Influence of Fermentation Duration on Rice Bran Fermented with Local Microorganisms Derived from Kacang Goat Rumen Fluid and Palmyra Sap

Rice bran is a by-product of rice milling commonly used as a feed ingredient for poultry and livestock (Debi et al., 2022). It can be included up to 10% in poultry diets (Kim et al., 2017). However, its utilization is limited by high crude fiber content 24 g/100 g (Koni et al., 2022) and phytic acid concentration 7.30 mg/100 g (Koni et al., 2025), which reduce nutrient digestibility and mineral bioavailability. Fermentation is an effective biological process to decrease crude fiber and phytic acid content, thereby improving feed quality (Munira et al., 2016; Ibrahim and Usman, 2019). Microbial inoculants used in fermentation can be derived from local resources such as rumen fluid and natural plant saps. Goat rumen fluid contains cellulolytic and phytase-producing microorganisms (Islam et al., 2022). Goat rumen harbors diverse microbial phyla, including Bacteroidetes, Firmicutes, and Proteobacteria, which are dominated by genera such as Prevotella, Ruminococcus, Butyrivibrio, and Succinivibrio. These microorganisms contribute to the degradation of crude fiber, protein, and lipids in feed materials (Liu et al., 2017). Ruminococcus is composed of two strong fiber digesting bacterial species, Ruminococcus albus and Ruminococcus flavefaciens, which can produce a large amount of cellulases and hemicellulases (Odeyemi et al., 2020). Goat rumen fluid inclusion in rice bran fermentation has been shown to reduce crude fiber (Ermalia et al., 2016). Similarly, palmyra sap (Borassus flabellifer) is rich in fermentable sugars and contains Saccharomyces cerevisiae and lactic acid bacteria (Chayaningsih, 2006; Irmayuni et al., 2018), both of which enhance fermentation. palmyra sap supplementation at 10% was previously found to improve the nutritional profile of rice bran (Koni et al., 2023).

This study utilized a mixture of Kacang goat rumen fluid and palmyra sap to produce local microorganisms (LM-KGRFPS) based on the modified method of Sio et al. (2022). The duration of fermentation influences microbial activity and enzyme production (Mantut et al., 2019), which are key determinants of nutrient modification. Therefore, this study aimed to evaluate the effects of fermentation duration using LM-KGRFPS on the fermentation characteristics and nutrient composition of rice bran.

Rice bran was obtained from a local rice mill in Kaniti, Kupang Regency, East Nusa Tenggara, Indonesia. Palmyra sap was collected from palm tappers in Lasiana, Kupang City, and Kacang goat rumen fluid was obtained from a local slaughterhouse in Pasir Panjang, Kota Lama Kupang City.

Rice bran was cleaned to remove impurities such as husks and stones. The cleaned material was analyzed for initial nutrient composition at the Nutrition and Animal Feed Laboratory, Politeknik Pertanian Negeri Kupang. The proximate and mineral composition of the unfermented rice bran is presented in Table 1.

Goat rumen fluid from Kacang goats was mixed with palmyra sap and a sugar solution following a modified procedure of Foenay et al. (2025). The mixture contained 1000 mL Kacang goat rumen fluid, 100 mL palmyra sap, and 500 mL sugar solution (prepared by dissolving 250 g sugar in 500 mL water). The mixture was incubated in airtight containers at room temperature for eight days to allow fermentation.

Table 1: Nutrient composition of rice bran before fermentation.

*Analyzed at the Nutrition and Animal Feed Laboratory, Politeknik Pertanian Negeri Kupang (2025). ** Laboratory of Nutritional Biochemistry, Faculty of Animal Science, Universitas Gadjah Mada (2025).

Fermentation was conducted following Koni et al. (2023). The rice bran was adjusted to 65% dry matter and 35% moisture, mixed with 10% LM-KGRFPS (v/w), and placed in 2-kg plastic jars. The jars were sealed anaerobically and incubated for 0, 6, 12, and 18 days.

The pH was measured using a pH meter following the procedures of Bernardes et al. (2019). Ammonia nitrogen (N-NH₃) and lactic acid were determined according to Matias et al. (2020) and Ergin and Gumus (2020) respectively. Nutrient composition (crude protein, crude fiber, crude fat, ash, calcium, and phosphorus) was analyzed using Association of Official Analytical Chemists (AOAC, 2005) procedures.

The experiment followed a completely randomized design with four treatments (0, 6, 12, and 18 days) and five replications. Data were analyzed using Analysis of variance and significant differences among means were determined by Duncan’s Multiple Range Test.

The pH, lactic acid, and N-NH₃ concentrations of rice bran fermented with LM-KGRFPS for different durations are presented in Table 2. The pH of rice bran decreased significantly (P < 0.05) after fermentation, indicating active microbial metabolism and acid production. Lactic acid bacteria (LAB) present in LM-KGRFPS produced organic acids, mainly lactic acid, leading to a drop in pH. Anaerobic fermentation conditions favoured LAB growth and inhibited the development of spoilage microorganisms. A low pH is desirable because it improves preservation quality and prevents the growth of undesirable bacteria such as Clostridium spp. (Queiroz et al., 2018). The final pH values (3.91–4.80) obtained in this study were within the range reported for good-quality silage (Despal et al., 2011; Bernardes et al., 2019).

Lactic acid concentration increased (P < 0.05) with fermentation duration, confirming efficient conversion of soluble carbohydrates into organic acids by LAB. The lactic acid content (49.20–123.17 mg/100 g) was within the range reported by Cherney and Cherney (2015), who indicated that levels above 3% (30 g/kg) are characteristic of well-preserved silage.

Table 2: Changes in pH, lactic acid, and Ammonia nitrogen (N-NH₃) contents of rice bran fermented with LM-KGRFPS at different fermentation durations.

Values are means ± standard deviation. Mean in the same column and followed by the same superscript letter means no difference (P>0.05) T0 = unfermented; T1 = 6 days; T2 = 12 days; T3 = 18 days.

The lowest nitrogen ammonia (N–NH₃) concentration was observed in the 6-day treatment (T1), suggesting limited proteolysis at this stage. Lower N–NH₃ values indicate reduced protein degradation and better preservation of nitrogen compounds (Samadi et al., 2015). According to Despal et al. (2011), ammonia values below 50 g/kg total N reflect high-quality silage. Therefore, fermentation for six days appeared optimal for maintaining nitrogen integrity in rice bran.

Table 3 presents the nutrient composition of rice bran fermented with LM-KGRFPS for different durations. Fermentation duration had a significant effect (P < 0.05) on the dry matter content of rice bran. Prolonged fermentation for 12 and 18 days resulted in a marked decrease (P < 0.05) in dry matter content compared with shorter fermentation periods. This reduction is attributed to the metabolic activity of microorganisms during fermentation, which produces water as one of its by-products. The accumulation of water over time consequently decreases the dry matter proportion in the substrate. This finding is consistent with the statement of Irawati et al. (2019), who reported that as the fermentation period increases, microorganisms reach their optimal growth phase, utilizing more nutrients from the substrate and generating a higher amount of water through metabolic processes. Therefore, extended fermentation tends to lower dry matter content due to the increased metabolic activity and moisture accumulation within the fermenting material.

Ash content increased (P < 0.05) in samples fermented for 12 and 18 days. The increase could be related to the reduction of organic matter as microorganisms utilized available nutrients, thereby concentrating the mineral fraction. Comparable trends were observed by Superianto et al. (2018), while Sabuna et al. (2024) found that palmyra sap concentration did not significantly affect ash levels in fermented Putak meal (Putak is the inner pith of the Corypha gebanga palm). Crude protein content did not differ significantly (P > 0.05) among treatments, suggesting that microbial protein synthesis did not increase with longer fermentation periods. These results differ from Koni et al. (2025), who reported an increase in crude protein in Putak (Corypha gebanga) fermented with 10–30% palmyra sap, and from Irawati et al. (2019), who found gradual protein enrichment in fermented water hyacinth up to 14 days.

Table 3: Nutrient composition of rice bran fermented with LM-KGRFPS at different fermentation durations.

Values are means ± standard deviation. Means in the same row and followed by the same superscript letter means no difference (P>0.05). Means in a row with different superscripts differ significantly (P < 0.05). T0 = unfermented; T1 = 6 days; T2 = 12 days; T3 = 18 days.

Fermentation duration had no significant effect on crude fat content (P > 0.05). The lack of difference indicates that microorganisms used other carbon sources rather than lipids as energy substrates. In contrast, Sao et al. (2021) observed an increase in crude fat in banana peel fermented with goat rumen fluid.

Crude fiber decreased significantly (P < 0.05) after six days of fermentation (T1). The reduction was attributed to cellulolytic microbial activity in LM-KGRFPS, which degraded cellulose and hemicellulose fractions through enzymatic hydrolysis. Similar reductions were reported by Helda and Sabuna (2012) in goat manure fermented with palmyra sap, and by Koni et al. (2021, 2023) in banana peel and rice bran, respectively.

Overall, fermentation for six days using LM-KGRFPS produced the most favorable results, characterized by lower pH and ammonia levels, increased lactic acid concentration, and reduced crude fiber content while maintaining crude protein stability. These findings indicate that a six-day fermentation period is optimal for improving the nutritional and fermentation quality of rice bran.

Fermentation of rice bran with local microorganisms derived from goat rumen fluid and palmyra sap significantly improved its fermentation quality. The six-day fermentation period produced the lowest crude fiber and ammonia contents while maintaining stable crude protein levels and high lactic acid concentration. This duration is recommended as the optimal fermentation time for enhancing the nutritional value and feed quality of rice bran.

The authors sincerely thank the Directorate General of Research and Development, Ministry of Higher Education, Science, and Technology, Indonesia, for supporting this study through the Regular Fundamental Research Scheme (Grant No. 193/C3/DT.05.00/PL, Batch II, 2025).

This study presents a novel fermentation strategy using a consortium of local microorganisms derived from Kacang goat rumen fluid and palmyra sap to improve the nutritional quality of rice bran. The integration of rumen cellulolytic microbes with fermentative microorganisms from palmyra sap enhances substrate degradation, with a six-day fermentation period identified as optimal for reducing crude fiber and ammonia contents.

TNIK contributed to the development of the research concept, actively participated in data collection, conducted the experimental procedures, performed data analysis, and was the main author of the manuscript. OH contributed to the experimental implementation, particularly in the preparation of LM-KGRFPS and the proximate analysis. SV and TAYF contributed to data analysis and critically reviewed and revised the manuscript for intellectual content.

Artificial intelligence tools were used only to assist with grammar correction and sentence editing. The authors affirm that all scientific content, data analysis, interpretation, and conclusions are entirely their own original work.

There was no conflict of interest in this research with other parties, both individuals and organizations.