Effect of Infusion Method and Parameters on Solid ... - PubAg - USDA

Food Bioprocess Technol (2009) 2:271–278 DOI 10.1007/s11947-008-0116-4

ORIGINAL PAPER

Effect of Infusion Method and Parameters on Solid Gain in Blueberries Junling Shi & Zhongli Pan & Tara H. McHugh & Edward Hirschberg

Received: 22 November 2007 / Accepted: 24 June 2008 / Published online: 15 July 2008 # Springer Science + Business Media, LLC 2008

Abstract In order to obtain optimal processing conditions for producing infused blueberries with high solid gain, we investigated the infusion characteristics of blueberries under various processing parameters in sugar solutions with 1:1 ratio of solution and berries. Static batch constant concentration infusion and dynamic batch infusion (DBI) were tested as the alternative operations for the traditional static batch infusion. The studied parameters were solution temperature (25 to 70 °C), concentration (20 to 70°Brix), and types of osmotic agent (fructose, dextrose, polydextrose, sucrose, maltodextrin, and corn syrup). The results showed that high solid gain can be achieved by maintaining high and constant concentration of infusion solution at high temperature with dynamic infusion. For DBI, high temperature and high solution concentration resulted in fast and high solid gain. The rate of water loss increased with an J. Shi College of Food Science and Engineering, Northwest A&F University, 28 Xinong Road, Yangling, Shaanxi 712100, China Z. Pan (*) : T. H. McHugh Processed Foods Research Unit, USDA-ARS-WRRC, 800 Buchanan St., Albany, CA 94710, USA e-mail: [email protected] J. Shi : Z. Pan Biological and Agricultural Engineering Department, University of California, One Shields Avenue, Davis, CA 95616, USA E. Hirschberg Innovative Foods Inc., 175 South Spruce St., South San Francisco, CA 94080, USA

increase in solution temperature and concentration. To obtain high quality sugar-infused products with high product yield, a DBI process of 50 °C and 50°Brix sugar infusion is recommended, which could have solid gain of 1.65 g/g after a 5-h infusion. Polydextrose showed higher solid gain than sucrose when infusion time was longer than 180 min, although it had lower solid gain in short-term infusion. Keywords Blueberries . Infusion . Mass transfer . Osmotic dehydration . Temperature

Introduction Blueberries (Vaccinium) are a rich source of antioxidants such as anthocyanins that protect against such diseases as memory loss, cancer, heart disease, urinary disease, vision problems, and aging (Sweeney et al. 2002; Schmidt et al. 2004; Wu et al. 2004; Kalea et al. 2005; Norton et al. 2005). Due to short shelf life of fresh blueberries, after they are harvested in fields, blueberries are usually subjected to freezing immediately and then to sugar infusion and drying subsequently to extend the shelf life of the product. Sugar infusion is widely used for process of blueberries because it can remove a large amount of water without heating, introduce sugar into fruits, and result in high yield and improved taste of final products (Lenart and Flink 1984; Li and Ramaswamy 2006; Nsonzi and Ramaswamy 1998). The infusion process involves both solid gain and water loss, which is also called osmotic dehydration. The terms of infusion and osmotic dehydration will be used interchangeably in this study. For application purpose, however, the focuses of infusion and osmotic dehydration are to obtain high product yield and maximum amount or high rate of

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water removal from fruits, respectively. The infusion aspect is the focus of this study. Dried products obtained through infusion process can be served as snacks or food ingredients for bakeries, tea, or capsules. Osmotic dehydration is the process of water removal by immersion of a water-containing cellular solid in a concentrated aqueous solution. A flux of water out of the food and of other solutes into the foodstuff develops due to the difference in osmotic pressure. The product thus loses water and gains solid from the external solution. Therefore, it is being widely used to reduce the water content of many fruits and vegetables (Lenart and Flink 1984; Li and Ramaswamy 2006). For achieving high yield of final product, the kinetics of solid gain is more important than that of water loss. Kinetics of water loss in osmotic dehydration has been extensively studied for many fruits, including blueberries (Nsonzi and Ramaswamy 1998; Dermesonlouoglou et al. 2005; Genina-Soto and Altamirano-Morales 2005; Sodhi and Komal 2006). Some patents are also available for processing shelf-stable semi-dried fruits by using osmotic infusion (Brimelow and Brittain 1980; Christopher and Brittain 1980; Amhers et al. 1985). In osmotic dehydration or infusion, the removal of water is mainly by diffusion and capillary flow, whereas solute uptake or leaching is only by diffusion. The mass transfer can be influenced by many factors including the concentration and temperature of infusion solution, properties of infusion agents, infusion methods, the ratio of food mass and infusion solution, and physicochemical properties of food materials (Islam and Flink 1882; Farkas and Lazar 1969; Hawkes and Flink 1978; Lerici et al. 1985; Shi 2003; Li and Ramaswamy 2006). It also determines the solid gain and final product yield. High temperature, high solute concentration, small osmotic agents, and stirring operation can speed up the mass transfer between the solution and food stuff (Islam and Flink 1882; Farkas and Lazar 1969; Hawkes and Flink 1978; Lerici et al. 1985; Shi 2003; Li and Ramaswamy 2006). The effect of processing parameters such as temperature and concentration of infusion solution, infusion method, and infusion agents on the infusion processing characteristics, especially for achieving high solid gain, of blueberries have not been well studied, and available literatures are limited (Nsonzi and Ramaswamy 1998). Previously reported research used high ratio of solution and food for infusion, which did not reflect the commercial infusion practice using the low ratio. In this research, to simulate the commercial practice, the 1:1 ratio of solution (volume) and blueberries (mass) has been used for achieving high solid gain. The objective of this study was to investigate infusion characteristics of blueberries under various processing

Food Bioprocess Technol (2009) 2:271–278

conditions, including temperature and concentration of infusion solution, infusion agents, and infusion method.

Materials and Methods Blueberries Blueberries used in the study are individual quick-frozen blueberries of the Patriot variety with weighted average diameter of 14 mm and 85% (wb) of moisture content. The blueberries were obtained from Gladwin Farms (Abbotsford BC, Canada). Frozen blueberries were thawed at 4 °C for 12 h, warmed up at room temperature for 2 h, and blotted with tissue paper to remove free water on the surface before sugar infusion. All experiments were replicated for two times, and the mean values are reported. Experimental Design Effect of Constant Solution Concentration Batch processing is widely used for infusion in food industry. However, during the infusion processing, the concentration of infusion decreases with the increased time, resulting in reduced product yield and prolong infusion time. In this part of tests, we studied the infusion characteristics with different initial concentrations under static condition (without agitation), which is called static batch infusion (SBI) in this study. To compare the results, a set of experiments with relatively constant concentrations were also carried out. The constant concentration was achieved by transferring blueberries into a new solution with the original concentration every 1 h during the infusion. The process is named as static batch constant concentration infusion (SBCCI). For both SBI and SBCCI, three different concentrations of sucrose solution, 40, 60, and 77°Brix were used for the tests at 60 °C. For each test, a sample of 50 g blueberries was placed in a 50-ml sugar solution in a 200 ml plastic bottle [in ratio of 1:1 (w/v)]. The bottle along with the sample was put into a water-bath shaker (New Brunswick Scientific, Model R-76, Edison, NJ, USA) without shaking for different infusion time periods from 2 to 8 h. Effect of Dynamic Infusion In order to enhance the rate and solid gain in blueberries during the infusion, dynamic batch infusion (DBI) and high temperature constant infusion concentration were tested. The dynamic infusion was carried out in the water-bath shaker with constant shaking at 120 strokes per minute.


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Static batch infusion and static batch constant concentration infusion were also tested for comparison. The detailed test conditions are listed in Table 1. Infusion Characteristics Under Dynamic Infusion with Various Temperature and Concentrations Based on our results, the dynamic batch infusion had high infusion rate. To further study the infusion characteristics of blueberries, a series of tests was conducted under dynamic batch infusion. The tested infusion temperatures were 25, 40, 50, 60, and 70 °C, and the solution concentrations were 20, 30, 40, 50, 60, and 70°Brix. Infusion Characteristics of Various Agents Under Dynamic Infusion To study the effect of infusion agents, monosaccharides, disaccharides, and polysaccharides were tested at 30 °C. The six different infusion agents used were monosaccharides (fructose and dextrose), a disaccharide (sucrose), and polysaccharides (polydextrose, corn syrup, and maltodextrin). All the agents were supplied by the Tate & Lyle (Decatur, IL, USA). The dextrose equivalent was 9% to 12% for maltodextrin and 42% to 45% for corn syrup. The polydextrose was a polymer consisting of ten glucose molecules with residual dextrose less than 4.0% and sorbitol less than 2.0%. All infusion agents were made into 60°Brix solutions for infusion. Sampling and Measurements After the samples reached a desired infusion time, the blueberries were removed from the infusion bottles and rinsed immediately with tap water (25 °C) for 30 s on a metal mesh. The original and final weights of the blueberries and solution were recorded. Soluble solid contents of the residual solution and infused blueberries were measured with ABBE refractometer (American Optical, NY, USA) using the method of Association of Official Table 1 Tests of infusion methods Infusion methods

Dynamic batch infusion (25 °C) Static batch infusion (25 °C) Static batch infusion (60 °C) Static batch constant concentration infusion (60 °C)

Solution Infusion concentration temperature (°Brix) (°C) 60 60 60 60

25 25 60 60

Analytical Chemists (AOAC) 990.35. The water content and water activity of blueberries were also measured. The water activity was determined with a water activity meter of Decagon Aqualab CX-2 (Decagon Devices, Pullman, WA, USA). Water content was determined by using the vacuumoven AOAC method 926.08. The solid gain and water loss of blueberries were calculated using the equations: SG ¼

Mt ð1 MCt Þ M0 ð1 MC0 Þ M0 M0 MC0

ð1Þ

WL ¼

M0 MC0 Mt MCt M0 M0 MC0

ð2Þ

Where SG is the solid gain per initial dry solid (g/g dry solid), and WL is the water loss per initial dry solid (g/g dry solid). M and MC are the wet weight of blueberries (g) and moisture content on wet basis (g/g), respectively. Subscripts of t and 0 indicate the value at time t and the initial value, respectively. Solid gain (SG) and water loss (WL) represent the total amount of solid absorbed by and the moisture loss from the blueberries after infusion for a certain time. They were expressed on the basis of initial dry weight of blueberries. A high solid gain means a high product yield which is desirable for many commercial applications. All data were analyzed using the software of Microsoft Office Excel 2003, and the average values are reported. The analysis of variance was done by using Turkey analysis method with the software of SPSS 11.5 for windows (SPSS, Chicago, IL, USA).

Results and Discussion Effect of Constant Concentration As expected, for both SBI and SBCCI, high solution concentration resulted in high yield and high rate of solid gain in blueberries. SBCCI had much quicker and higher soluble solids in blueberries than SBI (Fig. 1). For SBI, the soluble solids increased slowly, which indicated the low infusion rate due to the decrease in osmotic pressure that is resulted from the increase in water and decrease in sugar in the solution. However, when the infusion solution was kept at a constant level, the infusion rate increased significantly compared with the regular batch process (Fig. 1 and Table 2). The degree of increase was related to the concentration of solution. For SBCCI with 77°Brix sucrose solution, soluble solids in blueberries reached 60°Brix at about 240 min infusion,

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Fig. 1 Soluble solids of blueberries with static batch infusion (SBI) and static batch constant concentration infusion at 60 °C

which was compared with only 35°Brix soluble solids after 300 min infusion for SBI. At the 360 min of infusion, the solid gains were 0.95, 1.54, and 3.08 g/g under SBCCI and 0.36, 0.47, and 0.86 g/g under SBI for solution concentrations of 40, 60, and 77°Brix. The results indicated that using high solution concentration and maintaining the concentration during infusion are essential to achieve high solid gain in end products with minimized infusion time. Effect of Dynamic Infusion When dynamic infusion was tested, the soluble solids in blueberries significantly increased, especially at the early infusion stage which resulted in high solid gain in the infused products (Fig. 2). At the end of infusion process, the solid gain from dynamic batch infusion was 1.3 times higher than the SBI. This is because during infusion, the solute tends to accumulate on the surface and in the tissue cells under the surface of fruits. It could form a barrier of the mass transfer between the fruits and infusion solution and reduce the infusion rate. The dynamic infusion could

Table 2 Turkey analysis of the solid gain after infusion for 360 min at 60 °C with different infusion conditions Infusion condition SBCCI-77°Brix SBCCI-60°Brix SBCCI-40°Brix SBI-77°Brix SBI-60°Brix SBI-40°Brix

Mean value of solid gain (g/g) 3.08 1.55 0.95 0.86 0.47 0.36

Significance at α=0.05 level a b c c d d

SBCCI Static batch constant concentration infusion, SBI static batch infusion

Fig. 2 Soluble solids of blueberries under different infusion methods (DBI dynamic batch infusion; SBI static batch infusion; SBCCI static batch constant concentration infusion)

break or reduce the barrier, which resulted in increased infusion rate. Table 3 shows stirring operation without increasing temperature (DBI, 25 °C) could increase the solid gain to a similar level as increasing solution temperature to 60 °C from 25 °C when SBI is used. Combination of increasing temperature to 60 °C and constantly keeping solution concentration at high level (60°Brix) showed the highest solid gain. Therefore, to obtain high solid gain with reduced infusion time, dynamic infusion, keeping solution concentration at high and stable level, and increasing solution temperature are recommended. However, there are some concerns about the application of dynamic infusion which could cause breaking of fruits (Ponting et al. 1966). Breaking of fruits was also found when temperature was higher than 50 °C in this study (data not shown). Some other efforts have also been reported in some patents to keep the solution flowing and solution concentration stable (Brimelow and Brittain 1980; Christopher and Brittain 1980; Amhers et al. 1985). The solution was pumped through a membrane concentration system to reduce the resistance of mass transfer. However, contamination and Table 3 Turkey analysis of the solid gain after infusion in 60°Brix sugar solution for 360 min with different infusion conditions Infusion condition SBCCI-60 °C DBI-25 °C SBI-60 °C SBI-25 °C

Mean value of solid gain (g/g) 1.55 0.49 0.47 0.24

Significance at α=0.05 level a b b c

SBCCI Static batch constant concentration infusion, DBI dynamic batch infusion, SBI static batch infusion


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Fig. 3 Soluble solids of blueberries and solution during DBI infusion under different conditions

energy consumption were concerns in the operation. Therefore, gentle stirring of the solution might be an effective method. Infusion Characteristics Under Dynamic Infusion with Various Temperature and Concentrations During the first few hours of infusion, the solids decreased in the solution and increased quickly in blueberries, and then rates of changes decreased in the late stage of infusion (Fig. 3). The increase in soluble solids in blueberries was caused by both solid gain and water loss of blueberries. At the late stage of infusion, soluble solid content in blueberries was even higher than that in solution for some cases Fig. 4 Water loss of blueberries during DBI infusion with different temperatures and solution concentrations

because the solid state in blueberries had different properties in keeping water and solutes (Mujaffar and Sankat 2006). The water loss data also showed that in the early stage of infusion, the rate of water loss was very high compared with the change in soluble solids or solid gain in blueberries (Fig. 4). This indicated that dehydration effect in the early infusion stage was significant. High temperature and concentration of infusion solution resulted in faster sugar infusion and decrease in moisture content and water activity of blueberries compared with low temperature and concentration infusion (Figs. 5 and 6). The increase in water loss with the increase in solution concentration was also reported for the osmotic dehydration of blueberries at high ratio of solution and berries (Nsonzi

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Fig. 5 Moisture content of infused blueberries during DBI infusion with different conditions

and Ramaswamy 1998). It was explained that the solute could not diffuse as easily as water through the cell membrane at high temperature, and thus, the approach to osmotic equilibrium could be achieved primarily by flow of water from the cell (Rahman and Lamb 1990). Only high concentration (60 and 70°Brix) and high temperature (60 and 70 °C) could produce the product with moisture content lower than 0.6 g/g. All samples produced in the tests had water activities higher than 0.9. Therefore, the infused products need to be further dried to produce shelf-stable products. The trend on solid gains was similar to the change of soluble solids in blueberries, which was significantly influFig. 6 Water activity of infused blueberries during DBI infusion with different conditions

enced by both temperature and concentration of infusion solution (Fig. 7). The highest solid gain, 2.5 times of the original solid weight, was obtained with 70 °C and 70°Brix. This is different from what happened in solutions with solution-to-food mass ratio of 20:1, in which solid gain was less affected by temperature (Rahman and Lamb 1990). The reason was that temperature had more effect on viscosity in the low-ratio infusion than the high-ratio infusion. The solution concentration and temperature showed interaction on the mass transfer of sugar infusion of blueberries. For concentration higher than 50°Brix, soluble solids changed slightly when temperature was lower than


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Fig. 7 Solid gain of infused blueberries during DBI infusion with different conditions

50 °C compared with the temperatures at 60 and 70 °C. However, there was a heavy cooking smell and undesirable appearance of infused blueberries when the solution temperature was higher than 50 °C. For DBI, therefore, 50°Brix and 50 °C are recommended as the optimal solution concentration and temperature for efficiently and economically processing high-quality sugar-infused blueberries with maximum solid gain of 1.65 g/g in the tests. Solution concentrations higher than 60°Brix was not recommended since it did not show significant increase in solid gain at low temperature infusion. Infusion Characteristics of Various Agents Under Dynamic Infusion At same level of soluble solids content, monosaccharide, including dextrose and fructose, resulted in higher rate in solid gain and decrease in water activity compared with disaccharide and polysaccharides including polydextrose, Fig. 8 Soluble solids (a), water activity (b), and solid gain (c) of blueberries infused with different agents

corn syrup, and maltodextrin (Fig. 8). This agrees with the principle of osmosis which is related to the molecular weight of solute in infusion solution. The rate of water loss from the berries to the infusion solution with large molecular weight solute is lower than that of the solution with small molecular weight solute when both solutions are at the same mass concentration. It has been observed that maltodextrin might not be suitable for infusion of blueberries since it was easy to deposit on the surface of blueberries and thus inhibited the mass transfer between the fruit and solution. There was a layer of white maltodextrin sedimentation on the blueberries after the infusion, and the yield of dried infused blueberries was low. Fructose yielded the best product quality which was soft and sweet after heat drying following the infusion. Blueberries infused with sucrose were slight firmer than fructose-infused product. Corn syrup-, polydextrose-, and dextrose-infused blueberries had similar sweetness, but they were less sweet compared

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to fructose- and sucrose-infused products. Corn syrup yielded softer products than the other two agents. In general, fructose can be considered as the best infusion agent for blueberries. The appropriate infusion time should be 4 to 5 h to obtain high solid gain. To improve the infusion process and reduce the cost of infusion agents used, mixture of agents or step infusion with different agents could be used. For example, based on the profiles of soluble solids and solid gain, sucrose can be used for the early stage infusion (first 60 min), and then dextrose and fructose can be used in the later stage. After 60 min, fructose could be added or used.

Conclusions Temperature and concentration of osmotic solution had great influence on the osmosis characteristics of blueberries in sugar infusion. There is an interaction between temperature and solution concentration to the solid gain. High temperature and concentration resulted in fast solid gain but slow water loss in blueberries. Solutes with small weight size had high solid gain and significant decrease in water activity. Dynamic infusion speeded up the sugar infusion in blueberries and resulted in fast and high solid gain. Dynamic infusion was more effective than increasing temperature for increasing solid gain of blueberries in sugar infusion. Constant high concentration infusion also resulted in high rate and value of solid gain. To achieve high quality product with high solid gain, dynamic operation with stable solution concentration or DBI with 50 °C and 50°Brix solution is recommended as the optimal condition for sugar infusion of blueberries. Acknowledgements The authors thank Don Olson, Western Regional Research Center, USDA-ARS, for his support in the experiments and partial financial support from Innovative Foods Inc. under the USDA ARS CRADA No. 58-3K95-5-1089. The research was conducted at the Western Regional Research Center, USDA-ARS, and the Department of Biological and Agricultural Engineering, University of California, Davis.

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