Correlation between physical and sensorial properties of gummy confections with different formulations during storage

Abstract

Gummy confections are popular products formulated with sucrose, glucose syrups, gelling agents, acids, flavourings and colouring agents. They have various commercial types in terms of formulation, texture, taste and colour, however, there is inadequate investigation on storage behavior of these products. The aim of this study is to investigate the effects of glucose syrup:sucrose ratio (1.1 and 1.5), starch (0% and 1.5%) and gelatine concentration (3% and 6%) on texture profile, colour and sensory properties of gummy confections during storage. It was also aimed to correlate sensorial changes with physical properties measured by instrumental techniques during storage at 10 °C, 20 °C and 30 °C. The highest increase in hardness was observed for formulation with 1.1 glucose syrup:sucrose ratio, no starch and 6% gelatine. Storage temperature had no significant effect on cohesiveness. It was seen that rate of colour change increased with storage time and temperature. Formulation with glucose syrup:sucrose ratio of 1.5, no starch and 6% gelatine had the highest sensory scores. This formulation was found to be the most stable formulation in terms of hardness and gumminess, meaning that it would need a stable mastication during storage. Sensorial changes of gummy confections were found to be correlated with instrumental results of texture and colour.

Introduction

Gummy confections are sugar confectionery products, which have the industrial production steps of mixing, cooking, cooling, moulding, conditioning, demoulding, coating and packaging (Jackson 1990). Gummy formulations are typically composed of sucrose, glucose syrup, gelling agents, acids, flavourings, colouring agents and other ingredients. Sugar confectionery products have a wide texture range from soft to hard depending on the gelling agent type and the grade of glucose syrup used in the formulation (Hull 2010).

Gelatine is used for proper chewiness, texture and gelling in confectionery formulations. In most of the studies, gelatine was combined with other gelling agents such as starch (Delgado and Banon 2015; Marfil et al. 2012), pectin (DeMars and Ziegler 2001) and xanthan gum (Kim et al. 2014) in the production of gummy confections. Excluding moulding purpose, the role of starch in gummies is to give base to the gel and to contribute to the textural properties. Thin boiling type of starches are generally used in gummies (Belitz and Grosch 1999). In starch gels, the system does not remain static after gelation. The structure of gel starts to retrograde during storage at room temperature (Ratnayake and Jackson 2008). Retrogradation of starch was known to be inhibited by the presence of sugar (Kohyama and Nishinari 1991), low water content and presence of other gelling agents (Sworn 2011). Siegwein (2010) used acid thinned wheat starch up to 11% in starch confectionery. Marfil et al. (2012) studied texture and microstructure of gummies prepared with gelatine and acid modified corn starch at changing levels between 0 and 10%. Delgado and Banon (2015) investigated the mechanical properties of gummies containing 8.02% acid thinned corn starch and 3.39% gelatine.

Sucrose contributes to the texture and sensory properties of gummy confections. It is mainly used as sweetener in combination with glucose syrups. Sucrose addition to the gummy confections helps to reduce haziness, to enhance thermal stability and to promote gel structure (Holm et al. 2009; Kasapis et al. 2003). Furthermore, sucrose provides mouthfeel to the gummies and increases the mass of the product. Glucose syrups can improve the solubility of sucrose and retard the sucrose crystallization in confectionery products; thus sucrose is used together with glucose syrups in the formulations. In addition, glucose syrups prevent microbial growth by reducing water activity of the confectionery. Therefore, there is no need to add preservatives to the formulations, which is a desirable characteristic from the consumer side (Belitz and Grosch 1999; Burey et al. 2009; Porayanee et al. 2015). Although sucrose inversion reaction can occur due to heat and acid treatment during manufacturing of sugar confectionery, sugar spectrum of glucose syrups involved in the formulations do not vary during processing and storage. Hence, it is important to track the quality impacts of sugars, such as changes in mouth-feel of consumers due to mass gain and increase in sweetness after inversion. Besides, the effects of sugar inversion and crystallization on sensory quality should be monitored during storage in order to control the texture and shelf life.

Although gummy confections have many varieties in the global food market with different formulations and manufacturing methods, the sensitive interactions between the critical ingredients during processing and storage of these products are not studied before. Possible negative quality impacts due to these interactions can be prevented before launching the product to the food market by tracking the storage of gummy confections. Correlations between physical properties measured using instrumental techniques and sensory analysis were studied for many food products such as bread (Sabanis et al. 2009), cheese (Drake et al. 1999), dark chocolate (Owunsu et al. 2013) and roasted pistachio nut/kernel (Moghaddam 2016). However, there is no study involving the correlation between physical and sensorial properties of gummy confectionery. Thus, the major aim of this study was to correlate sensorial changes of gummy confections with the physical properties measured with using instrumental techniques during storage. This correlation information will have the potential usage in the sugar confectionery industry to reduce the cost of consumer tests and to save time. The other aim of the study was to understand the effects of ratio of glucose syrup to sucrose, type and concentration of gelling agent on the sensorial properties, texture and colour of gummy confections.

Materials and methods

Sample preparation

Gummy confections of 1000 g batches were prepared with different formulations. Slurry of the gummies was prepared by modifying the procedure described in the study of DeMars and Ziegler (2001) and moulding part was done by simulating a standard industrial production in the laboratory conditions. The effects of gelatine concentration (3% and 6%) (Halavet, Istanbul, Turkey), corn starch concentration (0% and 1.5%) (Roquette, Valencia, Spain) and glucose syrup (Cargill, Bursa, Turkey) to sucrose (Balkupu, Kocaeli, Turkey) ratio (1.1 and 1.5) on textural and sensorial properties and colour of gummy confections were studied. Samples were prepared by mixing gelatine and starch and soaking it in water at 55 °C. The mixture was stirred with a blender (Moulinex, DDF4 Optipro, Cedex, France) for 30 s at the lowest speed and deaerated in beakers in water bath (Nuve, BM 15/30, Ankara, Turkey) at a temperature of 90 °C. Sucrose, glucose syrup and water were cooked in an open saucepan with electric heating (Kumtel KH/LX 7010/7011, Kayseri, Turkey) until 78% dry solids was obtained. The solution was left to cool down to 90 °C. Gelling mixture was added to the cooked solution and mixed further with Hobart Mixer N50 (Troy, USA) for 2 min. Citric acid (Jungbunzlauer, Basel, Switzerland), colouring agent (Black carrot anthocyanin, Endemix, Kocaeli, Turkey) and strawberry flavouring (Aromsa, Kocaeli, Turkey) were added. The final desired mass was 1000 g. Starch trays were prepared by filling with dried warm moulding starch (Cargill, Bergen op Zoom, Holland) at 50 °C. Cubic shapes with dimensions of approximately 15 mm×15 mm×15 mm were formed in starch trays. The prepared slurry was deposited into the starch moulds. Trays were held at 20 °C and gummies were removed from starch after 83% dry solids were obtained. To determine the effects of storage temperature, gummies were stored at 10 °C, 20 °C and 30 °C using incubator for 12 weeks at 35±5% RH.

Texture profile measurement

A Texture Profile Analysis (TPA) test was conducted with a texture analyzer instrument (CT3 Brookfield, Middleboro, USA) weekly in two replicates. Gummies were compressed twice with a 3 mm diameter cylindrical probe. The samples were deformed without penetration. Texture settings for measurements were adjusted to two consecutive cycles of 50% compression, cross head moved at a speed of 30 mm/min and a trigger point of 0.05 N at 24 °C (Delgado and Banon 2015). Hardness (N), cohesiveness and gumminess (N) values were calculated from TPA diagram.

Colour measurement

Colour of the gummy confections were evaluated by measuring CIE L*, a*, b* parameters using Color Flex Ez Spectrophotometer (HunterLab, Reston, USA). Two replicates of colour data were recorded every week. Change in hue was calculated by the formula (1) with the help of formula (2).

$$\mathrm{\Delta }H\ast \left(\text{Change in hue}\right)={\left[{\left(\mathrm{\Delta }E\ast \right)}^2-{\left(\mathrm{\Delta }L\ast \right)}^2-{\left(\mathrm{\Delta }C\ast \right)}^2\right]}^{1/2}$$ 1

$$\mathrm{\Delta }E\ast \left(\text{Total colour difference}\right)={\left[{\left(\mathrm{\Delta }L\ast \right)}^2+{\left(\mathrm{\Delta }a\ast \right)}^2+{\left(\mathrm{\Delta }b\ast \right)}^2\right]}^{1/2}$$ 2

where ΔH* = Change in hue, ΔE* = Total colour difference, ΔL*= Change in whiteness/darkness value and ΔC* = Change in chroma. Colour of gummies prepared without the addition of colouring agent was used as a reference.

Sensory analysis

Ten trained staff of sponsor company were the assessors in sensory analysis of the study. Appearance, texture and taste were scored with hedonic scale of 9 points for every 4 weeks. Scale was expressed as the following; 1- dislike extremely, 2- dislike very much, 3- dislike moderately, 4- dislike slightly, 5- neither like nor dislike, 6- like slightly, 7- like moderately, 8- like very much and 9- like extremely. Overall acceptability score was determined by calculating the average of appearance, taste and texture scores.

Each batch was assessed twice and at least three samples were put in cups with coding of three digit random numbers. Three samples one of which were reference (fresh) were evaluated at each sensory session. At each session score sheets, and sugar free biscuits and water for neutralizing the mouth before tasting of each sample were given to the panelists.

Data analysis

Experimental results were shown as mean ± standard deviation. For statistical analysis, one-way Analysis of Variance (ANOVA) was conducted by using IBM SPSS Statistics 25 software. Means of the treatments were compared at a significance level of 0.05.

Multiple regressions were carried out to explain the relationships between independent and dependent variables by XLSTAT 2020.5.1.1039 with 3 interaction levels (glucose syrup to sucrose ratio, starch and gelatine).

Sensory and instrumental data were correlated using PLS modelling with Smart PLS 3 (http://www.smartpls.com) software.

Results and discussion

Texture of gummy confections

Recommended storage conditions of most of the commercial confectionery products vary between 15 and 25 °C. If they are formulated with gelatine, they generally have a melting temperature below 35 °C (Taylor 2010). Hence, in order to eliminate the effect of gelatine melting, storage conditions were selected as 10 °C, 20 °C and 30 °C in the study. Hardness of different gummy formulations before and after storage of 12 weeks at 10 °C, 20 °C and 30 °C were presented in Table 1. It was seen that hardness values of different formulations were similar when the samples were fresh. The average increase in hardness value was 0.03N, 0.01N and 0.05N after 12 weeks storage at 10 °C, 20 °C and 30 °C, respectively (Table 1).

Table 1.

Variation of hardness (N) of gummy confections with different formulations during storage at different temperatures for 12 weeks

G:S Ratio	Starch (%)	Gelatine (%)	Fresh	Aged 10 °C	Aged 20 °C	Aged 30 °C
1.1	0	3	(0.81±0.028)a, B	(0.84±0.018)a, AB	(0.81±0.008)a, B	(0.88±0.052)ab, A
1.1	0	6	(0.81±0.035)a, B	(0.84±0.012)ab, AB	(0.82±0.013)a, B	(0.90±0.062)a, A
1.1	1.5	3	(0.81±0.014)a, A	(0.84±0.022)ab, A	(0.82±0.029)a, A	(0.86±0.048)ab, A
1.1	1.5	6	(0.81±0.044)a, A	(0.84±0.028)ab, A	(0.81±0.018)a, A	(0.85±0.056)ab, A
1.5	0	3	(0.79±0.007)a, B	(0.82±0.004)ab, AB	(0.80±0.022)a, AB	(0.82±0.018)ab, A
1.5	0	6	(0.80±0.005)a, A	(0.81±0.002)b, A	(0.80±0.032)a, A	(0.81±0.009)b, A
1.5	1.5	3	(0.80±0.006)a, B	(0.83±0.006)ab, AB	(0.81±0.018)a, AB	(0.84±0.025)ab, A
1.5	1.5	6	(0.80±0.009)a, A	(0.83±0.007)ab, A	(0.81±0.024)a, A	(0.84±0.038)ab, A

G means glucose syrup and S means sucrose. Samples with common letters are not significantly different (p > 0.05). Lower case letters compare different formulations and upper case letters compare different storage temperatures

Hardness can be described as the strength of gel structure of a material under compression (Porayanee et al. 2015). Hardness of fresh sample being independent of ingredient effects might be due to the overall neutralizing resulting from individual effects of gelatine concentration, starch concentration and glucose syrup to sucrose ratio. From the point of gelling agents, hardness was expected to increase as the concentration of gelatine and starch increased in the formulation. As the concentration of gelatine increases, gel strength will be higher since high gelatine levels cause higher intermolecular contacts. Porayanee et al. (2015) also observed that hardness of gelatine gels increased as gelatine concentration increased. Starch was also reported to have the similar effect on the hardness due to the increase in interconnected network as starch increased in the recipe (Prokopowich and Biliaderis 1995). Unlike gelatine and starch, when the concentration of glucose syrup increased, hardness had a tendency to decrease due to its plasticizing property. In brief, the increasing effect of gelatine and starch on hardness might have compensated the decreasing effect of glucose syrup to sucrose ratio, so that hardness values did not change as the formulation changed.

Hardness of gummy confections formulated with glucose syrup to sucrose ratio of 1.1, no starch and 3% gelatine, glucose syrup to sucrose ratio of 1.1, no starch and 6% gelatine, glucose syrup to sucrose ratio of 1.5, no starch and 3% gelatine and glucose syrup to sucrose ratio of 1.5, 1.5% starch and 3% gelatine increased after storage of 12 weeks at 30 °C (Table 1). This was observed as a result of the simultaneous actions of gelatine and starch with sucrose, glucose syrup, water and other minor ingredients leading to a firm and chewy structure of gummy confections (Burey et al. 2009). Similarly, Marfil et al. (2012) observed that gelatine favoured elasticity, and addition of starch increased the hardness of gummies.

When the stability of gummies in terms of hardness was analysed, it was seen that formulations with glucose syrup to sucrose ratio of 1.1, 1.5% starch and 3% gelatine; glucose syrup to sucrose ratio of 1.1, 1.5% starch and 6% gelatine; glucose syrup to sucrose ratio of 1.5, no starch and 6% gelatine and glucose syrup to sucrose ratio of 1.5, 1.5% starch and 6% gelatine had the stable hardness values after 12 weeks storage at all conditions. The highest increase in hardness was seen for the formulation with 1.1 glucose syrup to sucrose ratio, no starch and 6% gelatine with an increase of 0.09 N after a storage of 12 weeks at 30 °C. This might be due to the fact that glucose syrup to sucrose ratio might have had stronger effects on the hardness as compared to the gelatine concentration. This result was also in accordance with the study of Porayanee et al. (2015), where concentration of sugars were shown to have stronger impact on textural properties as compared to gelatine concentration.

Ingredient impacts and interactions on the hardness of the gummy confections were also investigated by multiple regressions with the data given in Table 1. Linear regression equations showing the effects of glucose to sucrose ratio, starch and gelatine and their interactions on the hardness values (N) of samples, which are fresh, stored at 10 °C, 20 °C and 30 °C are shown in equations (3), (4), (5) and (6), respectively.

$$\begin{array}{cc}\hfill \text{Hardness}\left(\text{fresh}\right)& =0.595{\text{G:S}}^{\ast \ast \ast }+0.552{\text{starch}}^{\ast \ast }+0.170{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.412\text{G:S}\times {\text{starch}}^{\ast \ast }-0.126\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }-0.113\text{starch}\times {\text{gelatine}}^{\ast \ast }\hfill \\ \hfill & +0.084\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\ast }\hfill \\ \hfill \end{array}$$ 3

$$\begin{array}{cc}\hfill \text{Hardness}({10}^{\circ }\text{C})& =0.627{\text{G:S}}^{\ast \ast \ast }+0.566{\text{starch}}^{\ast \ast }+0.182{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.429\text{G:S}\times {\text{starch}}^{\ast \ast }-0.138\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }-0.119\text{starch}\times {\text{gelatine}}^{\ast \ast }\hfill \\ \hfill & +0.091\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\ast \ast }\hfill \\ \hfill \end{array}$$ 4

$$\begin{array}{cc}\hfill \text{Hardness}({20}^{\circ }\text{C})& =0.607{\text{G:S}}^{\ast \ast \ast }+0.601{\text{starch}}^{\ast \ast }+0.174{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.444\text{G:S}\times {\text{starch}}^{\ast \ast }-0.131\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }-0.127\text{starch}\times {\text{gelatine}}^{\ast \ast }\hfill \\ \hfill & +0.095\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\ast \ast }\hfill \\ \hfill \end{array}$$ 5

$$\begin{array}{cc}\hfill \text{Hardness}({30}^{\circ }\text{C})& =0.638{\text{G:S}}^{\ast \ast \ast }+0.618{\text{starch}}^{\ast }+0.223{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.463\text{G:S}\times {\text{starch}}^{\ast }-0.168\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }-0.156\text{starch}\times {\text{gelatine}}^{\ast \ast }\hfill \\ \hfill & +0.116\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\ast \ast }\hfill \\ \hfill \end{array}$$ 6

where G:S means glucose syrup to sucrose ratio, * means term is significant at p ≤ 0.05, ** means term is significant at p ≤ 0.01 and *** means term is significant at p ≤ 0.001. Coefficient of determination (R²) values of the models were 0.998, 0.998, 0.998 and 0.997 for equations (3), (4), (5) and (6), respectively. It was seen that hardness was affected significantly by ingredients, namely glucose syrup to sucrose ratio (p ≤ 0.001 for all samples), starch level (p ≤ 0.01 for fresh samples, samples stored at 10 °C and 20 °C and p ≤ 0.05 for samples stored at 30 °C) and gelatine level (p ≤ 0.001 for all samples). Hardness parameter can be associated with gel force. In a study, gel strength was found to be dependent on gelatine level in gellan and gelatine mixed gel (Lau et al. 2000), which were in accordance with this study. Starch effect might be explained by the interconnected network (Prokopowich and Biliaderis 1995) as mentioned earlier. Gel strength was reported to be changed with sugar in gelatine (Kasapis et al. 2003) and corn starch gel systems (Holm et al. 2009). In addition, the interactions between all of the ingredients studied were found to be significant on the hardness of gummy confections for all samples.

Cohesiveness values of gummy confections during storage at different temperatures were shown in Table 2. The average increase in cohesiveness value was 0.009, 0.004 and 0.010 after 12 weeks storage at 10 °C, 20 °C and 30 °C, respectively (Table 2). It was seen that gummies with glucose syrup to sugar ratio of 1.1, 1.5% starch and 6% gelatine had the highest numerical increase of 0.002 among all formulations after storage at 10 °C and 30 °C (Table 2).

Table 2.

Variation of cohesiveness values of gummy confections with different formulations during storage at different temperatures for 12 weeks

G:S Ratio	Starch (%)	Gelatine (%)	Fresh	Aged 10 °C	Aged 20 °C	Aged 30 °C
1.1	0	3	(0.56±0.015)a, A	(0.57±0.032)a, A	(0.56±0.010)a, A	(0.57±0.068)a, A
1.1	0	6	(0.56±0.005)a, A	(0.57±0.079)a, A	(0.56±0.029)a, A	(0.57±0.058)a, A
1.1	1.5	3	(0.56±0.021)a, A	(0.57±0.064)a, A	(0.56±0.026)a, A	(0.57±0.049)a, A
1.1	1.5	6	(0.55±0.032)a, A	(0.57±0.057)a, A	(0.56±0.020)a, A	(0.57±0.064)a, A
1.5	0	3	(0.55±0.003)a, A	(0.55±0.018)a, A	(0.55±0.023)a, A	(0.55±0.032)a, A
1.5	0	6	(0.55±0.007)a, A	(0.55±0.022)a, A	(0.55±0.024)a, A	(0.55±0.028)a, A
1.5	1.5	3	(0.55±0.012)a, A	(0.56±0.016)a, A	(0.56±0.025)a, A	(0.56±0.042)a, A
1.5	1.5	6	(0.55±0.003)a, A	(0.56±0.012)a, A	(0.56±0.015)a, A	(0.57±0.036)a, A

G means glucose syrup and S means sucrose. Samples with common letters are not significantly different (p > 0.05). Lower case letters compare different formulations and upper case letters compare different storage temperatures

Cohesiveness is the strength of internal bonds within a product and shows how well the product resists a second deformation relative to the first deformation (Besbes et al. 2009; Sandhu and Singh 2007). Cohesiveness of gummies did not change during storage at all temperatures for all of the formulations (Table 2), meaning that internal networks in these gummies remained relatively static. This finding was in accordance with several studies found in literature (Delgado and Banon 2015; Fisher 2011; Siegwein 2010).

Regression equations demonstrating glucose to sucrose ratio, starch and gelatine impacts and ingredient interactions on the cohesiveness of gummies, which are fresh, stored at 10 °C, 20 °C and 30 °C are given in equations (7), (8), (9) and (10), respectively.

$$\begin{array}{cc}\hfill \text{Cohesiveness}\left(\text{fresh}\right)=& 0.418{\text{G:S}}^{\ast \ast \ast }+0.398{\text{starch}}^{\ast \ast }+0.121{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.295\text{G:S}\times {\text{starch}}^{\ast \ast }-0.091\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.086\text{starch}\times {\text{gelatine}}^{\ast \ast }+0.063\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\ast \ast }\hfill \\ \hfill \end{array}$$ 7

$$\begin{array}{cc}\hfill \text{Cohesiveness}({10}^{\circ }\text{C})& =0.421{\text{G:S}}^{\ast \ast \ast }+0.395{\text{starch}}^{\text{NS}}+0.126{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.300\text{G:S}\times {\text{starch}}^{\text{NS}}-0.095\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }-\hfill \\ \hfill & 0.085\text{starch}\times {\text{gelatine}}^{\text{NS}}+0.065\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\text{NS}}\hfill \\ \hfill \end{array}$$ 8

$$\begin{array}{cc}\hfill \text{Cohesiveness}({20}^{\circ }\text{C})& =0.414{\text{G:S}}^{\ast \ast \ast }+0.375{\text{starch}}^{\ast }+0.115{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.275\text{G:S}\times {\text{starch}}^{\ast }-0.086\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.078\text{starch}\times {\text{gelatine}}^{\ast }+0.058\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\ast }\hfill \\ \hfill \end{array}$$ 9

$$\begin{array}{cc}\hfill \text{Cohesiveness}({30}^{\circ }\text{C})& =0.420{\text{G:S}}^{\ast \ast \ast }+0.421{\text{starch}}^{\text{NS}}+0.125{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.319\text{G:S}\times {\text{starch}}^{\text{NS}}-0.094\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.090\text{starch}\times {\text{gelatine}}^{\text{NS}}+0.069\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\text{NS}}\hfill \\ \hfill \end{array}$$ 10

where G:S shows glucose syrup to sucrose ratio, * shows term is significant at p ≤ 0.05, ** shows term is significant at p ≤ 0.01,*** shows term is significant at p ≤ 0.001 and NS shows term is not significant.

R² of the models were determined as 0.998, 0.995, 0.998 and 0.994 for equations (7), (8), (9) and (10), respectively. Cohesiveness was influenced by glucose syrup to sucrose ratio (p ≤ 0.001 for all samples) and gelatine amount (p ≤ 0.001 for all samples). Similarly, Porayanee et al. (2015) observed differences in cohesiveness when the amount of sugar changed. Starch level also affected the cohesiveness of fresh gummies (p ≤ 0.01) and that of the gummies stored at 20 °C (p ≤ 0.05). On the other hand, starch concentration did not impact cohesiveness of the samples stored at both 10 °C and 30 °C. Furthermore, interactions between all of the studied parameters were significant on cohesiveness for fresh samples and for the samples stored at 20 °C. On the other hand, no significant interactions of starch with glucose to sucrose ratio and gelatine were determined at 10 °C and 30 °C.

In the light of the findings of this study, it can be concluded that gelling agents like starch and gelatine can have significant effects on hardness of gummy confections during storage while having less effects on the cohesiveness of the products. Cohesiveness is a measure of attractive forces between similar molecules and hence structural integrity (Siegwein 2010). It should be a parameter that should be considered and measured freshly just after production since when cohesiveness is low (about 0.25), the product could be more prone to be moistened on the surface during storage (Masmoudi et al. 2010).

Gumminess results were obtained by multiplying hardness and cohesiveness of samples. Gumminess of samples having different formulations during storage can be seen in Table 3. It was noticed that gumminess values of fresh and aged samples were not significantly different. The only exception was observed in the confections with glucose syrup to sucrose ratio of 1.5, 1.5% starch and 6% gelatine. The gumminess value of this sample increased after storage at 10 °C and 30 °C (Table 3).

Table 3.

Variation of gumminess (N) values of gummy confections with different formulations during storage at different temperatures for 12 weeks

G:S Ratio	Starch (%)	Gelatine (%)	Fresh	Aged 10 °C	Aged 20 °C	Aged 30 °C
1.1	0	3	(0.46±0.013)a, A	(0.48±0.021)a, A	(0.45±0.006)a, A	(0.50±0.115)a, A
1.1	0	6	(0.45±0.006)a, A	(0.48±0.083)a, A	(0.46±0.016)a, A	(0.52±0.058)a, A
1.1	1.5	3	(0.45±0.014)a, A	(0.47±0.054)a, A	(0.46±0.017)a, A	(0.49±0.045)a, A
1.1	1.5	6	(0.44±0.057)a, A	(0.48±0.073)a, A	(0.45±0.003)a, A	(0.49±0.016)a, A
1.5	0	3	(0.43±0.006)a, A	(0.45±0.015)a, A	(0.44±0.040)a, A	(0.45±0.038)a, A
1.5	0	6	(0.44±0.006)a, A	(0.44±0.016)a, A	(0.44±0.045)a, A	(0.44±0.023)a, A
1.5	1.5	3	(0.44±0.012)a, A	(0.46±0.011)a, A	(0.46±0.023)a, A	(0.47±0.023)a, A
1.5	1.5	6	(0.44±0.004)a, C	(0.47±0.005)a, AB	(0.45±0.001)a, BC	(0.48±0.022)a, A

G means glucose syrup and S means sucrose. Samples with common letters are not significantly different (p > 0.05). Lower case letters compare different formulations and upper case letters compare different storage temperatures

There is limited information regarding the gumminess of sugar confectionery during long storage in the literature. Siegwein (2010) compared the gumminess of the formulation with 11% wheat starch with the one with 5.5% wheat starch and 5.5% soy protein isolate during storage of 20 days. It was mentioned that gumminess of sample with 11% wheat starch increased significantly and peaked at day 10, whereas, gumminess of the formulation with 5.5% wheat starch and 5.5% soy protein isolate did not increase significantly until day 20. Similarly, Fisher (2011) reported that confectioneries formulated with 10.1% corn starch at 14th day were significantly gummier than the ones at the 1st day. Under the light of mentioned studies and the findings of our study, changes in gumminess value might be more favoured when the gelling agent was starch and the concentration was high.

Regression analysis were also conducted with the gumminess values given in Table 3. Equations (11), (12), (13) and (14) depict the effects of ingredients and their interactions on the gumminess (N) of confections, which are fresh, stored at 10 °C, 20 °C and 30 °C, respectively.

$$\begin{array}{cc}\hfill \text{Gumminess}\left(\text{fresh}\right)& =0.331{\text{G:S}}^{\ast \ast \ast }+0.328{\text{starch}}^{\ast \ast }+0.102{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.242\text{G:S}\times {\text{starch}}^{\ast \ast }-0.076\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.072\text{starch}\times {\text{gelatine}}^{\ast \ast }+0.053\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\ast \ast }\hfill \\ \hfill \end{array}$$ 11

$$\begin{array}{cc}\hfill \text{Gumminess}({10}^{\circ }\text{C})& =0.352{\text{G:S}}^{\ast \ast \ast }+0.330{\text{starch}}^{\text{NS}}+0.114{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.253\text{G:S}\times {\text{starch}}^{\text{NS}}-0.087\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.074\text{starch}\times {\text{gelatine}}^{\text{NS}}+0.058\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\text{NS}}\hfill \\ \hfill \end{array}$$ 12

$$\begin{array}{cc}\hfill \text{Gumminess}({20}^{\circ }\text{C})& =0.334{\text{G:S}}^{\ast \ast \ast }+0.336{\text{starch}}^{\ast }+0.100{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.243\text{G:S}\times {\text{starch}}^{\ast }-0.075\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.074\text{starch}\times {\text{gelatine}}^{\ast }+0.054\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\ast }\hfill \\ \hfill \end{array}$$ 13

$$\begin{array}{cc}\hfill \text{Gumminess}({30}^{\circ }\text{C})& =0.357{\text{G:S}}^{\ast \ast \ast }+0.391{\text{starch}}^{\text{NS}}+0.137{\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.295\text{G:S}\times {\text{starch}}^{\text{NS}}-0.103\text{G:S}\times {\text{gelatine}}^{\ast \ast \ast }\hfill \\ \hfill & -0.102\text{starch}\times {\text{gelatine}}^{\ast }+0.077\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\ast }\hfill \\ \hfill \end{array}$$ 14

where G:S is glucose syrup to sucrose ratio, * expresses term is significant at p ≤ 0.05, ** expresses term is significant at p ≤ 0.01,*** expresses term is significant at p ≤ 0.001 and NS expresses term is not significant. R² values were 0.997, 0.994, 0.997 and 0.991 for equations (11), (12), (13) and (14), respectively.

Glucose syrup to sucrose ratio (p ≤ 0.001 for all samples) and gelatine amount (p ≤ 0.001 for all samples) affected gumminess significantly. Gumminess values of samples stored at 20 °C (p ≤ 0.05) and fresh samples (p ≤ 0.01) were affected by starch concentration, but this texture parameter was not affected at the other temperatures. These findings were similar to the cohesiveness regression results, which might be expected as gumminess was calculated by multiplying hardness and cohesiveness. When interactions were analysed, it was seen that ingredient interactions were more significant on gumminess for all samples except the ones stored at lowest temperature, at which there was only glucose to sucrose ratio and gelatine interaction. The case for 10 °C storage might be due to the starch effect, which was insignificant as a single ingredient at that temperature.

When the stability in terms of gumminess was concerned, it was seen that most of the gummies were stable during storage at all of the temperatures, and the formulation with 1.5 glucose syrup to sucrose, no starch and 6% gelatine was the most stable formulation with no change in gumminess value after 12 weeks regardless of storage temperatures (Table 3). This was in accordance with the results of hardness because gumminess was the multiplication of hardness and cohesiveness. In addition, the most stable gummy confection will need a stable mastication to dissolve during storage (Siegwein 2010).

Colour of gummy confections

Colour results are based on the changes of gummies over a period of storage up to 12 weeks at 10 °C, 20 °C and 30 °C. Colour changes increased linearly during storage for all formulations and predictive equations were shown in Table 4. It was seen that relative rate of colour change increased with increase in storage temperature (Table 4).

Table 4.

Predictive equations obtained for change in hue (ΔH*) of gummy confections with different formulations with respect to time (t) at different storage conditions

G:S Ratio	Starch (%)	Gelatine (%)	Storage temperature (°C)	Predictive equation	R2
1.1	0	3	10 20 30	${\mathrm{\Delta }H}^{\ast }=0.1007(t$)-0.0187 ${\mathrm{\Delta }H}^{\ast }=0.1527(t$)-0.0319 ${\mathrm{\Delta }H}^{\ast }=1.1784(t$)-0.7341	0.995 0.995 0.996
1.1	0	6	10 20 30	${\mathrm{\Delta }H}^{\ast }=0.1294(t$)-0.0229 ${\mathrm{\Delta }H}^{\ast }=0.2117(t$)-0.0500 ${\mathrm{\Delta }H}^{\ast }=1.6752(t$)-1.1522	0.995 0.995 0.994
1.1	1.5	3	10 20 30	${\mathrm{\Delta }H}^{\ast }=0.2484(t$)-0.0440 ${\mathrm{\Delta }H}^{\ast }=0.3934(t$)-0.1476 ${\mathrm{\Delta }H}^{\ast }=3.0865(t$)-1.8831	0.995 0.989 0.996
1.1	1.5	6	10 20 30	${\mathrm{\Delta }H}^{\ast }=0.2743(t$)-0.0486 ${\mathrm{\Delta }H}^{\ast }=0.4380(t$)-0.1123 ${\mathrm{\Delta }H}^{\ast }=3.0898(t$)-1.3380	0.995 0.995 0.996
1.5	0	3	10 20 30	${\mathrm{\Delta }H}^{\ast }=0.0788(t$)-0.0224 ${\mathrm{\Delta }H}^{\ast }=0.1065(t$)-0.0497 ${\mathrm{\Delta }H}^{\ast }=0.8445(t$)-0.5189	0.994 0.991 0.996
1.5	0	6	10 20 30	${\mathrm{\Delta }H}^{\ast }=0.1275(t$)-0.0384 ${\mathrm{\Delta }H}^{\ast }=0.1637(t$)-0.0770 ${\mathrm{\Delta }H}^{\ast }=1.3165(t$)-0.9446	0.994 0.992 0.995
1.5	1.5	3	10 20 30	${\mathrm{\Delta }H}^{\ast }=0.2387(t$)-0.0706 ${\mathrm{\Delta }H}^{\ast }=0.3219(t$)-0.1400 ${\mathrm{\Delta }H}^{\ast }=2.4275(t$)-1.4307	0.994 0.993 0.995
1.5	1.5	6	10 20 30	${\mathrm{\Delta }H}^{\ast }=0.3120(t$)-0.1072 ${\mathrm{\Delta }H}^{\ast }=0.4212(t$)-0.1800 ${\mathrm{\Delta }H}^{\ast }=2.8811(t$)-0.8868	0.995 0.995 0.993

G means glucose syrup and S means sucrose

Storage stability are known to decrease as deterioration in the sample increases (Hemanth et al. 2019). Colour change could be used as a storage parameter for the shelf life studies of gummy confections since it was observed that colour change of samples increased with storage time and storage temperature (Table 4). This might be due to the effect of gelatine, which is known to change in colour when held at high temperatures, by developing browning (Farahnaky et al. 2003) and increasing ΔH* values in a fast manner. In addition, in accordance to our results, Dabas and Kean (2014) mentioned that hard candy samples coloured with anthocyanin and prepared without stabilizers showed less storage stability in terms of colour with increased heat processing.

When predictive equations for change in hue with respect to time were analysed, it was seen that the slopes of the first order kinetic equation for the samples with glucose syrup to sucrose ratio of 1.5 were lower than the ones with glucose syrup to sucrose ratio of 1.1. This showed that gummies with 1.5 glucose syrup to sucrose ratio were more stable in terms of colour. Hull (2010) stated that the usage of glucose syrups could improve the appearance of confectionery products because they could overcome sucrose crystallization, which leads to opaque and dull appearance.

Sensory analysis of gummy confections

Table 5 depicts the overall acceptability scores of gummy confections, which were stored at different temperatures. It was seen that gummies with the highest gelatine level of 6%, had scores higher than 6.5 points out of 9 points. This meant that the mentioned gummies were liked moderately by the panelists and hence these products were determined as acceptable.

Table 5.

Overall acceptability scores of gummy confections stored at different storage temperatures for 12 weeks

Formulation			Overall acceptability
G:S ratio	Starch (%)	Gelatine (%)	Fresh	Aged 10 °C	Aged 20 °C	Aged 30 °C
1.1	0	3	(4.1 ± 0.26)c, A	(3.9 ± 0.36)c, A	(3.5 ± 0.30)b, A	(1.8 ± 0.30)bc, B
1.1	0	6	(7.2 ± 0.34)ab, A	(7.0 ± 0.84)a, A	(6.0 ± 0.32)a, A	(3.2 ± 0.22)ab, B
1.1	1.5	3	(5.2 ± 0.41)c, A	(5.0 ± 0.22)bc, A	(4.5 ± 0.74)ab, AB	(2.5 ± 0.54)abc, B
1.1	1.5	6	(8.6 ± 0.90)a, A	(8.4 ± 0.76)a, A	(6.6 ± 0.40)a, AB	(4.1 ± 0.67)a, B
1.5	0	3	(4.2 ± 0.25)c, A	(4.0 ± 0.48)c, A	(3.5 ± 0.90)b, A	(1.2 ± 0.25)c, B
1.5	0	6	(8.5 ± 0.27)ab, A	(8.3 ± 0.56)a, A	(6.5 ± 0.92)a, A	(4.1 ± 0.18)a, B
1.5	1.5	3	(4.0 ± 0.40)c, A	(3.9 ± 0.55)c, A	(3.6 ± 0.63)b, A	(1.2 ± 0.71)c, B
1.5	1.5	6	(6.9 ± 0.60)b, A	(6.7 ± 0.35)ab, A	(5.9 ± 0.37)a, A	(3.4 ± 0.44)a, B

G means glucose syrup and S means sucrose. Samples with common letters are not significantly different (p > 0.05). Lower case letters compare different formulations and upper case letters compare different storages

Sensory evaluations were performed at 10 °C, 20 °C and 30 °C for 12 weeks. Samples with 6% gelatine had scores higher than 6.5 points after 12-week storage at 10 °C (Table 5). This was similar to the results of fresh gummy confections. When the samples were stored at 20 °C for 12 weeks, it was seen that formulation with glucose syrup to sucrose ratio of 1.1, 1.5% starch and 6% gelatine and formulation with glucose syrup to sucrose ratio of 1.5, no starch and 6% gelatine had acceptable scores, which were more than 6.5 points. On the other hand, when the gummies were stored at 30 °C for 12 weeks, none of the samples scored more than 6.5 points.

By using the data from Table 5, regression equations (15), (16), (17) and (18) were constructed to study the ingredient effects and their interactions on the acceptability of gummies, which are fresh, stored at 10 °C, 20 °C and 30 °C, respectively.

$$\begin{array}{cc}\hfill \text{Acceptability}\left(\text{fresh}\right)& =0.275{\text{G:S}}^{\text{NS}}+2.483{\text{starch}}^{\text{NS}}+0.738{\text{gelatine}}^{\ast }\hfill \\ \hfill & -1.350\text{G:S}\times {\text{starch}}^{\text{NS}}+0.395\text{G:S}\times {\text{gelatine}}^{\text{NS}}+0.569\text{starch}\times {\text{gelatine}}^{\text{NS}}\hfill \\ \hfill & -0.541\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\text{NS}}\hfill \\ \hfill \end{array}$$ 15

$$\begin{array}{cc}\hfill \text{Acceptability}({10}^{\circ }\text{C})& =0.124{\text{G:S}}^{\text{NS}}+1.983{\text{starch}}^{\text{NS}}+0.698{\text{gelatine}}^{\text{NS}}\hfill \\ \hfill & -0.916\text{G:S}\times {\text{starch}}^{\text{NS}}+0.425\text{G:S}\times {\text{gelatine}}^{\text{NS}}+0.657\text{starch}\times {\text{gelatine}}^{\text{NS}}\hfill \\ \hfill & -0.617\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\text{NS}}\hfill \\ \hfill \end{array}$$ 16

$$\begin{array}{cc}\hfill \text{Acceptability}({20}^{\circ }\text{C})& =0.535{\text{G:S}}^{\text{NS}}+3.617{\text{starch}}^{\text{NS}}+0.850{\text{gelatine}}^{\text{NS}}\hfill \\ \hfill & -2.190\text{G:S}\times {\text{starch}}^{\text{NS}}+0.060\text{G:S}\times {\text{gelatine}}^{\text{NS}}-0.222\text{starch}\times {\text{gelatine}}^{\text{NS}}\hfill \\ \hfill & +0.071\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\text{NS}}\hfill \\ \hfill \end{array}$$ 17

$$\begin{array}{cc}\hfill \text{Acceptability}({30}^{\circ }\text{C})& =-0.610{\text{G:S}}^{\text{NS}}+4.083{\text{starch}}^{\text{NS}}+0.327{\text{gelatine}}^{\text{NS}}\hfill \\ \hfill & -2.760\text{G:S}\times {\text{starch}}^{\text{NS}}+0.322\text{G:S}\times {\text{gelatine}}^{\text{NS}}-0.229\text{starch}\times {\text{gelatine}}^{\text{NS}}\hfill \\ \hfill & +0.119\text{G:S}\times \text{starch}\times {\text{gelatine}}^{\text{NS}}\hfill \\ \hfill \end{array}$$ 18

where G:S is glucose syrup to sucrose ratio, * shows term is significant at p ≤ 0.05 and NS means term is not significant. R² values for the equations (15), (16), (17) and (18) were found as 0.994, 0.992, 0.974 and 0.971.

It was seen that only gelatine level (p ≤ 0.05) affected acceptability of fresh gummy confections. Moreover, there were no interactions among ingredients seen when sensory regression results were analysed.

It was found that gummy confections with glucose syrup to sucrose ratio of 1.1, 1.5% starch and 6% gelatine and glucose syrup to sucrose ratio of 1.5, no starch and 6% gelatine had the highest overall acceptability scores among all formulations before and after storage at all temperatures. According to Table 3, formulation with glucose syrup to sucrose ratio of 1.5, no starch and 6% gelatine had no increase in gumminess, which meant that the formulation had a stable mastication to be dissolved in the mouth. This might be one of the reasons why mentioned formulation was scored as one of the most acceptable formulations by the panelists (Table 5).

Finding a correlation between sensory and textural properties is crucial for the food researchers and producers since comprehensive sensory tests are expensive and time consuming (Moghaddam et al. 2016). Thus, the effects of gelling agents on texture liking of gummies were analyzed at 10 °C and 30 °C at glucose syrup to sucrose ratio of 1.1 (Fig. 1a). It was seen that gelatine concentration had more impact than starch concentration on texture liking at both 10 °C and 30 °C. When gelatine concentration increased, texture liking of panelists increased at both storage temperatures. This result was somewhat in accordance with the regression equation (15), where acceptability of gummies was affected only by gelatine concentration. Siegwein (2010) also mentioned significant improvements in texture liking scores of starch confections when some of the starch in the formulation was replaced with soy protein. However, instrumental results for hardness of gummies, stored at 10 °C and 30 °C for 12 weeks, were similar when gelatine level increased at glucose syrup to sucrose ratio of 1.1 (Table 1).

Fig. 1.

Correlation of sensory a texture liking and hardness for gummy confections formulated with glucose syrup: sucrose ratio=1.1 at different storage temperatures, b appearance liking and colour for gummy confections formulated with different glucose syrup: sucrose ratios at 30 °C storage. First letter: Starch (0, 1.5), Second letter: Gelatine (Low: 3%, High: 6%), Last digit: storage time in weeks (0th, 4th, 8th, 12th)

In addition, storage temperature of 10 °C affected the sensory texture liking scores during storage in a positive manner, however, storage temperature of 30 °C affected these scores adversely (Fig. 1a). This result was in accordance with the hardness values of gummies formulated with no starch at glucose syrup to sucrose ratio of 1.1. Hardness of the samples stored at 10 °C for 12 weeks were similar to the ones of the fresh samples; on the other hand, a significant increase in hardness was observed at the end of storage at 30 °C (Table 1). Hence, 10 °C and 30 °C storage temperatures were found to be suitable temperatures to be used as accelerated shelf life test temperatures in terms of hardness showing different possible storage climates for gummy confections formulated with gelatine and starch.

Figure 1b demonstrates the effect of gelling agents on appearance liking of the gummies when stored at 30 °C with different glucose syrup to sucrose ratios. It was seen that starch level was effective on appearance liking, however, gelatine level was not. Appearance liking of gummies decreased as the amount of starch increased.

According to Fig. 1b, starch level was effective on appearance liking, on the other hand, gelatine level was not. Appearance liking of gummies decreased as the amount of starch was elevated. This might be due to the opaque appearance of starch confectionery changing the confectionery from translucent to opaque (Hartel and Hartel 2014).

Colour sensory measurements showed clear changes with storage time at 30 °C as can be seen in Fig. 1b. This was in accordance with instrumental colour results as it was observed that the relative rate of colour change of gummies increased with increase in storage temperature and the fastest increase was seen at 30 °C for all of the formulations (Table 4). This might be due to the effect of gelatine in the formulation of gummies leading to browning at high temperatures (Farahnaky et al. 2003) and increasing ΔH* values promptly. Hence, 30 °C was found to be a useful test temperature for storage studies of gummies containing gelatine and starch.

Conclusion

It can be concluded that gelling agents and sweeteners can have significant effects on the texture of sugar confectionery products during storage. It was seen that relative rate of colour change increased with increase in temperature. Hence, hardness, gumminess, cohesiveness and colour can be used as the end of shelf life parameters for shelf-life determination in gummy confections.

Sensorial changes were correlated with the instrumental results. It was found that starch concentration was more effective on appearance while gelatine concentration was more effective on the texture of gummies, which might be an important result for the prediction of sensory quality (acceptability for consumers) of sugar confectionery products from texture and colour measurements. This information can be used in shelf-life determination of soft candy.

Gummies with no starch, 6% gelatine and glucose syrup to sucrose ratio of 1.5 had the most stable formulation in terms of critical quality parameters of confections, which were texture, colour and sensory properties.

Storage temperature of 20 °C can be used as the standard storage condition for accelerated shelf life testing (ASLT) of gummy confections containing gelatine and starch as the storage conditions of most of the commercial confectionery products are stored at 20±5 °C. Temperatures of 10 °C and 30 °C are appropriate to be selected as the test temperatures in ASLT of these type of products which are commercialized in both hot and cold climate markets since the failure in quality can be accomplished at these temperatures.