Ingredient and Salinity Variations in Doenjang Stews Sold in a College Town and Consumer Acceptance of Doenjang Stews among Korean College Students.

This study determined the ingredient and salinity variations in Doenjang stew sold near a college campus and determined its consumer acceptance with varying salinity levels. Doenjang stews from four restaurants near a college campus were collected around lunchtime for 3 days. The salinity and weight of each ingredient included in Doenjang stews were recorded. Consumer acceptance testing on the stews was also conducted (n=98). Overall, variations in Doenjang stew recipes, including salinity values and the weight of each ingredient, between and within restaurants were also observed (P<0.05). The salinity of Doenjang stews collected from different restaurants ranged between 1.2% and 1.7%, higher than that recommended by the Korean government. Doenjang stew with a salinity of greater than 1.3% was most liked by consumers, whereas a salinity of 1.2% was least liked. At the same salinity value, a high stock amount of Doenjang stew was preferred to a greater extent than that with a high number of ingredients in Doenjang stew, suggesting that various ingredients included in the recipe do not necessarily increase consumer acceptance of stew.

INTRODUCTION

Doenjang is one of the three most accepted soybean fermented food ingredients in Korea as part of the Korean cuisine, in addition to soy sauce and red pepper paste (Sun and Baek, 2008). It is typically sold as a paste and applied to a soup or stew as part of the recipe. The typical consumption scenario of Doenjang is either soup or stew in Korean cuisine (Paek et al., 2016; Chon and Kim, 2020). One difference between soup and stew is how it is served in a meal: soups in Korean cuisine can be served as one of the main dishes, whereas the stew is typically served as a side dish. Another difference is the concentration of Doenjang paste in water: soup requires a small amount of Doenjang paste, implying a watery mouthfeel, whereas stew exhibits a thicker texture. Although a standard recipe for Doenjang stew is available, it is not followed by cooks in each household and restaurant, meaning that recipes’ variations are widely applied based on different ingredients and types of stocks used for making stews. The standard Doenjang stew recipe includes Doenjang paste, green and red peppers, onions, dried mushroom, and red pepper seasoning (Kye et al., 1995). Different ingredients have been used in different studies: for example, Kim and Han (2008) used beef, mushrooms, green onions, ginger, and red peppers in boiling water; Joo and Shin (2005) used dried anchovies, garlic, red pepper powder, and green onions; Jeon et al. (2020) used beef stock, green onion powder, and garlic powder. Ingredient variations were reported in peer-reviewed journal papers, and considerable variations were observed in commercial restaurant recipes. According to different studies, variations are not limited to ingredients included in the recipes but the concentration of Doenjang pastes included in the Doenjang stew.

Sodium consumption among the Korean population is relatively high because its cuisine heavily depends on fermented foods, exhibiting a high salt content. As reported in the nutritional components data by Korean restaurants, the sodium content of Doenjang stew is ∼2,021 mg based on one serving size (400 g), corresponding to 1.26% salinity (Korea Food and Drug Administration, 2012). The Korean government recommends a salinity of less than 0.8% for soups and stews. However, Kim et al. (2009) reported that typically consumed soups and stews in restaurants exhibit considerably high salinity levels. A previous study reports that Doenjang soups collected from commercial restaurants indicate a salinity of ∼0.9% higher than the government recommendation of 0.8% (Lee and Song, 2009). Additionally, previous studies found that the saltiness of stew soup was high in the order of restaurants, home meals, and school meals (Park et al., 2020). In a similar study, the sodium content of Doenjang stew was higher in restaurants than in-home meals and food services (Jiang and Lee, 2017). Another study on Doenjang stew reported that consumers preferred Doenjang stew with a salinity of 1.4%, whereas the government recommended a salinity value of about 1.26% for Doenjang stew (Chon and Kim, 2020). Therefore, this indicates a gap between consumer preference and government recommendation. Chon and Kim (2020) showed that the salinity of Doenjang stew may vary as the concentration of Doenjang varies. There is a growing trend of research on low-salt Doenjang to lower the salinity of foods using Doenjang, such as Doenjang stew (Kang et al., 2016; Boo et al., 2017; Kim et al., 2017; Choi et al., 2018).

Variations in food ingredients within a restaurant are challenges of soup and stew foods, which is a limitation for developing strategies to reduce sodium in these food categories. To our knowledge, ingredient variations in soup- and stew-type foods have not been intensively investigated. Therefore, the objective of this study is two-fold: 1) to determine the ingredient and salinity variations in Doenjang stew sold near a college campus; and 2) to determine consumer acceptance of Doenjang with varying salinity levels among college students.

MATERIALS AND METHODS

Collection of Doenjang stew from restaurants near a college

Doenjang stew was purchased from four restaurants near the Jeonbuk National University-Jeonju campus. The restaurants were selected based on convenience, frequency of student visits, and restaurant location, with purchases made during lunchtime within a 1-h period. Upon collection, Doenjang stew was sifted, and the ingredients of Doenjang stew from different restaurants were collected. Additionally, Doenjang stews were collected on three different days from the restaurants to determine daily variations within a restaurant.

Ingredient variation and salinity of Doenjang stews

After collection, the recipe variation was monitored by weighing each ingredient in the stew and standardizing by the weight of the ingredient divided by one serving size. Ingredient weight was reported as gram per 100 mL of the stew. The total weight of one serving size, ingredients (g), and stock (mL) per serving size were measured accordingly. The stock-to-ingredient ratio was then calculated by the volume of stock (mL) divided by the total weight of the ingredient (g). In addition to the ingredient characteristics, the salinity (%) of Doenjang stew was analyzed according to Mohr’s method. Briefly, Doenjang stew was sifted through a sieve, followed by filter paper filtration (F1093-150, CHM GROUP, Barcelona, Spain). Salinity was then measured by titrating with 0.1 N AgNO3, and 1 mL of 2% K2CrO4 was used as a titrate indicator. The salinity of Doenjang stew was measured in triplicates for all 3 days.

Consumer acceptance testing

Consumer acceptance testing was conducted following the standard practice for such testing. Twenty servings of Doenjang stew were purchased from each restaurant 1 h before testing; therefore, a fresh batch of Doenjang stew from each restaurant was served to consumers. Then, all 20 servings were poured into a pot and mixed thoroughly to minimize the ingredient variation within the restaurant. Once mixed, Doenjang stew samples were kept at 60°C in a closed lid until consumer testing was performed. Then, 40 mL of Doenjang stew samples were served to participants in a 75-mL white plastic disposable cup labeled with a random three-digit code. All samples were served with white rice. The stew ingredients were evenly distributed in each cup. Samples were monadically presented to the participants, and the order of presentation was randomized and balanced using a Latin-square design.

Participants for consumer acceptance testing were mainly students from the Jeonbuk National University-Jeonju campus, which were recruited by placing flyers, social network service posting, and text messages to the consumer database. Before testing, participants were asked to answer demographic-related questionnaires and evaluate appearance characteristics. Next, participants were asked to taste Doenjang stew and evaluate their likes and dislikes of the samples, including overall liking and liking attributes, including flavor, mouthfeel, salty taste, sweet taste, and umami taste liking, on a 9-point hedonic scale (1=extremely dislike, 5=being neither like or dislike, and 9=extremely like). Open-ended questions were included to capture the consumers’ raw language on their likes. A paper ballot was used to collect data. After completing the consumer test survey, participants were compensated with a snack. The study protocol was approved by the Institutional Review Board of the Jeonbuk National University (approval no. JBNU 2020-08-007). The written informed consents were obtained from all participants.

Statistical analysis

Data analysis was conducted using XLSTAT (v.2020, Addinsoft, Paris, France). One-way analysis of variance was done using Duncan’s multiple range test to determine the differences between samples at the α=0.05 level.

RESULTS AND DISCUSSION

Salinity of Doenjang stews collected from different restaurants

Table 1 lists the salinity of Doenjang stews collected from different restaurants on three different days. The saltiness of the stew samples ranged from 1.2% to 1.7%, with values of 1.2% for DS1, 1.7% for DS2, 1.3% for DS3, and 1.3% for DS4 (DS means Doenjang stew). The salinity values for Doenjang stew range from 0.74% to 1.3% within the previously reported ranges (Song and Lee, 2008; Lee and Song, 2009; Kim et al., 2012). The values for Doenjang stews collected from the four restaurants were slightly greater than that recommended by the Korea Food and Drug Administration (0.8% salinity for stews). The saltiness of DS2 was greater than those of the other samples, and the salinity of DS1 was the lowest (P<0.05). Presumably, this could be related to the different addition amounts of Doenjang paste in the stews during preparation in each restaurant.

Table 1

Salinity of Doenjang stews (DSs) collected from different restaurants

	DS1	DS2	DS3	DS4
Salinity (%)	1.2±0.2b	1.7±0.2a	1.3±0.1b	1.3±0.1b

Data are presented as mean±SD of triplicate analyses.

Numbers in a row with different letters (a,b) represent significant differences (P<0.05).

Daily salinity variations in Doenjang stews collected on different days were also monitored (Fig. 1), with significant differences in the salinity of the stew within a restaurant observed in DS1, DS2, and DS4 (P<0.05). Ranges of salinity values obtained for each restaurant were as follows: 1.0∼1.3% in DS1; 1.6∼1.9% in DS2; 1.1∼1.4% in DS3; 1.2∼1.4% in DS4. As shown in Table 1, the average salinity value of DS2 was at its highest, whereas the daily variation in salinity value was highest in the DS1 and DS2 samples. This result revealed a significant variation in the salinity of Doenjang stew within restaurants. This variation may be attributed to the: 1) different concentrations of Doenjang paste addition to Doenjang stew and 2) different Doenjang pastes added in the stew, as different salinity values were reported in Doenjang paste according to the manufacturing method (Kim and Lee, 2014). Regardless, the salinity of Doenjang stew collected from each restaurant varies on different days and between restaurants.

Fig. 1

Day-to-day salinity variation in Doenjang stews (DSs) collected from the different restaurants. Numbers with different letters (a-c) within samples represent significant differences (P<0.05).

Ingredient variation in Doenjang stews collected from different restaurants

Table 2 lists ingredient characteristics of Doenjang stews collected from different restaurants. DS3 exhibited the most diverse ingredients, whereas DS4 exhibited the least diverse ingredients. DS1 contained five ingredients: mushroom, tofu, green onion, young squash, and clams. DS2 also contained five ingredients: potato, tofu, green onion, onion, and young squash; DS3 contained eight ingredients: mushroom, potato, tofu, green onion, onion, young squash, green pepper, red pepper, and clams; DS4 comprised four ingredients: tofu, green onion, onion, and young squash. All DS samples contained three similar ingredients: tofu, green onion, and young squash. Green onion was exclusively found in DS3. Among all ingredients, tofu accounted for the heaviest (by weight) ingredient in all DS samples.

Table 2

Ingredient characteristics of Doenjang stews (DSs) collected from different restaurants

Characteristic	DS1	DS2	DS3	DS4
Mushroom (g/100 g)	4.7±1.0b	0c	8.1±1.1a	0c
Potato (g/100 g)	0b	6.3±1.0a	0b	0b
Tofu (g/100 g)	23.5±5.03a	11.3±1.3bc	11.1±1.1c	16.5±1.6b
Green onion (g/100 g)	3.4±1.4b	2.8±1.1b	7.0±2.9a	3.4±2.1b
Onion (g/100 g)	0b	6.7±1.0a	6.8±3.1a	6.0±0.8a
Young squash (g/100 g)	9.6±1.8ab	10.8±1.79a	5.8±2.9bc	4.8±1.2c
Green onion (g/100 g)	0b	0b	8.2±3.2a	0b
Clam (g/100 g)	1.5±0.5b	0c	2.5±0.9a	0c
Total weight (g)	330.0±23.0c	432.4±31.9bc	516.5±41.2b	791.4±94.9a
Total stock (mL)	173.3±20.8b	226.7±28.4b	251.7±42.5b	490.0±78.1a
Total ingredient (g)	170.9±13.2b	210.6±31.3b	298.1±31.8a	305.9±25.2a
Stock-to-ingredient ratio	1.0±0.2b	1.1±0.2b	0.8±0.1b	1.6±0.2a

Data are presented as mean±SD of triplicate analyses.

Numbers in a row with different letters (a-c) represent significant differences (P<0.05).

Differences in the total weight of one serving size were observed among four samples. DS4 exhibited the highest weight of 791.4 g, whereas DS1 exhibited the lowest amount (330.0 g) per serving size, exhibiting a significant difference (P<0.05). The weights of one serving size in DS2 and DS3 were 432.4 g and 516.5 g, respectively. The stock-to-ingredient ratios of DS1, DS2, and DS3 were 1.0, 1.1, and 0.8, respectively, whereas DS4 was 1.6, significantly greater than those of the other samples (P<0.05). Considering that the weight of one serving size of DS4 was the highest, the majority accounted for DS4, possibly attributed to the stock weight rather than the ingredients. The stock-to-ingredient ratio of DS3 was 0.8, which was the lowest (P<0.05). Notably, DS3 contained the most diverse ingredients in the recipe; therefore, this factor possibly affects the low stock-to-ingredient ratio of DS3.

As expected from salinity variations, daily variations in ingredients were observed. Tofu, young squash, and green onion were included in all samples. For DS1 samples, the deviation of tofu was highest (59.7∼86.8; data not shown). In addition, the weight of tofu was the highest compared to the weight of other ingredients. The amount of young squash in DS2 was the highest compared to other samples (47.0 g). In the case of DS3, the most diverse ingredients were included in this sample than others. Red pepper that was excluded from other samples was included in DS3. The standard deviation of the amount of onion in DS3 was significantly high (21.9∼58.5; data not shown). However, unlike DS3, DS4 had the least number of ingredients. In DS4, the average weight of tofu, young squash, and onion excluding green onions was the largest compared to other samples.

The result indicates that cooks and chefs working in the restaurant does not follow the fixed recipe. Another possibility is that Doenjang stew was made in a large pot ahead of time, and ingredients were unevenly scooped out for one serving size. The difference between restaurant- and home-made Doenjang stews is that restaurants cook in a large pot for multiple servings, whereas only one or two serving sizes are typically prepared at home. Regardless, ingredient variations, such as types of ingredients included in different restaurants, types, and numbers of ingredients used within a restaurant, were observed in all Doenjang stew samples in this study.

Consumer acceptance testing results

Table 3 lists the results from the consumer acceptance testing of the four Doenjang stew samples. As participants were recruited from a college town, most were college students in their 20s (96.8%), with a monthly income of less than $1,000 (88.0%). In addition, participants were frequent Doenjang consumers; that is, ∼89% of the participants consumed Doenjang either at home or in a restaurant at least once every 2 to 3 months.

Table 3

Consumer acceptance testing for four different Doenjang stews (DSs; N=79)

Consumer acceptance	DS1	DS2	DS3	DS4
Appearance liking	5.7±1.4a	5.3±1.5ab	5.2±1.9b	5.5±1.5ab
Color liking	5.8±1.4a	5.3±1.6a	5.4±1.8a	5.5±1.6a
Overall liking	5.2±2.1b	5.7±2.0ab	5.3±2.0ab	5.8±1.7a
Flavor liking	5.2±1.7a	5.6±1.4a	5.4±1.7a	5.4±1.5a
Mouthfeel liking	5.7±1.5a	5.7±1.3a	5.4±1.5a	5.7±1.4a
Salty taste liking	5.2±1.6ab	5.4±1.7ab	4.9±1.9b	5.7±1.6a
Sweet taste liking	5.4±1.4a	5.5±1.3a	5.2±1.5a	5.6±1.5a
Umami taste liking	5.4±1.6a	5.6±1.6a	5.5±1.7a	5.7±1.6a

Liking attributes were rated on a 9-point hedonic scale with 1=dislike extremely and 9=like extremely.

Data are presented as mean±SD of 79 consumers.

Numbers in a row with different letters (a,b) represent significant differences (P<0.05).

Differences in several liking attributes, such as appearance, overall, and salty taste liking, were observed between samples (P<0.05). The appearance liking of DS3 was significantly less than that of DS1 (P<0.05), whereas significant differences were not observed between other samples (DS2 and DS4; P>0.05). DS4 exhibited the highest overall liking score (5.8), which was significantly greater than that of DS1 (P<0.05). Similar to the overall liking, DS4 exhibited the highest salty taste liking. Notably, the salty taste liking of DS4 was significantly greater than that of DS3 (P<0.05). Simultaneously, the salinity values of DS3 and DS4 were the same (1.3%), which is similar to those reported previously for the salinity of Doenjang stew that appeals to Korean consumers (Chon and Kim, 2020). Differences between DS3 and DS4 were observed in terms of the stock-to-ingredient ratio (Table 2) due to DS3 exhibiting the lowest stock-to-ingredient ratio (0.8). In contrast, DS4 showed the highest value (1.6), indicating that more ingredients were present in the recipe of DS3, and more stock was present in the recipe of DS4. Based on the consumer acceptance testing results, the consumer liking of Doenjang stew may not originate from the ingredients included in the recipe. Instead, compared with ingredients in Doenjang stew, more stock in Doenjang stew possibly affected the higher overall liking and salty taste liking with the same salinity of Doenjang stew. The low salty taste liking of DS3 can possibly be attributed to the presence of a spicy ingredient based on consumer responses collected from open-ended questions (data not shown). Of the total participants, 62.9% responded that DS3 was “too salty” and that the “DS3 sample was too spicy (22%)”, suggesting that the presence of a “spicy” ingredient in DS3 is falsely induce a high salty taste intensity in DS3, influencing the lower salty taste liking of DS3. Respondents thought the DS3 sample was spicy due to garlic or green onions added to the broth. Alternatively, it is not shown in the table, but red pepper powder may have been added to the stock of DS3.

This study monitored ingredient and salinity variations in Doenjang stew sold near the college campus, and the salinity of Doenjang stew appealing to college students was estimated. Based on this study, the salinity (%) of Doenjang stews collected from four restaurants on different days ranged from 1.2% to 1.7%, greater than the Korean government recommended (0.8%). Ingredient variations within restaurants were observed (P<0.05), showing significant differences in ingredient types and amounts as observed between restaurants, suggesting that the standard recipe for Doenjang stew is not followed in practice. The salinity of greater than 1.3% for Doenjang stew was most liked, whereas consumers least liked that of 1.2%. At the same salinity value (1.3%), a high amount of stock in the Doenjang stew recipe was preferred to a greater extent than a higher number of ingredients, suggesting that various ingredients included in the recipe do not necessarily increase consumer acceptance of Doenjang stew. The limitation of this study was the number of Doenjang stews included in this study, as Doenjang stews collected from four different restaurants near one campus town may not represent the Doenjang stews served in the Korean market. Future studies may require more Doenjang stew samples collected from different restaurants located in representative locations in Korea. Additionally, consumer acceptance testing with greater numbers of participants may be needed. Therefore, this can be conducted in a future study.