Effects of dietary α-linolenic acid on the conversion and oxidation of13C-α-linolenic acid

The effects of a diet rich in α-linolenic acid vs. one rich in oleic acid on the oxidation of uniformly labeled¹³C-α-linolenic acid and its conversion into longer-chain polyunsaturates (LCP) were investigatedin vivo in healthy human subjects. Volunteers received a diet rich in oleic acid (n=5) or a diet rich in α-linolenic acid (n=7; 8.3 g/d) for 6 wk before and during the study. After 6 wk, subjects were given 45 mg of¹³C-α-linolenic acid dissolved in olive oil. Blood samples were collected att=0, 5, 11, 24, 96, and 336 h. Breath was sampled and CO₂ production was measured each hour for the first 12 h. The mean (±SEM) maximal absolute amount of¹³C-eicosapentaenoic acid (EPA) in plasma total lipids was 0.04 ±0.01 mg in the α-linolenic acid group, which was significantly lower (P=0.01) than the amount of 0.12±0.03 mg¹³C-EPA in the oleic acid group. Amounts of¹³C-docosapentaenoic acid (DPA) and¹³C-docosahexaenoic acid (DHA) tended to be lower as well. The mean proportion of labeled α-linolenic acid (ALA) recovered as¹³CO₂ in breath after 12 h was 20.4% in the ALA and 15.7% in the oleic acid group, which was not significantly different (P=0.12). The cumulative recovery of¹³C from¹³C-ALA in breath during the first 12 h was negatively correlated with the maximal amounts of plasma¹³C-EPA (r=−0.58,P=0.047) and¹³C-DPA (r=−0.63,P=0.027), but not of¹³C-DHA (r=−0.49,P=0.108). In conclusion, conversion of¹³C-ALA into its LCP may be decreased on diets rich in ALA, while oxidation of¹³C-ALA is negatively correlated with its conversion into LCP. In a few pilot samples, low¹³C enrichments of n−3 LCP were observed in a diet rich in EPA/DHA as compared to oleic acid.     

Fatty acid transport across lipid bilayer planar membranes

The transport of palmitic acid (PA) across planar lipid bilayer membranes was measured using a high specific activity [¹⁴C]palmitate as tracer for PA. An all-glass trans chamber was employed in order to minimize adsorbance of PA onto the surface. Electrically neutral (diphytanoyl phosphatidylcholine) and charged (Azolectin) planar bilayers were maintained at open electric circuit. We found a permeability to PA of (8.8±1.9)×10⁻⁶ cm s⁻¹ (n=15) in neutral and of (10.3±2.2)×10⁻⁶ cm s⁻¹ (n=5) in charged bilayers. These values fall within the order of magnitude of those calculated from desorption constants of PA in different vesicular systems. Differences between data obtained from planar and vesicular systems are discussed in terms of the role of solvent, radius of curvature, and pH changes.     

Incorporation of lipids labeled with various fatty acids into the cytoskeleton of aggregating platelets

Earlier studies showed that during the first 20 to 25 seconds of aggregation induced by thrombin (0.1 U/mL) or adenosine diphosphate (ADP) (2μM) of rabbit or human platelets prelabeled with [³H]palmitic acid, labeled lipid became associated with the cytoskeleton (isolated after lysis with 1% Triton X-100, 5 mM EGTA [ethylene glycol-bis-(β-aminoethyl ether(N,N,N′,N′-tetraacetic acid] in the presence of 0.5 mM leupeptin and 50 mM benzamidine). In comparison with labeled lipid in intact platelets, the labeled lipid that was associated with the cytoskeleton was enriched in phospholipids and ceramide. To determine whether these effects were specific for lipids labeled with palmitic acid, we studied rabbit platelets in which lipids had been labeled by incubation of the platelets with pairs of¹⁴C- or³H-labeled palmitic, stearic, arachidonic, and linoleic acids. Examination of the distribution of label among the lipid classes of intact platelets showed that phospholipids contained most of the label. Under the conditions of limited, thrombin-induced aggregation used, labeled lipids were not lost from the platelets and the distribution of label among the lipid classes was essentially unchanged. There were major differences in the incorporation of labeled lipids into the cytoskeleton. The greatest incorporation (2.1 to 2.8% of the label in the platelets) was observed with palmitic acid-labeled lipids; by direct comparison, only 44% as much of the label of stearic acid-labeled lipids, 21% as much of the label of linoleic acid-labeled lipids, and only 6% as much of the label of arachidonic acid-labeled lipids was incorporated into the cytoskeleton. Thus the pool of phospholipid that is readily labeled with arachidonic acid appears to be selectively excluded from the cytoskeleton. Also noteworthy is the 4- to 5-fold enrichment of the cytoskeleton with labeled ceramide; an average of 16% of the label from stearic acid in the cytoskeleton was in ceramide. We suggest that ceramide and phospholipids that are readily labeled with saturated fatty acids are selectively incorporated into the cytoskeleton during the early stages of aggregation and may be specifically associated with the points of contact between platelets.     

Temperature shifts in regulation of lipids accumulated byLipomyces starkeyi

The effect of temperature on the accumulating triglycerides ofLipomyces starkeyi was studied in 10-L fermentation experiments. The temperature during the growth, lipid accumulation and postaccumulation phases was altered. The cellular lipid content, the glucose conversion efficiency and the specific lipid production rate were highest when the growth phase temperature was 28°C, instead of 16–18°C. The temperature of the accumulation phase had an influence on the lipid quality at the end of the accumulation. Oleic acid content increased from 52 to over 60% when the accumulation phase temperature was decreased from 28 to 15°C and, concomitantly, palmitic acid decreased from 33 to 26%. The degree of fatty acid unsaturation was the highest (0.75 Δmol⁻¹) when the accumulation phase temperature was the lowest (15°C) andvice versa. The temperature shift after the lipid accumulation phase affected neither the composition nor the amount of the accumulated lipids. In conclusion, the temperature profile for the highest lipid yield with the most desired composition should be: (i) a growth phase temperature that gives the maximum growth rate and (ii) an accumulation phase temperature that produces the desired ratio of palmitic to oleic acid.     

Plasma kinetics of a cholesterol-rich emulsion in young, middle-aged, and elderly subjects

Low density lipoprotein (LDL) plasma concentration is increased in the elderly. In this group, the incidence of coronary artery disease (CAD) is greater and LDL remains an important risk factor for CAD development. In this study, the plasma kinetics of a cholesterol-rich emulsion that binds to LDL receptors was studied in 10-subject groups of the elderly (70±4 yr), middle-aged (42±5 yr) and young (23±2 yr). All were normolipidemic, nonobese, nondiabetic subjects who did not have CAD. The emulsion was labeled with ¹⁴C-cholesteryl oleate and injected intravenously into the subjects. Blood samples were drawn at regular intervals over 24 h to determine the plasma decay curve of the emulsion radioactive label and to estimate its plasma fractional clearance rate (FCR, in h⁻¹). FCR of the emulsion label was smaller in elderly compared to young subjects (0.032±0.035 and 0.071±0.049 h⁻¹, respectively; mean±SD, P<0.05). FCR of the middle-aged subjects (0.050±0.071 h⁻¹) was intermediate between the values of the elderly and young subjects, although not statistically different from them. A negative correlation was found between the emulsion FCR and subjects’ age (r=−0.47, P=0.008). We conclude that aging is accompanied by progressively diminished clearance of the emulsion cholesterol esters and, by analogy, of the native LDL.     

Measurement of human chylomicron triglyceride clearance with a labeled commercial lipid emulsion

Human chylomicron triglyceride (TG) kinetics has been difficult to determine directly owing to technical limitations. This report describes a new method for studying chylomicron metabolism. Healthy volunteers (n=10) sipped a drink providing 175 mg fat·kg⁻¹·h⁻¹ for 7.5 h to produce a steady-state chylomicronemia. A commercial 10% intravenous lipid emulsion was labeled with [³H]triolein, purified by high-performance liquid chromatography, and sterilized. A trace amount of labeled emulsion was injected intravenously 30 min before (i.e., in the fasting state) and 5, 6, and 7 h after sipping began (i.e., triplicate determinations in the fed state). Chylomicron half-lives were calculated from the monoexponential decay curves, and apparent distribution volumes were estimated by back-extrapolation to time zero. Plasma and estimated chylomicron TG concentrations increased from 89±13 and 0.8±0.3 to 263±43 and 91±39 mg/dL (mean±SEM), respectively, with feeding. Tracer-determined chylomicron TG half-lives were 5.34±0.58 and 6.51±0.58 min during the fasting and fed states, respectively (P<0.01). The apparent distribution volume during the fasting state was 24% greater than plasma volume (4515±308 vs. 3630±78 mL, P<0.02), consistent with significant margination of lipid emulsion particles to endothelial binding sites. Margination was reduced during the fed state, suggesting that native chylomicrons competed with lipid emulsion particles for endothelial lipoprotein lipase. The results indicate that a radiolabeled commercial lipid emulsion is metabolized in a fashion similar to native chylomicron TG, and thus can be used to study chylomicron TG kinetics.     

Palmitic acid-labeled lipids selectively incorporated into platelet cytoskeleton during aggregation

Previous experiments showed that during the early stages (20–30 seconds) of aggregation induced by adenosine diphosphate (ADP, 2 μM) or thrombin (0.1 U/mL) of rabbit or human platelets prelabeled with [³H]palmitic acid, labeled lipid became associated with the cytoskeleton isolated after lysis with 1% Triton X-100, 5 mM EGTA [ethylene glycol-bis-(β-aminoethyl ether)]-N,N,N',N'-tetra-acetic acid. The association appeared to be related to the number of sites of contact and was independent of the release of granule contents. We have now investigated the nature of the labeled lipids by thin-layer and column chromatography and found differences between the distribution of the label in intact platelets (both stimulated and unstimulated) and the isolated cytoskeletons. In both species and with either ADP or thrombin as aggregating agent, 70–85% of the label in both intact platelets and in the cytoskeletons was in phospholipids. The distribution of label among the phospholipids in the cytoskeletons was similar to that in intact platelets except that the percentage of label in phosphatidylcholine was significantly higher in the cytoskeletons of human platelets than in the intact platelets, and the percentage of label in phosphatidylserine/phosphatidylinositol was significantly lower in the cytoskeletons of rabbit platelets and thrombin-aggregated human platelets than in intact platelets. The cytoskeletons contained a lower percentage of label in triacylglycerol, diacylglycerol, and cholesterol ester than the intact platelets. Contrary to a report in the literature, we found no evidence for the incorporation of diacylglycerol and palmitic acid into the cytoskeleton. Although intact rabbit platelets had more label in ceramide (6.7±2.9%) than intact human platelets (1.5±0.9%), platelets of both species exhibited a three- to four-fold enrichment of labeled ceramide in the cytoskeletons. Thus phospholipids and ceramide that are readily labeled with palmitic acid are selectively incorporated into the cytoskeleton during the initial stages of platelet aggregation.     

Chia seeds as a source of natural lipid antioxidants

Chia (Salvia sp) seeds were investigated as a source of natural lipid antioxidants. Methanolic and aqueous extracts of defatted chia seeds possessed potent antioxidant activity. Analysis of 2 batches of chia-seed oils demonstrated marked difference in the fatty acid composition of the oils. In both batches, the oils had high concentrations of polyunsaturated fatty acids. The major antioxidant activity in the nonhydrolyzed extract was caused by flavonol glycosides, chlorogenic acid (7.1 × 10⁻⁴ mol/kg of seed) and caffeic acid (6.6 × 10⁻³ m/kg). Major antioxidants of the hydrolyzed extracts were flavonol aglycones/kaempferol (1.1 × 10⁻³ m/kg), quercetin (2.0 × 10⁻⁴ m/kg) and myricetin (3.1 × 10⁻³ m/kg); and caffeic acid (1.35 × 10⁻² m/kg). Two methods were used to measure antioxidant activities. Both were based on measuring bleaching ofβ-carotene in the coupled oxidation ofβ-carotene and linoleic acid in the presence of added antioxidants.     

Heated fat-based oil substitutes, oleic and linoleic acid-esterified propoxylated glycerol

Four oils [triolein, trilinolein, oleic acid-esterified propoxylated glycerol (EPG-08 oleate), and linoleic acid-esterified propoxylated glycerol (EPG-08 linoleate)], each without added antioxidants, were heated for 12 h/d at approximately 190°C in a small deep-fat fryer until the polymer concentration exceeded 20%, as determined by high-performance size-exclusion chromatography. Increases in the free fatty acid content, total acid value, food oil sensor value, and p-anisidine value during heating indicated that significant thermal oxidation had occurred in each oil. Capillary supercritical fluid chromatography (SFC) was used to determine the substrate concentration of each oil after each heating interval. The average, apparent first-order reaction rate constant (as determined by SFC) for trilinolein was 0.0348±0.0034 h⁻¹, while the rate for EPG-08 linoleate was 0.0253±0.0032 h⁻¹. The average apparent reaction rate constant for triolein was 0.0256±0.0011 h⁻¹, while the rate for EPG-08 oleate was 0.0252±0.0008 h⁻¹. Triolein contained >20% polymer after 60 h of heating, EPG-08 oleate contained >20% polymer after 36 h of heating, and both trilinolein and EPG-08 linoleate contained >20% polymer after 24 h of heating.     

n-Butane conversion on sulfated zirconia: in situ 13C MAS NMR monitoring of the kinetics of the 13C-label scrambling and isomerization

The kinetics of the conversion of ¹³C-labeled n-butane adsorbed on sulfated zirconia (SZ) were monitored by in situ ¹³C MAS NMR spectroscopy. Rate constants of n- to isobutane isomerization and of the ¹³C-isotope scrambling from the primary to the secondary carbon atoms in n-butane were determined. The monomolecular scrambling of the ¹³C-label in adsorbed n-butane has an activation energy of 17 ± 3 kcal mol^–1 and occurs faster than the bimolecular process of n-butane isomerization which has an activation energy of 15.1 ± 0.2 kcal mol^–1. The transfer of the selective ¹³C-label from the primary to the secondary carbon atom in the adsorbed n-butane seems to consist of two reaction steps: (i) a hydride abstraction by SZ leading to the formation of sec-butyl cations and (ii) a label scrambling in the sec-butyl cations. This two-step process with the formation of sec-butyl cations as intermediate increases the apparent activation energy for the ¹³C-label scrambling, which is almost twice as large compared with the activation energy for carbon scrambling of sec-butyl cations in a superacidic solution.     

Diffusivity of bacteria

The effects of motility and aggregation on the diffusion coefficient for bacteria were studied in an aqueous system. The effects of cell concentrations, capillary tube sizes, and dilution rates on the diffusion coefficient were examined. In general, motile cells can diffuse about 1000 times faster than non-motile cells.Pseudomonas aeruginosa, a motile cell, andKlebsiella pneumoniae, a non-motile cell, were used for this research. Diffusion coefficients were measured by the capillary tube assay developed by Adler [1969]. From this procedure the diffusion coefficient ofPseudomonas aeruginosa was 2.1×10⁻⁵ (standard deviation: 1.0× 10⁻⁵) cm²/s and that ofKlebsiella pneumoniae was 0.9×10⁻⁵ (standard deviation : 0.5 × 10⁻⁵) cm²/s. The diffusion coefficient ofPseudomonas aeruginosa was about 2.3 times higher than that ofKlebsiella pneumoniae. The Stokes-Einstein equation could not be used for estimating the diffusion coefficients forKlebsiella pneumoniae andPseudomonas aeruginosa. The experimental value for the diffusion coefficient ofKlebsiella pneumoniae was about 2000 times higher than that (4.5×10⁻⁹ cm₂/s) obtained from the Stokes-Einstein equation. This discrepancy was due to the aggregation ofKlebsiella pneumoniae.     

Decreased lecithin: Cholesterol acyltransferase activity in the plasma of hypercholesterolemic pigs

Lecithincholesterol acyltransferase (LCAT) activity levels were determined, as function of plasma total cholesterol (TC) in 13 normocholesterolemic (TC<85 mg/dL) and in 28 hypercholesterolemic (TC>98 mg/dL) pigs. The normocholesterolemic group consisted of pigs that carried apo-B allelic genes other thanLpb ⁵ and orLpb ⁸. The hypercholesterolemic group consisted ofLpb ^5/x andLpb ^5/8 heterozygous andLpb ^5/5 homozygous animals. The data reported in this study show that the LCAT activity in the plasma of hypercholesterolemic (HC) pigs (79±43 units) was significantly lower (p<0.0005) compared to the normocholesterolemic controls (175±45 units). Furthermore, LCAT activity was positively correlated with TC in the normocholesterolemic group (r=+0.54; p<0.05), whereas it was negatively correlated with TC in the hypercholesterolemic group (r=−0.73; p<0.001). Additional data obtained from incubation experiments suggest that the lower LCAT activity in hypercholesterolemic pigs may be due, at least in part, to inhibition of LCAT activity by components found in the lipoprotein-deficient fractions of the plasma of hypercholesterolemic pigs.     

Stability of sodium hypochlorite in the presence of aqueous flavoring essence

The stability of NaOCl in the presence of aqueous flavoring essences (lemon, mint, osmanthus flowers, pineapple, and vanilla) at 40±1°C was studied. Data from determination of OCl⁻ showed: (i) The stability of NaOCl solution decreased in the presence of essences in the order: mint> lemon and osmanthus flowers>pineapple>vanilla (P<0.01); (ii) OCl⁻ loss with the addition of lemon after incubation for 15 d was significantly greater in solutions with initial pH of 13.50 compared with those initially at pH 12.50 (P<0.01); and (iii) OCl⁻ loss was not significantly influenced by the difference in initial pH value with or without the addition of other essences.     

Metabolism of long-chain fatty acids,alcohols and alkylglycerols in the fish parasiteParatenuisentis ambiguus (Acanthocephala)

Specific differences between the acyl composition of lipids on the helminthParatenuisentis ambiguus and its host eel, as shown previously, prompted us to study the lipid metabolism in this intestinal fish parasite. Adults and larvae ofP. ambiguus were fed various lipid precursors, e.g., fatty acids, long-chain alcohols and 1-O-alkylglycerols, which may occur as common nutrients of intestinal parasites. Incorporation of [1-¹⁴C]palmitic acid into neutral and polar lipids was found to be similar under aerobic and near-anaerobic conditions. In adult parasites maintained in culture medium supplemented with glucose, [1-¹⁴C]palmitic acid was incorporated mainly into triacylglycerols and phosphatidylcholines, whereas [1-¹⁴C]oleic acid was incorporated preferentially into triacylglycerols. In fasted adults, as well as in larvae, [1-¹⁴C]oleic acid was mainly transferred to phosphatidylcholines. Lipolytic activity was detected in adult parasites that had been incubated with radioactive trioleoylglycerol. [1-¹⁴C]Hexadecan-1-ol was oxidized inP. ambiguus at a high rate to labeled palmitic acid, which was incorporated into various lipid classes ofP. ambiguus. Small but significant proportions of radioactivity from hexadecan-1-ol were incorporated into ether glycerolipids of the parasite. A more direct precursor in ether glycerolipid metabolism, i.e.,rac-1-O-[1′-¹⁴C] hexadecylglycerol, was incorporated into alkyl and 1′-alkenyl moieties of choline and etha-nolamine etherglycerophospholipids ofP. ambiguus in high yield. High proportions of labeled diacylglycerols, triacylglycerols and steryl esters were detected in surface lipids as well as lipid extracts of the culture media after incubation ofP. ambiguus with [1-¹⁴C]palmitic or [1-¹⁴C]oleic acids. The results suggest that palmitic acid and oleic acid are incorporated into neutral and polar lipids ofP. ambiguus maintained in glucose medium quite differently with oleic acid showing a strong preference for triacylglycerols. However, the incorporation of palmitic acid in glucose-fed parasites was similar to that of oleic acid in fasted parasites, as well as in larvae. This may be explained by partial fatty acid depletion in fasted worms and rapid cell division in larvae, respectively.     

Relative contribution of trees and crops to soil carbon content in a parkland system in Burkina Faso using variations in natural 13C abundance

The origin of organic matter was studied in the soils of a parkland of karité (Vitallaria paradoxa C.F. Gaertn) and néré (Parkia biglobosa (Jacq.) Benth.), which is extensively cultivated without the use of fertilisers. In such systems, fertility (physical, chemical and biological) gradients around trees have been attributed by some authors to a priori differences in fertility, allowing for better tree establishment on richer sites. In reverse, other workers believed that these gradients are due to the contribution of trees to the formation of soil organic matter through litter and decay of roots. Measurements of the variations in the ¹³C isotopic composition allowed for a distinction between tree (C₃) derived C and crop and grass (C₄) derived C in the total soil organic C content. The organic carbon contents of the soils were recorded under the two species at two soil depths and at five distances going from tree trunk to the open area and their C isotopic signatures were analysed. The results showed that soil carbon contents under karité (6.43 ± 0.45 g kg⁻¹) and néré (5.65 ± 0.27 g kg⁻¹) were significantly higher (p<0.01) than in the open area (4.09 ± 0.26 g kg⁻¹). The δ¹³C of soil C was significantly higher (p<0.001) in the open area (−17.5 ± 0.3‰) compared with the values obtained on average with depth and distance from tree under karité (−20.2 ± 0.4‰) and néré (−20.1 ± 0.4‰). The C₄-derived soil C was approximately constant, and the differences in total soil C were fully explained by the C₃ (tree) contributions to soil carbon of 4.01 ± 0.71, 3.02 ± 0.53, 1.53 ± 0.10 g kg⁻¹, respectively under karité, néré and in the open area. These results show that trees in parklands have a directly positive contribution to soil carbon content, justifying the need to encourage the maintenance of trees in these systems in semi-arid environments where the carbon content of soil appears to be the first limiting factor for crop growth.     

Sterol ester hydrolase inFusarium oxysporum

Two electrophoretically different forms of sterol ester hydrolase (EC 3.1.1.13) were obtained from the cytoplasmic extract of the mycelia ofFusarium oxysporum. The entities, estimated at 60,000 (I) and 15,000 (II) molecular weights, were obtained in Sephadex G100 column chromatography of the ammonium sulfate precipitate from the cytoplasmic extract. A third form III, 75,000 MW, was obtained from the culture filtrate. The activity of the enzyme was increased by Triton X-100 and was not inhibited byp-chloromercuribenzoate (PCMB), a sulfhydryl reagent. The enzymes I and II were inhibited differentially by NaCl. The optimal activities of forms I, II and III occurred at pH 4.8, pH 8.0 and pH 7.0, respectively. the apparent Km values of 7.7×10⁻⁵, 8.3×10⁻⁵ and 10.5×10⁻⁵, respectively, indicate a similar order of affinity for cholesteryl oleate at pH 7.1. The rate of hydrolysis of cholesteryl esters were in the order: linoleate>oleate>valerate>butyrate > acetate. Cholesteryl benzoate and palmitate were not hydrolyzed. The properties of the microbial enzyme are discussed in relation. Contribution no. 1098.     

Elongation of (n−9) and (n−7)cis-monounsaturated and saturated fatty acids in seeds ofsinapis alba

Lipids in developing seeds ofSinapis alba contain appreciable proportions of (n−7)octadecenoic (vaccenic) acid besides its (n−9) isomer (oleic acid), whereas the constituent very long chain (>C₁₈) monounsaturated fatty acids of these lipids are overwhelmingly composed of the (n−9) isomers. Cotyledons of developingSinapis alba seed use [1-¹⁴C]acetate, [1-¹⁴C]malonate or [1,3-¹⁴C]malonyl-CoA for de novo synthesis of palmitic, stearic and oleic acids and for elongation of preformed oleic, vaccenic and stearic acids to their higher (n−9), (n−7) and saturated homologs, respectively. Moreover, elongation of preformed (n−7)palmitoleic acid to vaccenic acid is observed. Stepwise C₂-additions to preformed oleoyl-CoA by acetyl-CoA or malonyl-CoA yielding (n−9)icosenoyl-CoA, (n−9)docosenoyl-CoA and (n−9)tetracosenoyl-CoA are by far the most predominant reactions catalyzed by the elongase system, which seems to have a preference for oleoyl-CoA over vaccenoyl-CoA as the primer. The pattern of¹⁴C-labeling of the very long chain fatty acids formed from either acetate or malonate shows a close analogy in the mode of elongation of monounsaturated and saturated fatty acids.     

Soil and vegetation carbon pools in a mountainous watershed of Nepal

Assessment of carbon stocks in vegetation and soil is a basic step in evaluating the carbon sequestration potential of an ecosystem. We collected soil (core and composite) samples from 0–10, 10–20, 20–40, and 40–70 cm depths, or down to the bed rock, in the soil profile of four types of forest (managed dense Shorea (DS), degraded forest (DF), pine mixed (PS), and Schima–Castanopsis (SC) forest) and two types of cultivated land (irrigated low land (Khet) and rain-fed upland (Bari)) in the Pokhare Khola watershed of Nepal. In addition to other essential properties, soil bulk density and carbon concentration were assessed. Fine roots were also collected from each sampling site. The biomass of standing trees and shrubs was estimated by using allometric relationships after measuring their diameter and height, while the biomass of grasses was estimated by a direct measurement of grass from a defined area. The carbon stocks in all forest vegetation (trees, shrubs, and ground grass) and in the soil profiles under different land uses were estimated. The vegetation carbon pool was largest in DS forest (219 ± 34 Mg ha⁻¹) and least in SC forest (36 ± 5 Mg ha⁻¹), while its order among forest types was DS > DF > PS > SC. The soil organic carbon (SOC) pool was largest in Bari land (15.7 ± 1.5 kg C m⁻²) and least in PS forest (6.2 ± 0.5 kg C m⁻²) but the overall order among land uses was Bari > DF > Khet > SC > DS > PS. The total SOC stock in the whole watershed was 59 815 Mg, of which 36, 32, and 32% were in the 0–20, 20–40, and >40 cm soil depths, respectively. In the surface layer (0–10 cm), SOC stock was highest in Bari (36%) followed by DS (31%), and least was in PS forest (3%). This distribution pattern can primarily be assigned to SOC concentration and area covered by these land uses.     

Kinetics of geometrical isomerization of unsaturated FA in soybean oil

Laboratory treatment of soybean oil were carried out at the following conditions: atmospheric pressure in the presence of air or nitrogen at different temperatures ranging from 160 to 250°C for 12 to 72 h. These conditions were used to study geometric isomerization of cis,cis-linoleic and cis,cis,cis-linolenic acid in the presence or in the absence of oxidative degradation reactions. Based on these experiments, a model of consecutive, parallel reactions was developed to describe the reaction steps occurring in the soybean oil during heating at constant temperature. For both cis,cis-linoleic and cis,cis,cis-linolenic acid, the reaction of formation isomers followed a first-order reaction, and the rate constant of isomerization varied according to the Arrhenius law. The isomerization rate constant for linoleic acid was 9.57×10⁻³±0.50 h⁻¹ in the presence of oxygen and 7.39×10⁻³±0.39 h⁻¹ in its absence, and the isomerization rate constant for linolenic acid was 1.18×10⁻¹±0.10 h⁻¹ in the presence of oxygen and 0.87×10⁻¹±0.07 h⁻¹ in its absence (all obtained at 250°C).