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Effect of UV Processing Treatments on Soy Oil Conjugated Linoleic Acid Yields and Tocopherols Stability

Abstract

Photoirradiation has been used to synthesize 20 % conjugated linoleic acid (CLA) in soy oil with an iodine catalyst. CLA yields are affected by ultraviolet (UV) irradiation time, Magnesol® adsorbent treatment, iodine concentration and mixed tocopherols. However, these factors in combination had not been studied. Therefore, the objectives of this study were to determine the effect of (1) a combination of photoirradiation time, Magnesol® adsorbent treatment and added mixed soy tocopherols on CLA yields and the oxidative stability of CLA-rich soy oil, (2) UV light on mixed tocopherol stability, as tocopherols enhance CLA yields during photoirradiation. Soy oil was initially treated with 5 % Magnesol®. Iodine at 0 and 0.35 % was mixed with Magnesol®-treated soy oil and irradiated for 12 and 6 h. The irradiated oil was again treated with Magnesol®, mixed with 0, 0.35 or 0.175 % iodine; 1400 MT and irradiated for 12 or 6 more hours. CLA content in soy oil was determined by conventional gas chromatography-flame ionization detector. The oxidative stability of the oil was determined by measuring peroxide value (PV). The tocopherols stability was determined by high performance liquid chromatography. The results showed that increasing photoirradiation time increased CLA yields and lowered PV. Magnesol® adsorption produced highest CLA yield for all treatments by removing peroxides in RBD soy oil. The γ-tocopherols exhibited highest stability during UV irradiation. The order of tocopherol degradation was α-tocopherol > δ-tocopherol > γ-tocopherols.

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Abbreviations

CLA:

Conjugated linoleic acid

UV:

Ultraviolet

LA:

Linoleic acid

MT:

Mixed tocopherols

CLARSO:

CLA-rich soy oil

HPLC:

High performance liquid chromatography

RBD soy oil:

Refined, bleached and deodorized soy oil

GC-FID:

Gas chromatography-flame ionization detector

PV:

Peroxide value

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Acknowledgments

We are grateful to the Arkansas Soybean Promotion Board for financial support and Riceland Foods Inc. (AR) for providing us with the RBD soy oil.

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Correspondence to Andrew Proctor.

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Yettella, R.R., Henbest, B. & Proctor, A. Effect of UV Processing Treatments on Soy Oil Conjugated Linoleic Acid Yields and Tocopherols Stability. J Am Oil Chem Soc 90, 863–870 (2013). https://doi.org/10.1007/s11746-013-2219-y

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  • DOI: https://doi.org/10.1007/s11746-013-2219-y

Keywords

  • Conjugated linoleic acid
  • Mixed tocopherols
  • Soy oil
  • GC-FID
  • Peroxide value
  • Photoisomerization