Publisher Summary During frying, it is well-known that a wide variety of chemical reactions results in the formation of new compounds that differ in molecular weight and polarity. This chapter provides a summary of the main groups of alteration compounds formed during frying, resulting from the oil or fat being exposed to high temperatures in the presence of air and moisture. Hydrolysis occurs due to the presence of moisture in the food. This involves breaking ester bonds and releasing free fatty acids, monoglycerides, and diglycerides. These compounds have higher polarity and lower molecular weight than the original Triglycerides (TG). While diglycerides, monoglycerides, and fatty acids likewise originate in the stage before intestinal absorption and hence have no relevance from a nutritional point of view, non-volatile alteration products do modify the nutritional properties of oils and fats. Therefore, the evaluation of the complex mixture of non-volatile compounds, ingested as a part of fried food, and the understanding of its dependence on the main variables of the frying process are a subject of great interest not only for processors and food technologists, but also for nutritionists and consumers. The chapter addresses the major non-volatile alteration compounds in used frying oils and fats, oxidized monomeric, dimeric, and higher oligomeric TG, also named oxidized monomers, dimers, and polymers. It discusses their formation and the analytical techniques used for their quantitation, as well as their occurrence in used frying fats.

Formation and analysis of oxidized monomeric, dimeric, and higher oligomeric triglycerides.

The action of antioxidants to delay lipid oxidation in fats and oils is well known although most of the information is related to their effects at room temperature during storage or at the moderate temperatures of the accelerated tests to measure oil stability. However, oxidation at the high temperatures of food processes like frying, is more complex because the availability of air is unknown and both oxidative and thermal reactions are simultaneously involved. In this review, the main studies defining the action of natural and synthetic antioxidants at frying temperatures are summarized. This review has been divided into two main parts concerning the information on natural antioxidants, i.e. tocopherols and other phenolic compounds present in specific oils like olive, sesame and rice bran oils, and on synthetic antioxidants, i.e. BHA, BHT and TBHQ.

http://digital.csic.es/bitstream/10261/25856/1/1053.pdf

Action and fate of natural and synthetic antioxidants during frying

The stability of camellia oil (saturated fatty acid: monounsaturated fatty acid: polyunsaturated fatty acid = 1:7:1) after frying potatoes was compared with palm oil (saturated fatty acid: monounsaturated fatty acid: polyunsaturated fatty acid = 4:4:1) and peanut oil (saturated fatty acid: monounsaturated fatty acid: polyunsaturated fatty acid = 2:4:4). Oil samples were evaluated for acid value, iodine value, peroxide value, p-anisidine value, total oxidation value, tocopherols content, and fatty acids composition. There was the least change in fatty acid composition in camellia oil among the three edible oils. The α-tocopherol was more vulnerable to heat degradation than γ-tocopherol and δ-tocopherol, and α-tocopherol was completely degraded before the whole frying process was done for palm and peanut oils. The oxidative stabilities of the three edible oils were in the order of camellia oil > palm oil > peanut oil. The oxidative stability was mainly determined by the calculated oxidizability value relate...

https://www.tandfonline.com/doi/pdf/10.1080/10942912.2014.913181

Comparison of Oxidative Stability among Edible Oils under Continuous Frying Conditions

The main goal of this work was to investigate the stability of standard palm olein (SPOo) and special quality palm olein (SQPOo) under continuous frying conditions. The rate of free fatty acid (FFA) formation was slightly higher for SPOo than SQPOo during 56 h of frying. An equilibrium state was reached at around 40 h for SPOo and 32 h for SQPOo, whereby FFA varied within a narrow range of 0.30–0.32 and 0.22–0.25%, respectively. Smoke point of SPOo and SQPOo progressively dropped from 212 to 184 °C and from 227 to 191 °C. Tocols of SPOo and SQPOo declined from 550 to 273 mg kg−1 and from 720 to 447 mg kg−1 after 56 h of frying, respectively. Oxidative stability of both oils decreased after the successive frying. Induction time of SPOo dropped from 22.3 to 14.9 h while SQPOo decreased from 25.5 to 18.3 h. Polar and polymer compounds increased as frying progressed. The SPOo had higher levels of polar compounds, averaging 11.8%, compared to the 10.2% in SQPOo. However, SPOo had lower levels of polymer compounds compared to SQPOo, averaging 2.1 and 2.5%, respectively. Hence, this work confirms that frying performance using SPOo was comparable to SQPOo for use in industrial production of snack foods (potato chips).

Comparison of the Frying Stability of Standard Palm Olein and Special Quality Palm Olein

The objective of this study was to compare two oils with different polyunsaturated/saturated (P/S) fatty acid ratios, refined olive oil (P/S 0.75) and palm olein (P/S 0.25), in frying French fries. The chemical qualities of the oil residues extracted from the French fries were assayed for five consecutive batches fried at 1-h intervals. The levels of total polar compounds, free fatty acids, p-anisidine value and phytosterol oxidation products (POPs) were elevated in French fries fried in both oils. The level of total polar compounds increased from 4.6 in fresh refined olive oil to 7.3% in final batches of French fries. The corresponding figures for palm olein were 9.8–13.8%. The level of free fatty acid in fresh refined olive oil increased from 0.06 to 0.11% in final products. These figures for palm olein were 0.04–0.13%. The p-anisidine value increased from 3.7 to 32.8 and 2.5 to 53.4 in fresh oils and in final batches of French fries in refined olive oil and palm olein, respectively. The total amount of POPs in fresh refined olive oil increased from 5.1 to 9.6 μg/g oil in final products. These figures were 1.9 to 5.3 μg/g oil for palm olein.

Frying Quality Characteristics of French Fries Prepared in Refined Olive Oil and Palm Olein

Four vegetable oils with different polyunsaturated/saturated fatty acid ratio (P/S): 52 for sunflower oil, 3,4 for canola rapeseed oil, 04 for a blend of palm oleic and canola rapeseed oil (80:20), and 03 for palm olein were assayed for stability of crisps fried in these oils during storage at 60o C The action of ascorbyl palmitate with special attention to its synergistic effect on the natural antioxidants was also tested by addition to the fried potatoes The evolution of the oxidative stability was measured through peroxide value, quantitation of tocopherols and tocotrienols, and induction time (IT) by means of Rancimat Oil degradation during frying was very low as both polar compound percentages and natural antioxidant had similar levels to those present in refined oils Evolution of analytical parameters during storage results indicated that oil unsaturation degree or P/S had a much more importance on stability of the product than had the content and type of natural antioxidants and the addition of AP Nevertheless, addition of AP to the fried potatoes had a significant effect resulting in higher retention of natural antioxidants, higher IT and lower PV at any storage time

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C. Urra

Papers

Stability of potato chips fried in vegetable oils with different degree of unsaturation. Effect of ascorbyl palmitate during storage