In a major pathway of the autoxidation of methyl linolenate, peroxyl radicals of the internal hydroperoxides undergo rapid 1,3-tyclisation to form hydroperoxyepidioxides. Because linolenate hydroperoxides are relatively unstable, free radical antioxidants are much less effective in linolenate oils than in linoleate oils. Tocopherols and carotenoids effectively inhibit photosensitised oxidation of vegetable oils. Direct gas chromatographic analyses of malonaldehyde do not correlate with the TBA test. Model fluorescence studies indicate that malonaldehyde may not be so important in crosslinking with DNA. In contrast to oxidised methyl linoleate, oxidised trilinolenin does not form dimers. Although trilinolein oxidises with no preference between the 1(3)-and 2-triglyceride positions, the n-3 double bond of trilinolenin oxidises more in the 1(3)- than in the 2-position. Synthetic triglycerides oxidise in the following decreasing relative rates: LnLnL, LnLLn, LLnL, LLLn (Ln = linolenic and L = linoleic). To estimate the flavour impact of volatile oxidation products their relative threshold values must be considered together with their relative concentration in a given fat.

Review. Recent advances in lipid oxidation

Problem statement: Jatropha curcas is a wonder plant with a variety of applications and enormous economic potentials. Oil from the seeds can be used as alternative fuel and for making biodiesel which aims to overcome energy crisis problems. In this study, extraction of Jatropha oil from seeds was optimized using organic solvent based on the amount of the extracted oil. The kinetics of extraction was also investigated and its parameters were determined based on a second order model. Approach: The effects of five operating parameters on the oil extraction namely type of solvents, temperature, solvent to solid ratio, processing time and particle size of the meal were investigated to optimize the processing conditions for achieving maximum oil yield. The kinetics of extraction was assumed based on a second order mechanism. The initial extraction rate, the saturated extraction capacity, the rate constant of extraction and the activation energy were calculated using the model. Results: The optimum conditions were found at 8 h reaction time, temperature of around 68°C, coarse particle size (0.5-0.75 mm), solvent to solid ratio of 6:1 and hexane as solvent. The activation energy was found to be 8021.9 J moL−1. Conclusion: Hexane was found to be the best solvent for the process as compared to petroleum ether, the kinetics of extraction conforms well to the second order model and the extraction of Jatropha seeds was an endothermic process.

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Extraction of Oil from Jatropha Seeds-Optimization and Kinetics

To understand the reasons for differences in oxidative stability among edible oils, the temperature dependence was investigated for the development of volatile lipid oxidation products in fish oils and in vegetable oils. A rapid headspace capillary gas chromatographic method was developed to determine volatile oxidation products of omega-6 (n-6) polyunsaturated fats (pentane and hexanal) and omega-3 (n-3) polyunsaturated fats (propanal) at different decomposition temperatures. Headspace gas chromatographic analyses of partially oxidized menhaden, bonita and sardine oils could be performed at 40°C, whereas soybean, canola, safflower, high-oleic sunflower and high-oleic safflower oils required temperatures greater than 100°C. Volatile formation by thermal decomposition of oxidized oils had lower apparent activation energies in fish oils than in vegetable oils, and significantly higher apparent activation energies in high-oleic oils than in polyunsaturated oils. The activation energy data on headspace volatiles provided another dimension toward a better understanding of the thermal stability of flavor precursors in unsaturated fish and vegetable oils.

Formation of headspace volatiles by thermal decomposition of oxidized fish oilsvs. oxidized vegetable oils

The oxidative stability of soybean oil triacylglycerols was studied with respect to composition and structure. Crude soybean oils of various fatty acid and triacylglycerol composition, hexane-extracted from ground beans, were chromatographed to remove non-triacylglycerol components. Purified triacylglycerols were oxidized at 60°C, in air, in the dark. The oxidative stability or resistance of the substrate to reaction with oxygen was measured by determination of peroxide value and headspace analysis of volatiles of the oxidized triacylglycerols (at less than 1% oxidation). The correlation coefficients (r) for rates of peroxide formation (r=0.85) and total headspace volatiles (r=0.87) were related positively to oxidizability. Rate of peroxide formation showed a positive correlation with average number of double bonds (r=0.81), linoleic acid (r=0.63), linolenic acid (r=0.85). Rate of peroxide formation also showed a positive correlation with linoleic acid (r=0.72) at the 2-position of the glycerol moiety. A negative correlation was observed between rate of peroxide formation and oleic acid (r=−0.82). Resistance of soybean triacylglycerols to reaction with oxygen was decreased by linolenic (r=0.87) and increased by oleic acid (r=−0.76)-containing triacylglycerols. Volatile formation was increased by increased concentration of linolenic acid at exterior glycerol carbons 1,3 and by linoleic acid at the interior carbon 2. Headspace analysis of voltiles and high-performance liquid chromatography of hydroperoxides indicated that as oxidation proceeded there was a slight decrease in the linolenic acid-derived hydroperoxides and an increase in the linoleic acid-derived hydroperoxides. The oxidative stability of soybean oil triacylclycerols with respect to composition and structure is of interest to the development of soybean varieties with oils of improved odor and flavor stability.

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Effect of triacylglycerol composition and structures on oxidative stability of oils from selected soybean germplasm.

To understand the present widespread interest in protease inhibitors (PI), one must look back to the vast amount of research that has been conducted for over 50 years. Intensive investigations, like wave motions on the water, followed a highly cyclical pathway depending upon the interest and support for research in various disciplines. Nutritionists were concerned with the potential adverse effects of the inhibitors of trypsin and chymotrypsin in the intestinal tract of man and animals (Liener and Kakade, 1980; Liener, 1981; Rackis and Gumbmann, 1981); biochemists recognized that the peculiar properties of PI’s may yield fundamental information concerning protein-protein interactions especially the mechanism of proteolytic hydrolysis (Richardson, 1981; Ryan, 1979); medical scientists envisioned an important role for PI’s in the treatment of various metabolic disorders (Katunuma et al., 1983; Vogel et al., 1968; Weyer, 1968), and biologists foresaw an important physiological role of PI’s to regulate plant growth, protein synthesis and resistance to microbial and insect pests (Richardson, 1977, 1981; Ryan, 1973, 1979).

Protease inhibitors in plant foods: content and inactivation.

A new method of total oil analysis is proposed in which the solvent was equilibrated with dissolved oil inside and outside of soybean particles rather than exhaustively removing all oil. By filtering, evaporating, weighing and multiplying by a factor (based on total miscella volume/sample volume) a satisfactory analysis could be done. Particle size was found to have a profound effect on amounts of oil in soybeans extracted by a conventional procedure. Sieving ground, dehulled soybeans into three particle sizes gave 15.3, 21.9 and 24.8% oil for >40 mesh, 40–100 mesh and <100 mesh, respectively, and 23.1% oil for the unsieved sample. Evidence is presented to support the idea that the amount of oil found in the smallest particle size was the true oil content of the soybeans analyzed. Using the equilibrium method to analyze the <100 mesh particles led to a rapid and economical analysis procedure. A comparison of the equilibrium and exhaustive extraction methods showed the exhaustive extraction gave a consistently larger oil content but less than 1% larger. The difference could be attributed to phospholipid.

Analysis of total oil in soybeans: a new equilibrium extraction method and the effect of particle size.

Soybean oil extraction techniques were studied in which solvent was recirculated or pumped once through a suspension of soybean tissue. Both refractive index and ultraviolet absorbance were used to monitor the extraction continuously. Slices of soybean tissue showed rapid extraction from damaged tissue, followed by slow extraction from intact tissue. When soybean flakes were extracted, a continuously decreasing rate was noted. When solvent was forced through flakes, extraction was more rapid than when solvent was allowed to diffuse in and out of flakes. Reextraction of partially defatted flakes showed that the last soybean oil to be extracted was not inherently resistant to extraction. The adsorption of soybean oil to defatted flakes may account for slow removal of small quantities of oil at the end of the extraction.

Analysis of the oil extraction process in soybeans: a new continuous procedure.

Heated soy flours have been analyzed by the pH stat successfully for tryptic proteolysis and for residual trypsin inhibitor in previous studies Unheated soy flours give a sudden release of hydrogen ion followed by a constantly decreasing proteolysis rate and consequently are difficult to analyze We have found that by adjusting the pH of the trypsin preparation to 9 (the pH of the analysis) the pH stat method measured proteolysis and trypsin inhibitor in unheated soy flours The unheated soy protein was hydrolyzed at 40% of the rate of heated soy protein and contained 68 mg/g of Kunitz trypsin inhibitor equivalents

Kurt L. Wiese

Papers

Analysis of total oil in soybeans: a new equilibrium extraction method and the effect of particle size.

Analysis of the oil extraction process in soybeans: a new continuous procedure.

Use of the pH Stat to Evaluate Trypsin Inhibitor and Tryptic Proteolysis of Soy Flours