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The phenolic compounds of Thompson grape bagasse were extracted using a 95:5 (vol/vol) ethanol/water mixture. Measurement of the antioxidant activity in refined soybean oil of bagasse grape extract was performed by using two different methods, the Rancimat method and the Schaal oven method in conjunction with peroxide value determination. The antioxidant activity of the extract was compared to the tertiary butyl hydroquinone (TBHQ) and butylated hydroxyanisole (BHA) activity. The bagasse grape extract showed similar antioxidant activities in both methods employed. At all concentrations tested [0.1, 0.3 and 0.5% of total phenols (TP)] the extract exhibited appreciable activity, which exceeded the activity of BHA. At some concentrations (0.3 and 0.5% TP) the extract exhibited activity comparable to that of TBHQ. Bagasse is a byproduct with a high content of phenolic compounds and is a good source of natural antioxidants.

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The purpose of this study was to evaluate the trans fatty acid (TFA) composition and the tocopherol content in vegetable oils produced in Mexico. Sample oils were obtained from 18 different oil refining factories, which represent 72% of the total refineries in Mexico. Fatty acids and TFA isomers were determined by gas chromatography using a 100-m fused-silica capillary column (SP-2560). Tocopherol content was quantified by normal-phase high-performance liquid chromatography using an ultraviolet detector and a LiChrosorb Si60 column (25 cm). Results showed that 83% of the samples corresponded to soybean oil. Seventy-two percent of the oils analyzed showed TFA content higher than 1%. Upon comparing the tocopherol contents in some crude oils to their corresponding deodorized samples, a loss of 40-56% was found. The processing conditions should be carefully evaluated in order to reduce the loss of tocopherols and the formation of TFA during refining.

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The effect of natural antioxidants was tested by oxidative stability index (OSI) in refined soybean oil (RSO) using Rancimat method. Phenolic compounds of Thompson grape pomace were extracted with 95:5 (v : v) ethanol : water. The antioxidant activity of grape pomace extract (GPE) obtained was compared with those of rosemary extract (RE), and tocopherols mix (TM) known as covi‐ox T‐70. The synergistic effect of citric acid was also evaluated. Results showed a total phenols content of 17.39 mg (+)‐catechin equivalents per g of GPE. Thompson GPE at 0.3 and 0.5% (w/w) exhibited greater antioxidant activity than TM. RSO containing GPE or RE at 0.5% (w/w) showed an OSI higher than 48 h at 110C. Citric acid did not show synergistic effect with GPE. However, a synergistic effect for TM at 0.02% (w/w) with citric acid at 1.0% (w/w) was observed. Citric acid at 2.0% (w/w) with RE at all concentrations tested also displayed synergism. PRACTICAL APPLICATIONS Synthetic antioxidants are widely used in the food industry to delay fat oxidation; however, their utilization has been questioned due to toxicology concerns. Researchers have recognized the need to identify new natural antioxidants to use as additives. In this study, we measured total phenolics content of Thompson grape pomace extract (GPE) and found that the antioxidant activity of this extract was stronger than tocopherols from soybean oil. We propose that GPE can have applications as a food antioxidant.

The stability parameters of 22 samples of soybean oil produced in Mexico were determined. Samples were analyzed for moisture, color, free fatty acids, peroxide value, p-anisidine value, fatty acid profile, metals, flavor, and Rancimat test for oxidative stability. Results obtained were compared with the stability parameters of soybean oils produced in the United States and Costa Rica. The fatty acid profile in all samples analyzed corresponded to the expected profile for a 100% soybean oil. Sixtyfour percent of the oils had oxidative stabilities similar to those reported for soybean oils from the United States and Costa Rica. This suggests that in spite of the good quality, the soybean oil production process in Mexico needs further improvement. Especially important is maintaining appropriate control during the degumming and bleaching steps. Special consideration should be given to preserving the natural antioxidants present in the oil.