Variability in Biochemical Composition and Cell Wall Constituents among Seven Varieties in Ghanaian Yam (Dioscorea sp) Germpalsme

Abstract

This work characterized the most cultivated and consumed yam (Dioscorea) cultivars within the Ghanaian yam germplasm based on their biochemical and cell wall constituents to assess their potential alternative food and industrial processing applications. Samples were analyzed for their biochemical composition - starch, amylose, amylopectin, total sugars, reducing sugars and non-reducing sugars along the head, middle and tail regions of each tuber using standard analytical methods. Cell wall constituents - acid detergent fibre, neutral detergent fibre, acid detergent lignin, cellulose and hemicellulose of each tuber were also determined using standard analytical methods. The results showed no significant differences at p<0.05 in biochemical compositions along the length of the studied cultivars. D. cayenensis (Pure-yellow), D. rotundata (Pona) and D. alata (Matches) were found to have high starch contents (63.16-65.69%, 63.54-65.30% and 63.24-65.17% respectively). Amylose content was observed to vary along the length of the tubers for the varieties studied. D. alata (Matches) was observed to contain the highest amylose content of 19.66-20.64%. No identifiable trend was however, observed for the amylopectin content along the length between the varieties investigated. D. bulbifera recorded the lowest amylopectin content of 41.29%, 43.59% and 44.63% while D. esculenta had the highest with 49.84%, 50.24% and 50.13% along the tail, middle and head sections respectively. Total sugar content varied significantly (p<0.05) along the lengths of all the varieties investigated. It was higher at the tail portions for all the varieties studied than the head regions; the middle portions recorded the least. D. bulbifera recorded highest total sugar contents (4.74-4.84%) and total sucrose (3.58-3.64%). There were significant differences (p<0.05) in the cell wall constituents of the yam varieties. Cellulose was found to be the most common cell wall component with D. rotundata having the highest level of 3.36% whilst D. dumetorum had the least (1.56%). Hemicellulose content ranged between 0.42 g/100g in D. alata to 4.58 g/100g in D. esculenta whiles lignin content ranged from 1.56 g/100g in D. dumetorum to 2.87 g/100g for D. praehensalis. There were significant differences (p<0.05) in the neutral detergent fibre found in Dioscorea esculenta and the other yam species. It ranged from 1.18 g/100g in D. alata to 5.46 g/100g in D. esculenta. Less than 1% of acid detergent fibre was identified in the yam varieties, suggesting varied levels of biochemical composition and cell wall constituents in the different yam varieties.

Key words: Biochemical quality, cell wall composition, yams