Changes of hydroxyl-linoleic acids during Chinese-style sausage processing and their relationships with lipids oxidation

Highlights

• Changes of hydroxyl-LAs were observed during Chinese-style sausage making.

• Ratio of 13- to 9-HODE was used to study the evolution of lipids oxidation pattern.

• LOX-catalyzed oxidation predominated in curing and the early stage of drying.

• LOX-catalyzed oxidation was the major contributor to total lipids oxidation.

Abstract

A Chinese-style sausage was processed using pork as the raw material. During the whole process, 13-hydroxyoctadecadienoic acid (13-HODE), 9-hydroxyoctadecadienoic acid (9-HODE), 9,10-dihydroxyoctadecenoic acid (9,10-DHODE) and 9,10,13-trihydroxyoctadecenoic acid (9,10,13-THODE) kept increasing. All of them were found to be correlated negatively and significantly with lipoxygenases (LOX) activity, and positively and significantly with peroxide value (POV) and thiobarbituric acid reactive substances (TBARS). The ratio of 13-HODE to 9-HODE decreased slowly during drying stage and stayed higher than 2 during the whole process, and it was found to be positively and significantly with LOX activity. The ratio of variation of 13-HODE to variation of 9-HODE in every sampling period (the ratio of Δ13-HODE to Δ9-HODE) decreased sharply from 2.75 in the stage of curing for 12 h to 1.37 in the stage drying from 24 d to 30 d. The changes of ratio of 13HODE to 9-HODE and ratio of Δ13-HODE to Δ9-HODE indicated LOX-catalyzed oxidation predominated in curing and early drying stages, and such predominance was taken over by non-enzymatic oxidation during late drying stage; LOX-catalyzed oxidation was the major contributor to lipids oxidation during the whole process of the Chinese-style sausage preparing.

Introduction

Linoleic acid (LA, C18:2), the most common polyunsaturated fatty acid in meat products, is susceptible to enzymatic oxidations catalyzed by lipoxygenases (LOX) and cytochrome P450, etc. (Konkel & Schunck, 2011), and non-enzymatic oxidation induced by metal ions and free radicals, etc. (Kim, Jang, & Hou, 2002). Oxidations of LA yield a series of secondary products containing hydroxyl, carbonyl and carboxyl, etc. Hydroxyl-linoleic acids are one group of those products containing the same carbon skeleton as LA with different number of hydroxyl(s), including hydroxyoctadecadienoic acids (HODEs), dihydroxyoctadecenoic acids (DHODEs) and trihydroxyoctadecenoic acids (THODEs), etc. Hydroxyl-linoleic acids have positional isomers, among which HODEs include 9- and 13- HODE, DHODEs include 9,10- and 12,13-HODE, while THODEs have more isomers and mainly include 9,10,11-, 9,10,13- and 9,12,13-THODE, etc. (Levandi et al., 2009, Püssa et al., 2009).

Hydroxyl-linoleic acids have been found to be of biological significance and have been paid a great deal of attention to. HODEs were reported to increase apoptosis in macrophages, which was a key process in the development of atherogenesis (Vangaveti et al., 2014). 13-HODE was supposed to play important roles in developments of some human cancers, e.g. prostate cancer (Hsi, Wilson, & Eling, 2002), breast cancer (Klil-Drori & Ariel, 2013). 9,10- and 12,13-DHODE, also called leukotoxin diols and isoleukotoxin diols respectively, were considered to be associated with vasodilatation and pulmonary edema (Hu et al., 1988, Ishizaki et al., 1995). The exogenous 9,10-DHODE has been reported to disrupt estrous cyclicity and sexual behavior in rats, and promote cell mitosis and stimulate MCF-7 cell proliferation (Markaverich et al., 2005; 2007). The levels of 9,10,13- and 9,12,13-THODE in the bronchoalveolar lumen in patients with asthma were found to be much higher than those in healthy individuals’ bronchoalveolar lumen, THODEs might be involved in the propagation of inflammation (Caligiuri, Aukema, Ravandi, & Pierce, 2014).

In recent years, there is an increasing concern about hydroxyl-linoleic acids in diets (Püssa et al., 2009), since exogenous hydroxyl-linoleic acids were found to exert the same biological impacts as those endogenous compounds (Markaverich et al., 2007). In 2015, The International Agency for Research on Cancer (IARC, 2015) published the latest assessment, in which processed meat was classified as carcinogenic to humans (Group 1). Although the specific compounds that can be connected with human cancers’ development remain largely unknown, lipids oxidation products in processed meat products have been considered as one of major potential contributors to developing cancers (Domingo & Nadal, 2017).

Cured meat product is an important category of processed meat products, including ham, sausage and bacon, etc. During making of cured meat products, lipids undergo enzymatic and non-enzymatic oxidations, which have been regarded as a major source of characteristic flavor (Sojic et al., 2014). In the evaluation of lipids oxidation, peroxide value (POV) and thiobarbituric acid reactive substances (TBARS) are the most common parameters to reflect the degree of lipids oxidation, standing for the primary oxidation products and the secondary products, respectively. However, neither of them can give exact information for the specific oxidation products, including hydroxyl-linoleic acids. Therefore, merely conducting the analysis on conventional parameters (e.g. POV and TBARS) is not enough to yield the whole profile of lipids oxidation, and investigation on variations of other specific substances may help better understand lipids oxidation during making of cured meat products.

In the previous study (Song et al., 2016), we quantitatively analyzed levels of HODEs, DHODEs and THODEs in uncooked and cooked cured meat products, e.g. ham, sausage, bacon, air-dried duck and etc. All samples were found to contain HODEs, DHODEs and THODEs simultaneously, in order of HODEs > THODEs > DHODEs, and contents of HODEs in some sausages were more than 50 µg/g. In China, sausage making has a long history and many varieties, differing in flavoring/spicing ingredients, the raw meat(s) and manner of processing, etc. Traditionally, Chinese-style sausage is made solely from pork with a fat content of approximately 20–30%, and is not cooked until consumption. The sausage is generally produced in winter and just hung out-doors under the sun to naturally dehydrate after stuffing (Yu, Chai, Zeng, He, & Chen, 2018). Currently, high-temperature drying is used to shorten the drying time of Chinese-style sausage in commercial production instead of natural drying. In the present study, one kind of Chinese-style sausage was processed with pork as the raw meat in our lab. The objectives of this paper were: 1) to investigate lipids oxidation in sausage during the whole process by measuring POV, TBARS and LOX activity, 2) to observe changes of HODEs, 9,10-DHODE and 9,10,13-THODE in sausage during curing and drying, and 3) to study relationships between hydroxyl-linoleic acids and lipids oxidation.