A comparative study on the formation of heterocyclic amines and cholesterol oxidation products in fried chicken fiber processed under different traditional conditions

Highlights

• Formation/inhibition of HAs & COPs in fried chicken fiber during processing were determined.

• HAs & COPs contents as affected by different oils, flavorings & temperatures were determined.

• A total of 5 HAs & 7 COPs were determined in fried chicken fiber.

• Harman & Norharman dominated in HAs, while 7α-OH & 7β-OH in COPs.

• Frying chicken fiber without soy sauce at 150 °C for 40 min reduced HAs & COPs.

Abstract

This study aims to determine the formation of heterocyclic amines (HAs) and cholesterol oxidation products (COPs) in fried chicken fiber (FCF) processed under different traditional conditions. An ultra-performance liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry technique was used to analyze various HAs and COPs respectively in chicken meat and FCF. Five HAs were produced in FCF during processing with the amount ranging from 0.052 to 106.005 ng/g and decreasing in the following order: 1-methyl-9H-pyrido[3,4-b]indole(Harman)>9H-pyrido[3,4-b]indole(Norharman)>2-amino-5-phenylpyridine(Phe-P-1)>2-amino-3-methyl-imidazo[4,5-f]-quinoxaline(IQx)>3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole(Trp-P-1). Chicken fiber fried in lard at 180 °C/20 min generated a higher level of HAs (106.005 ng/g) than in soybean oil (77.823 ng/g), but with frying at 150 °C/40 min, the total HAs contents were reduced by 26.4% and 6.2% respectively. Seven COPs were produced in FCF with the maximum level being 35.220 μg/g and both cholesterol-5α-6α-epoxide (5,6α-EP) and cholesterol-5β-6β-epoxide (5,6β-EP) dominating. A lower level of COPs was formed in chicken fiber fried in lard (12.999 or 11.182 μg/g) than in soybean oil (35.220 or 28.553 μg/g) during frying at 150 °C/40 min or 180 °C/20 min, with the former reducing COPs by 77.9% without soy sauce. Comparatively, the formation of both HAs and COPs could be substantially reduced by processing FCF in lard at 150 °C/40 min without soy sauce flavoring.

Introduction

Heterocyclic amines (HAs), composed of carbon, hydrogen and nitrogen atoms with a polycyclic aromatic structure, are often present in cooked protein-rich meat products. To date more than 30 HAs have been identified in heated foods, in which a portion of HAs such as 2-amino-3-methyl-imidazo[4,5-f]-quinoline (IQ), 2-amino-3,4-dimethyl-imidazo[4,5-f]-quinoline (MeIQ), 2-amino-3,8-dimethyl-imidazo[4,5-f]-quinoxaline (8-MeIQx), 2-amino-9H-pyrido[2,3-b]indole (AαC), 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeAαC), 2-amino-6-methyldipyrido-[1,2-a:3′,2′-d]imidazole (Glu-P-1), 2-aminodipyrido-[1,2-a:3′,2′-d]imidazole (Glu-P-2) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) has been reported to be mutagenic and carcinogenic (Alaejos & Afonso, 2011). Accordingly, HAs can be classified into thermic HAs and pyrolytic HAs, with the former being generated at 100–300 °C and the latter produced at >300 °C. More specifically, thermic HAs can be formed through Maillard reaction between 6-carbon reducing sugar and amino acid for formation of α,β-dicarbonyl compound, followed by formation of α-amino-carbonyl compound through Strecker degradation, pyridine or pyrazine formation through cyclization, reaction with aldehyde and creatinine for formation of imidazole and subsequent reaction with quinoline or quinoxaline to form IQ or IQ-type HAs (Felton, Knize, Hatch, Tanga, & Colvin, 1999). While for pyrolytic HAs, they can be formed through degradation of amino acids or proteins during heating. For instance, both 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-p-1) and Trp-p-2 can be formed through degradation of tryptophan while AαC and MeAαC formed through degradation of soybean globulin (Abdelhameed, Li, & Leblanc, 2013).

Many factors such as food variety, cooking methods, temperature, time and addition of flavorings or antioxidants can affect the amount and variety of HAs formed. For example, Borgen, Solyakov, and Skog (2001) studied the formation of HAs as affected by meat variety and reported both 2-amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine (PhIP) and 2-amino-1,6-dimethyl-furo[3,2-e]imidazo[4,5-b]-pyridine (IFP) were prone to be formed in chicken meat while 8-MeIQx formed in pork and beef. Furthermore, in dried heating system 2-amino-1,6-dimethylimidazo[4,5-b]-pyridine (DMIP), IFP and PhIP were more susceptible to be formed, whereas 8-MeIQx formed in moist heating system (Borgen et al., 2001). Also, the higher the temperature and the longer the heating time, the more the formation of HA variety and content (Gibis, Kruwinnus, & Weiss, 2015; Oz & Zikirov, 2015). Cooking methods such as boiling and microwave was shown to produce a lower level of HAs than that by charcoal grilling, roasting, frying or baking (Stavric, 1994). Interestingly, the addition of water-soluble vitamins (B1, B3, B6, B7, C) was shown to inhibit HA formation in beef patties (Wong, Cheng, & Wang, 2012), while the addition of ice sugar and soy sauce was found to promote HA formation in marinated meat (Lan & Chen, 2002).

Cholesterol oxidation products (COPs), formed through oxidation of cholesterol during heating or illumination or in the presence of oxidative enzyme can also be present in high levels in cholesterol-rich meat products. More than 100 COPs have been characterized in heated foods, and a portion of COPs were shown to be associated with incidence of coronary heart disease (Brzeska, Szymczyk, & Szterk, 2016). The mechanism of cholesterol oxidation has been demonstrated to be similar to lipid oxidation. In the presence of triplet oxygen (atmospheric oxygen), the cholesterol hydroperoxides (7α-OOH or 7β-OOH), the initial product of cholesterol oxidation at the 7th carbon can be formed, followed by reduction to form 7α-hydroxy cholesterol (7α-OH) or 7β-hydroxy cholesterol (7β-OH) or dehydration to form 7-keto cholesterol (7-keto) (Tai, Chen, & Chen, 2000). Alternatively, in the presence of singlet oxygen, cholesterol hydroperoxides such as 5α-OOH, 5β-OOH, 6α-OOH or 6β-OOH can be formed through photooxidation of cholesterol, followed by formation of 7α-OOH or 7β-OOH through rearrangement (Barnaba, Rodriguez-Estrada, Lercker, Garcia, & Medina-Meza, 2016). In addition, cholesterol epoxides such as cholesterol-5α-6α-epoxide (5,6α-EP) or cholesterol-5β-6β-epoxide (5,6β-EP) can be formed from cholesterol in the presence of 7α-OOH or 7β-OOH, followed by 5α-cholestane-3β-5α-triol (triol) formation under moist and acidic conditions (Tai et al., 2000). Also, a side-chain oxidation product such as 20-hydroxy cholesterol (20-OH) or 25-hydroxy cholesterol (25-OH) can be formed from cholesterol (Tai et al., 2000). In heated foods the most common COPs present include 5,6α-EP, 5,6β-EP, triol, 7α-OH, 7β-OH, 7-keto, and 25-OH (Lee, Chien, & Chen, 2006).

Like HAs, the variety and amount of COPs present in foods can be affected by many factors such as heating time, temperature, pressure, illumination, pH, processing method, storage condition, antioxidant and addition of flavoring (Brzeska et al., 2016). For instance, when cholesterol standard was heated at 120–220 °C for 30–180 min, it was shown that the higher the temperature and the longer the heating time, the faster the cholesterol degradation (Derewiaka & Molinska, 2015). In another study Broncano, Petron, Parra, and Timon (2009) studied the effects of broiling, roasting, frying and microwave cooking on COP formation in pork, only 7α-OH, 7β-OH, 25-OH and 7-keto were detected. Interestingly, only triol and 25-OH were detected in pork cooked by steam, roasting and microwave, while 7β-OH, 5,6α-EP and 7-keto remained undetected (Min et al., 2016), probably due to further degradation. In an earlier study Kim and Nawar (1993) studied the effect of pH on cholesterol stability and reported that cholesterol could undergo higher loss at alkaline pH (7.4). Also, COPs were produced at a higher level in dry-cured ham when treated with high pressure processing at 900 MPa than at 600 MPa (Clariana & Garcia-Regueiro, 2011). Following illumination of turkey meat, some more COPs were generated with white light (6000 °K, 36 W) than with red light (3000 °K, 36 W) (Boselli et al., 2005). Lee, Chien, and Chen (2008) further reported that the incorporation of antioxidants such as BHA and Trolox was effective in inhibiting COPs formation in marinated meat. However, the addition of 0.1% vitamin E may possess prooxidant effect in marinated eggs. Some other reports also showed the antioxidant activity of polyphenols such as catechin, chlorogenic acid, quercetin and anthocyanin when incorporated into meat products during heating (Osada, Hoshina, Nakamura, & Sugano, 2000).

Fried chicken fiber (FCF), a popular meat product sold in Asian countries, especially Taiwan and China, can be produced through boiling of chicken meat, beating to filaments, flavoring, stir-frying and addition of edible oil for frying. As high temperature and long heating time are often employed during processing of FCF, it is possible that a high level of HAs and COPs can be generated. Also, the formation and inhibition of HAs and COPs in FCF as affected by processing condition, flavoring and frying oil remains unexplored. The objectives of this study were to compare both type and content of HAs and COPs formed in fried chicken fiber under different flavoring, oil type and frying conditions.