Effect of microbial fermentation on nutritional and antinutritional contents of cassava leaf

Metagenomic insights into protein degradation mechanisms in natural fermentation of cassava leaves

Cassava (Manihot esculenta Crantz) leaves, the primary by-product of cassava processing, constitute a significant protein source, accounting for 18 to 38 percent on a dry weight basis. Despite their nutritional value, a substantial portion of these leaves is often discarded post-harvest, resulting in notable resource waste. This study employs metagenomic technology to investigate the protein degradation mechanism in cassava leaves, aiming to provide a technical reference for value-added of this by-product. Following a 36-hour period of natural fermentation, the protein degradation rate reached 58%, a phenomenon intricately linked to both the microbial community structure and its functional properties. Notably, Lactococcus and Enterobacter, recognized for their abundant protease activity, were predominant. Metagenomically assembled genomes further revealed Lactococcus's substantial role in producing flavors and active compounds, including amino acids and peptides. This study offers novel perspectives to the foodization and high-value utilization of cassava by-products, emphasizing the sustainable exploitation of biomass resources.

Effect of Growth Stages and Lactic Acid Fermentation on Anti-Nutrients and Nutritional Attributes of Spinach (Spinacia oleracea)

Spinach (Spinacia oleracea) is a winter-season green, leafy vegetable grown all over the world, belonging to the family Amaranthus, sub-family Chenopodiaceae. Spinach is a low-caloric food and an enormous source of micronutrients, e.g., calcium, folates, zinc, retinol, iron, ascorbic acid and magnesium. Contrarily, it also contains a variety of anti-nutritional factors, e.g., alkaloids, phytates, saponins, oxalates, tannins and many other natural toxicants which may hinder nutrient-absorption. This study was aimed at investigating the effect of fermentation on improving the nutrient-delivering potential of spinach and mitigating its burden of antinutrients and toxicants at three growth stages: the 1st growth stage as baby leaves, the 2nd growth stage at the coarse stage, and the 3rd growth stage at maturation. The results revealed the significant (p < 0.05) effect of fermentation on increasing the protein and fiber content of spinach powder from 2.53 to 3.53% and 19.33 to 22.03%, respectively, and on reducing total carbohydrate content from 52.92 to 40.52%; the effect was consistent in all three growth stages. A significant decline in alkaloids (6.45 to 2.20 mg/100 g), oxalates (0.07 mg/100 g to 0.02 mg/100 g), phytates (1.97 to 0.43 mg/100 g) and glucosinolates (201 to 10.50 µmol/g) was observed as a result of fermentation using Lactiplantibacillus plantarum. Fermentation had no impact on total phenolic content and the antioxidant potential of spinach, as evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric-reducing antioxidant power (FRAP) assays. This study proposes fermentation as a safer bioprocess for improving the nutrient-delivering potential of spinach, and suggests processed powders made from spinach as a cost-effective complement to existing plant proteins.

Effects of Aspergillus niger on cyanogenic glycosides removal and fermentation qualities of ratooning sorghum

Introduction

Cyanogenic glycosides (CNglcs) are bioactive plant products involving in plant defense against herbivores by virtue of their abilities to release toxic hydrogen cyanide (HCN). Aspergillus niger has been shown to be effective in producing β-glucosidase, which could degrade CNglcs. However, whether A. niger could remove CNglcs under ensiling conditions is still unknown.

Methods

In this study, we first investigated the HCN contents in ratooning sorghums for two years, then the sorghums were ensiled with or without the addition of A. niger.

Results

Two years' investigation indicated that the contents of HCN in fresh ratooning sorghum were larger than 801 mg/kg FW (fresh weight), which could not be reduced by silage fermentation under safety threshold (200 mg/kg FW). A. niger could produce β-glucosidase over a range of pH and temperature, which degraded the CNglcs and removed the hydrogen cyanide (HCN) at early days of ratooning sorghum fermentation. The addition of A. niger (2.56 × 10⁷ CFU/ml) altered the microbial community, increased bacterial diversity, improved the nutritive qualities, and reduced the HCN contents in ensiled ratooning sorghum lower than 100 mg/kg FW after 60 days of fermentation. Overall, the addition of 150 ml A. niger + 50 ml sterile water per 3 kg silage could efficiently remove CNglcs from ratooning sorghum silage.

Conclusion

In conclusion, A. niger could produce β-glucosidase which degraded the CNglcs during the early days of fermentation, benefiting the ensiling process and improving the utilization of ratooning sorghum.