Effect of drying condition on physicochemical and antioxidant properties of dried Moringa leaf powder

Profile of physicochemical and antioxidant activity of dried Moringa leaves from Bangladesh are presented. Moringa is beneficial for health because it has a lot of nutritional and medicinal values. The leaves were collected and washed with distilled water at different temperatures in an oven dryer, and then the fine powder is taken as a sample by grinding and sieving method. This research was done to compare the changes in physicochemical and antioxidant elements at different temperatures (60°C, 70°C and 80°C) and to find the right temperature at which the nutrient loss will be the lowest. This study showed that as the drying temperature changed, so did the nutrient component of Moringa leaves. Physicochemical parameters (moisture, ash, protein, carbohydrate, fat, color) and antioxidant activity (Total phenol content, DPPH free radical scavenging activity, vitamin C, and ß-carotene) were extracted using a variety of methods. The protein content, carbohydrate content was estimated by the Kjeldahl and phenol sulfuric acid method respectively. Total phenol content (38.30 mg/100g), DPPH (77.79%), and ßcarotene (22.71mg/100g) were measured by the spectrophotometric method. And the colorimeter instrument is used for determining the optical properties. It can be seen that the moisture, ash, protein, carbohydrate, Total phenol content, Vitamin C, DPPH free radical scavenging activity, ß-carotene contents decrease significantly with increasing drying temperature, whereas fat content increases. At 60°C drying temperature the nutrient loss was lowest compared to 70°C and 80°C drying temperature, so it can be concluded that 60°C is the most suitable temperature for drying Moringa leaves.


Introduction
Moringa oleifera is residential principally in India, Bangladesh, Afghanistan, Pakistan, Brazil, Southeast Asia, West Asia, Sri Lanka, East and West Africa, Southern Florida, West Indies, and from Mexico to Peru and Paraguay (Chaudhary and Chaurasia, 2017). Moringa oleifera Lam. tree flourishes in numerous tropical and subtropical regions. Moringa oleifera tree has a place with the group of Moringaceae. In some countries, Moringa is called a "drumstick tree" or horseradish tree and is privately called "zogale" in Hausa, Nigeria. It is familiar for its multipurpose qualities (Bashir et al., 2016). Moringa oleifera is familiar with its excellent quality such as fast-growing even in impoverished soil, drought tolerant, deciduous tree (Ferreira et al., 2008). It develops excellent in hot, semi-dry, and moist regions and the suitable soil is sandy or loamy soils. The seed must be moderately new to give decent germination. Warm temperatures are significant for germination. Someone called Moringa "Miracle Tree" or "Mother's best friend" also for its high nutritional quality (Daba, 2016). Moringa has multipurpose use like medicinal uses, industrial uses, nutritional uses, economic uses, which can be used for water conservation and green manure also (Daba, 2016). Moringa plant has importance for human beings because almost all parts of Moringa (seed, pods, flower, and leaf) are edible (Daba, 2016). Moringa leaves are exceptionally perishable and require processing to protect against losses during postharvest. The best way of preserving Moringa leaves is drying. After the drying process, dry leaves require to convert into leaf powder and store (Emelike and Ebere, 2016;Affandi et al., 2017).
Traditionally, Moringa oleifera is utilized to treat numerous maladies all around the world and a large number of them are experimentally demonstrated, which for the most part incorporate, antiasthmatic, antihypertensive, antibiotic, antiulcer, CNS-depressant, anthelmintic, anti-inflammatory (Isitua et al., 2015). In many developing countries, many people cannot get the opportunity of medical services, they suffer from many kinds of diseases. Therapeutic plants offer possible cures with huge chances (Kumbhare et al., 2012). As a medicinal plant, Moringa is a blessing for many countries, especially those who are suffering from poor health conditions and poverty. For the water purification method, the watery extract of kernels of Moringa is used (Makkar and Becker, 1997).
Moringa is wealthy in numerous nutrients. It has more than 90 nutrient components. It has many antioxidant components and all eight vital amino acids with good proportions (Offor et al., 2014). The leaves of Moringa have high nutritional components. It contains vitamin C, β-carotene, protein, minerals such as iron, potassium, and calcium, also. Moringa has flavonoid components that help to prevent diseases such as heart diseases and give protection against chronic degenerative diseases (Coppin et al., 2013). The iron substance of the leaves is high and they are recommended for iron deficiency and are utilized in the treatment of scurvy skin maladies (Abbas et al., 2018). During pregnancy, if a woman takes 6 teaspoons of dried Moringa leaves powder regularly they can meet iron and calcium demand (Gopalakrishnan et al., 2016). Moringa oleifera leaves are additionally great resources of phytonutrients, for example, tocopherols and carotenoids. These supplements are known to scavenge free radicals at the point when joined with a reasonable eating regimen and may have immunosuppressive impacts (Oyeyinka and Oyeyinka, 2018). Moringa oleifera leaves act as an antidiabetic agent (Gopalakrishnan et al., 2016). Moringa leaves have Vitamin A content more than carrots, Vitamin C content more than oranges, calcium more than milk, potassium more than bananas, and iron more than spinach (Fahey, 2005). The moisture content of a product plays a pivotal role in determining the shelf life of the product. Drying can reduce the moisture content of Moringa leaf but it also causes different nutrient losses. Thus, an optimum temperature is needed for drying to minimize the nutritional loss and moisture content (Olabode et al., 2015). The present study aimed to evaluate the impact of drying conditions on the physicochemical and antioxidant properties of dried Moringa leaves powder.

Sample handling and preparation
Fresh Moringa leaves were collected from the Sunamganj district of Bangladesh. The stalk and branches of the leaves were removed followed by washing with distilled water. Then the leaves were dried in an oven dryer at different temperatures: 60°C, 70°C and 80°C for 2 hrs. The dried Moringa leaves were then ground into powder form and sieved in a 100 mesh to obtain fine particles. The powder found from Moringa leaves dried at different drying temperatures was stored in a different airtight vessel.

Moisture content determination
The moisture content of the dried Moringa leaf powder was determined according to a method described by (Rajput et al., 2017;Moazzem et al., 2019). Firstly, the powder was taken into a crucible and weighed (W 1 ). Then it was dried at 105℃ for 24 hrs in an oven drier and weighed again (W 2 ). The moisture content of the sample was calculated according to the following equation:

Ash content determination
A method described by (Akubugwo et al., 2007) was followed to determine the ash content of the dried Moringa leaf powder. Approximately 3 g of Moringa leaf powder was taken into a crucible. The sample was then heated at 550°C for 8 hrs in a muffle furnace and residue was determined.

Fat content determination
The fat content of the dried Moringa leaf powder was determined according to a method described by (Ravichandran and Parthiban, 2000). Firstly, 5 g of dried Moringa leaf powder was mixed with 25 mL methanol and chloroform mixture (2:1) in a separating funnel. Then 5 mL of 0.9% sodium chloride was added. Three layers were seen in the separating funnel. The lowest layer was collected in a pre-weighed beaker and heated at 80°C in a water bath. The residue amount was then measured.

Protein content determination
According to the Kjeldahl method described by (Offor et al., 2014) protein content of the dried Moringa leaf powder was estimated. Firstly, the digestion of the powder was done with a digestion mixture and sulfuric acid. After digestion, the distillation of the digested sample was carried out in a distillation chamber. The eISSN: 2550-2166 © 2021 The Authors. Published by Rynnye Lyan Resources FULL PAPER titrate value was then measured by HCl. The percentage of nitrogen content was found by this method. To determine the protein content, nitrogen percentage was multiplied by a conversion factor.

Carbohydrate content determination
Carbohydrate content was estimated according to Phenol sulfuric acid method described by (Agrawal et al., 2015). Firstly, 0.1 g dried Moringa leaf powder was boiled in a water bath for 3 hrs. The sample was then neutralized by adding solid sodium carbonate. The volume of the sample was made 100 mL by adding distilled water and centrifuging. The supernatant was used as the sample for further process. 0.2 mL sample was made 1 mL by adding distilled water. After that, 1 mL of 5% phenol and 5 mL of 96% sulfuric acid were incorporated into the sample and the absorbance of the sample was taken at 490 nm wavelength by spectrophotometer. The percentage of carbohydrate content was determined by using Glucose standard curve.

Optical properties
The optical properties of dried Moringa leaf powder were evaluated by a colorimeter. A standard plate (L*: 89.87, a*: 2.52 and b*: -3.36) was used to measure the L*,a* and b* values of the dried Moringa leaf powder (Zzaman et al., 2014).

Total phenol content
Total phenol content was determined according to a method described by (Amorim et al., 2008;Shin et al., 2015). At first extract, the solution was prepared by adding 80% methanol to 0.5 g dried Moringa leaf powder. Then, 0.5 mL extract was mixed with 8.5 mL distilled water and 0.5 mL Folin-Ciocalteu and kept for a few minutes. 1 mL of 35% sodium carbonate solution was then added to the mixture and absorbance was taken at 765 nm wavelength. Total phenol content was determined by the Gallic acid standard curve.

Determination of DPPH free radical scavenging activity
DPPH free radical scavenging activity was determined according to the method described by Chang et al. (2001). At first extract, the solution was prepared. Then, 2 mL extract sample incorporated into 2 mL DPPH (0.16 mM) methanol solution and kept in dark condition. The absorbance of the mixture was measured at 517 nm wavelength by spectrophotometer.

Determination of vitamin C content
According to a method described by (Ranganna, 1986), vitamin C content was determined. At first 5 mL standard ascorbic acid and 5 mL Meta phosphoric acid was taken into a conical flask. The dye solution was put into a burette for titration of the sample. Dye factor was obtained by this process. Then titration of the 5 g sample was done by adding 3% of HPO 3 .

Determination of β-carotene
β-Carotene content was determined by using a method described by (Biswas et al., 2011;Hossain et al., 2021). Approximately 5 g of chilled acetone and 1 g of sample was taken in a test tube. The mixture was then centrifuged and the supernatant was taken into another test tube. After making the standard β-Carotene content absorbance of extract and standard β-Carotene solution was taken at 421 nm wavelength by spectrophotometer.

Statistical analysis
The SAS software (version 9.4, SAS Institute Inc., Cary, NC, USA) was used with one-way analysis of variance (ANOVA). Duncan multiple range tests (p < 0.05) was performed to statistically analyze the mean values. All experiments were repeated at least 3 times and the data were represented as mean±standard deviation.

Physicochemical properties of dried Moringa leaf powder
The moisture content of the Moringa leaf powder dried at 60°C samples, 70°C samples and 80°C samples were found 4.96%, 2.89% and 2.57% respectively (Table  1). Different drying temperature affects the moisture content of dried Moringa leaf powder. (Alakali et al., 2015) reported that increasing drying temperature reduces the moisture content of Moringa leaves. According to Sanni et al. (2006) sample containing lower moisture content has a longer shelf life. Singh and Prasad (2013) reported that unblanched Moringa leaf dried at 60°C contain 5.67% moisture content. Rajput et al. (2017) showed fresh and dried Moringa leaves contain 72.83% and 7.43% moisture content respectively.
Ash content for the sample dried at 60°C, 70°C and 80°C were found 10.3%, 9.81% and 9.39% respectively. A significant decrease in ash content was found with increasing drying temperature. Oluduro (2012) reported similar results and found 10.64 % ash content in dried Moringa leaf powder. According to Alakali et al. (2015), the ash content of Moringa leaf powder dried at 60°C and 70°C were 5.22% and 5.20% respectively which illustrates a similar decrease in ash content with Fat content for the Moringa leaf powder dried at 60°C , 70°C and 80°C were found 4.96%, 5.19% and 5.33% respectively. The change in fat content is significant but very small which may be due to inherent variation of the composition of natural products. Ilyas et al. (2015) found 2.89% of fat content in dried Moringa leaf. A similar result for fat content was reported by Sengev et al. (2013).
A significant difference was found for the protein content of Moringa leaf powder dried at different temperatures. Moringa leaf dried at 60°C, 70°C and 80°C contained 24.67%, 21.65% and 19.89% protein respectively. The significant decrease in protein content of the Moringa leaf powder with increasing drying temperature was due to increased protein denaturalization (Alakali et al., 2015). The protein content of Moringa leaf powder dried at 60°C and 70°C were found 20.75% and 19.89% respectively (Alakali et al., 2015). Chinwe et al. (2015) reported that dried Moringa leaf powder contains 24.31% protein.
The carbohydrate content of Moringa leaf powder dried at 60°C, 70°C and 80°C were found 45.57%, 43.4%, and 41.57% respectively. Carbohydrate content decreased with increasing drying temperature. A decrease in carbohydrate content may be the result of the thermal degradation of carbohydrates during drying (Lemus-Mondaca et al., 2016). Oluduro (2012) found 45.43% carbohydrate in dried Moringa leaf powder which is similar to this study.

Optical properties
From Table 2, the L* value of the powder increased continuously from 42.38 to 43.24 with the increased drying temperature of Moringa leaf powder. A significant increase in lightness is indicated by the increase in the L* value of the powder. The b* value of the powder decreased from 32.63 to 28.24 with the increase of drying temperature which indicates a decrease in yellowness of the Moringa leaf powder. The increase in lightness and decrease in yellowness of the dried powder may be due to the breakdown of chlorophyll with increasing drying temperature (Sejali and Anuar, 2011).

Antioxidant properties of dried Moringa leaf powder
Total phenol content of the sample dried at 60°C samples, 70°C samples and 80°C samples are found 38.30 mg/110 g, 27.77 mg/100 g and 16.39 mg/100 g respectively (Table 3). Total phenol content decreased with the increasing drying temperature of the dried Moringa leaf powder. Potisate and Phoungchandang (2015) reported that reduction in drying time helps to retain higher total phenol content.  Vitamin C content for the sample dried at 60°C samples, 70°C samples and 80°C samples were found 21.45 mg/100 g, 17.81 mg/100 g and 17 mg/100 g respectively. Vitamin C is heat sensitive and thus reduced with increasing drying temperature (Igwemmar et al., 2013). 19.3 mg of vitamin C content per 100 g of dried Moringa leaf powder was collected from Nigeria (Mensah et al., 2012) Beta-carotene content of the Moringa leaf powder dried at 60°C, 70°C and 80°C were found 21.45 mg/100 g, 17.81 mg/100 g and 17. mg/100 g respectively. βcarotene content decreased with increasing drying temperature of Moringa leaf. Subadra et al. (1997) found 17.4 mg of ß-carotene content per 100 g of fresh Moringa leaves and found that ß-carotene reduces after drying.

Conclusion
From this study, the drying temperature affects the nutrient component of Moringa leaves. And from this, the sample dried at 60°C temperature has higher amount of antioxidant and physicochemical content than another sample. And with the increasing of temperature, the loss of nutrient component occurs at most. Thus, the temperature of the sample in oven drying should maintain not more than 60°C temperature to get desirable product. Further studies needed to be carried out to analyse the stability of developed product from dried Moringa leaves and how many grams of dried powder should be given to pregnant women as an alternative to iron tablet.