Improvement of cocoa powder properties through ultrasonic- and microwave-assisted alkalization

Dimas Rahadian Aji Muhammad; Dion Pratama; Danar Praseptiangga; Setyaningrum Ariviani; Mary Faith Adan; Sastia Prama Putri; Eiichiro Fukusaki

doi:10.1515/opag-2022-0400

Artikel Open Access

Improvement of cocoa powder properties through ultrasonic- and microwave-assisted alkalization

Dimas Rahadian Aji Muhammad , Dion Pratama , Danar Praseptiangga , Setyaningrum Ariviani , Mary Faith Adan , Sastia Prama Putri und Eiichiro Fukusaki

Veröffentlicht/Copyright: 11. Dezember 2024

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Abstract

Improving the process efficiency is still a challenge in the alkalization process of cocoa powder. This research aims to study the effect of ultrasonic- and microwave-assisted alkalization on the quality attributes of cocoa powder. Three levels of process duration were used (5, 10, and 15 min), and then the physical and antioxidant properties of the cocoa powder were evaluated. The results show that ultrasonic- and microwave-assisted alkalization is more effective in improving cocoa powder’s darkness and red intensity than the conventional alkalization process. The cocoa powder produced using ultrasonic- and microwave-assisted alkalization significantly improved the pH to 7.59, solubility from 20 to 28% and wetting time to almost twice, depending on the type and duration of the process. However, both advanced methods caused a significant decrease in total phenols, flavonoids, and antioxidant activity by about 35, 22, and 38%, respectively, compared to the conventional method. This research provides further information on the potential use of ultrasonication and microwave techniques, particularly in cocoa powder processing that has not been explored previously.

Keywords: alkalization; cocoa powder; microwave; ultrasonic

1 Introduction

Cocoa is a vital economic agroforestry product in many countries, and it can be processed into many products, including cocoa powder, chocolate, and beverages [1]. The products of the cocoa agroindustry are highly competitive in the market, and thus, innovation of cocoa-derived products by the industry is needed mainly to attract consumers. Some attempts have been made previously by developing chocolate and cocoa drinks enriched with probiotics, various herbs and spices, and other functional ingredients [2–4]. However, up till now, innovation in cocoa powder products and production processes is still scarce.

Cocoa powder is one of the main products of the cocoa industry, which is widely used as an ingredient for baking and beverages. However, natural cocoa powder has some limitations for its application, particularly for beverage production purposes, including poor dispersibility and unappealing appearance. Hence, additional research must be carried out to ameliorate the characteristics of cocoa powder [5]. Alkalization is a strategy that can be carried out to improve cocoa powder properties. Basically, alkalization generally consists of mixing natural cocoa material with an alkali solution and treating this mixture with the combined effects of temperature and pressure. Thus, in this research the alkalization was conducted using a pressured pan in which the working principle is boiling with an increased pressure [6]. This method is usually done to improve cocoa powder dispersibility in water as well as for enhancing its flavor and color. Many research groups have attempted to design more effective alkalization methods and investigate its effects on the physicochemical and sensory properties of the alkalized cocoa. It is presumed that the process of alkalization can be improved by combining the conventional method with advanced techniques.

Ultrasound and microwave are successfully employed in many areas, including food production. Microwave, with its wavelength ranging from 10⁶ to 10⁹ nm, induces rapid chemical reactions due to the increase in temperature during its application. It has a frequency range of 0.3–300 GHz and is proven to be a process with high reproducibility [7]. Meanwhile, ultrasound is composed of mechanical sound waves with a frequency of >20 kHz, which can form cavitation bubbles that induces biochemical reactions [8]. Thus, microwave treatment and ultrasonication are techniques that can potentially be combined with alkalization process to alter the properties of cocoa powder. It is hypothesized that waves produced by microwave and ultrasonic devices can cause rapid chemical reactions and cavitation, respectively, in the cocoa powder, assisting the acceleration of alteration of cocoa powder characteristics.

To the best of our knowledge, there is no study involving microwave and ultrasound treatment in alkalization process. Recent research studies related to modification of cocoa powder for food and beverage making purposes only include the effect of cocoa powder production method on the flavor compounds [9], the impact of alkaline type and concentration on the quality of cocoa powder [10], and the influence of various types of cocoa powder and stabilizers on the quality attributes of cocoa beverages [5]. Therefore, it is important to investigate the feasibility of microwave- and ultrasound-assisted alkalization which can be applied in small-scale industry. As emphasized by Valverde-Garcia and colleagues [6], the effects of alkalization on the nutritional and functional properties of cocoa need to be deeply investigated since this process can substantially affect cocoa powder characteristics. Hence, this research aims to examine the effect of ultrasonic- and microwave-assisted alkalization on the physicochemical properties and antioxidant activities of cocoa powder.

2 Materials and methods

2.1 Samples and chemicals

Natural cocoa powder, also known as non-alkalized cocoa powder, was obtained from PT Cargill Cocoa and Chocolate Gresik (Indonesia). KOH, FeCl₃, ascorbic acid, sodium carbonate, acetic acid, and Folin–Ciocalteu reagent were purchased from Merck KGaA (Darmstadt, Germany). Meanwhile tannic acid, quercetin, gallic acid, and trichloroacetic acid were purchased from Sigma-Aldrich (Stenheim, Germany). 2,2-Diphenyl-1-picrylhydrazyl (DPPH) for molecular biology was obtained from HiMedia Laboratories Pvt. Ltd (Nashik, India) AlCl₃ and K₃[Fe(CN)₆] were purchased from PT Smart Lab Indonesia (Tangerang, Indonesia). All the chemicals and reagents are of analytical grade.

2.2 Sample preparation

An alkali solution made of 1% KOH (w/v) in distilled water was prepared. The selected alkali concentration followed the previous study of Li et al. [11], in which 1% is considered light alkaline. Light alkali produced alkalized cocoa powder with higher antioxidant properties than heavy alkaline. The alkali solution was mixed with natural cocoa powder at a ratio of 3:1 (v/w) by manually stirring for about 3 min to get a homogenous mixture. The mixture was then separated into two parts in which one part was treated by ultrasonication at 40 kHz and 120 W using ultrasonicator (Baku BK-2000, Baku Guangdong, China) and the other part was treated with the lowest power (900 W) of the microwave (Sammic HM1001, DKSH Group, Bangkok Thailand). Ultrasonication and microwave treatment were conducted for 5, 10, and 15 min. After the treatments, the samples were then boiled in a small-scale pressured pan (Maxim 20 cm/4 L Maspion Group, Sidoarjo, Indonesia) for 15 min. Afterward, the samples were poured in a 20 × 20 baking pan with a thickness of 0.5 mm. Then, the samples were dried in an oven (Memmert 75, No. F-0109.0088, Schwabach, Germany) at 80°C for 16 h to obtain the dry alkalized cocoa powder. The dried samples were milled using a miller (Retsch ZM 200 Ultra Centrifugal Mill, Retsch GmBH, Haan, Germany). A maximum peripheral rotor speed of 92.8 m/s was set during the milling until the fineness of the product was smaller than 10 mm. Natural cocoa powder (without alkalization) and conventionally alkalized cocoa powder (without ultrasonication and microwave treatment) were also prepared as controls. The sample preparation is shown schematically in Figure 1.

Figure 1

Schematic diagram of the experimental design.

2.3 Analytical determination

2.3.1 Wettability

A method described by Muhammad et al. [5] was used as the reference for the wetting time which is also known as wettability. The wetting time was determined by rapidly pouring 4 g of the milled cocoa powder in a glass with 40 mL of water (80°C), and then the time duration by which the poured cocoa powder becomes totally wet and has disappeared from the surface of the water was observed.

2.3.2 Solubility

The solubility analysis was conducted by initially mixing cocoa powder and water (80°C) in a ratio of 1:4 (w/v) using a magnetic stirrer for 30 min, after which the solution was centrifuged at 492g (2,000 rpm) for 10 min (Kokusan H-107, Kokusan Corp., Saitama, Japan). The supernatant was then collected and dried in an oven dryer at 120°C until a stable weight was reached. Solubility was stated as the percentage of the weight of soluble matter per weight of the initial material [5].

2.3.3 Sedimentation index (SI)

SI analysis was performed to determine the stability of the cocoa powder suspension. SI was calculated using equation (1) after visual assessment to see the relatively clear area where V is the total sample volume and V _S is the volume of the relatively clear area after 24 h [5]

(1) SI = ( V S / V ) × 100 .

2.3.4 pH and morphology

The pH of the cocoa powder was determined using a pH meter (Ohaus ST3100, Ohaus Co., NJ, USA) at 20°C, while the morphology analysis was conducted using a scanning electron microscope (SEM) (Quanta 250 FEG, FEI Company, OR, USA). A double-sided adhesive carbon tape was used to embed the sample and the stubs. An acceleration voltage of 10 kV at a pressure of 80 Pa was employed. Electron micrographs were obtained from secondary electrons collected by a large-field detector.

2.3.5 Color properties

The color coordinates of CIELAB. (L*, a*, b*) were determined using a spectrophotometer (ColorFlex EZ 45/0 LAV, Hunter Associates Laboratory Inc., VA, USA). Following the method as described by Muhammad et al. [5], the obtained L*, a*, b* values were further used to calculate the level of the Chroma (C*), the °Hue, and the redness intensity of the samples, as well as the color difference between the alkalized and natural cocoa powder (ΔE) using equations (2)–(5), respectively:

(2) C ⁎ = a ⁎ 2 + b ⁎ 2 ,

(3) ° Hue = arctan ( b ⁎ / a ⁎ ) ,

(4) Redness intensity = a ⁎ / b ⁎ ,

(5) Δ E = ( L 1 ⁎ − L 2 ⁎ ) 2 + ( a 1 ⁎ − a 2 ⁎ ) 2 + ( b 1 ⁎ − b 2 ⁎ ) 2 .

2.3.6 Extraction of antioxidant compound

Antioxidant compound extraction is substantial prior to the antioxidant properties determination. Extraction was carried out following the method of Muhammad et al. [12]. Briefly, the fat content of cocoa powder (10 g) was removed by washing with 50 mL of n-hexane thrice. Afterward, n-hexane was discarded, and the cocoa powder was air-dried for 24 h to obtain the defatted cocoa powder. The dried defatted cocoa powder (4 g) was mixed with 10 mL of extractive solvent composed of acetone, distilled water, and acetic acid (70:29.8:0.2) in an ultrasonic bath for 30 min to extract antioxidant compounds, mainly phenols and flavonoids. It was then centrifuged for 10 min at 1,107g (3,000 rpm) and the supernatant was collected. The procedure was repeated twice. The collected supernatant was filtered to remove the residual particles and obtain the cocoa powder extract. The extract was then used for further analyses following the methods of Muhammad et al. [13].

2.3.7 Total phenol content

In the total phenol analysis, a solution of the cocoa powder extract (200 µL), distilled water (1 mL), and Folin–Ciocalteu reagent (200 µL) were prepared. After which, 7% of Na₂CO₃ (2.5 mL) solution and distilled water (2.1 mL) were added. The mixture was placed at ambient temperature condition (±25°C) in the absence of light for 1.5 h. After the incubation, the absorbance was measured at 760 nm in an UV-vis spectrophotometer (Shimadzu BioSpec-1600, Shimadzu Corp., Kyoto, Japan). A standard curve of gallic acid was constructed to determine the total phenolic content expressed as milligram gallic acid equivalent per gram dry weight (mg GAE/g DW).

2.3.8 Total flavonoid content

In the total flavonoid content analysis, 0.1 M AlCl₃ (4 mL) was mixed with 160 µL of extract, followed by incubation for 40 min at ambient temperature (±25°C) in a dark condition. The absorbance was measured at 415 nm and the total flavonoid content was expressed as milligrams of quercetin equivalent per gram of dry weight (mg QE/g DW).

2.3.9 Ferric reducing antioxidant power (FRAP)

FRAP assay was performed by incubation (50°C) of a mixture containing cocoa powder extract (1 mL), phosphate buffer (0.2 M, pH 7, 2.5 mL), and 1% of K₃[Fe(CN)₆] (2,5) for 0.5 h. After that, 10% trichloroacetic acid (2.5 mL) was added to the mixture and then centrifuged (1,107g, 10 min) to remove the large particles and get the supernatant. Distilled water and 0.1% FeCl₃ were then added to the supernatant. The ratio of distilled water, FeCl₃ solution, and the supernatant was at 5:1:5. The absorbance was measured at 700 nm. A standard curve of ascorbic acid was prepared (0–100 µg/mL). Thus, FRAP was expressed as milligrams of ascorbic acid equivalent per gram of the extract (mg AAE/g).

2.3.10 DPPH-radical scavenging activity

In the DPPH assay, the cocoa powder extract (100 µL) was mixed with 4 mL of DPPH solution (0.01 mM). After incubation in the dark for 0.5 h, the absorbance was determined at 517 nm, and then the DPPH radical scavenging activity (% inhibition) was calculated using equation (6). The DPPH radical scavenging activity was expressed in IC₅₀ (the concentration required to scavenge 50% of the initial DPPH radicals):

(6) % inhibiton = ( Absorbance of the control ( Ac ) − Absorbance of the sample ( As ) ) × 100 Absorbance of the control ( Ac ) . .

2.3.11 Experimental design and statistical analysis

The parameters that were considered to be affecting the characteristics of the alkalized cocoa powder were the technique and the duration. The experiment was performed by means of a completely randomized design, and the results represented the means of three replicates, except for SEM analysis. One-way ANOVA method followed by Duncan’s Multiple Range Test to test the differences among the samples. The differences were considered significant at 0.95 confidence level. The statistical analysis was executed by SPSS 23.0 Software (SPSS Inc., Chicago, IL, USA).

3 Results and discussion

3.1 Effect of ultrasonic- and microwave-assisted alkalization on physical properties of cocoa powder

Table 1 shows that alkalization using 1% KOH increased the pH of cocoa powder in which the pH of natural cocoa powder was 5.72 and the pH of alkalized cocoa powder (all treatments) was 7.48 or even higher. It was shown that ultrasonic- and microwave-assisted alkalization resulted in a very slight effect in the pH as compared to the conventional alkalization. Yet, statistical analyses showed a significant difference between alkalized cocoa powder obtained by conventional method and ultrasonic-/microwave-assisted alkalization method (p < 0.05). It is also shown that the increase in pH of the alkalized cocoa powder was linearly correlated with the duration of microwave and ultrasonic treatment. It is believed that those treatments caused more intense chemical reactions, resulting in a higher pH alteration.

Table 1

pH wetting time, solubility, and SI of alkalized cocoa powder

Treatment	pH	Wetting time (s)	Solubility (%)	SI
Control (natural cocoa powder)	5.72 ± 0.01^a	80.87 ± 0.38^c	20.52 ± 0.08^a	50.67 ± 0.94^d
Conventional alkalization	7.50 ± 0.04^b	89.24 ±± 0.51^e	24.29 ± 0.17^b	49.06 ± 0.27^cd
Ultrasonic-assisted alkalization
5 min	7.60 ± 0.02^c	22.31 ± 0.36^b	24.79 ± 0.61^bc	48.47 ± 0.39^cd
10 min	7.68 ± 0.02^cd	92.23 ± 0.37^f	25.56 ± 1.01^d	45.65 ± 0.54^ab
15 min	7.59 ± 0.01^cd	158.04 ± 0.84^h	27.68 ± 1.02^e	44.19 ± 0.09^a
Microwave-assisted alkalization
5 min	7.48 ± 0.01^cd	6.81 ± 0.49^a	25.43 ± 0.53^cd	47.05 ± 0.28^bc
10 min	7.53 ± 0.01^cd	86.73 ± 0.55^d	26.00 ± 0.10^d	44.61 ± 0.95^ab
15 min	7.49 ± 0.01^d	141.97 ± 0.34^g	28.81 ± 0.28^f	43.92 ± 0.13^a

Mean values with different lowercase notations within the same column differ significantly (p < 0.05).

Substantial improvement in the solubility of cocoa powder was also observed in the microwave- and ultrasound-assisted alkalization. As shown in Table 1, alkalized cocoa powder produced by ultrasonic- and microwave-assisted alkalization had better solubility than that produced by conventional alkalization as well as natural cocoa powder. As such, the solubility of natural cocoa powder and alkalized cocoa powder processed using conventional method were about 20.52 and 24.29%, respectively, while the alkalized cocoa powder processed by ultrasonic- and microwave-assisted methods were about 27.68 and 28.81%, respectively. The statistical analyses showed a significant difference between alkalized cocoa powder obtained by conventional method and ultrasonic-/microwave-assisted alkalization method (p < 0.05). Table 1 also shows that increasing the duration of alkalization notably increased the solubility, regardless of the type of the treatments (p < 0.05).

In any case, the improvement in solubility by alkalization is attributed to the chemical modification due to alkali treatment. As for microwave-assisted alkalization, the microwave increased the temperature, triggering rapid chemical reactions [7]. Meanwhile, mechanical sound waves formed cavitation bubbles for ultrasonic-assisted alkalization, inducing more intense biochemical reactions [8]. In both cases, therefore, at a similar duration of the process, the solubility of alkalized cocoa powder assisted by microwave or ultrasonic process is better than that of the powder obtained by a conventional process.

In addition to solubility, a significant improvement was shown in the wetting time parameters. As shown, the conventional alkalization resulted in wetting time of 89 s, while the ultrasonication (10 and 15 min) resulted in the wetting time of 92 and 158 s, respectively, and the microwave treatment (15 min) resulted in the wetting time of 141 s. It is interesting that the duration of assisted alkalization was directly proportional to the wetting time implying that ultrasonication and microwave treatment had significant effect on this parameter. Furthermore, it is also notable that the lower duration of ultrasonication and microwave treatment resulted in a lower wetting time as compared to conventional alkalization. Up until now, this phenomenon is still under investigated.

Table 1 shows that ultrasonic treatment resulted in a longer wetting time than microwave treatment at a similar duration (p < 0.05). As such, ultrasonic-assisted alkalization at 5, 10, and 15 resulted in the wetting time of 22.31, 92.23, and 158.04 s, respectively. In contrast, microwave-assisted alkalization at the duration of 5, 10, and 15 resulted in the wetting time of 6.81, 86.73, and 141.97 s, respectively. Wetting time indicates the interfacial dynamics of particle–water interactions and it is substantially affected by hydrophobic properties of the particle. It was also reported by Amer et al. [14] that the higher alkalization degree, such as longer alkalization duration in this case, causes more intensive base-catalyzed hydrolysis reactions increasing the chemical sorption sites for water molecules in cocoa particles.

Wetting time has a linear correlation with suspension stability [5], which is also presented in this study. Cocoa powder can be suspended in the drink for a longer period in the condition of longer wetting time. Suspension stability is an important parameter in the quality of cocoa drink indicating how fast the cocoa powder deposits as sediment. The suspension stability can be measured by SI. The results showed that ultrasonic- and microwave-assisted alkalization had lower SI (p < 0.05) (Table 1), meaning that the treatments resulted in more stable suspensions. Interestingly, longer duration of treatments led to lower SI. For instance, ultrasonic-assisted alkalization at 5, 10, and 15 resulted in the SI of 48.47, 45.65, and 44.19, respectively. Meanwhile, microwave-assisted alkalization at the duration of 5, 10, and 15 resulted in the SI of 47.05, 44.61, and 43.93, respectively. Muhammad et al. [5] stated that insoluble matter may also affect the sedimentation of particles. Therefore, it is rational if the SI aligns with solubility, as clearly shown in Table 1. It is also noted that at 10 and 15 min, the SI between cocoa powder obtained by ultrasonic and microwave treatments was not statistically different (p > 0.05).

SEM analysis was able to visualize the physical modification of cocoa powder after the ultrasonic- and microwave-assisted alkalization. As revealed in Figure 2, natural cocoa powder had a regular and oval form. However, alkalization generally causes disruption of the powder structure; in the case of ultrasonic- and microwave-assisted alkalization, the disruption may be more intense, and thus the alkalization effect may be more pronounced. As well known, the microwave provides an alternative heat source and can create the opportunity to induce rapid chemical reactions [7], while ultrasonic wave creates cavitation bubbles causing hotspots and extreme local condition. These hotspots expedite the biochemical reactions in its vicinity [8]. Simply put, ultrasonication provides more access for alkali solution to interact with cocoa powder surface.

Figure 2

Microstructural properties of natural cocoa powder (a) and cocoa powder with alkalization – control (b), ultrasonic-assisted alkalization (c), and microwave-assisted alkalization (d).

The effects of ultrasonic- and microwave-assisted alkalization were also visibly shown in the color properties of cocoa powder. Generally, alkalization can darken the color of cocoa powder due to oxidation caused by the alkali. As shown, the lightness of the natural cocoa powder was 21.31 and that of alkalized cocoa powder was 14.19. In this study, the application of ultrasonic and microwave in the alkalization process led to a more pronounced effect of alkalization to the color properties of the cocoa powder (Table 2). Ultrasonic- and microwave-assisted alkalization caused darker powder, lower value of chroma and °Hue than conventional alkalization (p < 0.05). At the same time, it led to higher redness intensity (p < 0.05) and higher value of color difference between the alkalized and the natural cocoa powder (p < 0.05). The variation in color properties was also shown to be linearly correlated with the duration of the treatment. Nevertheless, at a similar duration, the color properties of the cocoa powder obtained by ultrasonic treatment were not significantly different with that obtained by microwave treatment. The appearance of the alkalized cocoa powder is presented in Figure 3.

Table 2

Color properties of alkalized cocoa powder

Sample and treatment	Lightness	Chroma	°Hue	Redness intensity	∆E
Control (natural cocoa powder)	21.31 ± 0.09^d	14.35 ± 0.06^e	43.95 ± 0.20^c	1.04 ± 0.01^a	—
Conventional alkalization	14.19 ± 0.06^c	10.14 ± 0.04^d	39.54 ± 0.25^b	1.21 ± 0.01^d	8.33 ± 0.09^a
Ultrasonic-assisted alkalization
5 min	14.08 ± 1.03^c	9.83 ± 0.73^cd	39.44 ± 0.52^b	1.22 ± 0.02^d	8.52 ± 1.05^ab
10 min	13.51 ± 0.34^ab	9.65 ± 0.30^bc	38.35 ± 0.45^a	1.26 ± 0.02^c	8.51 ± 0.38^cd
15 min	13.09 ± 0.02^a	9.59 ± 0.36^bc	38.04 ± 1.14^a	1.28 ± 0.05^c	9.58 ± 0.03^de
Microwave-assisted alkalization
5 min	13.76 ± 0.05^bc	9.81 ± 0.03^cd	38.37 ± 0.31^a	1.26 ± 0.01^c	8.87 ± 0.03^b
10 min	13.42 ± 0.19^ab	9.34 ± 0.17^ab	38.22 ± 1.31^a	1.27 ± 0.01^b	9.41 ± 0.25^de
15 min	13.04 ± 0.03^a	9.13 ± 0.22^a	37.93 ± 1.04^a	1.28 ± 0.05^a	9.85 ± 0.09^e

Mean values with different lowercase notations within the same column differ significantly (p < 0.05).

Figure 3

Appearance of alkalized cocoa powder.

3.2 Effect of ultrasonic- and microwave-assisted alkalization on antioxidant properties of cocoa powder

These results evidently show the potential use of ultrasonic and microwave treatment in alkalization process. However, the treatments also have drawbacks such that it reduced the phenolic content and antioxidant activity of the cocoa powder (Table 3). In general, the total phenols, total flavonoids, and antioxidant activity of alkalized cocoa powder were lower than that of natural cocoa powder (p < 0.05). The additional treatment of ultrasonic and microwave resulted in more noticeable reduction which may be due to a more intense chemical reaction during the alkalization process. As such, the total phenols and flavonoids of cocoa powder produced by conventional alkalization were about 20.90 mg GAE/g and 0.89 mg QE/g, respectively, while those of cocoa powders produced by advanced treatments were less than 20 mg GAE/g and 0.89 mg QE/g, respectively. Longer duration of treatments also caused lower phenol and flavonoid content. Similar phenomenon was also found in the FRAP activity as one of the antioxidant activity parameters of cocoa powder. It is understandable since FRAP activity had a positive correlation with phenolic content according to previous reports [13]. This result is also confirmed by the result of IC₅₀ DPPH radical scavenging activity. As shown, the higher degree of alkalization caused the higher IC₅₀ value meaning that more concentration of cocoa powder extract is required to inhibit 50% of radical reaction. This indicates that the antioxidant activity of the samples is lower. A similar phenomenon was found in the study of Sioriki et al. [15] explaining the decrease of active compounds after alkalization. Several studies reported a similar reduction in active compounds after alkalization [16–18].

Table 3

Antioxidant properties of alkalized cocoa powder

Treatment	Total phenolic content (mg GAE/g)	Total flavonoid content (mg QE/g)	DPPH IC₅₀ (ppm)	FRAP (mg AAE/g)
Control (natural cocoa powder)	35.23 ± 0.04^g	2.85 ± 0.02^d	35.07 ± 0.45^a	28.03 ± 0.27^d
Conventional alkalization	20.90 ± 0.01^f	0.89 ± 0.01^c	57.95 ± 0.65^b	21.40 ± 0.03^c
Ultrasonic-assisted alkalization
5 min	19.20 ± 0.45^e	0.88 ± 0.01^c	81.62 ± 0.02^c	15.15 ± 0.50^b
10 min	15.36 ± 0.09^c	0.81 ± 0.01^b	82.48 ± 0.50^cd	14.21 ± 0.94^ab
15 min	14.99 ± 0.73^c	0.78 ± 0.01^b	84.76 ± 0.10^cd	13.47 ± 0.76^a
Microwave-assisted alkalization
5 min	17.74 ± 0.01^d	0.72 ± 0.03^a	82.15 ± 0.82^cd	14.76 ± 0.59^ab
10 min	14.32 ± 0.01^b	0.70 ± 0.09^a	82.72 ± 0.04^cd	13.70 ± 0.78^ab
15 min	13.63 ± 0.56^a	0.68 ± 0.03^a	85.75 ± 0.76^d	13.25 ± 0.08^a

Mean values with different lowercase notations within the same column differ significantly (p < 0.05).

Phenolic content and antioxidant activity have gained high interest nowadays because they are closely associated with beneficial health effects [19,20]. This study shows that the alkalization coupled with microwave or ultrasonic may negatively impact these parameters. However, the primary purpose of alkalization is to improve the pH, color, solubility, and stability of cocoa powder. In these aspects, microwave or ultrasonic treatment demonstrates a significant contribution to improving the process of obtaining cocoa powder with a more intense color and better solubility and suspension stability. Further study related to the sensory profile of cocoa powder is recommended to investigate the other possible positive impacts of microwave- and ultrasonic-assisted processes.

Despite its limitations, this study provides the first attempt to involve microwave and ultrasonic processes and strengthen the new paradigm in combining the advanced method with conventional alkalization. The methods proposed in this study can be alternatives in addition to a recent method combining alkalization with extrusion and cold plasma technique [21,22]. As all the novel proposed alkalization methods still have limitations, particularly regarding the bioactive content, finding a new alkalization method for retaining the phenolic content and antioxidant activity of the cocoa powder is encouraged to be explored in the future. To better understand the bioactive compounds’ stability during alkalization, analysis using metabolomic approaches is highly recommended [23].

4 Conclusion

To sum up, ultrasonication and microwave treatment were potentially used in the alkalization process to improve the physical properties of cocoa powder to some extent. Ultrasonication and microwave treatment modify the color properties of cocoa powder to be more appealing by increasing the darkness and red intensity. The color difference of cocoa powders produced by the treatments was higher than that of the cocoa powder produced by conventional alkalization. Cocoa powders produced by using ultrasonic- and microwave-assisted alkalization are suitable for beverage making purposes as the technique is proven to improve the pH, solubility, and wetting time, and at the same time decrease the SI of cocoa powder. However, the methods also cause significant decrease in total phenols, flavonoids, and antioxidant activity. Based on the evaluation of each parameter, ultrasonic-assisted alkalization seems more promising in changing the physical properties of cocoa powder with a better retainment of antioxidant properties. However, the solubility of the alkalized cocoa powder obtained by ultrasonic treatment was lower than that obtained by microwave treatment. Thus, the results obtained in this study are still considered not satisfying. Further research by combining other advanced methods with alkalization process may be required. Despite the limitation of each method, this research provides new insights for the application of ultrasonic and microwave treatment to assist alkalization process. Metabolomic approach may be significant to understand the behavior of bioactive compounds during ultrasonic- and microwave-assisted alkalization.

Acknowledgements

The authors thank PT Cargill Cocoa and Chocolate Gresik (Indonesia) for giving the opportunity for the second author (D.P.) to do internship and giving free sample of natural cocoa powder.

Funding information: This research was financially supported by Universitas Sebelas Maret through Hibah Kolaborasi Internasional 2023 (Grant no. 228/UN27.22/PT.01.03/2023).
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and consented to its submission to the journal, reviewed all the results and approved the final version of the manuscript. D.R.A.M.: conceptualization, funding acquisition, supervision, writing – review and editing; D.P. (2nd author): data curation, formal analysis, investigation; D.P. (3rd author): validation, writing – review; S.A.: writing – review & editing; M.F.A.: writing – review and editing; S.P.P.: supervision; E.F.: supervision.
Conflict of interest: The second author (D.P.) did internship at PT Cargill Cocoa and Chocolate Gresik (Indonesia). The company gave free sample of natural cocoa powder, but was not involved in the experimentation, data interpretation, writing, or publication of this study at Universitas Sebelas Maret. The other authors declare that they have no conflicts of interest to disclose. None of the authors received payment for consultation or expert testimony and do not own stock or stock options from PT Cargill Cocoa and Chocolate Gresik (Indonesia).
Data availability statement: The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

References

[1] Praseptiangga D, Zambrano JMG, Sanjaya AP, Muhammad DRA. Challenges in the development of the cocoa and chocolate industry in Indonesia: a case study in Madiun, East Java. AIMS Agric Food. 2020;5(4):920–37.Suche in Google Scholar

[2] Muhammad DRA, Rahayu ES, Fibri DLN. Revisiting the development of probiotic-based functional chocolates. Rev Agric Sci. 2021;9:233–48.Suche in Google Scholar

[3] Faiqoh KEN, Muhammad DRA, Praseptiangga D. Ginger-flavoured ready-to-drink cocoa beverage formulated with high and low-fat content powder: consumer preference, properties and stability. Food Res. 2021;5(2):7–17.Suche in Google Scholar

[4] Muhammad DRA, Zulfa F, Purnomo D, Widiatmoko C, Fibri DLN. Consumer acceptance of chocolate formulated with functional ingredient. In IOP Conference Series: Earth and Environmental Science. Vol. 637, No. 1. IOP Publishing; 2021. p. 012081.Suche in Google Scholar

[5] Muhammad DRA, Kongor JE, Dewettinck K. Investigating the effect of different types of cocoa powder and stabilizers on suspension stability of cinnamon-cocoa drink. J Food Sci Technol. 2021;58(10):3933–41.Suche in Google Scholar

[6] Valverde Garcia D, Perez Esteve E, Barat Baviera JM. Changes in cocoa properties induced by the alkalization process: a review. Compr Rev Food Sci Food Saf. 2020;19(4):2200–21.Suche in Google Scholar

[7] Kumar A, Kuang Y, Liang Z, Sun X. Microwave chemistry, recent advancements, and eco-friendly microwave-assisted synthesis of nanoarchitectures and their applications: a review. Mater Today Nano. 2020;11:100076.Suche in Google Scholar

[8] Kumar K, Srivastav S, Sharanagat VS. Ultrasound assisted extraction (UAE) of bioactive compounds from fruit and vegetable processing by-products: a review. Ultrason Sonochem. 2021;70:105325.Suche in Google Scholar

[9] Mohamadi Alasti F, Asefi N, Maleki R, SeiiedlouHeris SS. Investigating the flavor compounds in the cocoa powder production process. Food Sci Nutr. 2019;7(12):3892–901.Suche in Google Scholar

[10] Alasti FM, Asefi N, Maleki R, SeiiedlouHeris SS. The influence of three different types and dosage of alkaline on the inherent properties in cocoa powder. J Food Sci Technol. 2020;57(7):2561–71.Suche in Google Scholar

[11] Li Y, Feng Y, Zhu S, Luo C, Ma J, Zhong F. The effect of alkalization on the bioactive and flavor related components in commercial cocoa powder. J Food Compos Anal. 2012;25(1):17–23.Suche in Google Scholar

[12] Muhammad DRA, Saputro AD, Rottiers H, Van de Walle D, Dewettinck K. Physicochemical properties and antioxidant activities of chocolates enriched with engineered cinnamon nanoparticles. Eur Food Res Technol. 2018;244:1185–202.Suche in Google Scholar

[13] Muhammad DRA, Praseptiangga D, Van de Walle D, Dewettinck K. Interaction between natural antioxidants derived from cinnamon and cocoa in binary and complex mixtures. Food Chem. 2017;231:356–64.Suche in Google Scholar

[14] Amer A, Schaumann GE, Diehl D. The effect of pH modification on wetting kinetics of a naturally water-repellent coniferous forest soil. Eur J Soil Sci. 2017;68:317–26.Suche in Google Scholar

[15] Sioriki E, Tuenter E, Van de Walle D, Lemarcq V, Cazin CS, Nolan SP, et al. The effect of cocoa alkalization on the non-volatile and volatile mood-enhancing compounds. Food Chem. 2022;381:132082.Suche in Google Scholar

[16] Demirci S, Elmaci C, Atalar İ, Toker OS, Palabiyik I, Konar N. Influence of process conditions of alkalization on quality of cocoa powder. Food Res Int. 2024;182:114147.Suche in Google Scholar

[17] Sioriki E, Lemarcq V, Alhakim F, Triharyogi H, Tuenter E, Cazin CS, et al. Impact of alkalization conditions on the phytochemical content of cocoa powder and the aroma of cocoa drinks. Lwt. 2021;145:111181.Suche in Google Scholar

[18] Greño M, Herrero M, Cifuentes A, Marina ML, Castro-Puyana M. Assessment of cocoa powder changes during the alkalization process using untargeted metabolomics. Lwt. 2022;172:114207.Suche in Google Scholar

[19] Cerit I, Demirkol O, Avcı A, Arkan BS. Phenolic content and oxidative stability of chocolates produced with roasted and unroasted cocoa beans. Food Sci Technol Int. 2024;30(5):450–61.Suche in Google Scholar

[20] Razola-Díaz MDC, Aznar-Ramos MJ, Verardo V, Melgar-Locatelli S, Castilla-Ortega E, Rodríguez-Pérez C. Exploring the nutritional composition and bioactive compounds in different cocoa powders. Antioxidants. 2023;12(3):716.Suche in Google Scholar

[21] Palabiyik I, Kopuk B, Konar N, Toker OS. Investigation of cold plasma technique as an alternative to conventional alkalization of cocoa powders. Innov Food Sci Emerg Technol. 2023;88:103440.Suche in Google Scholar

[22] Valverde D, Behrends B, Pérez-Esteve É, Kuhnert N, Barat JM. Functional changes induced by extrusion during cocoa alkalization. Food Res Int. 2020;136:109469.Suche in Google Scholar

[23] Palma-Morales M, Rangel-Huerta OD, Díaz C, Castilla-Ortega E, Rodríguez-Pérez C. Integration of network-based approaches for assessing variations in metabolic profiles of alkalized and non-alkalized commercial cocoa powders. Food Chem: X. 2024;23:101651.Suche in Google Scholar

Received: 2024-02-19

Revised: 2024-10-10

Accepted: 2024-11-12

Published Online: 2024-12-11

This work is licensed under the Creative Commons Attribution 4.0 International License.

Artikel in diesem Heft

https://doi.org/10.1515/opag-2022-0400

Schlagwörter für diesen Artikel

alkalization; cocoa powder; microwave; ultrasonic

Creative Commons

BY 4.0