Pretreatments, Dehydration Methods and Packaging Materials: Effects on the Nutritional Quality of Tomato Powder

Review Article

Austin J Nutri Food Sci. 2022; 10(2): 1167.

Pretreatments, Dehydration Methods and Packaging Materials: Effects on the Nutritional Quality of Tomato Powder

Yegrem L* and Ababele L

Ethiopia Institute of Agricultural Research, Debre Zeit Centre, Ethiopia

*Corresponding author: Lamesgen Yegrem, Ethiopia Institute of Agricultural Research, Debre Zeit Centre, EIAR, P.O. Box 2003, Addis Ababa, Ethiopia

Received: August 16, 2022; Accepted: September 13, 2022; Published: September 20, 2022

Abstract

Pretreatments and drying are commonly used before drying tomatoes to inactivate enzymes, improve the drying process, and improve the quality of dried tomato powders. In this review, the effects of different pretreatments (osmotic solutions), dehydration methods and packaging materials on quality attributes of tomato powder were summarized. They include pretreatments and osmotic agent solution (potassium metabisulphite, calcium chloride, sodium metabisulphite, ascorbic acid, citric acid, sodium chloride and sodium benzoate), thermal blanching (steam blanching and hot water) and non-thermal processes like freezing, sulfuring, etc. and drying methods (oven, sun and indirect solar dryer).Tomato powders have been dried in order to preserve, store, and transport them. Drying implies not only physical changes, which the consumer can easily detect through visual inspection, but also chemical modifications. These are responsible for alterations in color, flavor and nutritional value, which compromise the overall quality of the final tomato powder. Maximum lycopene and vitamins A and C content were found in freeze dried and direct sun dried than samples dried using other methods in low drying temperature, freeze driers showed in keeping the nutritional quality of tomato powder with combination of different pretreatments. Different pretreatments including osmotic agent solutions have their own merits and demerits on the final tomato powder. To overcome nutritional quality drawbacks, non-thermal pretreatment categories may be a better alternative to thermal blanching, and more fundamental research is required for better design and scale up.

Keywords: Drying methods; Pretreatments; Nutritional quality and tomato powder

Introduction

Tomato (Lycopersicun esculentum L.) is the family Solanaceae. After carrots, lettuce, and onions, tomatoes are the world 4th most popular fresh vegetable. The production of tomato is growing dramatically in the world as like its consumption. According to the data provided by FAOSTAT world has produced 182,301,395 tons tomatoes in 2017. To achieve this production, almost 5 million hectares were used. However, China, India and the USA are the top most countries dominating in the production of tomatoes. Tomato is considered as one of the most important vegetables produced in commercial agriculture because of income generated from export. Moreover, tomatoes contribute to a healthy, well-balanced diet and are rich in carotene, vitamins B, ascorbic acid (vitamins C) and other nutrients that are valuable for human growth and health.

Domestic production of tomato concentrate in Ethiopia offers attractive investment opportunities, with the existing producers unable to meet the ever-growing local demand. Urban population growth in Ethiopia is about 4% while GDP has been growing by more than 7% per annum for the last few years. Ethiopia’s tomato processing sector represents untapped market potential for export to regional, European and Middle Eastern Markets. Regionally, tomato is one of the commodities with the most potential, especially as tomato concentrate is the most commonly-used ingredient in African cooking, Europe is facing change in the tomato industry with decoupling of subsidies in European countries, resulting in increased costs for domestic production of tomatoes. Europe’s are number one importer of tomato concentrate, Italy, imports the majority from the USA, Spain and China. Ethiopia has advantage over the USA and China due to its geographic proximity, availability of land and low labor costs. UAE import $USD 41.6m worth of processed tomato, of which $USD17.9m is sourced from China alone. This is almost double the value of Ethiopia’s export of raw tomatoes. There is potential for Ethiopia to capture some of this market share.

Tomato is highly perishable in its natural state after harvest due to its high moisture content and high rate of metabolic activities; hence, it is prone to high postharvest losses. Fresh tomatoes difficult to preserve due to their high moisture content leading to wastages and losses during harvesting and storage especially in sub- Saharan Africa. Losses in tomato productions are also accrued to poor postharvest handling practices. Therefore, the prevention of these losses and wastage is paramount especially in the developing countries like Ethiopia whose populace are all year-round heavy tomato consumers and there is subsequent imbalance in demand and supply at the harvesting off-seasons. The term drying usually refers to the operation by which the moisture present in a material evaporates because of heat and matter exchange between the product and the working medium. Drying is one of the most common preservation methods for extending the shelf life of tomatoes by reducing the water content to a level so as to prevent the growth and reproduction of microorganisms and to inactivate many of the moisture-mediated deteriorative reactions [2]. Tomatoes are usually subjected to physical or chemical pretreatment before drying to shorten the drying time, reduce the energy consumption and preserve the quality of products [3]. The drying rate and quality of products do largely relate to the pretreatments carried out before drying process [4].

The most antique and traditional consists of placing the agricultural products on beaten earth, floor covering or floor exposed to the sun. Although sun energy-based methods present economic advantages, being for this reason largely used in tropical countries, the product quality parameters and food safety-related issues become often difficult to monitor and control. Osmotic, convective, fluidized bed, ohmic, microwave, vacuum or freeze-drying techniques have been applied for tomatoes dehydration. The foremost used drying techniques promote water vaporization from a food product by using heat through conduction, convection and radiation, being the formed vapor subsequently removed through forced air.

The demand for dried tomato is increasing rapidly both in domestic and international market with major portion being used for preparation of convenience food. And the reason of preparing dehydrated tomato powder also concerns the ease of transportation handling and storage without extra care. If powder can be prepared then it will help to reduce wastage, price and increase the availability of powdered tomato throughout the year [5]. The dehydrated tomato powder can also be used as substitute of raw tomato to develop new food recipe. Quality of dehydrated tomato powder was influenced by storage condition including packaging material during storage period, and subsequent storage of product in metalized polyester bags is suggested to protect product against light, oxygen, and humidity and retard the quality changes of tomato powder during storage period [6].

The drying process has also a crucial role in the chemical composition and nutritional value of final dried tomatoes. Chemical modifications subjacent to drying include Mail lard reactions, vitamins degradation, lipids oxidation, color changes and flavor losses. To prevent or minimize these alterations and maintain as high as possible the nutritional similarities with the fresh product, the tomatoes are often submitted to treatments before the drying process. Tomatoes are commonly subjected to various chemical and/or physical pretreatments prior to thermal drying to shorten the drying time, reduce the energy consumption and preserve the quality of products. In this review paper the authors try to provides an overview of the effects of different pre-treatments, dehydration methods and storage materials and conditions on the physicochemical, sensory and storage stability of tomato powder.

Tomato Productions

The tomato is warm season crop. Temperatures of 20-25°C are considered ideal for tomato cultivation, and tomatoes develop an excellent quality red color at temperatures of 21-24°C. Due to intense heat (temperature above 43°C), the plants get burnt, and flowers and small fruits also fall, whereas less than 13°C and greater than 35°C decreases the fruits and the red color production ratio. The tomato plant is a vine that grows approximately 180 cm above the ground. The plant is a dicot that grows in the form of a series of branching stems. The terminal bud is responsible for the actual growth. The vines are covered with short, fine hairs that turn into roots on coming in contact with the ground. Most of the plants have compound leaves while some have simple ones. The fruit of the plant is classified as a berry and is the part that is consumed. The fruit bears hollow spaces that are laden with seeds and moisture.

Tomato has been consumed since the ancient times. The Aztecs of South America used the fruit in their dishes as per evidence. By about 500 BC, tomato was already being cultivated in southern Mexico and a few other areas. The tomato plant was probably first introduced to Europe by the Spanish conquistador Hernan Cortes. Soon, it became a popularly cultivated crop across Europe and was also introduced to other parts of the world by European explorers and colonists.

Tomato is grown practically in every country of the world in outdoor fields, greenhouses, and net houses. China, India, the United States, Turkey, Egypt, Iran, Italy, Spain, and Brazil are the world’s leading tomato producers. China, the leading producer of tomatoes, accounted for 31% of the total production. In China, tomatoes are widely cultivated in open fields or plastic tunnels. In 2014, tomatoes accounted for 23% of total fresh vegetable output in the European Union. Of this, more than half was produced in Spain, Italy, and Poland. It covers approximately 4.73 million hectares and produces 163.96 million tons globally [52]. After potatoes and onions, it is the world’s third largest vegetable crop. Tomatoes are a vital vegetable crop in terms of both income and nutrition. In its fruit contain vitamins like A and C and antioxidant in abundance quantity. Tomato demand remains nearly constant throughout the year due to the unique properties contained in its fruit.

Nutritional and Health Importance of Tomato

Tomatoes contain numerous phytochemicals, the most wellknown of which is lycopene. In addition, other carotenoids (e.g., β-carotene, phytoene, phytofluene), phenolics (e.g., coumaric and chlorogenic acids, quercetin, rutin and naringenin), moderate amounts of the antioxidant vitamins and trace elements selenium and zinc, some sulfur compounds and other individual substancesare present (Table 1). Carotenoids are found in a wide variety of vegetables and fruits, but lycopene is more concentrated in tomatoes, guava, rosehip, watermelon, and pink grapefruit. Lycopene is a carotenoid pigment that is primarily responsible for the deep red color of ripe tomato fruits and tomato products. It is absorbed in the human body and is one of the most common circulating carotenoids. Other tomato carotenoids may also be bio available for our body. Many factors influence the bioavailability of lycopene and other carotenoids, including the nature of the food matrix, thermal processing, and the presence of fat. Of the phenolics, naringenin from tomatoes has been shown to be bioavailable, but data on other phenolics are lacking. Tomatoes are high in vitamins such as vitamin C and vitamin A equivalents (in the form of -carotene), as well as vitamin E, folic acid, potassium, and other trace elements.