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. 2023 Jan 5;32(7):949–957. doi: 10.1007/s10068-022-01224-7

Physicochemical and sensory characteristics of commercially available rice-based Doenjang and their correlation to consumer acceptability for Korean young adults

Yongwoo Jo 1, JungJae Lee 1, Mina K Kim 1,2,✉
PMCID: PMC10130271  PMID: 37123067

Abstract

There is an increased demand for rice doenjang by consumers who are allergic to beans as well as for those seeking diverse flavors. The objective of this study was to characterize the physicochemical and sensory characteristics of commercially available rice-based doenjang in Korea and to identify the perception of Korean consumers about rice-based doenjang. Rice doenjang exhibited a lower pH, acid value, and an NH3–N content, as well as a higher total sugar, reducing sugar, and alcohol content than soybean doenjang. Descriptive analysis results revealed that rice doenjang made in Korea has similar aroma characteristics as in miso, such as Katsuobushi aromatic. The rice doenjang purchased from Japan was characterized by high intensities of sweet attributes, such as butter cracker, grape juice, and pineapple. Consumers preferred soybean doenjang instead of rice doenjang among three doenjang samples. These results suggest that the familiarity of soybean-based doenjang affects consumer preference and choice.

Keywords: Descriptive analysis, Doenjang, Rice doenjang, Consumer acceptability

Introduction

Doenjang, which is similar to cheonggukjang and soy sauce, is one of the well-known soybean-based fermented foods in Korea. Traditionally, doenjang has widely been used in the Korean diet due to its high protein (amino acid) content as well as unique taste. Functional health benefits associated with the consumption of doenjang in the Korean diet have been well documented, including the antioxidant effect, thrombolytic effect, anti-cancer effect, anti-hypertension effect, and anti-mutagenic effect (Kim, 1998; Lim et al., 1999; Oh and Kim, 2007; Shin et al., 1995). Depending on its method of fermentation, doenjang is categorized into traditional and commercial types (Kim and Lee, 2014). Traditional doenjang is naturally fermented by germs and fungi, such as Bacillus subtilis and Bacillus licheniformis, to transform soybeans into meju (dried soybean brick). However, in traditional methods, the completion of fermentation is time-consuming, which is a limitation for the mass production of products. Commercial doenjang is prepared by making koji, which is a culture of Aspergillus oryzae in starch materials (e.g., wheat, rice, soybeans, and barley). Koji contains various degradation enzymes, which convert starch and protein into sugars and amino acids to improve the taste and flavor of doenjang (Kim et al., 2012; So and Lee, 2010). Therefore, the use of koji can accelerate the fermentation of doenjang and aid in mass production. Previous studies conducted on koji have focused on the optimization of fermentation conditions (Bechman et al., 2012), physicochemical and sensory characteristics (Hong and Kim, 2020), metabolomic profiling of rice koji (Lee et al., 2016a; 2016b), formation of volatile components in rice koji doenjang (Kum et al., 2015), and changes in enzymatic activities of rice koji doenjang (Jo et al., 2021).

In Korea, about 98,000 tons of doenjang in all kinds, is consumed annually (Shin et al., 2019). Rice doenjang is only produced by three to four major companies in the Korean market, and Japan’s miso using rice (comemiso) contributes to a considerable amount of the rice doenjang market (Kim et al., 2011). Rice doenjang is typically manufactured by mixing rice koji in the steamed soybean before the fermentation, in order to accelerate the fermentation process. Rice is the staple food of Koreans, and it is an indispensable source of starch in their diet. Furthermore, it is imperative to develop rice-based doenjang with excellent quality to solve the problem of demand development and consumption expansion of rice, which has been oversupplied in recent years (Jung et al., 1994).

In the production of doenjang, wheat is mainly used as a starch source for koji. Research on the application of microorganisms to manufacture wheat doenjang has been actively conducted, but studies on its production using rice as a raw material are not sufficient. Research and industrialization of soybean doenjang has been actively conducted, while research on rice doenjang has been insufficient. In Japan, where various materials are used for miso, research regarding processing by high-pressure treatment after producing koji using various grain mixtures such as brown rice, corn, and rice to help the growth of koji mold (Sasagawa et al., 2005) and the production of miso using buckwheat, sesame, and corn kernels (Kawakami and Kawahara, 2002; Ratnaningrum et al., 2018; Takasaki et al., 2010) is being conducted. However, in Korea, the use of various raw materials in the manufacture of doenjang is extremely limited. Therefore, in this study, the physicochemical and sensory characteristics of commercially available rice-based doenjang in Korea were analyzed to characterize the rice-based doenjang. In addition, consumer acceptance testing on rice-based doenjang is conducted to identify the perception of Korean consumers about rice-based doenjang.

Materials and methods

Doenjang samples included in this study

Three doenjang samples were included in this study: Soybean doenjang was purchased from a local grocery store, and two rice doenjang samples were purchased from an online shopping mall. Sample D1 was the most common commercial soybean-based doenjang in Korea, which was selected as the “control.” D2 was commercial rice-based doenjang made in Korea, and D3 was a commercial rice-based doenjang made in Japan. D3 was shipped directly from Japan. Table 1 lists the detailed information of the samples, including the ingredient list. Only two rice-based doenjang samples were included in this study, as we could not find the commercially-available rice-based doenjang from Korean market as of June, 2020, based on ingredients listed in the product label. These two rice-base doenjang (D2 and D3) included in this study utilized rice as one of the major ingredient. All doenjang samples were purchased within 6 months from the date of manufacture.

Table 1.

Three doenjang samples included in this study

Sample Ingredient
D1 Filtered water, soybean, wheat flour, refined salt, Korea soybean paste, meju soybean paste, ethyl alcohol, meju powder, meat stock base, seed malt
D2 Soybean paste (rice, soybean, refined salt, meju, seed malt), katsuo extract, fermented anchovy sauce, ethyl alcohol, kombu extract
D3 Rice, soybean (genetically modified), common salt, ethyl alcohol, katsuo extract, katsuo powder, kombu extract
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Physicochemical and enzymatic activity analysis of rice-based doenjang

Physicochemical analysis, including salinity (%), pH, titratable acidity (TA), acid value, NH3–N (%), total and reducing sugar content (mg/g), moisture content (%), alcohol content (%), and color measurements (L*, a*, b*), was conducted according to the methods of Korean Food Standards Codex (MFDS, 2012; Jo et al., 2021). Enzyme activities of amylase (α- and β-) and protease (acidic- and neutral-) were analyzed according to a previously reported method (Jo et al., 2021). All analyses were conducted in triplicate.

Descriptive analysis of doenjang

A sensory panel comprising six highly trained panelists participated in the evaluation of doenjang samples. Each of the panelists received intensive training from the Sensory Science Laboratory at the Jeonbuk National University, and each had more than 400 h of experience in the sensory analysis of products related to doenjang. Prior to the assessment, the trained panel had a 20-h calibration session to recall the use of universal scale in the Spectrum™ method, where 0 = none, 15 = very strong, presented in line scale. Panelist performances including panelist-to-panelist variation and within panelist variation were checked prior to actual evaluation. A sensory lexicon to describe the sensory characteristics of doenjang was generated, and the definition and reference for each term were given during the lexicon generation process to use the same terminology for the same aroma characteristics. Only the aroma attributes were evaluated in this study, as this trained panel is specialized in aroma evaluation. From the preliminary examination of sensory characteristics of each doenjang sample, panel recognized that the texture (mouthfeel) characteristics of rice-based doenjang were quite different from soybean-based doenjang in terms of granule size, springiness, residual mouthfeel, particle size and these differences were above the range of what we called normal standard characteristics of doenjang. To minimize the possible bias from abnormal texture variations among doenjang samples, only the aroma attributes were evaluated in this study. To prepare doenjang samples for sensory evaluation, about 5 g of doenjang paste was added into a 75-mL white plastic cup, which was labeled with a three-digit random number and covered with a lid. The doenjang samples were prepared 2 h before the evaluation and were placed at room temperature until the assessment. For the evaluation of flavor-related attributes, panelists were asked to open the lid of the sample container and smell the product three times using the bunny-sniff technique. Panelists were forced to rest for 2 min between the samples, and water and unsalted crackers (Cham® cracker, Crown, Seoul, Korea) were provided for palate cleansing. Each panelist examined the doenjang samples three times, and effect of panelist, repetition and interaction between panelists and repetition were checked. On completion of the evaluation, panelists were invited for an appreciation dinner to compensate for their participation in the descriptive sensory analysis of doenjang samples.

Consumer acceptance testing of doenjang samples

A total of 63 consumers attending the Jeonbuk National University participated in the consumer acceptance testing of doenjang. All participants in the consumer were at least product acceptor of doenjang-related products. The test was conducted at the Jeonbuk National University Sensory Service Center; thus, the majority of participants are students and staff members of college. A paste of each of the doenjang samples was provided to the participants, and each sample comprised about 5 g of paste in a 75-mL white plastic cup with a lid. All samples were stored at a refrigerated temperature (4 ℃) before evaluation. Participants were asked to taste doenjang with vegetable sticks, such as cucumber or albatross cabbage, to reflect the actual accompaniments served alongside doenjang, and vegetable sticks also were served in a 75-mL white plastic cup. Participants were asked to select either cucumber or albatross cabbage based on their preference on vegetable type during their liking evaluation. As mentioned above, the textural differences (such as color, appearance and mouthfeel-related attributes) among doenjang samples were apparent. Therefore it was important to let participants recognize these differences while evaluating their acceptance of each doenjang samples. Therefore, doenjang samples were served in a paste form with vegetable sticks.

In addition, participants were provided with sufficient water and were asked to rest for 2 min between samples to minimize the carry-over effect. Each plastic cup was labeled with a random three-digit number. Samples were uniformly provided to participants. The consumer acceptance test questionnaire included consumer’s demographic information (i.e., age, residence status, education, monthly income, consumption frequency of doenjang, purchase frequency of doenjang, factors affecting doenjang purchase, and manner of eating doenjang), overall liking, and other attributes (such as appearance, color, flavor, mouthfeel liking, salty taste, sweet taste, and umami taste liking). Consumers evaluated the sample preference using a 9-point hedonic scale (1 = dislike extremely and 9 = like extremely).

Ethics statement

This study protocol was reviewed and approved by the Institutional Review Board of Jeonbuk National University (IRB #: JBNU-2020-08-007-001).

Statistical analysis

The results of the physiochemical characteristics and enzymatic activities of the doenjang samples were expressed as the mean ± standard deviation of a triplicate analysis. A significant difference in the physiochemical and sensory characteristics (descriptive analysis and consumer acceptance testing) of the doenjang samples was analyzed using one-way analysis of variance, followed by Duncan’s multiple range test for the determination of sample differences at α = 0.05 level. Statistical analyses were performed using XLSTAT (v.2020, Addinsoft, Paris, France).

Results and discussion

Analysis results of physicochemical characteristics and enzymatic activities

Table 2 lists the physicochemical characteristics and enzymatic activities of rice-based doenjang, including salinity, pH, TA, NH3–N, reducing sugar and total sugar content, alcohol content, acid value, and color measurement results. The salinity of doenjang samples ranged from 13.3 to 13.7%, and no significant difference was observed among three samples (p = 0.779). Differences in pH was observed: The pH of D1 was the highest (5.89), followed by D3 (5.76) and D2 (5.50, p < 0.0001). The TA values for doenjang samples D1, D2, and D3 were 1.3 mL, 1.4 mL, and 1.13 mL, respectively (p = 0.031). Acid values for doenjang samples D1, D2, and D3 were 17.95 KOH/g, 12.34 KOH/g, and 11.35 KOH/g, respectively; these values were significantly different (p = 0.001). Difference in acid values may be attributed to the difference in raw materials between samples D1 (soybean) and D2–3 (rice). Soybean doenjang generates several free fatty acids and short-chain organic acids during lipolysis and amino acid degradation (Kim et al., 2018a; 2018b); hence, the NH3–N (mg/%) content of D1 (373.3 mg/%) is greater than that observed in rice doenjang samples D2 and D3 (p = 0.001). The total sugar content values for the D3, D2, and D1 samples were 179.33 mg/g, 174.50 mg/g, and 115.75 mg/g, respectively (p < 0.0001). Similarly, D1 exhibited the lowest value of 6.62 mg/g for the reducing sugar content (p = 0.001). The total sugar and reducing sugar contents of rice-based doenjang were greater than those of soybean-based doenjang (p < 0.05). This is the difference between the amount and decomposition of starch derived from soybean and rice, which are raw materials, during the fermentation of doenjang (Lee et al., 2012; Park et al., 1995). The moisture content (%) of D3 (45.7%) was significantly less than those of the other doenjang samples (D1, 49.9%; D2, 54.89%; p = 0.047). The alcohol content of the samples ranged from 2.15 to 3.02%, with that of rice-based doenjang was greater than that of soybean-based doenjang. Higher alcohol levels observed in D3 may be attributed to the high sugar content as sugar can be converted into alcohol during fermentation. Hence, the sugar content of rice-based doenjang is greater than that of soybean-based doenjang (Gil et al., 2016). In addition, color differences were observed among samples (p < 0.0001). With regard to the L* value (brightness), D2 exhibited the lowest value, and the a* value (redness) and b* value (yellowness) for rice doenjang (D2 and D3) were less than those for soybean doenjang. In summary, pH, acid value (KOH/g), and NH3–N (mg/%) content were higher in soybean doenjang, while TA, total sugar and reducing sugar content, and alcohol content were higher in rice doenjang (p < 0.05).

Table 2.

Physiochemical quality characteristics of three doenjang samples

Item D1 D2 D3 p-value
Physiochemical characteristics
 Salinity (%) 13.3 ± 0.84ns 13.2 ± 0.59ns 13.7 ± 1.22ns 0.779
 pH 5.89 ± 0.01a 5.50 ± 0.01c 5.76 ± 0.00b  < 0.0001
 Titratable acidity (mL) 1.13 ± 0.06b 1.4 ± 0.10a 1.3 ± 0.12ab 0.031
 Acid value (KOH/g) 17.95 ± 2.10a 12.34 ± 0.65b 11.35 ± 0.43b 0.001
 NH3–N (mg/%) 373.3 ± 40.40a 192.5 ± 30.3b 204.7 ± 10.1b 0.001
 Total sugar (mg/g) 115.75 ± 2.75b 174.50 ± 6.70a 179.33 ± 2.40a  < 0.0001
 Reducing sugar (mg/g) 6.62 ± 0.39b 9.63 ± 0.28a 9.57 ± 0.63a 0.001
 Moisture (%) 49.9 ± 1.50a 52.89 ± 1.30a 45.7 ± 0.56b 0.047
 Alcohol (%) 2.15 ± 0.21b 2.97 ± 0.05a 3.02 ± 0.12a 0.000
Color
 L* 47.67 ± 0.45a 41.63 ± 0.41b 48.13 ± 0.21a  < 0.0001
 a* 14.8 ± 0.01a 13.97 ± 0.02b 11.43 ± 0.12c  < 0.0001
 b* 26.03 ± 0.32a 21.13 ± 0.30c 22.43 ± 0.45b  < 0.0001
Enzymatic activities
 α-Amylase (unit/g) 31.1 ± 0.26a 9.9 ± 2.18b 30.66 ± 0.64a  < 0.0001
 β-Amylase (unit/g) 10.8 ± 0.99b 13.22 ± 0.73a 10.56 ± 0.47b 0.010
 Acidic protease (unit/g) 42.52 ± 0.26ns 44.10 ± 1.61ns 41.14 ± 2.86ns 0.241
 Neutral protease (unit/g) 31.33 ± 0.995a 32.11 ± 1.63a 25.55 ± 0.78b 0.001
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Means in a row that does not share the same alphabetical letter represent significant differences at p < 0.05

The α‐amylase activities for D1, D2, and D3 were 31.1 unit/g, 9.9 unit/g, and 30.66 unit/g, respectively. The β‐amylase activities for D1, D2, and D3 were 10.8 unit/g, 13.22 unit/g, and 10.56 unit/g, respectively. The α‐amylase activity of D2 was significantly less than those of the other samples, but its β‐amylase activity was significantly higher (p < 0.05). In previous studies, the α-amylase activity of commercially available doenjang (soybean) ranged from 17.0 to 675.9 units/g and β‐amylase activities ranged from 13.6 to 308.6 units/g (Lee et al., 2012). A previous study has reported that the amylase activities of rice doenjang are greater than those of soybean-based doenjang (Kim et al., 2011). However, this study finds different results that the amylase (α‐ and β‐) activities of rice doenjang were at parity or lower than that found in soybean doenjang. Different pattern found in amylase activities in this study needs to be further investigated in future study with more samples. Protease hydrolyzes soybean protein during the fermentation of doenjang to produce amino acids, which is a key factor that affects the final quality of doenjang as it affects the content of free amino acids produced during fermentation (Lee et al., 2016a; 2016b; Rhee et al., 2008). No significant differences were observed in the acidic protease activities among samples, with the activities ranging between 41.14 and 44.10 unit/g (p = 0.241). However, the neutral protease activity of D3 (25.55) was significantly less than those of the other samples (D1, 31.33; D2, 32.11; p < 0.001). This result is consistent with that reported previously: a low protease activity for barley and rice koji during fermentation has been reported (Bechman et al., 2012). It is worth to note that D3, which showed significantly lower neutral protease activities than other two samples, had larger amount of rice than D2. Difference in amount of rice included in the sample ingredient list may have influenced the lower neutral protease activity in D3.

Descriptive sensory analysis result

Table 3 lists the results obtained from the descriptive sensory analysis of doenjang, as well as a sensory lexicon with definitions and references for each term. The effects of panelist, repetition and interaction between panelist and repetition were insignificant (p > 0.05), suggesting that the performance of descriptive analysis panel is up-to-date. The lexicon identified a total of 14 odor-related descriptions for the sensory characteristics of doenjang, including alcohol, sour, cheonggukjang, katsuobushi, butter cracker, musty, anchovy, burnt, Japanese soy sauce, black taffy, saline water, pear, grape juice, and pineapple, respectively. Significant differences were observed between the three doenjang samples in 9 aroma terms out of 14 attributes (p < 0.05). Nine aroma attributes including alcohol, sour, butter cracker, musty, anchovy, burnt, Japanese soy sauce, saline water, and pear, were commonly found in all samples, and four aroma attributes, including cheonggukjang, black taffy, grape juice, and pineapple, respectively, were characteristic aromatics of one sample. Compared to previous studies in terms of the descriptive analysis of doenjang, eight sensory lexicons, including alcohol, sour, cheonggukjang, butter cracker, musty, anchovy, burnt, and Japanese soy sauce, respectively, were in agreement with those published previously (Chung and Chung, 2008; Hong and Kim, 2020; Hong et al., 2012; Jo et al., 2011; Kim et al., 2010; Kim et al., 2018a; 2018b). Significant differences were observed in the descriptors of cheonggukjang, butter cracker, musty, anchovy, burnt, and Japanese soy sauce among others (p < 0.05).

Table 3.

Descriptive sensory analysis result of three doenjang samples

Descriptors (odor) Definition Samples p-value
D1 D2 D3
Alcohol The aromatics associated with ethyl alcohol [Ref. 30% (v/v) ethyl alcohol, intensity 3.0] 1.3 ± 0.3 ns 1.3 ± 0.2 ns 1.8 ± 0.3 ns 0.082
Sour The aromatics associated with acetic acid [Ref. 10% (w/v) acetic acid in distilled water, aroma intensity 3.0] 1.0 ± 0.4ns 0.6 ± 0.4ns 1.1 ± 0.3ns 0.105
Cheonggukjang The aromatics associated with Cheonggukjang [Ref. Cheonggukjang powder, Hwang-tou-bang, aroma intensity 3.0) 1.5 ± 0.4a 0.2 ± 0.2b 0.0b  < 0.0001
Katsuobusi The aromatics associated with Katsuobusi soup (Ref. Katsuobusi soup, E-mart, Namyangju, Korea, aroma intensity 3.0) 0.5 ± 0.2b 2.1 ± 0.1a 0.3 ± 0.2b  < 0.0001
Butter cracker The aromatics associated with Butter cracker (Ref. Butter waffle, Crown®, Daejeon, Korea, aroma intensity 2.0) 0.6 ± 0.1b 0.0c 1.3 ± 0.3a  < 0.0001
Musty The aromatics associated with wet moldy basement (Ref. Blue cheese, Ullerslev, Denmark, aroma intensity 3.0) 1.3 ± 0.4a 0.2 ± 0.3b 0.3 ± 0.3b  < 0.0001
Anchovy The aromatics l associated with dried anchovy (Ref. Dried anchovy, Baeksong Food, Songpa-gu, Korea, aroma intensity 4.0) 1.4 ± 0.5a 1.0 ± 0.4a 0.0b  < 0.0001
Burnt The aromatics l associated with burnt wood (Ref. burnt match, Songwol, Daegu, Korea, aroma intensity 2.0) 0.0b 1.5 ± 0.5a 0.0b  < 0.0001
Japanese soy sauce The smell associated with flavored soy sauce (Ref. Japanese soy sauce, Hwami, Yeongdeungpo, Korea, aroma intensity 3.0) 0.5 ± 0.3b 1.9 ± 0.3a 0.8 ± 0.5b  < 0.0001
Black taffy The aromatics associated with Black taffy (Ref. black taffy, Changseongdang, Jeongeup, Korea, aroma intensity 1.0) 0.0b 1.2 ± 0.4a 0.0 ± 0.3b  < 0.0001
Saline water The aromatics associated with high concentration of saline water [Ref. 50% salt (w/v) in warm distilled water, Beksul, Busan, Korea, aroma intensity 3.5] 2.0 ± 0.4a 1.0 ± 0.5b 1.6 ± 0.5ab 0.001
Pear The aromatics l associated with pear (Ref. Pear-flavored beverage, Haitai, Cheonan, Korea, aroma intensity 4.0) 1.1 ± 0.5a 0.1 ± 0.1b 0.4 ± 0.4b  < 0.0001
Grape juice The aromatics associated with Grape juice (Ref. Grape juice, Minute maid, Yangsan, Korea, aroma intensity 4.0) 0.0b 0.0b 1.9 ± 0.5a  < 0.0001
Pineapple The aromatics associated with Pineapple candy (Ref. Crushed pineapple flavored candy, Chupa Chups, Yongin, Korea, aroma intensity 1.0) 0.1 ± 0.2b 0.0b 1.3 ± 0.4a  < 0.0001
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Numbers in a column that dose not share the same alphabetical letter represent significant differences at p < 0.05. Numbers represent mean values of triplicate analysis of each item

The aroma characteristics related to D1 were cheonggukjang, musty, anchovy, and pear. Cheonggukjang is another fermented soybean food in Korea, which uses certain microorganisms (such as Bacillus natto, B. subtilis) (Kim et al., 2003). Doenjang and cheonggukjang share similar flavor properties due to the use of soybeans as the main ingredient (Moon et al., 2015; Park et al., 2015). Musty was a representative fermentation-related aroma attribute. Previously, musty has been reported to be a flavor attribute attributed to soybean doenjang (Kim et al., 2018a; 2018b). In addition, D1 exhibited the strongest aroma of anchovy and anchovy sauce (fermented fish), possibly resulting from the uneven fermentation of microorganisms and a long fermentation period (Kim et al., 2010). All aroma characteristics of the D1 sample, except for that of pears, were consistent with the characteristics of soybean doenjang reported in previous studies.

The aroma characteristics associated with D2 and D3 (rice doenjang samples) were katsuobushi, burnt, Japanese soy sauce, black taffy, butter cracker, grape juice, and pineapple. D2 exhibited a significantly higher content of katsuobushi (p < 0.05). This specific aromatic may be attributed to the Katsuo extract included in the D2 sample (Table 1), not relevant to fermentation-related aromatics. D2 exhibited a high aroma intensity of Japanese soy sauce (1.9), and it was significantly greater than those observed in the other samples (D1, 0.5; D3, 0.8; p < 0.05). Burnt and black taffy were only observed in D2. Previous studies have reported burnt as a doenjang-related aroma (Chung and Chung, 2007).

D3 exhibited a significantly higher content of butter cracker than those in the other samples (p < 0.05). Cracker aroma was caused by carbonyl compounds such as proline carbonyl and lysine carbonyl (Griffith and Hammond, 1989; Kang and Lee, 1994), the contents of these carbonyl compounds increase during the fermentation of Japanese rice doenjang (Wang et al., 2019). Overall, the sweetness-related characteristics, such as black taffy, grape juice, and pineapple, in rice doenjang were greater than those in soybean doenjang. Aroma intensity of Katsuobusi aromatic was lower in D3, while Katsuo powder is added in D3. This may be due to the lower amount of Katsuo powder included in D3, as Katsuo powder is listed almost at the end of the ingredient list in D3, while Katsuo extract was presented in the middle of ingredient list in D2.

Consumer acceptance testing result

The consumer acceptance test was conducted to identify Korean consumers’ preferences of doenjang with different sensory characteristics. A total of 63 consumers participated in the consumer acceptance test, and most of the participants were college students. Table 4 lists the demographic information of participants in consumer testing. All of the participants were in their twenties, and they often lived away from their own families; all of them earned more than $1,000 per month. With respect to the factors affecting the purchase of doenjang, flavor was the most important factor at 63.5%, price was ranked second at 12.7%, and brand and recommendation were each ranked 9.5%. In addition, the method of eating doenjang was 69.8% in stews, 25.4% in soups or with vegetables, and 1.6% in others.

Table 4.

Demographic information of participants in consumer testing (n = 63)

(%)
Age
 21–29 years 100
Resident
 Dormitory 25.4
 Live apart from one's own family 47.6
 Boarding house 3.2
 Residence with family 23.8
Education
 High school graduate 3.2
 4-year college students 93.7
 Graduate school students 3.2
Monthly income
 < $1,000 100
Frequency of consuming doenjang
 Once a week 3.0
 Once in 2–3 weeks 6.1
 Once a month 4.5
 Once in 2–3 months 7.6
 One to two times a year 39.4
 Never consuming doenjang 39.4
Frequency of purchasing doenjang
 Everyday 1.6
 Once in 2–3 days 6.3
 Once a week 23.8
 Once in 2–3 weeks 23.8
 Once a month 11.1
 Once in 2–3 months 15.9
 One to two times a year 12.7
 Never purchasing doenjang 4.8
Factors affecting purchase of doenjang
 Flavor 63.5
 Price 12.7
 Brand 9.5
 Recommendation of one's 9.5
 Others 4.8
How to eat Doenjang1
 Stew 69.8
 Soup 25.4
 With vegetable 25.4
 Others 1.6
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1Participants were able to check more than one response (Check-all-that-apply), therefore the sum does not add up to 100%

Table 5 lists the consumer acceptance test results for the doenjang samples. Among the total eight liking attributes including overall liking, significant differences between samples were observed (p < 0.0001). All of the liking attributes pointed toward strong consumer preference for D1, with an overall liking score of 6.0 on the 9-point hedonic score, while D2 and D3 received scores of 5.0 and 5.1, respectively. Previous consumer studies on doenjang have consistently revealed that sweet and umami tastes drive consumers to like the product and that there are certain clusters of consumers favor doenjang with these characteristics (Kim et al., 2010; Kim and Lee, 2018). Although significant differences in sweet taste liking were not observed (p = 0.335), a significantly higher umami taste liking was observed for D1, possibly affecting the high overall liking of D1. Notably, college students constituted the majority of participants in this consumer testing, and their drivers for liking doenjang were previously reported as strong sweet and umami tastes rather than versatile aroma characteristics (Jo and Kim, 2020; Kim et al., 2018a; 2018b). Consumer demographics possibly affected the strong consumer preference toward D1.

Table 5.

Consumer acceptance test results (n = 63)

Liking attribute Sample p-value
D1 D2 D3
Appearance liking 6.3 ± 1.4a 5.2 ± 1.7b 4.1 ± 1.5c  < 0.0001
Color liking 6.3 ± 1.5a 5.1 ± 1.6b 3.6 ± 1.3c  < 0.0001
Overall liking 6.0 ± 1.6a 5.0 ± 1.9b 5.1 ± 1.3b 0.001
Flavor liking 6.3 ± 1.5a 5.1 ± 1.6b 5.2 ± 1.5b  < 0.0001
Mouthfeel liking 6.5 ± 1.3a 5.9 ± 1.5b 5.0 ± 1.1c  < 0.0001
Salty taste liking 5.9 ± 1.7a 4.9 ± 1.9b 5.7 ± 1.6a 0.002
Sweet taste liking 5.5 ± 1.5ns 5.1 ± 1.4ns 5.2 ± 1.5ns 0.335
Umami taste liking 6.3 ± 1.3a 5.7 ± 1.5b 5.1 ± 1.4b  < 0.0001
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Numbers in a column that does not share the same alphabetical letter represent significant differences at p < 0.05

There is an increased demand for rice doenjang by consumers who are allergic to beans as well as for those seeking diverse flavors. Based on this study, D1 sample (soybean-based doenjang) was most liked by consumers strongly correlated with aroma attributes of cheonggukjang, musty, acid value, and NH3–N content. In the previous study, musty attributes were defined as soybean-related characteristics in soybean-based doenjang (Kim et al., 2018a; 2018b). A high acid value and NH3–N content are attributes related to soybean, a raw material of doenjang. During the fermentation of doenjang, several free fatty acids and short-chain organic acids are generated by lipolysis of lipids present in soybean. Also, NH3–N is produced during the decomposition of amino acids in soy protein (Kim et al., 2018a; 2018b; Lee and Mok, 2012). D2 (commercial rice-based doenjang made in Korea) was correlated to the properties of miso (katsuobushi, Japanese soy sauce, burnt). This result is as expected because the Katsuo extract is included in the ingredient. D3 (commercial rice-based doenjang made in Japan) had strong flavor characteristic such as grape juice and pineapple. The unique sensory characteristic of D3 may associated with the total sugar, reducing sugar, and alcohol contents. The alcohol attribute was related to the high sugar content as sugar can be converted into alcohol during fermentation. Fruit flavor can be observed when alcohol and organic acids react to form ester compounds. In a previous study, the flavor of over-aged fruits was found as an ester compound produced by alcohol generated during the ripening of rice koji (Hong and Kim, 2020).

Discussion

Compared to soybean doenjang, rice doenjang exhibited physicochemical characteristics different from those of typical soybean doenjang, including lower pH, acid value, and NH3–N content, as well as higher total sugar, reducing sugar, and alcohol contents. This result is due to the difference in raw materials because soybeans produce an increased amount of fatty acid, organic acids, and NH3–N in the process of decomposition, while rice produces sugar during the decomposition of large amounts of starch. These differences in the physicochemical characteristics between soybean and rice doenjang also affected the sensory characteristics in that soybean doenjang exhibited characteristic aromatics of traditional Korean doenjang (Cheonggukjang, musty, anchovy, and saline water), and rice doenjang made in Korea exhibited characteristics of Japanese doenjang miso (Katsuobushi, Japanese soy sauce). The rice doenjang made in Japan exhibited sweet attributes, such as butter cracker, grape juice, and pineapple. While the differences were evident, consumers preferred soybean doenjang instead of rice doenjang. Previous studies have reported that sweet and umami taste are drivers for liking soybean doenjang (Kim et al., 2010; Kim and Lee, 2018); therefore, the samples with a high umami taste liking (D1) possibly receive the highest overall liking score (p < 0.05). In addition to umami taste liking, appearance-related attributes such as color possibly affected the overall liking, as appearance and color were the key attributes that explain the characteristics of doenjang (Jo and Kim, 2020; Kim and Lee, 2014; Kim and Lee, 2018). According to the results of color analysis shown in Table 1, the rice doenjang color was significantly less in the redness (a*) and yellowness (b*) values than that of soybean doenjang; hence, this unfamiliar color of doenjang possibly affects the overall acceptability.

Product familiarity is one of the most important factors affecting consumers’ overall preference for traditional fermented foods such as doenjang (Choi et al., 2015; Hong et al., 2014; Roh et al., 2018). The familiarity and preferences for traditional doenjang by consumers of different ages in older consumers were greater those in younger consumers, indicating that older consumers tend to accept traditional types of product as they are more likely to be exposed to these products compared to younger consumers (Roh et al., 2018). In addition, consumers’ expectations for familiar products with previous experience were more clearly formed and had specific criteria for evaluation. However, unfamiliar products possibly caused consumers to provide ambiguous hedonic responses (Hong et al., 2014). Consumers prefer soybean doenjang over rice doenjang possibly because of the fact that Korean consumers are not familiar with the sensory characteristics (color and flavor) of rice doenjang; therefore, the preference direction may have been directed towards soybean-based doenjang. Product preferences are considerably affected by personal factors, such as familiarity, information, experience, and diversity, as well as the effects of flavor, taste, and color. Therefore, future studies should be conducted from a broader perspective by considering the correlation between product familiarity and preference for rice doenjang by consumers.

In this study, the characteristics of rice-based doenjang were investigated by analyzing the physicochemical and sensory characteristics. In addition, a consumer acceptance test was conducted to identify the Korean young adults consumers' perceptions of rice-based doenjang. Clear differences were noted in the physicochemical and sensory characteristics between soybean-based doenjang and rice-based doenjang. While differences in physiochemical and sensory characteristics were evident, consumers preference direction was toward soybean-based doenjang, which was contrary to expectation that they would prefer sweetness. These results suggested that the familiarity of soybean-based doenjang affects young adults consumers’ food preferences and choices. The limitation of this study was small numbers of sample included in this study. Rice-based doenjang samples included in this study were commercially-available doenjang samples in Korean market at that time when research was conducted, but it is still small numbers to comprehensively conclude the finding of this study. Also, criteria to select the rice-based doenjang was very strict in this study, in that only the samples utilized rice as one of the main ingredient was included. Similar study with larger pool of samples, possibly include any doenjang samples including rice as major and minor ingredient (i.e. rice koji), in a near future, when more rice-based doenjang samples are commercially available, is needed to further investigate the finding of this study.

Acknowledgements

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (Grant Number NRF-2020R1C1C1011279).

Data availability

Author elects to not share data.

Declarations

Conflict of interest

Authors declare no conflicts of interests on this work.

Footnotes

Publisher's Note

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Contributor Information

Yongwoo Jo, Email: jjw9670@naver.com.

JungJae Lee, Email: prooska@naver.com.

Mina K. Kim, Email: minakim@jbnu.ac.kr

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