J. Cent. South Univ. Technol. (2008) 15(s1): 509-515

DOI: 10.1007/s11771-008-411-2

Rheological properties in supernatant of peach gum from almond (Prunus dulcis)

WANG Sen(王 森)¹, XIE Bi-xia(谢碧霞)¹, ZHONG Qiu-ping(钟秋平)¹, DU Hong-yan(杜红岩)²

(1. School of Resources and Environment, Central South University of Forestry and Technology,

Changsha 410004, China;

2. Economic Forest Research and Development Center, CAF, Zhengzhou 450003, China)

Abstract: The rheological properties in the supernatant of peach gum from Prunnus dulcis were discussed in order to provide more scientific technical parameters and references for developing peach gum as a kind of medicinal gum. The rheological properties in the supernatant of peach gum were comparatively studied in different material ratios, temperatures, shaking times, pH values and salinities. The results show that, 1) the mathematical model of shear rate with material ratio and shear stress is Y=0.069X₁²+0.035X₂ -1.174, R²=0.942; 2) the mathematical model of shear rate with temperature and shear stress is Y=4.936X₁²+0.023 2X₂-1.688, R²=0.937; 3) the mathematical model of shear rate with shaking time and shear stress is Y=0.005 192 X₁³-0.140 73X₁²+1.249 045X₁+ 0.036 546 X₂-3.644 29, R²=0.954 3; 4) the effects of pH value on the rheological properties in the supernatant of peach gum are comparatively complicated with a varying range of 3-11 and the shear rate shows a change trend of saddle model; 5) the mathematical model of shear rate with the concentration of NaCl and shear stress is Y=-0.037 44X₁+0.012 93 X₂, R²=0.998; 6) the mathematical model of shear rate with the concentration of CaCl₂ and shear stress is Y=0.025 789X₁+0.016 19X₂, R² =0.999; and    7) the mathematical model of shear rate with the concentration of sorbic acid potassium and shear stress is Y=0.079 5X₁+0.017 3X₂, R²=0.998. The results show that the material ratio, temperature, shaking time, pH value significantly affect the rheological properties in the supernatant of peach gum, and the concentrations of NaCl and CaCl₂ also significantly affect the rheological properties expect the concentration of sorbic acid potassium.

Key words: peach gum; supernatant; rheological property

1 Introduction

The peach gum, a kind of transparent gum, is excreted from the trunk of Prunnus dulcis under environmental stress and belongs to edible gum of original peach gum^[1]. The traditional Chinese physicians   consider that the peach gum has many medical functions for stranguria due to hematuria, urolithic stranguria, dysentery, diarrhea^[2], concretion　and diabetes^[3-4]. The supernatant of peach gum is an active polysaccharides rich liquid. The latest researches indicated that the supernatant of peach gum also has the function for leukemia, so in order to develope peach gum as a kind of new medicine, it is necessary to study its rheological property.

Rheology, a branch of mechanics, is the science of studying the substance’s transfiguration under the force or flow. The rheological property of medical gum can be used to forecast and explain the flow, transfiguration and quality change when the gums are treated by different chemical reagents. Therefore, the rheological property of medical gum is very important for manufacture equipment designing, quality control, preservation stability, reactive blend and functional estimate. LIU et al^[5-8], SONG et al^[9], CHEN et al^[10] and WANG et al^[11] have studied the rheological property of Artemisia sphaerocephala Krasch gum and flax seed gum, respectively. In this work, the rheological properties in the supernatant of peach gum were comparatively studied in different material ratios, temperatures, shaking times, pH values and salinities, in order to provide more scientific technical parameters and references for developing peach gum as a kind of medicinal gum.

2 Materials and methods

2.1 Materials and apparatus

The peach gum was harvested from Prunnus dulcis cv. Italian No.1 grown in Jiangshan Garden in Luoyang City, Henan Province of China in September, 2006. All of the chemical reagents were analytically pure.

TDL80-2B desk centrifuge: Shanghai An-ting Scientific apparatus manufactory. DKZ-2 electro-thermostatic water cabinet: Shanghai Jinghong Experimental Equipment Co. Ltd. 1010-4 electric blast drying oven: Shanghai Experimental Equipment Co. Ltd. AR1140/C analytical balance: OHAWS CORP.USA. FW80 high speed universal pulverizer: Tianjin Taisi Equipment Co. Ltd. PHS-3C cidimeter: Shanghai Hongyi Apparatus and Meters Co. Ltd. DV-II+ programmable viscometer: Brookfield Co. USA. SPX-250B-Z biochemical incubator: Shanghai Boxun Industrial Co. Ltd.

2.2 Methods

2.2.1 Preparation of supernatant using different material ratios

The peach gum solutions were prepared in different concentration of 2%, 4% and 6% (w/v). 50 mL of the peach gum solutions were shaken in electro-thermostatic water cabinet at 95℃ for 12 h, and after 3 times filtration the supernatants were incubated for 4 h at 20 ℃, and then 16 mL of the supernatants were taken for determining the rheological property.

2.2.2 Preparation of supernatant under different tempera- tures

50 mL of 2% peach gum was shaken for 12 h at 95 ℃ after filtration and incubated for 1 h at 60 ℃, and then 16 mL of the supernatants were taken for determining the rheological property at 60, 40, 30, 20 and 10 ℃, respectively.

2.2.3 Preparation of supernatant using different shaking time

50 mL of 2% peach gum was shaken at 95 ℃ for 3, 6, 12, 16 and 24 h, respectively. After filtration it was incubated for 4 h at 20 ℃, and then 16 mL of the supernatants were taken for determining the rheological property. Because of shaking for 24 h, all of the peach gum was hydrolyzed completely.

2.2.4 Preparation of supernatant in different pH values

50 mL of 2% peach gum with different pH value (3, 5, 7, 9 and 11) were shaken at 95 ℃ for 1 h. After filtration it was incubated for 4 h at 20℃, and then 16 mL of the supernatants were taken out for determining the rheological property.

2.2.5 Preparation of supernatant in different concentra- tions of NaCl

50 mL of 2% peach gum with different concentrations of NaCl (0.1%, 0.3%, 0.5%, 1% and 2%) was shaken at 95 ℃ for 1 h. After filtration it was incubated for 4 h at 20 ℃, and then 16 mL of the supernatants were taken for determining the rheological property.

2.2.6 Preparation of supernatant with different concentra- tions of CaCl₂

50 mL of 2% peach gum with different concentrations of CaCl₂ (0.1%, 0.3%, 0.5%, 1% and 2%) was shaken at 95 ℃ for 1 h. After filtration it was incubated for 4 h at 20 ℃, and then 16 mL of the supernatants were taken out for determining the rheological property.

2.2.7 Preparation of supernatant with different concentra- tions of sorbic acid potassium

50 mL of 2% peach gum with different concentrations of sorbic acid potassium (0.01%, 0.03%, 0.05%, 0.09% and 2%) was shaken at 95 ℃ for 1 h. After filtration it was incubated for 4 h at 20 ℃, and then 16 mL of the supernatants were taken out for determining the rheological property.

2.3 Data statistical analysis

Data variance analysis and images treatments were carried out by Software SPSS 13 version.

3 Results

3.1 Effects of material ratio on rheological properties of supernatant of peach gum

The concentration of the supernatant of peach gum is an important factor that affects its rheological properties (Fig.1). The shear stress of the supernatant increased with the increase of the concentration. There were more gum molecules in the solution with the increase of the concentration, so the flow resistance and the shear stress also increased.

Fig.1 Effects of material ratio on rheological properties of supernatant of peach gum

The mathematical model of the shear rate with concentration and the shear stress was established by stepwise regression as Eqn.(1):

Y=0.069X₁²+0.035X₂²-1.174, R²=0.942            (1)

where  Y is the shear stress; X₁ is the concentration of the supernatant of peach gum; and X₂ is the shear rate.

The concomitant probability significance showed that both of the concentration and the shear rate had extremely significant effects on the shear stress (Table 1).

3.2 Effects of temperature on rheological properties of supernatant of peach gum

Fig.2 showed that at the same shear rate, the shear stress decreased slowly in the temperature range of 10-20 ℃, and decreased rapidly in the temperature range of 20-60 ℃, especially 20-40 ℃.

Fig.2 Effects of temperature on rheological properties of supernatant of peach gum

The mathematical model of the shear rate with temperature and the shear stress was established as Eqn.(2) by stepwise regression:

Y=4.936X₁²+0.023 2X₂²-1.688, R²=0.937          (2)

where  Y is the shear stress; X₁ is the temperature; and X₂ is the shear rate.

The concomitant probability significance showed that temperature and shear rate had extremely significant effects on the shear stress (Table 2).

3.3 Effects of shaking time on rheological properties of supernatant of peach gum

Fig.3 showed that at 95 ℃ the shaking time had extremely significant effect on the shear stress in 2% (w/v) of supernatant of peach gum. The shear stress did not change obviously when shaking time was 3-6 h and 6-12 h. The shear stress changed obviously when shaking time was 12-16 h. The changing of shear stress in different shaking time is due to the fact that peach gum has a different solubility. The soluble saccharide was dissolved during 3-6 h, so the first dissolution peak appeared after shaking for 6 h. But the dissolution of the insoluble saccharide needs more energy to break hydrogen bond before dissolution. Before most of hydrogen bonds were broken, the shear stress had not increased rapidly until shaking for 12 h. For this reason, the shear stress showed an “S” shape of increasing trend.

Fig.3 Effects of shaking time on rheological properties of supernatant of peach gum

The mathematical model of the shear rate with temperature and the shear stress was established as Eqn.(3) by stepwise regression:

Table 1 Rheological properties regression coefficient of material ratio of supernatant of peach gum

Table 2 Rheological properties regression coefficient of supernatant of peach gum at different temperatures

   (3)

where  Y is the shear stress; X₁ is the shaking time; and X₂ is the shear rate.

The concomitant probability significance showed that both of the shaking time (X₁) and the shear rate had extremely significant effects on the shear stress (Table 3).

3.4 Effects of pH value on rheological properties of supernatant of peach gum

Fig.4 showed that the pH value affected the rheological properties of the supernatant of peach gum. The apparent viscosity gradually decreased with the decrease of pH value at the range of 3-7; the apparent viscosity gradually decreased with the increase of pH value at the range of 7-9; but when pH value increased to larger than 9, the apparent viscosity started to increase. So the apparent viscosity reached its maximum at pH=7.

Fig.4 Effects of pH value on rheological properties of supernatant of peach gum

Table 4 showed the effects of pH value on the characteristic of texture of peach gum. The shear stress of the supernatant of peach gum showed different change

curves, suggesting that significant differences at 0.01 probability level were present among the five kinds of peach gum supernatant treated with different pH values.

3.5 Effects of salinity on rheological properties of supernatant of peach gum

3.5.1 Rheological properties of supernatant of peach gum with different concentration of NaCl

The rheological properties of the supernatant of peach gum after adding different concentration of NaCl showed that at the same shear rate, the shear stress had a trend of gradual decrease. The shear stress had a minimum when the concentration of NaCl was 0.3% and the shear stress only deceased in a very small extent (Fig.5).

Fig.5 Reological properties of supernatant of peach gum with different concentration of NaCl

The mathematical model of the shear rate with concentration of NaCl and the shear stress was established as Eqn.(4) by stepwise regression:

Y=-0.037 44 X₁+0.012 93 X₂, R²=0.998          (4)

where  Y is the shear stress; X₁ is the concentration of NaCl; and X₂ is the shear rate.

The concomitant probability significance showed that both of the concentration of NaCl and the shear rate had extremely significant effects on the shear stress (Table 5).

Table 3 Rheological properties regression coefficient of supernatant of peach gum in different shaking time

Table 4 Significance analysis of pH value on rheological properties of supernatant of peach gum

Table 5 Regression coefficient of supernatant of peach gum with different concentrations of NaCl

3.5.2 Rheological properties of supernatant of peach gum with different concentration of CaCl₂

The rheological properties of the supernatant of peach gum after adding different concentration of CaCl₂ showed that at the same shear rate, the shear stress had a trend of gradual decrease. The shear stress had a minimum when the concentration of CaCl₂ was 0.3% and the shear stress only deceased in a very small extent when the concentration of CaCl₂ was larger than 0.5% (Fig.6).

Fig.6 Rheological properties of supernatant of peach gum with different concentrations of CaCl₂

The mathematical model of the shear rate with concentration of CaCl₂ and the shear stress was established as Eqn.(5) by stepwise regression:

Y=0.025 789 X₁+0.016 19 X₂, R²=0.999            (5)

where  Y is the shear stress; X₁ is the concentration of CaCl₂; and X₂ is the shear rate.

The concomitant probability significance showed that concentration of CaCl₂ (X₁) and shear rate (X₂) had extremely significant effects on the shear stress (Y) (Table 6).

3.5.3 Rheological properties of supernatant of peach gum with different concentrations of sorbic acid potassium

Fig.7 showed that adding different concentrations of CaCl₂ did not affect the rheological properties of the supernatant of peach gum, indicating that peach appeared stable characteristics after adding antiseptic.

Fig.7 Rheological properties of supernatant with different concentrations of sorbic acid potassium

The mathematical model of the shear rate with concentration of NaCl and the shear stress was established as Eqn.(6) by stepwise regression:

Y=0.079 5 X₁+0.017 3 X₂, R²=0.998               (6)

where  Y is the shear stress; X₁ is the concentration of sorbic acid potassium; and X₂ is the shear rate.

The concomitant probability significance showed that both of the concentration of sorbic acid potassium (X₁) and shear rate (X₂) had extremely significant effects on the shear stress (Y) (Table 7).

Table 6 Regression coefficient of supernatant of peach gum with different concentrations of CaCl₂

Table 7 Rheological properties regression coefficient of supernatant of peach gum with different concentrations of sorbic acid potassium

4 Discussion and conclusions

1) The shear stress of the supernatant in peach gum increases with the content of peach gum varying from 2% to 6%. The increase of peach gum causes the increase of solute (water-soluble peach gum molecules), thereby flowing resistance of fluid increases and the shear stress of the supernatant increases accordingly. Results suggest that the peach gum supernatant appears as a kind of Newtonian fluid, and that the meltage of water-soluble polysaccharide has yet not reached condensation in 50 mL.

2) The rheological properties of 2% peach gum supernatant are very sensitive to the change of temperature. Results indicate that it is necessary to pay attention to the control of temperature. In addition, adjustment of the rheological properties by temperature control is feasible in the processing and pharmacy of the peach gum supernatant.

3) The solubility of peach gum is significantly affected by the shaking time. Most of the soluble saccharide has been dissolved after shaking at 95 ℃ for 6 h, showing the first-stage solution peak. With prolonging the shaking time, the insoluble saccharide begins to dissolve and causes a gradual increase of the peach gum supernatant viscocity. Therefore, the shear stress of peach gum supernatant shows an increasing trend of “S” shape. Results suggest that the saccharide can be completely dissolved at 95 ℃ only by prolonging the shaking time, which has prevalent meaning of guidance in pharmaceuticals industry.

4) The pH value has an extremely significant effect on the rheological properties of peach gum supernatant of 2%. Peach gum is a kind of polyanionic polysaccharides and occupies large volume in solution, which results in the increase of flowing resistance and solution viscosity. In contrast, the peach gum occupies   smaller volume in solution, which causes the decrease of flowing resistance and solution viscosity. The present study suggests that the change of pH value can cause the change of the rheological properties of peach gum supernatant and the degradation of peach gum saccharide, therefore, the rheological properties of peach gum supernatant can be adjusted by changing the pH value. Results would be useful for rapid and complete hydrolysis of peach gum saccharide which plays a key role in production of natural green glue.

5) NaCl and CaCl₂ have a close capacity of changing the rheological properties of peach gum supernatant. When adding different contents of NaCl and CaCl₂, the pattern of NaCl decreasing the rheological properties of peach gum supernatant is identical to that of CaCl₂. When electrolyte reaches an ultimate value, the shear stress of peach gum supernatant does not decrease possible due to the saturation of antiparticles of Na⁺ and Ca²⁺. The present study indicates that the rheological properties of peach gum supernatant are affected by electrolyte, and that potassium sorbate has no obvious effect on the rheological properties of peach gum supernatant in peach gum-associated food industry. The further work is to study the rheological properties if peach gum supernatant is used in medicine production.

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(Edited by YANG Bing)

Foundation item: Project(2006BAD18B02) supported by the 11th Five-Year Plan of National Key Technology R&D Program of China; Project(07006B) supported by Youth Fund of Central South University of Forestry and Technology, China; Project(080929) supported the Education Fund of Hunan Province, China

Received date: 2008-06-25; Accepted date: 2008-08-05

Corresponding author: WANG Sen, Associate Professor; Tel: +86-731-5623467; E-mail: csuftwangsen@163.com