Physicochemical and Biochemical Characterization, Total Phenolic and Energy Value from Bulbs of Different Onion (<i>Allium cepa</i> L.) Varieties in Senegal

Abstract

The purpose of this study is to investigate the physicochemical properties of some local varieties of onion ( Allium cepa L.) and compare them with an imported variety, all collected in May 2021. Proteins, reducing sugars, lipids, a nd polyphenol content were estimated according to the AFN OR standardized methods. The determination of calcium, magnesium, iron, sodium, potassium and phosphorus was performed by atomic absorption spectrophotometer coupled with a CCD detector. The results highlighted an average acidity of 0.377% ± 0.002% lower than the value of the imported variety which is 0.520 % ± 0.001%. Local varieties have a pH ranging from 6.35 ± 0.003 to 6.42 ± 0.004, while the variety has a pH of 6.36 ± 0.003. The ash and dry matter contents vary respectively from 4.788 % ± 0.004 % to 8.253% ± 0.003% and 7.945 % ± 0.021 % to 11.945 % ± 0.007% for the local varieties. Moreover, the imp orted one has ash and dry matter contents of 5.175 % ± 0.007% an d 10.035 % ± 0.021% respectively. The results show that the protein, reducing sugar and lipid contents in the local onion varieties vary respectively from 2.815 ± 0.000 to 15.634 ± 0.001 g · 100 g -1 ; 4.691 ± 0.001 to 12.596 ± 0.002 g · 100 g -1 and 0.006 ± 0.001 to 0.050 ± 0.057 g · 100 g -1 . Furthermore, the imported variety has a protein, reducing sugar and lipid content of 5.649 ± 0.002; 8.565 ± 0.002 g · 100 g -1 and 0.011 ± 0.010 g · 100 g -1 respectively. The maximum levels of total polyphenols are obtained in the imported variety, Bellani and Gandiol, respectively 9.973 ± 0.001, 4.535 ± 0.002, and 3.425 ± 0.006 mg EAG/g of dry matter. The local varieties have a significant calorific intake of between 35.451 ± 0.001 and 112.980 ± 0.003 kcal · 100 g -1 compared to the imported one with an energy value of 56.953 ± 0.001 kcal · 100 g -1 of dry matter. The bulbs of different onion varieties studied have a fairly high content of mineral elements. The potassium content of local varieties is between 502.16 ± 0.06 mg · 100 g -1 and 582.77 ± 0.04 mg · 100 g -1 while the imported variety has a content of 536.62 ± 1.30 mg · 100 g -1 . They note that the local varieties have a better calcium content (249.75 ± 0.07 to 434.20 ± 0.57 mg · 100 g -1 ) and magnesium (142.15 ± 0.07 to 162.60 ± 0.42 mg · 100 g -1 ) than the imported variety (229.58 ± 0.04 mg · 100 g -1 ) except for the varieties White Grano (228.29 ± 0.01 mg · 100 g -1 ) and Rouge Amposta (117.00 ± 0.42 mg · 100 g -1 ) respectively. These results reveal that Gandiol, Dayo and Orient F1 are nutritionally found better due to their higher antioxidant property, proteins, carbohydrates, and reducing sugar and should be included in diets to supplement our daily allowance needed by the body.