Properties of Saeu Jeotgal (Shrimp Jeotgal) Prepared with Different Types of Salts
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Microbiol. Biotechnol. Lett. (2017), 45(3), 218–225 http://dx.doi.org/10.4014/mbl.1703.03001 pISSN 1598-642X eISSN 2234-7305 Microbiology and Biotechnology Letters Properties of Saeu Jeotgal (Shrimp Jeotgal) Prepared with Different Types of Salts Jae Min Shim1, Kang Wook Lee1, Zhuang Yao1, Jeong A Kim1, Hyun-Jin Kim1,2, and Jeong Hwan Kim1,2* 1Division of Applied Life Science (BK21 plus), Graduate School, 2Institute of Agriculture and Life Science, Gyeongsang National University, Jinju 52828, Republic of Korea Received: March 14, 2017 / Revised: August 4, 2017 / Accepted: September 5, 2017 Saeu (shrimp) jeotgal (SJ) was prepared by mixing with 25% salt with different types: purified salt (PS), solar salt aged for 1 year (SS), and bamboo salt. SJ was fermented for 22 weeks at 15℃. Bacilli and marine bacteria were detected throughout the entire fermentation period, and marine bacteria were present in the largest numbers. Lactic acid bacteria (LAB) were detected only during the first 8−10 weeks, but yeasts appeared at the sixth week and later. Archaea were detected in low numbers only from SS-SJ during the first 8 weeks. BS- SJ showed higher pH and lower titratable acidity (TA) values than other SJs because of strong alkalinity of bamboo salt. Amino-type nitrogen (ANN) contents of SJs increased during fermenta- tion, especially, after 2 and 6 weeks. SS-SJ showed the highest ANN content from the beginning to the end of fermentation. Ammonia-type nitrogen (AMN) contents also increased like the amino-type nitrogen during fermentation. The highest volatile basic nitrogen (VBN) was also observed in SS-SJ. Salinity was kept constant after 4 weeks. SS was better than other salts for SJ fermentation in terms of protein hydrolysis. Keywords: Saeu jeotgal, solar salt, bamboo salt, purified salt Introduction taste of jeotgals during fermentation [3]. Salt has been considered to be important for quality of fermented Jeotgals are traditional Korean salted and fermented foods. For this reason, solar salt is popular for the prepa- seafoods produced from whole fishes, fish organs, fish ration of many fermented foods in Korea including eggs, or shell fishes [1]. Many different types of jeotgals kimchi, soybean paste, soybean sauce, and jeotgals. are produced depending upon locations, seasons, and Solar salt is produced by crystallization of salt by vapor- personal preferences [2]. But the procedure for jeotgal izing seawater in a saltern by solar heat and wind [4]. production is basically the same, raw materials are The Korean natural sea salt is reported to have lower mixed with salt (20−30%, w/w) in a container, and fer- NaCl concentration and higher mineral contents includ- mentation starts spontaneously. Salted raw materials ing Ca, Mg, K, S, and other elements as compared to are stored for several months or years in some cases at imported salts [5]. Recently, bamboo salt is used for fer- room temperature. The main function of salt is preven- mented foods. Bamboo salt is believed to possess some tion of growth of spoilage microorganisms [2]. In addi- medicinal activities and started to be used for fermented tion, salt contributes to the development of flavor and foods regardless of its high price [6]. But not enough sci- entific data are available on the effects of solar salt and *Corresponding author bamboo salt for the qualities of fermented foods. Espe- Tel: +82-55-772-1904, Fax: +82-55-772-1909 cially, the effects of different types of salts have been E-mail: [email protected] © 2017, The Korean Society for Microbiology and Biotechnology rarely studied on the growth of microorganisms during http://dx.doi.org/10.4014/mbl.1703.03001 Saeu jeotgal with Different Types of Salts 219 fermentation. Different types of salts have different agar plates, and 48 h at 30℃ for MRS and YM agar chemical compositions and this can affect the growth of plates. microorganisms and the activities of enzymes from raw materials and microorganisms [4]. This eventually pH and titratable acidity (TA) measurements affects the final qualities of jeotgals. For these reasons, Ten gram of a homogenized jeotgal sample was mixed studies on the effects of each salt-type for the quality of a with 40 ml of distilled water, shaken in a water bath fermented food are necessary. In this work, saeu (shrimp) (150 rpm, 30℃) for 1 h, and the supernatant was jeotgals were prepared with different types of salts: puri- obtained after centrifugation (4,000 ×g, 20 min). pH of fied salt (PS), 1-year aged solar salt (SS), and bamboo the supernatant was measured using a pH meter (DMS, salt melted and recrystallized for 3 times (BS). Jeotgal Korea) and TA was calculated by titrating the superna- samples were fermented for 22 weeks at 15℃. During tant with 0.1 N NaOH until pH 8.4. The amount of fermentation, the growth of various microorganisms was NaOH was used to calculate the amount of lactic acid (%). examined together with other properties of jeotgal samples. Amino-type nitrogen (ANN), ammonia-type nitrogen (AMN), and volatile basic nitrogen (VBN) measurements Materials and Methods ANN was measured by formol titration method [7]. Five gram of a homogenized jeotgal sample was mixed Preparation of saeu jeotgals with 95 ml of distilled water, and the mixture was Saeu (shrimp, Acetes chinensis) was purchased from a shaken in a water bath (150 rpm, 30℃) for 1 h. Superna- local Suhyup at Shinan county, Jeonnam, Korea in tant (10 ml) was titrated with 0.1 N NaOH until pH 8.4. December 2015. Immediately after the purchase, saeu Sample was mixed with distilled water (10 ml) and form- was washed three times under running tap water. After aldehyde solution (pH 8.4, 10 ml) and stood for 10 min at removing excess water by standing for 10 min, each room temperature. Titration with 0.1 N NaOH was 10 kg of saeu was mixed with different types of salts: PS repeated until pH 8.4 and the amount of NaOH was (Hanju, Ulsan, 2015, NaCl content 99.18%), SS (Taepong used to calculate ANN content as shown below. salt farm, Shinan, Jeonnam, 2015, NaCl content 79.84%), Amino-type nitrogen (mg%) and BS (Insanga, Hamyang, Gyeongnam, 2014, NaCl = [sample titration (ml) − blank test (ml)] × 1.4 × F × D content 94.54%). The final NaCl concentration of saeu × 100/S jeotgals was adjusted to 25% (w/w) by adding different amount of each salt: 2,520 g of PS, 3,131 g of SS, and 1.4 corresponds to ANN (in mg) equivalent to 1 ml of 2,644 g of BS. Salted jeotgals were fermented for 22 0.1 N NaOH. F is the factor of 0.1 N NaOH, D is dilution weeks at 15℃ and analyzed at every 2 weeks. fold, and S is the amount of sample (5 g). AMN was measured by indophenol blue method [8]. Viable cell counting Five gram of a homogenized jeotgal sample was mixed Ten gram of each saeu jeotgal (SJ) sample was mixed with 95 ml of distilled water, and the mixture was with 90 ml of peptone water prepared with peptone shaken in a water bath (150 rpm, 30℃) for 1 h. Superna- (Sigma-Aldrich, P7750, 0.1%, w/v), and homogenized tant (1 ml) was mixed with 3 ml of solution A (phenol using a stomacher (Stomacher®80, Seward, USA). The 10 g, sodium niropursside dehydrate 1 g, EDTA 4 g, dis- homogenate was filtered with a bag filter (Interscience, tilled water 1 L) and stood for 5 min at room tempera- France) and diluted serially with peptone water. Diluted ture. Then 5 ml of solution B (Na2HPO4·12H2O 9 g, samples (0.1 ml) were spreaded on MRS agar plates for NaOH 6 g and NaOCl 10 ml, distilled water 1 L) was lactic acid bacteria (LAB) counting, marine agar plates added and reacted for 20 min at 37℃. Changes in absor- for marine bacteria counting, LB agar plates for bacilli bance at 665 nm were measured with a spectrophotometer counting, YM agar plates for yeasts counting, and (UV-1601, Shimadzu, Japan), and AMN was determined DSMZ954 agar plates for archaea counting. Plates were on the basis of the standard curve of (NH4)2SO4. incubated for 24 h at 37℃ for marine, LB, and DSMZ954 VBN was determined by Conway’s method with some September 2017 | Vol. 45 | No. 3 220 Shim et al. modifications [4]. A homogenized jeotgal sample (10 g) experiment in which equivalent amount of distilled was mixed with distilled water (30 ml) and 20% trichlo- water was used in place of sample solution. 0.28 is the roacetic acid solution (20 ml). Then the sample was cen- result of 14 (molecular weight of nitrogen) multiplied trifuged (8,000 ×g, 10 min, 4℃) and filtrated with a with the concentration of H2SO4 solution, 0.02, and S is membrane filter (0.45 µm, ADVATEC, Tokyo, Japan). the weight of the sample. Pretreated sample (1 ml) was transferred to the outer room of a Conway unit with 1 ml of 1% H3BO3 solution Salinity and color changes in the inner room. Saturated K2CO3 solution (1 ml) was For salinity measurements, 10 g of a homogenized mixed carefully with the sample solution in the outer jeotgal sample was mixed with 40 ml of distilled water. room and the Conway unit was sealed and incubated for Supernatant was obtained after shaking in a water bath 1 h at 37℃. The mixture in the outer room was neutral- and centrifuged as stated above. Salinity of supernatant ized with 0.02 N H2SO4 solution until the H3BO3 solu- was measured by using a saltmeter (PAL-SALT, Atago, tion turned to pink color.