Optimization of the spray-drying process for developing guava powder using response surface methodology
Graphical abstract
Spray dried guava powder
Introduction
Drying is the process of preserving foods since ancient times. Hundreds of variants are recently used in the drying of particulate solids, pastes, continuous sheets, slurries or solutions; hence it provides the most diversity among food process engineering unit operations. The quality of a food powder is based on a variety of properties depending on the specific application. In general, the final moisture content, solubility, dispersibility and vitamin C are of primary importance [1]. Food powders are instantly present in routine life. They are generally obtained from agricultural raw materials by different processes such as fragmentation or spray-drying processes. Among the food products, the food powders are easy to preserve, transport, store, weight and process [2].
The growing of fruits is limited in many countries to certain seasons and localities. In order to meet the demand of the market throughout the year in all areas, the commodities are preserved using different techniques. High moisture content will lead to the drop of quality and, indirectly, to a decrease in quantity. The drying of fruits controls the moisture content by either removing moisture or binding it so that the food becomes stable to both microbial and chemical deterioration. Drying is a common and economical preservation method for many fruits in many countries. Although most of the drying methods are traditional and primitive, there is an impelling need to apply advanced techniques such as spray drying, with the objectives of increasing productivity and obtaining closer control of the process to achieve a product quality. This requires basic data on drying together with knowledge of the fundamental principles involved. Nowadays, the fast economic development has changed the pattern of consumption of food from calories assurance to diet nutrient fortification. The consumers today are well educated and well informed [3].
Hence, it is important today to develop new nutritional food, maximize their nutrient content in both processing and storage and extend the shelf-life, and thus to meet the requirement of the market. In this regard, the information on nutrient change in processing and storage will be of great importance. Guava, with the scientific name, Psidium guajava, belonging to family Myrtaceae. It is an important food crop and medicinal plant cultivated or grows wild throughout the tropical and subtropical regions, widely used in food and folk medicines around the world [4]. The fruit is reported growing in more than 50 countries in the world, whose major producers are India, Brazil, and Mecca. India was reported leading in the world in guava production.
As fresh, guava is delicious and is one of the most nutritious fruits. Guava is the second richest vitamin C content among all the fruits. Hence, there is a worldwide growing demand for guava as a healthy and nutritive fruit [3].
In India much attention is given to the characteristics of local and introduced guava cultivars and their suitability for various purposes. Guava is the fifth most important commercial fruit in India in area and production after mango, banana, citrus and grapes. At present it occupies nearly 0.15 million hectares of land with a production of 1.80 million tons and productivity of 12 t/ha fruit per year in India. The other guava producing countries are America, South Africa, South Florida, Brazil, Mexico, Colombia, Cuba, Kenya and Taiwan. Different varieties of guava include the following: Apple color, Behat coconut, Chittidar, Lucknow 42, Lucknow 49, Safeda, Smooth green, Allahabad and Nagpur. Among red-fleshed cultivars in India there are Anakapalle, Florida seedling and Hybrid red supreme Kothrud and Red-fleshed Elisabeth and Acid speer Pink Indian and Patricia [5].
Guava is a seasonal fruit and is primarily consumed fresh. Currently, world trade in the processed guava products is not as much as other common fruits. However, for its nutritional value and being a seasonal fruit, the demand of processed guava products in the future is likely to have steady and significant increase. Presently, the following products are being processed from guava; ascorbic acid (vitamin C), canned slices, cheese, concentrate, dehydrated products, jam, jelly, juice, nectar, pectin, puree, spread, syrup and yoghurt [6], [7].
Spray drying is one of the unit operations, which are widely used in almost all food industry and it is one of the most practical methods by which the solution of solids in water can be dehydrated to yield a solid final product. Other methods for the removal of water from such solutions e.g. freeze-drying are usually quite expensive, while liquid–liquid extraction requires the use of solvents, which is often undesirable [1]. A new technique for spray drying using concentrated orange juice maltodextrin as drying agent was developed. Various methods capable of producing a free flowing fruit juice powder have been proposed: addition of drying aids (maltodextrin) [8].
Guava fruit has a characteristic flavor, to which its acidity (pH 4.0 to 5.2) contributes [6]. It is a rich source of ascorbic acid, containing over 100 to 300 mg/100 g. The drying process is also capable of causing a reduction in ascorbic acid content of the juice due to oxidation and temperature change. There is also potential for use of an instant guava powder in formulated drinks, baby foods and other products. Transportation costs would be reduced significantly when shipping this product to distant markets. However, the detailed information about guava powders does not exist in the literature. Guava has the best nutritional properties and drying operations must be carefully designed to maintain these nutritional properties. Nutrient retention in different temperature and after drying must be investigated to determine temperature effect and water activity level or moisture content effect on guava juice and to design the best drying process. Therefore, to utilize the produce at the time of glut and to save it from spoilage, the development of low cost processing technology of guava is highly required. It will also generate enough opportunities of self-employment by starting small scale processing unit or a cottage industry that will be remunerative to the growers.
Drying is defined as the application of heat under controlled conditions to remove the majority of the water normally present in a food by evaporation. It is a complicated process involving simultaneous heat and mass transfer in which heat penetrates into the product and moisture is removed by evaporation into an unsaturated gas phase [9].
Guava drying can be done by many ways. The spray-drying process has a higher retention of vitamin C and the pro-vitamins A and beta-carotene. The juice is dispersed or atomized to form droplets and sprayed into a heated chamber where it is dried and forms a “free-flowing” powder. The more common technologies such as convection, cabinet and drum drying are more costly, more labor-intensive, more complicated, and more likely to cause “powder burns”.
Spray drying is used to produce a wide range of products including heat sensitive materials [10], [11]. The flexibility of drier designs provides opportunities to produce the powders that consistently meet industrial specifications [12], [13]. The production capacity can be expanded to over 25 t of product per hour [14]. The process is continuous and easily automated which can reduce labor costs [11], [13]. There are less sticking and corrosion problems in spray drying if the material does not contact the equipment walls until it is dry [15]. It is a powerful tool for delivering cost effective, high quality products [14].
The first spray dryers were manufactured in the USA in 1933. Spray drying is one of the best drying methods to convert directly the fluid materials into solid or semi-solid particles [16]. Spray drying is a unit operation by which a liquid product is atomized in a hot gas current to instantaneously obtain a powder. The gas generally used is air or more rarely an inert gas, particularly nitrogen gas. The initial liquid feeding can be a solution, an emulsion or a suspension [17]. It can be used to both heat-resistant and heat sensitive products.
Spray drying involves complex interactions of process, apparatus and feed parameters which all have an influence on the final product quality [18]. The spray-drying process can produce a good quality final product with low water activity and reduce the weight, resulting in easy storage and transportation. The physico-chemical properties of the final product mainly depend on inlet temperature, air flow rate, feed flow rate, atomizer speed, types of carrier agent and their concentration. Spray drying is often selected as it can process material very rapidly while providing relative control of the particle size distribution [19].
Section snippets
Spray dryer
The spray dryer is a device used to produce dried foods. It takes a liquid stream and separates the solute or suspension as a solid and the solvent into a vapor. The solid is usually collected in a drum or cyclone. The liquid input stream is sprayed through a nozzle into a hot vapor stream and vaporized. The solid forms as moisture contents quickly leave the droplets. A nozzle is usually used to make the droplets as small as possible to maximize the heat transfer and rate of water vaporization.
Results and discussion
Four response surface models were obtained for the moisture content, solubility, dispersibility, and vitamin C content value. Table 4 shows the ANOVA data for response variables and their significance at 90% confidence level along with correlation coefficients. A high correlation coefficient explained the goodness of fit of the experimental data in the response surface models of moisture content, solubility, dispersibility and vitamin C content value.
The different graphs of four responses were
Conclusion
Thirteen different runs according to the CCRD were used to study the quality parameters of guava powder at various levels of inlet air temperature and maltodextrin concentration. The response surface methodology was used to optimize the processing conditions using moisture content, solubility, dispersibility and vitamin C content value as responses. The models for moisture content, solubility, dispersibility, vitamin C content and overall color difference value were statistically significant.
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