Starch Content in Various Types of Cane Sugars as a Criterion of Quality and Authenticity

Abstract

Contrary to beet sugar, which on the market is used practically only as white sugar, cane sugar is used in a wide range of products for direct consumption. This article presents results of determination of starch content in different types of cane sugars: raw cane sugar, refined white cane sugar, plantation white sugar, and commercial “unrefined” brown and yellow sugars. The content of starch in various “brown” cane sugars ranged from 74 to 415 mg/kg, while in white sugars its content ranged from 51 to 214 mg/kg. The starch content in cane sugars should be an important criterion for the quality of cane sugars, which allowed to differentiate cane sugars from beet sugar containing no starch.

Keywords:

• Sugar authenticity
• Starch
• Raw cane sugar
• Refined cane sugar
• Brown cane sugar

INTRODUCTION

Contrary to beet sugar, which on the market is used practically only as white sugar, cane sugar is used in a wide range of products for direct consumption. The following types of cane sugars are distinguished: refined white sugar, plantation white sugar, and various kinds of partly unrefined cane brown sugars. Refined white cane sugar is obtained from raw sugar by means of the refining process, whose main stages are affination and melting, clarification, filtration, evaporation, and crystallization. The main aim of the refining process is to remove color and reduce the quantity of soluble and insoluble impurities. Refined white cane sugar is comparable with beet sugar as regards to its quality and price. Plantation white sugar (PWS) is low quality white sugar (color ≤150 IU) obtained directly from cane in a sugar mill, without the refining process.^{[ 1 ]} PWS sugar can be used for direct consumption, however, its quality is lower than that of refined white cane sugar.

At present, various kinds of brown sugars enjoy great popularity on the market and are accepted by many consumers as organic, low-processed food products. The term “brown sugars” covers a wide range of products including raw sugar of various grades of purity (often referred to as “unrefined sugar”) and white sugar blended with caramelized, brown-colored by-products of cane processing (e.g., molasses, run-off syrups).^{[ 2 ]}

The main raw material for the production of various kinds of consumption cane sugars is raw cane sugar. Raw sugar is produced at sugar mills, in which juice, pressed from sugar cane, is clarified, filtered, evaporated, and crystallized. During crystallization, raw sugar is obtained, which, besides sucrose, contains a significant amount of mother liquor. It contains impurities that cannot be removed during cane processing. Four grades of raw sugar are distinguished. They are very, very high polarization (V-VHP), very high polarization (VHP), high polarization (HP), and low polarization (LP). Table 1 shows typical values of analyses of polarization, moisture, reducing sugars, ash, color, and the content of polysaccharides, such as starch and dextran for various grades of raw sugar. Irrespective of the quality of the raw sugar all the sugars contain starch. According to Australian and South African standards, starch content should be from 40 to 110 mg/kg. Brazilian standards allow starch content in V-VHP sugars up to 250 mg/kg; in lower quality sugars starch content may be several times higher.^{[ 3 ]}

Table 1 Grades of cane raw sugar according to Australian and South African standards

	V-VHP	VHP	HP	LP
Polarization, °Z	99.6	99.3	98.9	97.8
Moisture, %	0.06–0.12	0.10–0.18	0.24–0.29	0.35–0.60
Reducing sugars, %	0.07–0.11	0.14–0.16	0.27–0.50	0.51–1.1
Color, IU	450–650	1100–1500	1800	2200–3300
Ash, %	0.11–0.12	0.15–0.18	0.17–0.25	0.20–0.45
Dextran, mg/kg	20 (350*)	20–90	22–90	90
Starch, mg/kg	40 (250*)	50–110	60–110	80–110
*Brazilian standards.

As a result of the 2006 reform of the sugar market regime, Europe moved from the position of a significant exporter of white sugar to the position of the second in the world, after Russia, importer of sugar. Cane sugar can be imported to the European Union in two ways: as sugars for direct consumption or as raw sugar for refining. According to the requirements of the reform, cane sugar should be imported mainly as raw sugar from economically poor countries in African, Caribbean, and Pacific Group of States (ACP) and refined in Europe.^{[ 4 ]} This will result in some European sugar factories becoming refineries producing refined white cane sugar. The increasing entrance of cane sugar to the European market requires proper reaction of both sugar producers and industrial users of sugar. Thus, it is quite justified to carry on analysis of cane sugars concerning their quality as well as functional properties and microbiological purity.^{[ 2 ]} Although the quality and functional properties of refined white cane sugars are similar to those of beet sugars, there are, however, subtle differences. The quality of unrefined cane sugars is strongly differentiated and it depends on the kind of sugar and on the conditions of cane processing.

One such specific criteria in the process of evaluating the quality of cane sugars is the content of starch. Starch is a component present in cane sugar, but absent in beet sugar. Starch is a natural component of sugar cane; it is present in cane in the form of small (1–10 μm) water-insoluble granules and constitutes a reserve carbohydrate food.^{[ 5 ]} Cane starch consists of two fractions, amylose and amylopectin, both of which are polymers of glucose. The ratio of both the fractions of starch varies with plant species and also with plant age and maturity. Cane starch contains from about 15 to 20% of amylase. The starch content depends strongly on cane variety, and can vary from 275 to 1500 mg/kg solids. The higher concentration of starch is observed in the growing point and in the leaves, but mature cane has a lower starch content.^{[ 6 ]}

From cane, starch gets into all products of cane processing, including raw as well as refined sugar.^{[ 7 ]} The fine granules of sugar cane starch can be dispersed readily in juice by heating in clarification, during which gelatinization and maceration take place. Approximately 30% of starch in juice ultimately appears in the raw sugar crystal, and in this way it is transferred to the refinery. The presence of starch in raw sugar results in an increase of juice viscosity, which leads to lowering of the effectiveness of juice filtration and to poorer results of the processes of purification and decolorization, that is, it leads to an increase of the losses of sucrose. Besides, the presence of starch is an obstacle in the process of crystallization because the growing sugar crystals strongly adsorb starch from mother liquor and interfere with the deposition of sucrose molecules on the growing crystal surface. Finally, the high presence of starch leads to lower effectiveness of the refinery.^{[ 5, 7 − 9 ]}

The increasing interest of consumers in various kinds of cane sugars results in particular significance of studies of the quality and usefulness of different kinds of cane sugar. The aim of the study presented in this article was to determine starch content in different types of cane sugars: raw cane sugar, refined white cane sugar, plantation white sugar, and commercial “unrefined” sugars.

MATERIALS AND METHODS

Samples

The material for analysis consisted of 25 samples of raw sugar collected during a refining campaign in two European sugar factories (10 samples from one factory) (CRS-A) and 15 samples from another factory (CRS-B); 6 samples of cane refined white cane sugar (CWS); 4 samples of plantation white sugar (PWS) and, for comparison, 10 samples of beet white sugar (BWS); and 19 samples of various kinds of commercial “unrefined” cane sugars for direct consumption. The analyzed samples of cane “unrefined” sugars were divided into two groups. The first group consisted of 14 samples of “brown sugars” (CBS) in which the color was above 1000 IU; the second group consisted of 5 samples of “yellow sugars” (CYS) in which the color was below 1000 IU.

Analytical Methods

All analyses were performed in accordance with the methods accepted by the International Commission for Uniform Methods of Sugar Analysis (ICUMSA). The content of starch in the investigated materials was measured by means of ICUMSA GS1-16 method. This method measures spectrophotometrically starch in sugar as a blue starch-iodine complex. The starch is dissolved in calcium chloride solution and the color of the starch-iodine complex is measured spectrophotometrically at a wavelength of 700 nm.^{[ 10 ]}

In the analyzed samples, the conductivity ash and the color of the sugar solution were also determined. The conductivity ash content was measured using the ICUMSA GS2/3-17 method in white sugars and ICUMSA GS1/3/4/7/8-13 method in the remaining sugars. The conductivity ash is a measure of the concentration of ionized soluble salt present in sugar solution. The color of the sugar solution was measured according to the ICUMSA GS2/3-10 method in beet sugars and ICUMSA GS1/3-7 method in the other sugars. These methods measure sugar color as absorbance of filtered sugar solution at a wavelength of 420 nm. In raw sugar samples, the polarization grade using ICUMSA GS1/2/3/9-1 method, moisture content using ICUMSA GS2/1/3/9-15 method, and reducing sugars content using ICUMSA GS1-5 method were also determined.^{[ 11 ]}

Apparatus

A model U-1800 spectrophotometer (Hitachi, Japan) with 2.0 and 10.0 cm glass cells was used for recording the absorbance spectra. Conductivity of sugar solution was measured by automatic conductometer WTW inoLab 740 (WTW, Germany). Polarization grade of raw sugar solution was measured by Sucromat VIS/NIR (Dr. Kernchen, Germany).

Reagents and Standards

The reagents for starch analysis were acetic acid (2 mol/L), calcium chloride solution (40%), potassium iodate solution (0.0017 mol/L), and potassium iodide (10%); soluble starch from potato (Sigma-Aldrich®, Europe) was used as the standard. Conductivity standard 0.01 mol/L calcium chloride (LGS Standards, Europe) was used for calibration of a conductometer.

Statistical Analysis

All of the analyses were performed in duplicate. Data were subjected to basic statistics and one-way analysis of variance with the post-hoc Tukey test for identification of differences between the groups. Statistical analyses were carried out using STATISTICA data analysis software system, with a level of confidence of p < 0.05.^{[ 12 ]}

RESULTS AND DISCUSSION

Cane Raw Sugars

In this study, raw sugars from two different producers collected during 2008 and 2009 campaigns from European refineries were studied. The average values and basic statistical data for polarization, reducing sugars, ash, moisture, and starch content for these sugars are presented in Table 2. According to Table 1, both the analyzed raw sugars were classified as low polarization sugars. Sugar CRS-B was of better quality than sugar CRS-A; it was characterized by a statistically higher polarization and statistically lower content of moisture, reducing sugars and color. No significant difference was found in the content of ash in both the sugars. The lower quality raw sugar (sample CRS-A) showed a very high amount of starch—about 400 mg/kg, that is, almost four times higher than the refinery requirement for low polarization raw sugar. The CRS-B raw sugar contained a three times lower amount of starch—about 126 mg/kg. Statistical analysis showed no correlation between the content of starch and the other parameters of raw sugars. Starch, as a normal constituent of the sugar cane plant, is present in raw sugar as the result of starch pressed into cane juice during milling. It is assumed that starch content in raw sugar higher than 250 mg/kg affects significantly negatively refinery operations. The starch content in raw sugars given in the literature^{[ 6, 9, 13 ]} ranges from 76 to 590 mg/kg and depends on the kind of cane, way of harvesting, and processing technology. The presented considerable differences of starch content in raw sugar and its negative impact on the economic efficiency of the refining process justify including the content of starch in evaluating the quality of raw sugar.

Table 2 The average value and basic statistical data for polarization, reducing sugars, moisture content, and starch content for analyzing two different cane raw sugars

	Raw sugar sample CRS-A (n = 10)				Raw sugar sample CRS-B (n = 15)
	Average	Minimum	Maximum	SD	Average	Minimum	Maximum	SD
Polarization, °Z	97.9*	96.4	99.2	1.1	98.7*	98.5	99.0	0.1
Moisture, %	0.45*	0.11	0.85	0.31	0.23*	0.21	0.31	0.03
Reducing sugars, %	0.52*	0.17	1.00	0.35	0.32*	0.29	0.34	0.02
Color, IU	5390*	3800	6900	798	4240*	3560	4490	224
Ash, %	0.36	0.22	0.49	0.09	0.31	0.28	0.32	0.01
Starch, mg/kg	390*	342	415	23	126*	74	153	22
*Statistically important differences between samples CRS-A and CRS-B (p ≤ 0.05).

Cane White Sugars

The starch, which is present in the raw sugar, is not totally eliminated during the refining process; thus, it is also present in refined white cane sugar. The color and content of ash and starch of the analyzed cane and beet white sugars are presented in Table 3. Plantation white sugars (PWS) are white sugars produced directly in sugar mills, without the refining process. The quality of PWS is regulated by Codex Alimentarius, whereas there are no European regulations for this kind of sugar.^{[ 1 ]} The presented analyses show that cane sugar, irrespective of the degree of purification, contains some traces of starch. The mean starch content in PWS was three times higher than in refined sugar, which, however, contains about 50 mg/kg of starch. The content of starch in white sugar significantly influences the filterability of sugar solutions, which is very important for industrial sugar users, for instance, beverages producers. It should be stressed that, from the point of view of an individual consumer, traces of starch in refined white cane sugar are of very slight significance. For the sake of comparison, the content of starch in some samples of beet sugar was also determined; in none of them was any starch was found (Table 3). The absence of starch in beet sugar makes it possible to treat the presence of starch in sugar as one of the criteria of identifying its origin.

Table 3 The average value and standard deviation (SD) for color, ash content, and starch content for two types of cane white sugars and beet white sugar

	Color, IU		Ash, %		Starch, mg/kg
	Average	SD	Average	SD	Average	SD
Cane white sugars
Plantation white sugar (PWS) (n = 6)	111 ^a	31	0.035 ^a	0.003	214 ^a	89
Refined white sugar (CWS) (n = 4)	39 ^b	2	0.005 ^b	0.001	51 ^b	10
Beet white sugar (BWS) (n = 10)	31 ^b	2	0.010 ^c	0.001	nd	—
^a,b,cHomogeneous groups (p ≤ 0.05).
nd: Not detected with LOD = 20 mg/kg.

Cane “Unrefined” Sugars for Direct Consumption

As mentioned above, the analyzed cane sugars for direct consumption were divided into two groups with reference to their color. The first group consisted of 14 samples of “brown sugars” and the second group consisted of 5 samples of “yellow sugars.” The color, ash content, and starch content in brown and yellow sugars are presented in Table 4.

Table 4 The content of color, ash, and starch in commercial “unrefined” cane sugars for direct consumption (n = 2)

	Color, IU		Ash, %		Starch, mg/kg
	Average	SD	Average	SD	Average	SD
Cane “brown” sugars (Color >1000 IU):
CBS1	4140	207	0.388	0.003	226	32
CBS2	2490	120	0.199	0.002	205	21
CBS3	3260	163	0.308	0.003	233	22
CBS4	2610	127	0.178	0.002	306	23
CBS5	2550	103	0.418	0.003	255	26
CBS6	1500	130	0.219	0.002	228	28
CBS7	1610	75	0.118	0.001	170	15
CBS8	1610	102	0.178	0.002	188	16
CBS9	2070	81	0.146	0.001	283	28
CBS10	2000	140	0.363	0.002	258	32
CBS11	2920	83	0.169	0.002	274	22
CBS12	2350	98	0.159	0.001	290	24
CBS13	1370	117	0.169	0.002	264	22
CBS14	1960	68	0.049	0.001	165	18
Cane “yellow” sugars (Color ≤1000 IU):
CYS1	923	30	0.088	0.002	178	20
CYS2	687	22	0.058	0.001	126	11
CYS3	661	20	0.058	0.001	122	15
CYS4	323	30	0.069	0.001	161	17
CYS5	300	25	0.049	0.001	145	15

Brown sugars form a very inhomogeneous group consisting of various cane sugars present on the market as brown unrefined sugars. The color in this group ranged from 1368 IU (CBS13) to more than 4000 IU (CBS1); the average value of color in this group was 2317 ± 766 IU. The investigated brown sugars were characterized by an even greater differentiation as regards the content of ash. The lowest ash content was found in sample CBS14 (0.0491%), while the highest value of ash was found in sample CBS5 (0.4182%).

The group of yellow sugars consisted of various commercial cane sugars produced probably by blending white sugar with cane molasses rather than directly from unrefined sugars. The mean color of sugars in this group was 579 ± 265 IU. The ash content was statistically lower than in the group of brown sugars and it amounted on average to 0.065 ± 0.015%.

The content of starch in “brown sugars” was highly variable and it extended from 165.1 mg/kg for sample CBS14 to 306.3 mg/kg for sample CBS4. The mean value of starch in this group was 239 ± 44.6 mg/kg. In the group of “yellow sugars” the starch content in all samples was significantly lower than in brown sugars, and equaled on average to 150 ± 23.6 mg/kg.

CONCLUSIONS

On the basis of the above investigations, the following conclusions can be formulated: (i) The determination of starch content may be treated as one of the indicators differentiating white cane sugar from beet sugar, which contains no starch, and (ii) the content of starch in cane sugars should be an important criterion of the quality of sugar as raw material for various branches of food industry.

ACKNOWLEDGMENTS

The study was supported by research grant No. NN312 165934 from the Polish Ministry of Science and Higher Education.