Investigation of physical properties, antioxidant activity, and sensory attributes of cocoa drink with the addition of torch ginger flower (Etlingera elatior) and xanthan gum

Indonesia is one of top cacao beans producer globally. Other than chocolate, cocoa drink is one of the popular cocoa derivates. The cocoa beverage is usually produced by mixing ingredients such as cocoa powder, sugar, creamer, and stabilizer. Cocoa powder is a great source of antioxidant as it contains polyphenolic compounds. However, the bioactive compounds like polyphenols might decrease during the processing of cocoa drinks. This study aimed to investigate the effect of torch ginger or kecombrang (Etlingera elatior) and xanthan gum addition on the physical properties, antioxidant activity, and sensory attributes of cocoa drink. The addition of torch ginger flower powder increased the antioxidant activity of the cocoa drink, but decrease the pH of the cocoa drink and consumers’ acceptance of aroma and taste of the cocoa drink. The addition of xanthan gum at 0.09 g resulted in the increased total solubility and reduced the sedimentation of cocoa drink.


Introduction
Over the past 40 years, the production of cocoa (Theobroma cacao L.) has increased steadily.The International Cocoa Organization (ICCO) reported that around 4.9 million tonnes of cocoa beans were produced globally in 2021/2022, with over 60% of cocoa produced by Côte d'Ivoire and Ghana.In Asia, however, Indonesia is the largest cocoa-growing country, accounting for 3% of cocoa production in the world [1].In Indonesia, cocoa has been a potential agricultural and important export commodity to the country's income.Other than chocolate, cocoa drink is one of the popular cocoa derivates.Besides its specific and favorable sensory attributes, historically, the cocoa drink has been consumed for its healthbeneficial effects associated with its high polyphenolic content [2].The cocoa beverage is usually produced by mixing ingredients such as cocoa powder, sugar, creamer, and stabilizer.Cocoa powder possesses polyphenols with a concentration of up to 50 mg per gram, further exerting antioxidant activities [3].However, the bioactive compounds like polyphenols might decrease during the processing of cocoa drinks.For this reason, in recent years, food researchers and industries have gained interest in the antioxidant activities of cocoa beverages [4].According to [5], there are two approaches to produce cocoa derivatives with high functionality, namely maintaining the polyphenol content throughout the manufacturing and enriching the final product with a phenolic-rich compound.The latter option, however, is considered more feasible.Promising substance to increase the antioxidant activities of cocoa drink is edible flower.
Edible flowers have traditionally been utilized for their appealing visual and scents, however, interest in edible flowers as natural source of bioactive compound is growing due to its contribution towards health improvement [6].The health benefits of edible flower were associated with the great variety of antioxidants such as anthocyanins, flavonoids, and other phenolic compounds [7,8].The antioxidant activities in edible flower have been proven to possess anti-inflammatory, anticancer, antidiabetic, and antimicrobial properties.Several edible flowers which grow in Southeast Asia like roselle (Hibiscus sabdariffa), butterfly pea (Clitoria ternatea), rose (Rosa), and jasmine species have been deeply studied for their bioactive potencies [8][9][10][11][12][13].However, there was a scarce information regarding the valorization of torch ginger flower.Torch ginger (Etlingera elatior) is one of Indonesian native flower which have been utilized for many traditional dishes.In Indonesia, the flower has several names depending on the region, for instance, kecombrang (Central Java), honje (West Java), and kincung (North Sumatra).Several studies reported the phytochemicals of torch ginger and their contribution to medicinal functionality.Terponoids, quercetin, saponin, kaempfrol and tannins were identified as potential bioactive compounds in torch ginger [14,15].
Addition of torch ginger flower to cocoa drink was expected to increase the functionality of the beverage.However, the stability of the suspension remained be a challenge.The challenge of incorporating the edible flower powder to the cocoa drink includes the sedimentation of solid particles [16].Hydrocolloid such as xanthan gum is often used as a stabilizer.The addition of stabilizer is hypothesized to improve the suspension stability of cocoa drink.This study therefore aims to investigate the effect of torch ginger and xanthan gum addition on the physical properties, antioxidant activity, and sensory attributes of cocoa drink.

Cocoa drink preparation
The study was started by preparing the torch ginger or kecombrang flower powder.The torch ginger (E.elatior) powder was prepared by grinding the dried torch ginger flower purchased from local manufacturer (Kaya Rempah Indonesia, Jakarta) for 5 minutes.The ground flower was then sieved using 400-mesh sieve.The next step was the development of cocoa drink that was done by adopting the method of Aribah et al. [17].The cocoa drink was made by mixing the cocoa powder (Bumitangerang Mesindotama, Tangerang), sucrose (Sugar Group Companies, Lampung), corn starch (Egafood, Jakarta), non-dairy creamer (Sari Incofood, Jakarta), torch ginger flower, salt (UnichemCandi Indonesia, Sidoarjo), and xanthan gum (Fufeng Group Ltd., Jinan).The formulation of cocoa drink is shown in Table 1.The water was added to the mixture and heated at 80ºC for 5 minutes.The physical analysis was carried out to identify the color, pH, total soluble solid, and sedimentation index of the cocoa drink.The color of cocoa drink was measured using a portable colorimeter and expressed in CIELAB system.The parameters such as L* (lightness component), a* (green to red), and b* (blue to yellow) values were recorded to calculate the degree of difference (∆E) between cocoa beverage containing torch ginger flower and xanthan gum with cocoa beverage control.The degree of color difference was calculated using Equation ( 1) [5].The pH of the cocoa drink was measured with pH meter at temperature of 25°C.Furthermore, the total soluble solid was determined using hand refractometer and expressed in °Brix.The stability of cocoa beverage's suspension was visually observed for 72 hours.Prior to the measurement of suspension stability, the samples were stored at 8°C.The volume of total sample (denoted as V) and the volume of liquid in which the solid particles have settled-down (denoted as Vs) was measured every 24 hours.The sedimentation index (SI), as shown in Equation ( 2), was then assessed every 24 hours [16,18]. (2)

Antioxidant analysis.
Antioxidant activity of the cocoa drink was determined with 2,2-diphenyl-1-picrylhydrazyl (DPPH).Briefly, 40 mL cocoa drink was centrifugated for 5 minutes at 4000 rpm and 25°C.The supernatant (1 mL) was mixed with methanol (5 mL) and 0.1 mM DPPH (2 mL).The mixture was vortexed and then incubated for 30 minutes.The absorbance of the sample was determined using UV-VIS spectrophotometer at 517 nm.Meanwhile, as for the blank, the cocoa drink sample was replaced by aquadest.The percentage of DPPH inhibition was calculated using Equation (3) [19].

Sensory evaluation.
The sensory evaluation of the cocoa drink was done by running a hedonic test which involved 40 untrained panellists.There were in total 13 of ready-to-drink cocoa beverages consisting of the 12 samples as mention on Table 1 and 1 control sample without addition of kecombrang flower and xanthan gum.All samples were served at 5-7°C.Each panellist was asked for their acceptance toward several sensory attributes of the cocoa drink, namely color, aroma, cocoa taste, and mouthfeel.The six-scale was used to define panellist's acceptance, from 1 indicating "very dislike" to 6 indicating "very like".

Statistical analysis.
The result of physical characteristics and hedonic test of the cocoa drink was analysed using one-way analysis of variance (ANOVA) with 5% significance followed by Tukey's post hoc test to investigate whether the effect of the formula was significant.The statistical analysis was carried out using Minitab.

Physical characteristics
The characteristics of the cocoa drinks is shown in Table 2.The result of pH analysis showed that there was a significant contradictory impact of torch ginger addition on the pH of cocoa drink.Increasing concentration of the torch ginger flower powder caused a decrease of the pH value of the cocoa beverage.
On the other hand, different concentration of xanthan gum did not influence the pH value.According to this study, addition of 4g kecombrang flower resulted in the lowest pH of cocoa beverage.Kecombrang flower contains different kinds of acid such as chlorogenic acid, formic acid, and decanal which was able to relase H+ ion during the processing causing pH reduction [11,20].Based on Table 2, the addition of torch ginger powder did not affect the total soluble solid of the total soluble solid of the cocoa drink, but the addition of xanthan gum increased the total soluble solid of the torch ginger-contained cocoa drinks.Hydrocolloid such as xanthan gum may enhance the interaction between the water molecules and the polar compounds, hence, the total soluble solid and the stability of the suspension was increased [21].
The color analysis showed that in term of lightness and compared to the control sample, kecombrang flower addition did not give significant effect at the xanthan gum concentration of 0.03 g and 0.06 g.However, at xanthan gum concentration of 0.09 g, addition of 2-4 g kecombrang flower resulted in higher lightness value.However, the ∆E values were relatively low (< 2.00) indicating the color difference was perceptible only through a close observation.The finding was similar to the study by [17] in which the color difference caused by the addition of hydrocolloid was barely noticeable.The sedimentation index of the cocoa drink is presented on Table 3.As can be seen, the sedimentation increased the longer the cocoa drink was stored.However, the addition of xanthan gum increased the stability of the kecombrang-contained cocoa drink indicated by lower sedimentation index.Concentration of xanthan gum at 0.09 g resulted in the lowest sedimentation index.A study reported that the addition of xanthan gum caused a network in the colloidal system of cocoa drink which resisted the gravitational force during the beverage storage [16].

Antioxidant activity
The antioxidant activity of the cocoa drink with addition of torch ginger flower and xanthan gum is displayed on Figure 1.The DPPH inhibition of A1, B1, dan C1 samples were comparable with control cocoa drink, which indicated that 1 g addition of kecombrang flower did not result in significant increase of antioxidant activity, but that the addition of kecombrang flower at higher concentration increased the antioxidant activity of the cocoa drink.The result also showed that at the same concentration of torch ginger flower, increasing concentration of xanthan gum did not significantly affect the antioxidant activity of the cocoa drink.Torch ginger flower contains bioactive compounds such as flavonoid (quercetin and kaempferol), anthocyanin, saponin, and tannin which were reported to exhibit antioxidant properties [14].Studies showed that kecombrang flower extract contained phenolic and flavonoid compound around 39 mg gallic acid equivalent/g and 39 mg quercetin equivalent/g extract, respectively [14,15].

Sensory evaluation
The result of hedonic test of cocoa drink with addition of torch ginger flower and xanthan gum is shown in Table 4.The different formula of cocoa drink did not affect the consumers' acceptance toward the color of the beverage.The result was aligned with the instrumental color measurement in which the color difference was relatively small.The addition of kecombrang, however, decreased consumers' acceptance on the aroma and cocoa flavor of the beverage.The decrease of consumer acceptance may be linked with aromatic and phenolic compound of the kecombrang which left strong acidic aroma, bitter taste and astringency [15,22].The panelists' acceptance on the mouthfeel of the cocoa drink was also decreased along with the increase of the torch ginger flower powder addition.The addition of xanthan gum showed an improvement of consumer acceptance to the mouthfeel of the cocoa drink.This may be caused by the ability of the xanthan gum to stabilize the cocoa drink suspension.

Conclusion
The addition of torch ginger flower (E.elatior) powder increased the antioxidant activity of the cocoa drink.In term of physical characteristics, the addition of torch ginger flower reduced the pH and slightly increase the total soluble solid, but did not affect the color of the cocoa drink.The addition of xanthan gum at 0.09 g resulted in the increased total solubility and reduced the sedimentation of cocoa drink.However, the drawback of torch ginger flower addition on the cocoa drink tase and aroma was observed, as the consumers' acceptance toward the mentioned sensory attributes decreased.Based on the result of this study, it was suggested to further investigate the effect of torch ginger flower particle size.The processing of the torch ginger flower and the formulation of the cocoa drink could be improve to boost consumers' acceptance while retaining the antioxidant activity of the cocoa drink.

Table 1 .
Formula of cocoa drink with addition of torch ginger and xanthan gum.

Table 2 .
Characteristics of cocoa drink: pH value, total soluble solid, and color.
aDifferent superscript in the same column indicates a significant difference based on one-way ANOVA and Tukey post hoc test.

Table 3 .
Sedimentation index of cocoa drink during the storage.

Table 5 .
Sensory evaluation of cocoa drinks through hedonic test.Different superscript in the same column indicates a significant difference based on one-way ANOVA and Tukey post hoc test.