Drying Technologies for Nigerian Walnut (Tetracarpidium conophorum): A Review of Quality Characteristics and Processing Efficiency
1,2*Ayoola, A. S., 1*Jekayinfa, S. O., 1Idowu, D. O., 2Lung’aho M., 3Mushoriwa, H., 2Adesokan, M., 4Alamu, E. O..
1Department of Agricultural Engineering, Ladoke Akintola University of Technology (LAUTECH), Ogbomoso, Oyo State, Nigeria.
2Food and Nutrition Sciences Laboratory, International Institute of Tropical Agriculture (IITA), Ibadan, Oyo State, Nigeria.
3International Institute of Tropical Agriculture (IITA), Ibadan, Oyo State, Nigeria.
4Nice-Pak Products Inc., Montvale, New Jersey, USA.
DOI: 10.36108/laujoces/6202.61.0291
Abstract
Nigerian walnut (Tetracarpidium conophorum) is an underexploited nutritious nut which is rich in oil. The nut has great importance not only from nutritional and medicinal point of view but economically as well, especially in tropical countries. However, its high moisture content poses a problem of fast deterioration due to which it becomes very important to dry it before storing or processing. Therefore, this review article is focused on various technologies for drying Nigerian walnut and related oil rich nuts, with special reference to their impact on the quality of the nuts as well as ease of processing. Conventional drying techniques such as sun drying, solar drying, oven drying, and cabinet drying have been analysed along with new innovations in drying technologies. Studies show that increased drying temperature from 50 to 80°C decreases drying time from 7 to 8 hours to 4 hours and effective moisture diffusivity varies from 4.94 × 10⁻¹⁰ to 4.72 × 10⁻⁷ m²/s depending on drying methods used. Infrared drying can help decrease drying time from 240 min to 40 min while decreasing specific energy consumption from 31.56 MJ/kg to 7.76 MJ/kg. In addition, effects of different drying methods on quality attributes, the importance of proper drying process for increasing storage ability, minimizing post-harvest losses and making processing easy has also been mentioned. Nevertheless, energy usage, non-uniformity and quality degradation continue to be serious issues related to processing of Nigerian walnuts despite advances in drying technologies. There is a need for optimizing drying techniques as well as development of suitable drying processes for developing countries.
Keywords: Nigerian walnut; drying technologies; quality characteristics; processing efficiency; post-harvest processing; Tetracarpidium conophorum.