Bacillus subtilis Fermented Mango Peel: A Potential Strategy for Modulating Short-Chain Fatty Acid Levels in Rat Gut

The mammalian gastrointestinal tract hosts a complex consortium of microorganisms that produce short-chain fatty acids (SCFAs), which are critical signaling molecules and energy substrates influencing colonic health, systemic metabolism, and immune homeostasis. Mango peel, an abundant agro-industrial by-product constituting approximately 15–20% of the whole fruit, remains underutilized despite being remarkably rich in dietary fibers, polyphenols, and carotenoids with prebiotic potential. However, the crude fiber in mango peel is often poorly fermented by resident gut microbiota due to its complex matrix, a limitation that can be overcome through microbial fermentation. This study was carried out to evaluate the effect of Bacillus subtilis-fermented mango peel on the modulation of short-chain fatty acid levels in the gut of broiler chicks and to investigate its potential as a gut health modulator. The fermenter used in this study was obtained following standard microbiological techniques. Mango peel was collected, processed, homogenized, and fermented using solid-state fermentation method, and this was incorporated as a feed additive and assessed for its impact on SCFAs of chick gut using in vivo techniques. The fermenter was characterized culturally, morphologically, biochemically, and molecularly, and definitively identified as Bacillus subtilis strain PK5-17. Results showed that the fermented mango peel significantly modulated SCFA levels in the test group compared to the control. Acetate increased from 66.32% to 69.80%, remaining within the reference range of 50–72%. Propionate increased from 22.30% to 27.44%, staying within the normal range of 15.40–30.30%. N-valerate exhibited a slight increase from 3.01% to 3.08%, within the reference range of 0.80–5.00%. However, n-butyrate markedly decreased from 2.04 mg/L in the control group to 0.66 mg/L in the test group, moving from above the reference range (0.80–1.00 mg/L) to below the normal range. These effects were statistically significant (P < 0.05) except for n-valerate. The study concludes that Bacillus subtilis-fermented mango peel exhibited pronounced activity on the levels of short-chain fatty acids in the gut of broiler chicks, significantly increasing acetate and propionate production. However, the decrease in n-butyrate below the normal range suggests that Bacillus subtilis, being an aerobic bacterium, is not a butyrate-producing organism. Hence, while the fermented mango peel shows potential as a gut health modulator, further optimization may be required to enhance butyrate levels.