Enhancement of Cassava (Manihot esculenta Crantz) Retting Efficiency Using Pectinolytic and Cellulolytic Streptomyces sp. in the Traditional Starter Sta_96

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Abstract
Background: This study aimed to improve the cassava retting efficiency of starter Sta_96, a fermented cassava flour obtained after four days of fermentation, by incorporating bacteria of the genus Streptomyces. Methods: Streptomyces isolates were obtained from Sta_96, farm soils, and a cassava peel dump. The subsequent pectinolytic and cellulolytic activities, along with the associated ability to soften cassava roots, were evaluated. The most effective isolates were incorporated into Sta_96 at a concentration of 106 CFU/g, and the associated retting and detoxification efficiencies were assessed. Results: Of the 33 Streptomyces isolates recovered, 24 produced pectinases, with hydrolysis halos ranging from 11.0 ± 1.4 mm to 42.5 ± 3.5 mm. Sixteen of these displayed cellulase activity, with halos ranging from 16.0 ± 0.1 mm to 40.0 ± 0.1 mm. STF 16 showed the highest softening efficiency, achieving a retting time of 38.6 ± 0.4 h, and significantly improved the performance of Sta_96 by reducing the retting duration from 44.5 ± 0.6 h to 24.3 ± 0.4 h, representing a 45.39% reduction. STF 16 also demonstrated substantial detoxification efficiency (~85%). Conclusions: This is the first report demonstrating that Streptomyces species can act as efficient cassava retting agents. Incorporation of STF 16 into the Sta_96 starter markedly accelerated root softening to about 24 hours while ensuring complete elimination of cyanide. This approach represents a promising strategy for improving fermentation efficiency and product safety in cassava-processing industries.

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