Fatty acid esters, high in linoleic acid, were prepared and stored for long-term engine tests. Storage tests with these esters were undertaken to obtain more information on optimal storage requirements and general stabi1ity characteristics.Samples were kept at three temperature levels (20 C, 30 C and fluctuating around SO C) for a 90-day period and were removed at regular intervals for chemical and physical analysis. The influence of air, temperature, light, TBHQ and contact with mild steel was evaluated by comparing the free fatty acid, peroxide, anisidine, ultraviolet absorption, viscosity and induction periods. A statistical model was used to evaluate the data and to reduce the large number of data points to comparable curves.Storage of esters in contact with air, especially at a temperature above 30 C, resulted in significant increases in peroxide, ultraviolet absorption, free fatty acid, viscosity and anisidine values. Exclusion of air retarded oxidation at all temperature levels.A direct relationship between viscosity increases and oxidation parameters was evident. Exposure to light caused a small increase in the oxidation parameters of esters stored at the highest temperature level. Addition of TBHQ prevented oxidation of samples stored under moderate conditions. Under unfavorable storage conditions the anti-oxidant was no longer effective. Mild steel had very little effect on the oxidation parameters. Only the anisidine values of samples stored at the highest temperature level were slightly increased. Methyl esters performed slightly better than ethyl esters during the storage test.The following practical guidelines for storage of fatty acid ester fuels are: (i) airtight containers should be used; (ii) the storage temperature should be <30 C; (iii) mild steel (rust free) containers may be used, and (iv) TBHQ has a beneficial effect on oxidation stability.
BACKGROUND: Oil yield from avocado fruit may be influenced by fruit pre-treatment and extraction method. Unripe and ripe avocado fruit pieces were deep-frozen at −20• C and either freeze-dried or oven-dried (80 • C). Oil yield from these samples was determined after extraction with hexane and supercritical carbon dioxide (SC-CO 2 ). The fruit samples were examined using scanning electron microscopy before and after oil extraction.
New legislation introduced in South Africa for the quality of used frying oils has resulted in the need to identify quicker, more suitable methods that correlate well with results from two official methods, namely, total polymerized glycerides and total polar components. Oil and product samples were taken at regular intervals during a commercial frying process in palm olein. Oil samples were analyzed for a number of different quality parameters viz. tocopherol content, dielectric constant, total polymerized glycerides, total polar components, tertiary butylhydroquinone (TBHQ) content, anisidine value, Rancimat induction period, and free fatty acid content, and the results statistically compared to results from official methods. Oil was expressed from product stored under accelerated conditions and analyzed for the same quality parameters. Fried product was also subjected to sensory evaluation to measure the degree of oil deterioration and sensory preference. The frying trial was successfully executed with refined, bleached, and deodorized palm olein and the frying oil used to a free fatty acid (FFA) content of 0.41%. Oil and product sampling were done at different FFA value levels. Frying oil quality was verified at the onset of the trial and at regular intervals. The frying oil total polar component value increased to approximately half of the limit set by the official regulation. This point was reached mainly due to the high starting value of the fresh oil. Frying oil total polymerized glycerides increased from below 1% to 2.1%. This increase is negligible when compared to the general trend for polyunsaturated oils. The alternative laboratory methods used for predicting oil quality can be rated as follows: total tocopherol content > dielectric constant > FFA > TBHQ content > anisidine value > Rancimat induction period. The first three methods correlated well with total polar component levels and it is recommended that the dielectric constant and FFA measurements be applied for monitoring oil condition during frying. It is possible that viscosity changes could be used for the monitoring of polyunsaturated frying oils. Evaluation of oil extracted from product revealed a negligible effect of non-oil components on oil quality parameters. The same was observed when product was stored at -10°C and at 37°C.Paper no. J8849 for JAOCS 76, 731-738 (June 1999).Palm olein is preferred for industrial deep frying of snack products in South Africa either in pure form or combined with other oils. Although several locally produced oils are available, at competitive prices, the main deciding factor in selecting frying oil is based on the shelf life requirements of the fried products. Another deciding factor is the recent introduction of regulations for controlling the quality of used frying oil in South Africa (1). The Department of Health selected two oil quality evaluation parameters, total polymerized glycerides (2) and total polar component contents (3). The two official methods proved to be adequate for regulatory purposes b...
Six quality indices, namely free fatty acids (FFA), peroxide value (PV), anisidine value (AV), oxidative stability index (OSI), total tocopherols and headspace volatiles (hexanal, t-2-hexenal and t,t-2,4-decadienal), were evaluated in a long-term storage trial of 52 weeks at 50 • C of palm-olein, a monounsaturated oil. Three concentrations of copper (0.035, 0.17 and 0.69 mg kg −1 ) were added. FFA values for all the sample treatments increased slightly over the storage period but remained within acceptable limits. PV of the copper-containing samples declined initially and then remained stable up to week 40, after which it increased slightly for the 0.035 and 0.17 mg kg −1 samples. However, PV of the control (no added copper) increased steadily to above the acceptable limit. AV of the copper-containing samples increased much more than that of the control. OSI and total tocopherol values of the coppercontaining samples were markedly lower than those of the control. t-2-Hexenal did not increase during the storage period, whereas hexanal increased in the copper-containing samples but at a slower rate than in the control. Conversely, the copper-containing samples had high levels of t,t-2,4-decadienal but the control had none. AV, OSI and total tocopherols are the most valuable quality indices for assessing monounsaturated oil quality, whereas FFA, PV and headspace volatiles can be misleading.
This article seeks to explain some of the outlines of the legal philosophy of L. J. du Plessis, without pretending that a meticulously coherent system of thought can be deduced from his deverse legal writings. Much rather the claim is made that his endeavours display a marked “environmental involvement", hence placing his contribution in the framework of Even though Du Plessis relies heavily on the Dooyeweerdian Philosophy o f the Comonomic Idea, he also shows himself to be a profoundly original thinker at the same time. The spearhead of this originality manifests itself in the way in which het intergrates a socto-eschatological view o f reality in his legal thought, to an extent unsurpassed by his like-minded contemporaries. The first part of the this article introduces Du Plessis as a jurist displaying a marked environmental sensitivity. It also attempts to contextualixe bis contributionin the field o f legal theory. The second part deals with the foundationallines i along which his legal thought had developed as well as the distinctivecharacteristics o f his contribution.
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