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Optimization of Variables for Aqueous Extraction of Gum from Grewia mollis

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Article in Journal of Polymers · March 2014

DOI: 10.1155/2014/926850

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Hindawi Publishing Corporation
Journal of Polymers
Volume 2014, Article ID 926850, 10 pages
http://dx.doi.org/10.1155/2014/926850

Research Article
Optimization of Variables for Aqueous Extraction of Gum from
Grewia mollis Powder

Emmanuel Panyoo Akdowa,1,2 Thaddee Boudjeko,3 Alice Louise Woguia,3

Nicolas Njintang-Yanou,4 Claire Gaiani,2 Joel Scher,2 and Carl Moses F. Mbofung1
1
ENSAI, University of Ngaoundere, P.O. Box 454, Ngaoundere, Cameroon
2
Laboratoire d’Ingénierie des Biomolécules, Université de Lorraine, 2 avenue de la Forêt de Haye, B.P. 172,
54500 Vandoeuvre-lès-Nancy, France
3
Department of Biochemistry, Faculty of Science, University of Yaounde I, P.O. Box 812, Yaounde, Cameroon
4
Faculty of Science, University of Ngaoundere, P.O. Box 454, Ngaoundere, Cameroon

Correspondence should be addressed to Nicolas Njintang-Yanou; njintang@yahoo.fr

Received 29 August 2013; Accepted 27 November 2013; Published 23 March 2014

Academic Editor: Yves Grohens

Copyright © 2014 Emmanuel Panyoo Akdowa et al. This is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.

Grewia gum is a polysaccharide derived from the inner stem bark of the edible plant Grewia mollis. Juss (family Tiliaceae). It
is a savanna shrub that grows wildly but is usually cultivated in Nigeria and Northern part of Cameroon. The main goal of the
present study was to investigate the effect of aqueous extraction conditions on the extraction yield and physicochemical properties
of the Grewia mollis. The studied aqueous extraction variables were water/powder (W/P) ratio (10 : 1–80 : 1 w/p), temperature (25.0–
85.0∘ C), time (1–3 h), and pH (4.0–10.0). The results indicated that the aqueous extraction variables exhibited the least significant
(𝑃 < 0.05) effect on the yield and the viscosity of the gum. The result shows that the ratio of extraction is the main factor affecting
the extraction of gum. The optimized extraction condition for higher viscosity was at the powder/water ratio of 1 : 55.4, pH of 7,
time of 1 h, and temperature of 50∘ C. However, the optimized extraction condition for higher yield was at the powder/water ratio
of 1 : 80, pH of 4, time of 3 h, and temperature of 73∘ C.

1. Introduction the presence of tannins, saponins, flavonoids, glycosides,

phenols, and steroids and the absence of alkaloids [4].
Grewia mollis is a shrub or tree widely distributed in Sudano- In overall and in the limit of our knowledge, the literature
Sahelian region and found in Cameroon and Nigeria. The on Grewia reported mainly the evaluation of the performance
dried and pulverized inner stem bark is used as a thickening of fine powder of stem bark as binders substitute in tablet
agent in some local dishes [1]. In the Adamawa region of formulation [2] and the toxic effect of the powder on exper-
Cameroon in particular, the powder is used as binding agent imental rats [5]. Results revealed that Grewia gum compares
in the preparation of maize fried cake. This functionality is favorably with the standard binder Polyvinylpyrrolidone
also exploited in Nigeria where it is used in cooking soup, (PVP) and could be a useful substitute binder in parac-
or dried and pulverized to mix with bean meal to make etamol tablet formulations [2]. In addition consumption of
cakes locally called in Hausa “Kosai” [2]. The functional Grewia powder by rat models showed no significant effect
properties of Grewia powder have been associated with on serum alkaline phosphatase activity, urea, creatinine,
the presence of mucilage, a polysaccharide nature [3]. In triglycerides, cholesterol, glucose concentrations, and body
addition, the mucilage of the bark is used traditionally by the and organ weights. However significant (𝑃 < 0.05) increase in
Yoruba people of Nigeria at child birth [2]. Phytochemical serum transaminases activities was observed, accompanied
studies on the leaves and stem bark of Grewia mollis indicate by decrease in food intake in rats fed 10% stem bark suggest-
2 Journal of Polymers

ing some liver injury upon consumption of high level of the pH was adjusted with 0.1 M HCl or NaOH. Water was
powder. While studies on Grewia have been interested on the preheated to a designated temperature before the powder was
powder of the stem back, a fundamental question concerning added. The powder water slurry was mixed throughout the
the functionality of the isolate Grewia stem bark gum is still extraction period (1 h to 3 h). Separation of the gum from the
to be answered. In doing this, the extraction conditions of the swollen powder was achieved by passing the powder through
gum need to be determined and the question underlying the an extractor with a rotating plate that scraped the gum layer
present study is what are the effect of extraction conditions on the powder surface. The collected gum was filtered and
on the viscosity and the yield of Grewia gum since these dried in an oven (45∘ C overnight). The dry gum was packed
parameters constitute the determinant factors conditioning and stored at cool and dry conditions [14].
their trade, technological and nutritional qualities? In fact the
most important properties of hydrocolloids are their viscosity 2.3. Determination of the Response Variable. Two response
(including thickening and gelling) and water binding. Other variables were used in this work, the gum yield and the
significant functions include emulsion stabilisation, preven- viscosity. The yield was calculated as the ratio of dry weights
tion of ice recrystallisation, and improvement of organoleptic of the powder obtained after lyophilization to the initial
properties [6]. And the food hydrocolloid industry represents powder weight and expressed as g/kg. The apparent viscosity
a market of over US$3.0 billion [7]. To our knowledge, very of the hydrated samples (2.5% w/w) was measured at constant
few if no studies have been conducted on the extraction and conditions (temperature 25∘ C, pH 7, and shear rate 1000 s−1 )
evaluation of the functional properties of Grewia gum. using a rotational viscometer (Kinexus, Malvern instruments)
Generally, hot-water treatment has been used for extrac- fitted with plate geometry.
tion of hydrocolloid gums and is time, temperature, pH,
and water to mass ratio dependent [8]. Several studies are 2.4. Monosaccharide Profile. The monosaccharide profile of
reported on various gums and the extracting conditions the gum powder extracted at optimum conditions was
which give the optimal viscosity and yield varied from one determined as reported earlier [15]. In the procedure, 2 mg
plant species to another [9, 10]. It is important therefore to of lyophilized gum was hydrolysed in 2 mL of 2.5 M tri-
optimize the extraction process in order to obtain the highest fluoroacetic acid at 100∘ C for 2 h in a sealed tube under
yield and quality polysaccharides. In the extraction pro- nitrogen. After hydrolysis the acid was removed on a rotary
cesses, there are multiple independent variables affecting the evaporator, and the hydrolysate was reduced with sodium
responding factors. In addition, the possibility of interactions borohydride and acetylated [16]. The resulting alditol acetate
between the independent variables should be considered in derivatives were separated on a 1.85 m × 4 mm column
order to determine the optimal experimental conditions [9]. of 3% SP2 on 100/120 Supelcoport, in a Hewlett-Packard
Response surface methodology (RSM) has been reported to model 5710A gas chromatograph. The chromatography was
be an effective tool and successfully used for optimization of conducted isothermally at 215∘ C with an N2 -carrier-gas flow
a process when the independent variables have a combined rate of 60 mL/min.
effect on the desired response [10, 11]. However, no study has
been conducted on the extraction process of Grewia mollis 2.5. Experimental Design and Statistical Analysis. Response
gum. surface methodology (RSM) was used to fit the independent
Therefore, the objectives of the present work are (1) to variables to the response variables apparent viscosity (Pa⋅s)
study the effect of extraction time, temperature, pH, and and gum yield (g/kg). A face-centered central composite
water to powder ratio on the extraction yield and viscosity design was used with 4 factors, namely, extraction temper-
of gum from stem bark Grewia mollis (2) to find out the atures (25–85∘ C), pH (4–10), water to seed ratio (10 : 1–80 : 1),
optimum conditions for extraction of the gum from Grewia and extraction time (1 h–3 h). The design variables in this
mollis powder using response surface methodology. study with actual and coded levels are shown in Table 1. The
statistical package Minitab 16 was used for statistical analysis.
2. Material and Methods The experimental design was composed of 30 experiments
including 24 full factorial design points, 8-star points, and 6-
2.1. Sampling and Proximate Analysis. Grewia mollis stem centre points. The significant terms in different models were
barks were procured from the local medical plant market, in found by analysis of variance (ANOVA) for each response.
Maroua, Cameroon. The stem barks were manually cleaned Significance was judged by determining the probability level
to remove all extraneous matter such as dust, dirt, stones, that the 𝐹 statistic calculated from the data is less than 5%.
and chaff. The cleaned barks were then packed in plastic bags, Numerical optimization technique of the sigma plot software
sealed, and preserved in a dry and cool place. The moisture, was used for simultaneous optimization of the multiple
ash, fat, and protein contents of the bark were measured [12]. responses. The desired goals for each variable and response
The available sugar content was determined as previously were chosen. All the independent variables were kept within
described [13]. range while the responses were maximized.

2.2. Gum Extraction Procedure. Aqueous Grewia mollis stem

bark gum was extracted from the bark powder using distilled
3. Results and Discussion
water (water to powder ratio 10 : 1 to 80 : 1) at pH 4 to 10 3.1. Chemical Composition of Grewia mollis Bark Powder.
following the experimental design shown in Table 1. The The chemical composition of Grewia mollis bark powder is
Journal of Polymers 3

Table 1: Matrices of the face-centered central design for the independent variables (experimental and coded levels).

Factors Responses variables

Number run
Time (H) pH Temperature (∘ C) Ratio Viscosity (Pa⋅s) Gum yield
1 (+1) 3 (−1) 4 (−1) 25 (+1) 80 0.4339 0.6226
2 (−1) 1 (−1) 4 (+1) 85 (+1) 80 0.2551 0.8174
3 (−1) 1 (+1) 10 (+1) 85 (−1) 10 0 0
4 (−1) 1 (−1) 4 (−1) 25 (−1) 10 0 0
5 (0) 2 (−1) 4 (0) 55 (0) 45 0.3119 0.3248
6 (0) 2 (+1) 10 (0) 55 (0) 45 0.3481 0.2438
7 (0) 2 (0) 7 (0) 55 (0) 45 0.8363 0.231
8 (0) 2 (0) 7 (+1) 85 (0) 45 0.3085 0.227
9 (0) 2 (0) 7 (0) 55 (0) 45 1.023 0.945
10 (0) 2 (0) 7 (0) 55 (0) 45 1.1 0.409
11 (+1) 3 (+1) 10 (−1) 25 (+1) 80 0.543 0.5436
12 (+1) 3 (+1) 10 (−1) 25 (−1) 10 0 0
13 (0) 2 (0) 7 (0) 55 (0) 45 0.834 0.285
14 (+1) 3 (+1) 10 (+1) 85 (−1) 10 0 0
15 (−1) 1 (+1) 10 (+1) 85 (+1) 80 0.3931 0.2006
16 (+1) 3 (+1) 10 (+1) 85 (+1) 80 0.3107 0.3014
17 (+1) 3 (−1) 4 (+1) 85 (−1) 10 0 0
18 (0) 2 (0) 7 (0) 55 (−1) 10 0 0
19 (−1) 1 (−1) 10 (−1) 25 (−1) 10 0 0
20 (+1) 3 (0) 7 (0) 55 (0) 45 0.6979 0.177
21 (−1) 1 (0) 7 (−1) 25 (0) 45 1.214 0.285
22 (−1) 1 (+1) 10 (−1) 25 (+1) 80 0.8223 0.1608
23 (0) 2 (0) 7 (0) 55 (+1) 80 0.4639 0.092
24 (−1) 1 (−1) 10 (−1) 25 (+1) 80 0.4084 0.3346
25 (+1) 3 (−1) 4 (−1) 25 (−1) 10 0 0
26 (0) 2 (0) 7 (0) 55 (0) 45 0.5126 0.187
27 (−1) 1 (−1) 10 (+1) 85 (−1) 10 0 0
28 (0) 2 (0) 7 (−1) 25 (0) 45 0.4045 0.272
29 (+1) 3 (+1) 10 (+1) 85 (+1) 80 0.2885 0.5906
30 (0) 2 (0) 7 (0) 55 (0) 45 1.333 0.343

presented in Table 2. The bark powder was relatively low in Table 2: Chemical composition of Grewia mollis shrub powder.
moisture and mainly composed of available sugars. Ash was
Parameters Levels
also highly represented but the protein level was average. This
was the first time, at the best of our knowledge, the proximate Moisture content (g/100 g) 12.3 ± 0.11
composition of the bark of Grewia mollis was reported. The Proteins (g/100 gDM) 7.8 ± 0.55
composition generally reflected the composition of bark of Ash (g/100 gDM) 12.6 ± 0.05
other plants reported in the literature. In fact our previous Available sugars (g/100 gDM) 43.9 ± 2.13
report on Scorodophleus zenkeri and Hua gabonii barks Lipids (g/100 gDM) 2.5 ± 0.42
revealed range compositions of 9.7–96 g/100 mg DM for ash,
10.2–14.2 g/100 g DM for proteins, 2.5–3 g/100 g for lipids, and
The mean relative concentration of these sugars in the
3.2–20.5 g/100 g DM for available carbohydrate. Basically the
polysaccharide is glucose (80%), rhamnose (19%), xylose
structure of plants bark is mainly composed of fibers and may (5%), galactose (1%), and arabinose (2%). Our results are
contain resin, calcium oxalate cristal, tannins, and secretory quite similar to those previously reported by Nep and Conway
elements [17]. The high level of available sugars in our bark [3] composed of glucose (67.1%), rhamnose (6.2%), arabinose
sample reflected the high level of gum which has been shown (12.7%), xylose (2.7%), and galactose (9.61%). Our sample
to be essentially carbohydrate nature [3] such as Arabic gum, also presented considerable levels of galacturonic acid and
Tragacanth gum, and Karaya gum. glucuronic acid which have been revealed earlier in Grewia
gum by Fourier transformed infrared spectroscopy [18]. The
3.2. Monosaccharide Composition of the Gum. The monosac- difference in composition of our gum with reported data
charide composition of Grewia gum is presented in Figure 1. may reflect the difference in the molecular weight of the
4 Journal of Polymers

80 design (coded value equal to zero). Figure 2(a) showed that an

70 increase in water to powder ratio from 10 : 1 to 51 : 1 induced
Sugars level (% sugars)

60 an increase in yield to an optimum of 0.78% followed by

50 a decrease in a yield value of 0.37% when the ratio varied
from 51 : 1 to 80 : 1. Similar quadratic behavior of the effect of
40
water to powder ratio was observed on the viscosity which
30
showed an optimum at ratio 69 : 1, equivalent to a maximum
20 viscosity of 0.39 Pa⋅s. The effects of extraction time, extraction
10 temperature, and pH represented, respectively, in Figures
0 2(b), 2(c), and 2(d) showed no significant variation on the
Ara Rha Fuc Xyl Man Gal Glc Gal A Glc A viscosity and gum yield as confirmed by the ANOVA in
Sugars Tables 3 and 4.
Figure 1: Monosaccharide profile by gas chromatography analysis. The effect of extraction time and temperature, water to
mass ratio, and pH on the gum yield and viscosity has been
reported in various cases. Koocheki et al. [11] reported that
polysaccharides which has been reported to vary depending the yield increased exponentially with temperature and time
on a number of factors such as the pathway and environment of extraction. At higher temperature around 75∘ C and higher
of synthesis, and the prevailing conditions under which the time around 3 h, yield reached nearly equilibrium. Similar
polysaccharide was extracted [19]. We used hot aqueous trends were reported for gum materials such as flaxseed
extraction in this work while Nep and Conway [3] used room gum [9], boat-fruited Sterculia seeds polysaccharide [10], and
temperature extraction followed by drying using varying Yanang leaves gum extraction [6]. These results contrasted
methods. our results and probably reflected the nature of gum origin.
In fact, while our gum source is more rigid in structure, then
3.3. Data Analysis of the Extraction Process. The analysis less affected by temperature, most reported sources of gums
of the data generated from responses surface methodology are either seeds or leaves.
generally assumes a second order polynomial equation show- It was also demonstrated that increase in water to seed
ing relationship between the response variable(s) and the ratio tended to increase the extraction yield, probably due
factors. In this equation the linear (𝑥𝑖 ), the interactions (𝑥𝑖 𝑥𝑗 ), to the available more liquid which increased the driving
and quadratic (𝑥𝑖 2 ) effects of each factor on the response force of gum out of the material [8, 22]. Conversely, some
variable(s) are determined. Tables 3 and 4 give the values authors found a higher extraction yield at a low water to solid
of the effects and the associated analysis of variances for ratio [6]. The difference in the behavior of gum extraction
viscosity and extraction yield, respectively. 𝑃 value less than yields towards the extraction time here again highlighted the
0.05 indicated significant coefficients. In this respect the effect of the nature of the gum source, but this needs to be
linear effect of the ratio was the most significant either for the investigated. In addition the difference in the gum structure
viscosity (𝑃 < 0.0062) or the yield (𝑃 < 0.0009). In addition may affect the extract yield; in particular solubility of charged
the quadratic effects of ratio (0.0212) and time (0.0542) were gum is highly subjected to variation in pH. The effect of pH
significant for the viscosity. On a comparative basis, the on the yield reported for some gums origins revealed minor
importance of the independent variables on viscosity could effect in agreement with our finding [8, 10] but contrasted
be ranked in the following order water to powder ratio > with findings by others who reported higher extraction yield
extraction time > extraction temperature > extraction pH. at alkaline [23] or acidic pH [24]. According to Karazhiyan et
Koocheki et al. [11] working on extraction of Qodume Shirazi al. [22] the effect of alkaline pH may result from hydrolysis
gum also found similar significant effect of water : seeds ratio and dissolution of insoluble constituents, which in our case
and temperature on the yield and viscosity of the gum while may not happen due to the woody nature, shrub, of our plant
pH has a lesser effect. Reversely Razavi et al. [20] observed material.
a nonsignificant effect of water : seed ratio on the viscosity The effects of extraction conditions on the viscosity
and a significant effect on yield. Amid and Mirhosseini [21] of extracted gums of various natures have been reported.
observed a significant effect of ratio, temperature, and pH on Koocheki et al. [8] found that, as the time and temperature
the extraction yield of gum from durian (Durio zibethinus) of extraction increased, the viscosity of the extracted gum
seeds. The difference in the effect of factors on the responses decreases in a parabolic manner as a result of irreversible
variables may reflect the chemical structure of the gum. change in their conformation [25]. In addition they reported
Grewia gum has been shown to be composed of mainly increase in water to seed ratio also conducted to a gum with
neutral sugars, and some uronic acid [18] is revealed here as lower viscosity while pH has no significant effect, particularly
galacturonic acid and glucuronic acid. at lower water to seed ratio. Karazhiyan et al. [22] also
reported similar effect of water to seed ratio, temperature, and
3.4. Effect of Factors on the Yield and Viscosity. The effect pH on viscosity.
of ratio water/powder, time, temperature, and pH on the
responses factors is presented in Figures 2(a), 2(b), 2(c), 3.5. Contours Plotting, Interaction Effect, and Optimization.
and 2(d), respectively. The quadratic equations used were Figure 3 presents the contours plot of the interaction effect
delivered when other factors were kept at the centre of the of water to powder ratio and extraction time on the viscosity
Journal of Polymers 5

Table 3: Coefficients and analysis of variance of the effect of time, pH, temperature, and powder to water ratio on the viscosity of Grewia
gum extract.

Source Coefficient Sum of square Df 𝐹 ratio 𝑃 value

Linear 1.0657
Constant
Time (h) −1.4624 0.0656 1 1.03 0.3266
pH 0.394686 0.0180 1 0.28 0.6032
Temperature (∘ C) 0.0353305 0.0261 1 0.41 0.5318
Ratio 0.0391614 0.6450 1 10.11 0.0062∗
Quadratique
Time × time 0.324119 0.2773 1 4.35 0.0546
pH × pH −0.029087 0.2058 1 3.23 0.0926
Temperature × temperature −0.000305 0.2001 1 3.14 0.0968
Ratio × ratio 0.000326 0.4221 1 6.62 0.0212∗
Interaction
Time × pH 0.00995434 0.0079 1 0.12 0.7305
Time × temperature 0.00053787 0.0001 1 0.00 0.9698
pH × temperature −0.0000661 0.0003 1 0.00 0.9451
pH × ratio 0.00018535 0.0033 1 0.05 0.8222
Time × ratio −0.00008227 0.0030 1 0.05 0.8321
Temperature × ratio −0.00008382 0.0883 1 1.38 0.2578
Total error 0.956746 0.9567 15
Total (corr.) 4.57207 4.5721 29
∗
the corresponding coefficients are significant.

Table 4: Coefficients and analysis of variance of the effect of time, pH, temperature, and powder to water ratio on the yield of Grewia gum
extract.
Source Coefficient Sum of square Df 𝐹 ratio 𝑃 value
Linear 0.0601778
Constant
Time (h) −0.452027 34.8446 1 0.10 0.7577
pH 0.0502871 619.909 1 1.76 0.2048
Temperature (∘ C) 0.00641689 37.7153 1 0.11 0.7482
Ratio 0.0131883 5999.3 1 17.00 0.0009∗
Quadratique
Time × time 0.0993363 20.2103 1 0.06 0.8141
pH × pH −0.00276491 55.711 1 0.16 0.6967
Temperature × temperature 0.000007664 10.5134 1 0.03 0.8653
Ratio × ratio −0.000088 365.476 1 1.04 0.3249
Interaction
Time × pH 0.014648 185.664 1 0.53 0.4794
Time × temperature −0.000926884 339.648 1 0.96 0.3421
pH × temperature −0.000718786 101.004 1 0.24 0.6005
pH × ratio −0.000289118 173.185 1 0.49 0.4943
Time × ratio 0.000972389 75.5734 1 0.21 0.6501
Temperature × ratio 0.0000096834 9.5103 1 0.03 0.8718
Total error 0.607627 5292.5 15
Total (corr.) 1.80606 14902.5 29
∗
the corresponding coefficients are significant.
6 Journal of Polymers

1.0 Yield (%) = 0.7645 − 0.2177 ∗ ratio + 1.0 1.0 1.0

0.609 ∗ ratio ∗ ratio

0.8 0.8 0.8 0.8

Viscosity (Pa·s)
Viscosity (Pa·s)

0.6 0.6 0.6 0.6

Yield (%)
Yield (%)
Yield (%) = 0.7245 − 0.0455 ∗ time +
0.0115 ∗ time ∗ time
0.4 0.4 0.4 0.4

0.2 0.2 0.2 0.2

Viscosity (Pa·s) = 0.3216 + 0.2035 ∗ ratio Viscosity (Pa·s) = 0.3216 + 0.0243 ∗ time +
− 0.1495∗ ratio ∗ ratio 0.0355∗ time ∗ time
0.0 0.0 0.0 0.0
−1.0 −0.5 0.0 0.5 1.0 −1.0 −0.5 0.0 0.5 1.0
Ratio Time

Yield (%) Yield (%)

Viscosity (Pa.s) Viscosity (Pa.s)
(a) (b)
1.0 1.0 1.0 Yield (%) = 0.7612 − 0.0846 ∗ temperature − 0.0983 1.0
Yield (%) = 0.7858 + 0.0249 ∗ pH − 0.2527 ∗ pH ∗ pH ∗ temperature ∗ temperature

0.8 0.8 0.8 0.8

Viscosity (Pa·s)

Viscosity (Pa·s)
Yield (%)

0.6 0.6 0.6 0.6

Yield (%)

0.4 0.4 0.4 0.4

0.2 0.2 0.2 0.2

Viscosity (Pa·s) = 0.3152 − 0.051∗ pH Viscosity (Pa·s) = 0.3207 + 0.0143 ∗ temperature +
− 0.0734 ∗ pH ∗ pH 0.0316 ∗ temperature ∗ temperature
0.0 0.0 0.0 0.0
−1.0 −0.5 0.0 0.5 1.0 −1.0 −0.5 0.0 0.5 1.0
pH Temperature (∘ C)

Yield (%) Yield (%)

Viscosity (Pa.s) Viscosity (Pa.s)
(c) (d)

Figure 2: Quadratic representation of the effect of powder to water ratio (a), extraction time (b), extraction pH (c), and temperature (d) on
the viscosity and yield of Grewia gum.

and yield of Grewia gum. Each contour plot was drawn when was observed (Figure 4(a)). The effect on yield was also quite
the other parameters were at the centre of the domain, that is, visible at water/powder ratio higher than 50 : 1 where an
ratio 55 : 1, time 2 h, temperature 55∘ C, and pH 7. As shown in increase in pH led a nonsignificant decrease in yield from
Figure 3(a), the extraction time had no effect on the viscosity 0.5% to 0.2%. The effect of temperature was similar to that of
at water/powder ratio 10–40 and 60–80, while, between the time with no significant effect at lower water powder ratio and
ratio ranges 40 and 60, an increase in the extraction time some observed effect around ratio 40–60 (Figure 5). In this
induced a decline in the viscosity from 1.2 Pa⋅s to less than range of ratio an increase in temperature seemed to reduce
0.8 Pa⋅s. On the other hand, irrespective of the extraction viscosity and similar change was observed on yield.
time, an increase in water/powder ratio from 10 to 55 was The results obtained in this study revealed that viscosity
associated with an increase in viscosity after which a decline and yield were most affected by the water : powder ratio, and
was observed. The highest viscosity was 1.2 Pa⋅s observed only to a lesser extent by time, pH, and temperature of extraction.
at lower extraction time, a maximum which diminished as In order to identify the optimal conditions of Grewia gum
the extraction time increased. The interaction effects of the extraction, the contours plot presented was used. In this
water/powder ratio and time on the yield showed no marked respect the most suitable condition was considered optimal
change with viscosity fluctuating between 0.1 and 0.4. for Grewia gum extraction at the highest extraction yield and
The interaction effect of pH and water to powder ratio viscosity. Optimum was achieved graphically by identifying
shown in Figure 4 revealed that pH exerted influence on zones of maximum viscosity and gum yield as stripped in the
the viscosity at water/powder ratio around 50 : 1. In these contours plots in Figures 3, 4, and 5. The optimal extraction
conditions an increase in pH from 4 to 7 led to an increase conditions zones for Grewia gum viscosity corresponded to
in viscosity (from 0.4 to 0.8 Pa⋅s) above which a decrease the range temperature 25∘ C–85∘ C, pH 6–8, water to powder
Journal of Polymers 7

80 80 0.1
0.2 0.2
0.6 0.3 0.4
70 0.6 70 0.2
0.8 0.3
0.6 0.6
0.3
60 60
1.0 0.8
Water/powder ratio

Water/powder ratio
0.3
50 50
1.2
0.3
0.2
40 1.0 0.8 40
0.6 0.6 0.3
0.3

30 0.6 30 0.2
0.8
0.4 0.4 0.2 0.2
0.6 0.1
0.4
20 20 0.1
0.4 0.2 0.2 0.1 0.1
0.2 0.2
10 0.0 0.0 10 0.0 0.0
1.0 1.5 2.0 2.5 3.0 1.0 1.5 2.0 2.5 3.0
Time (h) Time (h)
(a) (b)

Figure 3: Interaction effects of water/powder ratio and extraction time on the viscosity Pa⋅s (a) and yield % (b). pH and time extraction
conditions were 7 and 2 h, respectively.

80 80
0.5 0.5 0.5 0.4 0.1
0.4 0.2 0.2
0.6
0.6 0.3 0.3
70 0.5 0.6 70
0.6 0.5
0.7 0.2
0.7
60 0.6 60 0.5
0.4 0.8 0.4 0.3
0.7 0.6
Water/powder ratio

Water/powder ratio

0.7
0.5 0.4
50 0.8 50
0.5 0.4
0.8 0.3
40 0.3 0.6 40 0.3
0.4 0.7 0.7
0.5 0.6 0.3
0.3 0.2
0.6 0.4 0.2
30 0.5 30
0.3 0.4 0.5 0.2 0.2
0.2
0.4 0.1
20 0.3 0.3 20 0.1 0.1
0.1 0.2 0.2 0.1
0.2
0.1 0.1
0.1
10 0.0 0.0 10 0.0 0.0
4 5 6 7 8 9 10 4 5 6 7 8 9 10
pH pH
(a) (b)

Figure 4: Interaction effects of water/powder ratio and pH on the viscosity Pa⋅s (a) and yield % (b) of Grewia gum. Extraction time and
temperature conditions were 2 h and 55∘ C, respectively.

ratio 40 : 1–60 : 1, and time of extraction 1 h–1.5 h while the to establish the overall optimum area of aqueous extraction
corresponding zone for optimum yield was temperature 30– condition as shown in Figure 6. Since only water to powder
60∘ C, pH 4–7, water to powder ratio 50 : 1–70 : 1, and time ratio and time had significant effects on the viscosity and
of extraction 1-2 h, respectively. The optimum conditions of yield, only the graphs involving the water to shrub ratio
extraction were also computed for each yield and viscosity and time as factors were used. Based on this, the extraction
and the values given in Table 5 reflected the optimum deter- condition that maximized viscosity and yield of Grewia gum
mined graphically. Multiple graphical optimizations were was water to powder ratio 50 : 1–60 : 1 and extraction time 1–
performed by drawing the overlaid contour plot in order 1.5 h.
8 Journal of Polymers

80 80 0.1
0.6 0.5 0.3
0.6 0.4 0.4
0.4 0.3 0.2
70 0.7 70 0.2
0.7 0.6 0.5
0.8 0.3
60 0.7 60 0.3
0.8 0.4
Water/powder ratio

Water/powder ratio
0.3
50 0.6 50
0.5
0.8 0.8 0.3
40 0.7 40
0.7 0.4 0.3
0.7 0.3 0.2
0.6 0.3
0.6 0.6 0.2
30 0.5 30
0.5 0.5 0.2
0.4 0.2
0.4 0.4
0.3 0.2 0.1 0.1
20 0.3 0.3 20 0.1
0.2 0.2 0.2 0.1
0.1
0.1 0.1 0.1
10 0.0 0.0 10 0.0 0.0
30 40 50 60 70 80 30 40 50 60 70 80
Temperature (∘ C) Temperature (∘ C)
(a) (b)

Figure 5: Interaction effects of water/powder ratio and temperature on the viscosity Pa⋅s (a) and yield % (b) of Grewia gum. Extraction time
and pH conditions were 2 h and 7, respectively.

80 0.1 Table 5: Computed predicted optimum conditions of extraction of

0.2 0.2 Grewia mollis gum.
0.6 0.3 0.4
70 0.6 0.2
0.8 0.3 Factor Optimum viscosity Optimum yield
0.6 0.6
0.3
Times 1.0 3
60 pH 7.1 4
1.0 0.8
0.3 Temperature 50.3 73.2
Water/powder ratio

50 Water : shrub ratio 55.4 : 1 80 : 1

1.2 Bold values were overlaid selected optimum conditions.
0.3
0.2
40 1.0 0.8 0.6
0.3 0.6
0.3 The viscosity of 2.5% gum extracted in these conditions falls
0.2 0.6 within the range of values generally reported for other plants
30 0.8 gum: 581.4 mPa⋅s for Ocimum basilicum seed gum [20] and
0.2 0.4 0.2 0.4
0.6 0.1 518.9 mPa⋅s for Lepidium perfoliatum [8]. In addition, the
0.4
20 0.1
0.4 0.2
yield, however, was lower compared to most seeds gums
0.1 0.20.1
0.2 0.2 reported in previous studies such as Yanang gum 4.54% [6],
0.0 0.0 0.0 0.0 Flaxseed gum 7.9% [9], Opuntia mucilage 19.4% [26], and
10
1.0 1.5 2.0 2.5 3.0 Mesquite seed gum 24.9% [25], but much higher compared
Time (h) to 1.2% reported for Durio zibethinus seed gum [27].
Based on its lower extraction yield compared to the most
Viscosity commercial gum, the use of Grewia gum as a novel food
Yield
hydrocolloid is questionable. In addition the part of the plant
Figure 6: Overlaid plotting for multiple optimization of aqueous used, the shrub, can also lead to the destruction of the plants
extraction of Grewia shrub gum. if harvesting is not appropriately conducted.

4. Conclusion
As shown in Table 5 the numerical optimum corre-
sponded to temperature 73∘ C, time 1 h, pH 7.0, and water to Results showed that extraction conditions significantly influ-
powder ratio 55 : 1. In these conditions, the gum was extracted enced the extraction yield and apparent viscosity. The most
with a yield of 0.32 g/100 g DM and the gum solution pos- important variable is the water to powder ratio, whereas
sessed a viscosity of 0.98 Pa⋅s, values which were close to the effects of extraction temperature, time, and pH are less
desired values of 0.4 g/100 g DM and 1.2 Pa⋅s, respectively. important. Increasing water to powder ratio resulted in an
Journal of Polymers 9

increase yield and viscosity up to maximum at ratio 55 : 1 seeds by response surface methodology,” Food Chemistry, vol.
from which a decrease is observed. Based on numerical 105, no. 4, pp. 1599–1605, 2007.
optimization and significant factors, the optimal extraction [11] A. Koocheki, S. A. Mortazavi, F. Shahidi, S. M. A. Razavi, R.
condition of Grewia gums is temperature 73∘ C, pH 7, time Kadkhodaee, and J. M. Milani, “Optimization of mucilage extr-
1 (h), and water to powder ratio 55 : 1. This investigation action from Qodume Shirazi seed (Alyssum homolocarpum)
confirms the use of Grewia gum as gelling agent and the using response surface methodology,” Journal of Food Process
carbohydrate nature of its gum. Studies of its gelling power Engineering, vol. 33, no. 5, pp. 861–882, 2010.
need to be studied. However the yield is lower compared to [12] AOAC, Methods of Association of Official Chemist. Official
commercial gum and this hypothesizes its eventual use as a Methods of Analysis, Association of Official Analytical Chem-
new source of hydrocolloid for industry. ists, Arlington, Va, USA, 15th edition, 2005.
[13] N. Y. Njintang, C. M. F. Mbofung, and K. W. Waldron, “In vitro
protein digestibility and physicochemical properties of dry red
Conflict of Interests bean (Phaseolus vulgaris) flour: effect of processing and incor-
poration of soybean and cowpea flour,” Journal of Agricultural
The authors declare that there is no conflict of interests regar- and Food Chemistry, vol. 49, no. 5, pp. 2465–2471, 2001.
ding the publication of this paper. [14] H. Karazhiyan, Extraction optimization and physical properties
of cress seed hydrocolloid using response surface methodology
Acknowledgment [Ph.D. thesis], Ferdowsi University of Mashhad, Mashhad, Iran,
2008.
The authors would like to thank the Cooperation pour la Rec- [15] R. M. Nguimbou, T. Boudjeko, Y. N. Njintang, M. Himeda, J.
herche Universitaire (CORUS-IRD ref 6052, FRANCE) for Scher, and C. M. F. Mbofung, “Mucilage chemical profile and
financial support. antioxidant properties of giant swamp taro tubers,” Journal of
Food Science and Technology, 2013.
[16] P. Albersheim, D. J. Nevins, P. D. English, and A. Karr, “A met-
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