Enhancing rice bran quality through the application of commercial Saccharomyces cerevisiae yeast

Ryan Aryadin Putra¹, Dahlanuddin¹, Oscar Yanuarianto¹, Muhamad Ali¹, Ica Ayu Wandira¹, Azhary Noersidiq¹, Aminurrahman¹, Wulandari², Slamet Widodo² and Luis Tavares³

¹ Faculty of Animal Science, University of Mataram, Mataram-83125, West Nusa Tenggara, Indonesia
ryan@unram.ac.id
² Research Center for Animal Husbandry, National Research and Innovation Agency (BRIN), Bogor, 16915, Indonesia
³ Faculty of Agriculture, National University of Timor Lorosa’e (UNTL), Dili-Timor Leste

Abstract

The study investigated the effects of Saccharomyces cerevisiae (S. cerevisiae) dose and fermentation duration on rice bran (RB) nutrient quality and digestibility from circular rice mill machines. A completely randomized design with a factorial arrangement was used, with the first factor being the S. cerevisiae dose (0%, 2% and 4%) and the second factor being the fermentation duration (7, 14 and 21 days). The variables tested included chemical composition and ruminal in vitro digestibility. Results showed that the S. cerevisiae dose significantly influenced all tested variables (p<0.05) except for dry matter (DM) and lignin content. Fermentation duration also had a significant effect on most variables (p<0.05), excluding organic matter (OM) and hemicellulose content. The interaction between the S. cerevisiae dose and fermentation duration increased crude protein (CP) content and reduced ether extract (EE), cellulose, acid detergent fiber (ADF) and neutral detergent fiber (NDF) content (p<0.05). The highest CP content was observed with 4% S. cerevisiae and a 14-day fermentation period, while the lowest was in the 2% S. cerevisiae treatment with a 7-day fermentation period (p<0.05). Both factors improved dry matter digestibility (DMD) and organic matter digestibility (OMD) of fermented rice bran (FRB) (p<0.05). However, no significant interaction between the dose and duration was observed. In conclusion, combining 2-4% S. cerevisiae and 14-day fermentation duration enhanced nutrient quality and digestibility of FRB from circular rice mill machines.

Keywords: enhancing quality; nutrition; Saccharomyces cerevisiae; rice milling

Introduction

Rice is a primary global staple crop, producing approximately 600 million tons annually (Chen et al 2012). Rice milling typically yields 5 - 11% rice bran (Oliveira et al 2011; Ribeiro et al 2017). Rice bran (RB), a nutrient-rich byproduct, is an excellent secondary feed source for livestock due to its affordability, availability and non-competition with human food. It contains 8–12% crude protein and essential fatty acids, making it a valuable feed ingredient often included in rations up to 30% without adverse effects (Fujihara et al 2003; Rosani et al 2024). However, rice bran quality can vary and contamination with rice husks may negatively impact livestock if consumed in excess.

Our prior study underscores considerable diversity in the quality of scattered RB utilized as a raw material for animal feed, mostly due to contamination from rice husk. This contamination occurs during milling using mobile hullers, which combine bran and husk as a single byproduct (Dilaga et al 2022). The presence of rice husk increases indigestible lignocellulose and silica complexes, reducing fermentability, digestibility and livestock performance (Rosani et al 2024). This issue remains unresolved in Indonesia, particularly in West Nusa Tenggara (WNT). Therefore, an accessible and scalable solution for smallholder farmers is urgently needed, with the fermentation process emerging as a promising approach to enhance RB quality.

The fermentation process, which employs the metabolic activity of microorganisms to induce substantial alterations in the physicochemical composition of raw materials, constitutes a highly effective and versatile technique for enhancing the bioavailability of nutrients in feed. This process facilitates the breakdown of complex compounds into simpler, more digestible forms, enhances the release of essential nutrients and reduces anti-nutritional factors that may impede nutrient absorption. By optimizing the nutritional quality of feed, fermentation improves livestock utilization and contributes to overall feed efficiency and productivity in animal production systems.

Yeast Saccharomyces cerevisiae S. cerevisiae) is widely used in livestock feed as a fermentative agent. This yeast is notable for its substantial protein, amino acid, functional properties and mineral composition (Izah et al 2017; Razzaq et al 2020). It is readily available and easily accessible in the market. Supplementing livestock feed with S. cerevisiae offers multiple benefits, including enhanced growth performance, improved immune function and increased feed efficiency. It also reduces phytic acid and other anti-nutrients (Prabhu 2014; Roopashri and Varadaraj 2015; Azrinnahar et al 2021), while improving the sensory properties of fermented feed (Ardiansyah et al 2021; Xie et al 2024). Numerous authors have proven that S. cerevisiae markedly improves the health and production of diverse livestock species, highlighting its significance in animal nutrition (Elghandour et al 2020; Sanchez et al 2021; Cuenca et al 2022; Marins et al 2023; Abd-Elrahman et al 2024; Chae et al 2024; Kamal et al 2024; Kim et al 2024; Maina et al 2024).

While the results are encouraging, the effectiveness of S. cerevisiae exhibits variability. Consequently, further research is necessary to standardize its application and optimize the dose for various feed components. The objective of this study is to ascertain the optimal S. cerevisiae dose and fermentation duration to enhance quality, particularly for RB derived from rice mill machine runoff.

Materials and methods

Rice bran and S. cerevisiae preparation

Rice bran samples were randomly collected from East Lombok, Central Lombok, West Lombok and North Lombok regencies in West Nusa Tenggara, Indonesia. The collected samples were homogenized and analyzed for initial nutrient content via proximate analysis (Table 1). The fermentation inoculum consisted of commercial dry yeast S. cerevisiae (Fermipan®) with a spore density of 3 × 10⁶ cells/g, purchased from a commercial provider. Fermentation was conducted at a laboratory scale using polyester plastic silos.

Fermentation process and in vitro incubation

For each treatment, 500 g of RB were mixed with Saccharomyces cerevisiae inoculum at concentrations of 0%, 2% and 4% (w/w). Each mixture was sprayed with 100 mL of distilled water to achieve 20% moisture content and manually homogenized. The RB samples were fermented for 7 and 14 days and then left for 21 more days.

Fermented rice bran samples were taken after 7, 14 and 21 days, with 200 g of each sample evaluated for chemical content. The analysis includes dry matter, organic matter, crude protein, crude fiber and ether extract using AOAC (2012) methods. Fiber fractions comprising cellulose, hemicellulose, acid detergent fiber (ADF), neutral detergent fiber (NDF) and lignin were analyzed using the procedures specified by Van Soest et al (1991).

For in vitro digestibility tests, 0.5 g of each sample were examined to determine digestibility levels. Rumen fluid was sourced from a nearby slaughterhouse, ensuring adherence to animal welfare standards. Dry and organic matter digestibility were determined using the In vitro technique by Tilley and Terry (1963). Samples were incubated in tubes containing rumen fluid and McDougall’s solution at 1:4. One-liter McDougall’s solution was prepared by dissolving 9.8 g NaHCO₃, 10 g Na₂HPO _{4 12}H₂O, 0.57 g KCl, 0.47 g NaCl and 0.12 g MgSO_{4 7}H₂O. Carbon dioxide (CO₂) was infused to maintain anaerobic conditions during incubation, which was carried out in a water bath at 39–40°C for 48 hours.

Study design and experimental setup

This study employed a completely randomized factorial design with two factors: S. cerevisiae inoculum dose and fermentation duration. Each treatment was performed five times. The treatments were as follows: 0%, 2% and 4% of S. cerevisiae inoculum, with each dose fermented for 7, 14 and 21 days. Each treatment combination corresponds to a specific inoculum dose and fermentation duration, enabling a thorough analysis of how these variables influence the study outcomes.

Statistical analysis

All data were computed and submitted for analysis using R software version 4.4.0 using the "agricolae" module in the CRAN package (R Core Team, 2022). Significance was defined at p<0.05. The statistical model used was: yij = µ + τi + ɛij, where yij represents the observed value of each individual, µ denotes the overall mean, τi represents the treatment effect and ɛij denotes the residual error (variation among replicates for each treatment).

Results and discussion

Dry matter and organic matter content of fermented rice bran

The results indicate that fermentation duration significantly affects the DM content of  FRB from circular rice milling (p<0.05), as shown in Table 2. However, the inoculum dose of S. cerevisiae and its interaction with fermentation duration did not significantly influence the DM content. Overall, the DM content of FRB ranged from 84.52% to 86.56%. The treatment with a 14-day fermentation duration resulted in the highest DM content (86.39%) compared to the 7-day (84.74%) and 21-day (84.87%) fermentation durations (p<0.05). The higher DM content observed in the 14-day fermentation can be attributed to peak cell proliferation of S. cerevisiae, which occurs over a more extended period, reaching its maximum at 14 days. Following this peak, a decline in DM content was observed, continuing through the 21-day fermentation period.

In contrast, FRB OM content showed a 4% S. cerevisiae dose higher than the 0% inoculation treatment (84.52% vs. 83.09%; p<0.05, Table 2). There were no significant differences in OM content between the 0% and 4% inoculation treatments compared to the 2% inoculation, which had an OM content of 83.87%. The OM content of the FRB increased linearly with the increasing inoculation dose. This is likely due to the contribution of microbial biomass from S. cerevisiae, which serves as a source of organic matter in the RB and acts as a growth medium. The availability of nutrients and optimal environmental conditions promote the fermentation process, thereby enhancing microbial biomass (Ribeiro et al 2017; Garofalo et al 2022).

Crude protein content of fermented rice bran

Our findings indicate that inoculation dose, fermentation duration and their interaction significantly affect the CP content of FRB (p<0.05). The CP content ranges from 5.76% to 7.38%, with the highest value observed in rice bran treated with a 4% inoculation dose (7.26%), significantly surpassing treatments with 0% and 2% doses (6.75% and 6.73%, respectively, p<0.05). According to Shuvo et al (2022), the increase in protein from fermented products is attributable to microbial biomass. Furthermore, Azrinnahar et al (2021) asserted that S. cerevisiae, a single-cell protein, can enhance activity and proliferate within a favorable environment, thereby potentially increasing the levels of peptides and free amino acids in fermented feed (Sun et al 2015).

A similar pattern was found with the fermentation duration, where the 21-day fermentation period resulted in a higher CP content than shorter fermentation durations (p<0.05). This finding aligns with Ribeiro et al (2017) showed 2 times increase in CP of fermented bran compared to unfermented. Previously, Joseph et al (2008) reported a 3-7% increase in crude protein in soybean meal, along with a significant rise in essential amino acids, as fermentation duration increased. Additionally, Nwachukwu et al (2018) indicated that extended fermentation times led to higher protein content, suggesting that longer fermentation durations improve the nutritional profile of feed. The rapid growth of yeast during fermentation is probably the reason for the increased protein content.

Our results indicate a significant interaction effect on CP content between S. cerevisiae dose and fermentation duration. The highest CP content was observed when a 4% inoculum dose interacted with a 14-day fermentation period (p<0.05). Overall, the CP content of fermented RB varied between 5.76% and 7.64%. Moreover, this study's CP content of FRB is slightly below the quality standard of Class III rice bran, requiring a minimum CP content of 8% (SNI 2024).

Ether extract content of fermented rice bran

Fermentation of RB using S. cerevisiae significantly reduces their EE content. As shown in Table 2, fermentation with 2% and 4% doses reduced the lipid content by 0.87% and 0.96%, respectively. Similarly, the duration of fermentation significantly impacted the EE content, with a 21-day fermentation duration reducing EE content by 0.96%. This reduction is attributed to S. cerevisiae cells degrading complex organic materials, including fats, into simpler organic compounds (Seyoum et al 2022). Consistent with the findings of Sitohang et al (2012), the decrease in fat content is attributed to the utilization of fat in the substrate as an energy source for metabolism within the S. cerevisiae cells. The interaction between S. cerevisiae dose and fermentation duration also resulted in a significant decrease in the crude fat content of rice bran (p<0.05). Our study achieved FRB EE content ranging from 3.35% to 5.96%.

Rice bran shows most palmitic, oleic and linoleic (Dunford, 2019). Crude rice bran oil comprises 3–4% wax, 0.8% glycolipids and 1–2% phospholipids (Kim and Godber 2014), as well as 4% unsaponifiable lipids that include bioactive compounds such as γ-oryzanol, tocopherols and phytosterols (Sahu et al 2018). These fatty acids undergo oxidation by the lipase enzyme produced by S. cerevisiae, forming short-chain carbon compounds such as aldehydes, which contribute to the rancid of RB. The reduction in crude fat content observed in this study provides an advantage by limiting excessive fat oxidation in RB. When included in the diet of ruminant animals, this helps prevent the diet from becoming rancid quickly. Furthermore, maintaining crude fat levels below 5% ensures the diet remains safe for ruminants. Therefore, managing the quality of rice bran under proper storage conditions and optimizing its industrial application are critical (Rashid et al 2023).

Crude fiber of fermented rice bran

The crude fiber (CF) content of FRB was significantly affected by both the S. cerevisiae inoculation and the fermentation duration (p<0.05). However, there is no interaction effect between these two treatment factors. The treatments with 0%, 2% and 4% doses resulted in significantly different CF contents (p<0.05; Table 3). The highest CF content was observed in the treatment with 0% dose (29.41%). This CF content decreased to 27.95% with a 2% dose and 27.15% with a 4% dose, exhibiting the lowest. Overall, the CF content of the FRB ranged from 26.13% to 32.26%. The percentage reduction in CF content observed in this study is higher than that reported by Sitohang et al (2012), where the CF content of RB fermented with S. cerevisiae was reduced by 17.34%.

The decrease in crude CF content is attributed to the fermentation process, which breaks down lignocellulosic bonds. This transformation occurs as complex carbohydrate compounds, such as CF, are converted into more straightforward, more soluble carbohydrates through the action of cellulase enzymes produced by S. cerevisiae. Dilaga et al (2022) state that S. cerevisiae can produce a group of cellulase enzymes that are highly efficient in breaking down these lignocellulosic bonds. As a result, complex carbohydrates like CF are converted into more accessible and soluble forms.

The addition of microbes during fermentation facilitates the breakdown of complex components into simpler compounds, enhancing their digestibility. This process is driven by the metabolic activities of cellulolytic, which produce extracellular cellulase and hemicellulose enzymes to degrade that portion to soluble sugar and reduce overall CF content. Microbial fermentation also alters the structure of cell wall tissues, breaks lignocellulosic bonds and decreases lignin content. Sharma et al (2020) highlight that microbes can catabolize complex organic compounds during fermentation, converting them into simpler components. Additionally, microorganisms obtain energy through a cycle of redox processes, where part of the substrate carbon is oxidized while another portion is reduced. This process is facilitated by various enzymes produced by the microbes (Cabrol et al 2017).

Cellulose, hemicellulose and lignin content of fermented rice bran

The content of cellulose, hemicellulose and lignin in FRB was significantly influenced by the dose of S. cerevisiae, the fermentation duration and their interaction (p<0.05). A 14-day fermentation resulted in the lowest cellulose content (18.1%). As shown in Table 3, cellulose content consistently decreases over the 14-day fermentation period. Cellulose, a polysaccharide composed of glucose units linked by β (1-4) glycoside bonds, can only be cleaved by microbes that produce cellulase enzymes. According to Akram et al (2021), cellulase enzymes, including endo-β-1,4-glucanase, cellobiohydrolase and β-glucosidase, are essential for breaking down cellulose into simpler glucose units, which can be used as an energy source (Dilaga et al 2022). On a broader scale, the enzymatic processes that transform plant biomass into fermentable sugars hold significant industrial value, especially in biofuel production (Annamalai et al 2016).

A noticeable increase in cellulose content is observed when the fermentation duration is extended to 21 days (p<0.05). This rise in cellulose content during the 21-day fermentation period is attributed to the significant accumulation of S. cerevisiae biomass proliferating throughout fermentation. As the process continues, they generate mycelium, a fiber component. This finding aligns with the results of Kang et al (2018), who reported that most fungal species, including S. cerevisiae, possess cellulose as a cell wall component made up of β-1,4 bonds. The primary constituents of fungal mycelial cell walls are chitin, β-glucans, proteins and lipids, varying concentrations depending on the fermented substrate (Manan et al 2021). Additionally, a study by Haneef et al (2017) found that mycelium from G. lucidum and P. ostreatus exhibited higher levels of chitin. This suggests that mycelium becomes more rigid when the substrate is more complex and challenging to digest.

Hemicellulose is a polysaccharide composed of glucose units linked through β(1-4) glycoside bonds (Dilaga et al 2022). Some forms of hemicellulose are known to be digestible by strong acids and bases. In this study, fermentation using S. cerevisiae at 0%, 2% and 4% significantly increased hemicellulose content from 11.19% to 12.54% and 16.57%, respectively (p<0.05). Contrasting result was reported by Wu et al (2020), who found that S. cerevisiae strains engineered with essential genes and metabolic networks for xylose metabolism through the deletion of cAMP phosphodiesterase PDE1 and PDE2 genes were able to enhance xylose utilization. Interestingly, the duration of fermentation and its interaction with the S. cerevisiae dose did not appear to significantly influence the hemicellulose content of FRB in this study.

Our study demonstrates that the lignin content in RFB is significantly influenced only by the duration of fermentation (p<0.05; Table 3). The lack of significant effects from the S. cerevisiae dose on lignin content aligns with Sangadji et al (2019), who observed a similar outcome in fermented sago pith with added urea. Although lignin is not classified as a carbohydrate, it is closely related to carbohydrates and is a structural component that reinforces plant stems, making them more digestive resistant. Lignin degradation is thought to occur enzymatically, involving enzymes such as laccase, manganese peroxidase, versatile peroxidase and lignin peroxidase (Wang et al 2018; Kamimura et al 2019). However, our findings suggest that the S. cerevisiae strain used in this study may lack the capability to produce these lignin-degrading enzymes.

ADF and NDF content of fermented rice bran

The ADF fraction represents the RB residue that remains undissolved after treatment with strong acids and bases. This fraction includes cellulose, hemicellulose, lignin and silica. As shown in Table 3, applying S. cerevisiae at 2% and 4% doses significantly reduces the ADF content from 51.41% to 48.98% and 44.59%, respectively (p<0.05). Similarly, fermentation durations of 14 and 21 days substantially decrease the ADF content FRB from 49.32% to 47.68% and 47.98%. These findings are consistent with those of Sangadji et al (2019), who observed that fermenting sago pith with urea significantly reduced their ADF content. The reduction in ADF fraction is attributed to the ability of S. cerevisiae to release or break down hemicellulose bound to lignin in the RB cell wall. Additionally, partial digestion of hemicellulose contributes to the lower ADF content. Feedstuff with low ADF values benefits ruminant livestock, enhancing digestibility and nutrient availability.

The NDF fraction in FRB decreases significantly with applying 4% S. cerevisiae, dropping from 62.50% to 61.15%. Likewise, fermentation duration plays a crucial role in reducing the NDF fraction, with a notable decrease from 62.50% to 61.14% observed on 14 days of fermentation (p<0.05; Table 3). These findings align with those of Dilaga et al (2022), who reported reductions in ADF and NDF content in rice bran fermented with various inoculants, including S. cerevisiae. The results suggest that using 4% S. cerevisiae combined with a 14-day fermentation period effectively lowers the NDF content in rice bran. This combination is particularly suitable for FRB from circular milling machines, improving its potential as a ruminant feed ingredient by enhancing fiber digestibility.

Digestibility of fermented rice bran

When fermented with S. cerevisiae, FRB exhibited a significant improvement in both DMD and OMD (p<0.05). Additionally, the fermentation duration substantially enhanced DMD and OMD values. However, no interaction was detected between the treatment factors regarding digestibility improvement. As shown in Table 4, the DMD and OMD of FRB increased linearly with higher S. cerevisiae doses. The highest DMD value was observed in the treatment with 4% S. cerevisiae, while the lowest was recorded in the 0% S. cerevisiae treatment. These results highlight the effectiveness of S. cerevisiae fermentation in enhancing the digestibility of RB, making it more suitable for ruminant feed applications.

Similar results were observed for FRB organic matter digestibility. Previous studies have also reported a consistent increase in DMD and OMD of FRB with higher S. cerevisiae inoculation doses (Dilaga et al 2022). Comparable findings were obtained in experiments on rice straw, which demonstrated improved dry matter and organic matter digestibility through fermentation (Jafari et al 2007). The close relationship between DMD and OMD is well-documented, as high dry matter digestibility typically corresponds to high organic matter digestibility (Putra et al 2017; Sutaryono et al 2023; Mudhita et al 2024; Dahlanuddin et al 2024).

The enhancement in DMD and OMD of RB is closely linked to the activity of S. cerevisiae, which can break down complex compounds such as starch, hemicellulose and cellulose. Fermentation is a viable approach to optimizing the use of RB as livestock feed. This process involves metabolic reactions facilitated by microbial enzymes, including oxidation, reduction and hydrolysis, leading to chemical transformations of the organic substrate and yielding specific products. Beyond its role as a probiotic, it improves the digestibility of high-fiber feed. Phesatcha et al (2022) demonstrated that S. cerevisiae supplementation enhances nutrient digestibility, increases ruminal volatile fatty acid (VFA) production, reduces ammonia nitrogen (NH₃-N), stabilizes rumen pH and promotes the growth of ruminal microbial propagation.

Conclusion

The fermentation using S. cerevisiae resulted in favorable changes in rice bran's chemical composition. Inoculation at 2% to 4% over 14 days effectively enhances rice bran's nutrient quality and digestibility.

Acknowledgment

Sincere gratitude is extended to the Research and Community Service Institute (LPPM) of the University of Mataram for supporting this study through its grant. Heartfelt appreciation is also directed to the students for their unwavering dedication and active participation throughout the research process.

Conflict of interest

The authors declare that they have no conflict of interest.

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