Effect of the Processing Steps on Cactus Juice

Food Bioprocess Technol DOI 10.1007/s11947-013-1098-4

ORIGINAL PAPER

Effect of the Processing Steps on Cactus Juice Production Taiana Maria Deboni & Márcia Bündchen & Celio Volpi Junior & Dachamir Hotza & Raquel Piletti & Mara Gabriela Novy Quadri

Received: 11 December 2012 / Accepted: 18 March 2013 # Springer Science+Business Media New York 2013

The Cereus hildmannianus K. Schum juice was obtained by enzymatic and mechanical treatments, both followed by a pasteurization process. The effects caused by these processes were evaluated considering physicochemical and histological properties, as well as its rheological behavior. When compared with mechanical treatment, enzymatic treatment was responsible for yields increase (up to 22 %), viscosity decrease, and suspended solids content. When associated with heat, enzymatic treatment increased the soluble solids concentration, as well as their pH level, promoting viscosity reduction if compared with the mechanical treatment. Histological evaluations showed gradual degradation of cells and mucilage, as the juice processing steps proceeded. The non-Newtonian behavior of the “in natura” pulp and the juice obtained by mechanical treatment have been well described by the Casson and Bingham models, respectively. The enzymatically treated juice behaved as Newtonian fluid. All samples showed a reduction in the viscosity levels when subjected to higher temperatures, as described by the Arrhenius-type equation: the activation energy varied from 3.8 to 4.5 kcal mol−1. Sensory analysis of pure Cereus h. juice and its mix with traditional orange and lime juices were well accepted by the surveyed audience, and the addition of the cactus juice was easily perceived by those who participated in the research.

Abstract

T. M. Deboni : C. V. Junior : D. Hotza : R. Piletti : M. G. N. Quadri (*) Chemical and Food Engineering Department, Universidade Federal de Santa Catarina (UFSC), Campus Universitário, Trindade, P. O. Box 476, 88040-900, Florianópolis, Santa Catarina, Brazil e-mail: [email protected] M. Bündchen Ciência e Tecnologia do Rio Grande do Sul, Instituto Federal de Educação, Rua Cel Vicente, 281, 90030-040, Porto Alegre, Rio Grande do Sul, Brazil

Keywords Enzymatic treatment . Pasteurization . Rheology . Chemical analysis . Modeling . Cactus

Introduction The fruit juices market has substantially grown in recent years mainly due to the trend involving naturally healthy foods. Consumers are not only looking for top-quality products, they are also in search of new, exotic flavors (Vendrúsculo and Quadri 2008; Sabbe et al. 2009). Based on that, many products which had not been considered by the food industry up until some time ago, have now become raw material for juices. An example of that is the cactus fruit. Cactaceae plant family present high mucilage content, which is considered a dietary fiber. Mucilage is associated to several positive effects in the human body, such as the control of cholesterol and glucose levels, the reduction of chronic constipation, and the decreased risk for the development of some cancer types (Cecchi 2003; Sáenz et al. 2004). Many industrialized juices have no fibers in their composition since the presence of fiber depreciates its appearance in most cases. Cereus hildmannianus K. Schum’s fruit, from the Cactaceae plant family, is rich in mucilage, potassium, and calcium, with low sodium levels and no lipids, which makes it suitable for special diets (Porto 2009). Little is known about the Cereus genus. No reports about it have been found in the literature so far. There is also no information about its juice. What is recently known, though, is that there is about 2,000 small seeds in each unit of the Cereus genus fruit (Bündchen et al. 2009), as well as high mucilage content and viscosity levels (Porto 2009)—which poses a number of difficulties when it comes to transforming it into juice. The most traditional way of processing pulps is the use of depulpers which squeezes the raw material. Although, in the case of the Cereus h., the seeds are neither great nor

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strong, and this procedure results in a juice containing pieces of smashed seeds. Viscosity’s elevated level makes it hard to separate the seeds from the fruit’s liquid form. As this paper shows, the use of enzymatic and/or mechanical treatments promote the disintegration of the vegetable tissues (Vendrúsculo and Quadri 2008; Abdullah et al. 2007). These methods are mainly used to extract juice from the pulp, resulting in products with greater or lower viscosity levels, depending on the adopted method and the chosen vegetable. The analysis of physicochemical and rheological properties are not just a quality measure, they are essential to the designing process and the industrial installations (Rai et al. 2005; Chin et al. 2009). The juice’s rheological behavior is strongly affected by its qualitative and quantitative compositions; therefore, this result depends on the fruit types and treatments to which they are subjected to during the manufacturing process (Vandresen et al. 2009). Plant-based food suspensions consist of particles from triturated vegetable tissue in a continuous serum phase; their behavior is determined by particle properties which affect the rheology. However, only a few reports consider the influence of the processing steps on rheology (Vendrúsculo and Quadri 2008; Vandresen et al. 2009; Jaeger et al. 2012) and specially the evaluation of the physical modification of the solids microstructure in such plant suspensions. Different equations have been used to describe the rheological behavior of fluid food, and the simplest flow type is Newtonian. However, most fluid foods require more complex mathematical descriptions for their characterization. The most commonly rheological models are those of Ostwald-De-Waele, Bingham, and Casson (Holdsworth 1971; Vitali and Rao 1984). In addition, temperature is one of the most important influenceable parameters for the rheological behavior of food (Maceiras et al. 2007). The effect of temperature on apparent viscosity is generally described by an Arrhenius-type equation (Rao and Anantheswaran 1982). The objective of this study was to evaluate the effect caused by different processing steps on the Cereus h. K. Schum’s juice, characterized by the physicochemical, rheological, histological, and sensory properties.

packed and stored at a temperature of −4 °C until further analysis. Two different methods were used in the process of separating the pulp from the seeds (Quadri et al. 2012). The first one applied was mechanical and consisted in magnetically shacking a predetermined pulp sample at a 1,200-rpm speed for 40 min. The action decreased the fruit’s viscosity and facilitated the removal of its seeds. The juice from it was then centrifuged at a speed of 3,600 rpm for 20 min and then filtered through a 100-mesh cloth filter. The second method consisted in treating the pulp with Pectinex Clear and Cellubrix (Novozymes, Denmark), with a 0.004 % enzyme concentration. Pectinex Clear is a mixture of the polygalacturonases and pectin lyases enzymes, produced by Aspergillus aculeatus and Aspergillus niger; whereas, Cellubrix is made of cellulose enzymes produced by Trichoderma reesei. In this case, the pulp sample was kept at room temperature for 25 min, after which the enzymes were inactivated by heating at 90 °C for 5 min in a water bath (Lee et al. 2006). All of it was followed by centrifugation at a speed of 3,600 rpm for 20 min and vacuum filtration. Thermal treatment was applied to both samples in accordance to the recommended conditions by Carrandi (1995): 100 °C temperature for a period of 20 min. Sample aliquots were removed after each step of the process, and analysis was carried out. A schema of the process is shown in Fig. 1.

Reception Cleaning/Selection

Pulp extraction

Enzymatic treatment

Agitation

Enzymatic inactivation

Centrifugation

Centrifugation

Filtration Juice I

Filtration

Thermal treatment Juice III

Materials and Methods

Juice II

Raw Material and Juice Production The 2007 and 2008 crops of Cereus h. K. Schum came from a city called Zortéa, in Santa Catarina State, South of Brazil. The crops were cut and had their pulps removed with a sanitized spoon. The entire pulp (pulp + seeds) was

Thermal treatment Juice IV

Fig. 1 Flow diagram showing points where samples were obtained to study the influence of the process on the Cereus h. K. Schum juices properties

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Histological Analysis

Rheological Characterization

An optical microscope (model Lambda LQT 2 ATTO Instruments Co.) was used for analysis. Pulp samples (mesocarp) obtained from ripe fruits—with formaldehyde, 70 % ethanol, and acetic acid—were analyzed and compared under eight different conditions:

Rheological behavior was determined by using a rotational viscometer equipped with concentric cylinders (Thermo Scientific Haake DC 10, VT model 550, USA). Measurements were performed at 8, 15, 25, 35, 45, 55, 65, 75, and 85 °C, with the temperatures controlled by a thermostatic bath. The rheological analysis was carried out varying the shear rate from 0 to 1,600 s−1 (ascending curve) and 1,600 to 0 s−1 (descending curve), within a 3-min interval for each curve. All experiments were duplicated.

a. While fresh fruit, referring to “in natura” mesocarp; b. While pulp in natura, referring to the integral pulp with seeds; c. While stirred pulp, referring to the extracted and magnetically shaken mesocarp; d. While stirred pulp after centrifugation; e. While stirred pulp after pasteurization; f. Enzymatically treated pulp; g. Enzymatically treated pulp after centrifugation; and h. Enzymatically treated pulp after pasteurization. For the histological evaluations, semi-permanent blades were prepared from manually obtained sections of the mesocarp, with the help of a scalpel (in the case of fresh fruit). For liquid samples, a Pasteur pipette was used and a small amount of seedless pulp (pulp in natura and stirred pulp) was added to the microscopic blades. Histochemical tests were conducted to identify the following cellular metabolites: starch, with Lugol (Berlyn and Miksche 1976); lignin, with acidified phloroglucinol (Kraus and Arduin 1997); lipids, with Sudan III (Sass 1951); and mucilage, with methylene blue (Costa 1972). Yield Analysis After the filtration step, the yield (Y) was obtained as shown in Eq. 1, where: mj = mass of extracted juice, and mp = pulp mass including seeds:   mj Y ¼  100 ð1Þ mp Physicochemical Characterization Samples were characterized by total solid content: gravimetric method (AOAC 934.01 method 1997); soluble solids, measured in digital refractometer with resolution of 0.1°Brix (Reichert, AIR model 200, USA); reducing sugars, DNS (Miller 1959); total sugar content, by Dubois et al. (1956); pH level, a potentiometer (Analion, model in 2000, Brazil) at 25 °C (AOAC, method 42.1.04 1997); protein, Bradford reagent (1976); and titratable acidity, by titration with NaOH 0.1 mol L−1 until the pH 8.2. All analyses were conducted in triplicate.

Modeling The models of Newton, Casson, Ostwald-De-Waele, and Bingham, shown in Eqs. (2) to (5) (Holdsworth 1971), were fitted to the rheological data obtained in the different processing steps. The criteria for selecting the models were the higher correlation coefficients and their simplicity. Newton :

t ¼ μ g

ð2Þ

Casson :

t 0:5 ¼ koc þ kc g 0:5

ð3Þ

OstwaldDeWaele :

Bingham :

t ¼ k g n

t ¼ t 0 þ ηp g

ð4Þ ð5Þ

On the formulas above, τ is the shear stress (in Pascal), μ is the viscosity (in Pascal seconds), g_ is the shear rate (in seconds), koc is Casson’s initial tension (in Pascals), kc and k are Casson and Ostwald-De-Waele’s consistency index, respectively (in Pascal seconds), n is the flow behavior index (dimensionless), τ0 is the initial shear stress (in Pascals), and ηp refers to Bingham’s consistency index—also called plastic viscosity (in Pascal seconds). The flow index values (n) for Ostwald-De-Waele indicate the fluid behavior. For n = 1, the fluid is Newtonian. The fluid is called dilatant if n > 1; it is pseudoplastic if n < 1. The effect of temperature on viscosity was studied by fitting the Arrhenius-type equation to the rheological data, where ηa is the apparent viscosity (in Pascal seconds); η0 is an empirical constant (in Pascal seconds); Ea is the activation energy (in kilocalories per mole); Rc is the gas constant (1.978×10−3 kcal mol−1 K−1); and T is the temperature (in Kelvin):   Ea ηa ¼ η0 exp  ð6Þ Rc T

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Sensory Analysis

Histological Analysis

The methods used for the sensory evaluation were the acceptance test and the discriminatory duo–trio test (Meilgaard et al. 1999). They were carried out for the treated and pasteurized C. hildmanninaus enzymatic juice. Evaluations were also made in mixtures with orange and lime juices in a ratio of one third of the cactus juice to two thirds of the aforementioned traditional ones. For the acceptance tests, the sensory panel was formed by 30 untrained men and women aged 20 to 55. The judges received 10 mL of the three juice samples, all randomly coded and maintained at a 12 °C temperature. A hedonic scale was divided into nine categories, going from (1) extremely dislike, up to (9) extremely like. For the duo–trio test, 17 untrained panelists within the same age range received a standard juice and two samples; one of the samples were identical to the standard (which were the orange and lime juices). The objective was to identify the orange and/or lime juice sample to which Cereus h. was added.

Cereus h. K. Schum’s mesocarp structure is characterized by the presence of isodiametric and mucilaginous cells, loosely arranged and aggregated in the adjacencies of its small vascular bundles. Histochemical tests showed there is no starch nor lipids in the cells of the mesocarp. Lignin has only been detected in the xylem vessel elements. Mucilages are the most present cells components, which contributes to the pulp’s homogeneity. Fresh fruit samples revealed intact cells (CPI in the Fig. 2a) with isodiametric format and little extracellular mucilage. Fresh pulp removed from the fruit (Fig. 2b), though, presented disrupted cells (CPR), releasing large mucilage amounts (Mu), forming a dense and homogeneous network. This happens because the disruption evidenced Cereus h. pulp cells’s fragility. The pulp’s magnetic agitation caused the following alterations: disaggregated and less homogeneous aspect of the mucilage (Fig. 3a) and a large amount of dispersed cellular fragments. The pulp’s enzymatic treatment degraded the long polysaccharide chains from the cell walls and mucilage, which can be observed microscopically. This was shown by the use of methylene blue in the analysis, an indicator dye of mucilage that did not react after treatment with enzymes (Fig. 3b). Degraded mucilage does not appear clearly in the figure, and the cells may be observed only weakly stained. After the centrifugation and pasteurization processes, the supernatant presented the same aspects after both treatments—enzymatic and mechanical: absence of cellular elements thus reflecting the efficiency of centrifugation to remove the suspended solids; also, indication of polysaccharide chain degradation from the negative response of methylene blue in the sample; and the presence of mono- or disaccharides or smaller chains of polysaccharides (Fig. 3c). The mechanical disintegration of particles by high-speed pulp agitation also promoted the wrap of long molecules (Vendrúsculo and Quadri 2008).

Statistical Analysis Significance Results were statistically evaluated by the Tukey test for a p level of ≤0.05. These calculations and modeling were performed by Statistica 8.0 software.

Results and Discussion Yield Analysis Through mechanical treatment, juice yield hit a 56.86 % mark; whereas, enzymatic treatment increased the aforementioned percentage to 78.91 %, a significant difference of 22.05 %. Results found are in accordance with several authors in the literature (Demir et al. 2004; Sharma et al. 2005). Fig. 2 Cereus h. K. Schum Pulp a in fresh fruit and b in the extracted pulp

Food Bioprocess Technol Fig. 3 Pulp of Cereus h. K Schum a stirred, b enzymatically treated, and c centrifuged

Physicochemical Characterization of Juices Table 1 shows the physicochemical characterization of the juice obtained after the studied methods. The percentages of total and soluble solids in suspension for the enzymatic treatment with polygalacturonases, pectin lyases, and cellulases were lower than the ones from the mechanical process. The reason why that happened is because enzymes enable an easier suspended particles removal through centrifugation/filtration. The explanation to that is that vacuum filtration produced a clearer juice, while the 100 mesh cloth allowed the draining of suspended solids; vacuum filtration was not a feasible process to be applied to the mechanical treatment due to its inherent high viscosity level. Pasteurization process was responsible for an increase in the juice’s total soluble solids obtained through pulp agitation. Table 1 Physicochemical characterization of the pulp from different treatments Where: juices obtained from: I mechanical treatment, II mechanical treatment and pasteurization, III enzyme treatment, and IV enzyme treatment and pasteurization. Values with the same letter are not statistically different by the Duncan test at 5 % significance level

This may be due to changes regarding the ion distribution on the surface of particles, caused by heating (Binner et al. 2000; Ng and Waldron 1997). There was no significant variation in the solids content level observed in the enzyme treated juice when pasteurization was applied. Significant differences were observed with an increase in the pH level and decrease in acidity for the mechanically treated juice after the pasteurization process. According to Maia et al. (2007), the degradation of the organic acids may occur during heating. Comments are found in literature about the chemical oxidation of ascorbic acid and/or thermal degradation as a result of whitening, cooking, pasteurization, sterilization, freezing, and dehydration (Burdurlu et al. 2006; Polydera et al. 2005). The reduction of the sugar levels was also shown in the juice’s enzymatic treatment, which can be associated to a lower total solids’ value resulting from the filtration process.

Parameters

Juice I

Juice II

Juice III

Juice IV

Total solids (%) Soluble solids (°Brix) pH Titratable acidity (g citric acid/100 g) Total sugars (g/100 mL) Reducing sugars (g/100 mL) Proteins (g/100 mL)

13.41±0.05 a 12.20±0.01 a 4.8±0.1 a 0.34±0.02 a

13.4±0.2 a 12.40±0.01 b 4.93±0.01 b 0.196±0.003 b

11.04±0.02 b 10.80±0.01 c 4.68±0.07 a, c 0.384±0.001 c

11.49±0.05 b 10.85±0.07 c 4.73±0.09 a 0.34±0.02 a, d

10.6±0.9 a 8.9±0.2 a 0.10±0.01 a

11.2±0.6 a 8.4±0.7 a, b 0.12±0.01 a

7.0±2.0 b 7.2±0.2 c 0.47±0.01 b

10.6±1.6 a 7.79±0.06 b, c 0.29±0.04 c

Food Bioprocess Technol Table 2 Juices apparent viscosities obtained at different processing steps

Where: juice obtained from: I mechanical treatment, II mechanical treatment and pasteurization, III enzyme treatment, and IV enzyme treatment and pasteurization. Values with the same letter are not statistically different by the Duncan test at 5 % significance level

Temperature (°C)

Apparent viscosities (mPa s)

08 15 25 35 45 55 65 75 85

Pulp

Juice I

23.0±3.0 a 17.9±0.9 b 14.0±0.4 c 12.1±0.3 c,d 9.6±0.4 d, e 7.4±0.2 e, f 6.3±0.2 f 5.9±0.2 f 5.9±0.0 f

15.7±0.4 13.5±0.4 11.0±0.2 9.0±0.1 7.5±0.1 6.2±0.3 5.2±0.4 4.3±0.5 3.5±0.3

Higher protein amounts were found in the enzymatically treated juice. According to Whitaker (2002), pectinases are able to solubilize proteins included on cell wall polysaccharides. Heat treatment had a significant effect on protein levels reduction only for the juice which was enzymaticaly treated. This can be attributed to denaturation and also the use of amino acids in Maillard reactions (Wang et al. 2006). Rheological Behavior of Pulp and Juices Results obtained for viscosities as a function of the shear rate have shown a pseudoplastic behavior for the mechanical and mechanical-pasteurization treatments. For the enzyme and enzyme-pasteurization juices, viscosity remained virtually constant with the increase in shear rate value, characterizing a Newtonian behavior. For all samples, the viscosity level decreased as temperatures increased. Table 2 shows the apparent viscosity values for the pulp without seeds and juices obtained at different processing steps, from 8 to 85 °C. Duncan's test was applied to the results, and significant differences among viscosities at different temperatures were shown by superscript letters. The adjustment of the rheological models' parameters was done considering the statistical significant difference between these intervals (Vandresen et al. 2009). Results have shown that the temperature increase did not significantly change viscosity levels at temperatures above 55 °C. Similar results were obtained for enzymatic and enzyme-pasteurized treated juices, under temperatures above Table 3 Parameters of the Casson’s model for the pulp

Temperature (°C) koc

kc

R

08 15 25–35 45–55 65–85

0.072 0.077 0.067 0.054 0.039

0.992 0.997 0.996 0.995 0.989

2.117 1.497 1.250 1.011 1.010

a b c d e f g h i

Juice II

Juice III

Juice IV

9.6±0.2 a 7.8±0.1 b 6.0±0.0 c 4.6±0.0 d 3.7±0.0 e 3.0±0.1 f 2.6±0.3 g 2.0±0.0 h 1.8±0.2 h

2.8±0.1 a 2.2±0.1 b 1.8±0.2 c 1.4±0.1 d 1.1±0.1 e 0.8±0.0 f 0.6±0.1 f 0.7±0.1 f 0.7±0.0 f

2.7±0.7 2.2±0.2 1.7±0.4 1.4±0.2 1.1±0.0 1.0±0.1 0.7±0.1 0.7±0.1 0.8±0.0

a a, b b, c c, d c, d c, d d d d

55 and 45 °C (juices III and IV), respectively. However, the juice obtained through mechanical treatment (juice II) presented a significant difference in viscosity levels under all temperatures; the pasteurized juice (juice III) also showed significant differences for all temperatures, except for the 75 and the 85 °C ones. Data description by rheological models was satisfactory as evidenced by the correlation coefficient values. Casson model provided fitting parameters somewhat better for the in natura- (Table 3) and mechanical-treated pulps (Table 4). Bingham model gave best results for the juice obtained by mechanical-pasteurization treatment (Table 5). This behavior is in accordance with what has been reported by Telis-Romero et al. (1999) who found an additional resistance to flow for concentrated pulp fruit juices, that may appear and is represented by the yield stress (koc and τ0) present in such models. It may also be noted that the plastic viscosity represented by Casson and Bingham consistency indexes (kc and ηp) decreased with increasing temperature for these samples. Ostwald-De-Waele’s model (data analysis not shown here) revealed that index values, n, varied from 0.48 to 0.60 for the in natura pulp; from 0.72 to 0.77 for the stirred juice; and from 0.85 to 0.89 for the stirred-pasteurized juice, indicating a pseudo-plastic behavior—a characteristic of fruit pulp and Table 4 Parameters of the Casson’s model for the mechanical-treated juice

Temperature (°C) koc

kc

R

08 15 25 35 45 55 65 75 85

0.088 0.082 0.074 0.067 0.061 0.056 0.053 0.047 0.044

0.998 0.998 0.998 0.995 0.995 0.996 0.987 0.989 0.988

0.978 0.908 0.827 0.725 0.685 0.597 0.514 0.492 0.384

Food Bioprocess Technol Table 5 Results of the Bingham model for the juice obtained by mechanical-pasteurization treatment

Temperature (°C) τ0

ηp

R

08 15 25 35 45 55 65 75–85

0.008 0.007 0.005 0.004 0.003 0.002 0.002 0.002

0.997 0.997 0.994 0.985 0.983 0.988 0.973 0.973

1.02 0.766 0.480 0.422 0.373 0.348 0.336 0.209

concentrated juices (Pelegrine et al. 2000; Branco and Gasparetto 2003). Also, n approaches to 1, and consequently to Newtonian behavior, as processing steps are added. Thus, Newton's model can be used for results description since it provided a good correlation coefficient with greater simplicity. Tables 6 and 7 show the models' parameters set at different temperature intervals. These results are in accordance with the literature (Bhattacharya and Rastogi 1998; Pelegrine et al. 2000; Ibarz and Pagán 1987; Ibarz 1992, 1994). In this case, it was also noted that the viscosity level (μ) decreased with increasing temperature, and this parameter showed very similar numbers between the two samples. Figure 4 illustrates the different models for the pulp and the four juices researched at a temperature of 25 °C. Temperature Effect The results of the Arrhenius equation fitted to the viscosity data are shown in Table 8, and the determination coefficients is quite satisfactory. They indicate a tendency observed for an apparent viscosity decrease with a temperature increase: the greater the activation energy, the greater the temperature effect on viscosity (Silva et al. 2005). The processing steps did not have significant influence on the Ea as shown by Duncan's test, at a 5 % significance level. The values found were similar to those reported by Vandresen et al. (2009) for carrot juice (3.66 kcal g−1 mol−1), and Vitali et al. (1974) for passion fruit juice (4.5 kcal g−1 mol−1). Table 6 Parameters of the Newton's model set at different temperature intervals

Temperature (°C)

μ

R

08 15 25 35 45 55–85

0.00276 0.00220 0.00176 0.00144 0.00110 0.00072

0.993 0.982 0.968 0.970 0.943 0.955

Table 7 Parameters of the Newton's model set at different temperature intervals

Temperature (°C)

μ

R

08–15 25–35 45–85

0.00239 0.00153 0.00086

0.991 0.985 0.951

Comparison of the Processing Steps Figure 5 shows the influence of the different treatments related to the Cereus h. viscosity. It was possible to observe that viscosity level decreases as follows: pulp > mechanically treated juice > mechanically treated + heated juice > enzymatically treated juice ≅ enzymatically treatment + heated juice. Even though very low shear forces promoted by low speed agitation with no cutting blade were used here, pulp disintegration was observed due to the fragility of the Cereus h. cells. Vegetable disintegration is generally observed in opposite processing conditions: high shear forces caused by cutting knives at high speed conditions (Vendrúsculo and Quadri 2008) or by pressing. The procedure presented here (Quadri et al. 2012) facilitated the detachment of the seeds retained between the saccharide chains and decreased viscosity probably because of the stretching of the large and complex molecules involved in the flow (Lucas et al. 2001; Teraoka 2002). Heat treatment provided a large decrease in the juices' viscosity. According to Rao (1987), the pulps’ rheological behavior is related to the content of soluble solids in the suspension and depends on shape, size, and concentration of suspended particles, as well as the system’s structure. Physicochemical analysis did not confirm a significant increase in the soluble solids for all juices, and no information was found in the correspondent literature on the effects caused by humid heating on mucilages. Additional studies are already being carried out by this research group in order to understand the behavior of this sugar under several operational conditions. Some of the data that have not been included in this paper have revealed that sugar does not respond as celluloses, hemicelluloses nor starches under that stimulus. Enzyme treatment of the seeded pulp promoted lower viscosity when compared with the pulp of the mechanically treated juice. Levels similar to water viscosity (1 mPa s) were found, and there were no significant changes when heat was applied. The juice has not shown significant changes in soluble solids either. From the industrial point of view, the apparent reduced viscosity level facilitates pulp flow, heat exchange during the process, and less air incorporation, which in excess may cause problems regarding the pumping operation, including oxidation and contamination (Branco 1995). This decreasing viscosity level has been

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a

Shear stress (Pa)

16

12

8

Experimental Casson

4

0 0

400

800

1200

1600

-1

Shear rate (s )

b

c

16

10

8

8

Experimental Casson

4

Shear stress (Pa)

Shear stress (Pa)

12

400

800

1200

4

Experimental Bingham

2

0 0

6

0

1600

0

400

-1

Shear rate (s )

800

1200

1600

-1

Shear rate (s )

e

d 4,0

3,5

3,5

3,0 2,5

Shear stress (Pa)

Shear stress (Pa)

3,0 2,5 2,0 1,5 1,0

Experimental Newton

0,5 0,0 0

400

800

1200

1600

-1

Shear rate (s )

2,0 1,5 1,0

Experimental Newton

0,5 0,0 0

400

800

1200

1600

-1

Shear rate (s )

Fig. 4 Models fitted to a pulp without seeds, b juice I, c juice II, d juice III, and e juice IV, at 25 °C

researched by several authors (Imungi et al. 1980; Matta 1999). According to Rombouts and Pilnik (1980), this is due to a very specific enzymatic activity. Enzymes are more effective than the mechanical treatment to degrade or modify complex polysaccharides—in this case, the mucilage—which is responsible

for the pulp’s high viscosity level. Furthermore, the enzymatic attack inhibits repulsion between particles, facilitating its separation (Lea 1998). The observed Newtonian behavior can also be related to the mucilage degradation and may be due to the reduction of particles in suspension. Likewise, the rheology of

Food Bioprocess Technol Table 8 The results of the Arrhenius equation fitted to the viscosity data

Table 9 Acceptance test of the Cereus h. juice and blends Sample

Parameter

Pulp

Juice I

Juice II

Juice III

Juice IV

−1

Ea (kcal mol ) 4.1±0.4 a 3.7±0.2 a 4.5±0.2 a 4.4±0.3 a 3.8±0.6 a η0∙105 (Pa s)

1.7±1.0

2.2±0.9

0.3±0.1

0.1±0.1

0.3±0.3

R

0.991

0.999

0.999

0.987

0.979

Where: pulp obtained from: I mechanical treatment, II mechanical treatment and pasteurization, III enzyme treatment, and IV enzyme treatment and pasteurization. Values with the same letter are not statistically different by the Duncan test at 5 % significance level

aqueous solutions of Opuntia ficus indica mucilage showed pseudoplastic behavior described by Ostwald-De-Waele’s model (Medina-Torres et al. 2000). Sensory Analysis Table 9 shows the acceptance level of samples according to the average value attributed to each. As we can see, when mixed to the lemon and orange juices, the cactus juice was well accepted by the participants, with a 100 % level of acceptation for the lemon mix, and over 80 % for the orange mix. When served without an add on, though, the drink has been rejected at a 5 % significance level according to the Tukey test. The duo–trio tests has shown that, for the lemon–cactus blend, 88 % of the surveyed participants have identified the cactus-flavored free samples as being similar to the standard of lemon juice, and, for the orange–cactus blend, 95 % of them have said it to be similar to the standard orange juice. The statistical difference of 5 % happened when we

28

Pulp Juice I Juice II Juice III Juice IV

24

Viscosity (mPa.s)

20 16 12 8 4 0 400

800

1200

Meana % approvalb % indifferent % rejectionc

1600

-1

Shear rate (s ) Fig. 5 Viscosity as a function of the shear rate at 25 °C for the in natura pulp and the different juices obtained

Lemon+cactus Orange+cactus C. hildmannianus juice

7.1a 7a 3.5b

97 84 17

0 3 7

3 13 76

Observation: a Values with equal letters have no statistical difference at 5 % of significance level by the Tukey test b

evaluations higher than 5

c

evaluations lower than 5

compared new formulations of the traditional juices. This confirms that the cactus-flavored drink changes the sensory characteristics of traditional juices even when added in minimum amount for the purpose of providing an increased fiber level to products labeled as “source of fibers.” In Brazil, a product is only recognized as a source for fibers if it contains a minimum of 15 g fibers/100 mL−1 of juice. The panelists have also reported that the Cereus h. juice affects the drink’s consistency even when mixed to other fruit juices.

Conclusions The mechanical and enzymatic treatments have satisfactorily allowed the extraction of juice from the pulp of Cereus h. K Schum. The juice obtained had not broken seeds and its viscosity could be reduced, especially in the enzymatically treated unit. However, mechanical treatment enabled the preparation of a stable juice with a larger amount of suspended solids. The pasteurization process affected some characteristics of the juice, especially its viscosity on the mechanical treatment, and its protein content in the enzymatic treatment. It was also possible to analyze that the high viscosity levels of the mucilage are not easy to mask. Consumers are able to perceive the presence of the Cereus h. juice, even after the enzymatic treatment. However, the acceptability is good when the juice is mixture with traditional juices, since its nutritional and functional values are priceless. The data obtained in this study helped us to understand the product features that are essential to design process and industrial installations. Acknowledgments Thanks to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and Fundação de Amparo à Pesquisa e Inovação do Estado de Santa Catarina (FAPESC), for their financial support.

Food Bioprocess Technol

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