters of food product, such as retention of maximal color, and nutrient and bioactive components. Water present in solid form during drying does not affect much the texture of food samples and has minimal volume reduction (Bhatta et al., 2020). Freeze-drying is widely recognized for its ability to preserve heat-sensitive bioactive components (phenolic content and antioxidant activity) because of its sublimation-based dehydration process, which minimizes the thermal degradation of food products while drying. The freeze-dried food sample has less volume reduction or less shrinkage, more rehydration ratio (Ratti, 2001), and retains volatile flavor and aroma (Stapley, 2008). Reducing sugar is one of the most important factors to consider, as it contributes to food taste, flavor, and the overall acceptability (Song et al., 2015). Heat-induced reactions during drying affect reducing sugar to a greater extent; however, freeze-drying helps to overcome this effect, as it does not involve higher temperatures. Freeze-drying poses considerable energy consumption and cost challenges despite its numerous benefits. The process requires a freeze dryer, which works under vacuum conditions, leading to prolonged drying time and high energy consumption (Bhatta et al., 2020; Uscanga et al., 2021). Capital investment is also high for freeze-drying equipment, contributing to the overall cost (Bhatta et al., 2020). Bhatta et al. (2020) also reported that freeze-drying requires 4 to 10 times more energy than the traditional HAD, which makes it economically a less feasible option for large-scale applications. Similarly, a recent study compared the energy cost of freeze-drying with IRD of persimmon and reported that freeze-drying was more than 11–13 times more expensive than IRD (Polat et al., 2024).

To overcome these drawbacks, recent development has focused on incorporating pretreatment methods, such as pulsed electric field, high hydrostatic pressure, and ultrasound to enhance mass transfer and reduce drying time (Rybak et al., 2021; Xu et al., 2021; Zhang et al., 2022). Uscanga et al. (2021) suggested that a higher shelf temperature could help to shorten processing time without affecting quality of the product. This signifies that the research efforts are focused on overcoming the drawbacks of the energy-intensive nature of freeze dryers and making this drying process more sustainable and economically feasible.

The reduced sugar content during freeze-drying was highest, compared to HAD, and combined hot air-MW drying (Jia et al., 2019). Presence of oxygen-less atmosphere and low temperatures during drying help to reduce degradation reactions during drying. Hence, these two main reasons promote the retention of more bioactive compounds during freeze-drying. This also justifies the retention of ascorbic and phenolic contents after freeze-drying. Similarly, the browning index is observed to be lowest in the case of freeze-dried powder. The freeze-dried sample recorded the highest value for lightness among all three methods of drying, namely HAD, VOD, and freeze-drying (Anjum et al., 2021; Çalışkan and Dirim, 2015; Karaman et al., 2014; Kayacan et al., 2020). This could be attributed to higher pigment concentrations, such as β-carotene and lycopene in freeze-dried samples.

Retention of β-carotene content in freeze-dried samples was better with the combined hot air-MW drying technique and HAD chips. Freeze-dried samples retained more total flavonoids, phenolic content, and β-carotene because of the lower extent of thermal and chemical degradation, and the icecrystals that were formed during freeze-drying could rupture the cell membrane and lead to the extraction of bioactive components (Kayacan et al., 2020; Zhao et al., 2021). On the contrary, ice crystals sometimes lead to cell rupturing and result in the loss of pigments and other bioactive components. Considering all these, freeze-drying offers a better quality of dried product, compared to other forms. However, the major difficulty with freeze drier is its complexity, longer running time, and high expenditure.

Microwave drying

Microwaves are parts of electromagnetic spectrum having a frequency range of 300 MHz–300 GHz (Wray and Ramaswamy, 2015). MWD has gained popularity in the food industry for the last two decades; for industrial usage, two narrow bands are designed, which are 915 MHz and 2,450 MHz. MW heating is faster than conventional heating methods (Zahoor et al., 2023). MW heating is also known as dielectric heating. Rather than heat transfer, electromagnetic energy is converted into thermal energy during MW heating (Sun et al., 2016). The MW–matter interaction involves two major mechanisms: dipolar rotation and ionic conduction. Dipole rotation tends to orient itself in the direction of electric field. This results in the rotation of nonpolar molecules in food. The molecules change their rotation 0.915 billion times in the case of 915-MHz frequency (Changrue et al., 2006; Wray and Ramaswamy, 2015). In ionic conduction, ions start to align themselves in a direction similar to changing electric fields, which can lead to collisions and friction that result in heat generation (Changrue et al., 2006). MWD is considered as fourth-generation drying, and factors, such as power density, loading amount, power, and exposure time, affect MW-assisted drying (Zhang et al., 2006).

Nonuniform drying is the main issue associated with MWD, leading to the formation of hotspots, where excessive energy damages the quality of fruit and under-dried regions, which compromise the drying efficacy and product consistency. To mitigate these issues, several efforts are made; for instance, optimization of MW parameters (power, frequency, and pulse modulation) (Jia et al., 2019; Jiang et al., 2020; Song et al., 2013), application design, and material handling (stirrers, rotating trays, and pretreatments) (Jahanbakhshi et al., 2020; Rattanadecho and Makul, 2016; Zhanyong, 2009), and using the hybrid methods of drying (Dai et al., 2022; Jia et al., 2019; Tomas-Egea et al., 2021).

Increase in power reduces drying time. The drying time was found to reduce by 87.47% when the MW power was increased by five times from 120 W to 600 W for 5-mm persimmon slices, and drying time increased by 1.86 min at 600 W when the thickness of the slices was increased from 5 mm to 9 mm (Çelen, 2019). Increase in both thickness of slices and MW power increases effective diffusivity whereas activation energy decreases with an increase in slice thickness. The shrinkage of slices increased with an increase in power, and decrease was observed with increased thickness of slices.

The color change observed was lower with an increase in thickness whereas an increase in power from 120 W to 460 W lead to a decrease in color change by 56% for 5-mm slices (Çelen, 2019). This could be ascribed to a longer drying duration at lower power levels, resulting in burnt regions formed due to the nonuniform distribution of liquid content. Vitamin C, total sugars, soluble tannins, TPC, and antioxidant activity increased with an increase in MW power and slice thickness (Wei et al., 2022). Retention of vitamin C could be attributed to lower exposure time at high temperatures. This results in comparatively high retention of vitamin C at high MW, and less thickness of slices resulted in a lower value of vitamin C, as its contact with air increased, causing oxidation. TPC and tannin content increased on drying with MWD. It could be possible because higher MW energy leads to the breakage of bonds inside fruit cells, and the cell wall structure also changes, which results in bounded phenols from the cell wall. Increasing soluble tannins and phenols also increases antioxidant activity, as these are the main contributors. Increase in slice thickness increases soluble tannins, TPC, and antioxidant activity. This could be attributed to thermal effect with an increase in thickness, which decreased thermal degradation and better retention of components (Wei et al., 2022).

The loading of sample in MWD also plays a crucial role in the retention of its bioactivity. Increase in loading from 1.0 kg/m² to 1.9 kg/m² results in better retention of vitamin C and total sugars. Soluble tannins, total phenols, and antioxidant activity decreased as loading increased (Wei et al., 2022). This could be possible because increase in loading resulted in longer exposure that resulted in the formation of polyphenol hydroxyl structure with unstable chemical properties, resulting in lower values of soluble tannins, total phenols, and antioxidant activity.

Combined hot air-MW drying system and intermittent MWD are some of the advances in the field of MW drying to save energy and prevent nonuniform drying. The drying time gets reduced with increased power density in both advanced drying systems (Jia et al., 2019; Qin et al., 2022). Similar to conventional drying methods, conjugated systems, such as these, are also associated with changes in the composition of persimmon on drying. The percentage of soluble sugars increases with an increase in power density; this could be ascribed to the fact that degradation of polysaccharides at higher temperatures is due to lower water-holding capacity as the cell membrane is damaged, resulting in higher soluble sugar content. Soluble tannins and vitamin C contents increased with the power density of intermittent MWD. However, soluble proteins and the overall sensory acceptance decreased with increasing intermittent MW power density. The decrease in proteins could be possible as higher temperature caused the disintegration of protein structure, resulting in lower soluble protein, and a reduced sensory score could be attributed to overheating that degraded pigments and imparted poor sensory properties (hard texture and bitter taste; Qin et al., 2022).

Spray drying

In spray drying, the convective heat medium converts atomized droplets into fine solid particles or powders. Short drying time, low heat stress (suitable for heat-sensitive food materials), high flavor, nutrient retention, and great economic potential are some features that match requirements of the food industry. Fruit juices or purees contain high amounts of sugars that directly hinder their conversion into powders. Direct conversion results in the stickiness of powders because of hygroscopicity and thermoplasticity, and is facilitated by drying air humidity and high temperature. This could be attributed to the fact that low glass transition temperatures (T_g) of sugars, such as fructose, glucose, and sucrose, were 26°C, 31°C, and 62°C, respectively. A lower glass transition temperature (due to sugar-rich foods) can cause collapsing and also result in caking and stickiness (Silva-Espinoza et al., 2019). However, addition of carrier agent can overcome this effect. Hence, addition of carrier agent to juice or purees is required to increase T_g (Etzbach et al., 2020). Feed material (temperature, flow rate, and initial concentration), atomization (feed pressure, air pressure, and rotation speed), inlet airflow (temperature, flow rate, and humidity), and outlet airflow (temperature and humidity) are the main operating parameters of spray drying. These factors also influence quality of the product (Woo and Bhandari, 2013).

Du et al. (2014) studied the effect of different carrier agents (gum arabic, maltodextrin, whey protein concentrate, starch sodium octenyl succinate, and egg albumin) on the physicochemical properties of powder and its recovery. Pulp with 30% gum arabic gave the highest powder yield whereas the lowest yield was observed when the concentration of maltodextrin was 25%. Maltodextrin and starch sodium octenyl succinate-containing pulp showed better retention of polyphenols and reconstitution properties. SD helps to better retain phenolic components than freeze-dried samples (de Jesus et al., 2023). Chen et al. (2016) observed that different cultivars have different characteristics, such as powder recovery (%), moisture content (%), hygroscopicity (g/100 g), solubility (g/100 mL), vitamin C value, and phenolic retention (%). It was observed that pectin and sugar influenced powder recovery, solubility, and hygroscopicity.

Alterations in Various Quality Characteristics of Persimmon

The drying of persimmon renders the fruit with poor quality characteristics. This section describes the changes in such characteristics. Physical characteristics, such as color, texture, sensory attributes and rehydration ratio are discussed. Similarly, the effect of drying on bioactive components of persimmon, such as carotene, ascorbic acid, phenolic content, and antioxidant activity, is also summarized.

Physical characteristics

Color

Color is considered as one of the most essential and primary parameters for the quality of any food product. Color influences customer’s perception, which affects procuct’s market value. Change in color of food during drying depends on different parameters, such as time and temperature combination; if the temperature is high, then the time required for drying is less, which means less exposure time and less effect on product’s color, compared to low temperature and long time combination. Changes in the color of food product is attributed to different reactions during drying, such as browning (both enzymatic and nonenzymatic), oxidation, degradation, decomposition, and so on. The longer the exposure time, the more prominent is the effect of these reactions. The effect of drying temperature on the color of dried persimmon is graphically depicted in Figure 3.

Figure 3. Effect of drying temperature and time on total color change of persimmon slices (Senadeera et al., 2020). I: 45°C (540 min); II: 50°C (465 min); III: 55°C (420 min); IV: 60°C (360 min); and V: 65°C (320 min).

When dried at 65°C, persimmon slices show better color retention than at 45, 50, 55, and 60°C temperatures, as the exposure time was the least at 65°C. The authors observed the least total color change at 65°C, and the highest was at 45°C (Senadeera et al., 2020). At lower temperatures, the drying time increases, which increases the value of the total color change, which could be attributed to the fact that the browning reactions take longer at lower drying temperatures. At higher temperatures, the total color change value decreases as the reaction time for the browning reaction reduces, which cannot alter the pigments much (Xu et al., 2019). The thickness of the slices also decides the fate of the color of the dried form; as reported by one of the authors, slices with a lower thickness on drying witnessed a less total color change than the thicker slices in VOD. This could be attributed to the longer drying duration amidst the slice’s higher thickness.

Texture

Texture is also an essential factor that must be considered for quality assurance and food safety in the food industry because it gives a clear idea of how a particular product affects consumer acceptance and its market value (Kadam et al., 2015). The texture of dried products depends upon various parameters, such as the type of dryer used, drying temperature, final moisture content, type of the product, and maturity level.

Pretreatment, such as dipping in osmotic solution, impact the texture of dried persimmon. The syrup-treated sample needs more force for the probe to penetrate, compared to the control HAD sample, as sugar syrup replaces the voids in between the dried sample, and the distance of penetration is less in the case of treated sample (Igual et al., 2011). The HAD sample exhibited a penetration depth of nearly 1.5 mm, while the syrup-treated sample showed a depth of ∼2.0 mm, where maximum force was applied. The maximum force required for penetration was 20 N for HAD sample whereas the syrup-treated sample recorded more than double this force (∼46 N). This hardening effect could be due to sugar replacing air during osmotic pretreatment, which was more dominant when the product’s water ratio was low.

Drying methods significantly influence the texture of dried products; freeze-dried samples exhibited superior crispiness compared to combined hot air-MW drying and HAD, which could be attributed to their porous structure and improved rehydration capacity (Jia et al., 2019). Crispiness is inversely related to rupture time, with shorter rupture time indicating better crispness. Freeze-dried samples had the shortest rupture time (0.32 s) and 545.28 g firmness whereas hot air-MW drying recorded a rupture time of 0.44 s and firmness of 743.21 g; HAD samples had the highest firmness of 929.43 g among the three drying methods, reflecting a less crispy texture.

The rupture time and firmness value of slices increase with the power density of MW. In MWD, power density is the most dominant criterion for deciding product characteristics. An increase in power density leads to higher firmness and rupture energy in dried samples; at power density of 6.8 W/g, firmness was 874.99 g and rupture energy was 1537.92 gs whereas at power density of 40.0 W/g, firmness increased to 1000.94 g and rupture energy was 1648.47 gs (Jia et al., 2019). The hardness value of HAD samples increased with increase in drying temperature. The sample dried at 50°C demonstrated a hardness value of 2,890 g, which was increased to 3,400 g at 65°C. With an increase in temperature by 15°C , the hardness value increased by 560 units (Bölek and Obuz, 2014). This could be attributed to improved moisture removal, structural shrinkage, and sugar crystallization.

It is worth noting that not only the drying method but also the variety and maturity index affect the textural properties of dried product. This was observed when the recorded deformative force was lower for the samples dried for 14 days after harvest than the samples dried for 21 days after harvest (Vilhena et al., 2020). A thicker secondary epidermis developed in the first maturity, offering much deformation resistance.

Sensory attributes

Sensory attributes are one of the prominent parameters that decide customer acceptance. Freeze-dried samples have the highest consumer acceptability, compared to hot air-MW-dried and hot air-dried samples (Jia et al., 2019). Among sun drying, conventional oven, and VOD, the sun-dried sample has maximum sweetness, color, chewing ability, and the least astringency sensory scores. Sensory attributes varied with drying temperature. Bölek and Obuz (2014) observed that the texture and color scores increased with an increase in hot air temperature, with decrease in flavor scores. This could be ascribed to increased drying temperature, reduced exposure time, and prevention of color degradation.

Pretreatments also influence the sensory attributes of the dried product. Igual et al. (2011) reported that slices without osmotic dehydration were the preferred samples for taste and texture. In contrast, acceptable color was observed in the case of sucrose-pretreated samples. Sucrose pretreatment decreased astringency and increased sweetness and chewing ability, compared to the control dried sample (Khademi et al., 2019). Astringency removal pretreatment resulted in color degradation and decreased astringency and chewing ability. The appearance and texture scores improved when slices were pretreated with a 3% ascorbic acid solution whereas pretreatment with 3% sodium metabisulfite increased appearance scores (Bölek and Obuz, 2014). The overall acceptability of the product decreased with an increase in MW power density in the case of MWD (Qin et al., 2022).

Rehydration ratio

Rehydration ratio is a critical quality parameter that reflects the dried product’s microstructure. A higher rehydration ratio signifies better dried product quality, as it indicates the ability of a dried product to gain moisture effectively. Drying air temperature has a more significant impact on rehydration ratio than air velocity and thickness of slices (Vivek et al., 2021). This is attributed to rapid removal of moisture at elevated temperatures, which may lead to the formation of hardened outer layer. This hardened surface restricts the removal of bound moisture and causes structural shrinkage, ultimately reducing the product’s ability to absorb water during rehydration (Gupta and Shukla, 2017). Higher HAD temperature and increased power density decrease rehydration ratio due to structural damage and case hardening (Bölek and Obuz, 2014). Higher power density increases temperature that alters food’s structure and surface properties, diminishing water absorption and retention (Jia et al., 2019). For instance, drying at 10.7 W/g resulted in a rehydration ratio of approximately 4.30, which declined to 3.40 at 40 W/g, highlighting the adverse impact of higher power levels. Rehydration ratio was lower at higher drying temperature, compared to the samples dried at lower temperatures.

Sun drying often results in a better rehydration ratio among vacuum and conventional oven drying; this is attributed to a lower temperature that minimizes structural damage and shrinkage (Khademi et al., 2019). Freeze-drying exhibited a rehydration ratio of 4.16, comparable to combined hot air-MW drying with a rehydration ratio of 3.96, as both methods effectively preserve structural integrity (Jia et al., 2019). PVD further improved the capacity of rehydration (∼3.05) (Yang et al., 2022), outperforming conventional HAD (∼2.35 at 65°C), as vacuum conditions created pore surface and internal pores that enhanced water absorption (Yang et al., 2022).

Pretreatments, such as blanching and application of chemicals, improved rehydration ratio by reducing shrinkage during drying (Bölek and Obuz, 2014; Doymaz, 2012) when the balanced sample subjected to HAD at 55°C achieved a rehydration ratio of ∼3.30, compared to ∼3.00 for unblanched samples under similar drying conditions (Doymaz, 2012). Figure 4 provides the approximate values of rehydration ratios for various drying methods and conditions.

Figure 4. Rehydration ratios with respect to different drying methods and conditions, I: HAD (65°C) (Yang et al., 2022); II: PVD (65°C) (Yang et al., 2022); III: MWD (at 10.7 W/g power density); IV: MWD (at 40 W/g power density); V: freeze-drying; VI: combined hot air-MW drying (70°C and 10.7 W/g power density); VII: HAD (70°C) (Jia et al., 2019); VIII: control HAD (55°C,1.2 m/s air speed) (Doymaz, 2012); and IX: blanched (70°C for 2 min), then HAD (55°C, 1.2 m/s air speed) (Doymaz, 2012).

Bioactive components

β-carotene

Persimmon fruit is a rich source of bioactive components, including carotenoids, with β-carotene being the most predominant constituent. During ripening, level of β-carotene increases, and is enzymatically converted into β-cryptoxanthin (Butt et al., 2015; González et al., 2021). β-carotene is responsible for color pigments, such as yellow, orange, and red, and serves as a precursor of vitamin A (Zhou et al., 2011). However, β-carotene is highly susceptible to degradation through oxidation, isomerization, and cleavage reactions. The trans-form of β-carotene is biologically more active and can be readily converted into the less active cis-form, particularly under conditions promoting oxidation, such as prolonged exposure to increased temperatures (Bhatkar et al., 2021). Activation energy required for the degradation of β-carotene is small; it is reportedly 33.33 kJ/mol for carrot β-carotene (Demiray and Tulek, 2017a).

The drying method employed significantly influences the retention of β-carotene, as depicted in Figure 5. Freeze-drying exhibited the highest retention (97.97%), outperforming IRD (88.14%), USV (79.18%), and HAD at 55°C (67.12%) (Kayacan et al., 2020). This trend is attributed to low temperature used in freeze-drying, which minimizes thermal degradation, and the formation of ice crystals, which rupture the cell walls and enhance the extraction of bioactives (Zhao et al., 2021).

Figure 5. Retention of β-carotene by different drying methods (Kayacan et al., 2020). I: freeze-drying; II: IRD (at 88-W power); III: USV (at 55°C); and IV: HAD (at 55°C).

Higher drying temperatures generally accelerate β-carotene degradation because of increased oxidation and isomerization (Zhao et al., 2021). Jia et al. (2019) and Zhao et al. (2021) reported that freeze-dried samples had significantly higher β-carotene levels than HAD at 50°C, 60°C, and 70°C, while hot air-MW drying showed the lowest retention of β-carotene among the three drying methods. However, González et al. (2021) observed an exception, noting improved β-carotene retention at higher temperatures (0°C and 60°C for 23 h and 9 h, respectively). The improvement could be attributed to the reduced exposure time, which minimized oxidative and thermal stress (González et al., 2021).

Ascorbic acid

Ascorbic acid is one of the main components of persimmon (Khademi et al., 2019). Ascorbic acid prevents diseases, such as scurvy, and serves as an important biological antioxidant . L-ascorbic acid or dehydro L-ascorbic acid (oxidized form) are the two forms of vitamin C present mainly in persimmon (Domínguez Díaz et al., 2020). Vitamin C is easily degraded by light, presence of enzymes, pH, oxygen, temperature, and metallic catalysts (Santos and Silva, 2008). The degradation of vitamin C increases with temperature (Jia et al., 2019). Bölek and Obuz (2014) observed this trend when the temperature increased from 50°C to 65°C, with approximately 21% degradation. A 17.32% decrease in vitamin C was reported when the temperature increased further by 15°C. Ascorbic acid in the sample dried at 60°C was more than that dried at 70°C and 80°C (Jia et al., 2019). Vitamin C is a thermo-sensitive bioactive compound, meaning that its concentration decreases because of thermal degradation when exposed to high-temperature drying. In contrast, samples dried at lower temperatures retained higher levels of vitamin C, as the reduced heat exposure minimized nutrient loss (Mieszczakowska-Frąc et al., 2021; Mphahlele et al., 2016).

Vivek et al. (2021) reported that ascorbic acid concentration was mainly affected by temperature, followed by thickness of the sample and air velocity. The freeze-dried product retains better vitamin C than the hot air-dried sample. The concentration of vitamin C decreases with increase in the power of MWD. The sun-dried sample showed better retention of vitamin C than HAD and vacuum-dried samples(Khademi et al., 2019). The freeze-dried and hot air-MW-dried samples showed almost similar retention of vitamin C whereas HAD showed less retention. Khademi et al. (2019) reported that ascorbic acid in the HAD persimmon pulp decreased by 36.724%, compared to fresh pulp.

Khademi et al. (2019) also reported that pretreatments can potentially affect vitamin C content in persimmon. It was observed that the least vitamin C retention was in astringency removal pretreatment dried slices whereas the highest vitamin C was retained in sucrose-pretreated slices, followed by control dried slices. This was because osmotic treatment cut the exposure of samples from air, reducing oxidative losses. At the same time, the least retention in astringency removal pretreatment (ARP) was due to the presence of CO₂, which accelerated the oxidation of vitamin C. Likewise, pretreatment with 3% ascorbic acid and 3% sodium metabisulfite showed better retention of vitamin C.

Total phenolic and flavonoid contents, and antioxidant activity

Phenolic components are known for their numerous health benefits, with antioxidant, antiviral, antimicrobial, anti-tumor, and antibacterial properties (Haminiuk et al., 2012). The other component contributing to antioxidant activity is flavonoids, a subgroup of phenols. Drying conditions, temperature, exposure time, thickness, and pretreatments are some of the influencing factors that decide the concentration of these components. Increase in drying temperature results in thermal and chemical degradations. Zhao et al. (2021) reported that total phenolic and flavonoid concentrations were better at 50°C than at 60°C and 70°C. Reduced phenolic content during high-temperature drying is attributed to two possible mechanisms: the release of bound phenolic compounds from the plant matrix, which makes them more susceptible to degradation; and the onset of thermal degradation of these compounds. As a result, the antioxidant capacity of dried samples may decline due to these combined effects (Maillard and Berset, 1995; Méndez-Lagunas et al., 2017). The freeze-dried sample has better retention of TPC, compared to HAD (Anjum et al., 2021; Jia et al., 2019; Karaman et al., 2014; Kayacan et al., 2020; Zhao et al., 2021), VOD (Karaman et al., 2014), IRD, USV (Kayacan et al., 2020), and hot air-MW drying (Jia et al., 2019). The sun-drying method was better for retaining TPC than other dehydration methods (Park et al., 2006). Among HAD and PVD at the same temperature, PVD was found to provide better retention of TPC and antioxidant activity; this could be attributed to the fact that PVD samples had shorter drying time to reduce heat exposure, and limitation of oxygen during drying could result in better retention of TPC (Park et al., 2006). Maximum total flavonoid content (TFC) was reported in freeze-dried samples among vacuum oven drying, oven drying, and other drying techniques. The antioxidant activity (%) was better for freeze-dried samples than HAD, USV and IRD (Anjum et al., 2021; Kayacan et al., 2020). Maximum antioxidant activity was observed in sun-dried samples, compared to conventional oven drying or dehydrators (Khademi et al., 2019; Park et al., 2006) and VOD (Khademi et al., 2019) as higher drying temperature decreases antioxidant activity (González et al., 2021). The percentage retention of TPC in different drying techniques is graphically depicted in Figure 6. Furthermore, the percentage retention of TFC in different drying techniques is shown in Figure 7. In addition, Figure 8 represents the percentage retention of antioxidant activity during different drying techniques.

Figure 6. Retention of total phenolic content during different drying methods. I: HAD (at 55°C) (Kayacan et al., 2020); II: IRD (at 88-W power) (Kayacan et al., 2020); III: USV (at 55°C) (Kayacan et al., 2020); IV: freeze-drying (Kayacan et al., 2020); V: PVD (at 65°C) (Yang et al., 2022); VI: HAD (at 65°C) (Yang et al., 2022); VII: HAD (at 60°C) (Anjum et al., 2021); and VIII: freeze-drying (operating temperature 60°C and at pressure 4 × 10^-4 mbar) (Anjum et al., 2021).

Figure 7. Percentage retention of total flavonoid content (%TFC) in different drying methods. I: HAD (at 65°C) (Yang et al., 2022); II: PVD (at 65°C) (Yang et al., 2022); III: IRD (at 88-W power) (Kayacan et al., 2020); IV: USV (at 55°C) (Kayacan et al., 2020); and V: freeze-drying (Kayacan et al., 2020).

Figure 8. Percentage retention of antioxidant activity during different drying methods. I: HAD (at 65°C) (Yang et al., 2022); II: PVD (at 65°C) (Yang et al., 2022); III: IRD (at 88-W power) (Kayacan et al., 2020); IV: USV (at 55°C) (Kayacan et al., 2020); V: freeze-drying (Kayacan et al., 2020); VI: HAD at 60°C (Anjum et al., 2021); VII: freeze-drying (operating temperature -60°C and at pressure 4 × 10^–4 mbar) (Anjum et al., 2021).

Overall, the thermal degradation of phenolic components during drying is a major concern, as these heat-sensitive compounds, including flavonoids, phenolic acids, and anthocyanin, are valued for their antioxidant properties. Both drying temperature and drying time influence the stability of phenolic components. Drying at lower temperatures reduces thermal degradation but requires a longer drying time, which increases enzymatic activity and oxidative losses.

On the other hand, moderate temperature accelerates the drying process, significantly reducing drying time. A shorter exposure to heat restricts the duration of enzymatic activity and oxidative reactions, potentially leading to better retention of phenolic compounds, compared to elevated temperatures. Faster drying helps to preserve heat-sensitive phenolic compounds by removing moisture speedily, which otherwise acts as a source of enzymatic and oxidative degradation.

Applications of Dried forms of Persimmon Fruit

There is a huge demand for products with therapeutic benefits as an ingredient for developing new food formulations.. Dried persimmon has vast applications in various products. The hot air-dried persimmon is used to make chips with more than 1-year shelf life (Milczarek et al., 2020). Dried persimmon powder is used to develop gluten-free muffins whereas addition of persimmon in a dried form increases the antioxidant activity of muffins (Hosseininejad et al., 2022). Similarly, persimmon powder is used as a sugar substitute in cakes, as the cakes developed with 40% sugar replacement are more acceptable and exhibit good antioxidant properties (YeŞİLkanat and Savlak, 2021). Another potential application of the dried form of persimmon is the extraction of bioactive compounds. It is worth noting that the waste from persimmon possesses ample bioactives to be extracted and used for various applications. Conesa et al. (2020) demonstrated that the waste from persimmon has an appreciable amount of carotenoids, tannins, phenolic content, flavonoids, and lycopene. The same study demonstrated that persimmon waste is a suitable substrate for production of bioethanol. Dried peels of persimmon are a rich source of β-carotene, and some researchers have patented the technology for extracting β-carotene from these peels (바다누리, 2008). Therefore, demand for the dried form of persimmon is expected to grow in the future.

Conclusions

Persimmon is an underutilized fruit with huge potential as an ingredient for developing food products. Limited shelf life and seasonal availability hinder its application; hence, fruit drying is performed to preserve it for a longer period. Its quality characteristics, such as color, texture, sensory properties, and nutritional profile, are important. Hot air is the most commonly employed method in for drying. Freeze-drying is the best among all the available drying techniques to preserve its quality during drying process. However, it involves high initial investment and operation cost, making it economically inviable. Drying techniques, prevailing conditions during drying, and feed characteristics, such as variety and maturity stage, influence the quality of the final product. Undesirable changes to the quality characteristics of dried persimmon are inevitable. However, different drying techniques and pretreatments are studied to overcome such changes. The scaling up of process parameters and their optimization for industrial scale are required.