Nutritional Improvement of Starter Culture–Fermented Iru : A Comparative Study of Spontaneous and Controlled Fermentation of Parkia biglobosa Seeds

Background: Iru, a traditional fermented condiment, derived from the seeds of Parkia biglobosa (African locust bean), represents a nutritionally valuable product widely prized for its capacity to enhance both the flavor profile and nutritional quality of several Nigerian dishes. In Nigeria, iru production has conventionally relied upon spontaneous fermentation driven by naturally occurring indigenous microflora, a process that inherently compromises nutritional consistency and batch-to-batch reproducibility.

Aims: This study aimed to evaluate the feasibility of scaling up the microbial fermentation process of P. biglobosa seeds through the application of defined starter cultures, with the objective of achieving enhanced nutritional consistency, improved phytochemical profiles, and reproducible fermentation outcomes.

Methods: aw seeds of P. biglobosa were processed and subjected to two spontaneous fermentation regimens and controlled fermentation employing starter cultures of Leuconostoc mesenteroides subsp. mesenteroides NC-008 and Bacillus subtilis str.168 each applied independently over a 72-hour fermentation period. The resulting iru products were assessed for crude protein, phytochemical composition, antioxidant activity, and organoleptic properties.

Results: The total viable count recorded in the B. subtilis-fermented sample (8.65 log₁₀ CFU/g) did not differ significantly from that of the spontaneously fermented sample. However, the crude protein content of the B. subtilis-fermented iru (40.36 %) was significantly higher than that of all other fermentation groups, which ranged from 32.07 % to 38.63 %. Iru fermented with B. subtilis additionally exhibited markedly higher total phenolic and flavonoid contents, as well as significantly elevated ferric reducing antioxidant power (FRAP) activity relative to the other groups. The spontaneously fermented seeds recorded the highest tannin content (2.87 mg/g), whilst L. mesenteroides-fermented iru yielded the highest saponin and glycoside concentrations, although these differences were not statistically significant relative to the other experimental groups. Organoleptic evaluation revealed a marked reduction in ammonia odor in B. subtilis-fermented iru compared with the spontaneously fermented product; however, overall sensory acceptability did not differ significantly between the two groups.

Conclusions: The application of B. subtilis as a defined starter culture is recommended for the commercial-scale production of iru, on the basis of its demonstrably superior crude protein content, enhanced antioxidant capacity, and improved sensory characteristics relative to both spontaneous fermentation and L. mesenteroides-mediated fermentation. This approach offers a scientifically grounded pathway to achieving nutritional consistency, safety, and reproducibility in the industrial production of this traditionally significant fermented condiment.