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Physicochemical characteristics of kimchi powder manufactured by hot air drying and freeze drying
Biocatalysis and Agricultural Biotechnology 5 (2016) 193–198
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Biocatalysis and Agricultural Biotechnology journal homepage: www.elsevier.com/locate/bab
Physicochemical characteristics of kimchi powder manufactured by hot air drying and freeze drying Hyeon-Jin Park a, Yongjae Lee b, Jong-Bang Eun a,n a b
Department of Food Science and Technology and BK21 Plus Program, Graduate School, Chonnam National University, Gwangju 61186, South Korea Food Protein R&D Center, Texas A&M University, College Station, TX 77843, USA
art ic l e i nf o
a b s t r a c t
Article history: Received 7 November 2015 Accepted 2 February 2016 Available online 2 February 2016
Kimchi powder was manufactured by hot air drying at different temperature of 55 °C, 60 °C and 65 °C, and freeze drying until it reached about 10% moisture content. The water absorption index (WAI) and water soluble index (WSI) of freeze dried powder was higher than those hot air dried kimchi powder. Moreover, L*, a* and b* values of hot air dried kimchi powder were lower than those of freeze dried kimchi powder. During hot air drying, the browning index increased with increasing drying temperatures. The highest browning index was found in samples dried at 65 °C with inoculation of mixed Leu. mesenteroides and Lb. sakei. The freeze drying showed the lowest browning index compared to hot air drying (55 °C, 60 °C and 65 °C). In addition, the kimchi powder prepared by freeze dryer clearly received higher scores for overall acceptance than sample prepared by hot air dryer on sensory evaluation. Consequently, the kimchi inoculated Leu. mesenteroides as the starter has a similar quality with the naturally fermented kimchi. These results suggested that freeze drying method is more suitable for producing high quality kimchi powder than hot air drying. & 2016 Elsevier Ltd. All rights reserved.
Keywords: Kimchi powder Hot air drying Freeze drying
1. Introduction Kimchi is a fermented vegetable food and it is one of the most popular side dishes in Korea (Cho et al., 1997). Also, it has been recently introduced to many counties in the world and became a famous food (Cheigh, 2004; Lee et al., 2008). Chinese cabbage or radish are used as the major materials and seasonings including red pepper, garlic, ginger, green onion, and fermented anchovy sauce are generally used as the minor materials for kimchi production. The taste, the rate of the fermentation, and the properties of kimchi are dependent on the kinds of ingredients and seasoning used (Cho et al., 1997). Microorganisms involved in the fermentation of kimchi are originated from its ingredients (Pyo and Oh, 2011). Raw ingredients are utilized as the sources of nutrients and substrates for biological or biochemical reactions. Therefore, kimchi is characterized with its palatability, giving sour, sweet, and carbonated taste (Park, 1997). Recently, many researches on kimchi have pointed the superiority of kimchi out as a nutritive food (Cheigh and Park, 1994). Even though kimchi has many kinds of biological activities, it is difficult to integrate with other foods due to their high salted water contents (Lee et al., 2008). Abbreviations: WAI, water absorption index; WSI, water soluble index; ANOVA, analysis of variance n Corresponding author. E-mail address: [email protected] (J.-B. Eun). http://dx.doi.org/10.1016/j.bcab.2016.02.002 1878-8181/& 2016 Elsevier Ltd. All rights reserved.
To work with other foods, extend shelf life and become more cost effective during transport, kimchi is dehydrated by various methods such as hot air drying and vacuum freeze drying. Hot air drying involves a continuously flowing hot stream of air to remove the surface moisture of kimchi while freeze drying reduces the surrounding pressure to allow the frozen water in the material to directly sublimate from the solid to gas phase after freezing material with low temperature. (Meda and Ratti, 2005; Suvarnakuta et al., 2005; Hu et al., 2013). Hot air drying offers significant dehydrated products but the quality of dried product is usually significantly reduced compared to the original product. Vacuum freeze drying is considered the best method of dehydration with the high quality compared to other drying methods, but generally considered as a very expensive method (Ratti, 2001). Recently, kimchi powder has been developed as food ingredients and seasonings to other products such as snacks (Cho, 2004; Cho et al., 2004; Kim et al., 2015), noodles (Cho and Kang, 2003), seafood buns (Kang et al., 2001), fermented sausages (Han et al., 2001; Lee and Kunz, 2005; Lee et al., 1990), and breakfast sausages (Cho, 2005; Lee et al., 2008) by adding kimchi powder. However, very few studies were conducted regarding the physicochemical characteristics of kimchi powder which were produced by hot air and freeze drying under different drying conditions. Therefore, the aim of this study is to evaluate the chemical and sensory properties of kimchi powder which are produced by different temperature of hot air drying and freeze drying.
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2. Materials and methods
2.4. Water soluble index (WSI) and water absorption index (WAI)
2.1. Preparation of kimchi samples and starter culture
Water solubility index (WSI) and water absorption index (WAI) were determined according to the method described by Anderson et al. (1969). Two and a half grams of kimchi powder and 30 mL water were vigorously mixed in a 50 mL centrifuge tube; the mixture was incubated in a water bath at 30 °C for 30 min, and centrifuged at 3000 g for 15 min. The supernatant was collected in a pre-weighed Petri dish and the residue was weighed after oven drying at 105 °C overnight. The amount of solids in the dried supernatant as a percentage of the total dry solid pellet remaining after centrifugation was divided by the amount of dry sample. WAI and WSI were calculated by:
Kimchi was prepared using Chinese cabbage and other ingredients according to a traditional standard method and compositions. The raw materials were purchased from a local grocery marketplace in Korea. The cabbage was cut into 4–5 cm lengths and the other minor ingredients were added and blended by blender (NFM-8860, NUC, Korea) using the following ratio; cabbage: radish: green onion: sugar: red pepper powder: garlic: ginger: anchovy sauce ¼100:13:2:1:3.5:1.4:0.6:2.2. The final salt concentration was adjusted to 2.5–3.0% using 10% solar salt solution. The prepared kimchi were divided into five groups; 1) Inoculation with both Leu.mesenteroides and Lb.sakei after sterilization with gamma (ɣ)-irradiation (KMSG), 2 and 3) Inoculation with Leu. mesenteroides and Lb. sakei, respectively, after sterilization with irradiation (KMG and KSG), 4) Natural fermentation without inoculation and irradiation (KSF), and 5) Sterilization without inoculation (CON). Ten 500-ml plastic containers of each group containing 450 g of the kimchi were anaerobically packed and used for further research. The γ-irradiation of kimchi was carried out at the Korea Atomic Energy Research Institute (KAERI) in Jeongeup, Korea. The kimchi samples were irradiated in a cobalt-60 irradiator (Point source AECL, IR-79, MDS Nordion International Co., Ltd., Ottawa, ON, Canada) with 40 kGy absorbed doses at ambient temperature. Leuconostoc mesenteroides (KCTC 13302) and Lactobacillus sakei (KCTC 13416) were purchased from Korea Biological Resource Center, as a starter culture. Leu. medenteriodes and Lb. sakei were sub-cultured twice in deMan Rogasa Sharpes (MRS) broth at 30 °C and 37 °C for 2 days, respectively. The 10 mL of the suspension was centrifuged at 3000 g (4 °C) for 15 min, and then collected cells were washed in a sterile 0.85% NaCl solution twice. The number of microbes was adjusted to 1 107 CFU/mL and inoculated to kimchi samples. The ripening and fermentation of kimchi was carried out for 24 hours using an incubator (IB-600M, JEIO TECH, Korea) at 30 °C. Kimchi samples were collected every three hours after incubation and immediately measured for their pH and total acidity. All experiments were performed under standard aseptic condition. 2.2. Manufacturing of kimchi powder Kimchi powder was manufactured using each fermented kimchi which reached the pH 4.1–4.3 and total acidity 0.7–0.8%. Kimchi samples were collected and put into open pans and dried in a hot air dryer (NA-20, NOA Co., Korea) at 55 72 °C, 60 72 °C and 65 72 °C, respectively. On the other hand, kimchi samples were also dried by freeze dryer (Freeze-dryer, Bondiro DC1316 Iishin Lab Co., LTD). The samples were dehydrated until they reached a constant weight ( 10% final moisture) for 12 h at 557 2 °C, for 10 h at 607 2 °C and for 8.5 hours at 65 72 °C, and for 24 h at freeze dryer, respectively. Finally, hot air and freeze dried kimchi were finely pulverized to a particle size of 80 mesh and the powder was kept in the freezer at 80 °C until further used. All processing was conducted in triplicate.
WAI=
(Sediment + Weight of Tube) – (Weight of Tube) Sample Dry Weight
WSI =
(Weight of Container + Dried Supernatant) – (Weight of Container) Sample Dry Weight
For WAI and WSI, two determinations were carried out for each treatment sample. 2.5. Color and browning index The kimchi powder was transferred into different glass cells and measured with a Color Difference Meter (CM-3500d, MINOLTA Co., Ltd., Japan). The results were expressed as L* (lightness), a* (redness) and b* (yellowness) values. The measurement of color was repeated in duplicate (Petracci and Fletcher, 2002). Browning index was determined using the method described by Krishnan et al. (2010) with slight modification. One gram of dehydrated kimchi powder was extracted with 40 mL of distilled water and 10 mL of 10% trichloroacetic solution in a beaker. The extract was filtered through a Buchner funnel with Whatman No. 2 filter paper. After the solution stood for 2 hours at room temperature, its concentration was determined based on its absorbance at 420 nm (Optizen 2120UV, Mecasys, Korea). 2.6. Sensory evaluation Sensory evaluation was conducted by the 40 semi-trained sensory panelists, except for overall acceptance which had 50 panelists that participated in it, from the Department of Food Science and Technology at Chonnam National University (Gwangju, Korea). Samples of each kimchi powder were compared in terms of color, flavor, appearance, texture, taste and overall acceptance on a 7-point hedonic scale from 7 (like very much) to 1 (dislike very much), by the method of Meilgaard et al. (1987). 2.7. Statistical analysis There were five kinds of manufactured kimchi powder samples which carried out triplicate analyses. Results were expressed as mean values 7standard deviation. To detect the differences among the samples, ANOVA and Duncan’s multiple-range test were used for data analysis (p o0.05) (SPSS, 2008; SPSS Inc., Chicago, IL, USA).
2.3. Moisture content
3. Results and discussion
The moisture content of a dried sample was determined using an oven dry method (AOAC, 2005). About 3.0–4.0 g of the dried sample was dried at 105 °C until a constant mass was reached in a hot air oven (FO-600M, Jeio Tech Co. Ltd, Kimpo Kyeonggi-do, Korea). The moisture content was determined by weight difference and expressed as a percentage of the initial sample weight.
3.1. Moisture content The moisture content of kimchi powder manufactured with different drying temperatures is shown in Table 1. The moisture content of kimchi powder ranged from 10.82% to 7.86%. The moisture content of general commercial kimchi powder is below
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Table 1 Moisture content of kimchi powder manufactured by different hot air drying temperature and freeze drying (Unit: %). Drying temperature (°C)/h Hot air drying
55/12 60/10 65/8.5
Freeze drying/24
CON1
KSF2
KMG3
KSG4
KMSG5
10.417 0.32aA 10.477 0.47aA 9.98 7 0.48aA 8.187 0.11aB
10.117 0.52aA 10.58 7 0.52aA 10.137 0.89aA 7.86 7 0.27aB
9.89 7 0.21aA 10.63 7 0.12aA 9.88 7 0.15aA 8.45 7 0.45aB
10.25 7 1.01aA 10.82 7 0.87aA 9.95 7 0.41aA 8.777 0.22aB
9.99 70.33aA 9.54 70.51aA 10.17 70.62aA 8.2470.13aB
Values represent means of triplicates7 standard deviations. Dissimilar small alphabets within the same row are significantly different (p o 0.05). Dissimilar capital alphabets within the column are significantly different (p o0.05). 1 2 3 4 5
Treatment: CON (Control without inoculation after irradiation). KSF (Fermented naturally without inoculation and irradiation). KMG (Inoculation of Leu. mesenteroides). KSG (Inoculation of Lb. sakei). KMSG (Inoculation of mixed Leu. mesenteroides and Lb. sakei).
10%. Therefore, in this study, kimchi powder manufactured by hot air drying and freeze drying satisfied the commercial standard qualification. Drying time was decreased while the temperatures increased in all samples of hot air dried kimchi powder. In order to reduce the moisture content below 10%, it takes 12 h at 55 °C, 10 h at 60 °C and 8.5 h at 65 °C while freeze drying for 24 h. Also, all samples between treatments were not significantly different at any drying temperature and method. Drying time of hot air drying was significantly faster than freeze drying. This result could be due to vaporization of moisture in freeze drying which was slower than hot air drying. Mass transfer within the kimchi should be rapid during hot air drying because a large vapor pressure produced by air on the surface of kimchi. However, hot air drying is usually significantly reduces food quality while freeze drying protects the primary structure and does minimal reduction of food quality (Ratti, 2001; Ratti and Mujumdar, 1995; Irzyniec et al., 1995). 3.2. Water absorption index (WAI) and water soluble index (WSI) Table 2 shows the water absorption index (WAI) and water soluble index (WSI) of kimchi powder. The WAI of kimchi powder manufactured by hot air drying ranged from 4.93 to 5.18. Among the sample treatments (CON, KSF, KMG, KSG, and KMSG), kimchi powder manufactured by hot air drying were not significantly different. The WAI of the kimchi powder with freeze drying was significantly higher than those manufactures by hot air drying. Similar results were reported with garlic powder (Jung and Choi,
1990) and ginkgo nut powder (Kim et al., 2003). Kimchi powder manufactured by hot air drying has particle of polygon shape unlike kimchi powder manufactured by freeze drying. Also, structure of particle was not flat due to contraction and surface hardening by circulation of high heat for a short period of time. On the other hand, kimchi powder with freeze drying has porous structure. Hence, kimchi powder manufactured by freeze drying has great absorption area. The particle structure of freeze dried kimchi powder was porous than the hot air dried powder. Therefore, hygroscopicity of freeze sample was higher (Bhatty, 1993; Shand, 2000; Robertson et al., 2000; Lee et al., 2008). WSI of kimchi powder manufactured by freeze drying was higher than hot air dried kimchi powder. This observation was in agreement with the study by Kim (2004). A general trend appeared to be that WSI increased by decreasing of particle size. The particle structures of kimchi powder manufactured by freeze drying maintain porous shape. Therefore, water absorption and solubility of freeze dried kimchi powder was fast, and component of kimchi was not significantly changed by heat (Kim, 2004; Chung and Lee, 2015). Leuenberger (2002) explained that the high solubility of freeze dried powder is due to the small particle size. Therefore, small particle size of freeze drying powder has a higher solubility in the same amount of solution 3.3. Color evaluation The color was expressed as the L*, a* and b* values of the Hunter color system. The Hunter color parameters L*, a* and b*
Table 2 Water absorption index (WAI) and water soluble index (WSI) of kimchi powder manufactured by different hot air drying temperature and freeze drying (Unit: g/g). CON1
KSF2
KMG3
KSG4
KMSG5
55 60 65
WAI 5.17 70.12aB 4.98 7 0.07aB 5.137 0.08aB 6.477 0.15aA
5.05 70.08aB 5.18 70.02aB 5.13 7 0.16aB 6.357 0.02aA
5.177 0.02aB 4.93 7 0.10aB 4.99 7 0.04aB 6.46 7 0.03aA
4.92 70.06aB 5.08 70.07aB 5.15 70.01aB 6.29 70.07aA
5.09 7 0.08aB 5.117 0.05aB 5.147 0.07aB 6.377 0.06aA
55 60 65
WSI 0.0757 0.002aB 0.0747 0.007aB 0.073 70.004aB 0.085 7 0.008aA
0.0747 0.002aB 0.0787 0.002aB 0.0767 0.009aB 0.090 70.002aA
0.077 70.003aB 0.07570.001aB 0.0747 0.005aB 0.086 7 0.004aA
0.0737 0.001aB 0.0767 0.004aB 0.069 7 0.001aB 0.089 70.007aA
0.0767 0.003aB 0.0727 0.005aB 0.0747 0.002aB 0.088 7 0.008aA
Drying temp. (°C)
Hot air drying
Freeze drying Hot air drying
Freeze drying
Values represent means of triplicates7 standard deviations. Dissimilar small alphabets within the same row are significantly different (p o 0.05). Dissimilar capital alphabets within the column are significantly different (p o0.05). 1 2 3 4 5
Treatment: CON (Control without inoculation after irradiation). KSF (Fermented naturally without inoculation and irradiation). KMG (Inoculation of Leu. mesenteroides). KSG (Inoculation of Lb. sakei). KMSG (Inoculation of mixed Leu. mesenteroides and Lb. sakei).
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Table 3 L*, a* and b* value of kimchi powder manufactured by different hot air drying temperature and freeze drying. CON1
KSF2
KMG3
KSG4
KMSG5
55 60 65
L* value 47.75 7 0.09bB 46.84 7 0.33bB 43.75 7 0.21bC 54.58 7 0.32bA
53.84 7 0.13aB 52.117 0.12aB 49.677 0.17aC 60.977 0.14aA
47.137 0.08bB 46.23 7 0.42bB 44.617 0.09bC 55.277 0.60bB
47.85 7 0.81bB 47.92 7 0.33bAB 45.50 7 0.34bC 55.87 7 0.07bA
48.487 0.23bB 47.52 7 0.15bB 45.19 70.28bC 56.76 70.14bA
55 60 65
a* value 19.99 7 0.12bB 18.29 7 0.36bB 15.32 7 0.20bC 23.077 0.13bA
34.82 7 0.17aB 32.717 0.24aB 30.96 7 0.16aC 29.00 70.26aA
20.78 7 0.32bB 19.58 7 0.40bB 16.03 7 0.11bC 22.157 0.13bA
19.30 7 0.16bB 18.477 0.07bB 15.05 7 0.21bC 23.20 7 0.08bA
20.13 70.09bB 19.80 7 0.22bB 16.32 7 0.14bC 22.19 70.30bA
55 60 65
b* value 25.23 7 0.17bB 24.297 0.15bB 21.32 7 0.17bC 30.737 0.06bA
28.497 0.15aB 27.917 0.06aB 25.96 7 1.06aC 32.727 0.16aA
24.087 0.22bB 23.58 7 0.23bB 20.03 7 0.09bC 29.02 7 0.24bA
25.30 7 0.23bB 23.47 70.11bB 20.55 7 0.15bC 28.977 0.07bA
24.137 0.19bB 24.807 0.02bB 20.32 70.16bC 29.90 70.03bA
Drying Temp. (°C)
Hot air drying
Freeze drying Hot air drying
Freeze drying Hot air drying
Freeze drying
Values represent means of triplicates7 standard deviations. Dissimilar small alphabets within the same row are significantly different (p o 0.05). Dissimilar capital alphabets within the column are significantly different (p o0.05). 1 2 3 4 5
Treatment: CON (Control without inoculation after irradiation). KSF (Fermented naturally without inoculation and irradiation). KMG(Inoculation of Leu. mesenteroides). KSG (Inoculation of Lb. sakei). KMSG (Inoculation of mixed Leu. mesenteroides and Lb. sakei).
have been widely used to describe color changes during thermal processing of products. For the color, the L*, a* and b* values were significantly affected by the drying temperature and method (Table 3). The freeze-dried powder produced higher L* values than those dried with hot air. L* value represents the lightness of the sample, and a higher L* value shows a lighter color (Chung and Lee, 2015). This is probably due to hot air directly exposed on kimchi surface during the drying process. Among the hot air-dried, KSF had higher lightness compared to the other samples because L* of KSF without gamma (γ) irradiation before drying was already higher than other treatments. According to Lee et al. (2004), gamma-irradiation did not affect the lightness and the redness of red pepper powder. The Hunter a* value (redness) was higher in freeze-dried samples than those in hot air-dried samples, similar to the L* value. The browning, which was higher in hot air-dried samples, may be responsible for this. The reduction of redness was higher at higher drying temperatures (Chung and Lee, 2015). The Hunter a* values of these samples decreased severely due to the destruction of red pigments such as carotenoids, which included capsaicin, βcarotene, cryptoxanthin (Nieto-Sandoval et al., 1999; Cheigh, 2004). Hunter b* values (yellowness) were higher in freeze-dried
samples than those in dried with hot air, which might cause browning. Yellowness showed a slight decrease in its value as temperature increased as a result of generation of brown products due to non-enzymatic reaction. These results are in agreement with Keawpeng et al. (2007). Also, among hot air-dried samples, L*, a* and b* values of kimchi powder dried at 55 °C and 60 °C were not significantly different. Therefore, in case of kimchi powder manufactured by hot air drying, it is efficient to dry at 55 °C to establish the cost effective commercial process. 3.4. Browning index The effects of different temperatures of hot air drying and freeze drying on the browning index of kimchi powder are shown in Table 4. Hot air-drying resulted in higher browning index than freeze-drying. Samples dried with hot air at 55 °C and 60 °C did not significantly differ. A higher degree of browning occurs during hot air drying at 65 °C. The highest browning index was found in the samples dried at 65 °C while freeze drying showed the lowest. During freeze-drying, there is no oxygen in the drying chamber which is the main cause of browning by the Maillard reaction and ascorbic acid oxidation (Lee et al., 2007). It may indicate that the freeze drying produced less of non-enzymatic browning reaction
Table 4 Browning index of kimchi powder manufactured by different hot air drying temperature and freeze drying. Drying Temp. (°C) Hot air drying
Freeze drying
55 60 65
CON1
KSF2
KMG3
KSG4
KMSG5
0.197 0.06aB 0.197 0.05aB 0.277 0.08aA 0.157 0.01aC
0.20 70.06aB 0.19 70.03aB 0.28 70.03aA 0.15 70.03aC
0.20 70.01aB 0.19 70.01aB 0.25 70.01aA 0.14 70.04aC
0.21 70.07aB 0.22 70.04aB 0.28 70.02aA 0.14 70.08aC
0.22 7 0.07aB 0.22 7 0.08aB 0.29 7 0.02aA 0.157 0.02aC
Values represent means of triplicates7 standard deviations. Dissimilar small alphabets within the same row are significantly different (p o 0.05). Dissimilar capital alphabets within the column are significantly different (p o0.05). 1 2 3 4 5
Treatment: CON (Control without inoculation after irradiation). KSF (Fermented naturally without inoculation and irradiation). KMG (Inoculation of Leu. mesenteroides). KSG (Inoculation of Lb. sakei). KMSG (Inoculation of mixed Leu. mesenteroides and Lb. sakei).
H.-J. Park et al. / Biocatalysis and Agricultural Biotechnology 5 (2016) 193–198
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Table 5 Sensory evaluation of kimchi powder manufactured by hot air drying at 60 °C and freeze drying. CON1
KSF2
KMG3
KSG4
KMSG5
Hot air drying at 60 °C Color Flavor Texture Taste Overall acceptability
5.40 7 0.92a 5.10 7 1.14a 5.60 7 0.52a 5.00 7 0.72b 4.53 7 1.46b
5.30 7 0.78a 4.90 7 1.30a 5.50 7 0.71a 5.737 1.18a 5.84 7 1.01a
5.90 7 1.38a 5.30 7 1.19a 5.50 7 0.85a 5.83 7 1.22a 5.87 7 0.97a
5.60 7 1.11a 5.007 1.00a 5.80 7 0.63a 5.447 0.97b 4.737 1.49b
5.50 7 1.12a 5.20 7 0.60a 5.30 7 0.82a 5.22 7 1.14b 4.93 7 1.25b
Freeze drying Color Flavor Texture Taste Overall acceptability
5.00 7 0.67a 5.20 7 0.78a 5.60 7 0.50a 4.63 7 0.87b 5.12 7 0.72c
5.32 7 0.51a 5.30 7 1.19a 5.50 7 0.71a 6.687 0.97a 6.717 1.22a
5.337 0.87a 5.30 7 0.62a 5.80 7 0.63a 6.677 0.51a 6.687 0.89a
5.247 1.70a 5.007 1.01a 5.40 7 0.97a 5.89 7 0.68ab 5.93 7 1.01b
5.43 7 0.87a 5.107 1.14a 5.707 1.49a 5.80 7 0.72ab 5.677 1.10b
Values represent means of triplicates7 standard deviations. Dissimilar small alphabets within the same row are significantly different (p o 0.05). 1 2 3 4 5
Treatment: CON (Control without inoculation after irradiation). KSF (Fermented naturally without inoculation and irradiation). KMG (Inoculation of Leu. mesenteroides). KSG (Inoculation of Lb. sakei). KMSG (Inoculation of mixed Leu. mesenteroides and Lb. sakei).
in kimchi powder samples during drying. It is expected that the browning reactions would be minimized by a low temperature freeze drying process. These results are in agreement with the findings of Kim et al. (2007) and Son and Lee (2011). Additionally, Ko et al. (1999) showed similar results with shiitake mushrooms and Kim et al. (1982) with red peppers. 3.5. Sensory evaluation The results of sensory evaluation of kimchi powder manufactured by hot air drying at 60 °C and freeze drying are shown in Table 5. The color, flavor, texture, taste and overall acceptance of kimchi powder were evaluated by trained panelists. There is no significant difference in color, flavor and texture among the fivesamples by hot air drying. The taste and overall acceptance score were higher in kimchi powder manufactured using KSF and KMG than other kimchi powders. Also, results of sensory evaluation of kimchi powder manufactured by freeze drying are in agreement with the results above. Overall acceptability score was higher in kimchi powder manufactured by using freeze drying than hot air drying. The reason might be the less browning reaction that occurred during freeze drying. The similar results were reported by Hu et al. (2013) on hairtail fish meat gel. Consequently, when Leu. mesenteroides is used as the starter, it was similar to sensory evaluation of kimchi powder manufactured by natural fermentation.
4. Conclusion Kimchi powder was manufactured by hot air drying with different temperatures of 55 °C, 60 °C and 66 °C, and freeze drying. Moisture content reached about 10% after the drying process. The result indicated that the WAI, WSI, and L*, a* and b* values of freeze dried powder was higher than those of the hot air dried kimchi powder. The freeze drying showed the lowest browning index compared to hot air drying. In addition, the kimchi powder prepared by freeze dryer clearly received higher scores for overall acceptance than samples prepared by hot air dryer on sensory evaluation. On the basis of the results of this study, it is concluded that the freeze drying method is the most suitable drying method to produce high quality kimchi powder compared to hot air drying.
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Contents lists available at ScienceDirect
Biocatalysis and Agricultural Biotechnology journal homepage: www.elsevier.com/locate/bab
Physicochemical characteristics of kimchi powder manufactured by hot air drying and freeze drying Hyeon-Jin Park a, Yongjae Lee b, Jong-Bang Eun a,n a b
Department of Food Science and Technology and BK21 Plus Program, Graduate School, Chonnam National University, Gwangju 61186, South Korea Food Protein R&D Center, Texas A&M University, College Station, TX 77843, USA
art ic l e i nf o
a b s t r a c t
Article history: Received 7 November 2015 Accepted 2 February 2016 Available online 2 February 2016
Kimchi powder was manufactured by hot air drying at different temperature of 55 °C, 60 °C and 65 °C, and freeze drying until it reached about 10% moisture content. The water absorption index (WAI) and water soluble index (WSI) of freeze dried powder was higher than those hot air dried kimchi powder. Moreover, L*, a* and b* values of hot air dried kimchi powder were lower than those of freeze dried kimchi powder. During hot air drying, the browning index increased with increasing drying temperatures. The highest browning index was found in samples dried at 65 °C with inoculation of mixed Leu. mesenteroides and Lb. sakei. The freeze drying showed the lowest browning index compared to hot air drying (55 °C, 60 °C and 65 °C). In addition, the kimchi powder prepared by freeze dryer clearly received higher scores for overall acceptance than sample prepared by hot air dryer on sensory evaluation. Consequently, the kimchi inoculated Leu. mesenteroides as the starter has a similar quality with the naturally fermented kimchi. These results suggested that freeze drying method is more suitable for producing high quality kimchi powder than hot air drying. & 2016 Elsevier Ltd. All rights reserved.
Keywords: Kimchi powder Hot air drying Freeze drying
1. Introduction Kimchi is a fermented vegetable food and it is one of the most popular side dishes in Korea (Cho et al., 1997). Also, it has been recently introduced to many counties in the world and became a famous food (Cheigh, 2004; Lee et al., 2008). Chinese cabbage or radish are used as the major materials and seasonings including red pepper, garlic, ginger, green onion, and fermented anchovy sauce are generally used as the minor materials for kimchi production. The taste, the rate of the fermentation, and the properties of kimchi are dependent on the kinds of ingredients and seasoning used (Cho et al., 1997). Microorganisms involved in the fermentation of kimchi are originated from its ingredients (Pyo and Oh, 2011). Raw ingredients are utilized as the sources of nutrients and substrates for biological or biochemical reactions. Therefore, kimchi is characterized with its palatability, giving sour, sweet, and carbonated taste (Park, 1997). Recently, many researches on kimchi have pointed the superiority of kimchi out as a nutritive food (Cheigh and Park, 1994). Even though kimchi has many kinds of biological activities, it is difficult to integrate with other foods due to their high salted water contents (Lee et al., 2008). Abbreviations: WAI, water absorption index; WSI, water soluble index; ANOVA, analysis of variance n Corresponding author. E-mail address: [email protected] (J.-B. Eun). http://dx.doi.org/10.1016/j.bcab.2016.02.002 1878-8181/& 2016 Elsevier Ltd. All rights reserved.
To work with other foods, extend shelf life and become more cost effective during transport, kimchi is dehydrated by various methods such as hot air drying and vacuum freeze drying. Hot air drying involves a continuously flowing hot stream of air to remove the surface moisture of kimchi while freeze drying reduces the surrounding pressure to allow the frozen water in the material to directly sublimate from the solid to gas phase after freezing material with low temperature. (Meda and Ratti, 2005; Suvarnakuta et al., 2005; Hu et al., 2013). Hot air drying offers significant dehydrated products but the quality of dried product is usually significantly reduced compared to the original product. Vacuum freeze drying is considered the best method of dehydration with the high quality compared to other drying methods, but generally considered as a very expensive method (Ratti, 2001). Recently, kimchi powder has been developed as food ingredients and seasonings to other products such as snacks (Cho, 2004; Cho et al., 2004; Kim et al., 2015), noodles (Cho and Kang, 2003), seafood buns (Kang et al., 2001), fermented sausages (Han et al., 2001; Lee and Kunz, 2005; Lee et al., 1990), and breakfast sausages (Cho, 2005; Lee et al., 2008) by adding kimchi powder. However, very few studies were conducted regarding the physicochemical characteristics of kimchi powder which were produced by hot air and freeze drying under different drying conditions. Therefore, the aim of this study is to evaluate the chemical and sensory properties of kimchi powder which are produced by different temperature of hot air drying and freeze drying.
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2. Materials and methods
2.4. Water soluble index (WSI) and water absorption index (WAI)
2.1. Preparation of kimchi samples and starter culture
Water solubility index (WSI) and water absorption index (WAI) were determined according to the method described by Anderson et al. (1969). Two and a half grams of kimchi powder and 30 mL water were vigorously mixed in a 50 mL centrifuge tube; the mixture was incubated in a water bath at 30 °C for 30 min, and centrifuged at 3000 g for 15 min. The supernatant was collected in a pre-weighed Petri dish and the residue was weighed after oven drying at 105 °C overnight. The amount of solids in the dried supernatant as a percentage of the total dry solid pellet remaining after centrifugation was divided by the amount of dry sample. WAI and WSI were calculated by:
Kimchi was prepared using Chinese cabbage and other ingredients according to a traditional standard method and compositions. The raw materials were purchased from a local grocery marketplace in Korea. The cabbage was cut into 4–5 cm lengths and the other minor ingredients were added and blended by blender (NFM-8860, NUC, Korea) using the following ratio; cabbage: radish: green onion: sugar: red pepper powder: garlic: ginger: anchovy sauce ¼100:13:2:1:3.5:1.4:0.6:2.2. The final salt concentration was adjusted to 2.5–3.0% using 10% solar salt solution. The prepared kimchi were divided into five groups; 1) Inoculation with both Leu.mesenteroides and Lb.sakei after sterilization with gamma (ɣ)-irradiation (KMSG), 2 and 3) Inoculation with Leu. mesenteroides and Lb. sakei, respectively, after sterilization with irradiation (KMG and KSG), 4) Natural fermentation without inoculation and irradiation (KSF), and 5) Sterilization without inoculation (CON). Ten 500-ml plastic containers of each group containing 450 g of the kimchi were anaerobically packed and used for further research. The γ-irradiation of kimchi was carried out at the Korea Atomic Energy Research Institute (KAERI) in Jeongeup, Korea. The kimchi samples were irradiated in a cobalt-60 irradiator (Point source AECL, IR-79, MDS Nordion International Co., Ltd., Ottawa, ON, Canada) with 40 kGy absorbed doses at ambient temperature. Leuconostoc mesenteroides (KCTC 13302) and Lactobacillus sakei (KCTC 13416) were purchased from Korea Biological Resource Center, as a starter culture. Leu. medenteriodes and Lb. sakei were sub-cultured twice in deMan Rogasa Sharpes (MRS) broth at 30 °C and 37 °C for 2 days, respectively. The 10 mL of the suspension was centrifuged at 3000 g (4 °C) for 15 min, and then collected cells were washed in a sterile 0.85% NaCl solution twice. The number of microbes was adjusted to 1 107 CFU/mL and inoculated to kimchi samples. The ripening and fermentation of kimchi was carried out for 24 hours using an incubator (IB-600M, JEIO TECH, Korea) at 30 °C. Kimchi samples were collected every three hours after incubation and immediately measured for their pH and total acidity. All experiments were performed under standard aseptic condition. 2.2. Manufacturing of kimchi powder Kimchi powder was manufactured using each fermented kimchi which reached the pH 4.1–4.3 and total acidity 0.7–0.8%. Kimchi samples were collected and put into open pans and dried in a hot air dryer (NA-20, NOA Co., Korea) at 55 72 °C, 60 72 °C and 65 72 °C, respectively. On the other hand, kimchi samples were also dried by freeze dryer (Freeze-dryer, Bondiro DC1316 Iishin Lab Co., LTD). The samples were dehydrated until they reached a constant weight ( 10% final moisture) for 12 h at 557 2 °C, for 10 h at 607 2 °C and for 8.5 hours at 65 72 °C, and for 24 h at freeze dryer, respectively. Finally, hot air and freeze dried kimchi were finely pulverized to a particle size of 80 mesh and the powder was kept in the freezer at 80 °C until further used. All processing was conducted in triplicate.
WAI=
(Sediment + Weight of Tube) – (Weight of Tube) Sample Dry Weight
WSI =
(Weight of Container + Dried Supernatant) – (Weight of Container) Sample Dry Weight
For WAI and WSI, two determinations were carried out for each treatment sample. 2.5. Color and browning index The kimchi powder was transferred into different glass cells and measured with a Color Difference Meter (CM-3500d, MINOLTA Co., Ltd., Japan). The results were expressed as L* (lightness), a* (redness) and b* (yellowness) values. The measurement of color was repeated in duplicate (Petracci and Fletcher, 2002). Browning index was determined using the method described by Krishnan et al. (2010) with slight modification. One gram of dehydrated kimchi powder was extracted with 40 mL of distilled water and 10 mL of 10% trichloroacetic solution in a beaker. The extract was filtered through a Buchner funnel with Whatman No. 2 filter paper. After the solution stood for 2 hours at room temperature, its concentration was determined based on its absorbance at 420 nm (Optizen 2120UV, Mecasys, Korea). 2.6. Sensory evaluation Sensory evaluation was conducted by the 40 semi-trained sensory panelists, except for overall acceptance which had 50 panelists that participated in it, from the Department of Food Science and Technology at Chonnam National University (Gwangju, Korea). Samples of each kimchi powder were compared in terms of color, flavor, appearance, texture, taste and overall acceptance on a 7-point hedonic scale from 7 (like very much) to 1 (dislike very much), by the method of Meilgaard et al. (1987). 2.7. Statistical analysis There were five kinds of manufactured kimchi powder samples which carried out triplicate analyses. Results were expressed as mean values 7standard deviation. To detect the differences among the samples, ANOVA and Duncan’s multiple-range test were used for data analysis (p o0.05) (SPSS, 2008; SPSS Inc., Chicago, IL, USA).
2.3. Moisture content
3. Results and discussion
The moisture content of a dried sample was determined using an oven dry method (AOAC, 2005). About 3.0–4.0 g of the dried sample was dried at 105 °C until a constant mass was reached in a hot air oven (FO-600M, Jeio Tech Co. Ltd, Kimpo Kyeonggi-do, Korea). The moisture content was determined by weight difference and expressed as a percentage of the initial sample weight.
3.1. Moisture content The moisture content of kimchi powder manufactured with different drying temperatures is shown in Table 1. The moisture content of kimchi powder ranged from 10.82% to 7.86%. The moisture content of general commercial kimchi powder is below
H.-J. Park et al. / Biocatalysis and Agricultural Biotechnology 5 (2016) 193–198
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Table 1 Moisture content of kimchi powder manufactured by different hot air drying temperature and freeze drying (Unit: %). Drying temperature (°C)/h Hot air drying
55/12 60/10 65/8.5
Freeze drying/24
CON1
KSF2
KMG3
KSG4
KMSG5
10.417 0.32aA 10.477 0.47aA 9.98 7 0.48aA 8.187 0.11aB
10.117 0.52aA 10.58 7 0.52aA 10.137 0.89aA 7.86 7 0.27aB
9.89 7 0.21aA 10.63 7 0.12aA 9.88 7 0.15aA 8.45 7 0.45aB
10.25 7 1.01aA 10.82 7 0.87aA 9.95 7 0.41aA 8.777 0.22aB
9.99 70.33aA 9.54 70.51aA 10.17 70.62aA 8.2470.13aB
Values represent means of triplicates7 standard deviations. Dissimilar small alphabets within the same row are significantly different (p o 0.05). Dissimilar capital alphabets within the column are significantly different (p o0.05). 1 2 3 4 5
Treatment: CON (Control without inoculation after irradiation). KSF (Fermented naturally without inoculation and irradiation). KMG (Inoculation of Leu. mesenteroides). KSG (Inoculation of Lb. sakei). KMSG (Inoculation of mixed Leu. mesenteroides and Lb. sakei).
10%. Therefore, in this study, kimchi powder manufactured by hot air drying and freeze drying satisfied the commercial standard qualification. Drying time was decreased while the temperatures increased in all samples of hot air dried kimchi powder. In order to reduce the moisture content below 10%, it takes 12 h at 55 °C, 10 h at 60 °C and 8.5 h at 65 °C while freeze drying for 24 h. Also, all samples between treatments were not significantly different at any drying temperature and method. Drying time of hot air drying was significantly faster than freeze drying. This result could be due to vaporization of moisture in freeze drying which was slower than hot air drying. Mass transfer within the kimchi should be rapid during hot air drying because a large vapor pressure produced by air on the surface of kimchi. However, hot air drying is usually significantly reduces food quality while freeze drying protects the primary structure and does minimal reduction of food quality (Ratti, 2001; Ratti and Mujumdar, 1995; Irzyniec et al., 1995). 3.2. Water absorption index (WAI) and water soluble index (WSI) Table 2 shows the water absorption index (WAI) and water soluble index (WSI) of kimchi powder. The WAI of kimchi powder manufactured by hot air drying ranged from 4.93 to 5.18. Among the sample treatments (CON, KSF, KMG, KSG, and KMSG), kimchi powder manufactured by hot air drying were not significantly different. The WAI of the kimchi powder with freeze drying was significantly higher than those manufactures by hot air drying. Similar results were reported with garlic powder (Jung and Choi,
1990) and ginkgo nut powder (Kim et al., 2003). Kimchi powder manufactured by hot air drying has particle of polygon shape unlike kimchi powder manufactured by freeze drying. Also, structure of particle was not flat due to contraction and surface hardening by circulation of high heat for a short period of time. On the other hand, kimchi powder with freeze drying has porous structure. Hence, kimchi powder manufactured by freeze drying has great absorption area. The particle structure of freeze dried kimchi powder was porous than the hot air dried powder. Therefore, hygroscopicity of freeze sample was higher (Bhatty, 1993; Shand, 2000; Robertson et al., 2000; Lee et al., 2008). WSI of kimchi powder manufactured by freeze drying was higher than hot air dried kimchi powder. This observation was in agreement with the study by Kim (2004). A general trend appeared to be that WSI increased by decreasing of particle size. The particle structures of kimchi powder manufactured by freeze drying maintain porous shape. Therefore, water absorption and solubility of freeze dried kimchi powder was fast, and component of kimchi was not significantly changed by heat (Kim, 2004; Chung and Lee, 2015). Leuenberger (2002) explained that the high solubility of freeze dried powder is due to the small particle size. Therefore, small particle size of freeze drying powder has a higher solubility in the same amount of solution 3.3. Color evaluation The color was expressed as the L*, a* and b* values of the Hunter color system. The Hunter color parameters L*, a* and b*
Table 2 Water absorption index (WAI) and water soluble index (WSI) of kimchi powder manufactured by different hot air drying temperature and freeze drying (Unit: g/g). CON1
KSF2
KMG3
KSG4
KMSG5
55 60 65
WAI 5.17 70.12aB 4.98 7 0.07aB 5.137 0.08aB 6.477 0.15aA
5.05 70.08aB 5.18 70.02aB 5.13 7 0.16aB 6.357 0.02aA
5.177 0.02aB 4.93 7 0.10aB 4.99 7 0.04aB 6.46 7 0.03aA
4.92 70.06aB 5.08 70.07aB 5.15 70.01aB 6.29 70.07aA
5.09 7 0.08aB 5.117 0.05aB 5.147 0.07aB 6.377 0.06aA
55 60 65
WSI 0.0757 0.002aB 0.0747 0.007aB 0.073 70.004aB 0.085 7 0.008aA
0.0747 0.002aB 0.0787 0.002aB 0.0767 0.009aB 0.090 70.002aA
0.077 70.003aB 0.07570.001aB 0.0747 0.005aB 0.086 7 0.004aA
0.0737 0.001aB 0.0767 0.004aB 0.069 7 0.001aB 0.089 70.007aA
0.0767 0.003aB 0.0727 0.005aB 0.0747 0.002aB 0.088 7 0.008aA
Drying temp. (°C)
Hot air drying
Freeze drying Hot air drying
Freeze drying
Values represent means of triplicates7 standard deviations. Dissimilar small alphabets within the same row are significantly different (p o 0.05). Dissimilar capital alphabets within the column are significantly different (p o0.05). 1 2 3 4 5
Treatment: CON (Control without inoculation after irradiation). KSF (Fermented naturally without inoculation and irradiation). KMG (Inoculation of Leu. mesenteroides). KSG (Inoculation of Lb. sakei). KMSG (Inoculation of mixed Leu. mesenteroides and Lb. sakei).
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Table 3 L*, a* and b* value of kimchi powder manufactured by different hot air drying temperature and freeze drying. CON1
KSF2
KMG3
KSG4
KMSG5
55 60 65
L* value 47.75 7 0.09bB 46.84 7 0.33bB 43.75 7 0.21bC 54.58 7 0.32bA
53.84 7 0.13aB 52.117 0.12aB 49.677 0.17aC 60.977 0.14aA
47.137 0.08bB 46.23 7 0.42bB 44.617 0.09bC 55.277 0.60bB
47.85 7 0.81bB 47.92 7 0.33bAB 45.50 7 0.34bC 55.87 7 0.07bA
48.487 0.23bB 47.52 7 0.15bB 45.19 70.28bC 56.76 70.14bA
55 60 65
a* value 19.99 7 0.12bB 18.29 7 0.36bB 15.32 7 0.20bC 23.077 0.13bA
34.82 7 0.17aB 32.717 0.24aB 30.96 7 0.16aC 29.00 70.26aA
20.78 7 0.32bB 19.58 7 0.40bB 16.03 7 0.11bC 22.157 0.13bA
19.30 7 0.16bB 18.477 0.07bB 15.05 7 0.21bC 23.20 7 0.08bA
20.13 70.09bB 19.80 7 0.22bB 16.32 7 0.14bC 22.19 70.30bA
55 60 65
b* value 25.23 7 0.17bB 24.297 0.15bB 21.32 7 0.17bC 30.737 0.06bA
28.497 0.15aB 27.917 0.06aB 25.96 7 1.06aC 32.727 0.16aA
24.087 0.22bB 23.58 7 0.23bB 20.03 7 0.09bC 29.02 7 0.24bA
25.30 7 0.23bB 23.47 70.11bB 20.55 7 0.15bC 28.977 0.07bA
24.137 0.19bB 24.807 0.02bB 20.32 70.16bC 29.90 70.03bA
Drying Temp. (°C)
Hot air drying
Freeze drying Hot air drying
Freeze drying Hot air drying
Freeze drying
Values represent means of triplicates7 standard deviations. Dissimilar small alphabets within the same row are significantly different (p o 0.05). Dissimilar capital alphabets within the column are significantly different (p o0.05). 1 2 3 4 5
Treatment: CON (Control without inoculation after irradiation). KSF (Fermented naturally without inoculation and irradiation). KMG(Inoculation of Leu. mesenteroides). KSG (Inoculation of Lb. sakei). KMSG (Inoculation of mixed Leu. mesenteroides and Lb. sakei).
have been widely used to describe color changes during thermal processing of products. For the color, the L*, a* and b* values were significantly affected by the drying temperature and method (Table 3). The freeze-dried powder produced higher L* values than those dried with hot air. L* value represents the lightness of the sample, and a higher L* value shows a lighter color (Chung and Lee, 2015). This is probably due to hot air directly exposed on kimchi surface during the drying process. Among the hot air-dried, KSF had higher lightness compared to the other samples because L* of KSF without gamma (γ) irradiation before drying was already higher than other treatments. According to Lee et al. (2004), gamma-irradiation did not affect the lightness and the redness of red pepper powder. The Hunter a* value (redness) was higher in freeze-dried samples than those in hot air-dried samples, similar to the L* value. The browning, which was higher in hot air-dried samples, may be responsible for this. The reduction of redness was higher at higher drying temperatures (Chung and Lee, 2015). The Hunter a* values of these samples decreased severely due to the destruction of red pigments such as carotenoids, which included capsaicin, βcarotene, cryptoxanthin (Nieto-Sandoval et al., 1999; Cheigh, 2004). Hunter b* values (yellowness) were higher in freeze-dried
samples than those in dried with hot air, which might cause browning. Yellowness showed a slight decrease in its value as temperature increased as a result of generation of brown products due to non-enzymatic reaction. These results are in agreement with Keawpeng et al. (2007). Also, among hot air-dried samples, L*, a* and b* values of kimchi powder dried at 55 °C and 60 °C were not significantly different. Therefore, in case of kimchi powder manufactured by hot air drying, it is efficient to dry at 55 °C to establish the cost effective commercial process. 3.4. Browning index The effects of different temperatures of hot air drying and freeze drying on the browning index of kimchi powder are shown in Table 4. Hot air-drying resulted in higher browning index than freeze-drying. Samples dried with hot air at 55 °C and 60 °C did not significantly differ. A higher degree of browning occurs during hot air drying at 65 °C. The highest browning index was found in the samples dried at 65 °C while freeze drying showed the lowest. During freeze-drying, there is no oxygen in the drying chamber which is the main cause of browning by the Maillard reaction and ascorbic acid oxidation (Lee et al., 2007). It may indicate that the freeze drying produced less of non-enzymatic browning reaction
Table 4 Browning index of kimchi powder manufactured by different hot air drying temperature and freeze drying. Drying Temp. (°C) Hot air drying
Freeze drying
55 60 65
CON1
KSF2
KMG3
KSG4
KMSG5
0.197 0.06aB 0.197 0.05aB 0.277 0.08aA 0.157 0.01aC
0.20 70.06aB 0.19 70.03aB 0.28 70.03aA 0.15 70.03aC
0.20 70.01aB 0.19 70.01aB 0.25 70.01aA 0.14 70.04aC
0.21 70.07aB 0.22 70.04aB 0.28 70.02aA 0.14 70.08aC
0.22 7 0.07aB 0.22 7 0.08aB 0.29 7 0.02aA 0.157 0.02aC
Values represent means of triplicates7 standard deviations. Dissimilar small alphabets within the same row are significantly different (p o 0.05). Dissimilar capital alphabets within the column are significantly different (p o0.05). 1 2 3 4 5
Treatment: CON (Control without inoculation after irradiation). KSF (Fermented naturally without inoculation and irradiation). KMG (Inoculation of Leu. mesenteroides). KSG (Inoculation of Lb. sakei). KMSG (Inoculation of mixed Leu. mesenteroides and Lb. sakei).
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Table 5 Sensory evaluation of kimchi powder manufactured by hot air drying at 60 °C and freeze drying. CON1
KSF2
KMG3
KSG4
KMSG5
Hot air drying at 60 °C Color Flavor Texture Taste Overall acceptability
5.40 7 0.92a 5.10 7 1.14a 5.60 7 0.52a 5.00 7 0.72b 4.53 7 1.46b
5.30 7 0.78a 4.90 7 1.30a 5.50 7 0.71a 5.737 1.18a 5.84 7 1.01a
5.90 7 1.38a 5.30 7 1.19a 5.50 7 0.85a 5.83 7 1.22a 5.87 7 0.97a
5.60 7 1.11a 5.007 1.00a 5.80 7 0.63a 5.447 0.97b 4.737 1.49b
5.50 7 1.12a 5.20 7 0.60a 5.30 7 0.82a 5.22 7 1.14b 4.93 7 1.25b
Freeze drying Color Flavor Texture Taste Overall acceptability
5.00 7 0.67a 5.20 7 0.78a 5.60 7 0.50a 4.63 7 0.87b 5.12 7 0.72c
5.32 7 0.51a 5.30 7 1.19a 5.50 7 0.71a 6.687 0.97a 6.717 1.22a
5.337 0.87a 5.30 7 0.62a 5.80 7 0.63a 6.677 0.51a 6.687 0.89a
5.247 1.70a 5.007 1.01a 5.40 7 0.97a 5.89 7 0.68ab 5.93 7 1.01b
5.43 7 0.87a 5.107 1.14a 5.707 1.49a 5.80 7 0.72ab 5.677 1.10b
Values represent means of triplicates7 standard deviations. Dissimilar small alphabets within the same row are significantly different (p o 0.05). 1 2 3 4 5
Treatment: CON (Control without inoculation after irradiation). KSF (Fermented naturally without inoculation and irradiation). KMG (Inoculation of Leu. mesenteroides). KSG (Inoculation of Lb. sakei). KMSG (Inoculation of mixed Leu. mesenteroides and Lb. sakei).
in kimchi powder samples during drying. It is expected that the browning reactions would be minimized by a low temperature freeze drying process. These results are in agreement with the findings of Kim et al. (2007) and Son and Lee (2011). Additionally, Ko et al. (1999) showed similar results with shiitake mushrooms and Kim et al. (1982) with red peppers. 3.5. Sensory evaluation The results of sensory evaluation of kimchi powder manufactured by hot air drying at 60 °C and freeze drying are shown in Table 5. The color, flavor, texture, taste and overall acceptance of kimchi powder were evaluated by trained panelists. There is no significant difference in color, flavor and texture among the fivesamples by hot air drying. The taste and overall acceptance score were higher in kimchi powder manufactured using KSF and KMG than other kimchi powders. Also, results of sensory evaluation of kimchi powder manufactured by freeze drying are in agreement with the results above. Overall acceptability score was higher in kimchi powder manufactured by using freeze drying than hot air drying. The reason might be the less browning reaction that occurred during freeze drying. The similar results were reported by Hu et al. (2013) on hairtail fish meat gel. Consequently, when Leu. mesenteroides is used as the starter, it was similar to sensory evaluation of kimchi powder manufactured by natural fermentation.
4. Conclusion Kimchi powder was manufactured by hot air drying with different temperatures of 55 °C, 60 °C and 66 °C, and freeze drying. Moisture content reached about 10% after the drying process. The result indicated that the WAI, WSI, and L*, a* and b* values of freeze dried powder was higher than those of the hot air dried kimchi powder. The freeze drying showed the lowest browning index compared to hot air drying. In addition, the kimchi powder prepared by freeze dryer clearly received higher scores for overall acceptance than samples prepared by hot air dryer on sensory evaluation. On the basis of the results of this study, it is concluded that the freeze drying method is the most suitable drying method to produce high quality kimchi powder compared to hot air drying.
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