Time Dependent Rheological Characteristics of Pineapple Jam

Volume 3, Issue 3 2007 Article 1

International Journal of FoodEngineering

Time Dependent Rheological Characteristicsof Pineapple Jam

Santanu Basu, Punjab University, Chandigarh, IndiaUS Shivhare, Punjab University, Chandigarh, India

GSV Raghavan, McGill University

Recommended Citation:Basu, Santanu; Shivhare, US; and Raghavan, GSV (2007) "Time Dependent RheologicalCharacteristics of Pineapple Jam," International Journal of Food Engineering: Vol. 3: Iss. 3,Article 1.DOI: 10.2202/1556-3758.1229

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Time Dependent Rheological Characteristicsof Pineapple Jam

Santanu Basu, US Shivhare, and GSV Raghavan

Abstract

Jam is an intermediate moisture food containing fruit pulp, pectin, sugar and acid. The effectof sugar and pectin concentration, pH, shear rate and temperature on the time dependentrheological properties of pineapple jam was studied using a rheometer. Pineapple jam exhibitedthixotropic behavior. Shear stress of the pineapple jam at a particular time of shearing dependedon the shear rate, temperature and composition. Weltman, Hahn, and Figoni and Shoemaker,models were applied to describe the time dependent flow properties of pineapple jam. Hahn modeldescribed adequately the rheological characteristics of pineapple jam.

KEYWORDS: pineapple, jam, rheology, thixotropy

Author Notes: Correspondence: U.S. Shivhare, Department of Chemical Engineering &Technology, Punjab University, Chandigarh-160014, Tel: 91-172-2534906, Fax: 91-172-2779173,E-mail: [email protected]



1. Introduction

Jam is prepared by boiling the fruit pulp with sugar to a reasonably thick consistency, firm enough to hold the tissues in position. It should not contain less than 68.5% total soluble solids (TSS). Pectin, sugar, acid and water, which are the essential constituents of a jam, must be present approximately in the following proportions: pectin-1%, sugar-50-75%, fruit acid-1% and water-33-38% (on fruit pulp basis) (Lal et al., 1998).

Rheological properties are useful in determining ingredient functionality in the product development, quality control and correlation of food texture to sensory data (Saravacos, 1970; Kokini and Plutchok, 1987; Dervisi et al., 2001). Flow behavior of various food products, particularly fruit jams, jellies, spreads, and pulps, which contain high or moderate levels of sugars and/or very small amount of gelling agent, have been widely studied (Carbonell et al., 1991; Gabriele et al., 2001; Alvarez et al., 2006). It has been established that the rheological properties of the product are mainly affected by the amount and type of sugar added, proportion and kind of gelling agent used, fruit content and process temperature. (Glicksman and Farkas, 1966; Saravacos, 1970). However, little information is available on the applicability of time dependent flow models for different foods, although several foods exhibit time dependent flow changes. These foods include mixtures of xanthan and carob gums (Cuvelier et al., 1987), mango pulp (Bhattacharya, 1999), hot pepper-soybean paste (Yoo, 2002), food suspensions (Choi and Yoo, 2004) and icecream (Kus et al., 2005). Time dependent rheological characteristics of foods are important as it establishes relationship between structure and flow (Figoni and Shoemaker, 1983). No information is available in literature on time dependent rheological properties of pineapple jam.

Present study was therefore taken up to: (i) investigate time dependent rheological characteristics of pineapple jam and examine the applicability of different rheological models; (ii) investigate the effect of composition (pH, sugar and pectin concentration); and (iii) study the effect of shear rate and temperature on time dependent rheological behavior of pineapple jam.

2. Materials and Methods

2.1. Materials Pineapple pulp was procured from M/S Himalayan Frozen Foods Ltd, Rajpura (Punjab). The pH, acidity, and TSS of the pineapple pulp were 3.33, 1.1% and 11° Brix respectively. Sugar was procured from the local market while pectin and citric acid were purchased from Loba Chemie (Mumbai, India). Pineapple jam was prepared using selected levels of sugar, pectin and pH (Table1).

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Basu et al.: Time Dependent Rheology



Table 1. The detailed experimental plan

S.No. Parameter Level Details 1 Pineapple pulp - Base material 2 Sugar 5 50, 55, 60, 65 & 70% 3 pH 3 3.0, 3.2 & 3.4

4 Pectin 3 0.8, 1 & 1.2%

2.2. Procedure of Jam Manufacturing The pulp was weighed, and TSS was measured using hand refractometer (Erma, Japan). The pH of the pulp was measured using pH meter (Elico, India). Jams were prepared according to experimental plan reported in Table 1. Desired amount of sugar was added to the pulp and mixture was heated on a burner till it reached 55° Brix. TSS of the boiling mixture was continuously monitored. Pectin solution was prepared by adding 2-3 g of sugar and 2-3 mL of water and heating the solution until it formed a homogenous mixture. The pectin-sugar solution was then added to the boiling pulp-sugar mixture. The TSS was monitored until the mixture reached 65° Brix. Heating was stopped and the mixture was poured into a 50 mL glass beaker and cooled. The container was then covered with the ethanol dipped butter paper to prevent microbial growth and stored for 24h for proper setting of jam to 68.5o Brix TSS.

2.3. Time Dependent Rheology

Time dependent rheology of pineapple jam was studied by subjecting jam to constant shear rates (10, 50 & 100 s-1). Rheological properties of the pineapple jam were measured by using a MC1 rheometer (Paar Physica, Germany) at selected temperatures (30, 40 and 50oC). The samples were placed in cone and plate arrangement fitted with MP30 sensor (radius of measuring plate R=12.5 mm). For each run data was registered for shear stress, apparent viscosity and time. The temperature was controlled by using a constant temperature water bath (+1°C) fitted with a circulation pump. The data was acquired in a personal computer loaded with Physica software, version US 200/32 V2.50. The samples were sheared at a specified shear rate for 300s. For getting the equilibrium shear stress values, pineapple jam samples were sheared at specified shear rates for 2 h. Each measurement was conducted after a five min rest after loading, which facilitated temperature equilibrium.

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International Journal of Food Engineering, Vol. 3 [2007], Iss. 3, Art. 1

DOI: 10.2202/1556-3758.1229



Time-dependent behavior results from viscoelasticity, thixotropy, or a combination of the both (Cheng and Evans, 1965; Harris, 1972). Viscoelastic properties arise in a food due to retarded response to shear resulting from combined viscous and elastic nature of the material. Where as, in a thixotropic material, response to shear is instantaneous. Time-dependent behavior arises as the shearing process continually alters the structure of the system. Structural changes include disentanglement of polymer molecules in solution, deflocculation of globules in an emulsion, favorable spatial distribution of particles, and molecular association of biopolymers. Structure breakdown process under constant shear rate can be classified as completely reversible, partially reversible, or irreversible, depending on the extent of recovery of the original structural viscosity. Measurements of time dependent stress or viscosity decay at a constant shear rate have been used by many workers to characterize structure breakdown process (Figoni and Shoemaker, 1981; Barnes, 1997).

Time dependent shear stress decay characteristics have been mathematically described by several researchers (Weltman, 1943; Hahn et al., 1959; Figoni and Shoemaker, 1983). Weltman model (1943) assumed logarithmic decay of shear stress values in the absence of any equilibrium conditions. Weltman model was later modified by Hahn (1959) to include an equilibrium shear stress term. Figoni and Shoemaker (1983) described the stress decay process as a first order kinetic model with a non-zero equilibrium value. To quantify time dependency of jam at selected shear rates and temperatures, shear stress-time of shearing data were fitted to the Weltman, Hahn and Figoni & Shoemaker models: Weltman model (1943): tBA ln−=σ (1)

Hahn model (1959): atPe −=− )log( σσ (2)

Figoni & Shoemaker model (1983): )exp()( max ktee −−+= σσσσ (3)

Where, σ is shear stress (Pa) at any given time of shearing (t), eσ is equilibrium shear stress (Pa), maxσ is the maximum shear stress (Pa), and A, B, P, a, and k are constants.

2.4. Statistical Analysis

All the experiments were carried out in duplicate to verify reproducibility and average values were used in the analysis. In all the jam samples, reproducibility was ±5% on average. Effects of sugar concentration, pH, pectin, shear rate and temperature on rheological properties were determined by using STATISTICA software Ver.5.0 (Statsoft Inc., 1995, Tulsa, USA).

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3. Results and Discussion

3.1. Effect of Shear Rate and Temperature on Time Dependent Rheological Properties Typical time dependent rheograms showed thixotropic behavior of pineapple jam indicating continuous breakdown or rearrangement of structure with time of shearing. Dependence of shear stress to time of shearing at selected constant shear rates is shown in Figure 1. Shear stress decreased with increasing time of shear, at a constant shear rate which characterizes time dependency phenomenon of pineapple jam. In all samples, shear stress decreased rapidly with time of shearing in the beginning (upto 100s) followed by slower rate of decrease later on, finally approaching a constant value corresponding to an equilibrium state.

0

300

600

900

1200

1500

1800

0 50 100 150 200 250 300 350

Time (s)

She

ar s

tres

s (P

a)

10 SR

50 SR

100 SR

HahnmodelS

Figure 1. Shear stress-time relationship for pineapple jam (68.5°Brix) at selected shear rates at 30°C (pH-3.0, pectin-1% and sugar concentration-60%).

Thixotropic behavior increased with shear rate (Figure 1) but reduced with increase in temperature (Figure 2). Similar behavior has been reported by several researchers (Ramos and Ibarz, 1998; Choi and Yoo, 2004). Equilibrium shear stress ( eσ ) values for pineapple jam samples were found to be dependent on the shear rate employed for measurements. Further eσ values were found to be independent of composition (sugar/ pectin concentration, pH) and temperature.

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DOI: 10.2202/1556-3758.1229



Equilibrium shear stress values were found to be very close (within ±5%) for all jam samples at a specific shear rate, the average value was therefore considered for calculation.

0

200

400

600

800

1000

1200

0 50 100 150 200 250 300 350

Time (s)

Shea

r stre

ss (P

a)

30C40C50CHahn model

Figure 2. Shear stress-time relationship for pineapple jam (68.5°Brix) at selected temperatures for constant shear rate=50s-1 (pH-3.0, pectin-1% and sugar concentration-60%).

Linear regression of equations (1-3) was carried out to describe time dependent rheological behavior of pineapple jam and the regression coefficients are reported in Table 2. The coefficients of equations (1-3) varied with shear rate and temperature. Hahn model (equation 2) described the time dependent rheological behavior better (R2 = 0.73-0.99, S.E. = 0.03-0.27) than Weltman model (equation 1, R2 = 0.57-0.99, S.E. =1.99-50.72) and Figoni & Shoemaker model (equation 3, R2 = 0.64-0.99, S.E. = 0.06-0.62). A typical plot of applicability of Hahn model to describe time dependent rheological behavior is shown in Figures 1 and 2.

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Table 2. Time dependent rheological models parameters for pineapple jam at selected temperatures (pH-3.0, pectin-1% and sugar concentration-70%).

Parameters A (Weltman model), P (Hahn model) and (σmax-σe) (Figoni & Shoemaker model) represent the shear stress needed for initiating the structure breakdown process during shearing process. Parameters A, P and (σmax-σe) increased with shear rate but decreased with increased temperature at a particular shear rate. In Weltman model, parameter B is the time coefficient of thixotropic breakdown and its magnitude represent the extent of thixotropy (Weltman, 1943). Magnitude of B increased with increasing shear rate for all pineapple jam samples, while parameters a (Hahn model) and k (Figoni & Shoemaker model) did not follow systematic trend.

3.2. Effect of Composition on Time Dependent Rheological Properties Shear stress decreased with the increase in the sugar concentration at a given pH and shear rate (Figure 3). Pectin forms a network of fibrils with water and sugar acts as a dehydrating agent, which disturbs the equilibrium existing between water and pectin. The network formation is more pronounced with increasing level of sugar leading to softening of the product. Thus at high sugar level, shear stress developed is lower. Thixotropic behavior reduced with increase in sugar concentration for all pineapple jam at given pectin concentration and pH.

SR Weltman model Hahn model Figoni & Shoemaker model Temp. (oC) s-1 A (Pa) B

(Pa.s-1) R2 SE P (Pa) a(x103 )

(Pa.s-1) R2 SE σmax-σe

(Pa) kx103

(s-1) R2 SE

30 10 285.8 19.43 0.85 6.93 1.59 4.36 0.97 0.14 39.54 10.00 0.88 0.33 30 50 405.7 31.63 0.94 7.15 1.95 6.09 0.98 0.08 89.98 14.02 0.98 0.19 30 100 705.4 54.94 0.95 10.66 2.15 3.77 0.98 0.07 139.98 8.69 0.96 0.16 40 10 164.8 7.22 0.86 2.54 1.17 2.71 0.74 0.14 14.84 6.24 0.74 0.33 40 50 356.1 14.32 0.89 4.32 1.56 4.17 0.89 0.12 38.07 12.58 0.92 0.32 40 100 470.3 26.66 0.87 8.79 1.79 6.35 0.89 0.21 61.54 14.61 0.89 0.48 50 10 118.3 4.79 0.81 1.99 1.16 1.67 0.75 0.08 14.33 3.84 0.75 0.19 50 50 213.8 9.72 0.89 2.97 1.24 4.14 0.73 0.22 17.35 9.52 0.74 0.50 50 100 305.8 8.16 0.57 6.16 1.56 3.99 0.74 0.27 36.03 9.20 0.64 0.62

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DOI: 10.2202/1556-3758.1229



0

200

400

600

800

1000

1200

0 50 100 150 200 250 300 350

Time (s)

She

ar s

tres

s (P

a)50%55%60%65%70%Hahn model

Figure 3. Shear stress-time relationship for pineapple jam (68.5°Brix) at at selected sugar concentrations at 30°C (pH-3.0, pectin-1% and constant shear rate=10 s-1).

Effect of varying sugar concentration on coefficients of equations (1-3) for jam (pectin-1%, pH-3, 30oC) at selected shear rates are reported in Table 3. Parameter A (Weltman model), P of Hahn model and (σmax-σe) of Figoni & Shoemaker model decreased with increase in sugar concentration, indicating lower shear stress needed for breakdown of the jam structure at higher concentration of sugar. Effect of pectin concentration and pH on model coefficients did not follow any systematic variation.

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Table 3. Time dependent rheological models parameters for pineapple jam at selected sugar concentrations (pH-3.0, pectin-1%, temperature-30oC).

SR Weltman model Hahn model Figoni & Shoemaker model Sugar concn. (%)

s-1 A (Pa) B (Pa.s-1)

R2 SE P (Pa) a(x103 ) (Pa.s-1)

R2 SE σmax-σe (Pa)

kx103

(s-1) R2 SE

10 1221.6 101.36 0.87 33.57 2.40 6.01 0.95 0.12 253.9 13.80 0.95 0.28 50 2079.7 116.12 0.90 32.44 2.46 2.38 0.82 0.09 290.2 5.45 0.82 0.23

50

100 2869.4 209.49 0.92 50.73 3.01 9.38 0.95 0.18 1013.2 2.15 0.95 0.41 10 731.9 62.93 0.95 12.30 2.33 5.45 0.78 0.22 214.9 1.25 0.78 0.49 50 1377.9 88.25 0.91 23.58 2.35 2.40 0.80 0.11 222.3 5.52 0.80 0.25

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100 1941.6 146.00 0.91 40.29 2.61 6.52 0.95 0.13 398.3 15.01 0.94 0.30 10 541.9 41.22 0.99 3.89 2.11 4.42 0.98 0.06 130.0 10.17 0.97 0.14 50 1230.8 94.50 0.93 22.60 2.28 7.33 0.98 0.09 302.2 16.88 0.97 0.23

60

100 1756.6 145.34 0.92 36.83 2.60 6.40 0.88 0.08 408.7 14.70 0.98 0.19 10 327.9 21.11 0.94 4.43 1.95 1.08 0.96 0.05 89.9 2.49 0.81 0.11 50 777.1 51.14 0.99 3.88 2.22 4.59 0.81 0.03 166.4 10.56 0.99 0.06

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100 1144.7 91.26 0.95 17.63 2.41 5.49 0.99 0.06 257.5 12.66 0.98 0.13 10 285.8 19.43 0.85 6.93 1.59 4.36 0.97 0.14 39.5 10.01 0.88 0.33 50 405.7 31.63 0.94 7.14 1.95 6.09 0.98 0.08 89.9 14.02 0.97 0.19

70

100 705.4 54.94 0.95 10.66 2.15 3.77 0.98 0.07 139.9 86.89 0.96 0.16

Pineapple jam samples exhibited thixotropic behavior over the range of shear rate and temperature employed for measurement. It was found that thixotrpic behavior increased with shear rates and mitigated by increasing temperature. Sugar concentration had a pronounced effect on time dependent rheological parameters, i.e. with increasing sugar concentration, shear stress values decreased at a constant shear rate, while pH and pectin concentration did not show any systematic relationship. During shearing, the structure of the jam breaks down irreversibly with a decline in shear stress values with time of shearing. The rate of structural breakdown was higher in the initial phase and the decrease was marginal at the later stage.

4. Conclusion

Pineappple jam exhibited thixortropic behavior and the thixotropy increased with shear rate but decreased with increase in temperature and sugar concentration. Effect of pectin concentration and pH on thixotropic behavior was not consistent. Hahn model was found to give a better fit of the experimental data for pineapple jam.

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DOI: 10.2202/1556-3758.1229



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DOI: 10.2202/1556-3758.1229



Time Dependent Rheological Characteristics of Pineapple Jam

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