Effect of sugar substitute on sucrose crystal growth rate.pdf

7/27/2019 Effect of sugar substitute on sucrose crystal growth rate.pdf

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Effect of sugar substitute on sucrose crystal growth rate

Jimmy Hea, Rajesh Bund

b, Richard Hartel

c

aJames Madison Memorial High School, Madison, WI,USA

b Department of food Science, UW-Madison, WI,USA ([email protected])c

Department of food Science, UW-Madison, WI,USA ([email protected])

ABSTRACT

Many food companies are in search of a good sugar substitute to reduce the caloric value of their products. In

certain products, like sugar-coated cereals, substitutes are needed that cause no/minimum inhibition of

sucrose crystal growth rate. The current work was targeted towards understanding the impact of sugar

substitutes on sucrose crystal growth rate at varying concentration. Sucrose crystal growth rate in

supersaturated sucrose solutions (sucrose (80):water (20)) with various substitutes (three sugarsfructose,

lactose, trehalose; two sugar alcohols maltitol and isomalt and three custom-designed corn syrups) at the

concentration of 5% and 10% were compared with pure sucrose solution. Solutions were observed under the

microscope in the presence of sucrose seed crystals (< 100 m). Images of a minimum 45 crystals were

recorded for each system for ~ 16 min at 2 min intervals. The images were analyzed using image analysis

software for average crystal growth rate. For all substitutes at all concentrations, characteristic growth rate

dispersion associated with sucrose crystallization was observed. The average crystal growth rate for pure

sucrose solution was ~ 8.9 m/min. All sugar substitutes inhibited sucrose crystal growth rate to some extent,

with the extent of inhibition increasing with an increase in the concentration of sugar substitute. Growth rate

inhibition was higher for the corn syrups (average growth rate at 5% concentration ~ 4.2-4.5 m/min)

compared to sugars and sugar alcohols (average growth rate at 5% concentration ~ 4.7-5.8 m/min).

Trehalose and isomalt showed the least inhibition. Trehalose, isomalt and maltitol appeared to be potential

sugar substitutes for application in sugar-coated cereals. The methodology developed can be effectively used

for screening other prospective sugar substitutes.

Keywords: Sugar crystallization; Sugar substitute; Sugar-coated cereals

INTRODUCTION

Food industries are currently looking for effective sucrose substitutes that reduce the caloric value of their

products. Controlled crystallization of sucrose in presence of these substitutes is essential for the quality of

the food products. Since the textural quality of a food product depends on the crystal size distribution, the

rate of growth of the sugar crystals is critical to the final product characteristics [1]. In certain products, like

sugar-coated cereals, sugar substitutes are needed that cause no/minimum inhibition of sucrose crystal growth

rate.

The previous research has shown that when tagatose, invert sugar, erythritol, fructose, dextrose, and high

fructose corn syrup were studied for sucrose growth rate inhibition, invert sugar was found to have the leasteffect on crystal growth rate while fructose had the most effect [2]. Quiazzane et. al. [3] observed decrease in

the growth rate kinetics of sucrose in presence of monosaccharides, glucose and fructose (3% w/w

concentration) and combination of both, the reduction being more pronounced for fructose.

Not only are sugar substitutes increasingly used by food industries because of their cheaper cost and longer

shelf-life, but also they are beneficial for people who struggle with obesity and diabetes. Compared to

sucrose, sugar alcohols, such as maltitol and isomalt, usually have a lower caloric value while still providing

the same or greater sweetness. Fructose exhibits synergistic sweetening effects when combined with another

sugar substitute [4] and is more cost-effective in achieving higher sweetness levels than sucrose. Apart from

this many of the sugar substitutes like fructose, isomalt, maltitol and lactose also have much lower glycemic

index compared to sucrose.


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Even though there are some studies demonstrating the effect of sugar additives like glucose and fructose on

sucrose crystal growth rate, majority of them focus on crystallization of sucrose as a final product (sucrose

batch crystallization process) and at low concentrations of sugar additives. In the present work, a variety of

sugars and sugar alcohols were studied at different concentrations in the presence of sucrose seed crystals to

identify sugar substitutes, which may have potential to be used in cereals.

MATERIALS & METHODS

Materials

Three sugars (fructose, lactose, trehalose), two sugar alcohols (maltitol, isomalt), and three custom-designed

corn syrups (#1, #2, #5) (DE= not known) from Tate & Lyle were tested as potential sugar substitutes. The

solutions added with different sugar substitutes were labeled as S+Fructose, S+Lactose, S+Trehalose,

S+Maltitol, S+Isomalt, S+Corn Syrup #1, S+Corn Syrup #2, and S+Corn Syrup #5, respectively.

Methods

Sample preparation

Control sucrose solution (with no additive) (80:20 sucrose:water ratio) and sucrose solutions (80:20

sucrose:water ratio) with added sugar substitute at desired concentration (5 and 10% w/w) were made.

Samples were prepared gravimetrically. Weighed quantities of sucrose and different sugar substitutes in

excess water were heated to dissolve the sugar. Weight of the beaker was continuously monitored to reach to

a desired concentration. Once the target weight was reached, samples were allowed to cool down to 50C

(supersaturated state). A small portion of each sample was placed on glass slide and quickly seeded with few

sucrose crystals (< 100 m). A cover glass was placed over the slide, and all the four sides were taped to

prevent evaporation of water. Slide fixtures thus made were observed under the microscope fitted with a

temperature control system maintained at 50C and a digital camera to track the growth rate of seed crystals.

For each type of sample at least 8-10 such glass slide fixtures were observed under the microscope with each

glass slide focused at 3-6 seeded sucrose crystals placed at a reasonable distance from each other. For each

glass slide fixture a separate sugar solution was made.

Image analysisPictures of seed crystals in different solutions were recorded by software Q Capture Pro, (Q Imaging,

Surrey, Canada) at 2 minute intervals up to 16 minutes. For control sucrose sample and each sugar substitute

based sample, a minimum of 45 crystals were manually traced using image analysis software Image-Pro

Plus 6.1, (USA) to measure mean diameter. Data for each crystals mean diameter was used to calculate the

average growth rates of different sugar systems.

Mean diameters for all the sugar systems were analyzed for p-value by t-test (at = 0.05) to evaluate the

statistical significance.

RESULTS & DISCUSSION

The pictures of seeded sucrose crystals growing in various sugar systems were recorded using a digital

camera fitted to microscope at fixed interval of time and were later utilized to measure the change in themean diameter of crystals over the period of time to assess the growth rate. A series of pictures of sucrose

seed crystals in S+trehalose 5% w/w and S+corn syrup #5-5% w/w solutions in comparison to the sucrose

control solution are shown in Figure 1. Crystals from sucrose systems clearly seemed to be growing faster

compared to treahalose and corn syrup substituted systems. Sucrose crystals from S+corn syrup #5-5% w/w

system appeared to be growing slowest compared to other two systems from figure 1. In the case of

sucrose+corn syrup systems the sucrose crystal growth rate is inhibited by adsorption mechanism. The

glucose end-groups in the corn syrup adsorb to the sucrose lattice structure and inhibit crystal growth since

energy needed for sucrose molecule to displace the glucose unit and incorporate into the lattice.

Crystallization rates of sucrose crystals were found to be greatly affected by addition of common food

ingredients [5]. However, growth rate of sucrose crystals, compared at constant supersaturation, in presence

of invert sugar and raffinose was inhibited to different extent. Raffinose, which actually is incorporated into

the crystal lattice, caused greater degree of inhibition compared to invert sugar, which inhibited by adsorptionmechanism [6].


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Each crystals growth rate (from figure 1) in these trials is depicted graphically in Figure 2. For each picture,

the crystals are numbered from top to bottom, followed by left to right. Sucrose crystals formed from the

saturated solution were not tracked. Similarly, crystals touching or very close to the field of focus were

omitted too, as with time they would grow out of the field of focus.

Figure 1: Microscopic images of sucrose crystals at different time intervals in control sucrose, sucrose+treahalose 5%

w/w and sucrose+corn syrup #5 5%w/w systems

Figure 2. Change in the mean diameter of sucrose crystals in control sucrose (Blue), S+Trehalose 5% w/w (Green), andS+Corn Syrup #5-5% w/w (Red) systems

Sucrose

(Control)

Sucrose +

Trehalose

5%

Sucrose +

Corn Syrup#5

5%

0 Minutes 6 Minutes 12 Minutes

0

50

100

150

200

250

300

0 2 4 6 8 10 12 14 16 18 20

Time (minutes)

MeanDia

meter(m)

Crystal 1

Crystal 2

Crystal 3

Crystal 4

Crystal 1

Crystal 2

Crystal 3

Crystal 4

Crystal 1

Crystal 2

Crystal 3

Crystal 4

Crystal 5


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For each sugar system, the change in the mean diameter of at least 45 crystals was plotted as shown in figure

2. The slope of each line (assumed linear) was the growth rate (m/min) for that crystal. Average of sucrose

crystal growth rates for different sugar systems are shown in Table 1.

Table 1. Effects of different additives (5 or 10% addition) on sucrose crystal growth rate (m/min)

Additive (A) S S+A(5%) S+A(10%)

8.87

(2.23)

N/A N/A

Fructose 8.87X

(2.23)

4.69a, Y

(1.07)

3.22a, Z

(0.66)

Lactose 8.87X

(2.23)

4.90b, Y

(1.02)

2.85b, Z

(0.77)

Maltitol 8.87X

(2.23)

5.40c, Y

(1.02)

3.33a, Z

(0.77)

Trehalose 8.87X

(2.23)

5.73cd, Y

(0.97)

3.95c, Z

(0.92)

Isomalt 8.87X

(2.23)

5.84d, Y

(1.04)

3.84c, Z

(0.92)

Corn Syrup #1 8.87X

(2.23)

4.23e, Y

(0.81)

2.67b, Z

(0.58)

Corn Syrup #5 8.87X

(2.23)

4.47ae, Y

(0.89)

2.24d, Z

(0.56)

Corn Syrup #2 8.87X

(2.23)

4.39ae, Y

(0.96)

2.65b, Z

(0.54)abcde (columns)and XYZ (rows) values with the same superscript(s) are not significantly different from each other at

=0.05.

values in parentheses indicate standard deviation (n=45)

The average crystal growth rate for pure sucrose solution was ~ 8.9 m/min. All sugar substitutes inhibited

crystal growth rate to some extent, with the extent of inhibition increasing with an increase in the

concentration of sugar substitute. Growth inhibition was higher for the corn syrups (average growth rate at

5% concentration ~ 4.2-4.5 m/min) compared to the sugars and sugar alcohols (average growth rate at 5%

concentration ~ 4.7-5.8 m/min). Trehalose and isomalt showed the least inhibition.

Statistical tests indicated that growth rates of sucrose seed crystals at different concentrations of respective

sugar substitutes were statistically different, p value < 0.05 (rows in table 1). However, growth rates for

different sugar substitutes at identical concentrations were not significantly different, p value > 0.05

(columns, table 1). For example, fructose and lactose were not statistically different when the inhibitor

concentration was 5% but were statistically significant at 10%. At 5% concentration of sugar substitute,

growth rate inhibition was lowest in the case of S+isomalt system and highest in the case of S+corn syrup #1system. At 10% concentration of sugar substitute the growth rate of sucrose crystals was reduced

substantially (lower than 50%). Gowth rate inhibition was lowest in the case of S+Trehalose system closely

followed by S+isomalt system and was highest in the case of S+corn syrup #5 system. Laos et al. [7], in their

water activity based crystallization characterization study, observed that the presence of fructose, glucose and

corn syrup (DE=37.5) inhibited sucrose crystallization. They also observed that crystallization inhibition was

highest in the case of fructose and least in the case of glucose. However, in the present study corn syrups

showed highest inhibition compared to others including fructose. The rate of inhibition due to corn syrup

would also depend on the dextrose equivalance of corn syrups thus present study may not be directly

comparable with the earlier study. Hartel and Bhandari [8], also observed that crystallization of sucrose was

delayed by presence of lower molecular weight sugars like fructose, glucose and mixture of fructose and

glucose.


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In the case of control sucrose and the sugar substitute based systems, the sucrose seed crystals used had mean

diameter in the range of 60-100 m. All the seed crystals for the individual samples showed different crystal

growth rate and showed no trend with respect to initial diameter of the respective seed crystals. This

phenomenon is called growth rate dispersion, which is a characteristic of sucrose crystals [9]. Growth rate

dispersion was observed in the case of all the sugar systems studied in the present work. As a representative

of the systems, growth rate dispersions in the case of control sucrose, S+Trehalose 5% w/w, and S+CornSyrup #5-5% w/w systems are shown in figure 3. A lower degree of growth rate dispersion was observed in

the presence of the impurities.

Figure 3. Growth Rate Dispersion in Sucrose, S+Trehalose 5% w/w, and S+Corn Syrup #5-5% w/w

CONCLUSION

Sucrose crystal growth rate was inhibited in the presence of all sugar substitutes. However, the extent of

inhibition was different. Trehalose and isomalt inhibited sucrose growth the least for both concentrations

studied. As the concentration of individual sugar substitutes increased, sucrose crystal growth rate decreased.

In the case of all sugar systems, a characteristic growth rate dispersion associated with sucrose crystallization

was observed. Since trehalose, isomalt and maltitol have low glycemic index and isomalt and maltitol have a

low caloric value compared to sucrose, they can be used as the potential sugar substitutes for food industries.

More studies are warranted in the direction of identifying optimum sucrose supersaturation and the substitute

concentration for application in the sugar-coated cereals. The methodology developed in this study can be

effectively used for screening other prospective sugar substitutes for food applications.

REFERENCES

[1] Roos, Y.H. 1995. Phase transitions in Foods. Academic Press, USA.

[2] Varsos T. & Hartel R.W. 2006. Growth rate of sucrose crystals in a syrup inhibited by a sugar replacer. Unpublished

work.

[3] Quiazzane S., Messnaoui B., Abderafi S., Wouters J. & Bounahmidi T. 2008. Modeling of sucrose crystallization

kinetics: The influence of glucose and fructose, Journal of Crystal Growth, 310, 3498-3503.

[4] White J.S. & Osberger T.F. 2001. Crystalline Fructose. In: OBrien L. (Ed.). Alternative Sweetners, Marcel Dekker,

New York, USA.

[5] Hartel R.W. & Shastry A.V. 1991. Sugar crystallization in food products. CRC Critical Reviews in Food Science andNutrition, 30, 49-112.


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[6] Smythe B.M. 1967. Sucrose crystal growth rate: II. Rate of crystal growth in the presence of impurities. Australian

Journal of Chemistry, 20, 1097-1114.

[7] Laos A. K., Kirs B. E., Kikkas C. A. & Paalme D. T. 2007. Crystallization of the supersaturated sucrose solutions in

the presence of fructose, glucose and corn syrups. Proceedings of European Congress of Chemical Engineering

(ECCE-6), Copenhagen, 16-20 September, 2007.

[8] Bhandari B.R. & Hartel R.W. 2002. Co-crystallization of sucrose at high concentration in the presence of glucose and

fructose. Journal of Food Science, 67(5), 1797-1802.

[9] Liang B.M., Hartel R.W. & Berglund K.A. 1987. Growth rate dispersion in seeded batch sucrose crystallization.

AIChE Journal, 33(12), 2077-2079.

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