Modification of black wheat bran by superfine grinding and Neurospora crassa fermentation: Physicochemical properties, mixed flour quality, steamed bread quality, and flavor
Anqi Liu
a,b, Haiqin Li
a,b, Wentao Xu
c, Longjiao Zhu
c, Shuangshuang Ye
a,b, Tianyi Li
a,b, Jingfang Li
a,b,*, Shimin Chang
a,b,**, Chanyuan Xie
a,b,***aCollege of Life Sciences and Food Engineering, Hebei University of Engineering, Handan, 056038, Hebei, China
bHandan Key Laboratory of Development of Natural Products and Functional Foods, Handan, 056038, Hebei, China
cDepartment of Nutrition and Health, China Agricultural University, Beijing, 100083, China
A R T I C L E I N F O Keywords:
Modified black wheat bran Physicochemical properties
Steamed bread with modified black wheat bran Volatile flavor compounds
A B S T R A C T
This study investigated the effects of superfine grinding (SG) andNeurospora crassa(Nc) fermentation on the properties of black wheat bran (BWB), the characteristics of its mixed flour, and the flavor of steamed bread.
Results showed that anthocyanin was increased by 91.07% through SG treatment (P<0.05). After Nc fermen- tation treatment, theβ-carotene content, total phenolic content, oil-holding capacity (OHC), ABTS+ radical scavenging ability, and freeze-thaw stability (FS) were increased by 208.16%, 104.39%, 43.68%, 11.82%, and 17.54%, respectively (P<0.05), while the water-holding capacity (WHC) of BWB was reduced by 42.19% and 13.42% after SG and Nc treatments, respectively(P<0.05). The color and pasting properties of BWB mixed flour were changed by both treatments, and the surface was made looser and more porous. Furthermore, 52 phenolic compounds were identified in SG modified BWB (SG-BWB) and 128 in Nc-fermented modified BWB (Nc-BWB).
The flavor compounds in steamed bread produced from mixed flour treated with SG and Nc fermentation were enhanced, particularly in alcohols and terpenes. Notably, hexanoic acid, cyclohexanone, 2-pentylfuran, and (E)- 2-hexenal in Nc-BWB steamed bread increased by 2.33, 2.09, 1.66, and 1.13 times, respectively. This study demonstrated SG and Nc fermentation treatment exhibit substantial potential as modification techniques for BWB.
1. Introduction
Wheat is currently one of the most widely cultivated grains in the world. According to the United States Department of Agriculture, global wheat production reached 777 million tons in the 2020/2021 crop year.
Wheat bran, a byproduct of wheat flour processing, accounts for approximately 25% of the total mass (Neves et al., 2006). It contains abundant natural active ingredients, including dietary fibers, flavo- noids, polyphenols, and oligosaccharides, which possess antioxidative, anti-fatigue, blood sugar and lipid regulating, and intestinal microbiota regulation effects (Dhua et al., 2021). Among different wheat varieties, black wheat (BW) has a higher content of anthocyanins, dietary fibers, phenolics, protein and minerals (Feng et al., 2022;Saini et al., 2021).
However, due to its high content of insoluble dietary fibers, rough texture, and hardness, wheat bran exhibits poor quality characteristics, hindering its application in the food industry (Kong et al., 2023).
Based on these characteristics, wheat bran typically undergoes modification processes before entering the food market and commercial use, aiming to achieve improved sensory attributes and higher nutri- tional value (Chen et al., 2023). Methods for modifying wheat bran primarily include physical, biological, and chemical modifications.
Physical modification was a typical method to enhance the functionality of cereal bran by altering the morphology and chemical structure of its polymers, thereby optimizing the physicochemical properties of insol- uble dietary fibers in cereal bran (Tian et al., 2024; C.Wang, Lin, et al., 2023). Superfine grinding (SG) technology has significantly reduced the
* Corresponding author. College of Life Sciences and Food Engineering, Hebei University of Engineering, Handan, 056038, Hebei, China.
** Corresponding author. College of Life Sciences and Food Engineering, Hebei University of Engineering, Handan, 056038, Hebei, China.
*** Corresponding author. College of Life Sciences and Food Engineering, Hebei University of Engineering, Handan, 056038, Hebei, China E-mail addresses:[email protected](J. Li),[email protected](S. Chang),[email protected](C. Xie).
Contents lists available atScienceDirect
LWT
journal homepage:www.elsevier.com/locate/lwt
https://doi.org/10.1016/j.lwt.2024.117049
Received 16 September 2024; Received in revised form 31 October 2024; Accepted 12 November 2024 LWT - Food Science and Technology 213 (2024) 117049
Available online 14 November 2024
0023-6438/© 2024 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by- nc-nd/4.0/ ).
bran’s particle size and surface roughness while enhancing the total phenolic content and antioxidant capacity (Liang et al., 2024). More- over, SG has been found to improve the cation exchange capacity and glucose binding strength of bran. In vitro digestion studies further revealed that SG enhanced the release of flavonoids and antioxidant activity during the digestion process of bran flour (Wang et al., 2023).
Additionally, SG effectively promoted protein release from bran by disrupting tissue structure and cell wall integrity of wheat bran (Li et al., 2023). Biological modification, with advantages such as operational safety, simplicity, controllability, and the ability to degrade specific macromolecules or anti-nutritional factors in cereal bran, represents a highly promising method for modifying cereal bran (Verni et al., 2019).
A previous study showed that solid-state bran fermentation using Rhizopus oryzae generates bioactive compounds with potential health benefits and improves its flavor characteristic (Janarny and Gunathi- lake, 2020). Optimizing of fermentation process parameters forTricho- derma reesei and Neurospora crassa (Nc) on wheat bran solid-state cultivation achieved a cellulase enzyme activity of 4.72 IU/mL (Verma
&Kumar, 2020). The fermentation of okara using Nc-a and Nc-b strains
significantly enhances cellulase and protease activities, increasing both the flavonoid content and diversity (Yao et al., 2023). Furthermore, polysaccharides derived from okara fermented by Nc are shown to mitigate DSS-induced intestinal barrier damage and microbial dysbiosis in mice (Huang et al., 2022). Chemical modification allows targeted alterations of the chemical structure to enhance the physical properties of grain dietary fibers and proteins, such as in maillard reactions, pH shifts, phosphorylation reactions, or through the addition of acylating agents for protein modification (Ou et al., 2024). However, due to the possibility of side reactions during the chemical treatment process, which may produce toxic gases and cause environmental pollution, the application of chemical modification in wheat bran research was mini- mal (Maini Rekdal et al., 2024).
In the production of whole wheat flour, bran separated from the wheat during milling is typically modified and then reintegrated into the flour at specified proportions. This practice improves the dough’s functional characteristics and enhances the final baked products’ nutritional and sensory qualities. Common bran products include high- fiber biscuits, whole wheat products, and Chinese steamed bread (Ma et al., 2021;Zhang et al., 2022). A study conducted byTang et al. (2024) investigated the fermentation of wheat bran using S. fibuligeraand P. pentosaceus, which was reincorporated into flour for the preparation of steamed bread. The results demonstrated that the steamed bread made with bran fermented byP. pentosaceusandS. fibuligerais rich in alcohols and acids, significantly enhancing its sensory flavor. However, research on the modification of black wheat bran (BWB), its character- istic changes, and its application in wheat-based products is rarely re- ported. Thus, a newly developed BW variety named Jizi439, selected from four different breeding lines, was used in this study. It was artifi- cially developed through the crossbreeding of Australian black wheat and Chinese white-grain wheat (Chen et al., 2022). This variety was developed by the Institute of Cereal and Oil Crops at the Hebei Academy of Agriculture and Forestry Sciences and was officially approved by the Hebei Provincial. Notably, it was the first new black wheat variety approved in Hebei Province, China (Lan et al., 2022). Moreover, SG and solid-state fermentation with Nc were selected to modify BWB. Then, we investigated the changes in physicochemical properties, phenolic com- pounds, and microstructure of BWB before and after modification.
Additionally, it explored the effects of gelatinization and color on reconstituted whole BW flour, preparing it for steamed bread. A comparative analysis was conducted on the volatile flavor characteris- tics of steamed bread. This research aims to promote the application of BWB in the food industry. These findings provide a solid foundation for further research and development in the functional food industry, particularly in the application of BW as a novel ingredient in health-oriented food products.
2. Materials and methods 2.1. Materials and chemicals
Commercial BW flour was produced by Guantao County Yueqing Agricultural Technology Co., Ltd. (Handan, China). BW flour contained 16.34% protein, 2.34% lipids and 9.07% moisture, and it was finely milled. The Nc (Strain number AS3.1603) and Potato Dextrose Agar (PDA) medium were both procured from the Microbiological Culture Collection Co., Ltd. (Shanghai, China). Food-grade Jinlongyu soybean salad oil was used, while ammonium formate, ammonia solution, formic acid, methyl tert-butyl ether, acetonitrile, methanol, and dichloro- methane were of chromatographic grade. All other reagents were of analytical grade.
2.2. BWB modification and BW mixed flour preparation 2.2.1. BWB modification treatments
The freeze-dried powder of Nc was inoculated onto PDA medium for second-generation expansion. An appropriate amount of activated Nc was selected and inoculated onto PDA medium. The culture was incu- bated at 27◦C in a culture chamber (HR40-II A2(KY) Biological Safety Cabinet, Haier Biomedical Co., Ltd., China) for 72 h for future use. BWB, sieved through a 0.425 mm screen, was finely ground and sterilized in a drying oven (BPG-9100BH high-temperature forced-air drying oven, Shanghai Lanbao Testing Equipment Co., Ltd., China) at 125◦C for 20 min. Eight grams of sterilized bran were weighed. The medium was prepared by adding the sterilized bran to sterile water at a ratio of 1:0.6 (g/mL). Nc spores were activated through two growth rounds and then inoculated into the BWB medium. The culture was incubated at 27◦C for 6 d, dried overnight at 55◦C, ground, and sterilized at 121◦C for 40 min to obtain the Nc-fermented modified black wheat bran (Nc-BWB).
The superfine grinding modified black wheat bran (SG-BWB) was prepared using a modified protocol based on Liang et al. (2024).
Initially, the BWB was baked at 70◦C for 2 h and then sieved through a 0.178 mm screen. SG was then performed using an Ultrafine Crushing Equipment (SAINA 160, Shanghai, China), which was set to an operating frequency of 350 Hz, with a fan frequency of 48 Hz and a feed rate of 170 g/h. The BWB was fed into the system at ambient temperature, and the outlet temperature was maintained between 50◦C and 70◦C during pulverization. The particle size of SG-BWB was measured using a laser diffraction particle size analyzer (Mastersizer 3000, Malvern In- struments, Worcestershire, UK), resulting in a particle size distribution of 10.6-18.5μm. All samples were sealed in pouches and stored at 4◦C for further analysis.
2.2.2. Whole BW mixed flour preparation
BWB, SG-BWB, and Nc-BWB were each incorporated at an 8% ratio and thoroughly mixed with BW flour to prepare 3 types of BWB com- posite flours. All samples were sealed in pouches and stored at 4◦C for further analysis.
2.3. Water holding capacity (WHC), oil holding capacity (OHC) and freeze-thaw stability(FS)
The WHC was measured as reported byJiang, Zeng, et al. (2024) with slight modifications. Two-gram samples (M1) were added to distilled water at a 1:20 (g/mL) liquid-to-material ratio. The mixture was heated in a water bath at 40◦C for 1 h and then centrifuged at 3000 rpm for 25 min. The supernatant was discarded, and the mass of the residue denoted as M2, was measured.Formula (1)was used to calculate the WHC (g/g) of BWB.
WHC(g/g) = (M2− M1)/M1 (1)
The OHC was measured as reported byLi et al., 2024with slight modifications. Two-gram samples (M1) were added to soybean oil at a
material-to-liquid ratio of 1:10 (g/mL). The mixture was mixed thor- oughly and allowed to stand at room temperature for 1 h. The mixture was then centrifuged at 3000 rpm for 25 min, the mass of the residue, designated M2, was measured. Formula (2)was used to calculate the OHC(g/g) of BWB.
OHC(g/g) = (M2− M1)/M1 (2)
The samples (2.0 g) were mixed with 20 mL of distilled water in a pre-weighed centrifuge tube. The contents were mixed thoroughly, and the tube was placed in a boiling water bath for 8 min. After heating, the tube was allowed to cool to room temperature before being placed in a freezer at -18◦C for 24 h. After freezing, the tube was removed and allowed to thaw naturally at room temperature. The thawed sample was centrifuged at 3000 rpm for 15 min. The tube was weighed post- centrifugation, and the supernatant was removed. The centrifuge tube was inverted to drain residual moisture, and it was weighed again.
Formula (3)was used to calculate the FS of BWB.
FS= (m2− m3)/(m2− m1) (3)
m1 represents the mass of the centrifuge tube, g; m2 represents the total mass of the sample and centrifuge tube after centrifugation, g; m3 represents the total mass of the sample and centrifuge tube after draining, g.
2.4. Measurement of total phenolic content, anthocyanins andβ-carotene accurately
The sample (1 g) was precisely weighed and added to 25 mL of 60%
ethanol solution. The mixture was subjected to sonication at 300 W and 40◦C for 1 h. Subsequently, the extraction was centrifuged at 8000 rpm for 20 min, after which the supernatant was collected as the modified extract of BWB.
The total phenolic content was determined using the Folin-Cio- calteu’s method with minor modifications (Xiao et al., 2014). Gallic acid standard or sample solution (25μL) was added to a 96-well plate. 125μL of Folin-Ciocalteu reagent (0.2 mol/L) was added and allowed to react at room temperature for 10 min. Then, 125μL of saturated Na2CO3solu- tion (10 g/100 mL) was added. The plate was slowly shaken using a shaker, and the absorbance was measured at a wavelength of 760 nm using a spectrophotometer (CS-820N, Shanghai Jiezhun Instrument Equipment Co., Ltd.). The total phenolic content was calculated using the linear regression equation derived from gallic acid standards (0-400 μg/mL), where y=0.0046x+1.73 (R2=0.9921). The results were expressed as mg gallic acid equivalents per gram dry weight (mg GAE/g DW), where GAE represents gallic acid equivalents used to quantify the concentration of total phenolic content.
To determine anthocyanin content, following the method of (Vel´asquez et al., 2021) with a few modifications, 0.2 mL of the extracted liquid was placed into 2 separate centrifuge tubes. 0.8 mL of KCl-HCl buffer (pH=1) and CH3COONa buffer (pH=4.5) were added to each tube. The mixture was centrifuged at 8000 rpm for 20 min to precipitate impurities. 200μL of the supernatant was added to a 96-well plate. 60% ethanol was used as a blank control instead of the extraction liquid. The absorbance was measured at a wavelength of 520 nm (A1.0 and A4.5).
To determine the β-carotene content of BWB, a 3 g sample was enzymatically digested using ascorbic acid, papain protease, and α-amylase. Following digestion, the sample was saponified with 25 mL of sodium hydroxide. The resulting mixture was extracted, concen- trated, evaporated under nitrogen, and dissolved in dichloromethane.
The solution was filtered through a 0.45μm membrane, and the filtrate was collected in a sample vial for subsequent analysis. Theβ-carotene content was characterized using high-performance liquid chromatog- raphy (LC-2010HT HPLC, Shimadzu Corporation, Ltd., Japan), equipped with a YMC Carotenoid C30 column (250 mm length, 4.6 mm inner diameter, 5μm particle size). The chromatographic conditions were as
follows: an injection volume of 20μL, a column temperature of 30◦C, and a flow rate of 1 mL/min. Detection was performed at a wavelength of 450 nm. The mobile phase consisted of methanol: acetonitrile: water in a ratio of 73.5: 24.5: 2 for phase A, and methyl tert-butyl ether for phase B. The following gradient was used: 0-15 min, 0-41% B; 15-18 min, 41%-80% B, 18-20 min, 80-100% B; 20-22 min, 100%-0% B.
2.5. Measurement of antioxidative activity 2.5.1. DPPH radical scavenging assay
At room temperature, 1 mL of the extract was mixed with 1 mL of 0.125 mmol/L DPPH ethanol solution and incubated in the dark for 30 min. After incubation, 200μL of the mixture was transferred into a 96- well plate, and the absorbance (As) was measured at 517 nm using a spectrophotometer. A control sample, prepared by replacing the extract with 60% ethanol, was also measured for its absorbance (Ac).Formula (4)was used to calculate the DPPH radical scavenging activity of BWB.
DPPH%radical scavenging(%) =Ac− As
Ac (4)
2.5.2. ABTS radical cation scavenging assay
A mixture of 2.6 mmol/L K2S2O8 solution and 7.4 mmol/L ABTS stock solution in a 1:1 ratio was allowed to stand for 12-16 h to prepare the ABTS working solution. This solution was diluted until its absor- bance at 734 nm reached 0.70±0.02. For the assay, 0.2 mL of the extract was mixed with 1.5 mL of the ABTS working solution and incubated in the dark for 10 min. The absorbance (B1) at 734 nm was measured. A control sample, prepared by replacing the extract with 60%
ethanol, was also incubated and measured for its absorbance (B2).
Formula (5)was used to calculate the ABTS radical cation scavenging activity of BWB.
ABTS radical cation scavenging(%) =1− B1
B2 (5)
2.6. UPLC-MS/MS analysis of phenolic compounds 2.6.1. BWB extraction
Identification of phenolic compounds by UPLC-MS/MS was con- ducted with slight modifications to the methods described byLiang et al.
(2020)andViant et al. (2017). Three BWB powder samples (50 mg each) were weighed respectively using an electronic balance (MS105DМ), after which 1200μL of pre-cooled 70% methanolic aqueous internal standard extract (-20◦C) was added. The mixture was vortexed for 30 min every 30 s, repeated 6 times. The sample was centrifuged at 12,000 rpm for 3 min, and the supernatant was carefully aspirated. The samples were then filtered through a microporous NY membrane (0.22μm) and stored in an injection vial for subsequent UPLC-MS/MS analysis. UPLC conditions: All BWB samples were analyzed using two distinct LC/MS methods. An aliquot of each sample was analyzed under both positive and negative ionization modes, with elution performed on a T3 column (Waters ACQUITY Premier HSS T3 Column, 1.8μm, 2.1 mm×100 mm) using the same gradient. Solvent A consisted of 0.1% formic acid in water, while solvent B comprised 0.1% formic acid in acetonitrile, using the following gradient: 5%–20%, 2 min; 20%–60%, 3 min; 60%–99%, 1 min, held for 1.5 min; 99%-5% mobile phase B within 0.1 min, and held for an additional 2.4 min. The analytical conditions were as follows:
column temperature, 40◦C; flow rate, 0.4 mL/min; injection volume, 4 μL. TOF MS conditions: mass range, 50-1000 Da; accumulation time, 200 ms; and dynamic background subtraction, on. The product ion scan parameters were set as follows: mass range of 25–1000 Da; accumula- tion time, 40 ms; collision energy, 30 or -30 V in positive or negative modes, respectively; collision energy spread, 15; resolution, UNIT;
charge state, 1 to 1; intensity, 100 cps; exclusion of isotopes within 4 Da;
mass tolerance, 50 ppm; and a maximum of 18 candidate ions monitored per cycle.
2.6.2. Qualitative analysis of metabolites
The raw data from mass spectrometry was converted to mzXML format using ProteoWizard. Peak extraction, alignment, and retention time correction were performed using the XCMS program. Peaks with a missing rate greater than 50% in each sample group were filtered out.
Peak areas were corrected using the SVR method. The corrected and filtered peaks were identified by searching the laboratory’s in-house database, integrating public and predictive databases, and using the metDNA method for metabolite identification. Finally, substances with a comprehensive identification score above 0.5 and a CV value less than 0.5 in QC samples were selected. Positive and negative modes were combined, retaining substances with the highest quality level and the smallest CV value.
2.7. Scanning electron microscopy (SEM) analysis
The surface morphologies of modified BWB were visualized using an SEM spectrometer (SU-8100, Hitachi, Tokyo, Japan) operated at an acceleration voltage of 0.5 kV. Each BWB sample was sputtered with gold and observed at two magnifications of 30×and 800×.
2.8. Rapid viscosity analysis (RVA)
Following the method of (Wu et al., 2022) with minor modifications, a Rapid Visco Analyser RVA-4500 (Perten Instruments Ltd., Australia) was employed to investigate the gelatinization characteristics of the mixture consisting of 8% BWB and BW flour.The mixed samples (3.5 g mixture per 25.0 mL distilled water, 14% moisture content of the mix) were held at 50◦C for 60 s, then heated at 12◦C/min to 95◦C, held at 95◦C for 150 s, cooled to 50◦C within 230 s, and held at 50◦C for 120 s.
The paddle speed was set to 960 rpm at the first 10 s, and then 160 rpm during the remainder of the experiment. The curves obtained peak vis- cosity, trough viscosity, breakdown, final viscosity, setback, and pasting temperature.
2.9. The color characteristics of BWB and BW mixed flour
The color of BWB and BW mixed flour was measured using a digital precision colorimeter (Shanghai Junzhun Instrument Equipment Co., Ltd, China), to obtainL*,a*, andb*values.
2.10. Steamed bread procedure
The ingredients for steamed bread include 100 g of flour (BW flour, BWB mixed flour, SG-BWB mixed flour, Nc-BWB mixed flour), 1 g of low-sugar yeast, and 49 g of water. The low-sugar yeast was dissolved in 49 g of warm water, and flour was added to the dissolved yeast solution.
The dough was kneaded with an electric mixer 12 times until a round bun shape was formed, and then placed in a proofing box at 37◦C with a humidity of 60% for 35 min. The dough was steamed on high heat for 15 min, then switched to low heat and steamed for an additional 3 min.
After turning off the heat, the dough was allowed to sit for 2 min before being removed and left to cool for further analysis.
2.11. Specific volume (SV)
The steamed bread was weighed, and the volume was measured using the rapeseed displacement method (Dan et al., 2022). The SV was calculated by dividing the volume by the weight of the steamed bread and was expressed as mL/g.
2.12. Measurement of flavor compounds 2.12.1. GC-MS analysis of steamed bread
The volatile components of steamed bread were analyzed using GC- MS (TQ8050NX, Shimadzu Corporation, Ltd., Japan) (Shao et al., 2024).
The extraction head was aged in the GC injector for 60 min prior to use.
A sealed 20 mL headspace vial containing 3 g of the sample was pre- pared, and the aged extraction head was promptly inserted into the vial.
The sample was extracted for 40 min at 60◦C in a constant temperature water bath. Following extraction, the headspace vial was immediately introduced into the GC injector set to 250◦C, and the analysis was carried out over a 5 min period. Volatile components with a retention match greater than 90% were retained, while substances identified as column bleed (polymethylsiloxane compounds) were excluded from the analysis. The relative percentage content of the various retained volatile components was quantified using peak area normalization.
2.12.2. GC-IMS analysis of steamed bread
Based on a previous report (Li, Zhang, et al., 2024), the flavor of steamed bread was analyzed using Headspace Gas Chromatography-Ion Mobility Spectrometry (HS-GC-IMS) (FlavourSpec, g.a.s., Dortmund, Germany). The steamed bread (1 g) was placed in a 20 mL headspace vial and incubated at 80◦C for 15 min, with a non-split injection. The incubation speed was set at 500 rpm, and the injection temperature was maintained at 85◦C. GC Conditions: column temperature, 60◦C; carrier gas, high-purity nitrogen (purity ≥99.999%); programmed pressure increase, 2.00 mL/min, maintained for 2 min; 2-10 mL/min, 8 min;
10-100.00 mL/min,10 min.Total chromatographic run time: 20 min.
IMS conditions: ionization source, tritium source (3H); drift tube length, 53 mm; electric field strength, 500 V/cm; drift tube temperature, 45◦C;
drift gas, high-purity nitrogen (purity≥99.999%); drift gas flow rate, 150 mL/min; ion mode, positive ion mode. A mixed standard of six ketones was detected to establish a calibration curve for retention time and index. The VOCs were qualitatively analyzed using the GC retention index (NIST 2020) database and the IMS migration time database embedded in the VOCal software. The two-dimensional spectra, differ- ential spectra, and fingerprint plots of the volatile components were generated using the Reporter and Gallery Plot modules in the VOCal data processing software for comparing volatile organic compounds betwen steamed breads of BW, BWB, SG-BWB, Nc-BWB.
2.13. Statistical analysis
All experiments were conducted with triplicate biological replicates, and each sample was tested at least three times for technical replicates.
All data were analyzed using one-way ANOVA followed by the Duncan test to determine the significance of the differences atP<0.05using the SPSS statistical software (Version 25.0, SPSS Inc., Chicago, USA). The results were presented using mean ± standard deviation (SD). The experimental data were plotted using Origin 64-bit software (Version 2018, OriginLab Corporation, Northampton, Massachusetts, USA).
3. Results and discussion 3.1. WHC, OHC and FS
WHC, OHC, and FS of different modified BWB samples were measured, and the results are shown in Fig. 1. Dietary fibers are generally considered to interact with water through two mechanisms:
water retention via capillary action and bonding through hydrogen bonds and dipole interactions (F¨oste et al., 2020). Compared to BWB and Nc-BWB, SG-BWB showed the lowest WHC. This could be attributed to the porous matrix structure formed by polysaccharide chains during SG processing, which accommodates a significant amount of water through hydrogen bonding. However, the SG adversely affected the hydration properties of BWB by disrupting the polysaccharide chains (Gao et al., 2020). The WHC of Nc-BWB was significantly lower than that of BWB (P<0.05). Although the fiber components of BWB were decomposed by enzymes that were produced during fermentation by Nc, such as cellu- lase and ligninase, resulting in a more porous microstructure (Alhomodiet et al., 2022), it has also been reported that lignocellulosic
biomass can be directly converted into ethanol during fermentation by Nc (Chen et al., 2024). Furthermore, during fermentation, nutrients such as proteins and cellulose from the bran were utilized by Nc as carbon and nitrogen sources necessary for its growth. Research byGuan et al. (2023) indicated that the protein content of black rice dietary fiber significantly decreased from 4.45% to 2.4% following fermentation with Nc. Hyphae were also produced by Nc during fermentation, which supported rapid nutrient transport and fungal growth. These hyphae were primarily composed of chitin andβ-glucan, which provided structural support and protection (Honda et al., 2020). Additionally, these hyphae contained proteins, lipids, and trace amounts of minerals and other poly- saccharides. Thus, during the fermentation process, these chemical re- actions resulted in a reduction in the overall structural density of BWB, with disruptions to protein and polysaccharide molecular structures.
The exposure of covalent bonds between hemicellulose and cellulose, as well as ether bonds between lignin and hemicellulose, led to the for- mation of other compounds. Consequently, the physical trapping ability of Nc-BWB through capillary action was diminished, which in turn negatively impacted its WHC (Li et al., 2024).
There was no statistically significant difference in OHC values be- tween BWB and SG-BWB (P>0.05). The surface characteristics of dietary fiber particles, including surface area, porosity, surface site activity, structural looseness, and composition, were typically cited as being closely related to OHC (Yu et al., 2018). The highest OHC observed in Nc-BWB might be attributed to a more irregular network structure and a larger specific surface area (SSA), which helped expose additional nonpolar groups (Li, Zhang, et al., 2024;Qin et al., 2023). Therefore, Nc-BWB showed significant potential in the preparation of high OHC foods. High OHC bran prevents fat dissolution and quality deterioration during the processing of high-fat foods, which may help reduce cholesterol levels in the human body (Li et al., 2021;Zheng and Li, 2018).
FS was indicated by the degree to which a sample’s original tissue structure was maintained after being subjected to low-temperature freezing and subsequent thawing. It was reflected by the ability to withstand severe physical changes such as low-temperature freezing and melting (Wu et al., 2024). Several factors affected FS, including freezing rate, freezing time, and freeze-thaw temperature (Cheng et al., 2024).
Nc-BWB exhibited a lower drip loss rate, indicating significant potential for preparing frozen foods and pre-cooked products. SG-BWB showed a significantly higher drip loss rate compared to BWB, indicating poorer FS (Shen et al., 2024). The higher drip loss rate observed in SG-BWB could be attributed to its unique surface structure compared to Nc-BWB. Specifically, the smaller particle size in SG-BWB allows for the formation of more ice crystals between particles, which, along with an increased freezing rate, may result in greater water release during thawing (Yi et al., 2024).
3.2. Total phenolic content, anthocyanin andβ-carotene
Fig. 1D–F showed the changes in total phenolic content, anthocy- anin, andβ-carotene contents before and after the modification of BWB.
The total phenolic content of untreated BWB was 1.14±0.02 mg GAE/g DW. After SG and Nc fermentation, the total phenolic content of BWB increased by 28.95% and 104.39%, respectively, compared to the un- treated BWB group. These results are consistent with previous research findings, indicating that both SG and fermentation significantly increased the total phenolic content in BWB (Lin et al., 2024) (P<0.05).
SG physically overcomes the binding forces within the BWB, signifi- cantly breaking down the cell wall matrix and promoting the release of bound polyphenols in free form (Yi et al., 2024). During fermentation, Nc produced various digestive enzymes, such as cellulase, ligninase, and pectinase, which decomposed plant cell wall components and hydro- lyzed the ester bonds connecting phenolic compounds to the cell wall, Fig. 1.Modified BWB physicochemical properties. (A) Modified BWB water retention capacity. (B) Modified BWB oil adsorption capacity. (C) Modified BWB freeze- thaw stability. (D) Modified BWB anthocyanin content. (E) Modified BWBβ-carotene content. (F) Modified BWB total phenolic content. (G) Modified BWB DPPH radical scavenging rate. (H) Modified BWB ABTS radical scavenging rate.
thereby aiding the release phenolic substances from the matrix (Lin et al., 2020).
The anthocyanin content in BWB significantly increased after SG, reaching 135.26 ± 6.45 mg/kg, representing a 91.07% increase (P<0.05). This finding is consistent with previous research results (Jiang et al., 2024;Qiu et al., 2022). The anthocyanin content of BWB after Nc fermentation decreased to 59.41±0.89 mg/kg, representing a reduction of 16.08%. This decline is attributable to the metabolic pro- cesses during fermentation, in which anthocyanins are cleaved by fungal β-glucosidase, and the resulting sugar moieties are utilized by the fungus for growth and reproduction (Vattem&Shetty, 2002). Interestingly, the β-carotene content of Nc-BWB reached 119.69±3.35μg/kg, which was 3.08 times that of BWB. This is due to Nc synthesizing yellow-orange carotenoids through the mevalonate pathway (Gmoser et al., 2018).
However, the β-carotene content in SG-BWB decreased by 29.45%
compared to BWB, which may be attributed to β-carotene, being a fat-soluble compound with poor stability, was prone to cis-trans isom- erization and oxidative degradation. It was sensitive to light, heat, ox- ygen, acids, and metal ions. During the pulverization process, substantial heat was generated by the high rotational speed of the SG rotor, leading to the thermal decomposition ofβ-carotene. Additionally, the reduction in particle size increased friction, which contributed to its oxidative degradation (Ramezani et al., 2024;Rao et al., 2024).
3.3. Antioxidant activity
The antioxidant activity of BWB samples before and after the two modification methods was evaluated using DPPH radical scavenging Fig. 2. The impact of modification treatments on the phenotype of BWB. (A) Morphological observation of untreated, Nc-BWB, and SG-BWB. (B) Scanning electron microscopy displays the differences between untreated, Nc-BWB and SG-BWB samples at two magnifications (30×and 800×).
capacity and ABTS radical scavenging capacity (Fig. 1G, H). Nc-BWB demonstrated a strong ABTS radical scavenging capacity, reaching 84.11±0.18%, indicating that Nc fermentation can enhance antioxi- dant capacity. This enhancement was likely attributed to the production ofβ-carotene during the fermentation process, which may have facili- tated the reduction of ABTS radicals through activating antioxidant response elements (ARE) and antioxidant enzymes (Zhong et al., 2024).
The results of the DPPH radical scavenging assay indicated a significant decrease in the Nc-BWB sample compared to the BWB group, consistent with the findings of Janarny and Gunathilake (2020) (P< 0.05). In contrast, the ABTS and DPPH radical scavenging capacities of the SG-BWB sample significantly decreased compared to the BWB group.
This was likely due to the significant heat generated during the SG process, which caused structural changes in polyphenols and reduced their chemical reactivity with free radical ions (Altan et al., 2009).
3.4. The UPLC-MS/MS analysis of phenolic compounds
In this study, we utilized UPLC-MS/MS to analyze phenolic com- pounds in three types of wheat bran: BWB, SG-BWB, and Nc-BWB. A total of 185 phenolic metabolites were identified, including 90 phenolic acids and 95 flavonoids (details shown inTable S1). The SG modification of BWB resulted in the detection of 4 newly generated metabolites, including 6,7-dihydro-4-(hydroxymethyl)-2-(p-hydroxyphenethyl)-7- methyl-5H-2-pyrindinium, 3-caffeoyl pelargonidin 5-glucoside, typha- neoside, and 5-[(Z)-nonadec-10-enyl]benzene-1,3-diol, while 2 metab- olites, albanin F and dactilin, were found to be absent. In contrast, Nc- BWB yielded 7 newly generated metabolites, including 6,7-dihydro-4- (hydroxymethyl)-2-(p-hydroxyphenethyl)-7-methyl-5H-2-pyrindinium, 3-caffeoylpelargonidin 5-glucoside,N-(4-hydroxyphenethyl) tetracosa- namide, typhaneoside, 5-[(Z)-Nonadec-10-enyl]benzene-1,3-diol, 1-(2- Allylphenoxy)-3-morpholinopropan-2-ol, and 6-O-caffeoyl-D-glucose.
However, 8 metabolites, such as 6-O-acetylarbutin, trihydrox- ycinnamoylquinic acid, isorhamnetin-3-O-(6
″
-malonylglucoside), quer- cetin-3-O-(6″
-malonyl)galactoside, 4-O-Glucosyl-4-hydroxybenzoic acid, and luteolin-7-O-[β-D-glucuronosyl-(1->2)-β-D-glucuronide], were no longer detected. Notably, the metabolomic profile of Nc-fermented BWB exhibited greater conservation and diversity. To further analyze the phenolic components in BWB, the fold-change (FC) value (BWB/SG- BWB, BWB/Nc-BWB) was used as the screening criterion, with FC>2 or FC<0.5 serving as thresholds (Wei et al., 2023). This screening iden- tified 52 differentially expressed phenolic compounds in SG-BWB and 127 in Nc-BWB, with detailed information inTable S2. Compared to BWB, SG-BWB exhibited an upregulation of 13 phenolic acids, a downregulation of 17, as well as an upregulation of 7 flavonoids and a downregulation of 15. Among the phenolic acids, compounds with strong antioxidant activity, such as 2-naphthol, caffeic acid, 3-glucoside, and koaburaside, were reduced by 13.39, 6.2, and 27.96 times, respectively, compared to BWB. Moreover, 2-naphthol was found to have a strong correlation with DPPH antioxidant activity, which explained the decrease in ABTS, DPPH antioxidant activity after SG modification (S´anchez-García et al., 2023;Zhu et al., 2024). Flavonoids such as isorhamnetin-3-O-rutinoside (Narcissin) and kaempfer- ol-3-O-(2″
-acetyl)glucoside were also lower in SG-BWB compared to BWB. Other commonly known phenolic compounds, including proto- catechuic acid, Moracin (I, M), 1-O-glucosinoyl-β-D-glucose, 4,5-caf- feoylquinic acid, rutin, luteolin-7-O-[β-D-glucuronosyl-(1->2)- β-D-glucuronide], and rosmarinic acid, exhibited minimal change (0.5<FC < 2) (Fernandes et al., 2024; Suwannachot and Ogawa, 2024).
Compared with BWB, Nc-BWB showed an upregulation of 12 phenolic acids and a downregulation of 42, while an upregulation of 12 flavo- noids and a downregulation of 53. Notably, the content of ethyl gallate increased by 39.2 times relative to BWB, consistent with previous re- ports demonstrating an increase in methyl gallate content following Nc fermentation of pecans; studies have also shown that gallate ester pos- sesses a wide range of bioactivities, including antioxidant,
anti-inflammatory, anti-apoptotic, and antimicrobial properties(Choi et al., 2022;Rajan and Muraleedharan, 2017). The chlorogenic acids in BWB, such as chlorogenic acid, isochlorogenic acid A, and 4,5-caffeoyl- quinic acid, were found to be 114.05, 135.37, and 58.69 times higher than those in Nc-BWB, respectively. Similarly, anthocyanins such as peonidin-3-O-β-galactopyranoside, peonidin 3-(6
″
-acetylglucoside), and [(3S,6S)-6-[2-(3,4-dihydroxyphenyl)-5,7-dihydrox-ychromenylium-3-yl]oxy-3,4,5-trihydroxyoxan-2-yl] methyl acetate were found to be 90.65, 93.16, and 448.80 times higher in BWB compared to Nc-BWB, consistent with the results of anthocyanin content determination in Section3.2. The observed changes in phenolics could be attributed to the varying sensitivities of different phenolic com- pounds to heat treatment. Typically, heat treatment may decrease the content of some compounds due to thermal degradation, while in other cases, high temperatures may promote certain reactions, leading to increased retention of specific substances (Gil et al., 2021). Moreover, many studies have indicated that different anthocyanin compounds and polyphenols induce varying degrees of conformational changes in pro- teins, including alterations in secondary and tertiary structures, as well as the formation of protein-anthocyanin complexes (Cheng et al., 2020;
Jiang, Qi, et al., 2024;Ye et al., 2021). Therefore, during the fermen- tation process with Nc, proteins in BWB were likely consumed as a ni- trogen source for the growth of Nc, which contributed to changes in the phenolic content of Nc-BWB.
3.5. Microscopic structure
Morphological observations of different BWB groups are presented in (Fig. 2A). The microstructural differences of modified BWB were studied using SEM, and the results are shown in (Fig. 2B). It was evident that all samples exhibited an irregular stacked layered structure. The SEM image of the unmodified BWB showed a relatively flat surface with a dense, layered structure, primarily composed of the structural matrix of dietary fiber, with small portions of protein and starch granules attached to it.
The surface structure of Nc-BWB displayed a loose and irregular hon- eycomb structure with high porosity and evident cracks. Oil adsorption was facilitated by the structural feature, contributing to the improved OHC of Nc-BWB and aligning with the findings ofSaini et al. (2023)and Xiong et al. (2022). Furthermore, the exposure of protein particles in Nc-BWB increased, potentially leading to greater exposure of hydro- phobic groups, which, in turn, enhanced surface hydrophobicity and reduced WHC (Ma et al., 2024). The microstructure of SG-BWB exhibi- ted a powdery appearance with pronounced particle agglomeration. The reduction in particle size exposed internal cohesive groups, increasing electrostatic interactions among particles and promoting agglomeration.
Consequently, WHC, OHC, and FS in SG-BWB samples were reduced (Gan et al., 2024;Lai et al., 2022).
3.6. The pasting properties of BWB mixed flour
The pasting properties of the modified and unmodified BWB mixed flour are shown inTable 1. Adding BWB to BW flour reduced the peak viscosity, trough viscosity, breakdown value, and final viscosity. Two main reasons for this were: firstly, BWB replaced part of the BW flour, reducing the starch content. Secondly, BWB contained a large amount of dietary fiber, which had a strong WHC and competed with starch mol- ecules for water molecules, hindering the formation of starch gel (Wu et al., 2021). Additionally, the cellulose in the insoluble dietary fibers of BWB can obstruct the binding of starch-starch and starch-protein, reducing the number of viscous substances and thus decreasing the pasting viscosity (Li et al., 2023). The viscosity values of SG-BWB mixed flour were elevated compared to those of BWB mixed flour. This increase can be attributed to the reduction in WHC of SG-BWB compared to BWB, which subsequently led to enhanced interactions between starch mole- cules, thereby increasing the viscosity of the gelatinization system. This observation was consistent with the results presented in Section3.1. The
viscosity values of the Nc-BWB mixed flour were significantly lower than those of the BWB mixed flour group (P<0.05). This may be due to the gelatinization and degradation of some starch in Nc-BWB underhigh-t- emperature sterilization conditions (Hagenimana et al., 2006). The breakdown value, the difference between the peak viscosity and the trough viscosity (Wang et al., 2017), was the decrease in viscosity from the peak value during the holding stage of heating and followed the same trend as peak and final viscosities. The setback value characterizes the retrogradation properties of starch; a smaller setback value indicates better anti-aging properties. The setback value of Nc-BWB mixed flour was the lowest at 1102.33 cp, indicating strong resistance to undesirable degradation and an enhanced ability to extend shelf life. A higher pasting temperature indicates that more energy was required to break down the crystalline structure of starch molecules so they could gelati- nize and form a starch paste. The addition of BWB, SG-BWB, and Nc-BWB increased the pasting temperature of the mixed flour. The pasting temperature of SG-BWB mixed flour was the highest at 89.6◦C.
This phenomenon could be attributed to the increase in soluble dietary fibers and anthocyanin content in BWB following modification. The enhanced levels of soluble dietary fibers and anthocyanins likely inhibited starch leaching by interacting with starch chains and competing for water, thereby necessitating greater energy input to disrupt the starch structure during gelatinization. Similar findings have also been reported byLi, Zhang, et al. (2024).
3.7. The color of BWB and BWB mixed flour
Color was a critical quality attribute for all foods, including food powders. TheL*, a*,andb*color values of modified BWB and modified BWB mixed flour are shown inTable 2. Compared to the unmodified BWB group, there was no statistically significant difference in theL*
value of Nc-BWB (P>0.05); However, the brightness of SG-BWB signif- icantly increased, reaching anL*value reaching 77.03 (P<0.05). This increase was attributed to the smallest particle size of SG-BWB, ranging from 10.6 to 18.5μm, which increased the surface area of the powder, resulting in more reflected light and a whiter appearance of the sample.
Thea*value of both modified BWB significantly decreased, while theb*
value significantly increased (P<0.05). During fermentation of Nc, the internal structures of cellulose and hemicellulose in BWB were exposed and may degrade into monosaccharides and oligosaccharides or undergo Maillard reactions under high temperatures and sterilization conditions (Feng et al., 2024;Khasi and Azizkhani, 2022;Ko et al., 2020;Xiao et al., 2022). Additionally, variations in thea*andb*values were likely due to the release, formation and subsequent oxidation of colored compounds, such as carotenoids, chlorophyll, and anthocyanins, during the
modification process (Gan et al., 2023;Wang, Yang, et al., 2021).
Compared to BW flour, the incorporation of modified BWB reduced the brightness (L* value) of BW flour, increased the a* value, and decreased theb*value. Therefore, the color of foods containing modi- fied BWB can be adjusted by varying the amount of BW flour added, in order to meet consumer preferences (Aider et al., 2024).
3.8. The analysis of volatile flavor compounds in GC-MS of steamed bread
Table S3provides detailed information on volatile flavor substances and their corresponding relative contents in different types of steamed bread.Fig. 3A displays the relative contents of different volatile flavor substances in the four types of steamed bread (BW steamed bread, BWB steamed bread, SG-BWB steamed bread, Nc-BWB steamed bread). The differences in the relative contents of these substances lead to flavor variations among the four steamed bread types. The relative contents of alcohols in BW steamed bread, BWB steamed bread, SG-BWB steamed bread, and Nc-BWB steamed bread were 22.48%, 25.06%, 27.63%, and 27.13%, respectively. In terms of alcohol, the major contributors to the flavor in BW steamed bread were ethanol and n-hexanol. Furthermore, in BWB steamed bread, SG-BWB steamed bread, and Nc-BWB steamed bread, additional significant contributors included isobutanol and iso- amyl alcohol. Moreover, the relative contents of ethanol, isobutanol, and isoamyl alcohol were higher in SG-BWB and Nc-BWB steamed bread compared to BWB steamed bread. Ethanol, a key flavor compound shared by all four types of steamed bread, was primarily produced by yeast fermentation. Hexanol, generated through lipid oxidation, imparts a grassy and fruity aroma (Huang et al., 2023). The formation of isoamyl alcohol may be attributed to yeast utilizing leucine in the dough via the ehrlich pathway, with its content positively correlating with malty fla- vors (Zhang et al., 2024). It may also be due to the addition of modified BWB, which increased the phenolic content, potentially impacting the ehrlich metabolic pathway in yeast and thus influencing its accumula- tion (Ling et al., 2022). With its sweet and fragrant aroma, isobutanol provides a pleasant scent to steamed bread. Low concentrations of al- dehydes can enhance the flavor characteristics of the steamed bread.
Aldehydes are mainly produced through two pathways: One pathway is the degradation and reduction of initial Maillard products via the Strecker degradation, and the other is the oxidation of fats forming peroxides that further decompose to produce fatty aldehydes (Yao et al., 2022). Regarding aldehydes, the most significant contributors to flavor in BW steamed bread, SG-BWB steamed bread, Nc-BWB steamed bread, and BWB steamed bread were identified as nonanal, which imparts a citrus and cucumber-like aroma; heptanal, characterized by a green Table 1
Effect of modification treatment on the pasting and properties of modified BWB mixed flour.
Samples Peak viscosity (cP) Trough viscosity (cP) Breakdown (cP) Final viscosity (cP) Setback (cP) Pasting temperature (◦C)
BW 2292.33±17.93a 1591.33±38.14a 701.00±20.85b 2745.33±13.91b 1154.00±31.79b 70.47±0.38b
BWB 2033.00±5.72c 1347.00±1.63b 686.00±4.24b 2536.67±7.13c 1189.67±5.56ab 71.75±0.04b
SG-BWB 2123.00±10.98b 1371.67±6.02b 751.33±6.24a 2842.67±12.39a 1471.00±6.53a 89.60±0.04a
Nc-BWB 1782.00±15.12d 1140.33±7.76c 641.67±20.53c 2242.67±30.27d 1102.33±37.51c 80.95±7.67a
All values are mean±SD, n=3. Different letters in the same column indicate significant differences between parameters at the 0.05 level (P < 0.05).
Table 2
Modified BWB color and modified BWB mixed flour color.
Samples Bran color Samples Flour color Steamed bread volume (mL/g)
L* a* b* L* a* b*
BW 89.39±0.15a 0.02±0.01c 9.19±0.13a 2.65±0.11a
BWB 60.48±0.29b 4.60±0.10a 9.56±0.16c BWB 84.84±0.28d 0.52±0.04a 8.41±0.11b 2.03±0.03c SG-BWB 77.03±0.34a 3.66±0.06b 10.52±0.02b SG-BWB 86.96±0.24b 0.29±0.03b 7.79±0.29c 2.22±0.06b Nc-BWB 61.00±0.18b 3.88±0.16b 11.32±0.38a Nc-BWB 85.50±0.28c 0.43±0.07a 8.24±0.13b 2.23±0.02b
The values were expressed as the mean±standard deviation of triplicate experiments. Values in same column with different letter indicate significant difference (P<
0.05).
Fig. 3. Relative content of different types of volatile flavor substances in steamed bread. (A) Relative content of different types of volatile flavor substances in steamed bread by GC-MS. (B) Relative content of different types of volatile flavor substances in steamed bread by GC-IMS.
Fig. 4. GC-IMS analysis of volatile components in steamed bread. (A) GC-IMS differential spectrum of volatile components in steamed bread. (B) Fingerprint analysis of volatile components in steamed bread.
herbal scent; and hexanal, known for its fresh green note. Esters, which typically exhibit fruity, aromatic, and sweet flavors, were relatively less abundant in all four types of steamed bread, with relative contents of 3.38%, 3.20%, 1.87%, and 1.65%, respectively. Alkenes, particularly terpene compounds, have strong aromas and physiological activities.
Their low threshold values of these compounds play an important role in the overall flavor of steamed bread. The relative content of terpenes in Nc-BWB steamed bread was the highest, reaching 20.69%. This study is the first to report such high relative contents of D-limonene andβ-car- yophyllene in steamed bread, which account for 7.88% and 6.60% of the overall flavor of Nc-BWB steamed bread, respectively. This may be due to the fact that bothβ-carotene andβ-caryophyllene, generated during the fermentation of BWB, involve isoprene, which affects their relative content in Nc-BWB steamed bread. Among the four types of steamed bread, alkanes had the highest relative proportion, primarily consisting of long-chain alkanes such as tridecane, undecylcyclopentane, and hexadecane. Alkanes generally have high sensory thresholds, and most possess weak or no aroma, thus contributing little to the overall flavor of steamed bread. Alkanes mainly exert an indirect influence on the overall aroma through the synergistic effects among compounds (Wang et al., 2021). Other volatile components, such as 2-pentyl furan, were also
detected in all four types of steamed bread. This compound has been identified as the most aromatic furan in wheat, suggesting that BW whole flour retains the original aroma of BW (Yu et al., 2024). In sum- mary, these compounds coordinate and complement one another, resulting in the unique flavor characteristics of the four types of steamed bread.
3.9. The analysis of volatile flavor compounds in GC-IMS of steamed bread
Volatile compounds with different aroma characteristics in steamed bread were analyzed using GC-IMS. The spectrum of BW steamed bread served as the control group. The spectra of other samples were sub- tracted from the reference, resulting in various comparison charts, as shown in (Fig. 4A). If the content of volatile organic compounds in the target sample is the same as that in the reference, the subtracted back- ground would be white. At the same time, red indicates that the con- centration of the substance in the target sample is higher than in the reference. Blue indicates that the concentration of the substance in the target sample was lower than in the reference. Most detected signals exhibit retention times ranging from 100 to 1000 s, with drift times Table 3
Volatile compounds and their relative content in steamed bread samples.
No. Compounds Formula Steam Bread Relative content (%) Odor character
BW BWB SG-BWB Nc-BWB
1 Terpineol C10H18O 0.51 0.69 0.73 0.62 Pine terpenoid, citrus, woody, floral
2 (E)-2-nonenal C9H16O 0.78 0.97 0.97 0.81 Fatty, green, waxy, cucumber, melon
3 Nonanal D C9H18O 0.92 0.91 0.91 0.71 Rose, citrus, strong oily
4 Nonanal M C9H18O 0.25 0.31 0.33 0.19 Rose, citrus, strong oily
5 2-Heptanone D C7H14O 0.79 0.79 0.83 0.63 Pear, banana, fruity, slight medicinal fragrance
6 Hexanal D C6H12O 0.1 0.18 0.19 0.14 Fresh, green, fat, fruity
7 1-Pentanol D C5H12O 0.41 0.58 0.62 0.47 Balsamic
8 1-Pentanol M C5H12O 2.88 3.00 2.86 2.95 Balsamic
9 Hexanal M C6H12O 0.07 0.10 0.10 0.08 Fresh, green, fat, fruity
10 (E)-2-Heptenal D C7H12O 0.53 0.69 0.69 0.59 Spicy, green vegetables, fresh, fatty
11 (E)-2-Heptenal M C7H12O 0.58 0.97 1.10 1.10 Spicy, green vegetables, fresh, fatty
12 benzaldehyde D C7H6O 3.39 3.23 3.28 3.36 Bitter almond, cherry, nutty
13 Benzaldehyde M C7H6O 0.67 0.74 0.75 0.71 Bitter almond, cherry, nutty
14 Heptanal D C7H14O 7.96 8.12 7.54 6.75 Fresh, aldehyde, fatty, green herbs, wine, fruity
15 Heptanal M C7H14O 6.66 6.12 6.18 5.7 Fresh, aldehyde, fatty, green herbs, wine, fruity
16 2-heptanone M C7H14O 0.85 1.09 1.06 1.16 Pear, banana, fruity, slight medicinal fragrance
17 1-Hexanol M C6H14O 4.50 5.44 4.81 3.86 Fresh, fruity, wine, sweet, green
18 Linalool C10H18O 0.22 0.28 0.33 0.35 Citrus, rose, woody, blueberry
19 (E)-2-Octenal M C8H14O 0.47 0.88 0.96 1.25 Fresh cucumber, fatty, green herbal, banana, green leaf
20 (E)-2-octenal D C8H14O 1.41 2.02 2.25 1.90 Fresh cucumber, fatty, green herbal, banana, green leaf
21 Phellandrene C10H16 0.35 0.33 0.32 0.31 dill
22 Hexanoic acid M C6H12O2 0.51 0.57 0.58 1.19 Sour, fatty, cheese, pungent, Daqu liquor
23 Furfural M C5H4O2 0.97 0.93 1.00 1.38 Sweet, woody, almond, bready
24 Furfural D C5H4O2 0.46 0.56 0.62 0.65 Sweet, woody, almond, bready
25 ethanol M C2H6O 0.18 0.22 0.28 0.26 Aromaticity
26 1-Butanol C4H10O 13.48 10.44 10.19 9.20 Wine
27 2-Methylbutanal C5H10O 33.89 31.78 32.08 32.39 Almond, cocoa, malt
28 2-Pentylfuran C9H14O 2.86 3.44 3.69 4.75 Bean, fruity, earthy, green, vegetable
29 1-Octen-3-ol C8H16O 0.85 0.77 0.74 0.65 Mushroom, lavender, rose, hay
30 ethanol D C2H6O 0.22 0.23 0.23 0.27 Aromaticity
31 Myrcene C10H16 0.29 0.33 0.33 0.54 Must, spice, balsamic
32 1-Hexanol D C6H14O 0.65 1.05 1.28 1.03 Fresh, fruity, wine, sweet, green
33 phenylacetaldehyde C8H8O 0.6 0.61 0.52 0.41 Hyacinth, sweet fruity, almond, cherry, clover honey, cocoa
34 Limonene D C10H16 1.1 1.74 1.67 1.32 Lemon, sweet, orange, pine oil
35 Octanal C8H16O 2.95 2.68 2.51 2.45 Aldehyde, waxy, citrus, orange, fruity, fatty
36 1-heptanol M C7H16O 0.45 0.51 0.52 0.74 Grape, fruity, wine, violet, peony
37 1-heptanol D C7H16O 0.07 0.26 0.44 0.26 Grape, fruity, wine, violet, peony
38 2,3-Pentadione C5H8O2 0.75 1.02 1.30 1.01 Sweet, cream, caramel, nuts, cheese
39 Ethyl Acetate D C4H8O2 0.90 0.85 0.89 0.86 Fresh, fruity, sweet, grassy
40 ethyl acetate M C4H8O2 0.91 0.92 0.95 1.03 Fresh, fruity, sweet, grassy
41 Limonene M C10H16 0.38 0.60 0.57 0.44 Lemon, sweet, orange, pine oil
42 Acetophenone C8H8O 0.08 0.14 0.13 0.09 Sweet, spicy, almond
43 (E)-2-hexenal D C6H10O 0.07 0.08 0.06 0.27 Green, banana, fat
44 (E)-2-Hexenal M C6H10O 1.17 0.72 0.56 1.13 Green, banana, fat
45 Cyclohexanone D C6H10O 0.79 1.21 1.20 1.80 Strong pungent, earthy
46 Cyclohexanone M C6H10O 1.14 0.91 0.87 2.23 Strong pungent, earthy
