Muffins enriched with dietary fiber from kimchi by‐product: Baking properties, physical–chemical properties, and consumer acceptance

Abstract This study aimed to evaluate the effects of dietary fiber from Chinese cabbage outer‐leaf powder, which is a main by‐product of kimchi, on the quality, texture properties, and sensory evaluation of muffins. The kimchi by‐product powder (KBP, 36.2% dietary fiber) was added at 1%–4% dietary fiber content, by replacing wheat flour (w/w basis). The physico‐chemical and sensory properties of the baked muffins were measured. The height and volume of the muffins decreased with the addition of KBP. Increasing the KBP content resulted in increased hardness and reduced chewiness. No significant difference was observed in the overall acceptance among the muffins, up to the 2% added dietary fiber group, and the positive effect of the incorporated KBP was also confirmed in the sensory evaluation. These results indicate that it is possible to produce functional muffins with increased dietary fiber content by adding KBP in place of flour.

This study investigated the possibility of incorporating kimchi by-product, as a source of dietary fiber, into a bakery product. For this purpose, muffins were formulated with increased dietary fiber (0%, 1%, 2%, 3%, and 4%), by adding kimchi by-product powder (KBP) in replacement of wheat flour (w/w basis). The pasting properties, color, texture, dietary fiber content, and sensory attributes of the muffins were evaluated.

| MATERIAL S AND ME THODS
Commercial soft flour (CJ Co., Seoul, South Korea), sugar (CJ Co.), butter (Seoulmilk ICA, Seoul, South Korea), skim milk powder, vanilla powder, baking powder, eggs, and milk were purchased from a local market in Korea. Kimchi by-products were obtained from a kimchi factory, washed to remove soil and dirt, drained, and dried at 70°C for 24 hr, using a hot air drier (Lequip, Hwaseong, Gyeonggi-do, Korea). After cooling to room temperature (24°C), the material was ground and strained through a 50-mesh sieve (297 μm). The powder was stored in a polyethylene bag at −18°C. A total dietary fiber (TDF) assay kit (K-TDFR) was obtained from Megazyme International (Bray Co., Wicklow, Ireland). MES (2-N-morpholino ethanesulfonic acid) hydrate and Trizma base were purchased from Sigma-Aldrich (St. Louis, MO, USA).

| Muffin preparation
Muffin formulations are presented in Table 1 ; therefore, 4.14, 8.29, 12.43, or 16.57 g KBP was added, replacing an equal weight of wheat flour. Butter and sugar were mixed using a hand mixer (CONCEPT-190L, Penta Korea, Seoul, South Korea) for 3 min, and an egg was added, with four times mixing for 5 min at speed 4. After incorporating the dry ingredients (flour, baking powder, vanilla powder, skim milk powder, and KBP), by mixing for 1 min (speed 1), the batter was blended with the milk for 2 min (speed 2), divided (55 g aliquots) into paper molds, and baked at 180°C in a preheated electric oven (FDO-7102, Daeyung, Seoul, South Korea) for 25 min. The muffins were left to cool on a rack for 1 hr, to avoid accumulation of condensation (Goswami, Gupta, Mridula, Sharma, & Tyagi, 2015).

| Composition of the muffins
Moisture, protein, crude fat, and ash of muffins were analyzed according to the Association of Official Analytical Chemists [AOAC] methods (2012). Total carbohydrate content was determined by difference. TDF contents were measured by method 991.43 (AOAC, 2012). One gram of sample in MES-Tris buffer (adjusted to pH 8.2) was placed in a beaker. After α-amylase (50 μl) was added, the samples were incubated for 30 min (100°C) and then cooled to room temperature. After the addition of protease (100 μl), the samples were incubated at 60°C for 30 min. Once cooled, 5 ml HCl (0.561 N, pH 4.5 ± 0.2) and 200 ml amyloglucosidase were added, followed by incubation at 60°C for 30 min. After adding 200 ml ethanol (95%), the mixture was incubated at room temperature for 60 min. The residue and slurry were washed twice each with 15 ml of 78% and 95% ethanol, respectively. The final slurry was washed with 15 ml of 78% and 95% ethanol, respectively, and the TDF was measured. Half of the final slurry was used for crude protein analysis (Kjeldahl), and the other half was analyzed for ash by burning at 550°C for 5 hr.

| Microstructure of the muffin by scanning electron microscopy
The microstructure of the muffin crumbs was examined using a scanning electron microscope (Hitachi-S-3400N, Hitachi Ltd., Tokyo, Japan). In order to measure, the muffin crumb was cut into 10 mm TA B L E 1 Formulation of muffins containing kimchi by-product powder (KBP) cube and was sputter-coated with gold after freeze-drying. Each sample was observed at an accelerating voltage of 5 kV. The scanning electron microscopy (SEM) images of the muffins were acquired at 1,500× magnification (Manaf, Othman, Harith, & Ishak, 2017).

| Physical characteristics of the muffins
The height, volume, symmetry, and uniformity of muffins containing KBP were measured by using a caliper, and the weight and baking The baking loss rate was calculated by the following equation: Images of the muffins were photographed against a white background, using a digital camera.

| Color measurement
The colors of muffin crusts and crumbs were measured using an Ultrascan PRO Colorimeter (Hunter Lab, VA, USA), pre-calibrated with a standard white background tile (L* = 99.56, a* = −0.17, b* = −0.21). The color was measured 1 hr after baking.

| Texture profile
The texture of the muffins was analyzed using a texture analyzer (TA.HDi/500, Stable Micro Systems, UK) equipped with an SMS p/36R probe (Stable Micro Systems) following the method of Alvarez Herranz Jiménez and Canet (2017). To measure the texture of complete crumb lower half, samples were cut horizontally at the height of the mold; the upper half was discarded, and the 2.5-cm-high lower half was removed from the mold. The texture instrument parameters were as follows: 2 mm/s pretest and test speed, 4 mm/s post-test speed, 5 g trigger force, 30 mm distance, and 40% strain. The hardness, adhesiveness, springiness, cohesiveness, chewiness, and resilience were measured.

| Sensory properties
The appearance, color, texture, flavor acceptance for muffin, and overall acceptance for quality were evaluated by 120 panelists using a 7-point hedonic rating scale (1 = lowest acceptance; 7 = highest acceptance). The panelists aged between 20 and 40 years (25 ± 6 years), and 10% of the panelists was male and 90% of them was female. The muffins were removed from the oven, cooled at room temperature (24°C) for 1 hr, cut into four pieces, and randomly assigned a coded 3-digit number. One piece of each muffin was provided to the panelists, along with a cup of water to neutralize the taste between each sample.

| Antioxidant property of the muffins
The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of the muffins was determined according to the method of  with some modifications for filtration. Ethanolic extracts of muffins were prepared by mixing 5 g of sample with 45 ml of 70% ethanol on a shaking incubator at 37°C for 24 hr. The mixture was centrifuged (7,041 g) at 4°C for 10 min. An aliquot (0.1 ml) of the resultant supernatant was mixed with 0.1 ml of an ethanolic solution of DPPH (0.1 mM, 80%) and incubated at 25°C. After 30 min, the absorbance of the mixture was read at 517 nm on a microplate reader (Eon; BioTek Ltd., Winooski, VT, USA).

| Statistical analysis
Quantitative data are expressed as mean ± standard deviation (SD)  Table 2 shows the proximate composition of the muffins. The KBPcontaining muffins had a higher TDF content (8.64%-12.73%) than the control (6.71%). As expected, the dietary fiber level increased with the increasing addition of KBP. According to our previous study (Lee et al., 2016), Chinese cabbage outer-leaf powder, which had a high TDF content, was reported as a good source of functional ingredients. KBP-added muffins showed higher moisture contents than the control. The higher the KBP content, the higher the moisture content, owing to the water-holding capacity of the dietary fiber, as previously noted by Kim et al. (2012). Similar results were also dem-  The results for DPPH radical scavenging activity of muffins are shown in Table 2

| Physical characteristics of the muffins
From the baking properties of the muffins (Table 3) The crust and crumb color values of the muffins (Table 4)   high temperature necessary to accelerate the Maillard reaction, resulting in brown pigment formation. The browning index decreased with increased KBP, presumably due to the addition of KBP. Matos, Sanz, and Rosell (2014) and Shevkani and Singh (2014) demonstrated that the browning index is highly influenced by the original color of the added ingredients.
The texture (hardness, adhesiveness, springiness, cohesiveness, chewiness, and resilience) of muffins with added KBP was evaluated (Table 4). Textural characteristics are of prime importance since they can affect consumer acceptance of the products (Shevkani & Singh, 2014). The control showed the lowest hardness value (

| Sensory evaluation
The scores for product attributes and overall acceptance (Table 5) indicated no significant differences in appearance and color acceptance among all samples. For texture, there was no significant difference up to KBP 2, whereas KBP 3 and 4 had lower values than the others. As KBP was added and muffin hardness increased, the texture acceptance score decreased. The acceptance score for flavor decreased as the ratio of KBP increased, with a significant difference between KBP 3 and 4 compared to the control. For overall acceptance, there was no significant difference between the control, KBP 1 and 2 samples, but the acceptance slightly decreased with the addition of 3% or 4% dietary fiber (KBP 3 and 4). Therefore, the addition of up to 2% dietary fiber (derived from the KBP) was considered to be an appropriate amount, based on the sensory evaluation.

| CON CLUS ION
The results of this study show the possibility of using an abun-  the higher the antioxidant property of muffins. No significant dif-