Application of coconut shell liquid smoke on dried skipjack tuna (Katsuwonus pelamis) quality

Liquid smoke is produced from incomplete combustion, contains various compounds with functional properties that can provide aroma, taste, and color. Liquid smoke can be used as a preservative because it contains phenols and acids as anti-bacterial and antioxidant. Application of liquid smoke as a preservative can be done in the drying process using an oven. The purpose of this study was to determine the effect of the use of liquid smoke on the quality and organoleptic of dried skipjack tuna. The use of liquid smoke in the study was 0.5%, 1% and 1.5% consisting of 3 replications. Using a completely randomized design (CRD) and the smallest real test (BNJ). Parameters observed include water content, protein content, ash content and organoleptic test consisting of 25 panellists. The results showed that the lowest water content and the highest protein were found in the A2 treatment (use of liquid smoke 1%) at 47.7% and 50.71%, respectively. The highest ash content was found in treatment A1 (0.5% liquid smoke) at 4.56%. While the highest overall organoleptic assessment of color, taste, texture and aroma were the dried Skipjack Tuna with 1,5% liquid smoke with a score of 4.4.


Introduction
Coconut shells have a high potential for use as a raw material in the production of liquid smoke.Coconut shell contains high lignin (29.4%) and low cellulose (26.6%), as well as several other ingredients such as pentose (27.7%), water (8%), extraction solvent (4.2%), uronic anhydrous (3.5%), and ash (0.6%) [1,2].Liquid smoke from coconut shells is produced through a pyrolysis process, a combustion process Application of coconut shell liquid smoke on dried skipjack tuna (Katsuwonus pelamis) quality 1230 (2023) 012004 IOP Publishing doi:10.1088/1755-1315/1230/1/012004 2 that does not require oxygen except in a partial combustion process.Partial combustion requires oxygen to supply the heat energy needed in the pyrolysis process [3].
Pyrolysis is a three-stage thermal decomposition process for wood biomass.The stages of pyrolysis are solid, liquid, and gaseous phases, with three variations of pyrolysis: mild, slow, and fast.Large hydrocarbon molecules in wood biomass in the pyrolysis process are broken down into smaller or simpler hydrocarbon molecules.Wood biomass in the pyrolysis process produces water, acetic acid, carbon dioxide, methanol, and carbon monoxide [4].
Coconut shell processing into liquid smoke through a pyrolysis process can use an unstirred stainless steel semi-batch reactor at a pressure of 1 atm and is equipped with a condenser column that functions as a cooler [5], which changes the gas phase to liquid [1].The resulting liquid smoke is categorized into three classes based on the level of fineness and the resulting color difference [6].
The difference in class or grade based on the color produced and the purpose for which it is used is that class 1 has a very clear color and is used as a preservative in foods such as meatballs, noodles, and tofu.Class 2 is yellowish in color and is used as an antioxidant and antimicrobial.In contrast, class 3 has a very dark color and intense aroma and is used as a wood preservative, odor absorber, and coagulant in rubber [6].
Liquid smoke produced from coconut shells contains organic acids in the form of acetic acid and carboxylic acids, phenols, furans, aldehydes, and ketones.Liquid smoke also contains potentially carcinogenic compounds in the form of polycyclic aromatic hydrocarbon (PAH) compounds, which can be removed through a purification process [3].PAHs contained in liquid smoke, such as benzo-apyrene, can also cause damage to amino acids and vitamins [7].
Liquid smoke containing phenolic compounds in the food industry is widely used as a preservative for processed meats.Liquid smoke can also be used in the world of health, such as in topical applications for sunburn.Phenolic compounds in liquid smoke, which belong to aromatic compounds with strong antioxidant properties, are able to bind free radicals such as the formation of reactive oxygen species (ROS) and inhibit the production of nitric oxide (NO) [8].
Liquid smoke with a high phenol content that has passed the purification stage is safe to use in the processing process and as an alternative preservative because the levels of polycyclic aromatic hydrocarbons (PAHs) are below the maximum limits set by SNI (0.2-10 ppb).Phenol has antibacterial properties because it can inhibit the activity of the cytoplasmic membrane by interacting with bacterial cells through an absorption process involving hydrogen bonds [8].Phenolic compounds act as hydrogen donors and effectively inhibit oxidation reactions in small amounts [9].
The phenolic compounds in liquid smoke can function as an antibacterial, so it is widely used as a preservative for processed foods such as meat.One of the uses of liquid smoke is in fish processing, such as skipjack tuna.Skipjack tuna is widely preferred because of its abundant nutritional value, but it is easily spoiled, so the quality of the fish becomes low.The spoilage is caused by changes in biochemistry and microbiology during the process of handling fish for consumers [10].The spoilage resulted in organoleptic degradation [11].
Fish quality that has declined cannot be repaired, but it can be maintained [13].Efforts to maintain the quality of fish can be performed through preservation using liquid smoke.The application of liquid smoke as a preservative is starting to be widely carried out, so it is necessary to conduct a study to determine the chemical content and consumer acceptance of skipjack tuna preserved using liquid smoke.Processing fish with liquid smoke aims to give the smell and taste of smoke to fish products.The use of liquid smoke in the processing can maintain the quality of smoked fish and durability because the water content is quite low, increases the protein content, and improves the color appearance of fish [13].The aim of the research was to look at the effect of using liquid smoke on the chemical composition and panelist acceptance of the resulting smoked fish products.

Material
The main ingredient was used in the research is skipjack tuna, or cakalang, obtained from the Tilamutu fish auction market.Other materials were used include liquid smoke, H2SO4 (sulfuric acid), H2O2 (hydrogen peroxide), aquades, H3BO3 (boric acid), sodium, and hydroxide-thiosulfate.

Sample preparation
Before being dried with liquid smoke, skipjack tuna or cakalang was cleaned of parts that are not consumed.The skipjack tuna was then cut, and each piece weighs 500 g.The fish was smeared with liquid smoke evenly over the entire surface according to the concentration used (I1=0.5%,I2=1%, and I3=1.5%) by first adding 5% salt to each treatment.The fish that had been smeared with liquid smoke was dried in oven at 100°C for 6 hours.

Observation parameters
The parameters observed include water content, protein, ash [11], and panellist preferences in terms of color, taste, texture, and aroma.The preference test was performed using a scoring test involving 25 panellists who used to consume smoked fish.The samples were evaluated using a five-points hedonic scale (1=very dislike, 2= dislike, 3=rather like, 4=like, 5=very like) [15].

Statistical analysis
This study was conducted using a Complete Randomized Design (CRD), with three repetitions.The data obtained were analyzed for variance, and if the treatment had an effect, it was continued using the Least Significant Difference test (LSD).

Proximate levels of smoked skipjack tuna
Tests for proximate levels of smoked skipjack tuna with various concentrations (I1 = 0.5%; I2 = 1% and I3 = 1.5%) were carried out to determine the nutritional content in the form of protein and ash content after given liquid smoke treatment, as well as the water content of smoked skipjack fish.The test results become a quality assessment for each treatment.
. Analysis of water content in skipjack tuna with various concentrations of liquid smoke showed different water contents for the three treatments.The highest water content was found in treatment I1 (application of 0.5% liquid smoke) and the lowest in treatment I2 (application of 1% liquid smoke).The low water content in smoked skipjack fish products can be caused by the concentration of liquid smoke used.The higher the concentration of liquid smoke used, the higher the phenol content of the material, which will cause a decrease in its water content.
The water content of smoked skipjack tuna had a significant difference (p<0.05) for each treatment.This is influenced by the phenol content of the material, which can be as high as 21.59% [1], which can accelerate the evaporation process [10].The high water content in treatment I3 (application of 1.5% liquid smoke) can be influenced by the type of packaging and how smoked skipjack tuna is stored.The water content of smoked skipjack in treatments I2 (application of 1% liquid smoke) and I3 (application of 1.5% liquid smoke) (Figure 1) fulfilled the quality and safety requirements of smoked fish by hot smoking at 60% [16].
The low water content in smoked skipjack correlates with an increase in the protein content of smoked skipjack, as seen in treatment I2 (application of 1% liquid smoke) (Fig. 1).The high protein content is affected by the presence of heat treatment, which causes protein denaturation and a decrease in the amount of water in the material.According to [17], heat treatment above 60°C results in the release of water and protein denaturation during the drying process.
The protein content of a food ingredient will have a relationship with the protein content contained in the ingredient.The increase in protein content in smoked skipjack tuna fish can be influenced by the flavonoid content of liquid smoke.Flavonoids are able to increase collagen and protein and reduce lipid peroxidation in granulation tissue [18].The amino acid content in the form of threonine (C4H9NO3) combined with the nitrogen content contained in liquid smoke can increase the protein content [1].
The low protein content and high water content in treatment I3 (application of 1.5% liquid smoke) could be caused by delays in handling skipjack tuna or because the quality of skipjack tuna used was not the same in each treatment.High water content can cause damage to skipjack tuna meat due to the presence of microbes that cause food spoilage.High water content is one of the factors causing damage because it is a medium for growth and microbial activity, which produces proteolytic enzymes that break down proteins that cause food spoilage, as well as high osmotic pressure from liquid smoke [1,19].
Analysis of variance in protein content showed a significant difference (p<0.05) in each treatment, as well as in the ash content of smoked skipjack tuna.Ash content is the residue of organic matter found in food by combining organic components in the product [13,20].According to Figure 1, the highest ash content was found in treatment I1 and the lowest in treatment I2.
The difference in the amount of ash content in smoked skipjack tuna can be caused by the cooking process.This difference can also be caused by the chemical composition of skipjack tuna or the ingredients used.The chemical composition of food ingredients is partially dissolved or reduced in the processing, so it also affects the ash content in processed food, as shown in Figure 1, indicating that low water content has low ash content.Ash content can also be affected by different types of organisms that have different abilities to regulate and absorb metals due to the presence of water-soluble mineral salts or the time and processing temperature used [20].
The best treatment results were obtained with treatment I2, or the use of 1% liquid smoke.The best treatment is based on high protein content with low water content.The treatment of producing a good product or not can be seen from the low water content and high protein content as a source of nutrients needed by the body [1].

Panellists' response to smoked skipjack tuna
In this test, panelists were asked to respond to smoked skipjack tuna in terms of color, taste, texture, and aroma.Tests involving panelists make it possible to assess product deviations and determine the level of acceptance by panelists or consumers.Panelists can help describe the products produced, as well as assess whether there are changes that are desired or not.The response toward the level of preference for color, taste, texture, and aroma had a slightly like to like response.The panelists' response to treatment I3 had a better response to acceptance than the other treatments for all observation parameters.Parameters of color and aroma observations were preferred in treatment I2 (application of 1% liquid smoke) compared to treatment I1 (application of 0.5% liquid smoke).But the aroma in treatment I2 (application of 1% liquid smoke) was not significantly different (p>0.05) from treatment I3 (application of 1.5% liquid smoke).
The aroma in treatments I2 (1% liquid smoke) and I3 (1.5% liquid smoke) can be affected by the concentration of liquid smoke used, compared to treatment I1, which has a liquid smoke concentration of 0.5% by weight of the material.In treatments I2 and I3, the use of liquid smoke with a concentration of 1% and 1.5%, respectively, was able to change the fishy smell of fish to a smoky one compared to treatment I1.The changes in aroma caused by liquid smoke are due to the presence of phenolic compounds, which play a role in the formation of the specific aroma expected in smoked fish products [19,21].
Treatment I1 (0.5% liquid smoke) has a more favorable taste and texture compared to treatment I2 (1% liquid smoke).The panelist assessment parameters for texture in the three concentrations of liquid smoke treatments used had a panelist acceptance level that was not significantly different (p>0.05).The panelists' assessment parameters for the color of smoked skipjack tuna elicited a response that was slightly like to like.
The panelists' responses to color in the three treatments were not significantly different (p<0.05).The color of smoked skipjack tuna is caused by carbonyl and phenolic compounds, which are the main components giving it a golden yellow to brownish color that reacts with carbonyl compounds and amino acid groups [13,19].
The color, which is not significantly different, can be caused by the high water content of skipjack tuna, which causes the concentration of carbonyl and phenolic compounds to be low in the material during application.The water content in smoked skipjack tuna fish can affect the level of texture hardness.The range of water content between 47.08% and 90.69% had no significant effect on the texture of the smoked fish produced, with the panelists' responses tending to like (scoring values The level of hardness is influenced by the amount of water content contained in the material or the occurrence of protein coagulation as a result of heat treatment during mechanical drying [21]. The panelists' perception of acceptance of the taste of smoked skipjack fish in treatments I1 (0.5% liquid smoke) and I2 (1% liquid smoke) had a level of acceptance that tended to like it, and in treatment I3 (1.5% liquid smoke), the panelists' responses tended to really like it.The taste of smoked skipjack tuna fish products is influenced by the components of phenol, acid, and carbonyl compounds; these compounds, besides having properties as preservatives, also contribute to the product's distinctive taste, color, texture, and aroma [13,19].The different acceptance responses can be due to the habitual level of the panelists towards the acceptance of a food product [21].

Conclusion
This study aimed to determine the effect of the use of coconut shell liquid smoke on the quality and organoleptic assessment of dried skipjack tuna (Katsuwonus pelamis).Results showed that the lowest water content and highest protein were found in the I2 treatment (use of liquid smoke 1%) at 47.7% and 50.71%, respectively.The highest ash content was found in treatment I1 (0.5% liquid smoke) at 4.56%.The highest overall organoleptic assessment of color, taste, texture and aroma was the dried Skipjack Tuna with 1,5% liquid smoke with a score of 4.4.Coconut shells have a high potential for use as a raw material in the production of liquid smoke.

Figure 1 .
Figure 1.Proximate content of smoked skipjack tuna after application of liquid smoke

Figure 2 .
Figure 2. Panellists' test results on color, taste, texture and aroma of skipjack tuna fish applied with liquid smoke