The effect of thermal processing (roasting and boiling) on the nutritional, antinutritional, and antioxidant properties of African walnut was studied. Tetracarpidium conophorum (African walnut) was subjected to thermal treatment of roasting (RWIS), boiling with shell (BWIS), and boiling without shell (BWOS). The resulting samples with raw nut (RAAW) which served as control were analysed for proximate composition, antinutritional components, and antioxidant activity. The protein, fat, and ash contents of the samples on dry basis were 29.14%, 54.14%, and 3.32% (RAAW); 24.13%, 61.75%, and 2.77% (BWIS); 22.47%, 62.65%, and 2.16% (BWOS); and 24.25%, 60.52%, and 2.48% (RWIS), respectively. Thermal processing had significant effect on all the proximate principles; boiling and roasting generally reduced the protein and ash contents of the nut. Boiling with or without shell reduced the phytate and tannin contents of the nut while roasting increased the level of these two antinutritional components; walnut boiled without shell however, had the lowest phytate and tannin contents of 0.815？mg/100？g and 0.239？mg/100？g, respectively. The antioxidant activities of the samples were 8.47% (RAAW), 13.82% (BWIS), 14.96% (BWOS), and 7.29% (RWIS). This study reveals that thermal processing has a significant effect on the proximate principles, bioavailability, and antioxidant activity of African walnut. 1. Introduction Tetracarpidium conophorum is a woody perennial climbing plant which is commonly cultivated for the production of nuts (African walnut); it is usually found in some states of south-west and south-south geopolitical regions of Nigeria. African nut which is usually cooked and consumed as snacks has been identified to possess both nutritional and medicinal values. Enujiugba [1] and Ogunsua and Adebona [2] have reported on the high nutritional potential of the nut. African walnut has been known to possess antioxidant property [3] which is as a result of its constituent bioactive polyphenols. There is evidence that phenolic substances act as antioxidant by preventing the oxidation of LDL-lipoprotein, platelet aggregation, and damage of red blood cells [4]; this explains the reason that made the nut to be listed among the plant foods that are of great health benefit to human body. The nut has also been used as a male fertility agent in the southern part of Nigeria. African walnut is also known to contain some antinutritional chemical components such as phytate and tannin which have been reported to be responsible for the bitter taste usually observed upon drinking of
References
[1]
V. N. Enujiugba, “Chemical and functional characteristics of conophor nut,” Pakistan Journal of Nutrition, vol. 2, no. 6, pp. 335–338, 2003.
[2]
A. O. Ogunsua and M. B. Adebona, “Chemical composition of Tetracarpidium conophorum (conophor nut),” Food Chemistry, vol. 10, no. 3, pp. 173–177, 1983.
[3]
B. M. Olabinri, O. O. Eniyansoro, C. O. Okoronkwo, P. F. Olabinri, and M. T. Olaleye, “Evaluation of chelating ability of aqueous extract of Tetracarpidium conophorum (African walnut) in vitro,” International Journal of Applied Research in Natural Products, vol. 3, no. 3, pp. 13–18, 2010.
[4]
V. Cheynier, “Polyphenols in foods are more complex than often thought,” The American journal of clinical nutrition, vol. 81, supplement 1, pp. 223S–229S, 2005.
[5]
M. A. Ayankunbi, O. O. Keshinro, and P. Egele, “Effect of methods of preparation on the nutrient composition of some cassava products—Garri (eba), “Lafun” and “Fufu”,” Food Chemistry, vol. 41, no. 3, pp. 349–354, 1991.
[6]
H. El Gharras, “Polyphenols: food sources, properties and applications—a review,” International Journal of Food Science & Technology, vol. 44, no. 12, pp. 2512–2518, 2009.
[7]
AOAC, Official Method of Analysis, Association of Official Analytical Chemist, Washington, DC, USA, 15th edition, 1990.
[8]
D. A. Pearson, Chemical Analysis of Foods, Churchill Livingstone, Edinburgh, UK, 7th edition, 1976.
[9]
D. Oberlease, “Phytate,” in Toxicants Occurring Naturally in Foods, F. Strong, Ed., pp. 363–371, National Academy of Sciences, Washington, DC, USA, 1973.
[10]
S. A. Odoemelam, “Chemical composition and functional properties of conophor nut (Tetracarpidium conophorum) flour,” International Journal of Food Science and Technology, vol. 38, no. 6, pp. 729–734, 2003.
[11]
I. I. Ijeh, C. E. Ejike, O. M. Nkwonta, and B. C. Njoku, “Effect of traditional processing techniques on the nutritional and phytochemical compositions of African breadfruit (Treculia africana) seeds,” Journal of Applied Science and Environmental Management, vol. 14, no. 4, pp. 169–173, 2010.
[12]
T. F. Akinhanmi, V. N. Atasie, and P. O. Akintokun, “Chemical composition and physicochemical properties of cashew nut (Anacardium occidentale) oil and cashew nut shell liquid,” Journal of Agricultural, Food, and Environmental Sciences, vol. 2, no. 1, pp. 1–10, 2008.
[13]
G. E. De Almeida Costa, K. Da Silva Queiroz-Monici, S. M. P. M. Reis, and A. C. De Oliveira, “Chemical composition, dietary fibre and resistant starch contents of raw and cooked pea, common bean, chickpea and lentil legumes,” Food Chemistry, vol. 94, no. 3, pp. 327–330, 2006.
[14]
C. Nduagu, E. J. Ekefan, and A. O. Nwankiti, “Effect of some crude plant extracts on growth of Colletotrichum capsici (Synd) and Bisby, causal agent of pepper anthracnose,” Journal of Applied Biosciences, vol. 6, no. 2, pp. 184–190, 2008.
[15]
P. Siddhuraju and K. Becker, “Preliminary nutritional evaluation of Mucuna seed meal (Mucuna pruriens var. utilis) in common carp (Cyprinus carpio L.): an assessment by growth performance and feed utilisation,” Aquaculture, vol. 196, no. 1-2, pp. 105–123, 2001.
[16]
K. Vijayakumari, P. Siddhuraju, and K. Janardhanan, “Effect of domestic processing on the levels of certain antinutrients in Prosopis chilensis (Molina) Stunz. seeds,” Food Chemistry, vol. 59, no. 3, pp. 367–371, 1997.
[17]
E. A. Udensi, F. C. Ekwu, and J. N. Isinguzo, “Antinutrient factors of vegetable cowpea (Sesquipedalis) seeds during thermal processing,” Pakistan Journal of Nutrition, vol. 6, no. 2, pp. 194–197, 2007.
[18]
C. C. Ekwe and A. Ihemeje, “Evaluation of physiochemical properties and preservation of African walnut (Tetracarpidium conophorum),” Academic Research International, vol. 4, no. 6, pp. 501–512, 2013.
[19]
G. P. P. Lima, T. D. V. C. Lopes, M. R. M. Rossetto, and F. Vianello, “Nutritional composition, phenolic compounds, nitrate content in eatable vegetables obtained by conventional and certified organic grown culture subject to thermal treatment,” International Journal of Food Science & Technology, vol. 44, no. 6, pp. 1118–1124, 2009.
[20]
M. D. Castillo, J. M. Ames, and M. H. Gordon, “Effect of roasting on the antioxidant activity of coffee brews,” Journal of Agriculture and Food Chemistry, vol. 50, no. 13, pp. 3698–3703, 2002.
