Biodiesel is the mono-alkyl esters of long chain fatty acids derived from renewable lipid feedstock, such as vegetable oils and animal fats, for use in compression ignition (diesel) engines. The conversion of component triglycerides in oils to simple alkyl esters with short chain alcohols like methanol and ethanol amongst others is achieved mainly by transesterification. The transesterification reaction, a reversible process proceeds appreciably by the addition of catalysts, which can be acidic, basic or organic in nature, usually in molar excess of alcohol. The economy of the process depends on the type and quantity of catalyst used among other factors. The catalyst can be homogeneous or heterogeneous depending on whether it is in the same or different phase with the reactants; oils and alcohols. This paper attempts to give an insight into some of the various types of catalysts that have been used to effect the transesterification of vegetable, waste and animal oils in biodiesel production.

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The proximate, functional, antinutrient and antimicrobial properties of avocado pear (Persea americana) seeds were studied using standard methods. The proximate contents (%) of avocado peat seed flour, ASF, in decreasing order were moisture (13.09±0.14) followed by ash (3.82±0.00), fibre (2.87±0.00), protein (2.64±0.01) and fat (0.33±0.00). The energy value, carbohydrate and dry matter content respectively was 334.01±1.05%, 80.12±0.15% and 86.91±0.14% while the water absorption capacity and oil absorption capacity respectively was 2.70±0.00% and 1.80±0.00%. The anti-nutrients (mg/100g) in decreasing order were saponins (8.10±0.01) followed by alkaloids (2.14±0.00), flavonoids (1.81±0.01), tannins (1.14±0.01), cyanogenic glycosides (1.02±0.00) and phenols (0.29±0.01). The avocado pear seed extract (ASE) elicited antibacterial activity (mm) against Proteus mirabilis (23±0.14), Staphylococcus aureus (16±0.04) and Pseudomonas aeruginosa (15±0.11) though lower than the corresponding activity by the standard, Ciprofloxacin. ASE had higher activity (18±0.31mm) against the fungus, Aspergilus niger compared with the standard antifungal, Ketoconazole (8±0.22mm) while it had a comparable activity as the standard against Candida albicans but no activity against Penicillum notatum in contrast to the standard drug (6±0.24mm). Thus, ASF had appreciable nutrient and antinutrient contents with apparently moderate storage value while, out of the tested pathogens, ASE had a broad spectrum antibacterial activity, a selective antifungal activity and an overriding activity against Aspergilus niger. These while highlighting possible diet and drug potentials of ASF and ASE, respectively, provided basis for ethno-medicinal applications of avocado pear seeds, hence warranting further studies.

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Harnessing food wastes utilization in diets and drugs could improve food supply, health and the environment while antinutrients composition in a food provides an idea of the pharmacologic, dietary and toxic potentials of the food. Thus, this study assessed the antinutrient properties of the rind and seed of watermelon (Citrullus lanantus) which are usually discarded as food wastes in Nigeria, using standard protocols. The antinutrients (mg/100 g) in the rind and seed, respectively viz: saponin (3.0±0.03, 2.31±0.01), alkaloid (1.39±0.00, 0.36±1.03), tannins (1.33±0.01, 0.61±0.01), phenol (0.53±0.00, 0.12±0.01) and flavonoid (2.87±0.00, 2.03±0.02) were higher in the rind than in the seed. The content (mg/100 g) in the seed for cyanide (0.79±0.01), phytate (0.63±1.00) and oxalate (0.09±0.00) was higher than that in the rind for cyanide (0.00±0.00), phytate (0.46±0.00) and oxalate (0.08±0.01). The recorded difference in the antinutreints content in the rind and seed samples was not significant (p>0.05), hence negligible. The preponderance of these antinutrients in a comparatively lower amount in the samples suggests that the watermelon rind and seed may offer pharmacologic and dietary benefits at a possibly lower toxic risk. Thus, the study supports the use of watermelon rind and seed as food and/or as drug in ethnomedication. Further studies to harness and enhance the utilization of watermelon rind and seed in diets and drugs are required to reduce their attendant waste burden in the environment.