Effect of humidity on aflatoxin contamination for selected African leafy vegetables.

In this study, the aflatoxin contamination level of selected freshly harvested and dried African leafy vegetables was investigated after inoculation with Aspergillus flavus spores and incubation at 32%, 74%, 84%, and 96% static relative humidity. The study question was whether Aspergillus sp. growth on selected vegetables: Corchorus olitorius, Crotalaria ochroleuca, Vigna unguiculata, Solanum villosum, and Amaranthus blitum can produce aflatoxins. The experiment was replicated thrice and a control sample was included for each replicate. An Agilent 1260 Infinity HPLC system was used for analysis and we quantified the following aflatoxins; B1, B2, G1, and G2 in the selected vegetables. Our results show that aflatoxin B1, G1, and G2 were all present, with the B1 being prevalent. The contamination level increased with relative humidity increase for both freshly harvested and dried vegetables. However, the dried vegetables had a lower contamination level in comparison with freshly harvested. The findings affirm the importance of post-harvest crop preservation to avoid mycotoxin contamination. The vegetables can suffer aflatoxin contamination when exposed to high moisture and ambient temperature and drying is a suitable method of vegetable preservation.

Simulation of transient heat transfer during forced convection cooling of cocoyam (Colocasia Esculenta (L.) Schott) tubers.

In this study, a prediction model based on transient heat transfer was modified and validated using experimental data. The time required to cool tubers from field temperature of 30 ± 2 °C to the target storage temperature of 12 ± 0.2 °C was predicted directly from the model. Moreover, total cooling time ranged from 127.8 - 154.2 min for small tubers and 190.8-262.2 min for large tubers while the field heat removed ranged from 9.61 - 10.17 kJ for small tubers and 24.78-31.90 kJ for large tubers between the extremes of the air velocity. Tuber orientation to airflow neither influenced the heat transfer coefficients and Biot numbers nor the cooling time and amount of field heat removed. The results from this study could be applied in the design and optimisation of forced convection cooling systems to precool tubers immediately after harvest and for extended duration storage.