The chemical and physical changes that occur in frying fats during use and their significance to fat life and to finished product quality are reviewed. The more commonly used quality control tests for monitoring these changes are examined as is their applicability to food service institutions and food processors. The advantages and disadvantages of these tests and possible modifications to improve their ease for on-the-spot testing are discussed. Chemical tests such as free fatty acids (FFA), thiobarbituric acid (TBA) tests and peroxide value (PV) are available to those operations with laboratory facilities, whereas sensory and physical tests, including foam height, color, smoking, viscosity, odor and product flavor, are generally relied on by most food service facilities for on-the-spot assessment. The reliability of these tests, however, depends on the source and type of frying fat, the food being fried, and, in the case of the sensory and physical tests, on the skill and experience of the operator. Studies completed recently in this laboratory found a high correlation between polar compounds or FFA and length of frying time which suggests that either could predict oil abuse accurately. Recent adaptations which could facilitate on-the-spot testing by semi-skilled personnel (including a spot test for FFA and an instrument capable of monitoring the change in dielectric properties of an oil during frying) will be examined. Regardless of the quality control test used, the question remains of specifying reliable cutoff levels which can be related to the health and sensory constraints. This problem is also discussed.

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Canola meal, a by‐product of oil pressing, is a rich source of phenolic antioxidants. However, its use in the food and feed sector is still limited by the need for greener, sustainable, and more cost‐effective extraction methods. This study used accelerated solvent extraction (ASE) to enhance the extraction efficiency of the phenolic antioxidants. The high selectivity and short extraction time associated with ASE were ideal for obtaining high yields of these antioxidants. The structure‐based activity of phenolic compounds may be influenced by the high pressure and temperature of the greener ASE process. The present study evaluated the effect of temperature (140, 160, and 180 °C) and pressure (1,500 psi) on the extraction and yield of phenolic compounds from canola meal as well as the solvent type (ethanol and methanol) and concentration (30%, 40%, 60%, and 70% v/v). Antioxidant activity was determined by 2,2‐diphenyl‐1‐picrylhydrazyl, ferric reducing/antioxidant power assay, and ion‐chelating activity. The highest yield of phenolic compounds was obtained with 70% methanol (20.72 ± 1.47 mg SAE/g DM [milligrams of sinapic acid equivalents per gram of dry matter]) and 70% ethanol (24.71 ± 2.77 mg SAE/g DM) at 180 °C temperature. A similar trend was observed for the antioxidant activity of the extracts and their total flavonoid content. The structure‐based antioxidant activity of the extracts examined increased with the increase in the percentage of the extracting solvent (P > 0.05). This study established ASE as an efficient green method for extracting phenolic compounds from canola meal, with potential application for the production of natural bioactive compounds from underutilized agricultural by‐products. Practical Application ASE is an efficient eco‐friendly method for extracting phenolic compounds from agricultural by‐products such canola meal. Under the conditions of high pressure and temperature, ASE significantly improved the yields of phenolic compounds, sinapine, sinapic acid, and canolol. Under these conditions, water, as an extractant, was not effective in extracting sianpine. Moreover, it was much less effective than both 70% ethanol and 70% methanol in extracting sinapine or canolol. These phenolic compounds are of great interest as natural antioxidants for enhancing the shelf life of food products. They also represent new sources of neutraceuticals for improving human health.

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The search for endogenous components in food ingredients exhibiting antioxidant activity has been intensified in order to eliminate synthetic antioxidants. Tocopherols are widely used as natural antioxidants, although their protective ability is not always sufficient. Buckwheat seed components were evaluated for antioxidant and free radical-scavenging activities using solvents of different polarities to isolate components from hulls and groats. Components extracted from buckwheat hulls were pro-oxidant in canola oil. Antioxidant activity of extracts from buckwheat groats increased when more polar solvents were used for extraction. The highest activity was observed for the methanolic extract. Radical-scavenging activity of buckwheat extracts was analyzed with DPPH (2,2-diphenyl-2-picryl-hydrazyl). This activity increased when the more polar solvents were used for extraction, with the highest activity observed for the methanolic extract. It was also observed that the radical scavenging effectiveness of extracts was concentration dependent. Analysis revealed the presence of tocopherols in the hexane extract, while methanolic extracts were rich in phenolic acids and flavonoids. JAOCS 75, 1595-1601 (1998).

A study was conducted to compare the relationship between frying stability and levels and degradation rates of tocopherols in regular and three modified canola oils. Oils were heated at 175 ± 2°C for a total of 72 h, with french fries fried intermittently. Frying stability was compared based on the rates of formation of free fatty acids (FFA) and total polar compounds (TPC). Significant differences (P < 0.05) were identified between oils using analysis of covariance and t-tests for multiple comparisons. No significant differences were observed in the rates of FFA formation among the canola oils during frying. Nevertheless, regular canola (RCO) and high-oleic, low-linolenic acid canola (HOLLCO) oils produced less FFA compared to higholeic (HOCO) and low-linolenic acid (LLCO) canola oils. However, LLCO and HOCO both had significantly (P < 0.05) faster rates of TPC formation compared to HOLLCO or RCO. HOLLCO with the highest level of tocopherols (893 mg/kg) exhibited a slow rate of degradation which accounted for a halflife of 48-60 h of frying. RCO, with a lower level of tocopherols (565 mg/kg), however, had the slowest degradation rate with a half-life of >72 h. In contrast, HOCO and LLCO with 601 and 468 mg/kg tocopherols, respectively, both exhibited a half-life for tocopherols of 3-6 h of frying. An inverse relationship was observed between TPC formation and the reduction of tocopherol. Thus, the greater frying stability of RCO and HOLLCO appears to be affected far more by the rate of tocopherol degradation than by any changes in fatty acid composition.

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