Frying Oil Quality Research Articles

SHELF‐LIFE OF FRIED POTATO CHIPS USING RBD PALM OLEIN, SOYBEAN OIL AND THEIR BLENDS

ABSTRACTShelf‐life of potato chips fried in refined, bleached and deodorized palm olein (RBDPO), soybean oil (SBO) and their blends was evaluated. Potato slices were fried for 130 s at 180 PT 5C at 30 min intervals over a period of 5 h/day for 5 consecutive days. Indicators of frying oil quality with the shelf‐life of fried products chosen were total polar component and acid value. This study indicated that RBDPO was better than SBO for the preparation of fried potato chips in terms of shelf‐life of products. The blends were also slightly better than SBO with increasing proportion of RBDPO. However, the effects were minimal on the rate of development of rancidity in fried products beyond the fourth day of frying in the frying medium.

Palm olein quality parameter changes during industrial production of potato chips

AbstractNew legislation introduced in South Africa for the quality of used frying oils has resulted in the need to identify quicker, more suitable methods that correlate well with results from two official methods, namely, total polymerized glycerides and total polar components. Oil and product samples were taken at regular intervals during a commercial frying process in palm olein. Oil samples were analyzed for a number of different quality parameters viz. tocopherol content, dielectric constant, total polymerized glycerides, total polar components, tertiary butylhydroquinone (TBHQ) content, anisidine value, Rancimat induction period, and free fatty acid content, and the results statistically compared to results from official methods. Oil was expressed from product stored under accelerated conditions and analyzed for the same quality parameters. Fried product was also subjected to sensory evaluation to measure the degree of oil deterioration and sensory preference. The frying trial was successfully executed with refined, bleached, and deodorized palm olein and the frying oil used to a free fatty acid (FFA) content of 0.41%. Oil and product sampling were done at different FFA value levels. Frying oil quality was verified at the onset of the trial and at regular intervals. The frying oil total polar component value increased to approximately half of the limit set by the official regulation. This point was reached mainly due to the high starting value of the fresh oil. Frying oil total polymerized glycerides increased from below 1% to 2.1%. This increase is negligible when compared to the general trend for polyunsaturated oils. The alternative laboratory methods used for predicting oil quality can be rated as follows: total tocopherol content >dielectric constant >FFA >TBHQ content >anisidine value >Rancimat induction period. The first three methods correlated well with total polar component levels and it is recommended that the dielectric constant and FFA measurements be applied for monitoring oil condition during frying. It is possible that viscosity changes could be used for the monitoring of polyunsaturated frying oils. Evaluation of oil extracted from product revealed a negligible effect of non‐oil components on oil quality parameters. The same was observed when product was stored at −10°C and at 37°C.

Influence of used frying oil quality and natural tocopherol content on oxidative stability of fried potatoes

AbstractSunflower oil (SO) and high‐oleic sunflower oil (HOSO) were used to prepare fried potatoes by either discontinuous or continuous laboratory frying. Fried potatoes that had been fried in oils of differing quality were stored at 60°C for up to 30 d and evaluated for polar compounds, polymers, peroxide value, oil stability index, and α‐tocopherol content. Results obtained through the various methods applied were consistent and indicated that the length of the induction period could not be explained only on the basis of the degree of unsaturation or polar compound levels in fried potatoes before storage. α‐Tocopherol content also had a significant influence as potatoes fried in HOSO, with 16% polar compounds and only 10 mg/kg α‐tocopherol at the starting point of storage, were oxidized more rapidly than potatoes fried in SO with a comparatively higher degradation level, 19% polar compounds, and 100 mg/kg α‐tocopherol.

Effect of vacuum frying on the oxidative stability of oils

AbstractThe purpose of this study was to evaluate frying oil quality with different assessment methods during vacuum frying of carrot slices. In six consecutive days, palm oil, lard, and soybean oil were fried under vacuum at 105°C for 20 min each hour in an 8‐h shift. Peroxide value, acid value, carbonyl value, total polar components, dielectric constant (Food Oil Sensor reading), viscosity, and fatty acid composition were used to evaluate the quality of these oils. Results showed that palm oil and lard possess greater thermal stability than soybean oil. The decrease in C18:2/C16:0 ratio was greater for soybean oil than the other two oils. Of the assessment methods used, peroxide value, carbonyl value, total polar components, and dielectric constant all showed good correlation with frying time and between each other. Viscosity was suitable to assess vacuum‐fried lard and soybean oil, but not palm oil. The measurement of dielectric constant, on the other hand, appeared to be unsuitable to assess vacuum‐fried soybean oil.

Regulation of used frying fats and validity of quick tests for discarding the fats

During deep-fat frying, a complex series of reactions takes place resulting in hydrolysis, oxidation and polymerization of the oil. As quality of fried foods is affected by that of the oil, regulations or guidelines have been established in many countries to guarantee high quality foods. In this lecture, present regulations mainly focusing on oil deterioration and setting limits to alteration compounds are reviewed. Among analytical methods to control oil quality, polar compound and polymer determinations stand out. Studies carried out in different countries indicate the need for improving the quality of frying oil to produce more nutritious fried foods. Practical deep-fat frying can be divided in industrial and fast-food segments, characterized by the use of continuous and discontinuous fryers, respectively. From the analysis of a high number of samples it is deduced that the present situation is very different in both segments and that the main problem is to determine when the fat or oil has to be replaced where there are no laboratory facilities. Hence, simple rapid analytical tests to substitute for official methods are neccesary to monitor oil quality in restaurants and fried food outlets. Data of validity of rapid tests will be presented with particular emphasis on the utility of commercialized kits like Oxifrit-Test and Veri-Fry to improve the quality of frying fats and oils.

Industrial Frying Process

This paper is concerned with the industrial frying process and in particular the role of the frying oil and the influence this has on the food. Attention is drawn to various factors that can adversely affect the quality of the frying oil. In this paper the term «frying oil» is used. Other publications may refere to frying fat or frying shortening. As these are all used well above their melting points, and are fully liquid, the term oil is preferred by the present author, there being no quality difference between the products so named. The quality of oil or fat used for frying is of paramount importance with regard to the quality of the fried food. The amount of oil absorbed in different fried foods varies; battered fish or chicken absorb about 15% frying oil, while breaded fish or chicken absorb up to 20% frying oil. The amount of oil absorbed by doughnuts varies from 15-20% of their final weight. This is, of course, in addition to the shortening used in preparation of the dough, giving a final oil/fat content of up to 30%. Standard or traditional potato crisps absorb the highest quantity of oil, and up to 35 or 40% of the final food may be frying oil. Recently, modern technology has been introduced to produce low-fat crisps, but these still have about 20% absorbed oil. It should therefore be remembered that the fat used for frying becomes part of the food we eat. The most important aspect of industrial frying is therefore the frying oil, and in surveying factors that affect frying oil quality, this paper reviews (a) oil properties and composition; b) transport, packaging and storage of oil; c) the nature of the food fried and its interaction with the frying oil; d) the frying equipment and the process of frying; and e) the evaluation of the quality of the frying oil during use. Each of these factors is important in its own way, and it is of no advantage to concentrate on one or two, or even three, of these aspects without appreciating that there may be additional influences on the quality of the frying oil, and thus the fried food.

Regulating the use of degraded oil/fat in deep‐fat/oil food frying

During frying, the degradation of oil produces harmful compounds. Improper monitoring of oil‐discard times in restaurants either risks the public health or causes financial losses to industries. Measuring the oil quality is a complex problem and an online sensor is needed. The process of frying reviewed includes moisture, heat and fat/oil transfer, crust formation and various structural, textural and chemical changes in the product, and degradation of frying medium. Some of the European nations and the U.S. have specific regulations against the use of deteriorated frying oils. Due to the absence of a suitable online frying oil quality sensor for restaurant situations, it is difficult to implement any regulation against the use of deteriorated frying oil. Based on various regulations, a model regulation to increase the safety and quality of fried foods is discussed. Background and requirements for developing an online sensor to measure frying oil quality are discussed. Other related areas reviewed in this article are factors affecting oil penetration and absorption by the food, surfactant theory of frying, analytical indices, quick tests and acceptability of frying oil.

Calidad de las grasas de fritura en el sector de restauración de Andalucía

In this paper, analytical results obtained from 174 frying oil samples collected from 131 fast food shops and restaurants by Food Inspection Services, are summarized. Quantization of polar compounds indicated that about 35% of the samples had alteration levels higher than the limit established in the Spanish regulation for discarding frying fats (25% polar compounds). High levels of oxidized triglycerides and polymeric compounds were found in a significant number of oils which demonstrated the need for improving frying oil quality in this sector.

Tests Used for Examining the Quality of Frying Oils

AbstractThere are many tests available for examining the quality of frying oils. Since judgements can be quite different depending on the test used and the recommendations given the results are compared here and the best tests for examining the quality of frying oils are identified.

Effect of after‐cooking darkening inhibitors on stability of frying oil and quality of french fries

The effect of two after‐cooking darkening inhibitors, sodium acid pyrophosphate (SAPP) and calcium acetate (CaAc), and their combined effect on frying oil stability and quality of french fries produced were evaluated over a period of 72 h. Samples of frying oil and par‐fried french fries were taken at 3‐h intervals through each experiment and analyzed for selected chemical and physical parameters. As the frying time increased, all the oil samples contained increased amounts of deterioration products. The color index and free fatty acid (FFA) values were highly correlated with frying time. There were no significant effects on oil properties in terms of FFA until 9 h of frying among the 4 pretreatments. However, from 12 to 72 h of frying, oil used to fry potatoes treated with SAPP contained less FFA than oils exposed to CaAc alone or in combination with SAPP. The fat content of par‐fried french fries was approximately 0.11 g/g dry matter and remained relatively constant during extended frying. After‐cooking darkening of par‐fried french fries and final color of the fries were affected by the pretreatment, but not by the frying time.

Development and evaluation of a novel sensor for the in situ assessment of frying oil quality

An objective appraisal of the quality of frying oil is important to ensure a wholesome fried product of adequate shelf-life at an economical cost. A novel frying oil monitor has therefore been developed suitable for simple, reliable, in situ oil quality determination. A literature study was carried out which showed that the viscosity at 20–100°C was correlated with the frying oil quality. Extrapolation to frying temperatures yielded the specifications for a prototype probe which was subsequently adapted from a novel GEC Marconi viscometer. The probe was then evaluated for three frying media with differing chemical characteristics. The assay of polymerized and oxidized matter (POM) content was employed as the reference method. The trial showed that the probe can monitor the viscosity of frying media at 170°C and that this viscosity is correlated with the quality of the oil. In contrast to colour and free fatty acid content, which were also measured, the probe output showed only a weak dependence on the oil type. It was possible to define a cut-off value for the probe output for which the calibration curves for the three oils in the trial fell between the two limiting values given for the POM content of an acceptable frying oil, namely 10 and 15%. The probe can be used in situ in hot frying oil and is suitable for adaptation both as an inexpensive dip probe and as a continuous in-line monitor.

Effect of frying oil quality and TBHQ on the shelf‐life of potato crisps

AbstractThree different systems were used for the evaluation of the effect of frying oil quality and tertiarybutyl hydroquinone (TBHQ) on the shelf‐life of fried potato crisps. Batches of potato slices were fried for 4 min at 30 min intervals over a period of 5 h day−1 for eight consecutive days in refined, bleached and deodorised palm olein (RBD olein) without antioxidant (system 1); RBD containing 200 μg g−1 TBHQ at the start of the experiment (system 2) and RBD olein which had TBHQ topped up to a level of 200 μg g−1 at the start of each frying day (system 3). Sensory evaluation of crisps showed that there is an initial rapid decrease in shelf‐life with increase in fry number in all systems. There was only a comparatively smaller effect on shelf‐life with increase in fry number in later fryings. When the shelf‐life of crisps was related to the quality of oil in the frying medium, it was found that the shelf‐life of the product is only slightly affected when the oil had deteriorated beyond the acceptable limit of quality of frying oil, where the acceptable limit was taken as 27‐30% polar components and 1–2 mg potassium hydroxide g−1 oil. TBHQ does have a protective carry‐through effect. The protective effect is more pronounced when TBHQ is topped up to a level of 200 μg g−1 at the beginning of each frying day.

HPLC Analysis of Oxidative and Polymerized Decomposition Products in Commercial Vegetable Oils and Heated Fats

AbstractA high performance liquid chromatographic (HPLC) method has been developed to analyze oxidative and polymerized decomposition products in commercial vegetable oils and heated fats. The oil was passed through a SEP‐PAK where the minor constituents were concentrated. The SEP‐PAK was eluted with hexane‐ether 1:1 (v/v), and 2‐propanol. The first eluate contained unsaponifiables and neutral lipids, and the second eluate contained the more polar oxidative and polymerized decomposition products. The second eluate was analyzed by normal phase HPLC. Five commercial vegetable oils were analyzed, and similarities and differences were observed. Four soybean oil samples from different manufacturers also showed differences. Soybean oil heated at 185°C was collected periodically and analyzed. As the heating time increased, the oxidation and polymerization products also increased. Used frying fat samples from a commercial fried chicken manufacturer were analyzed. The frying oil quality reached an equilibrium during three days of operation, because the oil lost in frying was replenished daily with fresh shortening.