Abstract
This study aimed to develop texture-modified Dongchimi (TMD) that is safe, well-shaped, and easy to chew and swallow. As the fermentation proceeded, the pH decreased, and the total acidity and total number of lactic acid bacteria increased. The hardness of the TMD decreased significantly by more than 96% (p < 0.05) as compared to that of the control. Significant differences in the hardness and shape were observed between two TMD samples—TMD 1 and TMD 2. Sensory evaluation showed that TMD 1 and TMD 2 were adequate for the elderly people suffering from difficulties in mastication and deglutition. Compared to TMD 1, TMD 2 showed higher values of hardness and swallowness and was more preferred by the elderly. Thus, TMD that is easy to chew and swallow has sufficient competitiveness in food safety, food taste, and food preference.
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Keywords: Dongchimi, Texture modified, Hardness, Sensory evaluation, Elderly people
Introduction
The ageing process is accompanied by many physiological changes such as decreased sensory response and salivary flow, loss of teeth, and poor muscle strength, which lead to degradation of masticatory performance and difficultly in swallowing food (Laguna et al., 2015; Ship, 1999). The elderly population is exposed to various health risks due to inadequate nutrient intake, and poor masticatory or swallowing ability affects their choice of food (Moon and Kong, 2009; Morleyn, 1997). Foods for the elderly people often contain gelling agents for product stability; these agents improve texture by increasing viscosity (thickening), water retention, firmness, and smoothness (Hayakawa et al., 2014; Morris et al., 1999). Texture-modified foods are aimed to deform the food structure and to reduce the need to chew (Penman and Thomson, 1998). Texture-modified foods and thickening of fluid forms have been routinely employed to assess, improve masticatory performance, and resolve swallowing problems (Langmore and Miller 1994; Pardoe, 1993). The elderly people who consume such texture-modified foods gained weight, and their nutritional status was improved (Germain et al., 2006).
Dongchimi, a type of kimchi is prepared fermenting radish and a variety of vegetables in 2–4% saltwater with approximately twice the volume of its vegetative ingredients (Jeong et al., 2013). Radish, the main ingredient of Dongchimi, is a very hard material and difficult for the elderly people to chew and swallow. Therefore, it is necessary to develop a texture-modified Dongchimi that is suitable for the elderly people.
Therefore, the purpose of this research was to developed texture-modified Dongchimi by the elderly people, with the aim of fulfilling the needs of people with impaired chewing and/or swallowing ability.
Materials and methods
Materials
Radish, garlic, ginger, pear, chili pepper, and green onion were purchased from a commercial market in Seoul on the day of preparation. Salt (Sajo Haepyo, Seoul, Korea) was purchased from a local market (Seongnam, Korea). Gelatin was purchased from the Gelltec (Busan, Korea); xanthan gum was purchased from the Eden Town F&B (Incheon, Korea), and carrageenan was purchased from Esfood Company (Pocheon, Korea).
Preparation of Dongchimi and texture-modified Dongchimi
Dongchimi was prepared by slightly modifying a previously reported method (Noh et al., 2008). Cubes (20 × 20 × 15 mm) were cut out from the center portion of the radish. Other ingredients were rinsed and chopped, and then mixed with brine solution (2.3 ± 0.1% salt). A total of 100 g of radish was mixed well with 1 g garlic, 0.5 g ginger, 8.9 g pear, 3 g green onion, and 1 g chili pepper and then packed in a plastic container.
For the preparation of texture-modified Dongchimi, radish was ground in Blixer-5plus (R-5 plus, robot coupe, Japan) for 2 min. Next, 500 g of the ground radish was mixed with gelling agents (based on ground radish; TMD 1: 4% gelatin; TMD 2: 4% gelatin, 0.5% xanthan gum, 0.5% carrageenan), stirred at 500 rpm for 30 min, stored at 4 °C overnight, and cut into 20 × 20 × 15 mm cubes. The preparation of texture-modified Dongchimi followed the aforementioned procedure for Dongchimi. After fermentation for 24 h at 20 °C, all samples were stored for 20 days at 4 °C until further analysis.
pH, acidity, and lactic acid bacteria
The Dongchimi samples were collected from each 100 g of stored Dongchimi and TMD (including radish and liquid), homogenized in a homogenizer (T 25-ULTRA TURRAX, Staufen, Germany), and filtered through gauze to obtain the filtrate. The filtrate was centrifuged at 6000 rpm for 1 min (Eppendorf 5810 R, Hamburg, Germany), and the supernatant was used for further analysis. The pH was measured using a pH meter (827 pH lab, Metrohm, Switzerland).
For measuring acidity as per the Association of Official Analytical Chemists method (AOAC, 2000), 0.1 N NaOH was used to adjust the pH of 10 mL Dongchimi sample to 8.3. The lactic acid content (%) of this solution was measured and recorded as the titratable acidity. Each experiment was conducted in triplicate for obtaining mean and standard deviations.
To measure the number of lactic acid bacteria, 10 g of the Dongchimi sample was mixed with 90 mL of 0.85% sterilized peptone water and homogenized on a Stomacher 400 Circulator system (Seward, Inc., London, England) at 230 rpm for 1 min. The total number of lactic acid bacteria was determined by spread-plating onto the MRS agar after incubation at 37 °C for 48 h.
Texture measurement
The texture of Dongchimi was measured using a texture analyzer (TA. XT plus; Stable Micro Systems Ltd, London, England) equipped with a 490 N load cell. All analyses were carried out using Texture Exponent software version 6.1.7.0. (Stable Micro systems Ltd.). The hardness of the samples (20 × 20 × 15 mm) was measured using a 10 mm cylinder probe (instrument settings: mode, measure force in compression, pre-test speed, 1.0 mm/s; test speed, 2.0 mm/s; post-test speed, 10.0 mm/s; strain, 70%; trigger force, 0.049 N).
Sensory and preference test
One hundred twenty-five elderly subjects from local communities in Gwangjin-gu, Seoul, who were over 65 years old, participated in the sensory and preference tests. Fermented control and TMD samples were provided in the pH range 3.9–4.2, which is the optimal range for maturity (Cho et al., 2015). The 8-day fermented Dongchimi and 12-day fermented texture-modified Dongchimi at 4 °C were used for the sensory and preference tests. The sensory properties were evaluated in terms of intactness, moldy odor, sour taste, hardness, crispness, and swallowness on a 9-point hedonic scale (1: very weak, 9: very strong). The participants took the preference test of appearance, aroma, taste, texture and overall acceptability using a 5-point hedonic scale (1: Extremely dislike, 5: Extremely like). The Institutional Review Board (IRB) of the Chungnam National University Hospital approved all procedures for this study (CNUH 2014-09-021, period: 5 years).
Statistical analysis
Data from three parallel measurements were expressed as mean ± SD. All data were analyzed by one-way analyses of variance using the SPSS program (SPSS Version 12.0, SPSS Inc., Chicago, IL, USA). The significant means were compared by Duncan’s multiple range tests (p < 0.05).
Results and discussion
pH, acidity, lactic acid bacteria, and hardness
The changes in pH, acidity, lactic acid bacteria, and hardness of the Dongchimi and texture-modified Dongchimi during fermentation are shown in Table 1. With an increase in the fermentation time (0 to 20 days), the pH of all the samples decreased (p < 0.05). The optimal pH 3.9–4.2 was reached on day 8 for Dongchimi and on day 12 for texture-modified Dongchimi. On the 20 days of storage, a lower pH of 3.72–4.00 was observed, indicating significant difference between control and the treated groups.
Table 1.
Changes in pH, acidity and lactic acid bacterica of Dongchimi during fermentation at 4 °C
| Days | Dongchimi1) | TMD 11) | TMD 21) |
|---|---|---|---|
| pH | |||
| 0 | 6.16 ± 0.01a2)A3) | 5.58 ± 0.02aB | 5.58 ± 0.01aB |
| 1 | 4.67 ± 0.01bC | 5.13 ± 0.01bA | 4.95 ± 0.01bB |
| 4 | 4.15 ± 0.00cB | 4.50 ± 0.02cA | 4.46 ± 0.01cA |
| 8 | 3.93 ± 0.01dC | 4.29 ± 0.01dA | 4.22 ± 0.00 dB |
| 12 | 3.85 ± 0.00eB | 4.15 ± 0.00eA | 4.13 ± 0.00eA |
| 20 | 3.72 ± 0.00fB | 3.99 ± 0.00fA | 4.00 ± 0.01fA |
| Acidity (lactic acid%) | |||
| 0 | 0.07 ± 0.01fB | 0.07 ± 0.01fAB | 0.09 ± 0.00fA |
| 1 | 0.14 ± 0.00eA | 0.11 ± 0.00eB | 0.15 ± 0.00eA |
| 4 | 0.24 ± 0.00dA | 0.22 ± 0.01 dB | 0.25 ± 0.00dA |
| 8 | 0.33 ± 0.01cA | 0.31 ± 0.01cA | 0.33 ± 0.01cA |
| 12 | 0.39 ± 0.01bA | 0.37 ± 0.03bA | 0.41 ± 0.01bA |
| 20 | 0.50 ± 0.04aA | 0.48 ± 0.03aA | 0.51 ± 0.04aA |
| Lactic acid bacteria (log CFU/mL) | |||
| 0 | 4.19 ± 0.26cA | 4.78 ± 0.34dA | 4.69 ± 0.06dA |
| 1 | 7.43 ± 0.07bA | 7.49 ± 0.27bcA | 7.81 ± 0.22bcA |
| 4 | 8.23 ± 0.02aA | 7.96 ± 0.31bcA | 8.42 ± 0.07aA |
| 8 | 8.24 ± 0.17aAB | 8.07 ± 0.09abB | 8.44 ± 0.00aA |
| 12 | 8.34 ± 0.05aA | 8.17 ± 0.24aA | 8.28 ± 0.11bA |
| 20 | 8.04 ± 0.08aA | 7.39 ± 0.12cB | 7.58 ± 0.17cB |
| Hardness (N/m2) | |||
| 0 | 1.54 × 106 ± 1.18 × 105bA | 2.63 × 104 ± 1.05 × 103aB | 5.58 × 104 ± 8.51 × 102aB |
| 1 | 1.82 × 106 ± 1.89 × 105abA | 2.38 × 104 ± 5.80 × 101bB | 5.00 × 104 ± 7.03 × 102bB |
| 4 | 1.92 × 106 ± 2.89 × 105abA | 2.12 × 104 ± 1.07 × 103bcB | 4.41 × 104 ± 1.26 × 103cB |
| 8 | 1.95 × 106 ± 2.28 × 105aA | 1.99 × 104 ± 5.81 × 102cB | 4.28 × 104 ± 1.68 × 103cB |
| 12 | 1.85 × 106 ± 2.04 × 105abA | 1.96 × 104 ± 1.02 × 103cB | 3.61 × 104 ± 1.67 × 103dB |
| 20 | 1.76 × 106 ± 3.00 × 105abA | 1.45 × 104 ± 8.59 × 102dB | 3.28 × 104 ± 4.05 × 103dB |
1)Dongchimi; TMD 1, texture-modified Dongchimi containing 4% of gelatin; TMD 2, texture-modified Dongchimi containing 4% of gelatin, 0.5% of xanthan gum and carrageenan
2)a–fMeans within the same column with different letters are significantly different at p < 0.05 by Duncan’s multiple range tests
3)A–CMeans within the same row with different letters are significantly different at p < 0.05 by Duncan’s multiple range tests
The acidity of all the samples increased during fermentation. Acidity can be significantly affected by microorganisms, sugar content, salt concentration, and temperature (You et al., 2017). Considering the fermentation aspect, the acidity of TMD 1 and TMD 2 liquids was similar to that of the Dongchimi liquid (control). Therefore, the texture-modified Dongchimi could be substituted by Dongchimi.
The initial lactic acid bacteria count was 4.19 log CFU/mL (Dongchimi), 4.69 log CFU/mL (TMD 1), and 4.78 log CFU/mL (TMD 2). The total number of lactic acid bacteria increased after fermentation for 12 days (8.34 log CFU/mL for the control, 8.28 log CFU/mL for TMD 1, and 7.96 log CFU/mL for TMD 2) and then slightly decreased until 20 days. However, the samples showed no significant differences (p < 0.05). A similar result has been reported (Noh et al., 2009): the lactic acid bacteria count decreased by the acid generated during fermentation after the bacteria grew to some extent in kimchi.
The hardness of Dongchimi increased until the optimum fermentation (8 days) but slowly decreased thereafter. The highest hardness was seen for Dongchimi (1.54 × 106 to 1.85 × 106 N/m2); the hardness values of TMD 1 and TMD 2 were the lowest, hardness of TMD 1 decreased significantly to above 98% (1.45 × 104–2.63 × 104 N/m2) and that of TMD 2 to above 96% (3.28 × 104–5.58 × 104 N/m2) (p < 0.05). Although the hardness of Dongchimi radish was considerably high, hindering its chewability for the elderly people, it significantly decreased upon the addition of a gelling agent. TMD 1 and TMD 2 were suitable for the elderly people with mastication and swallowing problems. Therefore, TMD 2 showed improved textural properties compared to the those of TMD 1. This result can be helpful in the development of easily chewable and swallowable foods for the elderly people who can chew and ingest foods. Although the shape of TMD 1 was maintained during fermentation, shape maintenance was improved by the addition of xanthan gum and carrageenan (TMD radish 2). Haug and Draget (2009) reported that a low concentration of gelatin, which has a very weak structure, may be responsible for the indistinct fracture point. Xanthan gum and carrageenan are commonly used together to enhance the texture properties of food gels (Nussinovitch, 1997).
Sensory and preference test
Changes in sensory attributes of Dongchimi and texture-modified Dongchimi during fermentation are shown in Table 2. The intactness was higher in TMD 2 (6.18) than that in TMD 1 (5.70) (p < 0.05). Texture-modified Dongchimi with xanthan gum and carrageenan showed intactness of the cubes. Moldy odor and sour taste were the highest for TMD 1, followed by TMD 2. Hardness was the lowest for TMD 1 (1.64) and TMD 2 (1.89). In contrast, swallowness was the highest for TMD 1 (7.52), followed by TMD 2 (6.97) (p < 0.05). Gelatin gels melt at a low temperature (in the mouth) and are slow-setting. In addition, the blending of different polysaccharides offers an alternative route for the development of new texture. Gelling agents affect the texture of food, causing differences in sensory properties (Saha and Bhattacharya, 2010), as observed in this research. TMD 2 showed improved sensory properties (intactness, moldy, and sour taste) as compared to TMD 1. The results indicated that texture-modified Dongchimi, which is easy to chew and swallow by the elderly people, can be used for the development of elderly friendly foods.
Table 2.
Sensory attributes (9-point intensity scale) of Dongchimi (n = 125)
| Samples1) | |||
|---|---|---|---|
| Dongchimi | TMD 1 | TMD 2 | |
| Intactness | 7.75 ± 0.87a2) | 5.70 ± 2.26c | 6.18 ± 2.01b |
| Moldy odor | 2.95 ± 2.13b | 3.87 ± 2.37a | 3.37 ± 2.16ab |
| Sour taste | 4.88 ± 1.72b | 5.52 ± 1.87a | 5.39 ± 2.15a |
| Hardness | 6.30 ± 1.72a | 1.64 ± 0.82b | 1.89 ± 1.20b |
| Swallowness | 5.95 ± 1.94c | 7.52 ± 1.78a | 6.97 ± 2.28b |
1)Dongchimi; TMD 1, texture-modified Dongchimi containing 4% of gelatin; TMD 2, texture-modified Dongchimi containing 4% of gelatin, 0.5% of xanthan gum and carrageenan
2)Means within the same row with different letters are significantly different at p < 0.05 by Duncan’s multiple range tests
Table 3 shows the results of the preference test for Dongchimi and texture-modified Dongchimi during fermentation. Appearance, aroma, taste, texture, and overall acceptability in the control were scored significantly higher than those in TMD 1 and TMD 2 (p < 0.05). However, TMD 2 showed better results for the preference test than those of TMD 1, indicating that it was more preferred by the elderly people. Moreover, hardness and swallowness values in Table 2 indicated that TMD 1 and TMD 2 showed higher sensory values than those of Dongchimi. Kaufmann et al. (2005) suggested that dysphagia patients and elderly people preferred xanthan gum because it has lower calories, high fiber content, lower carbohydrates, and better overall taste and appearance. The texture of Dongchimi was softened by the addition of the gelling agent, which could help the elderly people who have difficulty in mastication and deglutition. Therefore, this study provides paves a way for the development of easily chewable and swallowable foods for the elderly people.
Table 3.
Preference test [5-point facial hedonic scale (1: extremely dislike, 3: neither dislike nor like, 5: extremely like)] of Dongchimi (n = 125)
| Samples1) | |||
|---|---|---|---|
| Dongchimi | TMD 1 | TMD 2 | |
| Appearance | 4.09 ± 0.71a2) | 3.17 ± 1.25b | 3.31 ± 1.11b |
| Aroma | 3.79 ± 0.78a | 2.76 ± 1.03b | 2.97 ± 0.99b |
| Taste | 3.83 ± 0.90a | 2.37 ± 1.09b | 2.46 ± 1.21b |
| Texture | 3.58 ± 1.03a | 2.61 ± 1.16b | 2.74 ± 1.10b |
| Overall acceptability | 3.73 ± 0.86a | 2.52 ± 1.03b | 2.62 ± 0.98b |
1)Dongchimi; TMD 1, texture-modified Dongchimi 1 containing 4% of gelatin; TMD 2, texture-modified Dongchimi 2 containing 4% of gelatin, 0.5% of xanthan gum and carrageenan
2)Means within the same row with different letters are significantly different at p < 0.05 by Duncan’s multiple range tests
Electronic supplementary material
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Acknowledgements
This research was supported by the Chungnam National University Hospital and by Main Research Program (E0145100-05) of the Korea Food Research Institute (KFRI) funded by the Ministry of Science and ICT.
Footnotes
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