A Study on the Possibility of Utilizing Coffee Waste as a Recycled Resource Material using Ultrasonic Extraction Method

I. INTRODUCTION

The development of the food industry and food processing technology, along with the improvement of the standard of living of modern people, has shaped the coffee culture [1, 2, 3]. Coffee has become an essential item in the preferences of contemporary individuals, to the extent that it is often referred to as the "second water"[4]. How to make a cup of Americano, coffee is extracted using water, roasted coffee beans, The seeds of the coffee tree's fruit[5].

During the coffee extraction process, coffee waste, which refers to the leftover residues after the coffee extraction process, is generated. When making a cup of coffee, approximately 15 grams of coffee beans are used, with 14.7 grams being discarded, and 0.3 grams, which is 2%, is consumed as a beverage [6]. Coffee waste is generated worldwide at a rate of 10 million tons annually, and the amount of coffee waste is increasing by coffee consumption. In 2019, an 149,038 tons of coffee waste were produced [7, 8]. If such coffee waste is incinerated or landfilled without recycling, it incurs an annual cost of KRW 35 billion [9, 10].

Decaffeination refers to removing caffeine from coffee beans, cocoa, tea leaves, and other

Decaffeination refers to the process of removing caffeine from coffee beans, cocoa, tea leaves, and other substances that contain caffeine. Therefore, decaffeinated coffee typically contains 1-2% of the original caffeine component, making it suitable for pregnant women, diabetes patients, and individuals with sensitive stomachs, and it is also known as 'caffeine-free' coffee [11]. The international standard for decaffeinated coffee is that more than 97% of caffeine is removed. Therefore, even in decaffeinated coffee, a small amount of caffeine may still be contained [12].

Caffeine is a compound formed by combining 'Coffee' with '-ine,' representing an alkaloid substance that collectively refers to basic organic compounds found within plant organisms. Alkaloid substances often exhibit significant physiological and pharmacological effects, with notable examples including nicotine, morphine, and caffeine. Caffeine has a stimulating effect on the central and the peripheral nervous system, which results in mental alertness and an increase in concentration and productivity $[13,14]$.

Therefore, caffeine may have some benefits for adults, but its impact on the central nervous system of children has not been sufficiently researched yet. The central nervous system of children is still in development, which raises concerns about the potential side effects and health implications of caffeine $[15]$. Caffeine can be absorbed through the skin, so caution is necessary when using caffeine-containing substances in items for children, such as educational aids.

Research on the utilization of coffee waste includes studies on artificial cover material manufacturing for sewage sludge using coffee sludge $[16]$, activated carbon adsorbents $[17]$, eco-friendly composting $[18]$, wastewater treatment $[19]$, coffee soap, and air freshener production $[20]$. However, the actual usage of coffee waste remains minimal. Furthermore, recently, some clay products for children have incorporated recycled materials, including coffee waste. However, existing clay products made with recycled coffee waste have limitations for use by children due to factors such as caffeine content.

Therefore, educational aids made from recycled coffee waste should minimize caffeine content, taking into account the age and sensitivity of children. Therefore, the purpose of this study is to confirm the reduction of caffeine using a repeated extraction method with coffee waste, investigate its decaffeination potential, assess the feasibility of coffee waste as a sustainable resource, and check its safety and potential as a recyclable resource material.

II. EXPERIMENT

2.1 Materials

The coffee waste used in this study were provided by Harmony Co., Ltd. in the form of coffee ground powder in February 2023 and were stored at room temperature for conducting experiments.

2.2 Extraction Condition Experiment for Coffee Waste I

For Experiment I of coffee waste extraction, distilled water and ethanol were used as solvents. The volume was set at 300 ml, with a sample weight of 30 g. Ethanol was used in varying concentrations of 0%, 30%, 50%, 70%, and 100%, and extraction was carried out at room temperature for 48 hours after immersion. The ultrasonic extraction conditions involved using an extraction device (ULTRA SONIC, BMWORKS, Daejeon, Korea) at a temperature of 20°C, operating at 20 kHz for 30 minutes. The extracted solution was subjected to decompressed filtration through a 5-8 μm filter (Hyun Dai, Micro, Korea) using a vacuum pump (DOA-P704-AC, GAST Manufacturing Inc, U.S.A). After the filtration, the coffee extract was dried in a 60°C Coven for 48 hours and stored at 4°C for GC-MS analysis and caffeine analysis.

2.3 Repeated Extraction Experimental Conditions for Coffee Waste II

For the repeated extraction of coffee waste in Experiment II, the same solvents, water and ethanol, were used as in Experiment I. For the ultrasonic extraction conditions for Experiment II, the volume was set at 300 ml, with a sample weight of 30 g, and 70% ethanol was used. The extraction was carried out in the same way as

Experiment 1 at room temperature for 48 hours after immersion. After filtration, the coffee waste was dried in a ${60}^{\circ }$ C oven for 48 hours, and the process of obtaining the coffee waste extraction material was repeated 1-3 times.

2.4 Caffeine Quantification in Coffee Waste Using LC-MS

The caffeine content in coffee waste was analyzed using HPLC (Agilent 1290). After a 50 mg sample was measured and injected into a vial, 2 ml of methanol was added, and sonication was carried out for 60 minutes. The analysis was conducted using a 0.45 $\mu$ m PVDF syringe filter. An LC column, Kinetex 2.6 $\mu$ m EVO C18 100Å 2.1×100 mm, was used. The column temperature was maintained at 40°C, with a flow rate of 0.300 mL/min, and an injection volume of $\mu \ell$. The MS was conducted under the conditions of a gas temperature of 300°C, a drying gas flow rate of 10 L/min, and a nebulizer pressure of 45 psi. The LC-MS analysis method for this experiment was carried out using in the same way.

2.5 Effective Active Ingredients Analysis in Coffee Waste Extract Using GC-MS

For the analysis of effective active ingredients in the coffee waste extract for ExperimentI, GC-MS (Gas chromatography-mass spectrometry) was used. For the GC analysis, a column (Agilent 19091S-433) was used with HP-5ms (30 m x 250 $\mu$ m x 0.25 $\mu$ m), and the analysis was conducted for 45 minutes. The injection volume was $\mu \ell$, and the carrier gas was helium maintained at a flow rate of 10 ml/min. The oven temperature was initially held at 40°C for 3 minutes and then increased at a rate of 5°C/min to a final temperature of 300°C, which was held for 1 minute during the analysis.

III. RESULTS AND CONSIDERATIONS

The results for the coffee waste recovered after ultrasonic extraction in this study are as follows. The coffee waste recovered after extraction in Experiment I was labeled as original materials (ORG) and A to E, depending on the ethanol content.

The coffee waste recovered after extraction with 0% ethanol ultrasonic extraction is labeled as A, 30% ethanol as B, 50% ethanol as C, 70% ethanol as D, and 100% ethanol as E, as shown in <Table 1>.

In Experiment II, depending on the number of extractions, the recollected materials were labeled as original materials (ORG) and G1 to G3.

The coffee waste recovered after ultrasonic extraction with 70% ethanol is labeled as G1 for the first extraction, G2 for the second extraction, and G3 for the third extraction, as shown in <Table 2>.

3.1. Caffeine Content Analysis of Coffee Waste Using LC-MS

The caffeine content of coffee waste analyzed using LC-MS is as follows.

As shown in <Table 3 & Figure 1>, the 70% ethanol ultrasonic coffee waste exhibited the lowest caffeine content at 404.89 $\mu$ g/g, showing a 72.1% reduction in caffeine compared to the initial caffeine content of the ORG <Table 4>.

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3.2 GC-MS Analysis of Effective Active Ingredients in Coffee Waste

The GC-MS analysis results of effective ingredients in the recovered coffee waste after extraction are presented in <Table 5>. No other compounds were detected in the coffee waste recovered after ultrasonic extraction except for caffeine. However, in the coffee waste recovered after extraction with 100% ethanol, compounds such as 2,4-Dimethyl-1-heptene, n-hexadecanoic acid, and Benzene were detected. The GC-MS results graph of the coffee waste recovered after extraction, based on the ethanol content, is shown in Figure 2.

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3.2 Quantitative Analysis Results of Caffeine Using LC-MS for This Experiment

The caffeine content in the coffee waste recovered after ultrasonic extraction is as follows.

As shown in <Table 7 and 8>, a significant caffeine reduction rate of 99.5% was observed in the coffee waste obtained from ultrasonic extraction using 70% ethanol after three times of repeated extraction. The Korea Food and Drug Administration has confirmed that decaffeination, with 90% removal of caffeine, can be achieved with just two repeated experiments of coffee waste extraction <Figure 3>.

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VI. CONCLUSION

This study utilized ultrasonic extraction to investigate the caffeine content and effective active ingredients in coffee waste, confirming its potential as a recyclable resource. The ultrasonic extraction method was used for coffee waste extraction, and preliminary experiments were conducted under conditions ranging from 0% to 100% ethanol content. The GC-MS analysis results of effective ingredients in coffee waste revealed that, except for the coffee waste recovered after 100% ethanol extraction, hardly any other components were detected in coffee waste recovered after extraction with different ethanol contents. The LC-MS analysis of caffeine content revealed a 72.1% reduction in caffeine in the coffee waste recovered after 70% ethanol ultrasonic extraction, compared to the coffee waste without ultrasound extraction.

Furthermore, additional research was conducted to confirm whether the caffeine content within coffee waste could be reduced by over 90% to meet decaffeination standards. The re-extraction was performed using 70% ethanol, which showed the highest caffeine reduction rate among the ethanol concentration ranges. In addition, repeated extraction was performed 1 to 3 times, and the extraction method was ultrasonic extraction conducted under preliminary experimental conditions. The quantitative analysis of caffeine in coffee waste using LC-MS revealed a high caffeine removal rate of 99.5% in the coffee waste recovered after three times repeated extractions with 70% ethanol. As a result of this study, the potential for decaffeination through the repeated ultrasonic extraction of coffee waste was confirmed, and this verified its potential as a recyclable resource material.

ACKNOWLEDGEMENT

This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (RS-2023-00281517), and 2023 Local University Revitalization Project funded by the National Research Foundation of Korea.