Frying Fats Research Articles

A new analytical and statistical approach to predict the sensory properties of deep frying fats and oils to determine the point of discard during processing

The aim of this work was to explore the feasibility and limits of analytical criteria to assess the sensory properties of used frying oils and different fried food. Over a period of 2 years, 148 used frying oils collected in restaurants bakeries, fish caterers, and industrial plants were analyzed for a wide range of parameters, including sensory tests, total polar compounds (TPC), dimerized and polymerized triacyl‐glycerols (DPTG), monomeric oxidized triacyl‐glycerols (MONOX), acid value (AV), para‐anisidine‐value (AnV), and iodine value (IV). All methods were judged for their relevance, concerning the sensory quality of used frying oils categorizing the qualities as good or bad. The binary results were statistically evaluated using logit regression. The statistical evaluation of the tests was used to calculate the probability of occurrence of off‐flavors which allows determining the point of discard and finally the point where the oil is certainly totally abused. All levels of degradation for used frying oils regardless of oil type and kind of food being fried can be statistically described and used to develop a simple equation using the TPC and AV value as variables (y = 117–8 × AV − 3 × TPC) to find the point of disposal and to monitor the degradation process. The new criterion has been proven in the controlling of various industrial frying processes, restaurants and bakeries and kitchen frying.Practical applications: A simple equation of linear regression using AV and TPC as variables (y = 117–8 × AV − 3 × TPC) has been developed to monitor the level of degradation and to determine the point of disposal of used frying fats and oils much more reliable than using only one of the recommended parameters (TPC, AV, or PTG). This criterion is independent of fat composition, food to be fried, or frying process conditions and effectively helps to overcome the limitations of TPC and other major regulatory parameters related to the frying/baking industry. The good correlation of the results of the equation with the sensory quality of the fried food provides a powerful predictive tool for accurate calculation of the oil disposal point. This is useful since the quality of the fried food strongly depends on the quality of the frying oil that is absorbed by the food and becomes a major ingredient in the final product. This tool can easily be used to improve frying oil quality which finally improves the quality of the food to be fried. With continuous improvement this tool can become useful in reducing time and costs required for a human sensory panel.Physical and chemical changes of oils during different frying processes affect the development of color, flavor, and taste of the oil and also the structure of the food being fried. A new analytical approach applicable for all types of frying oil from different sources (bakeries, fisheries, restaurants, and industrial fryers) is proposed to predict the sensory quality of the oil using the content of total polar compounds and acid value resulting in the probability of the point of discard (DEGLEV).

Characteristics of Mango Kernel Fats Extracted from 11 China‐Specific Varieties and Their Typically Fractionated Fractions

Abstract11 China‐specific mango varieties, i.e., Tainong, Xiangya, Okrong, Keitt, Chiin Hwang, Guifei, Yuexi, Biantao, Guixiang, Zihua and Guire, were selected from South China, and the kernels were separated from pulps and then dried to extract mango kernel fats (MKF). 5.65–11.14 % of the fats could be obtained from dried kernels using hexane extraction, and their iodine values, slip melting points, triacylglycerols, sn‐2 fatty acids and micronutrients were analyzed. MKF were comprised predominantly of triacylglycerols reaching 85.09–92.72, and 78.28–84.37 % of oleic at the sn‐2 position. 29.99–55.44 % of SOS, 11.17–23.34 % of SOO and 13.10–19.79 % of POS occupied the main percentages of triacylglycerols, indicating MKF have diversified application after fractionation. Certain variety characterized as moderate values mentioned above, therefore, was selected and then fractionated by two‐stage processes to produce typical MKF fractions. The stearin (Fraction‐II) fractionated from the first solid fraction (Fraction‐I) with 68.09 % of SOS and 15.43 % of POS was more suitable as cocoa butter improver, while the olein (Fraction‐III) produced from the first liquid fraction was rich in SOO (45.59 %), POO (11.37 %) and OOO (11.14 %), which are considered as ideal cooking oil or frying fat ingredients. In addition, high amounts of micronutrients, including sterol, tocopherol and squalene, were also found in MKF ranged from 3837 to 7085, 81 to 916, and 164 to 941 mg/kg among different varieties, respectively. In particular, squalene levels were higher compared with most of other vegetable oils.

Effect of frying fat substitution by vegetable oil and energy concentration on diets for productive performance of broilers

En la dieta de pollos de engorde se adicionan lípidos para mejorar su eficiencia productiva, generalmente grasa de fritura (GF), reciclada de restaurantes, por tener menor costo que el aceite vegetal (AV). El objetivo de este trabajo fue evaluar el efecto de la sustitución de GF por AV en dietas estándar (DEE) y dietas altas en energía (DAE) sobre el comportamiento productivo de pollos de engorde. Se alimentó durante 42 d a 200 pollos mixtos ROSS, de un día de edad y peso promedio de 37.2 g ± 0.89 g. El estudio se realizó en dos fases de 21 d: inicio y acabado. Se usó un diseño experimental al azar con arreglo factorial 2 x 2 con la fuente de lípidos (GF y AV), laconcentración de energía (DEE y DAE) y su interacción como efectos principales. La energía metabolizable en la fase de inicio fue 2 994 kcal/kg y 3 013 kcal/kg, y en la fase de acabado fue 3 081 kcal/kg y 3 111 kcal/kg en DEE y DAE, respectivamente. La fuente de lípidos no influyó (P > 0.05) sobre las variables de estudio. En la fase de inicio, los pollos alimentados con la DAE ganaron más peso y mostraron mejor conversión alimenticia (P < 0.05) que los pollos en la DEE, aunque el consumo de alimento fue similar (P > 0.05). En la fase de acabado, los pollos alimentados con la DAE ganaron más peso (P < 0.05) y consumieron más alimento (P < 0.05) que los pollos alimentados con la DEE. No se observó efecto de la concentración de energía sobre la conversión alimenticia (P > 0.05). Se concluyó que la fuente de lípidos no influyó en los parámetros productivos, pero el incremento en concentración energética mejoró significativamente el comportamiento productivo de los pollos de engorde. Archivo XML (SciELO)

Ingestion of frying fat leads to activation of the endoplasmic reticulum stress-induced unfolded protein response in the duodenal mucosa of pigs.

Ingestion of oxidized fats (OF) causes activation of stress signaling pathways such as nuclear factor-erythroid 2-related factor 2 (Nrf2) in the intestine. Activation of this pathway is mediated by ER stress-induced unfolded protein response (UPR). Herein, we hypothesized that ingestion of OF causes ER stress-induced UPR in duodenal mucosa of pigs. Six-wk-old cross-bred pigs received either a control diet with fresh fat or a diet with OF for 29 days. Pigs fed OF exhibited increased phosphorylation of the ER stress downstream target eukaryotic translation initiation factor 2α and induction of several genes involved in ER stress-induced UPR and Nrf2 target genes in duodenal mucosa. No signs of an impaired intestinal barrier function or a systemic inflammatory response could be found in pigs fed OF. Activation of ER stress-induced UPR by OF in the duodenal mucosa in pigs might be interpreted as a cytoprotective response to stress factors associated with ingestion of OF. Given the similarities between pigs and humans with respect to digestive physiology, it is possible that regular ingestion of fried foods containing OF activates the ER stress-induced UPR also in the intestinal mucosa of humans.

Epoxy fatty acids in used frying fats and oils, edible oils and chocolate and their formation in oils during heating

The occurrence of monoepoxy fatty acids in used frying oils and in other common foods has been determined. Monoepoxy fatty acids with trans‐9,10‐ and cis‐9,10‐epoxystearate and trans‐12,13‐, trans‐9,10‐, cis‐12,13‐ and cis‐ 9,10‐epoxyoctadecenoate were found at average levels of 3.7 g/kg in used frying fats and oils, but also at about 2 g/kg in the fat fraction of chocolate. They were also detected in pumpkin seed, sweet almond, groundnut, sunflower, and olive oils at average levels of 3.4, 1.7, 1.4, 1.0, and 0.2 g/kg, respectively. Their formation during heating at 175°C was observed for sunflower, rapeseed, soybean, and linseed oil and compared with the increase of polar compounds and polymerized triacylglycerols as other important quality indicators for frying oils. During heating for 16 h, the level of monoepoxy fatty acids increased to about 30, 18, 8, and 4 g/kg for olive, sunflower, linseed, and rapeseed oils, respectively. The influence of the heating temperature was surveyed for refined soybean oil at 160, 170, 180, and 200°C. Heating of two sets of five different refined and virgin rapeseed oils revealed a significant lower formation of monoepoxy fatty acids for refined oils at a median level of 4.6 g/kg compared to7.7 g/kg for virgin oils.Practical applications: Determination of fatty acid methyl esters is one of the most common analyses for the evaluation of oils and fats. The assessment of the monoepoxy fatty acids as part of these analyses can provide a first indication about used frying fats and oils, which reached the end of their applicability. The formation of monoepoxy fatty acids is affected by the fatty acid composition of the oil, the heating temperature, and the production of the oil. Therefore, frying oils may contain varying amounts of monoepoxy fatty acids at the maximum limit for polar compounds and polymerized triacylglycerols as used in the official food control. However, all used frying oils investigated by the official food control showing more than 7 g/kg of monoepoxy fatty acids had to be rejected due to the limits exceeded for polar compounds and polymerized triacylglycerols. Therefore, this limit of 7 g/kg monoepoxy fatty acids level is proposed as a level for screening the usability of used frying fats and oils.Epoxy fatty acids are formed in oils and fats during frying and heating. In addition, they are also detectable in unheated foods like chocolate and pumpkin seed oil. Frying fats and oils heated too much show contents of monoepoxy fatty acids above 7 g/kg.

Analysis and occurrence of dichloropropanol fatty acid esters and related process‐induced contaminants in edible oils and fats

A new sensitive method for the indirect determination of ester‐bound 2,3‐dichloro‐1‐propanol (2,3‐DCP), 1,3‐dichloro‐2‐propanol (1,3‐DCP), 2‐chloro‐1,3‐propanediol (2‐MCPD), 3‐chloro‐1,2‐propanediol (3‐MCPD) and 2,3‐epoxy‐1‐propanol (glycidol) in oil matrices is presented. It is based on a mild alkaline‐catalysed release of chlorohydrins and glycidol, followed by a transformation of glycidol to monobromopropanediol (MBPD) according to a modification of the AOCS Official Method Cd 29b‐13 (3‐in‐1 method). The dichloropropanols are separated from the monohalogenated diols and the oil matrix by l/l extraction and determined separately by headspace gas chromatography‐mass spectrometry (GC‐MS‐HS). Both MCPD isomers and the glycidol derivative are derivatised with phenylboronic acid (PBA) and analysed by GC‐MS separately. Method validation was performed in an oil matrix using isotopic labelled esterified standards. Linearity was verified for all analytes (r2 > 0.998). The limit of detection (LOD) for all analytes was ≤5 μg/kg. The modified determination of ester‐bound MCPD and glycidol was tested for accuracy by analysing reference samples. All free and bound analytes were investigated regarding their stability against undesired alkaline‐induced transformation. It was also demonstrated that bound MCPD and bound DCP might be generated in oil by heat treatment in the presence of a strong chloride donor. The method was applied to the analysis of a variety of different edible oils. None of the two tested dichloropropanols was detected. By contrast and as might be expected, both bound MCPD and bound glycidol were consistently detected in refined oils.Practical applications: The presented application is suitable for the parallel determination of ester‐bound dichloropropanols and monochloropropanols and ester‐bound glycidol in edible oils and fats using simple techniques for sample preparation. It covers more analytes and is more sensitive than other previously reported methods. Substitution of the double sample preparation, (a part of the AOCS Official Method Cd 29b‐13), by determining a correction factor for a whole set of samples, may reduce the effort required for sample preparation and raw data analysis. Furthermore, the investigation of basic transformations that may occur during sample preparation can be helpful for a better understanding of the complex chemistry in MCPD and glycidol analysis. Similarly, the results from heating frying fat in the presence of aluminium chloride might help to understand the distribution of chlorohydrin isomers in heat‐treated oils and fats.Assumed heat‐induced formation pathways of ester‐bound chlorohydrins in an edible oil.

Possible adverse effects of frying with vegetable oils.

The question of whether heated fats in the diet may be detrimental to health is nowadays of the upmost concern, but finding an answer is not easy and requires careful consideration of different aspects of lipid oxidation. This review is divided into two sections. The first part deals with the nature of the new compounds formed at high temperature in the frying process as well as their occurrence in the diet while the second part focuses on their possible nutritional and physiological effects. Oxidation products present in abused frying fats and oils are the compounds most suspected of impairing the nutritional properties of the oils or involving adverse physiological effects. The recent studies on their health implications include those related to their fate and those focused on their effects in metabolic pathways and the most prevalent diseases.

Changes in Quality Characteristics of Different Deep Frying Fats During Frying and Regeneration Potentials of Different Adsorbents in Wasted Frying Oils

Regeneration potentials of synthetic magnesium silicate, acid activated bleaching earth and natural bleaching earth for the fried soybean oil after progressive laboratory scale frying. The wasted palm olein and sunflower oils which were obtained from two different restaurants were investigated. As indication for development of deterioration reactions in oil during frying and regeneration potentials of so-called adsorbents, free fatty acid content (FFA), total polar material (TPM), dielectric constant (DC) and color measurement values (L, a and b) were measured. According to the results, synthetic magnesium silicate (SMS), acid activated bleaching earth (ABE) and natural bleaching earth (NBE) have different adsorbent characteristics that were significantly affected by the origin, physical and chemical properties and production method of that adsorbent. Laboratory scale frying operations were significantly increased FFA, TPM and DC as a result of thermal oxidation reaction. The usage of SMS in the wasted soybean oil reduced FFA content, TPM and DC values while lighten the color. Nevertheless, the reductions of these values were much more evident for in wasted sunflower oil from Restaurant A (WA) and wasted palm olein from Restaurant B (WB) when compared to wasted oil obtained from laboratory scale frying operations. All values were reduced with the use of adsorbents while L values of WB is increased with adsorbent usage. Generally SMS showed a higher reducing potential on FFA content, TPM and DC values which are considered as deterioration indices of oil quality during frying operation.

ZMĚNY TUKU V PRŮBĚHU FRITOVÁNÍ A VÝSLEDNÁ KVALITA JEMNÉHO PEČIVA

The purpose of this attemt was to evaluate the influence of deep-frying fat on the quality of frying pastry and observe chemical changes of frying fat during frying.The samples of frying pastry were provided by factory Penam s. r. o., Rosice. Four sorts of soft-centered friedcakes and not soft-centered friedcakes were evaluated. The samples of hydrogenated fat were taken twice always at the beginning and at the end of the frying. This lasted 7 days. Chemical analyse and qunatification fatty acid by using gass chromatography were took by these samples. The sensor eva­lua­tion was made by ten expert evaluators. Evaluators focused on following deskriptors: form, appearance, crumb, aroma, flavour of soft centred and flavour of product. We have found significant statistical differences between the products fried in the fat which was changed before and after the frying. The most differences were registered by porosity, plumpness, flavour of crumb and placement fill.Acidity number of fat increased linearly. Peroxid number decreased at the beginning and than increased again.

Effects of frying fat and preparation on carp (Cyprinus carpio) fillet lipid composition and oxidation

We investigated the changes in omega 3 enriched carp fillets caused by pan frying. The investigated characteristics were fat uptake, fatty acid (FA) composition, and oxidation. Four different fats were used and fillets were fried plain or battered. The fillet fat content increased during frying and FA composition in the fillets reflected the composition of the frying fat. Frying with sunflower oil negatively influenced the nutritional value by decreasing the n-3/n-6 ratio in the fillets. Frying with rapeseed oil preserved the favourable n-3/n-6 ratio without increasing the saturated fatty acids (SFA). Frying with lard and butter preserved the n-3/n-6 ratio but increased the SFA content. No increased oxidation occurred with the use of rapeseed oil. We concluded that using rapeseed oil for fish seemed to preserve the nutritionally valuable composition best.  

Effects of frying conditions on the formation of heterocyclic amines and trans fatty acids in grass carp (Ctenopharyngodon idellus)

The effects of frying temperature and the number of frying cycles on the formation of heterocyclic amines (HAs) and trans fatty acids (TFAs) in grass carp were investigated. 9t-18:1 FAs was detected in all samples. The TFA contents of samples fried at 150–210°C were not significantly different (P>0.05). The content and number of different types of HAs increased with increasing frying temperature. 9H-pyrido[3,4-b]indole (Norharman), 1-methyl-9H-pyrido [3,4-b]indole (Harman), and 2-amino-3,7,8-trimethylimdazo[4,5-f]quinoxaline (7,8-diMeIQx) were detected in most of the tested samples. The differences in the surface colour (ΔE) increased with frying temperature, and ΔE of samples fried at 170°C was significantly higher than that of 150°C (P<0.05). The analysis of different cycle times revealed that the TFA levels increased with an increase in the usage period of the frying fat, and 9t,12t-18:2 FAs was detected after the 40th frying cycle. As the number of frying cycles increased, the number of different types of HAs increased, seven types of HAs were detected after the 25th frying cycle.

Application of FT‐NIR spectroscopy in assessment of used frying fats and oils*

NIR spectroscopy (NIRS) was used to develop a fast and cost‐effective method to assess the quality of deep‐frying oil. A large number of fresh, used and discarded oils, used in fast food units, restaurants, fisheries, bakeries, and other frying industries, were analyzed for relevant parameters of thermo‐oxidative fat degradation such as total polar compounds (TPC), di‐ and polymerized tri‐acylglycerols (DPTG), anisidine value (AnV) and acid value (AV) using the standard DGF methods. Additionally, the fatty acid composition, including trans fatty acids, iodine value (IV) and the contents of monomeric oxidized tri‐acylglycerols (MonoxTG) were determined to describe the nutritional value of fried food. MonoxTG is a mixture of oxidized triglycerides of different molecular weight forming two groups separated in GPC. It is suggested to call them total oxidized products (TOP) as both groups of monomeric oxidized TAGs characterize, objectively and reliably, the whole spectrum of oxidized products in a used frying oil in contrast to AnV. Typical concentrations of this group of oxidized monomeric tri‐acylglycerols (TOP) in frying oils are 3 up to 15%. High calibration accuracy was obtained for all NIRS determinations. All methods were validated using test set validations. Partial least squares regression (PLS) was used to correlate spectral data with TPC, TOP, DPTG, AV, and AnV. High calibration accuracy was obtained for the NIR determination of all parameters analyzing used frying oils. For the TPC, the coefficient of determination R2 was 97.6 with an RMSEP of 1.56% over a range from 2.0 to 50.3%. Also DPTG was predicted successfully with R2 = 99.4 and RMSEP = 0.47% (0–31.3%). The AnV was measured over a broad range of 0.1 to 173 with R2 = 95.7 and RMSEP = 6.8. For acidity expressed as AV covering a wide range from 0 to 5.7 the R2 value was 97.4% with an RMSEP of 0.17%. A new parameter to monitor the degree of oxidation (TOP) has shown an R2 = 96.8 and RMSEP = 0.57%Practical applications: NIRS is a useful tool for monitoring the thermo‐oxidative changes in used frying fats and oils during the frying process. This helps to optimize the frying process and to improve the quality of the food to be fried. From the results obtained in this study, it can be deduced that the determination of the TPC is not sufficient. The determination of all oxidized monomeric triglycerides TOP provide better information of those compounds which are discussed to have a detrimental effect to human health.

Quality control of used deep‐frying oils

Quality of deep‐fried food is inseparably attached to the quality of the used deep‐frying oil. Taste, flavor, shelf life, consumer acceptance, and safety of fried food essentially depend on frying oil quality. Evaluation of frying oil quality therefore is an important issue for both frying operators and official food control agencies. Organoleptic evaluation is an essential step in the monitoring of frying fat quality. Several official laboratory methods are available to support the sensory evaluation. Total polar materials (TPM) and polymer TAGs (PTG) are the most reliable parameters for this purpose. Recommended and widely accepted limits are 24% for TPM and 12% for PTG. When oxidative alterations strongly predominate over thermal alterations, sensory defects can appear before TPM and PTG reach recommended values. In that case additional parameters like anisidine value, carbonyl value, or epoxy fatty acids should be considered. A number of physical and chemical rapid methods are available. Despite the limited informative value and the possibility of error of rapid tests, they are essential for fryer operators, because they deliver information about fat quality in real‐time. Most reliable for most applications are quick tests measuring TPM. A unique and powerful tool for the simultaneous detection of multiple parameters corresponding to thermal and oxidative alterations is near infrared spectroscopy (NIRS), which will become more and more important in future.

11th Euro Fed Lipid Congress, New Strategies for a High Quality Future (27–30 October 2013, Antalya, Turkey)

11th Euro Fed Lipid Congress, New Strategies for a High Quality Future (27–30 October 2013, Antalya, Turkey)

FT‐near infrared (NIR) spectroscopy – Screening analysis of used frying fats and oils for rapid determination of polar compounds, polymerized triacylglycerols, acid value and anisidine value [DGF C‐VI 21a (13)

The “Joint Committee for the Analysis of Fats, Oils, Fatty products, Related Products and Raw Materials (GA FETT)” has developed the following method for the fast determination of polar compounds, polymerized TAGs, acid value and anisidine value in used frying fats and oils. It will be included to Section C, Chapter VI of the German Standard Methods and will be part of the 19th amemdment to the second edition of the German standard method in autumn 2013. This very important method reflexes the need of the control laboratories to get fast and reliable results for the analyses of used frying fats and oils, it is with safe money and time. The method has been evaluated in an interlaboratory test with 11 laboratories.

Preparation of doughnuts using partially hydrogenated peanut oil and alternative products with reduced content of trans-fatty acids

Trans-fatty acids (TFA) should be avoided in the nutrition due to health concerns. Despite that there are several frying fats available on the market with reduced content of TFA this has to be implemented for the production of doughnuts in many bakeries. In this frying experiment the commonly used fat consisting of partially hydrogenated peanut oil (PHPO) and fats with a reduced content of TFA below 2 g/100 g were assessed at the same time for their oxidative stability, technological and sensorial performance for the production of doughnuts. Some of the TFA free products provided even better heat stability compared to PHPO and in addition also technological requirements were covered. However, the sensory assessment of the fats in the frying trial showed significant differences between the products. While a TFA free fat showed best assessment results during the whole course of the frying test others produced significant off-flavours. Surprisingly, for the reduction of TFA these fatty acids were not exchanged by saturated fatty acids. The best product showed a moderate content of 37 g/100 g saturated fatty acids and 55 g/100 g mono unsaturated fatty acids and a low content of about 8 g/100 g poly unsaturated fatty acids (linoleic acid).

Effect of frying in different culinary fats on the fatty acid composition of silver carp.

The influence of frying with four different oils (sunflower oil, soybean oil, olive oil, and corn oil) on the fatty acid composition of silver carp was evaluated. The fat content of the fillets increased after frying while the moisture content decreased in all evaluated samples. Mean saturated (SFA), monounsaturated (MUFA), polyunsaturated (PUFA) fatty acids, ∑ω3, and ∑ω6 contents of raw fish were 26.1 ± 0.5, 52.1 ± 1.1, 15.1 ± 0.6, 8.9 ± 0.1, and 6.1 ± 0.4%, respectively. Frying led to exchange of fatty acids between the silver carp lipid and frying fats. As a result of interactions, MUFA, PUFA, ∑ω6, and PUFA/SFA ratio of samples fried in sunflower, soybean, and corn oil significantly increased while the amounts of SFA decreased. Frying had a negative effect on the ∑ω3/ω6 ratio but reduction in olive oil-fried samples is the least among the other samples. Except in soybean oil, long-chain ω3-PUFA content of samples was not affected by frying.

Antioxidant Activity of Sesamin in Canola Oil

AbstractThe present study presents the antioxidant activity of sesamin in canola oil compared with that of butylated hydroxytoluene (BHT) by monitoring the oxygen consumption and the decrease in linoleic acid and α‐linolenic acid. The oxidation of canola oil was conducted at 35, 60, 90, 120 and 180 °C with addition of 50–400 ppm sesamin. Results from the oxygen consumption test showed that sesamin dose‐dependently inhibited the oxidation of canola oil at concentrations of 50–200 ppm at temperatures of 60–180 °C, however, sesamin lost its antioxidant activity at a low temperature of 35 °C. The fatty acid analysis also demonstrated that sesamin at 50, 100 and 200 ppm dose‐dependently prevented the oxidation of linoleic acid and α‐linolenic acid in canola oil. Both the oxygen consumption and the fatty acid analysis demonstrated sesamin was less effective than BHT as an antioxidant at temperatures of 60–180 °C. It was therefore concluded that sesamin could prevent the lipid oxidation of frying fats and oil, however, its antioxidant activity was not as potent as that of BHT.

Chemical and Biological Modulations of Food due to the Frying Process

The interactions between frying fat and fried foods are of great relevance for the nutritional quality of the final product. In particular, the amount of fat taken up can be positively influenced at the industrial but also at the household level by different pre- and post-frying conditions. The fat uptake during the frying process can also lead to a complete different fatty acid pattern of the product. The change is always towards the predominant fatty acids in the frying fat, which can be beneficial when replacing saturated fatty acids with monounsaturated fatty acids and polyunsaturated fatty acids, but can also be of disadvantage in the case of fish, when the initial content of n-3 fatty acids is significantly reduced. This has also to be considered for nutritional calculation so as not to misrepresent the nutrient composition of the fried product. There have been positive developments in producing frying fats which are low in trans-fatty acids, and fried products low in heat-induced compounds which can address toxicological concerns such as acrylamide formation.

Quality assessment of frying fats and fried snacks during continuous deep-fat frying at different large-scale producers

Changes in quality characteristics of frying oils and fried snacks were studied by means of two experiments carried out at six large-scale Spanish producers. Analytical parameters recorded in order to monitor oil degradation during continuous frying included viscosity, dielectric constant (DC), C18:2n − 6/C16:0 ratio, iodine value, acid value (AV), lipid UV absorption, p-anisidine value (AnV), and polymer and diacylglycerol contents. Changes in DC, AV, lipid UV absorption, AnV and polymer content were useful to monitor frying oil quality. Only in some oils and frying conditions, the evolution of AV paralleled the changes in the rest of useful parameters. For all tested conditions, parameters that were most closely related to oxidation, such as AnV, lipid UV absorption, polymer content and DC, were the best complement/alternative to AV for routine quality control of frying oils during continuous deep-frying. Lipid extracts from fried snacks were also analyzed and the results were similar to those obtained for their counterpart frying oils. We conclude that continuous deep-fat frying produces commercial fried snacks with a relatively uniform and high quality.