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Mechanisms of flavor release and perception in sugar-free chewing gum

Dissertation
Author: Rajesh Venkata Potineni
Abstract:
The flavor properties of chewing gum are undoubtedly a key product attribute for consumption. However little is known about how many of the various ingredients (i.e. flavor solvents) in chewing gum alter flavor delivery. Consequently, defining mechanisms which influence flavor release in chewing gum is important for understanding its product quality and possibly may also translate to drug delivery applications for the pharmaceutical industry. The first objective of this study investigated the influence of three flavor solvents on the aroma/taste/textural properties in a sugar-free chewing gum. Model chewing gums made with [0.67%; triacetin (TA) or propylene glycol (PG) or medium chain triglycerides (MCT)] and without flavor carrier solvent. The chewing gums were analytically characterized in vivo for three panelists over a period of 12 min. Volatile analysis of cinnamaldehyde, L-carvone, piperitone, jasmone was conducted using Atmospheric Pressure Chemical Ionization-mass spectroscopy (APCI-MS). Sorbitol release from saliva was tracked using High pressure Liquid Chromatography (HPLC) coupled with Refractive Index Detector (RID), while the textual properties (softness) were measured using TA-XT2. Furthermore, the perceived flavor properties of these chewing gum samples were measured using a time-intensity sensory study (TI) on the aroma (cinnamon-like), taste (sweetness) and textural (effort to chew) attributes using a trained sensory panel. Flavor solvent addition to chewing gum did not significantly influence the aroma release profiles of all the 4 compounds. However, the sorbitol release rate was significantly lower for chewing gum made with TA compared to the other treatments. The sensory analysis was in agreement with the analytically data; lower levels of sweetness and cinnamon-like flavor intensity were perceived for chewing gum made with TA were observed, suggesting taste-aroma interactions. Chewing gums formulated with TA or MCT were reported to be softer (based on texture analysis) then with PG or no flavor solvent addition. However, no correlations were reported between the instrumental texture analyses of the chewing gum (softness) and the flavor release. Overall, flavor solvent choice did influence the sorbitol release in chewing gum matrix due to unique plasticizing/softening mechanism of the solvent utilized. The second objective of this study was to investigate the mechanisms for cinnamaldehyde release in a sugar-free chewing gum. Chewing gums containing (25%-Paloja gum base, 61%-sugar alcohol, 4%-glycerine, 0.46% sweeteners, and 0.02% lecithin) were made with varying concentrations of cinnamaldehyde. Additionally chewing gums were made with p-cresol (similar log P as cinnamaldehyde). A cinnamaldehyde or cresol flavored gum base (no sugar alcohol) was also made to investigate the role of the gum base on flavor release. Three panelists were asked to chew gums or flavored gum base, while aroma release profile was tracked from the nose exhaled breath using APCI-MS over a period of 8 min. The release profile of cinnamaldehyde from chewing gum was found to correlate with the sugar alcohol release in a sugar free gum. Chewing gums made with varying amounts of cinnamaldehyde (0.29-2.9 mg/g of chewing gum) did not show any differences in release pattern suggesting no concentration effect. Furthermore, the cinnamaldehyde release pattern from the gum base was similar to cresol or as predicted from the log cP value (distribution coefficient between the gum base and water). These findings suggested cinnamaldehyde was interacting with the sugar alcohol phase, possibility due to transient hemi-acetal reactions mechanisms, which resulted in a more rapid release rate than would be predicted based on the hydrophobicity of this compound.

Table of Contents List of Figures ..............................................................................................................ix List of Tables ...............................................................................................................xi ACKNOWLEDGMENTS ...........................................................................................xii Chapter 1 Introduction .................................................................................................1 Chapter 2 Review of Literature ....................................................................................3 2.1 Confectionary industry ...................................................................................3 2.2 Chewing gum ..................................................................................................3 2.2.1 Market and trends: ................................................................................3 2.2.2 Benefits of chewing gum ......................................................................4 2.2.3 Typical chewing gum composition ......................................................5 2.2.3.1 Water Insoluble phase ................................................................6 2.2.3.1.1 Gum base ..........................................................................6 2.2.3.2 Water-soluble phase ...................................................................9 2.2.3.2.1 Sweeteners in chewing gum .............................................9 2.2.3.2.2 Physiological cooling agents (PCA) ................................11 2.2.3.2.3 Warming agents ...............................................................12 2.2.4 Process of making chewing gum ..........................................................13 2.3 Flavor release and perception .........................................................................13 2.3.1 Physiological process ...........................................................................14 2.3.2 Thermodynamics ..................................................................................16 2.3.2.1 Partitioning factors .....................................................................17 2.3.3 Mass transfer ........................................................................................19 2.3.3.1 Stagnant-film Model ..................................................................20 2.3.3.2 Penetration theory ......................................................................21 2.3.3.3 Non-equilibrium partition model ...............................................22 2.4 Flavor perception/measurement ......................................................................23 2.4.1 Commonly used analytical methods to measure flavor release ............25 2.4.1.1 Static/Dynamic headspace analysis ............................................25 2.4.1.2 Model mouth systems .................................................................26 2.4.1.3 Breath/volatile analysis (in vivo) ................................................27 2.4.1.4 Non-volatile analysis ..................................................................31 2.4.1.5 Time-Intensity sensory analysis .................................................33 2.5 Taste, aroma and texture interactions .............................................................35 2.5.1 Taste-aroma interactions ......................................................................35 2.5.2 Irritant effect on taste-aroma interactions .............................................39 2.5.3 Texture effects on flavor release ..........................................................40 2.6 Food Matrix interactions on flavor release .....................................................42 2.6.1 Proteins .................................................................................................42 2.6.2 Carbohydrates .......................................................................................43

vii 2.6.3 Lipids ....................................................................................................45 2.6.4 Flavor compound-compound interactions ............................................48 2.7 Flavor aspects of a chewing gum ....................................................................49 Chapter 3 Hypothesis I .................................................................................................54 Chapter 4 Influence of Flavor Solvent on the Mechanisms of Flavor Release in Sugar-Free Chewing Gum ................................................................................55 4.1 Abstract ...........................................................................................................55 4.2 Introduction .....................................................................................................56 4.3 Materials and Methods ...................................................................................59 4.3.1 Materials. ..............................................................................................59 4.3.2 Chewing gum models. ..........................................................................59 4.3.3 Quantification of aroma compounds. ...................................................60 4.3.4 Gas Chromatography (GC). ..................................................................61 4.3.5 Analysis of sorbitol/maltitol release. ....................................................61 4.3.6 High Performance Liquid Chromatography (HPLC). ..........................62 4.3.7 Aroma compound release analysis (In Vivo). .......................................62 4.3.8 Instrumental texture analysis. ...............................................................64 4.3.9 Gum volume analysis. ..........................................................................64 4.3.10 Plasticity index analysis. ....................................................................65 4.3.11 Sensory analyses. ................................................................................65 4.3.12 Statistical analysis. .............................................................................67 4.3.12.1 Instrumental data ......................................................................67 4.3.12.2 Sensory data .............................................................................67 4.4 Results and discussion ....................................................................................68 Chapter 5 Hypothesis II ...............................................................................................83 Chapter 6 Mechanisms of Flavor Release in Chewing Gum: Cinnamaldehyde ..........84 6.1 Abstract ...........................................................................................................84 6.2 Introduction .....................................................................................................85 6.3 Materials and methods ....................................................................................87 6.3.1 Materials. ..............................................................................................87 6.3.2 Chewing gum model. ............................................................................88 6.3.3 Flavored gum base model. ....................................................................88 6.3.4 Quantification of cinnamaldehyde/cresol in chewing gum or flavored gum base. .................................................................................89 6.3.5 Gas Chromatography (GC). ..................................................................89 6.3.6 Log P analysis. ......................................................................................90 6.3.7 Log cP analysis. ....................................................................................90 6.3.8 Breath analysis. .....................................................................................92 6.3.9 Sugar alcohol/glycerine release analyses. ............................................93 6.3.10 High Performance Liquid Chromatography (HPLC) analysis. ..........93 6.4 Results and discussion ....................................................................................94

viii Chapter 7 Future Research ...........................................................................................109 Bibliography ................................................................................................................112 Appendix A: Influence of thermal processing conditions on flavor stability in fluid milk: benzaldehyde ......................................................................................123

ix List of Figures

Figure 2-1 Various components that affect the flavor release .....................................14 Figure 2-2 Retronasal breath/volatile (in vivo) analysis using APCI-MS; [60] ...........29 Figure 2-3 Non-volatile analysis by HPLC in combination by ESI- MS/UV/RID [83] ..................................................................................................33 Figure 2-4 Flavor release profile from a sugar stick gum during the fist 10 min compared with that during the next 20 min (average of 10 people). 1) ethyl cinnamate (LogP: 2.99), 2)methyl cinnamate (Log P: 2.62), 3)methyl benzoate (Log P: 2.12), 4) cinnamyl alcohol (Log P: 1.95), 5) ethyl vanillin (Log P: 1.58), 6) 4-(p-hydro-xyphenyl)-butane-2-one (Log P: 1.48) and 7) Vanillin (Log P: 1.58) [51] ..........................................................51 Figure 2-5 Release of Sucrose release (·), menthone (-), and perceived intensity of overall mint flavor (TI curve) ( ), from a stick type commercial chewing gum [72]. ............................................................................52 Figure 4-1 Cinnamaldehyde release (in vivo) analyzed by APCI-Breath Analysis for 3 panelists for chewing gums made with different flavor carriers; each curve represents the mean of three replicates subsequently smoothed by a 1.5-s moving average trendline. ...................................................77 Figure 4-2 L-Carvone release (in vivo) analyzed by APCI-Breath Analysis for 3 panelists for chewing gums made with different flavor carriers; each curve represents the mean of three replicates subsequently smoothed by a 1.5-s moving average trendline .............................................................................78 Figure 4-3 Sorbitol release for 3 panelists from chewing gums consumed for 12 mintues made with different flavor solvent carriers; average of triplicate ................................................................................................................79 Figure 4-4 Time course gum volume measurements from chewing gums made with PG, Triacetin, MCT or No Solvent for 3 panelists consumed over 4 minutes ..................................................................................................................80 Figure 4-5 Total work done analyzed by TA-XT2 for 3 panelists from chewing gums made with different flavor solvent carriers; average of five replicates + 95% C.I. ............................................................................................81 Figure 4-6 Sensory time-intensity analysis of (i) cinnamon-like flavor, (ii) sweetness and (iii) effort to chew; average of 9 panelists ....................................82

x Figure 6-1 Release kinetics of cinnamaldehyde and sorbitol from a chewing gum made with VH1 gum base; adapted from Chapter 3 [178] ...........................102 Figure 6-2 Cinnamaldehyde, cresol and total sugar alcohol release in chewing gums made with PALOJA gum base for one panelist; (a) and (b) each curve represents the mean of three replicates subsequently smoothed by a 3-s moving average trendline, (c) curve represents the mean of three replicates +

95% confidence intervals ..................................................................103 Figure 6-3 Release patterns of cinnamaldehyde in chewing gum at two different cinnamaldehyde concentrations a) 2860 µg/g chewing gum, and b) 288 µg/g chewing gum for panelist 1; each curve represents the mean of three replicates subsequently smoothed by a 6-s moving average trendline. ...............................................................................................................104 Figure 6-4 Release of (a) cinnamaldehyde and (b) cresol release from gum base with MCT cinnamaldehyde or cresol release profile from chewing gum (figure 2) was also illustrated for comparison; each curve represents the mean of three replicates subsequently smoothed by a 6-s moving average trendline a ...................................................................................................105 Figure 6-5 Proposed release mechanism for cinnamaldehyde in chewing gum during mastication ................................................................................................106 Figure 6-6 Glycerine release in chewing gum and gum base made with MCT; average of triplicates + 95% confidence interval .................................................107 Figure 6-7 Release of anisaldehyde and carvone in chewing gum made with PALOJA gum base for panelist one; each curve represents the mean of three replicates subsequently smoothed by a 3-s moving average trendline ........108

xi List of Tables Table 2-1 Sale comparison of gum and mints segment between years 2000 and 2003, according to the mintel report [2] ...............................................................5 Table 2-2 Typical chewing gum composition for sugar and sugar-free gums [3] ..........................................................................................................................6 Table 2-3 Typical gum base composition of chewing gum [5] ...................................7 Table 2-4 List of various ingredients used across different categories in a typical gum base [5] ..............................................................................................9 Table 4-1 Chewing gum model formulation ................................................................73 Table 4-2 Compositional range of gum base ...............................................................73 Table 4-3 Composition of model cinnamon-like aroma and estimated Log P values ....................................................................................................................74 Table 4-4 Quantification data of aroma compounds in chewing gum samples made with PG, TA, MCT or no flavor solvent. ....................................................74 Table 4-5 Plasticity index values of gum bases made with different flavor solvents .................................................................................................................75 Table 4-6 Tukeys’ mean comparison of sorbitol release from chewing gums with different flavor solvents at 30 and 70 sec .....................................................75 Table 4-7 Tukeys’ mean comparison of sensory parameters of chewing gums with different flavor solvents ................................................................................76 Table 6-1 Chewing gum composition made with PALOJA gum base ........................99 Table 6-2 Volatile quantification of chewing gums made with PALOJA gum base .......................................................................................................................99 Table 6-3 Log P and Log Cp values for cinnamaldehyde and p-cresol .......................100 Table 6-4 Cinnamaldehyde, cresol and glycerine concentrations in flavored gum base models made with PALOJA gum base .................................................100 Table 6-5 Maximum average aroma concentration in the breath from 0-4 min and 6-8 min from chewing gum and gum base a ...................................................101

xii ACKNOWLEDGMENTS I would like to express my gratitude and sincere appreciation to my advisor, Dr. Devin Peterson, for taking me in as his first PhD student and therefore mentoring me during my graduate studies. I would also like to thank him for his guidance, friendship and for letting me develop into a better scientist. I am also indebted to Dr. John Coupland, Dr. John Floros, and Dr. Daniel Jones for serving on my committee. I specifically thank Marlene Moskowitz and Alicia Holt for helping me all throughout my project by being my project panelists. I am extremely grateful to them for their support, patience, time and encouragement. I am also grateful to Julie Peterson for helping me with sensory evaluations of chewing gums. I am grateful to Tom Caroll, Ruth Hollander, Christopher Bennett, Vennasa, my sensory panelists for helping me in my project. I would like to thank my lab group-Vandana, Stacy, Yuko, Marlene, Alicia, Amanda, Shalini, and Paula for the good times spent in the lab. I am grateful to friends, graduate students, office staff (esp. Melisa and Jaunita) and the Penn state cricket club for making my stay at Penn State more memorable. Last but not the least, I would like to thank my family, Celia and Sriram for their moral support, encouragement, to vent on occasion, and for making me laugh.

1 Chapter 1

Introduction

In order to sustain competition as well as growth, the candy and gum industry has focused on novel products with high flavor intensity, long lasting flavor and as unique applications drug delivery systems (i.e. nicotine). However most of these emerging technologies are in the form of patents, and do not provide any scientific literature to understand the mechanisms that impact compound delivery or flavor release and perception. This research project was conducted to investigating the mechanisms that impact flavor release and perception in chewing gum matrix. Flavor solvents, such as triacetin, propylene glycol, medium chained triglycerides, are used as dispersing agents in many food systems as well as plasticizing agents in chewing gum. However little is known about how these solvents, with unique physical-chemical properties ultimately influence the aroma, taste and texture properties of chewing gum. No scientific study has been conducted to understand the influence of flavor solvents in a chewing gum matrix. The first objective of this thesis was therefore to investigate the influence of flavor solvent type on aroma, taste and texture properties in a sugar-free chewing gum was investigated as well as any cross-modalities among these flavor stimuli. Furthermore, the gum and flavor industry use a simplified model to predict the flavor release of compounds in chewing gum; log P or log cP values (indicator of compound hydrophobicity or company affinity for the gum matrix). Compounds with

2 lower log cP (or log P) value are predicted to release faster any compounds with a high log cP (or log P) value. Based on the complexity of the flavor compounds and chewing gum ingredients, the use of log P or log cP model was considered to be likely an over simplified approach and therefore was the focus of the second objective of this research project.

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Chapter 2

Review of Literature

2.1 Confectionary industry The total sales of confectionery products ranked 3 rd behind carbonated beverages and milk in the United States, according to the 2005 IRI report with sales surpassing $28 billion [1]. Overall, these confectionery products consisted of 5 main categories: chocolate, non-chocolate, mints, gums and others. Based on the 2005 US Department of Commerce, NCA estimated an increase in retail sales for chocolate, non-chocolate and gum categories by 2.0%, 0.9%, and 4.1% respectively [1]. 2.2 Chewing gum 2.2.1 Market and trends: According to the latest Mintel’s report (2003), the consumption of breath freshening products such as gums, mints, and breath strips has increased by 41% since 1997[2] in the US marketplace. With respect to gum confectionery products, total sales reached a value of $385 million in UK and $ 2.2 billion in the US in 2002 (Conway, 2003). Sales of regular gums have declined by 5.6% from 2000 to 2002 while the demand for sugar-free gums has been increased with a jump in sales by 28% from 2000

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to 2002 (Table 2-1). The primary reasons for this sales boost may be due to new varieties of gums using different sweeteners, less calories, better mouth-feel and/or strong advertising. Currently, chewing gum has been consumed to a greater extent not only as a commercial flavor gum but also as a drug delivery system in the field of pharmacy, which demonstrated a 7% growth in sales for dental and nicotine gums from 2000 [3]. These gums carry various key functional compounds such as nicotine, fluoride (Fluogum ® , Flourette ® ), calcium carbonate (Surpass ® ), caffeine (Stay Alert ® ) and other compounds (Conway, 2003, #23). The basic factors affecting the drug release from a medicated gum includes the physiochemical properties of the drug and gum as well as the chewing efficiency [3]. Mintel’s report further predicts the total retail sales will grow by 27% from 2002 to 2007 in the category of gums and mints [2]. In the case of gum confectionary alone, sales are projected to rise by 13% to $4.7 billion, between 2003 and 2007 in the global marketplace [1]. This expanding market will be mainly driven by new product introductions for consumers at various age groups. New gum products making their way into the market include antacid gum (contains calcium carbonate), caffeine-containing gum as well as anti-emetics for travel sickness [3]. 2.2.2 Benefits of chewing gum

[4] • Improves concentration • Eases tension • Freshens breath and reduces the urge to smoke • Provides a low-calorie snack

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• Helps fight tooth decay • Helps one stay alert and awake • Acts as a pleasant way to take vitamins and medicine • Reduces ear discomfort during flight travel

Table 2-1 Sale comparison of gum and mints segment between years 2000 and 2003, according to the mintel report [2] 2.2.3 Typical chewing gum composition Chewing gums consist of two phases, 1) water-insoluble gum base phase and 2) water-soluble sugar or sugar alcohol phase. The ratio of soluble to insoluble phases has a great impact on the flavor release characteristics. Basic chewing gum composition for a sugar gum as well as a non-sugar gum is given in Table 2-2.

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Ingredients Sugar gum (%) Sugar free gum (%) Gum base 20 25-30 Sugar 60 - Glucose syrup / Corn syrup 18-20% - Polyols < 1% 50-60 Glycerin < 1% 5-6 Flavor 0.5 -1 1-1.5 High intensity sweeteners - Aspartame (0.01 -3%) Based on the sweetener type Table 2-2 Typical chewing gum composition for sugar and sugar-free gums [3]

2.2.3.1 Water Insoluble phase 2.2.3.1.1 Gum base: A typical gum base composition consists of elastomer, elastomer solvent, polyvinyl acetate, emulsifier, low molecular weight polyethylene, waxes, plasticizer and fillers. An example of a non-adherable chewing gum base composition and the function of these ingredients in chewing gum are given in Table 2-3 and Table 2-4, respectively [5]. The properties of these ingredients are furthermore discussed in more detail below. Elastomers provide the desired body, along with rubbery texture and cohesiveness. When present in low quantities, these gums may lack elasticity, while high concentrations renders the gum hard and too rubbery [5]. In addition to texture, flavor release characteristics of the gum base have also been reported to be affected by the type

7

of elastomer used. For example, gum bases made with poly (Isobutylene) showed higher affinity for flavor compounds (such as ethyl butyrate, cis-hexenal. 1-octanol, and limonene) compared to poly (vinyl acetate) [6]. Higher affinity results to longer lasting flavor during chewing. On similar lines, Sostmann et al. (2003) found that synthetic gum base made with Styrene Butyl Rubber (SBR) has greater affinity for ¶-electron flavor compounds such as anethole, octanal and isopropyl-pyridine [7]. Some elastomers have been reported to sequester the flavor molecules, thus preventing flavor release during chewing [8]. Elastomer solvents are often resins such as terpene resins. These solvents help in softening the elastomer rubber components. When present in low percentage, the chewing gum has unacceptable chewing characteristics [5]. On the other hand, excess solvent result in stickiness to dental surfaces. Ester resin gums are also known to have a high affinity for polar molecules such as alcohol and aldehydes [6].

Ingredients Weight (%) Elastomer 10-30% Elastomer solvent 2-18% Plasticizer 20–35% Polyvinyl acetate 15–45 % Emulsifier 2–10% Low MW Polyethylene 0.5 – 15% Waxes 0.5 – 10% Filler 0 – 5% Table 2-3 Typical gum base composition of chewing gum [5]

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Polyvinyl acetate (PVAc; (MW- 15,000 to 30,000) at low levels can destabilize the base resulting in non-uniform flavor release[5]. However, at higher levels, the gum bases are to hard and plastic. PVA has also been found to have a higher affinity for polar alcohols [7]. Emulsifiers (HLB: 1.6 – 7.0) provide a smooth surface to the gum and reduces its adhesive nature as well as aid in mixing the immiscible components to form a stable dispersion system leading to texture acceptability and stability [5]. However, higher amounts can lead to an unstable paste-like product. Furthermore, emulsifiers can sometimes function as plasticizers. Ingredients Examples Elastomer Styrene- butadiene copolymer (SBR), Polyisobutylene, Isobutylene-isoprene copolymers (Butyl gum), Natural gums such as chicle, natural rubber, jelutong, gutta-percha, lechi caspi, sorva, Polyvinyl acetate, LW Polyethylene Elastomer solvent Methyl, glycerol or pentaerythriol esters of rosins,Modified roisins such as hydrogenated, dimerized or polymerized roisins (wood roisin, tall oil roisin, terpene resins including polyterpene and polymers of alpha, - pinene or bete pinene) Plasticizer / softeners Hydrogenated vegetable oil, Lanolin, Stearic acid, Sodium stearate, Potassium stearate, Glycerine Emulsifier Glycerol monostreate (3.8), glycerol monooleate (2.8), Lecithin fatty acid monoglycerides (4.2), Diglycerides, Triglycerides, Proplylene glycol monostearate (3.4), Sorbitan monostearate (4.7) Wax Rice bran wax, polyethylene wax, microcrystyalline wax, natural wax, petroleum wax, paraffin, bee wax, carnauba wax, candelilla wax, cocoa butter, degreased cocao powder

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Fillers Titanium oxide, Aluminum hydroxide, Alumina, Aluminum salicates, Dicalcium phosphate, Talc, magnesium carbonate, kaolin, silicium oxide Table 2-4 List of various ingredients used across different categories in a typical gum base [5]

Waxes are used to soften the rubbery elastic gum base. Typical waxes are crystalline in nature with melting points (MP) above 170°C [5]. These texture modifiers provide better chewing properties compared to the low MP waxes which are known to impart tackiness to the product [5]. Waxes have a greater affinity for non-polar flavor molecules such as limonene, ethyl nonanoate and p-cymene [7]. Plasticizers are low molecular weight compounds that penetrate the structure of gum base, resulting to better chewability and mouth feel of the gum [5]. Also plastizers tend to absorb moisture and thus aid in flavor migration which lead to flavor loss [5]. Finally, fillers are added to the gum to provide color as well as reduce tackiness providing better mouth feel [5]. 2.2.3.2 Water-soluble phase 2.2.3.2.1 Sweeteners in chewing gum: Sugar sweeteners such as sucrose, dextrose, maltose, dextrin, dried invert sugar, fructose, galactose, and corn syrups can be used for regular (sugar) gums. In addition to providing sweetness, sugars also help mask the harshness of flavor compounds such as menthol and menthone [9]. In recent years, the huge growth of the sugar free gums has

10

led to the usage of sugar alcohols and high intensity sweeteners. The different polyols also act as bulking agents. The sugar alcohols used in sugar-free chewing gums include sorbitol, mannitol, xylitol, maltitol, lactitol, hydrogenated isomaltulose and hydrogenated starch hydrolysates. Xylitol containing gums have become popular due to its similar sweetness levels to sugar as well as cooling ability (endothermic heat of salvation) which complements the effect of the cooling agents [9]. However, because of the relatively high cost of this polyol, it is commonly used in combination of a lower cost polyol such as sorbitol, lactitol, or manitol with xylitol. Sorbitol, a commonly used polyol, has its own manufacturing challenges since this product is very hygroscopic and does not readily crystallize. Hence, various patents are in place suggesting different ways to incorporate these different polyols through different coating techniques [10-13]. With respect to flavor release, real-time breath analysis studies have reported a faster volatile release from sorbitol chewing gum compared to xylitol chewing gum for a given flavor dosage [14]; possibly because sorbitol would be predicted to undergo a relatively more rapid dissolution during mastication (more hygroscopic). In addition, efforts to incorporate different high intensity sweeteners such as aspartame, acesulfame –K, saccharine, and thaumatin into chewing gum have increased in the recent years [5]. These sweeteners usually range from 0.005 % to 5 % of the gum composition. However, these materials are mainly affected by factors such as pH, moisture, temperature, microbial growth and chemical reactions [15]. Aspartame, the most commonly used non-caloric sweetener in chewing gum, is prone to hydrolytic degradation in the presence of moisture, leading to loss of sweetness [13]. Furthermore, other factors such as temperature and pH can speed up this degradation process [13].

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Aspartame also reacts with aldehydes and ketones present in flavor oil leading to further loss of sweetness [13]. Hence, various technical use of HIS have been patented based on novel sweetener delivery systems which not only aid in protecting the sweetness over time but also helps in controlling it’s release rates. These different techniques include dispersing sweetener in a hydrophobic matrix [13] and encapsulation followed by drying and grinding [16-20]. Recently, chewing gums containing Neotame, a modified N- substituted form of aspartame, have been utilized to overcome the above mentioned limitations of aspartame [21]. Similarly, efforts have been made to control the release rates of acesulfame-K through encapsulation [13, 22]. 2.2.3.2.2 Physiological cooling agents (PCA): According to Wolf et al. [9], physiological agents are perceived as cold or cool when in contact with the mucous membranes of the mouth, nose, and throat during consumption. The basic advantage of adding these agents is to provide a cooling effect with an unexpected high flavor impact while reducing the harsh notes that are most commonly encountered in sugarless gums [9]. The harsh flavor is mainly caused by menthol, which is ubiquitous in chewing gum flavors such as spearmint, peppermint, wintergreen, and fruit flavors. The presence of menthol not only provides a cooling flavor in the initial stages of chewing, but also imparts a bitter, harsh and burning taste [9]. In the case of regular sugar gums, sucrose masks these harsh qualities, whereas in sugarless gums, polyols other than xylitol have been reported not to have this flavor masking quality. Another reported advantage of using PCA is a lower required usage of xylitol, an expensive sugar alcohol. Different PCAs used for chewing gum manufacture

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include menthyl succinate, menthyl lactate, 3-1-menthylpropane-1, 2-diol (TCA), menthone glycerol ketals, N-substiuted p-menthane carbamide (WS-3), acyclic carboxamide (W-23) and menthyl lactate [9]. These above cooling agents are normally used at low concentrations of about 0.001% to 2% per weight of the chewing gum. These PCAs have been categorized into three general groups based on their release rate during mastication: (1) slow release PCAs which includes menthone glycerol ketal, menthyl lactate and menthyl succinate; moderate release PCAs such ase WS-3 and WS-23 fall; and moderately fast release PCAs like TCA [9]. Efforts have been made to control the release of these cooling agents through various types of encapsulation: 1) agglomeration 2) spay drying followed by fluid bed coating, spray chilling and coacervation 3) absorption and 4) extrusion [9]. 2.2.3.2.3 Warming agents: Warming agents provide a heating sensation in the mouth in chewing gum. Some of the warming agents are: polyhydric alcohols, capsicum powder, capsaicin, vanillyl ethyl ether, vanillyl pentyl ether, gingeol etc [23]. These compounds are typically used in very low quantities (0.000001 to 0.001%) since they can cause strong skin irritation as well as excessively high warming effect [23]. Hence, these are typically preferred in combination with a cooling agent.

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2.2.4 Process of making chewing gum Conventionally, chewing gum is made by melting the gum base at a temperature ranging between 70ºC - 120ºC [5]. The molten gum base is mixed with a liquid plasticizer with or without an emulsifier for a targeted amount of time (2 to 8 minutes). About 2/3 rd of the sugars along with coloring agents are then added to the mix and stirred for another 1 to 4 minutes [5]. A slow mixing process is subsequently continued with the addition of the remaining sugar ingredients followed by addition of flavoring agents for 1 to 4 minutes [5]. The final step consists of addition of fillers, humectants as well as antioxidants with further mixing for 1 to 4 minutes [5]. The resultant gum mixture is then typically rolled to form thin ribbons which are coated with finely ground sugar powder to enhance the flavor as well as to keep the gum from sticking to the rollers cut into gum sticks [24]. If gum tablets are made, after rolling, the sheets subsequently broken up and spray dried with syrup mixture containing water, sweeteners, and color [24]. The hard coated gum centers are then packed in tablet form. 2.3 Flavor release and perception During the consumption of food, aroma compounds are initially released into the headspace of the mouth. The compounds are then further transferred to the nose, where the flavors are perceived by the brain via the nasal receptors [25]. Upon consumption of solid foods such as candies and chewing gums, the aroma compounds are released into the saliva before they are released in the headspace or air in the oral cavity. Hence, understanding the physiological process of consuming foods provides a greater insight

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into the mechanisms of flavor release in the mouth and to the olfactory receptors which ultimately transmit sensory signals to the brain. Flavor release

Figure 2-1 Various components that affect the flavor release 2.3.1 Physiological process: In general, the process of eating involves the mastication of food till it breaks down while it is being mixed with saliva. After saliva hydration, the breakdown product is swallowed. However, the link between how these physiological movements affects the flavor release were not fully understood fully till recent years. Harvey et al. [26] first reported that the act of swallowing is followed by the exhalation of 4 to 15 ml of air. Buettner et al. [27] studied the transfer of ethyl butyrate during the swallowing process using a videofluoroscopic and real-time MRI. This work observed a 3 stage swallowing process during the consumption of liquids. These 3 stages include: 1) the closure between the soft palate and the pharyngeal region upon introduction of food followed by, 2) the propulsion of the liquid into the orthopharynx by the action of the soft palate against the nasal cavity, and 3) the transfer of liquid into the epiglottis which closes the entrance of the trachea till Thermodynamics Mass transfer Physiology

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Abstract: The flavor properties of chewing gum are undoubtedly a key product attribute for consumption. However little is known about how many of the various ingredients (i.e. flavor solvents) in chewing gum alter flavor delivery. Consequently, defining mechanisms which influence flavor release in chewing gum is important for understanding its product quality and possibly may also translate to drug delivery applications for the pharmaceutical industry. The first objective of this study investigated the influence of three flavor solvents on the aroma/taste/textural properties in a sugar-free chewing gum. Model chewing gums made with [0.67%; triacetin (TA) or propylene glycol (PG) or medium chain triglycerides (MCT)] and without flavor carrier solvent. The chewing gums were analytically characterized in vivo for three panelists over a period of 12 min. Volatile analysis of cinnamaldehyde, L-carvone, piperitone, jasmone was conducted using Atmospheric Pressure Chemical Ionization-mass spectroscopy (APCI-MS). Sorbitol release from saliva was tracked using High pressure Liquid Chromatography (HPLC) coupled with Refractive Index Detector (RID), while the textual properties (softness) were measured using TA-XT2. Furthermore, the perceived flavor properties of these chewing gum samples were measured using a time-intensity sensory study (TI) on the aroma (cinnamon-like), taste (sweetness) and textural (effort to chew) attributes using a trained sensory panel. Flavor solvent addition to chewing gum did not significantly influence the aroma release profiles of all the 4 compounds. However, the sorbitol release rate was significantly lower for chewing gum made with TA compared to the other treatments. The sensory analysis was in agreement with the analytically data; lower levels of sweetness and cinnamon-like flavor intensity were perceived for chewing gum made with TA were observed, suggesting taste-aroma interactions. Chewing gums formulated with TA or MCT were reported to be softer (based on texture analysis) then with PG or no flavor solvent addition. However, no correlations were reported between the instrumental texture analyses of the chewing gum (softness) and the flavor release. Overall, flavor solvent choice did influence the sorbitol release in chewing gum matrix due to unique plasticizing/softening mechanism of the solvent utilized. The second objective of this study was to investigate the mechanisms for cinnamaldehyde release in a sugar-free chewing gum. Chewing gums containing (25%-Paloja gum base, 61%-sugar alcohol, 4%-glycerine, 0.46% sweeteners, and 0.02% lecithin) were made with varying concentrations of cinnamaldehyde. Additionally chewing gums were made with p-cresol (similar log P as cinnamaldehyde). A cinnamaldehyde or cresol flavored gum base (no sugar alcohol) was also made to investigate the role of the gum base on flavor release. Three panelists were asked to chew gums or flavored gum base, while aroma release profile was tracked from the nose exhaled breath using APCI-MS over a period of 8 min. The release profile of cinnamaldehyde from chewing gum was found to correlate with the sugar alcohol release in a sugar free gum. Chewing gums made with varying amounts of cinnamaldehyde (0.29-2.9 mg/g of chewing gum) did not show any differences in release pattern suggesting no concentration effect. Furthermore, the cinnamaldehyde release pattern from the gum base was similar to cresol or as predicted from the log cP value (distribution coefficient between the gum base and water). These findings suggested cinnamaldehyde was interacting with the sugar alcohol phase, possibility due to transient hemi-acetal reactions mechanisms, which resulted in a more rapid release rate than would be predicted based on the hydrophobicity of this compound.