Spray-dried tomato powder: reconstitution properties and colour

Abstracts

Powdered tomato was produced by spray drying the tomato pulp. A full 2³ factorial design with the central point was used, varying the feed flow rate (127-276 g/min), air inlet temperature (200-220ºC) and the atomisation speed (25,000-35,000 rpm). The responses analysed were: moisture content, solubility, wettability consistency and colour, but the factors only significantly affected the colour parameter. All the samples became significantly darker and less red with an increase of the variables under study. A low atomisation speed (25,000 rpm) and lower inlet air temperature (220ºC) produced the powders with a higher colour index (a/b) and less darkening.

spray dried tomato (Lycopersicon esculentum); colour; solubility; wettability

Tomate em pó foi produzido por secagem por atomização da polpa de tomate. Um planejamento 2³fatorial completo com ponto central foi conduzido variando a taxa de alimentação (127276 g/min), temperatura de entrada do ar (200-220ºC) e a velocidade de atomização (25000-35000 rpm). As respostas analisadas foram: conteúdo de umidade, solubilidade, molhabilidade, consistência e cor, ma os fatores somente afetaram significativamente a cor. Todas as amostras tornaram significantemente mais escuras e menos vermelhas com o aumento das variáveis sob estudo. Baixa velocidade de atomização (25000 rpm) e menor temperatura do ar de secagem (220ºC) produziram pós de maior índice de cor (a/b) e menor escurecimento.

FOOD SCIENCE AND TECHNOLOGY

Spray-dried tomato powder: reconstitution properties and colour

Alexandre Santos de Sousa^I; Soraia Vilela Borges^II,*; Natália Ferreira Magalhães^I; Hevandro Vaz Ricardo^I; Aline Damico Azevedo^I

^IDepartamento de Tecnologia de Alimentos; IT; UFRRJ; Km 47 da Antiga Rodovia Rio - SP; 23851-970; Seropédica - RJ - Brasil

^IIDepartamento de Ciência dos Alimento; UFLA; Campus Universitário; [e-mail]; 37200-000; Lavras - MG - Brasil

^IIISENAI; CETIQT; Rio de Janeiro - RJ - Brasil

ABSTRACT

Powdered tomato was produced by spray drying the tomato pulp. A full 2³ factorial design with the central point was used, varying the feed flow rate (127-276 g/min), air inlet temperature (200-220ºC) and the atomisation speed (25,000-35,000 rpm). The responses analysed were: moisture content, solubility, wettability consistency and colour, but the factors only significantly affected the colour parameter. All the samples became significantly darker and less red with an increase of the variables under study. A low atomisation speed (25,000 rpm) and lower inlet air temperature (220ºC) produced the powders with a higher colour index (a/b) and less darkening.

Key words: spray dried tomato (Lycopersicon esculentum), colour, solubility, wettability

RESUMO

Tomate em pó foi produzido por secagem por atomização da polpa de tomate. Um planejamento 2³fatorial completo com ponto central foi conduzido variando a taxa de alimentação (127276 g/min), temperatura de entrada do ar (200-220ºC) e a velocidade de atomização (25000-35000 rpm). As respostas analisadas foram: conteúdo de umidade, solubilidade, molhabilidade, consistência e cor, ma os fatores somente afetaram significativamente a cor. Todas as amostras tornaram significantemente mais escuras e menos vermelhas com o aumento das variáveis sob estudo. Baixa velocidade de atomização (25000 rpm) e menor temperatura do ar de secagem (220ºC) produziram pós de maior índice de cor (a/b) e menor escurecimento.

INTRODUCTION

The production of dry particles from a liquid feed in a single processing step makes the spray drying a unique and important unit operation. The design of a spray drying process includes the establishment of the operating conditions that increase the product recovery and produce an end product with a precise quality specification (Masters, 1991). The temperatures and drying conditions experienced by a droplet during the drying have an important influence on the powder properties (Masters, 1991). However, the effect of the process variables (e.g. the residence time of particles within the drying chamber, the atomisation conditions, the drying air temperature) on the powder properties are difficult to assess in general terms (Walton, 2000). This is due to a lack of information in the literature and to the specific drying nature of most materials.

Consumer demand for high quality, minimally processed products has increased remarkably in recent years. Preferences have shifted towards the fresh, healthy and rich flavoured ready-to-eat foods with an enhanced shelf life. Tomato powders are often used as an ingredient in the foods such as sauces and soups. Several food technology studies have been carried out to optimise the processing and storage of the tomato products by preventing the heat and oxidative damage on the antioxidants (Shi and Le Maguer, 2000). On the other hand, a useful optimisation criterion requires a global approach that includesall the quality characteristics of the tomato products. Hence, it is necessary both to minimize the damage to the sensory and nutritional quality and to maximize the safety and shelf life of the products.

Tomatoes are one of the most widely used and versatile vegetable crops. They are consumed fresh and are also used to manufacture a wide range of processed products (Madhavi and Salunke, 1998).Tomatoes and tomato products are rich in health-related food components, as they are good sources of carotenoids (in particular, lycopene), ascorbic acid (vitamin C), vitamin E, folate, flavonoids and potassium (Leonardi et al., 2000). The main antioxidants in the tomatoes are the carotenoids, ascorbic acid and phenolic compounds (Giovanelli et al., 1999).

The colour of foods is one of the most important sensory attributes for the product acceptance. Lycopene is responsible for the red colour of the tomatoes (Nguyen and Schwartz, 1999) and can be degraded by the thermal processing. During the spray drying, this property can be affected by the air conditions (temperature, flow rate), feed conditions (enzyme inactivation, additives, feed rate), and atomisation speed, amongst other factors (Masters, 1991; Desobry et al., 1997; Cai and Corke, 2000). Kalil and Sial (1974) studied the effect of these aspects with respect to the spray drying of the mango juice, and showed that the atomisation speed (40,000-50,000 rpm) had little effect on the colour. Abadio et al. (2004) also found insignificant variation in the values for a* and b* of the powdered pineapple juice. Goula and Adamapoulos (2005b) showed that the loss of lycopene increased with increases in air inlet temperature.

According to Desobry et al. (1997), the conditions favouring a high surface/volume ratio or a larger number of smaller particles tend to favour the pigment oxidation. In the case of spray drying, these conditions are favoured by high temperatures and atomisation speeds (Masters, 1991). The instant properties (penetration, wetting, dispersibility, solubility) are influenced by the nature of the feed (solids content, viscosity and temperature), type of spray dryer, operational speed and pressure and air inlet and outlet temperatures (King et al. 1984; Hall and Iglesias, 1997; Nath and Sapthy, 1998). Increases in the atomisation speed resulted in a reduction in the particle size and air incorporation in the feed, resulting in the porous products with low apparent density (Pisecky, 1978), making re-hydration more difficult (Maia and Golgher, 1983). The solubility of the powder is associated with the moisture content and operational conditions of the dryer, increasing with decrease in the moisture content (Papadakis et al., 1998; Goula and Adamopoulos, 2005a). The main objective of this study was to determine the effects of the spray dryer operational conditions on the moisture content, solubility, consistency wettability and colour index.

MATERIAL AND METHODS

Tomato pulp (brand KARAMBI, Brazil) was blended with 10DE malt dextrin (10% dm) and SiO₂ (1% dm), and spray dried in a pilot scale spray dryer (home made / DTA, UFRRJ, Brazil). The drying chamber was 2.5 m in diameter, 1.40 m cylindrical height and a conical base. All the internal surfaces in the contact with the product were of stainless steel AISI 316. It was equipped with a control panel (control of the atomizer speed, blower velocity and air inlet temperatures), rotary atomiser and gas burner. The feed was sprayed by a rotary atomiser and the co-current air entrance was carried out by a blower. The constant operational conditions were: outlet air temperature: 90ºC; blower velocity: 30,000 rpm. The variables atomisation speed (AS), feed flow rate (Q) and inlet temperature (T) were studied according to a complete 2³ factorial design, with three repetitions at the central point (Table 1). The powdered samples were filled into the low-density polyethylene pouches and stored at 10ºC until analysed. The results were submitted to an analysis of variance and the effect estimates (Barros Neto et al, 1995) using the statistical software STATISTICA 5.0.

The colour was measured in a spectrophotometer, (model CM-3600d, KONICA MINOLTA, NJ, USA), eight times for each sample. The CIE L*a*b colour space was used for the determination of the colour, with L* representing the lightness (0-black to 100-white), +a* the red direction, -a* the green direction, +b* the yellow direction, and b* the blue direction. The colour index was calculated from the relation of a/b. The solubility was determined by homogenisation, centrifugation and determination of the insoluble residue from the dissolution of 1g of the powdered juice in 10ml distilled water at 25°C, according to the methodology adopted by IAL (1977). The consistency was measured at 25°C using a consistometer (Alpári, 1976) and wettability was based on the time for immersion of the powdered product sprinkled on the surface of a liquid at 25°C (Bhandari et al., 1993). The moisture content (vacuum oven at 70°C) according to IAL (1977).

RESULTS AND DISCUSSION

Tables 2 and 3 present the assay results and the evaluation of the effects of the variables studied on the reconstitution properties and colour parameters. The results showed that the levels of the variables under the study did not the influence the moisture content, solubility, wettability and consistency. The value for the moisture content varied from 4.00 to 6.8 g/100g (dry matter), higher than the values found by Al Asheh et al, 2003 (3-1%) for the tomato powder in other drying conditions. However, in general, it was reduced by the increase of the inlet air temperature and of the atomization speed (Masters, 1991; Al-Asheh et al., 2003; Adamopoulos, 2005).

The values for the solubility were from 17.65 to 26.73%, low values when compared to the powdered tropical fruits, which shown values varying from 44.6 to 57.59%, for the passion fruit juice (Jorge et al., 2003) and 81.56% for the pineapple juice (Abadio et al., 2004). Thus, the tomato powder was of limited solubility in the water due to a low sugar content as compared to most fruits, and because it was rich in the liposoluble substances such as the carotenoids. This property has inversely been correlated with the moisture content, as lower moisture content favours a fast solubilization (Papadakis et al., 1998). Such relationship was found by Al Asheh et al (2003) and Goula and Adamopoulos (2005a) in the dehydrating tomato pulp studies, using the referred process. In the conditions used in the present study, both the properties were kept constant, and no significant correlation was found. This property was also related to the effects of the drying conditions on the degradation of the nutritive value due to the time of exposure to high temperatures. Smaller particles produced by the high-speed atomisation tend a to reach the higher temperatures at the surface (Perez - Muñoz and Flores, 1997) and were therefore, more sensitive to thermal damage and the loss of solubility. In relation to the feed flow rate, the Asheh et al (2003) also observed a loss of the solubility with increasing flow rate, and credited this to the increasing diffusion of the solute through a concomitant increase in particle size.The values for the wettability were from 10.00 to 15.00 g/min. Borges et al. (2002) found a value for the wettability of the powdered passion fruit juice of 0.192 g/min, less than the values found for the tomato powder. This property was improved by increasing the maltodextrin concentration (Bhandari et al., 1993) and by increasing the air exit temperature (Borges et al., 2002).

The value for the product consistency varied from 19.5 to 21.5 cm and also suffered no significant influence from the variables under study. The results showed that the Bostwick values for the reconstituted powder were higher than those of tomato pulp with the same concentration of the soluble solids (1.9 cm), that is, less consistent, showing greater leakage in the consistometer. A significant change in the consistency characteristics occurred, in agreement with Thakur et al. (1996), who observed that the processing caused a higher reduction in the viscosity as compared to the raw mashed tomato. This was partially caused by the heat or enzymatic degradation of the pectin. Henig and Manheim (1971) found tomato powder consistency values from 15.3 to 23.0, similar to the values found in this study.

The values for the colour index were in the range relations could be expressed by equations 1 and 2, from 0.9595 to 1.1677, considering that the inlet considering X3=0 and X2=0, respectively, giving drying air temperature and the atomisation speed a good fit with the experimental data (R²=0.9358 showed significant effects on this property. These for the two equations).

These models are represented by Fig. 1 and 2, respectively.

The a/b colour index for the tomato powder current study. Anguelova and Wathersen (2000) increased with decrease in the inlet temperature found a loss of 30 to 40% of lycopene in the spray (Fig. 1) and with decrease in atomisation speed dried tomato powder, this being the main pigment (Fig. 2). According to Shi et al (1999) the colour responsible for the red colour of the product. They retention in the tomato products was better at low attributed this loss to the oxidation of the product temperatures, and these authors found values for due to the use of high temperatures. Goula and the a*/b colour index of the dehydrated tomato to Adamapoulos (2005b), using lower inlet air the order of 1, 2, a value close to that found in the temperatures (110-140ºC), found a loss of 9 to 16%. Francisconi et al (2003) also observed a fall in the a* and b* values for the powdered passion fruit juice at higher atomisation speeds, because higher atomisation speeds produced smaller particles, which, when exposed to heat, tened to intensify the oxidation.

Lightness was also affected by the atomisation speed and inlet temperature, these relations being expressed by equations 3 and 4, considering X3=0 and X1=0, respectively, which had a good fit with the experimental data (R²=0.99 for the two equations).

These models were represented by Fig. 3 and 4, respectively, and indicated that increasing the atomisation speed and the inlet temperature cause an increase in the L values, resulting in a lighter product, this also being due to the pigment oxidation, as previously discussed. Francisconi et al. (2003) and Abadio et al. (2004) also observed higher lightness for the dehydrated fruits with increasing atomisation speed. Shi et al. (1999) found an L value for the dehydrated tomato in the range of 38, 40, smaller than the values found in this work.

In order to preserve the tomato powder colour and good reconstitution properties, the use of an atomisation speed of 25,000 rpm and an inlet temperature of 200ºC is recommended.

ACKNOWLEDGMENTS

We thank to FAPERJ for financial support in the restoration of the spray dryer and also to Food Karambi, Corn Products Brazil and Arinos Chemistry for supplying the raw material and additives.

Received: May 12, 2006;

Revised: March 29, 2007;

Accepted: March 24, 2008.

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*

Author for correspondence

Publication Dates

• Publication in this collection
  26 Aug 2008
• Date of issue
  Aug 2008

History

• Accepted
  24 Mar 2008
• Reviewed
  29 Mar 2007
• Received
  12 May 2006