Percentage Of Free Fatty Acids Research Articles

Determination of the Acid Value of Instant Noodles: Interlaboratory Study

An interlaboratory study was performed to evaluate the method for determining the acid value of instant noodles, based on the Japanese Agricultural Standard (JAS), with extraction of lipid using petroleum ether at a volume of 100 mL to the test portion of 25 g. Thirteen laboratories participated and analyzed 5 test samples as blind duplicates. Statistical treatment revealed that the repeatability (RSDr) of acid value was <6.5%, and the reproducibility (RSDR) of acid value was <9.6%. The HorRat values (RSDR/predicted RSDR) were 1.2-1.8, where the RSDR and the predicted RSDR were obtained in terms of free fatty acids in the noodles per unit weight, using the equation [acid value = percent free fatty acids (as oleic) x 1.99] and the extracted lipid contents. This method was shown to have acceptable precision by the present study.

Correlations between human skin bacteria and skin lipids.

Correlation matrices were constructed for various human skin variables (propionibacteria, micrococcaceae, sebum excretion rate, percentage of free fatty acids and free fatty acid production rate). Two independent populations were studied (n = 87 and n = 103), and a subpopulation (n = 30) was investigated on three occasions at intervals of I month. In this way consistently high correlations could be differentiated from 'fortuitous' correlations. Propionibacteria versus micrococcaceae showed the highest correlation coefficient and propionibacteria versus percentage free fatty acids was also highly correlated. A scatter diagram indicated a relationship between the lower threshold of microbial density and sebum excretion rate. An explanation based on relative duct and gland size is presented.

Chemical analysis and preliminary toxicological evaluation of Garcinia mangostana seeds and seed oil

The chemical analysis and preliminary toxicological evaluation of Garcinia mangostana seeds and seed oil have been investigated in order to determine the possibility of using them for human and/or animal consumption. Proximate analysis showed that the seeds had high amount of carbohydrate and were rich in oil (21.68 ± 6.18%) but have a low protein content. The physical properties of the oil extracts showed the state to be liquid at room temperature (25 ± 1 °C) and the colour of the oil golden-orange. The specific gravity of the oil was 0.98 ± 0.01. Among the chemical properties of the oil extracts, acid value, saponification number, iodine value, percent free fatty acid and peroxide value compared well with those of conventional edible oils. The seed flour was found to be a good source of minerals. It contained considerable amounts of potassium (7071 mg/kg), magnesium (865 mg/kg) and calcium (454 mg/kg). Fatty acid composition of the seed oil indicated that the oil contained one essential fatty acids small proportions: linoleic acid (1.30%). The most prevalent fatty acids were palmitic acid (49.5%) and oleic acid (34.0%). Weanling albino rats appeared to suffer no toxicological effects when fed with G. mangostana seed oil in their diet for 8 weeks. Weekly monitoring of the rats showed good physical appearance and steady weight increase. Histological examination of sections of the heart, liver, kidney, spleen and lung revealed that the kidney of some of the rats had some degrees of pathology which included diffuse glomerular and tubular degeneration. No lesion was found in the heart and liver of the rats. The seed oil could be useful as an edible oil and for industrial applications.

Isolation and Characterization of Neutral Lipids of Desilked Eri Silkworm Pupae Grown on Castor and Tapioca Leaves

The neutral lipid of desilked eri silkworm pupae (Samia cynthia ricini) grown on two different host plants, castor (Ricinus communis Linn.) and tapioca (Manihot utilizsima Phol.) leaves, was extracted with hexane. The oil content in pupae was estimated to be in the range of 18-20% (dry basis). The pupal oil was found to be enriched with alpha-linolenic acid (ALA) with palmitic acid as the second major fatty acid. The level of ALA in the oil of silkworm pupae was found to be significantly higher (P < 0.001) when grown on tapioca (58.3%) as compared to those grown on castor (42.9%). Other chemical parameters such as percent free fatty acid, peroxide value, phosphorus content, percent unsaponifiable matter, and composition of sterols were also determined in both of the oils and compared. Reversed-phase high-performance liquid chromatography analysis of triacylglycerol molecular species showed that the pupal oil is rich in molecular species with equivalent carbon numbers (ECN) C36, C40, C42, C44, and C48. There was a significantly higher level (P < 0.001) of trilinolenin (C36) in the oil of tapioca-based silkworm as compared to castor-based silkworm pupae. Regiospecific analysis of the oil showed a higher level of ALA at the sn-2 position of silkworm pupae grown on tapioca (60.2%) as compared to those grown on castor (47.3%) oil. Thus, the presence of a large amount of ALA and their predominance at the sn-2 position make the eri pupal oil highly nutritious, provided that the oxidative stability is ensured.

Palmitate oxidation during rest, exercise, and post‐exercise recovery

We sought to explore the effects of exercise duration and intensity on post-exercise lipid oxidation and used 13C-bicarbonate and -palmitate to determine the percentage of plasma free fatty acid (FFA) disposal that is oxidized (%Rdox) following exercise. Ten men received a continuous infusion of [1-13C]palmitate under 3 different conditions: (1) before, during and 3 hr after 90 min of exercise at 45% VO2peak (Mod), (2) before, during and 3 hr after 60 min of exercise at 65% VO2peak (Hard), and (3) during a time-matched resting control trial (Con) with breath samples collected for determination of 13CO2 excretion rates. Diet was controlled and exercise trials were isoenergetic. Trials were repeated with a primed continuous infusion of [13C]bicarbonate to derive correction factors for 13CO2 retention (k). Throughout Con, k was stable and averaged 0.83. During exercise, average k was 0.93 in Mod and 0.94 in Hard. After exercise, k returned rapidly to Con values in Mod but was less than Con at 30 and 60 min following Hard exercise (0.74 and 0.72, respectively, P < 0.05). FFA %Rdox increased over the 6 hr period in Con from 9 +/− 0.4% to 31 +− 1% (P < 0.05). During exercise, FFA %Rdox was greater in Hard than Mod with both elevated above Con (84 +− 2% and 109 +− 3% in Mod and Hard, respectively, P < 0.05). After exercise, %Rdox remained elevated above Con (P < 0.05) for 60 min in Hard and 30 min in Mod, but both subsequently returned to Con values. We conclude that FFA %Rdox is increased following prolonged exercise, reflecting a change in the relative partitioning of FFA between storage and oxidation. Supported by NIH grant AR42906 to GAB.

EFFECTS OF ENZYMATIC HYDROLYSIS ON CRUDE PALM OLEIN BY LIPASE FROM CANDIDA RUGOSA

ABSTRACT The effects of enzymatic hydrolysis on crude palm olein (CPOlein) by lipase from Candida rugosa were investigated. Reaction variables, namely water content, reaction temperature and enzyme concentration on hydrolysis of CPOlein were examined. Comparison was also made between CPOlein and hydrolyzed crude palm olein (HCPOlein) for melting point, percentage of free fatty acids (FFA) and viscosity. The optimum conditions for the production of hydrolyzed oil or FFA‐rich oil in enzymatic hydrolysis of CPOlein were reaction temperature of 50C, 1% (w/w) lipase from C. rugosa and 50% (w/w) water content. FFA in CPOlein increased to 97.9% after the hydrolysis process, which showed an increase of 61 folds. The differences in viscosity between the CPOlein and HCPOlein at different temperatures were statistically significant (P &lt; 0.05). The slip melting point of CPOlein was 17C. After hydrolysis, the melting point for CPOlein increased by 160%, reaching 44.4C.

Natural Compounds Obtained Through Centrifugal Molecular Distillation

Soybean oil deodorized distillate (SODD) is a byproduct from refining edible soybean oil; however, the deodorization process removes unsaponifiable materials, such as sterols and tocopherols. Tocopherols are highly added value materials. Molecular distillation has large potential to be used in order to concentrate tocopherols, because it uses very low levels of temperatures because of the high vacuum and short operating time for separation and, also, it does not use solvents. However, nowadays, the conventional way to recover tocopherols is carrying out chemical reactions prior to molecular distillation, making the process not so suitable to deal with natural products. The purpose of this work is to use only molecular distillation in order to recover tocopherols from SODD. Experiments were performed in the range of 140-220 degrees C. The feed flow rate varied from 5 to 15 g/min. The objective of this study was to remove the maximum amount of free fatty acids (FFA) and, so, to increase the tocopherol concentration without add any extra component to the system. The percentage of FFA in the distillate stream of the molecular still is large at low feed flow rates and low evaporator temperatures, avoiding thermal decomposition effects.

Microwave assisted drying of macadamia nuts

The macadamia tree (Macadamia integrifolia Maiden & Betche) belongs to the botanical family Proteaceae and is native to the Australian tropical forests. The most critical stage of macadamia nut processing is the drying of the kernels, as a minimum quality standard can only be achieved under specific controlled conditions. Otherwise there is deterioration of the nut and devaluation of kernel quality. This work aimed at verifying the feasibility of producing dried macadamia nuts by applying microwaves to assist the hot air drying process, thus reducing the drying time and increasing the industrial yield and quality of the kernels as compared to those from conventional processes. Another specific objective of this study was to analyse and model the drying kinetics of macadamia nut processing using microwaves. The quality of the kernels was controlled for a period of six months after processing by determining the peroxide values, free fatty acid percentages and sensory acceptance evaluations. The data obtained from these analyses were well below the limit stipulated by the Brazilian legislation and the product was very well accepted in the sensory evaluation.

PHYSICOCHEMICAL CHARACTERISTICS OF BINARY MIXTURES OF HYDROGENATED PALM KERNEL OIL AND GOAT MILK FAT

ABSTRACT The changes in physicochemical characteristics of fat blends containing hydrogenated palm kernel oil (HPKO) and goat milk fat (GMF), before and after chemical interesterification using sodium methoxide as catalyst, was evaluated. HPKO : GMF blends were prepared in six ratios: 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100 (w/w). Melting characteristics were studied by differential scanning calorimetry. Peak melting temperatures (Tp) of noninteresterified blends decreased as the percentage of GMF increased. Generally, the interesterified blends showed lower Tpvalues compared to the noninteresterified blends at their respective blending ratios. Decrease in melting enthalpy (Ep) occurred with the increase in percentage GMF in the blends for both the noninteresterified and interesterified blends. Interesterified blends had greater Epvalues than those of the noninteresterified blends at respective ratios. Results from X‐ray diffraction analysis showed that all blends possessed a β′ polymorph. HPKO : GMF (0:100) was the only blend in which the presence of both β′ and β polymorphs was detected. Chemical interesterification had no effect on polymorphic crystal behavior. Based on solid fat content (SFC) results, eutectic effect did not occur in all HPKO : GMF blends studied. It was shown that the percentage of SFC decreased as percentage of GMF increased. Decrease in percentage SFC of blends was brought about by interesterification. The HPKO : GMF (100:0) blend had the highest percentage of free fatty acid followed by HPKO : GMF (0:100). Interesterification caused a 2‐ to 3‐fold increase in the percentage of free fatty acids compared to noninteresterified blends. Iodine values of the blends increased with an increase in GMF proportion. A rapid increase in iodine was observed in blends containing 0–20% GMF. Interesterification did not have any effect on the iodine value of fat blends.

Deterioro de aceite de soja parcialmente hidrogenado empleado en la fritura de un alimento cárnico

Fil: Juarez, Maria Daniela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Tucuman. Instituto Superior de Investigaciones Biologicas. Universidad Nacional de Tucuman. Instituto Superior de Investigaciones Biologicas; Argentina

Elimination ofEscherichia coli O 157 : H7 and Listeria monocytogenes from raw beef sausage by γ-irradiation

The effectiveness of low gamma-irradiation doses in the destruction of Escherichia coli O 157 : H7 and Listeria monocytogenes in raw beef sausages was investigated. Raw samples of fresh manufactured beef sausage were subjected to gamma-irradiation at doses of 0, 1, 2, and 3 kGy. Then samples were cold-stored (4 +/- 1 degrees C) for 12 days and the effects of irradiation and storage on the counts of these harmful bacteria were studied. Moreover, the effects of irradiation and storage on the percentages of free fatty acids (FFAs) in lipids, on the p-anisidine values of lipids, solubility of sarcoplasmic and myofibrilar proteins, and water-holding capacity (WHC) were also determined. The results showed that gamma-irradiation at 1 and 2 kGy significantly reduced the counts of E. coli O 157 : H7 and L. monocytogenes, while 3 kGy dose effectively eliminated these bacteria by more than 4 log and 3 log units, respectively, and could keep their counts below the detection level during storage. Gamma-irradiation had no significant effects on the percentages of FFAs in lipids, solubility of sarcoplasmic and myofibrilar proteins, and WHC of samples, while it significantly increased the p-anisidine value of lipids. During storage, significant increases in the percentages of FFAs and p-anisidine values were observed for lipids of irradiated and nonirradiated sausages, while the solubility of sarcoplasmic and myofibrilar proteins showed no significant changes. Moreover, samples of irradiated and nonirradiated sausages showed significant decreases in their WHC during the first 6 days of storage at 4 +/- 1 degrees C, then showed no significant changes. Finally, gamma-irradiation at a dose of 3 kGy appeared to be sufficient to improve the microbiological safety of raw beef sausages without adverse effects on their chemical properties.

Assessment of industrial lipases for flavour development in commercial Idiazabal (ewe's raw milk) cheese

Three commercial lipases (lipases A1 and A2 were pregastric lipases and lipase A3 was a fungal lipase) from three different manufacturers were studied to develop the characteristic pungent flavour of Idiazabal (sheep's raw milk) cheese in experimental productions (50 L vats), both in summer and in winter. In the experimental productions, all lipases significantly increased the concentration of total free fatty acids (FFA), both after 90 and 180 days of ripening. Lipases A1 and A2 increased primarily the concentration of short-chain FFA (C4, C6 and C10), whereas C16:0 and C18:1 were the main FFA obtained with lipase A3. Cheeses made with no lipase had the lowest concentrations of total FFA, with C16:0 and C18:1 as the major FFA. The percent of short-chain FFA was 70–80% of the total for lipases A1 and A2, but 30–40% in cheeses made with lipase A3 or with no lipase. Sensory analysis was performed after 90 and 180 days of ripening. Cheeses made with lipases A1 or A2 or with lamb rennet paste (which contains pregastric lipase and was used as control for sensory analysis) had significantly higher scores in 6 of the 22 attributes analyzed (odour and flavour intensity, sharp odour, pungent flavour and rennet odour and flavour) than cheeses made with lipase A3 or with no lipase added. Lipase A1 was selected to conduct commercial cheese productions (200 L vats) made by artisan cheese makers adding 94 lipase units (LU)/50 L (high amount) or 8 LU/50 L (low amount). Control cheeses were made with lamb rennet paste having comparable amounts of lipolytic activity. After 90 and 180 days of ripening, cheeses made with the same amount of lipase (either as lipase A1 or present in lamb rennet paste) were indistinguishable from each other, both from the sensory and analytical points of view (comparable amounts of total FFA, and percent FFA composition). Those with low amount of lipase were rated as ‘mild’, whereas those with high amount of lipase were rated as ‘strong’. An industrial production (5000 L vat) with 100 LU/50 L yielded cheeses of ‘intermediate strength’ and intermediate levels of lipolysis. A linear correlation was observed between percent of short-chain FFA and the score for pungent flavour, for all amounts of lipase used in this study. We conclude that lipase A1 is an adequate commercial lipase to develop the characteristic flavour of Idiazabal cheese, both in artisan and industrial fabrications.

Effect of Season on Vitamin E, Fatty Acid Profile, and Nutritional Value of Fish By-Products from Cod, Saithe, Ling and Haddock Species Caught in Southern Irish Coastal Waters

ABSTRACT The value of fish is largely dependent on fillet size and species but greater value could be obtained by finding commercial uses for the remaining fish frame, particularly fish by-products. Vitamin E and polyunsaturated fatty acids, particularly docosahexaenoic acid (DHA) and eicosapentaenoic (EPA), are of economic importance to the food and pharmaceutical industries and are available for extraction from fish waste. The objective of this study was to compare α-tocopherol levels and the fatty acid profile from several demersal species (cod, ling, saithe and haddock, n = 15) caught in Irish coastal waters over a one-year period (2001). α-Tocopherol levels in samples of liver, viscera and cut-off (any residual flesh from belly flap) were extracted and subsequently measured by high performance liquid chromatography (HPLC). Total fatty acids were extracted and determined by gas chromatography (GC). Results indicated that a-tocopherol levels in liver were higher (P < 0.05) than those in viscera or cut-off. Regardless of species, α-tocopherol levels were found in the following order: liver > viscera > cut-off. In general, α-tocopherol levels were highest in autumn and lowest in spring. Overall, percent free fatty acid levels recorded in liver and viscera samples were higher (P < 0.05) than those in cut-off samples. Percent free fatty acid varied significantly (P < 0.05) with each season, and was generally greater in autumn samples. An inverse relationship was observed between percent fat and moisture levels recorded in this study. The major fatty acids identified in each fish species and each by-product were 16:0 (palmitic), 18:0 (stearic), 18:1 (oleic) 20:5n-3 (eicosapentaenoic acid, EPA) and 22:6n-3 (docosahexaenoic, DHA). The highest percent of total identified fatty acids were reported in the autumn catch, including the highest EPA and DHA levels. Overall, liver samples had the highest levels of EPA and DHA.

The Physiochemical Analysis Of Thermoxidized Soyabean-Oil And Its Effect On Growth In Rats

Physiochemical characteristics of Fresh and thermoxidized soyabean –oil were studied. Thermoxidized soyabean-oil was found to possess higher percentage of free fatty acids and peroxide value when compared with the fresh soyabean-oil. The rats fed with diet containing 5% and 15% level of thermoxidized soyabean-oil did not show any sign of retarded growth, but the weight gain was lower than those fed with Fresh soyabean-oil. The reason could possibly be as a result of mild accumulation of peroxide as well as gross accumulation of decomposition products of lipid peroxidation which are known to be toxic. Agro-Science Vol.2(1) 2001: 30-34

Beef and sheep mortadella: formulation, processing and quality aspects

SummaryBeef and lamb mortadella samples were prepared under controlled conditions and stored for 16 weeks under refrigeration. Moisture, protein, fat, ash and sodium chloride contents were measured initially and pH, percentage of free fatty acids, thiobarbituric acid values, total volatile nitrogen content, residual nitrite concentration and microbiological status were determined at regular intervals throughout storage. The sensory quality of the mortadellas during the first 2 months of storage was evaluated. The results of these tests permitted assessment of the quality and safety of beef and lamb mortadella. The products were satisfactory with regard to chemical and microbiological analyses, but after 2 months storage, the poor colour of lamb mortadella limited the sensory acceptability. Measurements of rancidity, caused by lipid deterioration and protein breakdown, were the best indicators of product quality.

Research and Development Trends in Biodiesel

AbstractBiodiesel, a derivative from plant oils or animal fats, has gained widespread acceptance in recent years as a sustainable alternative fuel to petroleum diesel due to its environmental benefits and renewability. Although there are several different ways in which biodiesel can be used or formulated as a fuel such as direct blending, microemulsions and thermal cracking, the most widespread remains the alkyl esters of fatty acids obtained through transesterification of the oils or fats. In transesterification, triglycerides which are the main chemical in oils or fats are converted into esters through reaction with simple alcohols. The physical and chemical properties of the esters thus obtained are very similar to those of the petroleum diesel.This paper reviews the current technologies available for the transesterifications of vegetable oils and animal fats and identifies that the biggest factor deterring a greater market uptake of biodiesel is its cost. It concludes that, in addition to government policy framework, e.g. to reduce the pump price of biodiesel through fuel tax exemption, further technological development presents significant scope for improvement. At present, there are no suitable and developed transesterification technologies that can handle cheap, low‐quality feedstocks including waste animal fats and spent cooking oils. These feedstocks contain high percentages of water and free fatty acids which are extremely detrimental to the yield and reaction rates of the transesterification processes. This paper also suggests some future research and development directions and requirements for more competitive biodiesel production.

Evaluation and characterization of the seed oils of Trichosanthes cucumerina (snake gourd) and Ricinodendron heudelotii (honey plum)

The estimation of the chemical composition and physical properties of the seed oils of Trichosanthes cucumerina and Ricinodendron heudelotii using standard methods of analysis showed that the seed of T. cucumerina and R. heudelotii have high oil content (46.3±4% and 42.5±5% respectively). Assessment of the physical constants revealed that Ricinodendron heudelotii had a low heat of combustion (12.9 ± 3kcal/g) when compared to that of Trichosanthes cucumerina (32.8 ± 4kcal/g). The refractive indices at 400C, boiling point, smoke point and flash points were high in the two oils. Their relative densities were high and their melting points were low. From the chemical parameters, the high ester value and saponification values of T. cucumerina and R. heudelotii qualifies them to be used in industries for soap making, while the high iodine value for R. heudelotii (158.8 ± 8gI/100g oil) qualifies it as a drying oil and suggest possible usefulness in the paint industry. Their percentage free fatty acid and acid values were low suggesting increased stability and usefulness in nutritional and industrial applications. Key Words: seed oil, chemical composition, Trichosanthes cucumerina, Ricinodendron heudelotii. (Global Journal of Pure and Applied Sciences: 2003 9(2): 217-220)

Optimisation of enzymatic hydrolysis for concentration of vitamin E in palm fatty acid distillate

Vitamin E was concentrated from palm fatty acid distillate (PFAD) in this study using a commercial immobilised Candida antarctica lipase (Novozyme 435). The PFAD and water mixture was hydrolysed at 65±1 °C. Free fatty acids (FFA) liberated were neutralised using an alkali and the salts formed were then washed off. Factors affecting the enzymatic hydrolysis and vitamin E concentration of extracted fraction were optimised using response surface methodology (RSM). A central composite design was employed to study the responses, namely percentage of FFA ( Y 1) and vitamin E concentration ( Y 2), while lipase concentration ( X 1), reaction time ( X 2) and water content of the reactant ( X 3) were the independent variables. Results showed that the regression models generated adequately explained the data variation and significantly represented the actual relationships between the reaction parameters and the responses. For both regression models of FFA and vitamin E, the first- and second-order variable of water content was the most significant factor. The optimum reaction parameters for maximum yield in FFA and vitamin E concentrations were identified from their respective contour plots. It was suggested that for maximum vitamin E concentration, the hydrolysis should be carried out with 2.5% (w/w) of lipase and 45.2–47.3% (v/w) of water for 5.5–5.7 h.

Chemical composition of selected Nigerian oil seeds and physicochemical properties of the oil extracts

Proximate composition, energy content and mineral concentrations of oil seeds used in the preparation of Nigerian diets were investigated. The paper also reports the physicochemical characteristics of the oil extracts from the seeds. Moisture content (on dry weight basis) was highest (23.13±0.44%) in coconut seeds (CNS), followed by palm kernel seeds (PKS) (14.26±0.35%) but was lowest (4.12±0.95%) in melon seeds (MS). Ash was highest (3.20±0.40%) in castor seeds (CS) followed by groundnut seeds (GNS) with a value of 2.77±0.65% and was lowest (0.43±0.32%) in CNS. Protein ranged from 6.94±0.10% in PKS to 26.5±0.27% in GNS. Dikanut seed (DNS) had the highest crude fat of 62.80±2.41%, followed by CS (57.33±1.63%), and the lowest value of 40.83±0.50% in GNS. Values for MS, oil bean seeds (OBS) and PKS did not differ significantly. Total carbohydrates were generally low in all the seeds and ranged from 12.5±0.94% in OBS to 26.9±1.01% in CNS. The energy content, in kilocalories, per 100g sample, was highest in DNS (688) followed by MS (643) and was lowest in CNS (516). The oil seeds were found to be good sources of minerals. Copper, potassium, sodium and sulphate were highest in OBS, chloride was highest in PKS; zinc and phosphate were highest in CS while iron ranged from 0.130±0.001 in GNS to 0.489±0.00l mg/100 g in CNS. The physical properties of the oil extracts showed the state to be liquid at room temperature (29±1 °C) and the colour to be pale-yellow or golden-yellow, in general. Melting point was highest in MS oil and lowest in PKS oil while setting point was highest in DNS oil, followed by CNS oil and lowest in MS oil (4.67±0.3 °C). Specific gravity ranged from 0.87 in PKS oil to 0.98 in MS oil. Among chemical properties of the oil extracts, acid value, saponification number, iodine number, percent free fatty acid, peroxide value and unsaponifiable matter were, respectively, highest in CS, MS, PKS, CS, DNS/CNS and GNS oils while the lowest values were, respectively, obtained in OBS, CS, GNS, OBS, PKS and OBS oils. It can be inferred that the oil seeds investigated are good sources of crude fat, crude protein, ash, energy and minerals. The oil extracts exhibited good physicochemical properties and could be useful as edible oils and for industrial applications.

LIBERATION OF 5,8,11,14,17‐EICOSAPENTAENOIC ACID AND OTHER POLYUNSATURATED FATTY ACIDS FROM LIPIDS AS A GRAZER DEFENSE REACTION IN EPILITHIC DIATOM BIOFILMS

Acute grazer toxicity of freshwater diatom biofilms was determined using Thamnocephalus platyurus Packard, an anostracan grazer, as the bioassay organism. The diatoms exhibited toxicity when the cells of the biofilm were freeze–thawed before the assay. The toxicity could be extracted from the biofilms with methanol and acetone, and only minimal toxicity was left in the insoluble residue. Bioassay‐guided HPLC separation of the methanolic extract was performed to trace the most toxic components. Analysis by UV spectrometry, gas chromatography, and mass spectrometry showed that 5,8,11,14,17‐eicosapentaenoic acid was responsible for most grazer toxicity. The 24‐h LC50 of this polyunsaturated fatty acid was 34 μM in the Thamnocephalus platyurus bioassay. The concentrations of other free fatty acids were not high enough to contribute significantly to the toxicity. Procedures that affected the integrity of the cells (e.g. solvent extraction, freezing and thawing, osmotic stress by addition of 20% NaCl, or grinding the cells in a mortar) were taken as model reactions for grazing and had the common effect of resulting in a dramatic increase of free polyunsaturated and saturated fatty acids. Under these conditions, about 30% of the total fatty acids of the diatoms was transformed from the bound into the free form. The time necessary for liberation was very short. With the exception of 5,8,11,14,17‐eicosapentaenoic acid, which continued to be liberated, the hydrolysis of the other fatty acids was terminated less than 1 min after initiating the reaction. The classical extraction procedures using methanol and other solvents led to the appearance of a high percentage of free fatty acids in live cells. Treatment of biofilms with these solvents did not stop the hydrolysis of lipids initiated by the disintegration of the cells. However, boiling acetone completely suppressed the hydrolytic reactions, and free polyunsaturated fatty acids were not detected in live biofilm organisms, although nontoxic saturated fatty acids were present in moderate concentrations. These results were interpreted as an indication that the frequently reported existence of free polyunsaturated fatty acids in live biomass is an analytical artifact.