Comparative Study of Raw and Fermented Oat Bran: Nutritional Composition with Special Reference to Their Structural and Antioxidant Profile

Abstract

Oat bran has gained significant attention among cereal brans owing to its comparatively higher presence of dietary fibers and phytochemicals. The objective of the current research is to personify the nutritional and functional aspects of oat bran after yeast-induced (Saccharomyces cerevisiae) fermentation. For this purpose, a comparative study of raw and fermented oat bran was conducted to investigate the nutritional profile, antioxidant activity and functional characteristics of oat bran. Furthermore, pre- and post-structural variations on fermented bran were determined through scanning electron microscopy (SEM). The results show that crude fat, protein and total dietary fiber (soluble and insoluble) contents were significantly improved after fermentation. Moreover, the post-fermentation value of soluble dietary fiber was increased from 5.01 ± 0.21 to 7.2 ± 0.1%. Antioxidant activity, DPPH-RSA and ferric reducing antioxidant power values of bran samples were also enhanced through fermentation and the anti-nutritional factor, i.e., phytate, was significantly reduced from 1113.3 ± 8.5 to 283.4 ± 3.5 mg/100 g in bran samples after fermentation. Furthermore, the surface morphology of fermented oat bran shows scattering and pores, while raw oat bran shows visible aggregation in SEM micrographs. Water-holding capacity was also enhanced up to 2.11 (5.68%) after fermentation. In conclusion, the post-fermentation results revealed that yeast-induced fermentation enhanced the physicochemical, structural and antioxidant characteristics of oat bran.

1. Introduction

Cereals are rich in bioactive compounds with various health-endorsing properties. They are significant staple crops and crucial sources of different nutrients. Cereal grains comprise a broad range of bioactive compounds, including dietary fibers and phenolic acids. The supplication of functional foodstuffs is increasing all over the world due to their health-endorsing properties [1]. Epidemiological studies showed that consumption of whole grains and cereal fibers, especially bran, significantly lowers the risk of severe medical ailments including diabetes mellitus (DM), cardiovascular diseases (CVDs) and cancer; among them, colorectal cancer is more dominant [2]. Some major cereals include wheat, maize, rice, barley oat and rye; however, oat (Avena Sativa) is low in cost and has gained considerable attention due to its high dietary fiber contents compared to other cereals. The nutritional composition of oat kernels contains carbohydrates (73.4%), protein (17.6%), fat (6.2%), crude fiber (1.3%) and dry ash (2.1%) on dry bases [3]. Oat grain mainly comprises three layers including bran, germ and endosperm, and the bran portion contributes 30% to the dry weight of oat grain. Oat bran has a good nutritional profile but discussion on its anti-nutritional activity is minimal in the limited research.

Bran is a low-cost cereal by-product high in non-starch polysaccharides and polyphenols. These bioactive compounds have many functional and nutraceutical aspects due to a satisfactory proportion of soluble and insoluble dietary fibers (especially β-glucans), which have been associated with cholesterol-lowering effects, serum glucose regulators and cardiac health enhancers [1]. Bran is widely used as an ingredient in health-oriented products due to its high dietary fiber and bioactive profiles. It has been used in the development of functional foods with a low glycemic index, although phenolic acids in oat bran have antimicrobial and antioxidant activity as well as anti-inflammatory, anti-allergic and anti-carcinogenic properties. The soluble dietary fibers of oat bran such as β-glucans have many health-endorsing properties. The health benefits of β-glucan have been attributed primarily to its ability to increase intestinal viscosity and prevent constipation. β-glucan is a major fraction of oat bran’s soluble fiber and contains several bioactive moieties reported to have cholesterol-lowering effects [4]. Oat bran acts as an active module in the maintenance of post-prandial blood glucose levels [5].

Due to oat bran’s higher content of phytic acid (myo-inositol hexaphosphate) as an anti-nutritional factor, consumption may cause adverse effects. Phytic acid is an anti-nutrient that reduces mineral and protein bioavailability. A significant amount of phytic acid persists in cereal and cereal-based products but phytic acid content is biodegraded during fermentation. According to previous studies, different methods such as fermentation, autoclaving, soaking, drying and malting tended to eliminate phytic acid [6]. Fermentation is an effective mechanism that significantly reduces the amount of anti-nutrients (phytates, tannins) in oat bran [7].

Many researchers have tried to recuperate the nutritional and antioxidant potential of different cereal brans by employing various techniques, and different studies have shown that fermentation is an effective approach to improving the nutritional, technological and functional properties of cereal bran of different cereals. Moreover, the fermentation process is an effective approach to decreasing the phytic acid content along with improving mineral bioavailability [8]. Due to its high phytic acid content, oat bran is least preferred, but now after extensive research and amelioration, it is now being used as a functional ingredient in the development of different health-oriented products.

The current research was conducted to explore the outcomes of fermentation on the nutritional profile, anti-nutritional compounds, antioxidant activity and structural analysis of oat bran. Further, yeast is widely used in the baking industry and is economical for bakers in producing baked products. In the current study, the main purpose in fermenting the oat bran using yeast (Saccharomyces cerevisiae) is to valorize the agro-industrial waste at a low cost.

2. Materials and Methods

The current study was conducted in the Department of Food Sciences, Government College University Faisalabad and Ayub Agriculture Research Institute, Faisalabad (AARI). Oat was procured from the cereal section of AARI and grains were subjected to milling using a lab-scale mill (Hammer-type Laboratory Mill LM-120, Perton, Sweden) in the milling section of AARI. The solid-state commercial compressed yeast cells (Saf Instant Yeast) were procured from Metro Cash & Carry, Faisalabad, Pakistan. Analytical-grade chemicals were procured from Scientific shops in Faisalabad, Pakistan.

2.1. Fermentation of Oat Bran

Oat bran samples were passed through a bran finisher. The slurry was prepared with distilled water and oat bran (8:1, v/w) and then dephytinized through fermentation by Saccharomyces cerevisiae. Then, the slurry was mixed with 4% viable cells of compressed baker’s yeast (Saf Instant Yeast) for 6 h at 37 °C in a temperature-controlled water bath which was covered with aluminum foil as previously described by Ozkaya et al. [9]. At the end of treatment, leftover bran was dried at 100 °C using a hot-air oven.

2.2. Comparative Study of Raw and Fermented Oat Bran

2.2.1. Proximate Composition of Raw and Fermented Oat Bran

Raw and fermented oat bran samples were analyzed for their biochemical profiles by following the relevant methods prescribed in the AACC [10] manual: moisture (method No. 44-15A), ash (method No. 08-01), crude protein (method No. 46-10), crude fat (30-20) and crude fiber (32-10).

2.2.2. Total Dietary Fiber (Soluble and Insoluble)

The total dietary fiber (TDF) including soluble and insoluble dietary fiber of raw and fermented oat bran was assessed through the AACC [10] method No. 32-07.01. Briefly, 2 g of both samples were taken and heat-stable α-amylase, protease and amyloglucosidase enzymes were added using a Megazyme enzyme kit (K-TDFR-100A). After the digestion of organic fractions, inorganic residues of ash were weighed and then washed with hot water and acetone at a 5:1 ratio, respectively. Then, ashing (650 °C for 4 h) for the quantification of inorganic residues was completed and the weight of fine ash was recovered after completion of the process. TDF, SDF and IDF contents were finally quantified by using the following formulas:

$$\% SDF=\frac{\mathrm{Weight} \mathrm{of} \mathrm{IDF} \mathrm{before} \mathrm{washing}-\mathrm{Weight} \mathrm{of} \mathrm{IDF} \mathrm{after} \mathrm{washing}}{\mathrm{Total} \mathrm{weight}}\times 100$$

(1)

$$\% IDF=\frac{\mathrm{Weight} \mathrm{of} \mathrm{sample} \mathrm{before} \mathrm{ashing}-\mathrm{Weight} \mathrm{of} \mathrm{sample} \mathrm{after} \mathrm{ashing}}{\mathrm{Total} \mathrm{Weight}}\times 100$$

(2)

$$\mathrm{Total} \mathrm{Dietary} \mathrm{Fiber}\left(\mathrm{TDF}\right)= \mathrm{Insoluble} \mathrm{Dietary} \mathrm{Fiber} \left(\mathrm{IDF}\right)+\mathrm{Soluble} \mathrm{Dietary} \mathrm{Fiber} \left(\mathrm{SDF}\right)$$

2.2.3. Mineral Contents

The mineral profiles of oat bran samples (raw and fermented) were examined using the standard method recommended by the AOAC [11] (method 931.01). Each sample (1 g) was digested with 7:3 HNO₃ to perchloric acid using a hot plate and the process continued until the solution became colorless and, finally, the total volume became 2–4 mL. Then, the digested sample was diluted up to 100 mL with distilled water for mineral assessment. Potassium, magnesium and calcium were quantified through a Flame Photometer-410 (Sherwood Scientific Ltd., UK), whereas copper, iron, and phosphorus were quantified through an atomic absorption spectrophotometer (Varian AA240, Australia).

2.2.4. Microstructure of Bran Samples

The microstructure of bran samples (raw and fermented) was obtained through scanning electron microscopy (SEM). For SEM analysis, dried bran samples were affixed on aluminum stubs and imaging was performed with a scanning electron microscope (Cube-Series, EmCrafts, South Korea). The images were captured under high vacuum conditions at a 5 kV acceleration voltage with magnifications of 900× and 2400×.

2.2.5. Total Phenolic Content (TPC)

The aggregate of total phenolic content present in the oat bran samples was evaluated through the method of Stanisavljević et al. [12]. Folin–Ciocalteu reagent was used for the reaction and gallic acid was used as a standard. Briefly, the Folin–Ciocalteu reagent oxidized 100 μL of extracts and sodium carbonate was used to neutralize the solution; then, the solution was diluted by the addition of distilled water up to 10 mL. The sample was placed in the dark for 120 min and the absorption was estimated at 760 nm after 2 h of incubation. The results are expressed as milligrams per kilogram (mg/kg) of sample gallic acid equivalent.

2.2.6. Total Flavonoid Content (TFC)

Raw and fermented oat bran samples were subjected to spectrophotometric measurement of TFC through the method used by Sultana et al. [13]. Briefly, 1 mL of an aqueous extract with 0.1 g of dry matter in unit milliliters was diluted with 5 mL distilled water (DW) and 0.3 mL NaNO₃ (5%) in a 10 mL volumetric flask and rested for 5 min. Then, 0.6 mL of AlCl₃ (10%) was added and again kept for 5 min, after which 2 mL of NaOH (1 M) was added and the remaining volume of 10 mL of the volumetric flask was filled with the addition of DW. Then, the samples were thoroughly mixed and absorbance was measured at 510 nm and the results were written as rutin equivalent (mg) per gram (g).

2.2.7. Antioxidant Potential

The antioxidant potential of bran samples (raw and fermented) was assessed through DPPH (diphenyl picryl hydrazyl assay) by following the procedure illustrated by Yen and Chen [14]. Both bran samples (raw and fermented) were individually mixed with DPPH solution (0.12 mM) using a test tube (ratio of 4:1) and kept in a dark place for 30 min, after which the absorbance was recorded at 593 nm through the application of a UV–visible spectrophotometer according to the methods of Lesjak et al. [15].

The ferric reducing antioxidant power of both raw and fermented bran samples was analyzed through the method used by Lopez-Contreras et al. [16] with some alterations. Briefly, 300 mM sodium acetate buffer, 10 mM TPTZ (2,4,6-tripyridyltriazine complex) and 20 mM iron chloride hexahydrate were mixed with a ratio of 10:1:1 at 37 °C and rested for 30 min at room temperature (37 °C). Then, the samples (50 µL) were mixed with FRAP solution (1500 µL) and the absorbance was measured through a spectrophotometer at 593 nm. A Trolox calibration curve with values ranging from 0 to 500 mol/L was used for the calculation of concentration through a linear regression equation and the results were expressed as milligram Trolox equivalent per 100 g (mg TE/100 g).

2.2.8. Phytic Acid Content

The phytic acid content of both bran samples (raw and fermented) was measured by a colorimetric method according to the methods of Haug and Lantzsh [17] with some modifications specified below. The phytic acid content in each bran sample was quantified through a spectrophotometer using phytate (reference solution), a ferric solution and a 2,2-bipyridine solution. Briefly, the sample (0.5 g) was collected by shaking for half an hour in a 10 mL HCl solution in a test tube. Then, an extract of 1 mL was added into the test tube. In the test tube, the 2 mL ferric solution was added and sealed with a stopper. The test pipe was fitted with a clip and then heated for 30 min in a water bath. Then, the test tube was cooled for 15 min in ice water and allowed to be calibrated to room temperature. 2,2-bipyridine solution (4 mL) was added and mixed thoroughly by shaking the test tube. The reaction mixture was transmitted to a spectrophotometer cuvette and the absorbance was assessed at 519 nm against deionized water after 30–60 s. For each study package, the system was calibrated with the reference solution as a replacement for the sample solution.

2.3. Physicochemical Properties

2.3.1. pH

pH of both raw and fermented bran samples was assessed according to AACC [10] method No. 02-52. The pH was calculated with the application of a digital pH meter (EUTECH pH 700) and results were averaged among 3 replicates. Briefly, bran samples (raw and fermented) were added to distilled water (DW) and an electrode was used for the measurement of pH.

2.3.2. Water-Holding Capacity (WHC)

The WHC of samples (raw and fermented) was measured through the method of Hussain et al. [18]. Briefly, 2 g bran samples were added to a 50 mL centrifuge tube and DW (30 mL) was individually added to both bran samples. Then, the individual samples were placed in separate centrifuge tubes and stirred thoroughly using a vortex mixer and then kept for 40 min at room temperature (37 °C). After this, samples were centrifuged (Apparatus: Heraeus Megafuge 8R Centrifuge) at 9500 RPM for 10 min. The supernatant was decanted by reverting the centrifuge tubes on Whatman filter paper. The samples were weighed and their WHC was calculated through difference and expressed as “g” water retained per “g” of dry matter.

2.4. Statistical Analysis

The results regarding fermented and non-fermented bran samples were subjected to statistical analysis and the level of significance was calculated using a complete randomized design (CRD) and analysis of variance (ANOVA) according to the method of Steel et al. [19].

3. Results

3.1. Biochemical Composition of Raw and Fermented Oat Bran

A comparison between the biochemical profiles of raw and fermented oat bran is presented in

Table 1. Biochemical Composition of raw and fermented oat bran.

Nutritional Composition	OAT BRAN
	Raw	Fermented
Moisture (%)	7.69 ± 0.08 a	5.3 ± 0.22 b
Ash (%)	2.1 ± 0.01 a	1.01 ± 0.01 b
Crude Fat (%)	1.00 ± 0.04 b	1.14 ± 0.02 a
Crude Fiber (%)	14.36 ± 0.06 b	15.83 ± 0.08 a
Crude Protein (%)	5.54 ± 0.02 b	9.03 ± 0.04 a
Phosphorus (mg/100 g)	531 ± 6.4 b	569 ± 7.8 a
Potassium (mg/100 g)	437 ± 2.7 b	472.3 ± 3.5 a
Calcium (mg/100 g)	47 ± 0.4 b	52.5 ± 0.6 a
Copper (mg/100 g)	1.48 ± 0.03 b	2.12 ± 0.02 a
Magnesium (mg/100 g)	189 ± 1.7 b	201 ± 2.4 a
Iron (mg/100 g)	3.5 ± 0.02 b	5.1 ± 0.05 a
Total Dietary Fiber (%)	24.21 ± 0.9 b	28.49 ± 1.3 a
Soluble Dietary Fiber (%)	5.01 ± 0.02 b	7.2 ± 0.02 a
Insoluble Dietary Fiber (%)	19.2 ± 0.1 b	21.31 ± 0.2 a

Different letters (^a, ^b) within the row indicate that the interactions of raw and fermented oat bran are significantly different (p ≤ 0.05). Results are expressed as the mean value ± standard deviation (n = 3).

and the results regarding the moisture content of both samples showed a significant variation, with moisture values of 7.69 ± 0.08 and 5.3 ± 0.02%, respectively, which was a favorable attribute imparted after the fermentation through dephytinization of the bran sample because high moisture in cereal and cereal-based products facilitate microbial growth. Ash contents of raw and fermented oat bran were 2.1 ± 0.01 and 1.01 ± 0.01%, respectively, and showed a decreasing trend after fermentation. However, a slightly increasing trend was observed in crude fiber content after the fermentation process: 14.36 ± 0.06 and 15.83 ± 0.08 in raw and fermented samples, respectively. The fat content of raw and fermented samples was 1.00 ± 0.04 and 1.14 ± 0.02%, respectively. The protein contents of raw and fermented oat bran were 5.54 ± 0.02% and 9.03 ± 0.04%, respectively. Protein content was significantly increased due to the addition of water-soluble proteins during the fermentation process. Fermentation is a metabolic process that breaks down complex molecules into simpler ones, and post-fermentation protein content increases due to yeast activity.

The results regarding TDF content in fermented oat bran were significantly higher than those of non-fermented oat bran: 24.21 ± 0.9 and 28.49 ± 1.3%, respectively. The increasing trend observed in the fermented oat bran sample was due to the structural degradation of fibers during the fermentation caused by yeast activity, as previously reported by Tu et al. [20]. The SDF content in raw oat bran was 5.01 ± 0.02% and post-fermentation SDF content was 7.2 ± 0.02%. A study conducted by Yang et al. [21] reported that soluble dietary fiber content of fermented wheat bran was higher than that of non-fermented wheat bran due to microbial activity. Oat bran comprises a higher aggregate of phytic acid which binds the dietary fiber content and the bioavailability of dietary fibers for gut microbiota becomes minimum. Fermentation with Saccharomyces cerevisiae increases the SDF fraction compared to its insoluble counterpart because yeast degrades phytic acid content, which has also been ascertained in rye sourdough production [22]. This traditional method has been used since ancient times and it can be industrially beneficial to produce soluble fractions of dietary fibers and water extractable arabinoxylan (WEAX) and lower phytic acid content and enhance the bioavailability of functional compounds through microbial dephytinization.

The IDF fraction of dietary fibers in raw oat bran was 19.2 ± 0.1% and that of fermented oat bran was 21.31 ± 0.2%. The results of the biochemical analysis showed that in fermented bran, TDF content was significantly higher compared to raw oat bran. However, the result supports the hypothesis that the increase in IDF is due to a higher proportion of phytic acid in the bran sample, and microbial enzymes reconstitute phytic acid with dietary fibers. Enhancement in the nutritional profile of the bran sample is supported by the study of Manini et al. [2], who reported that the post-fermentation nutritional composition of wheat bran showed an increasing trend compared to a raw sample. Manini et al. reported that yeast fermentation increases 30% soluble dietary fiber content with four- and ten-fold higher contents of water-unextractable arabinoxylans and ferulic, respectively, compared to raw wheat bran. The results regarding the biochemical composition of raw and fermented oat bran are shown in Table 1.

The mineral profiles of raw and fermented oat bran are shown in Table 1. In the present research, raw and fermented oat bran were investigated for mineral contents and the results are compared. In raw oat bran, the highest phosphorus contents (531 ± 6.4 mg/100 g) were observed. Mineral contents of raw oat bran were 437 ± 2.7, 47 ± 0.4, 3.5 ± 0.02, 1.48 ± 0.03 and 189 ± 1.7 mg/100 g in potassium, calcium, iron, copper and magnesium, respectively. In fermented oat bran, a phosphorus content of 569 ± 7.8 mg/100 g was the highest compared to other mineral contents, while potassium, calcium, iron, copper and magnesium contents were 472.3 ± 3.5, 52.5 ± 0.6, 5.1 ± 0.05, 2.12 ± 0.02 and 201 ± 2.4 mg/100 g, respectively. A study conducted by Frolich and Nyman [23] reported that potassium comprised 30% of the and sample and 0.8 g/100 g of a whole-grains sample. Similar findings by Marlett [24] showed that the mineral content in raw oat bran was 441 mg/100 g potassium, 6.4 mg/100 g iron, 0.17 mg/100 g copper and 171 mg/100 g magnesium.

3.2. Scanning Electron Microscopy (SEM) Study of Bran Samples

A comparison of raw and fermented oat bran samples by their amorphous and structural properties is shown in Figure 1a–d. Here, a and b represent the raw sample, whereas c and d represent the fermented bran sample’s micrograph. Scanning electron microscopy (SEM) studies on oat bran samples were performed to evaluate the bran’s surface morphology, and the SEM micrographs showed that bran samples have an amorphous form. The post-fermentation micrographs showed that the amorphous structure of fermented bran undergoes various structural changes leading towards the degradation and reconstitution of macromolecular structures during the fermentation process. After fermentation, the surface of fermented oat bran presented as a sponge-like porous structure. Furthermore, raw oat bran after fermentation was more porous from the surface, the tissue structure showed a sponge-like structure and the specific surface area was swelled. These results are in accordance with Yang et al. [20], who reported the structure of insoluble dietary fibers as porous, which consequently improved the adsorption capacity of fermented bran samples.

4. Discussion

4.1. Antioxidant Potential

4.1.1. Total Phenolic and Total Flavonoid Content

The total phenolic content of raw oat bran was 2721.27 ± 14.31 mg GAE/kg, while that of fermented oat bran was 2937.48 ± 7.37 mg GAE/kg (

Table 2. Bioactive profile of raw and fermented oat bran.

Bioactive Profile	Oat Bran
	Raw	Fermented
Total phenolic content (mg GAE/kg)	2721.2 ± 14.3 b	2937.4 ± 7.4 a
Total Flavonoid contents (mg RE/100 g)	81 ± 1.6 a	112 ± 1.8 b
DPPH-RSA (%)	40 ± 0.2 b	74 ± 1.5 a
FRAP (mg TE/100 g)	14 ± 0.5 b	18 ± 0.8 a

Different letters (^a, ^b) within the row indicate that the interactions of raw and fermented oat bran are significantly different (p ≤ 0.05). Results are expressed as the mean value ± standard deviation (n = 3).

). Furthermore, a significant increasing trend in the total phenolic content was observed in the fermented oat bran. These results show that the fermentation of cereal bran has positive effects on the phenolic acid content of cereal bran bioactivity. The current study is supported by the results of Calinoiu et al. [25], who exposed that the fermentation process is a crucial aspect in improving total phenolic content. The fermentation process increases the release of total phenolic acid under acidic conditions. Another study by Katina et al. [26] reported that fermentation of rye bran increases the number of phenolic acids, especially free phenolic acids in bran. In cereal bran, phenolic compounds, particularly phenolic acids, form cross-links with polysaccharides [1]. The phenolic acids can be released by hydrolyzing the bran under acidic conditions.

The total flavonoid content of raw and fermented oat bran samples is shown in Table 2. The total flavonoid content of raw oat bran was 81 ± 1.6 mg RE/100 g, while that of fermented oat bran was 112 ± 1.8 mg RE/100 g. The flavonoid content of cereal bran was found to be higher after fermentation relative to raw oat bran in this research.

4.1.2. DPPH Radical Scavenging Activity (DPPH-RSA)

DPPH-RSA is frequently used to evaluate the scavenging/antioxidant potential of bioactive compounds in the food system. The results regarding the comparative study of bran samples (raw and fermented) are illustrated in Table 2. DPPH radical scavenging activity of fermented bran possessed adequate antioxidant potential, i.e., the fermented bran sample showed a DPPH-RSA of 74 ± 1.5% and the non-fermented oat bran sample showed a DPPH-RSA of 40 ± 0.2%. The gradual increase in DPPH-RSA is due to the bioavailability of the functional components through yeast-induced fermentation present in the bran sample.

4.1.3. FRAP (Ferric Reducing Antioxidant Power)

FRAP (ferric reducing antioxidant power) of raw and fermented oat bran is shown in Table 2. Bran donated an electron, transforming Fe³⁺ to Fe²⁺. Antioxidant activity is strongly related to a reduction in strength. The current comparative study of raw and fermented oat bran indicated that fermented bran samples generated higher reductions in power. The current research results of the FRAP were 14 ± 0.5 mg TE/100 g in raw oat bran. After fermentation, oat bran showed an 18 ± 0.8 mg TE/100 g FRAP value. Moreover, raw bran showed minor neutralization of free radicals compared to fermented bran. Higher power reduction means a higher number of antioxidants that efficiently sublimate and scavenge free radicals.

4.2. Anti-Nutritional Factor

Phytic Acid (PA) Content

The phytic acid content in raw oat bran was 1113.3 ± 8.5 mg/100 g, while after fermentation, the phytic acid content in fermented oat bran was significantly reduced, i.e., 283.4 ± 3.5 mg/100 g. phytate-degrading ability is pH-dependent, for which the optimum pH is between the range of 4.3 to 4.5 at 38 °C, achieved through the production of carbon dioxide (CO₂) and organic acids during fermentation. Moreover, acidification activates the endogenous enzyme phytase to hydrolyze phytic acid [27] and degrades during the fermentation process by the phytase enzymes secreted by yeast [28]. The reduction in PA content reveals that fermentation degrades the phytate content with the intervention of the phytase-induced enzyme. Similarly, Hashemi et al. [29] reported phytic acid deterioration and degradation during the fermentation process. Another study by Ozkaya et al. [9] reported the same conclusion: that decreasing PA content is pH-dependent and CO₂ and organic acids contribute to lowering the pH during fermentation, which enhances phytic acid solubility. It has also been reported that phyton is contemporaneous in several microorganisms. Phytic acid contents are decreased by phytase, an endogenous enzyme secreted by yeast during fermentation [8].

4.3. Physicochemical Properties

4.3.1. pH

Table 3. Water-Holding Capacity of raw and fermented oat bran.

Bioactive Profile	Oat Bran
	Raw	Fermented
pH	6.3 ± 0.02 a	4.4 ± 0.02 b
WHC (H2O/g)	2.11 ± 0.02 b	5.68 ± 0.04 a

Different letters (^a, ^b) within the row indicate that the interactions of raw and fermented oat bran are significantly different (p ≤ 0.05). Results are expressed as the mean value ± standard deviation (n = 3).

shows the results regarding the pH of raw and fermented oat bran samples. The study showed that pH was decreased from 6.3 to 4.4 after 6 h of fermentation at 37 °C. Temperature and time of fermentation have a noticeable impact on the development of acidity. The conceivable description regarding the decline in pH is probably due to the production of organic acids during fermentation which leads to a decrease in the pH of the bran sample. pH plays a key role in the physicochemical and anti-nutritional properties of oat bran. Endogenous phytase could not be activated by lowering the pH, which supports the hypothesis that yeast phytase and phosphatase were crucial in the reduction of PA. In the current study, phytic acid content was reduced due to lower phytase-degrading ability in the fermented bran sample. A study conducted by Ozkaya et al. [9] reported that bounded phenolic compound moieties in oat bran were observed to be biologically available at 4 pH. However, limited data are available on the effect of pH on the availability of antioxidants, and the current findings and their comparison with the literature support the hypothesis that by lowering the pH, the availability of bioactive moieties could be enhanced.

4.3.2. Water-Holding Capacity (WHC) of Bran Samples

The WHC is directly associated with the soluble fraction of dietary fibers in the bran sample. Bran retains water content due to a better WHC and swelling capacity [18]. The WHC of raw and fermented oat bran is shown in Table 3. The water-holding capacity of raw oat bran was 2.11 g H₂O/g. After fermentation, the results regarding the WHC showed a significant increase (5.68 g H₂O/g) in the fermented bran sample. The current findings show that fermentation improved the WHC of the fermented bran sample because the soluble fraction of dietary fiber can retain much water compared to the insoluble fraction. Hussain et al. [18] reported that higher a water-holding capacity in bran-enriched flour is due to high fiber content and protein degradation. In previous research, Hemdane et al. [30] showed that 20% bran addition in a wheat flour sample resulted in a 0.84 g H₂O/g greater WHC than that of wheat flour. Another study by Lu et al. [31] reported that fermented wheat bran possessed a higher WHC than raw wheat bran.

5. Conclusions

Fermentation improves the physicochemical, nutritional and bioactive properties of oat bran and in the current research, it is observed that dietary fiber content, especially soluble dietary fiber (SDF), has various functional and nutraceutical functionalities. Total phenolic content (TPC), total flavonoid content and antioxidant activity of oat bran were also improved after fermentation of the bran sample. Results regarding SEM presented a visible variation in pre- and post-fermentation micrographs, in which post-fermentation micrographs showed a honeycomb-like structure with a porous surface. Furthermore, water-holding capacity (WHC) was improved, whilst the phytate content was reduced in the post-fermentation characterization of the oat bran sample. In conclusion, fermentation is an effective approach to improving the functional and nutritional properties of oat bran and is an acceptable approach in the utilization of agro-industrial waste and an appreciable step towards green agriculture. Furthermore, the incorporation of fermented oat bran can be a way forward for the development of a new range of functional foods.