|NUTRITION - REVIEW ARTICLE
|Year : 2021 | Volume
| Issue : 3 | Page : 181-188
Impact of the Drying Techniques on the Functional Properties of Citrus sinensis (Sweet Orange) Fruit − A Review
J. Shiny Derose1, G. Nagamaniammai1, Ghazi Daradkeh2, Walid M Qoronfleh3, Marwa Al-Mahrizi4
1 Department of Food Process Engineering, SRM Institute of Science and Technology (SRM IST), Kattankulathur, Chengalpattu, Tamil Nadu, India
2 Dietetics and Nutrition Department, AL − Khor Hospital − Hamad Medical Corporation, Qatar
3 Q3CG Research Institute (QRI), Research &, Policy Division, 7227 Rachel Drive, Ypsilanti, MI 48917
4 Department of Food Science and Nutrition, CAMS, Sultan Qaboos University, Muscat, Oman
|Date of Submission||20-Mar-2021|
|Date of Decision||06-Feb-2021|
|Date of Acceptance||28-Apr-2021|
|Date of Web Publication||28-Jul-2021|
PhD G. Nagamaniammai
Associate Professor, Department of Food Process Engineering, SRM Institute of Science and Technology (SRM IST), Kattankulathur, Chengalpattu District – 603203, Tamil Nadu
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Citrus sinensis, commonly known as sweet orange, is rich in antioxidants and widely produced worldwide. Sweet orange consists of the water-soluble vitamins C, B1, B2, essential oils, and phenolic components. This fruit is known for its health benefits such as immune booster, digestive aid, anticancer activity, and cardioprotective activity. Its shelf life is low and also it contains high moisture content and so drying of oranges can be done. This review compared the following drying methods: sun drying, spray drying, freeze-drying, microwave drying, inert fluidized bed drying, ultrasonic drying, and infrared drying. Both thermal and nonthermal drying techniques had an influence on the functional properties of the dried orange powder. The comparison of the drying techniques determined relationship between the temperature of the drying process and its subsequent changes on the orange components. At higher drying temperature, it was reported to have a lower color, higher browning effect, lower total phenol content, lower total flavonoid content, and lowered antioxidant activity in dried orange samples. Further studies should be done to determine a method for drying oranges which provides high yield with low power consumption, temperature, and cost.
Keywords: Drying techniques, functional properties, orange, total phenol content
|How to cite this article:|
Shiny Derose J, Nagamaniammai G, Daradkeh G, Qoronfleh WM, Al-Mahrizi M. Impact of the Drying Techniques on the Functional Properties of Citrus sinensis (Sweet Orange) Fruit − A Review. Int J Nutr Pharmacol Neurol Dis 2021;11:181-8
|How to cite this URL:|
Shiny Derose J, Nagamaniammai G, Daradkeh G, Qoronfleh WM, Al-Mahrizi M. Impact of the Drying Techniques on the Functional Properties of Citrus sinensis (Sweet Orange) Fruit − A Review. Int J Nutr Pharmacol Neurol Dis [serial online] 2021 [cited 2021 Oct 25];11:181-8. Available from: https://www.ijnpnd.com/text.asp?2021/11/3/181/322479
| Introduction|| |
C. sinensis (sweet orange) is a member of the Rutaceae family and Aurantioideae subfamily found in Nigeria, the South African country, and other tropical and subtropical regions of the world. Oranges have multiple roles in the food, drug, and cosmetic industries. They have high content of water-soluble vitamins such as vitamin C, thiamine, riboflavin, and niacin. The micronutrients present in them are calcium, potassium, and magnesium. They also contain phytochemical components, namely, the limonoids, synephrine, hesperidin flavonoid, polyphenols, and pectin., These fruits are found to be one of the highest consumed fruits in the world because of their high nutritional content and health benefits.
The orange is used in traditional medicine in many Asian countries due to its antioxidant, anti-inflammatory, antiviral, antibacterial, anti-sclerotic, and anticancer properties. It also improves the function of immune, digestive, and cardiovascular systems.. Etebu and Nwauzoma reported that the fruits prevent certain prevalent diseases such as stomach ulcers, kidney stones, and arteriosclerosis and lower the cholesterol level because of phytochemical compounds. The dietary fibre in the orange peel improves the bowel movement, thereby regulating the function and intestine’s function and health.
Although orange has a high nutritional and commercial value, the presence of high moisture content of about 80% can trigger the spoilage. The spoilage causes structural and functional changes in it. Certain microbial infections commonly found in the C. sinensis fruit includes Pierce’s disease caused by the bacterium Xylella fastidiosa. This gram-negative bacterium is transmitted by the leaf-eating insect that attacks the xylem part of the orange plant, where it multiplies rapidly, causing scorching of leaves. Xanthomonas axonopodis pv. citri causes lesions on the leaves, stem, and fruits, which is called the citrus canker disease. The viral infection caused by citrus tristeza virus (CTV) is considered the most harmful and highly destructive virus among citrus plants. CTV causes necrosis development in the phloem part of the orange plant. Citrus ringspot virus is another viral infection that causes scaly bark in citrus plants. The fungal infections include the citrus scab and citrus black spot diseases showing symptoms of scab lesions on citrus fruits and leaves and small black spots distributed over the fruit.
In order to minimize the microbial spoilage of sweet orange, appropriate processing methods need to be adapted. One such method is drying, adapted to increase shelf life, prevent microbial attack, and increase the economic value of oranges. Drying reduces the moisture content and causes inactivation of enzymatic and microbial actions, reducing the transportation cost. The drying reduces the moisture content of fruit up to 10% on dry basis. Different drying methods could be selected based on various intrinsic factors and extrinsic factors to dry oranges. The dried orange powders can be utilized as food flavors in products such as beverages, baked goods, dairy products, and candy.
The review paper explores the effect of different drying methods on the retention of functional and phytochemical properties of the orange. The typical drying methods used for sweet orange are spray drying, freeze-drying, inert fluidized bed drying, ultrasound-assisted drying, solar assisted drying, infrared drying, and microwave drying. In this study, the changes in the color, total phenol content (TPC), total flavonoid content, antioxidant activity, bulk density, essential oil characteristics, and the antibacterial activity of oranges concerning drying methods are discussed elaborately.
| Methods of Drying|| |
Drying is one of the oldest and most influential food processing methods to remove moisture content. The drying of food leads to changes in physical, chemical, and functional characteristics of the product. Thus, proper temperature and relative humidity conditions should be maintained to reduce the loss of product quality due to drying. Drying usually occurs at high temperature, but nonthermal methods in recent days also dry heat-sensitive materials. Proper temperature–time combinations for the drying process should be optimized to achieve uniform drying.
C. sinensis has a high content of vitamin C and other micronutrients which are heat sensitive. Hence, the drying temperature should be optimized such that the essential components present in the orange are not degraded during drying process.
Solar drying or sun drying is an ancient drying method where the sun is the source of heat energy. In sun drying, the product is directly placed under sunlight, which removes the moisture from the product. Solar drying is not widely used as the drying temperature can be neither maintained uniformly nor controlled during the process. However, the cost of solar drying is lower than the other methods.
The generalized method of drying is carried out by placing orange peels on a cloth under sunlight. The drying process occurs at temperature from 15°C to 37°C (30°C to 37°C in the morning and 15°C to 20°C at night). This process is done for about 48 hours until the moisture content is reduced to 10% (wet basis).
An advanced solar drying method is a solar hydro-distillation system. The said method is used to dry the orange placed along with water. The apparatus consists of a solar panel and a distillation unit with a capacity of 15 L of water as shown in [Figure 1]. It is further connected to a cylinder made of stainless steel. The parabolic reflector is covered nearly with 90% mirrors, mechanical and electronic apparatus to track the heat from sunlight. There are two reflectors, namely, the primary and secondary reflectors. The primary reflector acts by reflecting the radiation to the secondary reflector and it further reflects onto the distillation unit. The heat radiation produces the steam, which in turn condenses into essential oils of orange and along with anhydrous sodium sulfate at 4°C forms the orange powder. The Gas Chromatography-Mass spectroscopy (GC-MS) analysis of the essential oil of orange showed nearly 27 different compounds. The monoterpenes limonene and myrcene are present in high quantities in the essential oil.
The essential oil of orange shows a high antimicrobial activity. Thus, it can be used as a natural preservative in food industries. The essential oil of orange is incorporated in edible films, biodegradable polymers, microencapsulated polymers, and nanoemulsion coatings. These packaging materials with essential oils help in preserving the food. The antifungal properties make it as an effective insecticide.
Spray drying is the most commonly used method to obtain dried powder from liquids. The spray dryer works on the mechanism of atomization of liquids when they contact with the hot gas in the drying chamber. The moisture gets dispersed; hence, powder formed is settled at the bottom of the chamber. The spray dryer is used to reduce the moisture content effectively. It is also found to be cost-effective with minimal processing losses. The operating parameters such as the internal temperature, feed rate, pressure, and additive as a carrier for spray drying process show an impact on the physiochemical and functional properties of spray dried products.
Spray drying techniques mostly dry oranges. The spray drying process for orange juice begins with the concentration of feedstock before processing, followed by atomization, which will create a proper condition for evaporation. Then the orange juice is passed through hot gas. The moisture removal takes place in two stages. In the first stage, constant evaporation rate removes moisture from the droplet surface followed by complete evaporation of moisture in the second stage. The dried powder is separated from the drying chamber using bag filters, cyclone separators, or wet scrubbers.
Shofinita and Langrish experimented the spray drying method in assistance with the microwave drying for oranges. They described how the oranges are first pretreated by washing them in tap water followed by peeling the skin. The peels were cut into small pieces and microwaved with deionized water. The spray dryer parameters were maintained for 7 minutes at 135°C. The dried peels were then introduced into a cyclone spray dryer along with the drying agent maltodextrin. The solid to solvent ratio of maltodextrin was from 2 to 14. Maltodextrin as an additive improves the powder properties of dried orange powder.
Vacuum spray drying is also one of the widely used drying techniques for oranges. In this method, the internal dryer temperature was maintained at 40°C to 50°C than the regular spray drying temperature at 110°C to 140°C. The superheated steam at 200°C acted as the drying medium in this process. The juice is sprayed at 300 mL/hour into the chamber, and moisture removal occurs when it comes into contact with the superheated steam from the nozzle. The vacuum is maintained at 5 kPa at 40°C to 50°C and the orange powder is formed within the first or second cycle.
Freeze-drying is a low-temperature drying process in which the moisture is removed by sublimation under vacuum. The freeze-drying happens in the sequence starting from prefreezing followed by primary and secondary freeze-drying. In the primary and secondary drying, the solvent moisture is removed from the chamber.
In this study by Barbosa et al., orange juice powder was prepared using a modified drying technique. Initially 50 mL of orange juice was frozen at −80°C, then it was desiccated in the presence of vacuum for about 7 days, and finally it was further condensed at −55°C.
Freeze-drying can also be done by using an ultralow temperature freezer that can attain up to −80°C using liquid nitrogen with a boiling point of −195°C. The drying process was continued at −80°C for 24 hours to freeze orange juice. The frozen orange juice is milled by granulometry to obtain powder. The size of the dried powder depends on the operating conditions of the granulometry.
A third method of freeze-drying were reviewed based on work reported by Farahmandfar et al. They have reported that the glass lyophilizer cylinders were used to freeze-dry orange juices. The lyophilizer cylinders with samples were attached to a freeze dryer maintained at −50°C with 0.125 bar pressure. The process was continued for a day and the product reaches 10% of the moisture content. The frozen samples were crushed by a laboratory mill, then screened using a mesh, and finally were stored at −18°C in the airtight container.
Microwave drying is a substitute for high temperature hot air drying, where the efficiency of the drying is higher due to the uniform heating of the fruit with the same temperature. The microwave oven consists of a fan at the back end for airflow within the drying setup and magnetron cooling. The working principle is that the moisture of the material placed in the drying chamber is removed when hot air generated by the microwave is passed through the material. The moisture removed passes through the fan and goes out to the outer atmosphere. The microwave works with a maximum output of 1000 W at 2450 MHz. The drying temperature can be controlled in the microwave oven.
The microwave assisted hot air drying for oranges employed by microwave oven at the power of 2000 W at 2450 MHz energy was connected with the computer where the different process temperatures can be detected. The schematic representation of the equipment is given in [Figure 2]. The parameters need to be maintained in the oven before the drying process, that is, 2.5 m/s of velocity and 55°C temperature. The orange peels were placed facing up in the microwave oven and drying time was varied, and after the process the dried sample was reposed for 1 hour at 25°C on Decagon containers to eliminate the concentration profiles in the samples.
|Figure 2 Schematic description of the microwave assisted hot air-drying equipment used to dry samples.|
Click here to view
Microwave drying at vacuum conditions is used to dry orange slices. The equipment has a temperature control and a vacuum control. It works with power from 250 to 1000 W and vacuum pressure from 0 to 1000 mbar. The orange slices were dried at varying pressure and power ranges and the functional properties of the dried samples were tested.
Inert fluidized bed drying
Inert fluidized bed drying is the method of drying very compact particles. This method produces dried products with high quality than the traditional methods. The drying depends on the parameters, namely, the fluidizing gas temperature, the velocity, and the packing material.
The inert fluidized bed drying equipment has a working capacity of 6 L and operating parameters are maintained at 230 V, 50 Hz, and temperature range from 40°C to 120°C. The critical feature of the method is the inert material filled in the fluidized bed. Sand is used as the inert material with particle density of 2400 kg/m3. The orange slices are placed over the bed, and hot air flows on it for 10 minutes. The air temperature and velocity were effectively optimized. The dried samples were collected from the bottom of the bin.
Infrared is an electromagnetic radiation that can be used as an alternative to the heat source in drying. The infrared dryer included the installation of the infrared heater along with the typical hot air oven. In the study by Tunahan Sahan, and Oztekin in 2019, the operating conditions of output power 800 W and temperature between 70°C and 80°C were maintained. During the drying process, the thermocouple and programmable logic controller (PLC) devices were controlled to maintain the temperature.
The orange slices are dried using vacuum assisted infrared drying process where there is a rapid evaporation of slices due to the fast absorption of electromagnetic waves under vacuum conditions. Orange slices are dried by using an apparatus consisting of a fibre infra red (IR) indicator and a vacuum control. The operating conditions of power 500 W, temperature range from 50°C to 70°C, and the absolute pressure varying from 12.31, 19.88, and to 31.09 kPa are maintained. The dried orange slices have moisture content less than 10% (wet basis).
Ultrasound-assisted drying is a nonthermal method of drying by using ultrasound waves in combination with a common drying method. This drying technique improves the quality of the dried orange. An ultrasound drying device described by Garcia-Perez et al. in 2011 has a vibrating cylinder with a piezoelectric transducer that constitutes the drying chamber.
The operating parameters such as the air velocity at 1 m/s, temperature at 40°C, and the ultrasound field at 154.3 dB are maintained. The air relative humidity and temperature are monitored throughout the process. The drying is done until moisture content reduces to 10% (wet basis). The dried product is examined with the cryo-scanning electron microscopy.
A combined method of ultrasound with atmospheric freeze-drying was effective in drying orange slices. The orange slices are treated with the ultrasound, followed by the freeze-drying at −18°C. It was determined that ultrasound-assisted heating enhanced the drying rates of oranges.
Many functional properties of the orange change according to the drying process and methods. Hence, it is essential to review significant changes in some of the functional properties to determine the efficacy of drying processes. The changes in the functional properties such as color, TPC, density, flavonoid content, water content, and antimicrobial and antioxidant activities are listed in the [Table 1].
|Table 1 Effect of drying method on the physiochemical properties of the orange|
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| Conclusion|| |
Orange is a vital citrus fruit suitable to eat by all age groups. Oranges are considered to be good sources of vitamins and micronutrients and thus serve as the best immunity boosting fruit. The production quantity of oranges is considered to be two-thirds of the world’s total fruit harvesting. Complete utilization of oranges can be effectively done by any one of the postharvesting processes.
In general, drying is an inexpensive and useful method to extract the orange powder with fewer changes in the functional properties of the orange. This review is based on the study of the different drying techniques which can be employed to the orange and to the effectiveness of the product formed. The drying techniques include both thermal and the nonthermal methods.
Solar drying is a basic drying technique in which the orange is directly dried using sunlight. This method is considered to be cost-effective. However, the various physiochemical parameters of the orange were found to be lost due to high heating temperatures.
Spray drying is a common technique of drying oranges in which the operating conditions such as the inlet temperature, the ratio of drying agent (maltodextrin), and also the solvent to solid ratio can be optimized. By spray drying the water content of the oranges is reduced and the phenolic content of the sample is retained during the process.
Freeze-drying is a low temperature drying technique where lyophilization takes place and water gets sublimed into vapour. The freeze-drying of the sample does not alter the color of the sample. The freeze-dried samples had high retention of phenols and vitamin C in them.
The microwave heat drying is effective to remove the moisture from the sample, but the high temperature must be effectively monitored. It led to the loss of color and essential oil components. High temperature reduces the total phenolic content in the dried sample.
Inert fluidized bed drying is a new age method using sand as the inert material and the drying takes place in vacuum conditions. Owing to lower interaction of high temperature, the sample retains the polyphenol components in them.
Infrared and ultrasonic assisted drying uses electromagnetic waves and acoustic sound waves to dry the sample. These methods were administered in combination with another technique to deliver useful sample characteristics with minimal nutrient loss. The temperature of drying is lower in both the drying and hence the phenolic components are retained better.
The various physiochemical parameters observed and specific findings recorded such as the loss of color and the browning effect of the sample are due to the high temperature involved in the drying. The sample’s TPC also undergoes thermal degradation at very high temperatures; therefore, for high-temperature processes, the processing time should be reduced. The bulk density of particles depends on the temperature as well as the drying agent ratio. With the increase in temperature, the bulk density also increases, which results in the formation of porous dried powder. The antioxidant effect depends upon the amount of the TPC and vitamin C retention after the drying process. Thus, it can be concluded that each drying method has its own merits, but a lowered and cost-effective method can be preferred for drying oranges.
We would like to express our deepest gratitude to our Institution SRM Institute of Science and Technology (SRM IST). We would also like to thank all our departments and faculty members for their support. A special thanks to our corresponding author Dr G. Nagamaniammai for her consistent guidance, encouragement, timely help, motivation, and providing us with an opportunity to prepare this review paper.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]