This study aimed to determine the total antioxidant capacity of the essential oil (EO) of leaves of Bidens pilosa (Linn. Var. Radita) used as protectant of stored grains in Northern Cameroon. EO was characterized by GC‐FID, antioxidant activity (AA) was determined by combining: evaluation of radical‐scavenging activity, reducing power (RP) and co‐oxidation of β‐carotene methods. Tests were carried out on crude and stored EO kept for two weeks at 31.48 ± 2.88°C and 58.56 ± 6.78% relative humidity. These conditions are the same as those of grain storage. GC analyses enabled the identification of 27 compounds, representing around 97.57% of the total oil contents. The major constituents of the EO were α‐pinene (14.7%), ε‐caryophyllene (13.5), and β‐ocimene (12.8%). The AA of the crude and stored EO are proportional to the concentrations and time of exposition. Exposed at the day light, this EO inhibit 77.4–18.69% for the DPPH system, 59.55–19.14% for RP method and 91.88–21.8% for β‐carotene‐linoleate model system, respectively, from crude and 15 days storage EO at 20 mg L−1. For the EC50 values, β‐carotene method is excellent and in the decreasing order of DPPH method, PR with 2.52 mg L−1, 2.77 mg L−1 and 4.13 mg L−1, respectively, for the crude oil. The ET50 were 1.59 days for the RP method and 2.88 days DPPH system and β‐carotene‐linoleate model system at 20 mg L−1. These results showed that the EO of B. pilosa leaves exhibits AA that might be an added value for this EO preventing stored products from pest attacks.

The effect of solar and electric drying on physicochemical composition of onion (Allium cepa L) has been studied to reduce the post-harvest losses of onion bulbs. The physicochemical and biochemical composition of three varieties of onion (White of galmi, Violet of galmi and Goudami) were also investigated using the Fourier transform infrared (FT-IR) spectroscopy (4000-400 cm-1) and scanning electron microscopy (SEM). Protein, sugar, lipid, moisture, ash, vitamin C, and color parameters were assayed on fresh and dried onion powders. The results showed that water was the main constituent of the fresh onion bulbs (87%). They were also rich in available sugars ranging from 19 g to 59 g/100 g and proteins 4 g to 11 g/100 g of dry matter (DM). Moreover, Ca, K, P, and Mg were found to be the major minerals of the onion powders. In general, the drying process influenced significantly (P<0.05) all the parameters, especially vitamin C that decreased considerably during the process with 90.55%, 78.71% and 72.50% for White of galmi, Goudami and Violet of galmi respectively. The FT-IR spectra showed major peaks were at the wavelength of 1024 cm-1. This could be due to vibrational frequency of ACH2OH groups of carbohydrates for the three studied varieties and for the two types of drying. Finally, a nonsignificant correlation was observed between drying methods and varieties of onion powders.

This study was carried out to evaluate the overall antioxidant capacity of the essential oils of the leaves of Clausena anisata (Rutaceae) and Plectranthus glandulosus (Labiateae), commonly used in the traditional method of grain storage in the northern part of Cameroon. Towards this objective, the co-oxidation of βcarotene as well as the reducing power, the radical scavenging capacity and the conjugated dienes profile of the essential oils during storage for a period of 10 days at 28 ± 2.2 °C and 65±5.7% RH were determined. The least concentration necessary to prevent 50% oxidation (EC 50 ) of β-carotene was found to be 6.53 mg/l, 5.84 mg/l and 524 µg/l respectively for C. anisata, P. glandulosus and butylated hydroxytoluene (BHT) which was the control. On the other hand, the reducing power of the different oils in a decreasing order was found to be P. glandulosus (EC 50 =2.41) > C. anisata (EC 50 =1.77 mg/l) while the EC 50 of Scavenging abilities were 2.66 and 3.02 mg/l for C. anisata and P. glandulosus respectively. Based on the conjugated dienes profile, the essential oils showed higher antioxidant activity compared to Butylated hydroxytoluene (BHT) activity. The effective time (ET 50 ) of the formulation ranging from 300 to 1000 ppm varied from 2 to 8 days for C. anisata and from 3 to 11 days for P. glandulosus. For the control (BHT), the effect varied from 5 to 15 days at an exposition temperature of 50 °C.

No abstract

Maize occupies an important place in the resolution of food insecurity problems in the sub-Saharan region of Africa. However due to poor post-harvest technologies, more than 35% of annual crop yield is often lost during storage as a consequence of insect attack. While chemical pesticides constitute an efficient tool for reducing these losses, current excessive usage runs the risk of modifying the quality and safety of foods produced from these grains. The use of essential oils of plant origin for grain storage has been advocated as a non invasive method with limited or no effect on the quality and safety of the grains or their products. This study was carried out as an evidence of bioactivity of two essential oils of Clausena anisata (Willd.) Hook and Plectranthus glandulosus Hook F. against adults of Tribolium castaneum Herbst and Sitophilus zeamais Motschulsky, which are two important stored product insect pests in Northern Cameroon. Because of the low persistence of the insecticidal activities of these plants, their essential oils to achieve a complete protection of the stored products must be applied at frequent delays. The present investigation focuses on the occurrence of residues of these oils on treated maize grain and flour. The doses of crude essential oils used to treat adults of S. zeamais and T. castaneum in a contact and inhalation process were their LD 99 s. After the evaluation of their insecticidal activity the persistence of each essential oil was observed every 2 days till 14 days. After the disappearance of their insecticidal activities, essential oil was re-extracted and their residual compounds were identified from treated grain and flour. The major compounds of C. anisata are, estragole, α-humulene, germacrene D and (E)-nerolidol. In P. glandulosus they are: fenchone, α-terpinolene and piperitenone oxide. After 14 days, only 64.24% of compounds of C. anisata were recovered on treated flour and 55.16% on grains. Concerning P. glandulosus, 48.94% was recovered on grains and 61.23% on flour.