Shelf-life Estimation of Instant Pempek Rajungan (Portunus pelagicus) Rancidity with the Arrhenius Acceleration Method Pendugaan Umur Simpan Pempek Rajungan Instan Menggunakan Metode ASLT dengan Pendekatan Model Arrhenius

Rancidity is one of the potential damages to the instant pempek rajungan (Portunus pelagicus) during storage. The purpose of this study was to estimate the shelf life of instant pempek rajungan packed with polypropylene plastic (PP) based on the relationship between storage temperatures and free fatty acids produced. Estimation of shelf life using the acceleration method based on the Arrhenius model. Samples were stored for 30 days at three different temperatures, 25 ± 2 °C, 35 ± 2 °C, and 45 ± 2 °C. The parameter observed during the storage process was an assessment of the rancidity level based on the free fatty acids formed in the sample. Data were analyzed using linear regression and the equation obtained was used to calculate the shelf life of pempek rajungan at room temperature (27 °C). The results showed that the storage time for instant pempek rajungan products at temperatures of 25 ± 2 °C, 35 ± 2 °C, and 45 ± 2 °C could be estimated to be 78, 86, and 70 days respectively with an increase in the number of free fatty acids of 85.2018%, 265.3478%, and 253.1427%.


INTRODUCTION
Indonesia's territorial waters are 7.81 million km 2 , with fishery resource production reaching 6.4 million tons. Rajungan (Portunus pelagicus) is one of Indonesia's fisheries potentials, mainly in the Java region, Pasir Putih Village on the coast of Karawang, West Java, Indonesia. In accordance with the Indonesian Ministry of Marine Affairs and Fisheries, the average catch of rajungan in the village reached 393 tons in 2013 (Kementerian Kelautan dan Perikanan, 2016). Rajungan is generally used as an economic field for the people of Pasir Putih Village, Karawang in conventional form, or peeled meat to be sold in export markets, including the United States, Singapore, and Taiwan (Awaludin, 2019).
Rajungan fat or lemi is one part of the rajungan that is not used or becomes waste. Lemi is the material of the rajungan body, which is Shelf-life Estimation of ... located under the boiled shell. The nutritional content in lemi is no less high than rajungan meat, including protein (20.06%), fat (5.80%), water content (67.78%), ash content (2.52%), and carbohydrates (4.11%) (Anggo & Romadhon, 2006). The high protein content in lemi is a new potential for diversifying processed food products into instant pempek rajungan to have a higher selling value.
Instant food products have many advantages, including longer shelf life, practicality, and fast food so that consumers can save time (Lilly, 2014). Lifestyle changes currently make consumer demand for instant products increase (Srinivasan & Nirmala, 2014). Instant pempek is a dry product made through high-temperature processing by boiling and frying.
The deep-frying process of pempek with a high temperature of around 165-190 °C can cause mass food transfer, oil and air simultaneously encourage physical and chemical changes so that water loss, oil absorption, color change, flavor development, gelatinization, and oil oxidation will occur (Ma et al., 2016). The oil content in pempek is easily oxidized when exposed to oxygen which can cause rancidity (Ketaren, 2008). Rancidity is an unwanted type of damage to pempek, so it is necessary to know how long the food product can be stored in a condition that is still acceptable to consumers. Therefore, it is necessary to analyze the estimated shelf life of these products.
Estimation of shelf life aims to ensure that the product reaches consumers in good condition, safe for consumption, the quality of the product remains after the production process, packaging, and storage at certain temperature conditions so that changes in chemical, physical, microbiological, and sensory characteristics can be identified (Haouet et al., 2019). Estimation of shelf life using the Accelerated Shelf Life Test (ASLT) method is an estimation of shelf life by storing products under extreme conditions and checking periodically until the product safety limit is reached then projecting the shelf life under the actual storage conditions (Haouet et al., 2019).
The ASLT method can be used with the Arrhenius model approach and critical water content. The critical water content model is usually used for products that are easily damaged due to water absorption during storage, while the Arrhenius model uses temperature acceleration so that it can accelerate reactions that cause damage to the product. This model is usually used for products that are sensitive to changes in storage temperature. The purpose of this study was to es-timate the shelf life of instant pempek rajungan packed with polypropylene plastic (PP) based on the relationship between storage temperatures and free fatty acids produced.

METHODS
The research was conducted with a descriptive experimental method on samples of instant pempek rajungan stored at three storage temperatures: 25 ± 2 °C, 35 ± 2 °C, 45 ± 2 °C. Estimation of shelf life is carried out using the ASLT method of the Arrhenius acceleration model. Samples were stored in an incubator at three storage temperatures for 30 days. Observations were made on days 0, 5, 10, 15, 20, 25, 30. The main criteria used to estimate shelf life are the method of measuring the acid number or Free Fatty Acid (FFA) (American Oil Chemists' Society, 1998) and several supporting criteria, namely water content (Association of Official Analytical Chemists, 2000) and Total Plate Count (TPC) (Badan Standarisasi Nasional, 2008).

Quality Decrease Rate Kinetics of Free Fatty Acid Parameters
Free fatty acid content is a chemical property that describes the amount of free fatty acids in a material expressed in percent. The results of the observation data analysis of the free fatty acid content of instant pempek rajungan at three storage temperatures can be seen in Table 1. Table 1 shows that free fatty acids have been formed in the pempek rajungan product after processing or at the beginning of storage. The free fatty acid composition continued to increase after storage until the 6 th week. Storage at a temperature of 25 ± 2 °C can increase the formation of fatty acids up to 85.1790%, storage at a temperature of 35 ± 2 °C can increase the formation of fatty acids to 265.3478%, and storage at a temperature of 45 ± 2 °C can increase the formation fatty acids up to 253.1427%. Deep-frying processing can produce three reactions: hydrolytic reactions, oxidation reactions, and reactions due to temperature changes ( Table 2). The hydrolytic reaction occurs due to the evaporation of water from the material that changes into the oil phase, causing the formation of free fatty acids, mono and diacylglycerol, and glycerol. The oxidation reaction combines the degradation reaction of oxidation products to form short-chain fatty acids, aldehydes, ketones, hydrocarbons, epoxides, and other products called oxidized triacylglycerol (TAG). Temperature changes produce cyclic compounds, which are intramolecular reactions of dimers with polymers by conjugation of C-C chains in intermolecular reactions (Weisshaar, 2014).
The results (Table 1) show that the more extended storage and the higher the storage temperature will increase the amount of free fatty acids in the instant pempek rajungan. Increasing the temperature will multiply the molecules that have kinetic energy. This energy can make the particles involved in the reaction move faster (Table 2) so that the oil hydrolysis reaction will run faster with high-temperature treatment as a catalyst.
The value of the free fatty acids amount from the research results is then plotted so that the regression equation found is used to obtain the reaction order. The selection of the reaction order in determining shelf life is based on a regression equation that has a value of R 2 close to 1. Determination of the quality deterioration rate constant (k) for each storage temperature is carried out after knowing the reaction order used. The k value is obtained from the slope value of each regression equation in reaction order one. The value of k shows the reaction rate of changes in free fatty acids that occur during storage due to the effect of temperature on the reaction rate. The regression equation in determining the reaction order and the k value can be seen in Table 3.   Table 3 shows that the selected order is order one because it has a coefficient of determination R 2 greater than that of zero-order (R 2 order 0 < R 2 order 1). R 2 values that are close to 1 have better accuracy (Imamah, Hasbullah, & Nugroho, 2016). The value of k at each temperature has a negative value. This means that there is a decrease in the quality of the instant pempek rajungan due to the increase of free fatty acids amount along with the storage time. Determination of the shelf life of instant pempek rajungan can be done by plotting the K value of storage temperature in the Arrhenius equation, ln k = ln k0 -(Ea/R) (1/T). The parameters of the change in free fatty acids in ln k and 1/T of instant pempek rajungan can be seen in Table 4.
The plot result between 1/T and ln k is the Arrhenius equation: y = 1.2639x -4.0033 with R 2 = 0.97. The correlation coefficient obtained is close to 1. This means that temperature is very influential on changes in free fatty acids. Rancidity in deep-frying food products is caused by the activity of the lipase enzyme, which reacts with water vapor and temperature. The reaction will be fast if there is an increase in temperature and light. Oxidation reactions can be prevented by storing at low temperatures, removing oxygen in the package, avoiding light in direct contact with the product, or adding anti-oxidants. Oils with a high content of unsaturated fatty acids are more susceptible to oxidation damage, so they need packaging that better protects products from oxygen and light (Oke et al., 2018).

Estimated Shelf Life
Estimation of shelf life is done by calculating the activation energy (Ea) obtained from the Arrhenius equation using the formula Ea = slope x The lower the Ea value, the reaction speed for deterioration of quality will run quickly. The activation energy value of Ea is then substituted into the equation kT = k0.e -Ea/RT so that the kT value is obtained, which is used to estimate the shelf life of instant pempek rajungan. The kT value is then plotted in the first-order reaction kinetics equation with the formula ln kT = (Ea/R)(1/T) + ln k0. The results of the calculation of the shelf life of instant pempek rajungan at various storage temperatures can be seen in Table  5. Table 5 shows that the shelf life of instant pempek rajungan is shorter at higher storage temperatures. This means that the temperature increase causes the reaction rate to speed up, which causes the instant pempek rajungan to break down quickly so that the shelf life is getting shorter. The rate of chemical reactions is faster at higher temperatures, which means that the decline in product quality is fast (Palupi et al., 2010) Increasing the temperature will multiply the molecules that have kinetic energy. This energy can make the particles involved in the reaction move faster. Based on the parameters of free fatty acids, the instant pempek rajungan produced by Sumber Rizky has a shelf life of 86 days or two months 26 days at a storage temperature of 35 °C. The oil in the product will undergo oxidation and hydrolytic during storage. The reactions that occur are the same as the deep-frying process, but the reactions that run are slower (Bordin et al., 2013).

Characteristics of Instant Pempek Rajungan Total Plate Count (TPC)
Total Plate Count (TPC) is carried out as a test of supporting parameters. Testing of supporting parameters is carried out at the beginning of storage until the end of storage (day 30). The increase in the microorganisms number in instant pempek rajungan can be seen in Figure 1. The number of initial microorganisms at various storage temperatures was 2.5 x 101 CFU/g. The number of microorganisms at the end of storage was respectively 2.3 x 10 4 ; 2,6x10 4 ; 1x10 5 CFU/g at 25 ± 2 °C, 35 ± 2 °C, and 45 ± 2 °C. The Indonesian National Standard (SNI) sets the expected value for the number of microorganisms Shelf-life Estimation of .. in TPC units. According to SNI 2713: 2009, the maximum TPC limit for fish/mollusk-based dryprocessed products is a maximum of 5x10 4 CFU/g. This shows that the amount of TPC at the beginning of storage with various storage temperatures and at the end of storage at 25 °C, 35 °C still meets the standards, while the amount of TPC at 45 ± 2 °C storage temperature does not meet the standard, which means that instant pempek rajungan is not suitable for consumption. Figure 1 shows that the increase in the number of microbes is found at a temperature of 45 °C. This means that bacteria that grow in instant pempek rajungan can grow optimally at that temperature. The bacteria that usually grow at this temperature are thermophilic. Two factors influence the growth of microorganisms, namely extrinsic factors and intrinsic factors. Extrinsic factors include handling, processing, and storage. Intrinsic factors include moisture content in the product. Water is the most critical element in food that can determine the growth of microorganisms. Water activity (aw) is free water as a growth medium for microorganisms in food products (Sandulachi, 2012). Changes in aw can cause osmotic pressure, giving rise to a sporulation response to spore-forming microorganisms (Tapia, Alzamora, & Chirife, 2008). The lower the water content in food, the lower the ability of microorganisms to grow and become destructive to foodstuffs (Carter, 2008). The microorganisms found in instant pempek rajungan products after storage at critical temperatures have gram-positive morphology and in the cocci form ( Figure 2). According to Brooks et al. (2012), bacteria that may grow in fish products and their processed products are Pseudomonas, Micrococcus, and Microbacterium.

Water Content
Another supporting parameter tested is moisture content. Water content was tested at the beginning of storage until the end of storage (day 30). The water content of instant pempek rajungan before and after storage still meets SNI 2713: 2009 concerning fish-based dry-processed products, which is maximum water content of 12%. Observation data plotted on the graph can be seen in Figure 3.   Figure 3 shows that the water content increase in the instant pempek rajungan product occurred at storage temperatures of 25 °C, 35 °C, and 45 °C during storage. The increase in water content can be seen from the positive value of the slope of the equation line. The instant pempek rajungan stored at 25 °C had the highest increase in water compared to 35 °C and 45 °C. This is caused by differences in air humidity at various storage temperatures. In accordance with Arizka and Daryatmo (2015), storage temperature is related to the partial pressure of water vapor (RH). The product will absorb moisture from the environment through the packaging if the humidity of the ambient air is high, while the sample will release free water to the environment if the ambient air humidity is low so that the final weight of the sample will increase with the length of storage. Another factor that affects the increase in moisture content is the permeability of the packaging. Instant pempek rajungan is packaged using polypropylene plastic (PP). PP packaging has a permeability value of 1.114 g/cm 2 /24 hours. The low permeability value has the ability to hold water vapor into the package. The increase in water content of instant pempek rajungan was greater at hightemperature storage. This is due to the expansion of the package's pores so that it is easier for water vapor to migrate from the environment to the material (Puspita, Rangga, & Sartika, 2016).
The increase in pempek rajungan water content ( Figure 3) during storage is directly proportional to the increase in microorganisms' growth ( Figure 1) and the increase in the amount of free fatty acids formed in the product. This proves that the increase in water content is caused by the absorption of water vapor during the storage process. The deep-frying process causes the water in the ingredients to diffuse into the oil in the form of steam so that the water content of the product is low, the texture is crunchy, and contains higher fat (Raleng et al., 2019). After the frying process, the pempek rajungan will be hygroscopic, so it easily absorbs environmental moisture. The absorption of water vapor in the product greatly affects the growth of microorganisms because of the presence of free water and accelerates the process of forming free fatty acids, which can cause a rancid aroma.

CONCLUSIONS
The ASLT method with the Arrhenius model approach can estimate the shelf life of instant pempek rajungan packed with PP plastic with storage temperatures of 25 ± 2 °C, 35 ± 2 °C, and 45 ± 2 °C to 78, 86, and 70 days respectively with an increase in the free fatty acids number, respectively 85.2018%, 265.3478%, and 253.1427%. Storage at 35 ± 2 °C able to maintain the shelf life of instant pempek rajungan for 86 days with 2.6 x 10 4 CFU/g of microorganisms and 9.47% moisture content which has met SNI 2713: 2009.