Elsevier

Food Chemistry

Volume 84, Issue 2, February 2004, Pages 219-222
Food Chemistry

Two novel synthetic antioxidants for deep frying oils

https://doi.org/10.1016/S0308-8146(03)00205-XGet rights and content

Abstract

Lauryl tert-butylated hydroquinone (LTBHQ) and its oxidized compound, lauryl tert-butylated quinone (LTBQ) were synthesized from tert-butylated hydroquinone (TBHQ) and lauryl alcohol. Their antioxidant activities were investigated. At temperatures higher than 140 °C, the antioxidant activity of LTBHQ and LTBQ was higher than TBHQ. In emulsions, these two compounds had stronger antioxidant activity than TBHQ, butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA).

Introduction

Butylated hydroxytoluene (BHT), butylated hydroxyanisol (BHA), tert-butylated hydroquinone (TBHQ) and propyl gallate are the most widely used antioxidants in the food industry, especially for oils and fatty foods. These synthetic antioxidants are highly active and cheap. They are colourless, odourless and tasteless, but they are generally active only at low temperature. However, at high temperature, such as in deep frying and baking at 150–200 °C, these compounds are ineffective. At high temperatures, BHA, BHT and TBHQ are evaporated with steam and PG decomposes particularly when a large quantity of water is expelled from foods during frying or baking. (Lee & Kim, 1979, Kim & Pratt, 1990, Warner et al., 1986).

The frying oils are easily autoxidized at high temperatures and partly polymerized and partly decomposed on oxidizing at high temperature if adequate antioxidants are not present. The oils become viscous and darkened; nutritional components, such as VE, VA, VK, VD and essential fatty acids in the frying oils, are destroyed quickly (Weng, 1993). Moreover, foods fried in oxidized oil can develop an unpleasant flavour. The shelf lives of fried foods are short and might develop off-flavours if sufficient amounts of antioxidant do not remain in the foods after frying (Yagi, 1988).

Effective antioxidants, for deep frying of oils, are very important in practice. In this paper, two antioxidants, synthesized from TBHQ and n-lauryl alcohol for deep frying oils are reported and their antioxidant activity is investigated.

Section snippets

Materials

Lard was rendered in the laboratory and stored in a deep freezer for use. Soy oil was purchased from Shanghai Oil and Fat Co. (Shanghai, China). TBHQ, BHA, BHT and Tween 20 were purchased from Shanghai Chemical Reagent Co. (Shanghai, China). Other chemicals used in this experiment were all AR grade and from this company. Silica gel was from Qingdao Chemical Factory (Qingdao, China).

Synthesis and purification of the compounds

A mixture of TBHQ (5 g, 30 mmol) and n-lauryl alcohol (5.6 g) was added to 85% phosphoric acid (1.7 g). The

Results and discussion

Lauryl tert-butylate hydroquinone (LTBHQ) and lauryl tert-butylated quinone (LTBQ) were synthesized from n-lauryl alcohol and TBHQ. Phosphoric acid (0.5 mol/mol TBHQ) was used as catalyst. The mixture of TBHQ and lauryl alcohol (1:1, mol/mol) were refluxed in toluene (200 ml/mol TBHQ) for 6.5 h. The yields were 16.0±0.8% for LTBHQ and 6.1±0.9% for LTBQ.

The lauryl group can attach at the 5- or 6-position of TBHQ, but the 5-isomer may be slightly more than the 6-isomer, because the 5-position is

Acknowledgements

The authors thank the Natural Science Foundation Commission of China for the research grant (approval number: 20242007).

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