An experimental study of application of activated carbon from nipa fruit waste on herbal drinks

ABSTRACT Nipa is one of the palm family, and 60% of the fruit is biomass waste. One of the utilizations of the waste is to be converted into activated carbon. In the present research, the nipa waste was pyrolyzed, and the biochar, a by-product of the pyrolysis process, was activated using HCl. The nipa’s fruit waste activated carbon (NWAC) was then experimentally used to remove the distinct odours of Noni and Mangosteen herbal drinks. The characteristics of the NWAC produced in this study have a water content of 15.08%, ash content of 8.77%, volatile matter of 8.51%, carbon content of 67.6%, yield of 95.49%, iodine adsorption of 966.98 mg/g, and surface area of 1066.39 m2/g. The characteristics of the Noni herbal drink after NWAC adsorption showed that the highest total dissolved solids of 6.97 °Brix was treated with 25% NWAC addition. The lowest IC50 value was 4.4 ppm, and it was gradually increased with the addition of the NWAC. The addition of NWAC decreased the total phenol in the Mangosteen peel herbal drink, but the effect was insignificant in the Noni herbal drink. Antioxidant activity values ranged from 16% to 37% in the Mangosteen herbal drink, and 30% to 55% in the Noni herbal drink. The total dissolved solids ranged between 4 and 7 °Brix in both herbal drinks. Overall, the addition of NWAC improved the quality of the herbal drinks, but the optimum condition needs to be quantified.


Introduction
Activated carbon (AC) is a porous material with a carbon content of up to 85% to 95%.The AC is biochar made from biomass pyrolysis (Cui et al., 2022).Biochar can be activated using chemicals, vapour, or carbon dioxide.The activation process aims to open pores in biochar to increase adsorption of odour and colour (Kang et al., 2022).One of the biomass sources that has not been utilised is Nipa's fruit waste.
Nipa (Nypa fruticans Wurmb) is part of the mangrove forest ecosystem, belongs to the Palmae family, and grows in tidal areas.One nipa tree produces 5 kg fruits, of which the fruit waste reaches approximately 3 kg (Yub Harun et al., 2021).Fibre and shell of nipa's fruit contain high carbon element (Tamunaidu & Saka, 2011).The main contents of the nipa fruit waste are cellulose, hemicellulose, and lignin (Tamunaidu & Saka, 2011).The nature of the waste with high cellulose and hemicellulose content could produce effective AC.The characteristics of AC from nipa's shell contained approximately 1% of water, ash of 3.8%, and iodine absorption of 708.69 mg/g.Biochar from nipa's fibre that is activated using KOH has more porosity than that of charcoal without activation (Ding et al., 2022).
AC is widely used for preparation of food and nonfood products.The addition of AC may influence the physical, chemical, and sensory properties of fluid products by reducing the total solid dissolved (TDS) and total solid suspended (TSS; Sujiono et al., 2022).Application of AC can also reduce metal contaminations such as Fe and Mn (Yao et al., 2020), increase dissolved oxygen (DO), and reduce biological oxygen demand (BOD) and chemical oxygen demand (COD) values.The sensory characteristics could be affected by changing colour and aroma in liquid.
This research utilised waste from nipa fruits as an activated carbon to be applied into herbal drink to improve its characteristics.The selected herbal drinks were Noni and Mangosteen peel herbal drinks.The issue with both herbal drinks is the pungent aroma and aftertaste.Therefore, the application of nipa fruit waste activated carbon (NWAC) could improve the characteristics of Noni and Mangosteen peel herbal drink.

Material and methods
The nipa fruit waste was collected from Malang, East Java Indonesia.The waste contains nipa's shell and fibres.HCl and KOH (Merck's products) were purchased from a local chemical store.The Noni and Mangosteen herbal drinks were purchased from a local small medium enterprise of herbal drinks in Malang, Indonesia.
The biochar for NWAC was prepared by pyrolysis of nipa fruit waste.First, the nipa fruit waste was dried at 50 °C for 4 hours to reduce the water content, and then pyrolyzed at 500 °C for 2 hours, producing biochar and pyrolysis oil.The biochar was then ground and sieved at 100 mesh.The sieved biochar was then activated by submerging it in HCl 1 M for 24 hours.The biochar was then filtered from the solution and neutralised with KOH 0.1 N until the pH 7. The biochar was then dried at 110 °C for 5 hours, resulting in NWAC as the product.
The NWAC was then applied to Noni and Mangosteen herbal drinks.Six concentrations of NWAC (0%, 5%, 10%, 15%, 20%, and 25% w/v) were added into 100 ml of each herbal drink separately.The solution of herbal drinks and NWACs was then heatedup at 50 °C for 4 minutes.The solution was then centrifuged at 5000 rpm for 10 minutes to separate the NWAC.The property of the herbal drinks was then analysed.
The total dissolved solids (TDS) test was conducted on the Noni and Mangosteen peel herbal drinks using a refractometer, following ASTM D5907-18 procedure.The total phenol was determined (Siddiqui et al., 2017).The antioxidant activity of Noni and Mangosteen peel herbal drinks after NWAC absorption was tested with DPPH (1,1-diphenyl-2-picrylhydrazyl) method, by measuring the Inhibition Concentration (IC50; Ayanlowo et al., 2020).The organoleptic test was conducted to measure the sensory changes before and after NWAC addition.Three organoleptic characteristics-colour, fragrance, and taste-were used in this study as attributes.Five experts from the herbal beverage sectors served on the panel that conducted the organoleptic test.

Characteristics of activated carbon from nipa fruit waste
Table 1 compares the features of NWAC to the standard in terms of characteristics including yield, iodine adsorption, water content, ash content, volatile matter, carbon content, and surface area.Overall, NWAC's qualities were better than the standards.The ash content was less than the standard's maximum amount.Ash content shows the quantity of residue that fills the pores of activated carbon, including calcium, kalium, natrium, magnesium, and other minerals.The presence of ash reduces the efficacy of the activated carbon (Musyoka et al., 2020).
The volatile matter of NWAC was significantly lower than that of the standard.The majority of volatiles are dangerous to both the environment and human health (Zhang et al., 2022).In the process of AC making, the discharge of volatiles is primarily concentrated during carbonization, which results in the formation of a specific pore structure (Ge et al., 2022).As heating and biochar decomposition rates increased, volatile matter was released more quickly.Additionally, thermal physical parameters like specific heat capacity, thermal conductivity, and thermal diffusion coefficient had an impact on the heat transfer process in the raw material (Deng et al., 2017).The most temperature-sensitive properties in a nitrogenous atmosphere are specific heat capacity and thermal conductivity (Deng et al., 2017).
The carbon content of NWAC was slightly higher than the standard required, suggesting that the carbon content is high enough as a high-quality AC.AC quality is influenced by its complex pore structure, surface functional groups, carbon structure, fugitive state, and reaction characteristics (Li et al., 2022).However, the carbon content proportion is affected by the presence of ash content and other impurities.Research findings have demonstrated that chemical treatment is the most efficient way to get rid of impurities such as inorganic mineral/ash and using chemical multi-stage acid treatment can get rid of minerals from coal, coke, and biomass to give a stronger effect of purifying residual carbon (Waugh & Bowling, 1984).
A method is used to assess the adsorption potential of AC is iodine number.The amount of iodine adsorbed by 1 g of carbon at the mg level is the iodine number, which measures the porosity of the activated carbon.Iodine number can be used as an approximation for the surface area and micro-porosity of active carbons (Saka, 2012).The iodine adsorption of the NWAC was higher than that of the standard, suggesting that the NWAC has high absorption capabilities and surface area.The surface area of NWAC was 1066 m 2 /g.High specific surface areas, typically above 1000 m 2 /g, are present in the carbons derived from various precursors, and these surfaces get larger with rising activation temperatures (Gómez et al., 2022).

Application of the NWAC on noni herbal drink
The parameter used to determine the physical characteristics of the Noni herbal drink, which has been adsorbed by NWAC is the total dissolved solids (TDS).The TDS test shows the percentage content of dissolved substances in a solution.Figure 1 shows that the TDS of Noni herbal drink after adsorption had a range of 5.60 to 6.97 °Brix.This value is below the quality requirements set by SNI 3719:2014 for Noni herbal drink, which is 16 °Brix.The low value of total dissolved solids can be influenced by the absorption of the sugar constituent molecules in the Noni herbal drink in the activated carbon adsorption process.This is because the carbon structure in activated carbon has the ability to absorb cations, anions, and molecules in the form of organic and inorganic compounds (Zhao et al., 2022).
Figure 2 shows the effect of addition of NWAC on the total phenol.The average total phenol value ranged from 81.9 to 89.4 mg GAE/g.It is evident that, at a concentration level of 25%, the total phenol value reached its highest point of 89.4 mg GAE/g and at a concentration level of 5%, it reached its lowest point of 81.9 mg GAE/g.The total phenolic value of the fermented Noni herbal beverage was 54.46 mg GAE/ 100 g, though this value varies with storage time.As storage time lengthens, the total phenol value declines (Martayani et al., 2017).
Phenolic compound Noni fruit has various roles, including antiseptic, antibacterial, and antioxidant so that it is widely used for health (Wang et al., 2022).The antioxidant activity of the material increased along with the increase in the total phenol value, so the resulting relationship was directly proportional (Martayani et al., 2017).However, there is a possible difference in the correlation between antioxidant activity and total phenol due to the participation of antioxidant compounds other than phenolic compounds (Hussain et al., 2022).
Figure 3 shows the antioxidant activity after NWAC adsorption on Noni herbal drinks.The IC50 value and antioxidant activity are inversely proportional (Osei et al., 2022).The average value of IC50 ranged from 4.4 to 7.1 ppm.The lowest IC50 value was found in the  Noni herbal drink samples with 0% NWAC addition, while the highest IC50 value was found in the samples with addition of 20% NWAC.
In general, the value of antioxidant activity is identified by using the calculation of the IC50, which indicates the percentage of inhibition of a substance against free radicals.The lower IC50 value indicates that the antioxidant activity is getting higher.Specifically, there are four criteria for determining the category of antioxidant activity.The IC50 < 50 refers to a very strong antioxidant activity, IC50 between 50 and 100 shows strong antioxidant activity, IC50 between 100 and 150 shows moderate antioxidant activity, and IC50 of 51-200 shows weak antioxidant activity (Osei et al., 2022).
The antioxidant activity of Noni herbal drink adsorbed on activated carbon from nipa fruit waste was included in the very strong category.The difference in IC50 values in each concentration level treatment can be caused by differences in the adsorption reaction by activated carbon to phenolic compounds, flavonoids, and other antioxidative substances that also participate.It can be said that the total phenol value contained in Noni herbal drink is a factor that can affect antioxidant activity (Hussain et al., 2022).In addition, the length of time the sample is stored can affect the total phenol value produced (Martayani et al., 2017).

Application of the NWAC on Mangosteen Peel Herbal Drink
The average total dissolved solid (TDS) value ranged from 4.60 °Brix to 6.30 °Brix, as shown in Figure 4.With increasing NWAC addition, the TDS was generally fluctuating.The low proportion of TDS showed that the herbal drink was clear in colour.However, as TDS rises, particle aggregation and agglomeration can reduce the adsorbent's efficiency, demonstrating the absence of a separation process between the herbal beverage and AC.
Figure 5 shows the effect of NWAC addition on the total phenol value of Mangosteen peel herbal drink.Overall, the total phenol decreased with increasing NWAC addition.This is due to the addition of NWAC to absorb phenolic compounds with the herbal drink.The adsorbent concentration has the most significant effect on the adsorption process.AC can adsorb more than 50 g/L of polyphenols (Yangui & Abderrabba, 2018).
Figure 6 shows the average IC50 value of the Mangosteen peel herbal drink after NWAC adsorption ranged between 4.3 and 7.3 ppm.The lowest IC50 average value or the highest antioxidant activity was found in the control sample or the addition of 0%   concentration of NWAC at 4.3 ± 0.4 ppm.The IC50 value was then increased due to the adsorption of the phenolic compound with increasing NWAC addition.This phenomenon was then affecting the antioxidant activity of the Mangosteen peel herbal drink.The antioxidant activity prior adsorption was 37%.However, after the addition of NWAC, the antioxidant activity of the Mangosteen peel herbal drink value decreased to 16-17%, showing the effectiveness of NWAC.This promotes further investigation on the optimum conditions of NWAC addition to preserve the antioxidant activity.

The Effect of NWAC Addition on The Organoleptic Analysis
Examining sensory features allowed for the evaluation of attributes, scoring of preferences, and differentiation.The panellists evaluated flavour as the most significant feature for the herbal drink after adding NWAC, according to the attribute ranking and scoring results.
The preference scoring test revealed that, in the case of Noni herbal drink, the addition of 10% NWAC to the sample colour, 20% NWAC to the sample aroma, and 25% NWAC to the sample taste produced the most preferred results.All panellists also concurred that the herbal drink with 5% NWAC addition had the best colour, aroma, and flavour among the Mangosteen herbal drinks.

Conclusions
Nipa fruit waste has the potential to be used as raw material for the manufacture of NWAC.The characteristics of activated carbon made from nipa fruit waste met AC quality standards with a high yield and carbon content, high iodine adsorption, high surface area and low water, ash, and volatile matter contents.Application of the NWAC on Noni and Mangosteen peel herbal drink showed the improvement of the characteristics of both herbal drinks on the TDS.However, the addition of NWAC decreases the phenolic compound of herbal drinks, which in turn decreased antioxidant activity as indicated by an increasing value of IC50.It is advised to conduct more research on the optimum addition of NWAC.The organoleptic test showed that the herbal drinks with NWAC addition were preferred.

Figure 2 .
Figure 2. The effect of addition of NWAC on the total phenol value of Noni herbal drink.

Figure 3 .
Figure 3.The antioxidant activity after NWAC adsorption of Noni herbal drink.Figure 4. The average value of total dissolved solid after NWAC adsorption of Mangosteen peel herbal drink.

Figure 4 .
Figure 3.The antioxidant activity after NWAC adsorption of Noni herbal drink.Figure 4. The average value of total dissolved solid after NWAC adsorption of Mangosteen peel herbal drink.

Figure 5 .
Figure 5.The effect of NWAC addition on the total phenol value of Mangosteen peel herbal drink.

Figure 6 .
Figure 6.The antioxidant activity after NWAC adsorption of the Mangosteen peel herbal drink.

Table 1 .
Characteristics of NWAC