Systematic Investigation of Migration and Decay Characteristics of Sweeteners in Cigarette Tipping Paper: Kinetics, Mechanisms, and Stability Implications

Analytical sweetener standards of acesulfame, sodium saccharin, sucralose, and aspartame were purchased from Dr. Ehrenstorfer GmbH, Augsburg, Germany. Neotame was purchased from Toronto Research Chemicals (TRC) Co. Ltd, Vaughan, Canada. Acetonitrile and methanol were acquired from Sigma-Aldrich (Steinheim, Germany). Ultrapure water was produced using Milli-Q water purifcation system from Millipore (Darmstadt, Germany).

The tipping paper samples used in this experiment were provided by Wuhu Cigarette Company, China Tobacco Anhui Industrial Co., Ltd. (Wuhu, China). The samples included seven tipping paper samples (labeled as S1, S2, S3, S4, S5, F1, and F2), where S1–S5 were mono-component samples while F1 and F2 were hybrid-component samples. For the preparation of tipping paper samples, stock solutions were prepared at varying concentrations according to sweetener categories: sulfonamide-type sweeteners (acesulfame and sodium saccharin) at 2% (w/v), sucrose derivative (sucralose) at 1% (w/v), and dipeptide-type sweeteners (neotame and aspartame) at 0.1% (w/v). The detailed information is presented in Table 1.

Approximately 0.5 g of tipping paper was weighed and transferred into a 50-mL centrifuge tube. The sample was diluted to 30 mL with a 20% methanol aqueous solution, followed by ultrasonic extraction for 10 min. The mixture was subjected to centrifugation at 10,000 rpm for 10 min. The supernatant was carefully decanted and recentrifuged under identical conditions (10,000 rpm, 10 min). Prior to analysis, the clarified solution was passed through a 0.22 μm membrane filter to obtain the final test sample.

Sweetener analysis was conducted using Agilent 1290 Infinity II HPLC system (Agilent Technology, Böblingen, Germany) coupled with a triple quadrupole mass spectrometer. The analytical methodology followed our previously established protocol (11), with complete method details available in the Supplementary Information. Chromatographic separation was achieved using an Agilent Eclipse Plus C18 column (4.6 mm × 100 mm, 3.5 μm) maintained at 30 °C. Mass spectrometric detection parameters, including precursor/product ion, declustering potentials (DP) and collision energies (CE), were individually optimized for each analyte (Table S1). Quantification was performed using freshly prepared calibration standard solution analyzed concurrently with samples. All samples were processed in duplicate, and the average value was recorded.

The transfer rate of sweeteners from stock solution to tipping paper was calculated by formula [a]. [a] Transfer rate=C0Cs×100% Transfer\,rate = {{{C_0}} \over {{C_s}}} \times 100\%

The decay rate of sweeteners on the cigarette tipping paper was calculated by formula (b). [b] Decay rate=(C0−Ct)C0×100% Decay\,rate = {{({C_0} - {C_t})} \over {{C_0}}} \times 100\%

Where C_s (μg/g) indicates the concentration of sweeteners in stock solution, C₀ (μg/g) and C_t (μg/g) indicate the content of sweeteners on the tipping paper at initial time (0 day or 0 hour) and t time (d/h), respectively.

The tipping paper sample was exposed to the air at ambient temperature (25 ± 2 °C) and the contents of sweeteners in the tipping paper were monitored from production day (Day 0) to Day 180 using HPLC-MS/MS analysis. Sampling frequency was adjusted based on degradation kinetics: measurements were taken every 10 days during the initial 70-day period when degradation rates were highest, then extended to 20-day intervals for the remaining 130 days as the compounds reached stabilization phases with significantly reduced decay rates.

For accelerated stability testing, the tipping paper sample was exposed to the air at 60 °C and 90 °C with analyses conducted from time zero to 30 h. At both elevated temperatures, the quantitative measurements were performed at 3-hour intervals to record the degradation kinetics. All thermal exposure experiments followed identical protocols to ensure comparability of results.

Sweeteners are transferred from the stock solution to the tipping paper via a coating process. Due to the differences in sweetness potency, economic cost, and the tobacco industry's sustainability requirements, the stock solution concentrations were optimized for each sweetener while ensuring compatibility with actual production conditions. Seven pretreated tipping paper samples (pretreated according to Section 2.3) were analyzed using HPLC-MS/MS, with representative chromatogram presented in Figure 1. Figure 2 illustrates the transfer rates of five mono-sweetener to the tipping paper. The observed variations originated from differences in stock solution concentrations, molecular polarity, solubility, and surface interactions with the paper substrate, among which the initial stock solution concentration was the most important factor. Notably, when the initial concentration was 2%, sulfonamide sweeteners exhibited relatively high transfer rates: sodium saccharin reached 19.75%, while acesulfame achieved 8.8%. The transfer rate of sucralose was comparable to that of acesulfame at a 1% initial concentration (both about 8%). In contrast, dipeptide sweeteners (neotame and aspartame) at a lower initial concentration (0.1%) showed similar transfer rates of approximately 1.5%.

Figure 1.

The HPLC-MS/MS chromatogram of five sweeteners.

1 – Acesulfame, 2 – Saccharin sodium, 3 – Sucralose, 4 – Aspartame, 5 – Neotame.

Figure 2.

The transfer rate of sweeteners in tipping paper from mono-component and hybrid-component stock solutions.

Figure 2 also presents the comparison in transfer rates between mono-component and hybrid-component sweetener systems. When coated from hybrid-components stock solution, all sweeteners exhibited reduced transfer rates compared to mono-component applications, likely due to competitive adsorption on the limited paper surface area. For example, the transfer rates of acesulfame decreased from 8.80% (mono-component, S1) to 3.10% (hybrid-component, F2). Similar trends were observed for other sweeteners. This competitive effect implied that higher initial concentrations may be required in sweetener stock solutions to compensate for reduced transfer efficiency. Among the hybrid-component samples, sodium saccharin still retained the highest transfer rate (5.62%), outperforming the other components. This confirmed that the affinity between sodium saccharin and the surface of paper was stronger than that of the other sweeteners.

The physicochemical properties of the five sweeteners are summarized in Table 2. Sodium saccharin, containing a hydrophobic benzene ring, exhibits substantially lower aqueous solubility than acesulfame. Consequently, at equivalent high concentrations (2%), sodium saccharin demonstrated stronger affinity for the paper surface, resulting in superior transfer efficiency compared to acesulfame. Owing to their exceptionally high sweetness potency, dipeptide sweeteners (such as neotame) were applied at very low concentrations (0.1%). Combined with their lower solubility relative to sulfonamide sweeteners, this resulted in minimal transfer.

Table 2.

Sweetener	Structural formula	Molecular weight (g/mol)	pKa	Water solubility (mg/L)	Sweetness valuea
Acesulfame (Acs) C4H4KNO4S		201242	20	9.1 × 105	200
Sucralose (Suc) C12H19C13O8		397634	125	2.82 × 105	600
Neotame (Neo) C20H30N2O5		373463	4.1, 7.7	1.26 × 104	8000
Aspartame (Asp) C14H18N2O5		294303	2.9, 7.3	5.65 × 104	200
Sodium saccharin (Sac) C7H4NNaO3S		205170	13	3.3 × 105	450

a

Sweetness value: The relative value indicating the intensity of sweetness based on the sweetness of sucrose (12).

In order to further explore the decay characteristics of sweeteners on tipping paper, different kinetic models were employed to fit the experimental data for mono-sweeteners and determine the speed controlling step (40). According to Askarizadeh et al. (41), four primary models are widely used among the numerous drug release decay models: the zero-order, first-order, Higuchi, and Korsmeyer-Peppas models. These models are also applicable to the molecular release system at solid interfaces. Given that tipping paper products provide a porous structure for sweetener molecules and interact with them, this study employed these four established decay kinetics models to characterize the release kinetics of sweeteners from tipping paper. The four model equations are as follows: [1] Zero−order model:Q=a+kt \matrix{{{\rm{Zero}} - {\rm{order}}\,{\rm{model}}:} & {Q = a + kt} \cr} [2] First−order model:Q=Qm(1−e−kt) \matrix{{{\rm{First}} - {\rm{order}}\,{\rm{model}}:} & {Q = {Q_m}(1 - {e^{- kt}})} \cr} [3] Higuchi model:Q=kt1/2 \matrix{{{\rm{Higuchi}}\,{\rm{model}}:} & {Q = {kt}^{1/2}} \cr} [4] Korsmeyer-Peppas model:Q=ktn \matrix{{{\rm{Korsmeyer - Peppas}}\,{\rm{model}}:} & {Q = {kt}^n} \cr}

As shown in the decay curve in Figure 3, the release decay of each mono-sweetener coated on tipping paper at room temperature over 180 days can be segmented into three stages: 0–30 d, 30–70 d, and 70–180 d. Each stage was individually fitted using the above four models and the model with the highest R² value was selected as the optimal one and its parameters are listed in Table 3. The fitting lines with five sweeteners in three stages are shown in Figure 7.

Figure 7.

The optimal decay kinetics model of sweeteners in three stages. (a) Acesulfame, (b) Sucralose, (c) Neotame, (d) Aspartame, (e) Sodium saccharin.

Across all three stages, the decay processes of acesulfame, sucralose, aspartame, and sodium saccharin were most consistent with the Korsmeyer-Peppas kinetics model. In contrast, the degradation behavior of neotame follows the zero-order model in all three stages. The Korsmeyer-Peppas model is widely used to characterize substance release mechanisms, with the parameter “n” as a key descriptor (28). For n ≤ 0.5, the model describes dominated release – typical of substance release from inert frameworks where molecular diffusion prevails. For 0.5 < n < 1, release is co-driven by molecular diffusion and molecule-polymer framework interactions.

As shown in Figure 7(a), acesulfame best fitted the Korsmeyer-Peppas model across all three stages: n = 0.96 for 0–30 d, and n ≤ 0.5 for time beyond 30 d. This is attributed to electrostatic adsorption between K⁺ in acesulfame molecules and carboxyl groups on the tipping paper surface. In the initial 30 d, high transfer rate led to high ion levels and a thick diffusion layer, which meant that the surface adsorption force between the paper substrate and acesulfame in the outermost electric double layer tended to weaken and was prone to a higher decay rate. As acesulfame (and thus K⁺) concentration decreased afterward, electrostatic effects weakened, making the decay behavior more consistent with Fick diffusion.

As shown in Figure 7(b), for sucralose in samples S2, the Korsmeyer-Peppas model provided the optimal fit across all three time periods, with the fitting parameter “n” lower than 0.5 in each stage. This is attributed to the hydroxyl groups of sucralose structure, which readily form hydrogen bonds with cellulose on the paper surface. Such uniform binding between the molecule and the tipping paper renders the decay process more consistent with the Fick diffusion model.

As shown in Figure 7(c), for neotame in sample S3, the zero-order model best fitted its decay within all three stages. Neotame, a dipeptide compound containing tert-butyl groups, exhibits the strongest hydrophobicity among the five sweeteners. Due to steric hindrance, its interaction with the paper surface is relatively weak (42). Thus, significant decay conformed well to the zero-order model at all three stages – characterized by a constant elimination rate per unit time, independent of residual sweetener content on the tipping paper (i.e., constant decay). Concurrently, the decreasing “k” value indicated a slowing decay rate.

Like neotame, aspartame is a dipeptide sweetener with amino (−NH₂) and carboxyl (−COOH) groups. Its amino groups were apt to form hydrogen bonds with cellulose hydroxyls, while protonated carboxyl groups interact with paper's negative charges, resulting in higher paper transfer rate than neotame. As shown in Figure 7(d), the Korsmeyer-Peppas model provided the best fit for aspartame's decay behavior over time. During the initial 70 d, the release exponent (n) remained close to 1, indicating near-zero-order kinetics: 0–30 d: n = 1 (perfect zero-order kinetics); 30–70 d: n = 0.9958 (approaching zero-order). This suggests that aspartame's initial decay behavior was dominated by surface diffusion, likely due to molecular accumulation on the paper surface. Beyond 70 d, the decay behavior shifted and aligned more closely with the Korsmeyer-Peppas model where n = 0.05. This shift implies that after the initial rapid transfer phase, aspartame's migration became diffusion-limited, consistent with typical matrix-controlled release mechanisms.

As shown in Figure 7(e), sodium saccharin (in sample S5) also followed the Korsmeyer-Peppas model during the initial 70-day period. As an ionic compound, it formed ionic bond force between its sulfonyl groups and charged groups on paper surfaces – behavior mirroring acesulfame. After 70 days, decay transitioned to zero-order kinetics with a rate constant k = 6.8 units/d.

Overall, the Korsmeyer-Peppas model best described the overall decay kinetics of all five sweeteners on cigarette tipping paper products. For specific sweeteners during certain stage, the zero-order model (a special case of Korsmeyer-Peppas when n = 1) provided a more precise fit. This indicates that Fick diffusion dominates the decay process, though inter-facial interactions between sweetener molecules and groups on cigarette tipping paper surface also contribute obviously during certain time periods.

Tipping paper serves as a critical auxiliary material in modern cigarette production, fulfilling dual roles: structural support for tobacco shreds and sensory modulation through aroma/taste component adsorption. Its shelf-life stability, particularly under ambient storage conditions, directly determines cigarette quality, sensory profile, and market acceptance. For sweetener-function tipping paper, quantifying sweetener decay represents the primary shelf-life evaluation metric. According to the previous data of this article, the decay curve of sweeteners on the tipping paper at room temperature showed a consistent changing trend. The decay time points of five sweeteners were sorted out, and the time points with the difference value of decay rate less than 3% were defined as the suitable shelf life of the product. Table 4 shows the time points of mono- and hybrid-sweeteners of the five sweeteners. Obviously, within the first 30 days after production, the decay of the sweetener was relatively high whether in a mono-component or hybrid-component system. This was because the initial concentration of the sweetener was relatively high, and the accumulation of molecules on the surface of the paper product was unstable, so its content decreased relatively rapidly. After this relatively rapid decay, the sweetener entered a relatively stable period, during which the decay rate significantly slowed down, and the sweetness potency of the tipping paper entered a relatively stable state (about 60 d). In the following months and even for half a year, the content of the sweetener remained basically unchanged, confirming the stability of the tipping paper during its shelf life. Actually, the rapid decline period of sweeteners in the tipping paper during the first 30 days provides a relatively relaxed processing time window for cigarette production. In the subsequent stage, when the decay enters a stable period (about 60–180 d), the stability of the cigarette tipping paper further improves. This means that there is a stage of up to half a year for the storage of cigarette tipping paper and cigarette production, which can ensure the stability of quality and reduce sensory quality problems caused by the unstable decay of the sweetener, ensuring the reliability of long-term quality.