Proximate Composition, Physiological Changes during Storage, and Shelf Life of Some Nigerian Varieties of Yams (Dioscorea species)

Aims: The objectives of this work were to study the influence of proximate composition and physiological changes during storage, on the shelf life some Dioscorea sp. This is needed to complement knowledge of the influence of extrinsic factors of the storage environment in improving the shelf life, a key attribute of yam quality.
Place and Duration of Study: Department of Applied Microbiology & Brewing, Nnamdi Azikiwe University, Awka, Nigeria between January 2012 and July 2013.
Methods: AOAC and sensory methods were used to determine proximate composition and shelf life respectively, while physiological changes during storage were monitored by moisture and pH measurements.
Results: Moisture content of yams ranged from 61 - 70 %; protein, 0.48 – 1 %; fat, 0.39 – 1.67% and carbohydrates, 24 – 32 %. These contents varied among the yams at the varietal level. Ash ranged from 1.33 – 2.17 % and crude fibre, 2.83 – 4.33 % and were largely similar in all varieties. During storage, different varieties of yams maintained different contents of moisture (%) but all shared similar characteristics in respiratory activity. Methanolic extracts from the peels of some Dioscorea dumentorum and D. rotundata varieties inhibited the growth of Aspergillus sp. The shelf life of the yams ranged from low 27 weeks in D. alata to a high of 40 weeks in D. rotundata. Moisture content (P = 0.1) was negatively correlated while fat (P = .05) and carbohydrate contents were positively correlated with shelf life of yams.
Conclusion: The chemical composition of yams plays a role in the determination of their shelf lives. A better understanding of this relationship will help in efforts to increase yam production through the reduction of post harvest losses.