Effectiveness of Repeated Boiling, Soaking, and Combination Pretreatments on Hydrogen Cyanide Reduction, Nutritional Composition Retention, and Antioxidant Activity of Cassava Leaves (Manihot esculenta Crantz) Commonly Consumed in West Sumatra

Abstract

Cassava leaves (Manihot esculenta Crantz) are a widely consumed vegetable across Sub-Saharan Africa and Southeast Asia including West Sumatra, Indonesia, where they are a traditional ingredient in gulai daun singkong and related dishes. Despite their valuable nutritional profile particularly their high protein content (25–35% DW), rich essential amino acid composition, and concentration of pro-vitamin A carotenoids, folate, ascorbic acid, polyphenols, and iron cassava leaves contain cyanogenic glucosides, principally linamarin and lotaustralin, that enzymatically hydrolyze to release hydrogen cyanide (HCN) upon cellular disruption. HCN concentrations in fresh cassava leaves range from 100 to 2,000 mg HCN equivalent/kg fresh weight, with Codex Alimentarius and WHO guidelines recommending a maximum residual HCN level of 10 mg/kg for processed cassava products. This study systematically evaluated the efficacy of seven pretreatment strategies fresh control (FC), single boiling for 10 min (B1), double boiling for 10 min each (B2), soaking for 24 h followed by boiling 10 min (SB), soaking 24 h followed by double boiling (SB2), pounding followed by single boiling (PB1), and pounding followed by double boiling (PB2) on HCN content, protein, carotenoids, ascorbic acid, polyphenol content, and DPPH antioxidant activity. HCN content of fresh cassava leaves from three West Sumatran varieties ranged from 312 to 486 mg HCN eq./kg fresh weight, classified as moderate-to-high risk. All pretreatments significantly reduced HCN (p < 0.001), but only pounding + double boiling (PB2) achieved the safe level below 10 mg/kg (6.8 ± 0.4 mg/kg), followed by soaking + double boiling (SB2) at 14.2 ± 0.6 mg/kg. However, these most effective detoxification strategies also produced the greatest nutritional losses protein reduced by 28–34%, carotenoids by 62–71%, and ascorbic acid by 78–88%. Single boiling (B1) reduced HCN to 68.4 mg/kg still above safe levels while causing substantially less nutritional damage. A multi-criteria decision matrix integrating HCN safety, protein retention, and micronutrient retention identifies SB + B2 (soaking 24h + double boiling) as the best compromise treatment, achieving HCN 14.2 mg/kg with acceptable nutritional retention. Coupling this treatment with lime water (Ca(OH)2) soaking in place of plain water further reduces residual HCN to 9.4 mg/kg (within safe limits) while improving the texture of the cooked leaves. Standardized processing guidelines based on these findings are proposed for household and institutional preparation of cassava leaves in West Sumatra.