Good-quality oils

The volatile fraction of good quality oils is mainly formed by compounds produced enzymatically from polyunsaturated fatty acids through the lipoxygenase (LOX) pathway. Aldehydes (C6), alcohols (C6) and their corresponding esters are the most abundant products (Figure 2.7). 

Buffalo gourd (Cucurbita foetidissima). The buffalo gourd is a vine-Uke plant that grows in semiarid regions of the United States, Mexico, Lebanon, and India. The seed contains good quality oil (32-39%) and protein. The oil is very variable in fatty acid composition, thus lending itself to seed breeding. A typical sample contains 16 0 (9%), 18 0 (2%), 18 1 (25%), and 18 2 (62%) (88). 

In a more recent 30-month outdoor exposure study involving nine sites in the St. Louis, Missouri, area, the performance of good-quality oil- and latex-based house paints on stainless steel were evaluated by weight-loss measurements (1 ). The paints did not contain CaCO extender pigments. Spencer and Haynie reported no... 

This process eliminates the use of water washing and produces good quality oil. The key is to have high quality crude oil with low phospholipids. Otherwise the cost of hydrated silica can be prohibitive. 

Pressure systems yield good quality oil when the fruits themselves are in good condition and the filtering diaphragms are properly cleaned. Otherwise, oils are produced with a high level of undesirable components, such as n-octane, 2-methyl-propanol, 3-methylbutanol and acetic acid. 

The tocopherol content is highly variable. Concentrations may range from 5-300 mg/kg. Usual values for good quality oils lie between 100 and 300 mg/kg. Recent studies for the determination of tocopherols gave values ranging from 98-370 mg/kg in Greek oils (Psomiadou etal. 2000) and 36-314 mg/kg in Italian oils (Lo Curto et al. 2001). 

The para-anisidine value (PAV) is defined as 100 times the absorbance of a solution resulting from the reaction of 1 g of fat or oil in 100 mL of a mixture of solvent and p-anisidine, measured at 350 nm in a 10 mm cell. A drawback of the method is that nonvolatile aldehydes also, for example 2,5 oxo-glycerides, can contribute to the absorption. As a rule of thumb, it can be said that good quality oil should have a PAV of less than 10. A good correlation between the p-anisidine value of salad oils and their organoleptic scores has been rqxtrted in the literature. ... 

Oil is extracted either by pressing or increasingly by solvent extraction. The crude oil has a strong characteristic flavour and odour and has a dark reddish brown colour. The free fatty acid content of the oil depends on the conditions of harvesting and moisture content of the seed good-quality oil has free fatty acid of 0.5-1%. Normally it is increasingly difficult to bleach the oil satisfactorily as the free fatty add of the crude oil increases. However, there is no direct relation between the quality of the crude oil and the stability and flavour of the fully refined oil. 

Crude soybean oil can be obtained from the bean by pressing but more normally by hexane extraction. Good-quality oil is light amber in colour with a free fatty acid content of 0.5%. Oil from damaged beans is darker, higher in free fatty acids and modified lipids and is more difficult to bleach. The residual meal is a major source of animal feed. 

The preparation of oil-bearing raw materials prior to extraction is in all cases firstly concerned with the separation of extraneous matter and secondly with transforming the raw material into a state which will give a high yield of good-quality oil and meal. 

In one method, hot water and a chemical are circulated through the tank. On top of the water, a hydroearbon such as diesel is added. The density difference between warm water and the hydrocarbons in the sludge causes the sludge to rise, allowing the chemical to strip out water and solids. The method recovers good-quality oil, which can be processed in the refinery, and leaves behinds a relatively clean layer of solids on the tank bottom. 

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