Abstract
This study investigated the production of bakery and sweet paste products containing the prebiotic fructooligosaccharide (FOS) using an in situ method with invertase. The FOS formation method was optimized for each product to ensure high quality and appropriate sweetness. The method effectively decreased the sugar content in the final product by 12.7–68.4% while maintaining quality. The FOS content was 3.8–4.8% in castella, 0.6–3.6% in sweet dough bread, and 7.5–8.5% in sweet chickpea paste. By contrast, the commercial method of adding FOS decreased product quality; castella product height decreased by 20.8%, and hardness increased by 79%. The specific volume of the sweet dough bread decreased by 17.4% and hardness increased by 59%. Therefore, we developed a commercially feasible method to efficiently utilize FOS in sugar-containing foods while maintaining their quality.
Keywords: Fructooligosaccharide, Bakery products, Invertase
Introduction
Prebiotics are food compounds that foster the growth or activity of beneficial microorganisms such as bacteria and fungi (Cunningham et al., 2021). Fructooligosaccharide (FOS) is a leading prebiotic functional ingredient used in commercial production (Dominguez et al., 2014; Lin et al., 2022; Pengrattanachot et al., 2022). Many studies have attempted to incorporate FOS into bakery products to enhance health benefits by adding or replacing sugar and not compromising sensory properties (Schmiele et al., 2017; Mieszkowska & Marzec, 2016; Rodriguez-Sandoval et al., 2014; Padma Ishwarya & Prabhasankar, 2013; Ronda et al., 2005). However, a major challenge arises when FOS, particularly in the form of syrup, is directly added to dough before baking. For example, Sudha et al. (2022) demonstrated that adding short-chain FOS to bread improves quality characteristics, such as specific volume and moisture retention, whereas Park et al. (2016) reported that adding more than 6% FOS (baker’s percentage) harms proofing and loaf volume, indicating that the amount that can be added directly is substantially limited.
In situ production of FOS during baking is a new and emerging technology that has the potential to improve the nutritional value and quality of baked goods. FOS can be produced in situ by adding carbohydrate enzymes to the dough or batter, which hydrolyzes sucrose into FOS. This process is used to replace some or all of the sugar in baked goods, without affecting taste or texture.
The in situ production of FOS during baking has several advantages over adding pre-produced FOS to baked goods. First, it allows for the production of FOS that is tailored to the specific baking process. Second, it helps improve the nutritional value of the baked good by increasing the amount of prebiotics present. Third, it reduces the cost of baked goods containing FOS. Henderson et al. (2012) published a patent on the in situ process to produce FOS in food products, where they enzymatically produced FOS in sucrose-containing food products using fucosyltransferase but this patent only demonstrated limited application for beverages (fruit juice).
We developed and evaluated an in situ enzymatic process to contain an ample amount of FOS in bakery products using invertase, which will overcome the limitation of directly adding FOS as described by Park et al. (2016) and extend the application of Henderson et al. (2012) beyond beverages to solid food.
Materials and methods
Preparation of castella for in situ enzyme treatment
The following ingredients were purchased from a local grocery to prepare castella with different invertase dosages to produce FOS in situ: 280 g soft flour, 500 g sugar (30% of total weight), 670 g eggs, 125 g starch syrup (dextrose equivalent, 40–44, Daesang, Seoul, Korea), 30 g butter, 30 g milk, 7 g sake, and 2 g salt. The eggs, yolks, and sugar were placed in a mixing bowl (Kitchen Aid 5KPM5, Benton Harbor, MI, USA) and whisked at speed 6 with invertase (Novozym 280392, Novozymes, Bagsvaerd, Denmark) added at a concentration of 0.0 INU/g for the control group or 1.0 INU/g or 2.0 INU/g for the experimental groups. After sifting the soft flour by hand and adding it to the mixture, heated milk (36 °C), starch syrup, salt, butter, and sake were added and mixed well to make the batter. The final temperature and specific gravity of the batter were 21 ± 1 °C and 0.52–0.55 g/mL, respectively. The batter was poured into a mold and baked in an oven (Maruzen, Tokyo, Japan) for 30 min with top heat of 90 °C and bottom heat of 150 °C. When the upper surface of the batter turned brown, we covered it with an iron plate and baked it for another 45 min with top heat of 180 °C and bottom heat of 150 °C. After cooling, FOS content of the finished product was analyzed by high-performance liquid chromatography (HPLC) equipped with a refractive index detector.
Preparation of sweet dough bread for in situ enzyme treatment
The following ingredients were used to prepare sweet dough bread with different invertase dosages to produce FOS in situ: 1000 g hard flour, 250 g sugar (25% of total weight), 30 g powdered milk, 16 g salt, 130 g eggs, 14 g yeast, 150 g butter, and 520 g water. All ingredients were mixed with invertase added at various concentrations (Table 1). The dough was fermented at 27 °C and 70% humidity for 1 h and then divided into 32 g pieces. The pieces were rested at room temperature for 30 min and then shaped into balls and placed in a mold. The dough was proofed at 38 °C and 85% humidity for 1 h and then baked in an oven (Maruzen, Tokyo, Japan) with upper heat of 215 °C and bottom heat of 160 °C for 8 min. The total processing time was about 3.5 h.
Table 1.
Baking mixing ratio of sweet dough bread (SD-low: 0.2 INU/g, SD-mid: 0.6 INU/g, SD-high: 1.8 INU/g)
| Ingredient | Control | SD-low | SD-mid | SD-high |
|---|---|---|---|---|
| Flour | 1000 | 1000 | 1000 | 1000 |
| Sugar | 250 | 250 | 250 | 250 |
| Powder milk | 30 | 30 | 30 | 30 |
| Salt | 16 | 16 | 16 | 16 |
| Egg | 130 | 130 | 130 | 130 |
| Yeast | 14 | 14 | 14 | 14 |
| Butter | 150 | 150 | 150 | 150 |
| Water | 520 | 520 | 520 | 520 |
| Enzyme | – |
0.12 (0.2 INU/g) |
0.35 (0.6 INU/g) |
1.06 (1.8 INU/g) |
Sweet dough bread recipe: SD-low: sweet dough with low amount of invertase (0.2 INU/g)
SD-mid: sweet dough with medium amount of invertase (0.6 INU/g)
SD-high: sweet dough with high amount of invertase (1.8 INU/g)
Preparation of sweet chickpea paste for in situ enzyme treatment
The following ingredients were used to prepare sweet chickpea paste containing invertase to produce FOS in situ: 530 g chickpea paste, 310 g sugar (36.8% of total weight), 5 g xanthan gum, 160 g water, and 0.49 g invertase. The paste was prepared by boiling, crushing, and pressing chickpeas to remove supernatant. The chickpea paste was mixed with sugar, xanthan gum, and water in a mixer (Eurostar20, IKA, Staufen, Germany) and the resulting mixture was heated in a water bath (Julabo19, Julabo, Seelbach, Germany) with constant stirring until the temperature reached 55 °C. The invertase was added at a concentration of 0.5 INU/g and allowed to react for 1 h. The paste was concentrated to 54 Brix and the enzyme was inactivated by heating.
Comparison of in situ-produced FOS with commercial FOS
To compare the quality characteristics of baked products with commercial oligosaccharides or with in situ FOS produced from invertase, we used a commercial oligosaccharide product (CJ Cheiljedang, Seoul, Korea) and added it to the castella, sweet dough bread, and chickpea paste. The sugar content of these bakery products was adjusted to match the sugar composition of the enzyme-treated products and FOS was added accordingly.
FOS and sugar analyses
FOS from ground samples of castella, sweet dough bread, and sweet chickpea paste was extracted in 10 volumes of distilled water for 30 min at 85 °C. The samples were centrifuged at 3150×g for 10 min and then filtered through a 0.45 μm syringe filter (Hyundai Micro, Seoul, Korea). Fructose, glucose, sucrose, maltose, lactose, and kestose were purchased from Sigma Aldrich Co. (St. Louis, MO, USA) and used as standards to quantify sugar content. The sugar analysis was performed using HPLC (Osaka Soda Co., Ltd., Osaka, Japan) with a refractive index detector and a high-performance carbohydrate cartridge column (4 μm, 4.6 × 250 mm; Waters, Milford, MA, USA).
Physical properties of bread
Loaf volume
The specific volume of bread was measured using a volscan profiler (Stable Micro Systems VolScan Profiler, Stable Micro systems Inc., Surrey, UK).
Texture profile analysis
Texture profile analysis was conducted by slicing the bread to a thickness of 20 mm and measuring it using a CTX Texture Analyzer (AMETEK Brookfield, MA, USA).
Sensory evaluation
The sensory evaluation was made by 10 consumers under laboratory conditions using a 10-point hedonic scale (1-low quality,10-high quality).
Statistical analysis
All data are presented as the mean and standard deviation of triplicate determinations. Statistically significant differences were identified via one-way analysis of variance followed by the Sidak-Bonferroni method. A p-value < 0.05 was considered significant. GraphPad Prism version 6.0 software (GraphPad Software Inc., San Diego, CA, USA) was used for the analysis.
Results and discussion
FOS and sugar contents with various concentrations of invertase
To test different dosages of invertase to produce FOS in castella and sweet dough products, 0, 1.0, and 2.0 INU/g invertase was added to the castella and 0.0, 0.2, 0.6, and 1.8 INU/g invertase was added to the sweet dough bread. As shown in Fig. 1, as invertase activity increased, sucrose and total sugar content decreased due to hydrolysis. Kestose and FOS content increased in both products. Sucrose, which is the substrate for the enzyme reaction, decreased by 12.7–19.8% in castella and by 35.2–68.4% in the sweet dough bread. The FOS content of the final products ranged from 3.8% to 4.8% in castella and from 0.6% to 3.6% in the sweet dough bread. We performed a sensory evaluation of the enzyme-treated products and found that the products with a high enzyme concentration had less sweetness and were less preferred (Table 2). Therefore, we determined that the optimal enzyme concentration was 1.0 INU/g for castella and 0.6 INU/g for the sweet dough bread. In both products, we adjusted the FOS content by changing the enzyme concentration from 0.2 to 1.8 INU/g because we could not control the reaction time of the enzyme during the baking process. However, we optimized the reaction time for the sweet chickpea paste.
Fig. 1.
Sugar and FOS content according to invertase concentration
Table 2.
Sensory evaluation of castella and sweet dough with various enzyme concentrations
| Ingredient | CT_C | CT_low | CT_high | SD_C | SD_low | SD_mid | SD_high |
|---|---|---|---|---|---|---|---|
| Preference (dissatisfaction → satisfaction) | 7.8 ± 0.9a | 7.9 ± 1.1a | 6.0 ± 0.9b | 8.0 ± 0.8a | 8.1 ± 0.7a | 7.6 ± 0.8a | 5.7 ± 0.9c |
| Sweetness (not sweet → sweet) | 7.5 ± 0.8a | 6.8 ± 0.6a | 5.5 ± 0.9b | 7.8 ± 1.0a | 7.6 ± 0.7a | 6.8 ± 0.9b | 4.8 ± 1.0c |
| Saltiness (not salty → salty) | 4.7 ± 1.1a | 4.9 ± 1.2a | 4.6 ± 0.8a | 4.8 ± 1.0a | 4.6 ± 1.1a | 4.7 ± 0.9a | 3.9 ± 0.8a |
| Flavor (no flavor → flavorful) | 5.5 ± 1.0a | 5.2 ± 1.0a | 5.3 ± 0.8a | 4.7 ± 0.9a | 5.0 ± 1.0a | 5.0 ± 1.1a | 5.1 ± 0.8a |
| Crust color (bright → dark) | 8.2 ± 0.7a | 8.0 ± 0.9a | 8.2 ± 0.7a | 6.9 ± 0.9a | 6.9 ± 1.0a | 7.2 ± 0.9a | 7.1 ± 0.8a |
| Crumb color (bright → dark) | 3.3 ± 0.8a | 3.5 ± 0.7a | 4.1 ± 0.8a | 2.2 ± 0.7a | 2.2 ± 0.9a | 2.1 ± 0.8a | 2.4 ± 0.8a |
| Stickiness (non-sticky → sticky) | 4.9 ± 0.8a | 4.8 ± 0.7a | 5.9 ± 0.8a | 4.2 ± 0.9a | 4.3 ± 0.8a | 4.9 ± 0.8a | 5.1 ± 0.8a |
| Moistness (dry → moist) | 6.6 ± 0.8a | 6.7 ± 1.2a | 7.3 ± 0.9a | 4.0 ± 0.9a | 4.3 ± 0.8a | 4.2 ± 0.7a | 4.2 ± 0.7a |
The sensory evaluation was made by 10 consumers under laboratory conditions using a 10-point hedonic scale (1-low quality,10-high quality)
The different lowercase letters a–c represent significant differences (p < 0.05) in a row for the same attributes
Changes in FOS content during baking
FOS content was analyzed at each baking step to verify FOS production by invertase. Figure 2 shows the changes in sucrose and FOS content during the baking of castella and sweet dough bread with different invertase dosages. Castella had a short mixing time and no fermentation process but a long baking time, and the initial sucrose content was 35.0%. The sucrose content decreased and FOS content gradually increased during the mixing and baking steps, resulting in final sucrose content of 27.3% and kestose content of 4.6%. For the sweet dough bread, which had long mixing and fermentation times but a short baking time, FOS production started at the mixing stage and primarily occurred during fermentation. The final product after cooling had a sucrose content of 4.9% and a kestose content of 2.4%. The slight increase in FOS after baking was due to water loss. As shown in Fig. 2, FOS content increased as the reaction proceeded. The highest FOS production rate was 11.7%/h during the first 30 min, followed by 3.2–4.8%/h during the next 30 min. An excessively long enzyme reaction reduced product manufacturing efficiency and sweetness; thus, we confirmed that the optimal reaction time was 1 h.
Fig. 2.
Sucrose and FOS content produced during baking process
Comparison with commercial FOS-added products
Specific volume and textural analysis
We compared the quality characteristics of baked products treated with invertase to produce FOS in situ to those with or without commercial oligosaccharides. FOS levels of finished products were similar in enzyme-treated and commercial oligosaccharide-added groups (Table 3). However, the enzyme-treated group had better specific volume and hardness characteristics than the commercial group. The specific volume and hardness of the control group and the enzyme-treated group were similar. The commercial group had a lower specific volume and a higher hardness than the control group: by 20.8% (height) and 17.4% (specific volume) for castella and by 79% and 59% for sweet dough bread, respectively. This result is consistent with Park et al. (2016), who reported that adding more than 6% FOS negatively affects bread loaf volume and proofing volume, resulting in reduced baking quality of the dough. The enzyme-treated group maintained a similar specific volume as the control group, despite having similar FOS levels as the commercial group. This indicates that the in situ enzymatic process did not compromise the quality of the baked products. In sponge cakes, such as castella, volume is closely related to aeration, which depends on the emulsion stability of the raw materials, such as eggs (Ronda et al., 2005). Adding commercial oligosaccharides may have disrupted stability, resulting in a lower volume of castella. In addition, the sucrose content of the commercial product decreased by 10% to match that of the enzyme-treated group, which may have contributed to the deterioration in quality by affecting the fermentation or rheology of the starch and protein (Renzetti and van der Sman, 2022). In addition, adding commercial oligosaccharides to sweet chickpea paste resulted in a thin texture and a low-quality product, as shown in Fig. 3. Henderson et al. (2012) patented an in situ process to produce FOS in fruit drinks (e.g., orange juice or apple juice) using an enzymatic process. However, this process was limited to liquids. We developed an in situ process for producing FOS in various solid foods, such as castella and sweet dough bread, which overcame the limitations of the patent.
Table 3.
Comparison of texture and volume between control, invertase-added products and commercial fructooligosaccharide-added products
| Sample | Texture | Control | T1_enzyme | T2_commercial |
|---|---|---|---|---|
| Castella | Height (cm) | 9.09 ± 0.06a | 9.10 ± 0.04a | 7.20 ± 0.14b |
| Hardness (g) | 537.3 ± 31.9a | 515.5 ± 16.6a | 966.4 ± 53.9b | |
| Hardness (N) | 5.3 ± 0.3a | 5.1 ± 0.3a | 9.5 ± 0.5b | |
| Sweet dough | specific volume (mL/g) | 6.23 ± 0.08a | 6.24 ± 0.15a | 5.15 ± 0.25b |
| Hardness (g) | 319.0 ± 17.4a | 325.8 ± 24.0a | 509.7 ± 22.9b | |
| Hardness (N) | 3.1 ± 0.2a | 3.2 ± 0.2a | 5.0 ± 0.2b |
Values are shown as mean ± standard deviation and treatment was performed in quadruplicate
Different lowercase letters mean significant statistical differences (p < 0.05) between different treatment groups
Fig. 3.
Texture profile analysis of sweet dough bread
Bread staling
Sugar provides sweetness and prevents staling of confectionery and baking products. Reducing the sugar content negatively affects these functions. However, we used invertase to produce FOS from sucrose during manufacture, which inevitably reduced the sweetness of the products without changing their sugar content or staling rate. As shown in Fig. 3, the staling rate of the enzyme-treated group was similar to that of the control group containing full sugar, while the test group with reduced sugar levels had a higher staling rate.
We produced prebiotic FOS in baked products using an in situ enzymatic process with invertase. Castella, sweet dough bread, and sweet chickpea paste were prepared with different amounts of invertase and compared to products containing commercial oligosaccharides or without any additives. The quality characteristics, sugar content, and FOS levels of the products were measured and analyzed. The enzyme-treated products had lower sugar levels but similar quality characteristics as the products without additives, while the commercial oligosaccharide-added products had lower quality characteristics. The FOS content of the enzyme-treated products ranged from 2.4% to 8.0%, depending on the type and amount of invertase used. This study demonstrates that this in situ enzymatic process is a feasible and effective way to produce FOS in baked products without compromising quality.
Acknowledgements
This study did not receive any fund.
Declarations
Conflict of interest
The authors declare that they have no conflicts of interest.
Footnotes
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Sung Hoon Park and Sung Ho Lee have contributed equally to this work as corresponding authors.
Contributor Information
Sung Hoon Park, Email: sungpark@gwnu.ac.kr.
Sung Ho Lee, Email: sungholee@spc.co.kr.
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