ANTIOXIDANT POTENTIAL OF 5-n-PENTADECYLRESORCINOL

ANTIOXIDANT POTENTIAL OF 5-n-PENTADECYLRESORCINOL A. WINATA and K. LORENZ'

Department of Food Science and Human Nutrition Colorado State University Fort Collins, Colorado 80523 Accepted for Publication June 26, 1996

ABSTRACT The antioxidantpotential of 5-n-pentadecylresorcinolwas determined with jive different oils. Alkylresorcinol (AR) was added at 0.025%, 0.050% and 0.075%, respectively. For comparison, 0.01 % butylated hydroxyanisole (Bh!A) was used as antioxidant. Oils were incubated at 10, 25 and 4OC. Peroxide values were determined at different time intervals. Accelerated tests using a pro-oxidant were also conducted with each oil. AR was shown to slow oxidative rancidity of the oils. The ability ofAR to slow lipid oxidation in cereal products was also studied. Wheat bran, rye bran and whole grain millet meal were treated with 0.050% and 0.075% AR and B l U , respectively, and stored at 4OC. Peroxide values were determined at different time intervals. AR was shown to slow lipid oxidation in cereal products. INTRODUCTION Alkylresorcinols (AR) are amphiphilic phenolic lipids which have been found in plants from a number of different families notably the Anacardiaceae (such as poison ivy, cashew nut shell, poison oak), Proteaceae (such as GreviZZa pyramidalis), Gramineae (such as cereal grains), Araceae (such as Philodendron scandens) and certain bacterial and algae sources (Tyman 1979; Madrigal et al. 1977; Reffstrup et al. 1982; Kubus and Tluscik 1983; Reffstrup et al. 1985; Bandyopadhyay et al. 1985). Plant phenolic lipids have been classified as alkyl or alkenyl derivatives of catechol, resorcinol, and phenol. The characteristic feature of these compounds is the straight, odd-numbered aliphatic chain with the length dependent on the origin of lipid. The aliphatic chain is saturated or contains one to three double bonds of cis-conformation located mostly at the C8, C11 and C14 atoms of the chain.

' Corresponding author. Journal of Food Processing and Preservation 20 (1996) 417-429. All Righfs Reserved. O Copyright 1996 by Food & Nutrition Press, Inc., Trumbull, CT 06611

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Alkylresorcinols are structurally similar to commercially used antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG)and tertiary butylhydroquinone (TBHQ). They might, therefore, function as antioxidants when added to fats and oils and lipid-containing food products such as cereal brans. At the present time, these compounds do not have FDA approval.

MATERIALS AND METHODS Oil Samples and Treatments

Fresh samples of corn oil, olive oil, safflower oil, sunflower oil and soybean oil were obtained from commercial sources. Two hundred grams of each oil sample in Erlenmeyer flasks were subjected to five different treatments as follows: flask one served as a control, with no A R s added; to flasks two to four 5-npentadecylresorcinol (Aldrich Chemical, Milwaukee, WI), a commercially available AR, were added respectively, 0.02596, 0.050%, and 0.075% AR based on oil, and to flask five, 0.01% of BHA (butylated hydroxylanisole) was added. All oil samples were incubated at threedifferent temperatures (10,25 and 40C) respectively. Peroxide values were determined after certain time intervals. The experiments were stopped when peroxide value exceeded 70 Meqlkg. Accelerated Stability Test for Oil Samples Twenty mL of each oil were added to each of three test tubes. Alcoholic cupric chloride solution 0.0016% w/v, a pro-oxidant, was added to tubes 1 and 2. To tube 2, were added either 0.05% or 0.075%by weight of 5-n-pentadecylresorcinol (Aldrich Chemical, Milwaukee, WI)or, 0.05 9% or 0.075 % of BHA, a commercial antioxidant. Tube 3 served as a control with no antioxidant or pro-oxidaut added. All three tubes of a given oil sample were placed in a gently boiling water bath and air was passed through them for 1 h. Ten gram samples from each tube were used for peroxide value determinations. Peroxide Value Determination Two samples (10 g) from each variable were weighed into 500 mL Erlenmeyer flasks. Fifty mL of acetic acid-chloroform (60:40) were added. The flasks were shaken for 1 to 2 min until lipids were dissolved. Saturated potassium iodide solution (1 mL)was added while rapidly rotating the flask for 15-20 s. One hundred mL distilled water was then added, followed by 10 drops (approximately 0.5 mL) of 1% starch solution. The samples were titrated with 0.1 N sodium thiosulfate until the disappearance of blue color. A blank was run simultaneously by omitting only the oil (AOAC 1975).

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The peroxide values (P.V.)were calculated as follows:

P. B. (MeqJkg lipid) = {(S-B) x N x lOOO>/W where

s = B

=

N

=

mL of sodium thiosulfate to titrate samples mL of sodium thiosulfate to titrate blank normality of sodium thiosulfate solution (0.1N) weight of sample in grams (10 g)

w =

Statistical Design and Analysis For all experiments in this section, a completely randomized design (CRD) was used to determine the effects of antioxidants and lipid oxidation (Peroxide Value) in oils. All the results are the average values of two replicates. All of the data were analyzed by using the SAS system (SAS 1987). AR AS ANTIOXIDANT IN CEREAL SAMPLES

Samples Included in this study were rye bran (3.45% lipids), wheat bran (3.25% lipids), and a whole grain millet sample (3.97% lipids). The wheat, rye and millet samples were grown in Colorado in 1993. The wheat and rye samples were milled in a Quadrumat Junior mill (C.W. Brabender, South Hackensack, New Jersey) to obtain the bran samples. The millet sample was ground into a whole grain meal using a Udy Cyclone mill (Udy Corp., Fort Collins, CO). Percent crude fat was determined using AACC procedure 30-20(AACC 1983).

Treatments 5-n pentadecylresorcinol was dissolved in 60 mL 100% ethanol at 0,025%, 0.05%, and 0.075% based on the weight of the bran or meal. 0.01% of butylated hydroxyanisole (BHA) was also dissolved in 60 mL 100% ethanol based on the weight of the sample. One hundred grams of each bran and the whole grain meal in a mixing bowl were subjected to five different treatments as follows: Treatments:

(1) (2) (3) (4) (5)

control--no antioxidant. 0.025% AR added. 0.050% AR added. 0.075% AR added. 0.010% BHA added.

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Each sample was coated individually by mixing in a Kitchen Aid mixer (Hobart, Troy, OH) for 20 min. Samples were then placed into 200 mL beakers, and incubated at 4OC. Peroxide value was determined at certain time intervals using the same method as described previously.

Statistical Design and Analysis For cereal sample experiments, a completely randomized design (CRD) was used to determine the effects of antioxidants in slowing rancidity. All the results are the average values of two replicates. Tests of significance among treatment means were performed by Least Significant Difference (LSD). All of the data were analyzed by using the SAS system (SAS 1987).

RESULTS AND DISCUSSION Incubation at 10C At 1OC peroxide value of each oil changed only slightly during storage due to low temperature and lack of light. Under this condition, the oxidation process of oil proceeds very slowly. Even after 252 days or approximately 8.5 months, the oils were still not rancid-they had not reached 70 Meqkg. In comparison with the control without antioxidants, at day 252 of storage, AR and BHA with concentrationsof0.07596 and 0.0196 however significantly (p