EFFECT OF FUSARIUM NYGAMAI INFECTION ON THE CHEMICAL COMPOSITION OF FLOUR FROM TWO YAM VARIETIES

Abstract

Yams (Dioscorea spp) are among the oldest food crops. It is estimated that after six months of storage up to 56% of the crop is lost to rot.  In Nigeria, fresh yam tubers are used for production of Elubo (yam flour) for preparation of amala, as it is called among the Yoruba in Western Nigeria, and akwunaji in the east of the River Niger. Many researchershave emphasized the importance of microbial rotting in causing storage losses. This study evaluated the effect of yam rot on the nutritional values of Fusarium infected yam tubers.Tubers from two yam (Dioscorea rotundata Poir.)varieties-Nwopoko and TDr95/19177-were infected with Fusarium nygamai pure culture and stored for 12 weeks, after which the tubers were used to produce yam flour and were analyzed for their nutrient composition comprising: dry matter/ moisture content, ash, total sugar, starch, amylose, vitamin C, protein and tannins. Wholesome yams of the same varieties were also used to produce yam flour and equally evaluated for the same nutrients. Infection with Fusariumnygamai led to a significant reduction (p<0.05) in the nutrient composition of the infected yam flour compared with those ofwholesome samples. Vitamin C content reduced from 41.10 to 27.26 (mg/100g) in variety Nwopoko and 36.30 to 30.53 (mg/100g); in variety TDr95/19177. Corresponding values for protein content was from 5.05 to 4.60% and 4.93 to 4.62%; Ash Content from 1.32 to 1.30% and 1.36 to 1.24%; Total Sugar Content from 5.34 to 5.20% and 5.21 to 5.02%; Starch 78.71 to 77.61 and 89.28 to 81.53%; Amylose from 29.95 to 28.87% and 30.01 to 27.95%. However, an increase in the tannin content – (1.84 and 1.94 mg/g) as against (0.31 and 0.26 mg/g) in Nwopoko and TDr 95/19177 varieties respectively was observed. The increase in the tannin content implies an increase in the antinutrient composition. The tendency to produce Elubo used for preparation of amala with rotten yam (possibly Fusarium infected) should be discouraged.