Search

Used frying fats and oils with highly variable and uncontrolled quality are used for the production of biodiesel . The objective of this study was to define the analytical methods useful to obtaining information on the quality of the used frying oils as raw material for biodiesels as well as for the characterization of the biodiesels obtained from them. Twentyfour used frying oils from restaurants and domestic fryers were analyzed before and after transesterification to fatty acid methyl esters (FAME). From a detailed analysis of the samples by means of a combination of adsorption and size exclusion chromatography, the quantitative importance of polymeric compounds was deduced both from the direct analysis of the oils and from their FAME. Excellent linear correlation between polar compounds and polar FAME (R=0.9768) was found. The possibilities of interferences from polar fatty acid in the standard method to determine the ester content are defined. Finally, determination of non-polar FAME by silica column is proposed as a good alternative to the gas chromatography method.

An analytical evaluation of some by-products resulting from edible oil refining processing steps has been carried out. By-product samples were taken from four different local refineries that apply chemical refining technology. Pretreatment of the representative samples of the by-products were done prior to analysis followed by chromatographic isolation and derivatization of the minor components, namely, free and acylated sterol (FS and AS) as well as free and acylated sterylglycosides (FSG and ASG). However, tocopherols were directly determined in the pretreated samples. HPLC, using different detectors, was carried out for the determination of these minor components. Several authors have focused on the analysis of sterols and sterol esters, as well as tocopherols in the refining byproducts; however sterylglycosides, as biologically important components, have not been dealt with. This study throws light on the by – products enriched with certain minor components to be possibly utilized as sources for such components. Also, the role of the conditions of the refining steps followed in removing these valuable minor components from oils was discussed. It was found that soapstock samples contained various amounts of total tocopherols ranging from 80 to 230ppm; total FS and AS ranged from 240 to 4000 mg/100g while total FSG and ASG ranged from 1120 to 6375 mg/100g. In the case of deodorization distillate samples total tocopherols ranged from 960 to 7360ppm; total FS and AS ranged from 1020 to 4160 mg/100g and total FSG, ASG ranged from 395 to 880 mg/100g.

The principal components of the hexane extract from olive leaves are analysed, following an analytical procedure based on the extraction with hexane and the later separation of groups of compounds, according to their polarity, by means of column and thin-layer chromatographies. The following components are separated and identified: hydrocarbons, ester waxes, triglycerides, tocopherols, esterols, lineal and terpenic alcohols and terpenic dialcohols. The olive leaves from five different varieties were analyzed: Picual, Arbequina, Hojiblanca, Empeltre and Cornicabra; the concentration of some compounds ranged between: 2.057-3.400 ppm saturated hydrocarbons; 38-152 ppm squalene; 915-1.874 ppm ester waxes; 28-100 ppm β-carotene; 832-1.396 ppm triglycerides; 41-125 ppm α-tocopherol; 614-2.500 ppm β-sitosterol; 95-311 ppm alcohols and 342-837 ppm terpenic dialcohols.

This review presents the characteristics, advantages, limits and potential of three spectroscopic techniques: near-infrared spectroscopy (NIR), mid-infrared spectroscopy (MIR) and Raman spectroscopy. The theoretical aspects related with these techniques, the information that can supplied and the main features of the instrumentation are presented and briefly discussed. The last part of the review concerns the application of the spectroscopy to food analysis, with special emphasis on the lipid analysis. The illustrations and examples have been chosen to demonstrate the importance of spectroscopic techniques both in process (on-line) control and in laboratories for the analysis of major or minor compounds.

Supercritical extraction (SFE), using primarily environmentally-benign carbon dioxide (CO2) as the extracting agent, is reviewed with respect to its present status and future use. SFE was developed for analytical application in the mid 1980’s in response to the desire to reduce the use of organic solvents in the laboratory environment and is becoming a standard method for the preparation and analysis of lipid-containing sample matrices. Currently, analytical SFE is predominately practiced in the off-line mode, using both sequential and parallel extraction modes. Depending on the instrumental configuration, the preparation of up to 24 samples can be accomplished on one instrument on a daily basis. Several other benefits can be achieved using SFE, such as the processing of thermally-sensitive analytes and rapid analyte extraction kinetics relative to extraction with liquid solvents. Examples are provided not only of the analytical SFE of oils and fats, but of volatile solutes from an array of sample types. Finally, the relevance of analytical SFE to processing with supercritical fluids (SFs) is documented using examples from our own research involving a combinatorial approach to optimising processing conditions.

As the practice of vegetable oil adulteration becomes more sophisticated, the possibility to subvert detection using established techniques such as capillary gas chromatography is increasing. One of the most powerful techniques to be used in food authenticity studies is stable isotope ratio mass spectrometry (SIRMS) which utilises differences in the natural abundance of the stable isotopes of the ‘light’ bio-elements hydrogen, nitrogen, carbon, oxygen and sulfur to detect food fraud. SIRMS has found application in the authentication of a wide range of foodstuffs, including fruit juices, wines, spirits, honey and to detect the adulteration of flavour compounds with synthetic analogues. This papers reviews the current state-of-the-art for the authentication of vegetable oils using SIRMS and highlights emergent techniques such as compound- and position specific-isotope mass spectrometry. These latter developments offer the potential to provide more rapid and improved detection of the economic adulteration of vegetable oils.

Forty-one individual food samples were analyzed for their fatty acid contents by gas-liquid chromatography using capillary tubes. The samples belonged to 5 different food groups and included vegetable oils, butter & ghee, animal fats, dairy products, fishes, chicken & meats and other popular dishes. The results show that maize oil was lowest in its total saturated fatty acid content (11%) and richest in linolenic acid. On the other hand, total saturated fatty acids made up 42-62 % of the total fatty acid patterns of the lamb and camel fat tallow, respectively. Long chain polyunsaturated fatty acids (C20-C22) with two to six double bonds were present only in fishes. Estimate of fat intake amounted to 36 grams per subject per day and the % contribution of the analyzed fats was presented. The ratio of polyunsaturated to saturated fatty acids amounted to 0.96; which falls within the optimum dietary goals.

A rapid and simple method to obtain, from olive samples, enough quantity of oil to determine acidity grade is proposed. From paste samples of milled olives, different fraction are separated to be centrifugated during 5 minutes at 4500 r.p.m. Oil acidity results obtained from sodium sulfate anhidrous and natural microtalc added samples are compared with blank samples, and with those obtained by the Abencor extraction procedure. The correlation between the acidity of oil samples obtained by the Abencor method is also analyzed against other samples obtained by the normalized method in Spain, norm UNE 55070, Soxhlet system. Results show that in all the centrifugated samples enough amount of oil is obtained to determin the acidity grade, it also show that treatment with sodium sulfate anhidrous obtains a bigger recovery percentage, and that in all 3 cases, the acidity shows a good correlation with that of the Abencor system, doubling the number of samples analysed by the Abencor system. It also shows that the acidity grade obtained by using the UNE 55070 norm is aproximately 0,3 grades above that obtained by the Abencor system.

Aldehydic acids are generated in oxidized lipids as a result of decomposition of hydroperoxides by (β-scission reactions. Aldehydes are known to interact with proteins and DNA and to impair enzymatic functions. Aldehydic esters from oxidized lipids were reabsorbed to a significant extent in rats. This paper reviews the mechanism of formation of esterified aldehydic acids in frying oils and their physiological/toxicological effects. The paper also gives an overview of relevant basic analytical techniques that needs to be improved to establish reliable quantitative method (s).

The detection of lard in food products is of special interest for reasons of quality, dietetics or religious belief. Works carried out to date have mainly concerned fatty mixtures with others food components. This work studies a complex food products (dehydrated stock model) containing hydrogenated palm and beef fat. An appraisal is carried out regarding the detection sensitivity to the addition of 0.2% lard, using data on sterols and fatty acids in the β position. This last model only appears reliable for the goal proposed.

Resistant starch (RS), the dietary starch that scape digestion in the small intestine, can yields up to 20% of the starch in cereal and legume products. Several fractions contribute to the total RS of foods: retrograded amylose, starch inaccessible to digestive enzymes because of mechanical barriers, chemically modified starch fragments, undigested starch due to α-amylase inhibitors and starch complexed with other food components. RS is formed in products processed following heat treatments (baking, extrusion, autoclaving, etc.). RS produces significant fecal bulking and is partially fermentable by anaerobic bacteria of the colon. On the other hand, the relation of resistant starch with the glucose and insulin response in human subjects is an important nutritional effect. RS analytical methods are reported.

We make a bibliographical review on the main aspects related to the cholesterol oxidation products, including their biological effects, their presence and formation in food and their analytical determination.

Methods for the determination of the milk fat content of fat mixtures are usually based on a butyric acid determination. This fatty acid is specific for milk fat. A conversion factor is used to calculate the milk fat content from the butyric acid content of the mixture. When applying this procedure, the natural variation of the butyric acid content of milk fat is not taken into consideration. Recently published data show that a considerable error may thus be introduced, making the interpretation of analytical results difficult. It is therefore proposed to envisage a control procedure which takes this aspect into consideration.