Oxidation of a Lipid Emulsion by a Peroxidizing Microsomal Fraction from Herring Muscle

A microsomal fraction isolated from herring (Clupea harengus) muscle was shown to oxidize the lipids in an emulsion prepared from extracted lipids of herring muscle. The oxidation of the lipids of the emulsion was dependent on enzymic oxidation of the microsomal lipids. In the absence of either the microsomes or NADH (previously shown to be required for enzymic lipid peroxidation), no measurable oxidation occurred in either the lipid fraction of the microsomes or the lipids of the emulsion. Disappearance of eicosapentaenoic and docesahexaenoic acids from peroxidizing assay systems in presence and absence of lipid emulsion corresponded to the increase in TBA reactive substances.     

Lipid distribution and recovery during salt fractionation of cod muscle

Lipids and particularly free fatty acids have been implicated in the denaturation of fish muscle proteins in the frozen state. A fuller understanding of this phenomenon can only be obtained with knowledge of the distribution of lipids at the subcellular level and of their behaviour when muscle proteins are isolated. Attempts were made to determine the lipid distribution between myofibrils, supernatant and subcellular particles and to follow the extraction of lipid during the preparation of actomyosin and structural lipoproteins. It was found that whole cod muscle homogenates incubated at 0° for 24 h do not show phospholipase activity. Separation of cell particulate matter and supernatant by centrifugation causes considerable hydrolysis and loss of phospholipids even after 2 h at 0°. The losses are enhanced by time and by the extraction of proteins and accompanying lipids into strong salt solutions. Phospholipase-C-like activity appears to cause a considerable proportion of the lipid loss. These phenomena, which are thought to be largely due to oxidation, are not observed in the summer months. Attempts to determine the lipid distribution in tissues by subcellular fractionation when lipid recovery is not quantitative may lead to seriously erroneous conclusions.     

LIPID OXIDATION IN A CHICKEN MODEL SYSTEM: ROLE OF LIPID AND PROTEIN FIBERS

Chicken muscle model systems were exposed to varying concentrations of lipid and protein fibers to clarify the role of these constituents in lipid oxidation. In this study, the lipid substrates examined included triacylglycerols, membrane phospholipid fractions, isolated phospholipid fractions, and free fatty acids. In iron-ascorbate catalyzed systems, increases in lipid concentration failed to lead to enhanced levels of oxidation at the examined times. Lipid was therefore not considered a rate limiting factor in the oxidation of muscle systems. Protein fibers accelerated oxidation only in sarcoplasmic reticulum (SR) membrane systems when catalyzed by iron-ascorbate. Enhanced interaction of the low molecular weight iron with the membrane lipids may be responsible for this unique response. Preferential oxidation of sulfhydryl groups in protein fibers, on the other hand, could account for the antioxidant effect displayed by protein fibers in methemoglobin catalyzed systems.     

Lipid Peroxidation and Phospholipid Hydrolysis in Fish Muscle Microsomes and Frozen Fish

The interaction between lipid peroxidation and phospholipase A₂ was investigated in fish muscle microsomes and frozen fish muscle. Lysophosphatidylcholine (LPC), a phospholipid hydrolysis product produced by the activity of phospholipase A₂, was detected in the lipids extracted from microsomes peroxidized by incubation with NADH and ADP-Fe³⁺. No detectable level of LPC was found in the microsomal lipids when NADH was withdrawn from the reaction mixture nor in the untreated microsomal lipids. LPC level in the lipids extracted from unheated microsomes was considerably higher than that from heat-treated microsomes when both were peroxidized by incubation with ascorbate and Fe³⁺. Phospholipase A₂ was activated by either NADH-dependent or ascorbate-induced lipid peroxidation in vitro. The levels of lipid peroxidation in fish muscle were higher when fish were stored at higher frozen storage temperatures and so were the levels of LPC.     

小麦胚芽贮藏期内脂质水解酸败机理解析

以小麦胚芽为研究对象,构建脂质水解酸败的模拟体系以及原位体系,解析小麦胚芽贮藏期内脂质水解酸败的机理。结果表明:光照、氧气和脂肪氧合酶未对小麦胚芽模拟体系中的游离脂肪酸含量产生明显影响,而脂肪酶则显著提升游离脂肪酸生成量;此外,游离脂肪酸生成量随水分活度增加而增加,于水分活度为0.75时达峰值,且小麦胚芽内部结合水和不易流动水含量也呈显著增加趋势,水分以及脂质流动性增加;小麦胚芽原位体系中游离脂肪酸含量随贮藏时间延长而逐渐增加,磷脂酰胆碱含量恰相反,且小麦胚芽脂质体膜遭到破坏,游离出的甘油三酯聚集形成油滴。由此可见,小麦胚芽脂质水解酸败模式主要表现为其脂质体膜中的磷脂酰胆碱降解而释放甘油三酯,而后甘油三酯经由脂肪酶催化水解生成大量的游离脂肪酸,从而产生水解酸败现象。     

9种腌腊肉制品贮存过程中游离脂肪酸的变化、影响因素及其来源途径的研究

选取9种腌腊肉制品,通过比较肥瘦质量比例、贮藏温度、不同产地、灭酶与不灭酶产品游离脂肪酸的含量及酸性脂肪水解酶、中性脂肪酶、碱性脂肪酶的酶解后酶活力,饱和脂肪酸、单不饱和脂肪酸、多不饱和脂肪酸组成,分析腌腊肉制品贮存过程中游离脂肪酸的变化及其影响因素,进而考察游离脂肪酸的来源途径。结果表明:相同条件下,全瘦肠、肥瘦质量比3∶7腊肠、肥瘦质量比4∶6腊肠游离脂肪酸的含量依次降低;不同产地游离脂肪酸含量差异显著;贮存温度37℃时游离脂肪酸的含量明显高于25℃;灭酶腌腊制品比不灭酶产品的游离脂肪酸增幅较小,且差异逐渐增大。脂肪水解酶在腌腊肉制品游离脂肪酸产生过程中发挥了重要的作用,贮存前期,酶促反应的持续进行,游离脂肪酸不断产生,脂肪水解是主导作用,而贮存后期不饱和脂肪酸不稳定逐渐被氧化,脂肪氧化起到关键作用。     

草鱼片热风干制过程中脂质氧化特性研究

探讨热风干燥过程中青鱼片油脂的变化情况。在青鱼片的不同干燥阶段提取油脂,检测油脂氧化程度,油脂成分及脂肪酸组成的含量变化。在干燥过程中鱼片油脂的过氧化值、羰基价和酸价显著性升高(P<0.05)。随着甘油三酯和磷脂含量的下降,游离脂肪酸含量明显增加,表明在干制过程中油脂在酯酶和磷酸化酶的催化下发生了水解反应。在总油脂和总磷脂中多不饱和脂肪酸,尤其是二十碳五烯酸(EPA)和二十二碳六烯酸(DHA)含量下降。在游离脂肪酸中,除DHA以外的多不饱和脂肪酸含量均显著升高。研究结果表明,青鱼片热风干燥过程中其油脂被氧化,同时发生脂质降解,特别是不饱和脂肪酸被释放为游离态。     

Endogenous skeletal muscle antioxidants

Skeletal muscle is susceptible to oxidative deterioration due to a combination of lipid oxidation catalysts and membrane lipid systems that are high in unsaturated fatty acids. To prevent or delay oxidation reactions, several endogenous antioxidant systems are found in muscle tissue. These include α‐tocopherol, histidine‐containing dipeptides, and antioxidant enzymes such as glutathione peroxidase, superoxide dismutase, and catalase. The contribution of α‐tocopherol to the oxidative stability of skeletal muscle is largely influenced by diet. Dietary supplementation of tocopherol has been shown to increase muscle α‐tocopherol concentrations and inhibit both lipid oxidation and color deterioration. Dietary selenium supplementation has also been shown to increase the oxidative stability of muscle presumably by increasing the activity of glutathione peroxidase. The oxidative stability of skeletal muscle is also influenced by the histidine‐containing dipeptides, carnosine and anserine. Whereas carnosine and anserine are affected by diet less than α‐tocopherol and glutathione peroxidase, their concentrations vary widely with species and muscle type. In pigs, beef, and turkey muscle, carnosine concentrations are greater than anserine, while the opposite is true in rabbit, salmon, and chicken muscle. Anserine and carnosine are found in greater concentrations in muscle high in white fibers, with chicken white muscle containing over fivefold more anserine and carnosine than red muscle. Anserine and carnosine are thought to inhibit lipid oxidation by a combination of free radical scavenging and metal chelation.     

Lipolysis in intramuscular lipids during processing of traditional Xuanwei ham

Lipolysis in intramuscular lipids during the processing of Chinese Xuanwei ham has been studied by analyzing the changes of glycerides, phospholipids and free fatty acids in biceps femoris muscle. Results showed that the glycerides accounted for 73.2% of total lipid content in fresh ham, the phospholipids represented 25.3% and the free fatty acids 2.3% of the total lipid content, respectively. A rapid lipolysis of phospholipids occurred during the first 4 months of processing and slowed down during the rest period. A preferential hydrolysis for palmitic, linoleic and arachidonic acids in phospholipid fraction was observed. Glycerides only changed a little throughout the process, while an increase of free fatty acids during processing was observed. The results suggest that phospholipids are the main substrate of lipolysis in the intramuscular lipids of Chinese Xuanwei ham.     

Impact of free fatty acid concentration and structure on lipid oxidation in oil-in-water emulsions

Free fatty acids are strong prooxidants in both bulk and emulsified oils. Addition of oleic acid to an oil-in-water emulsions increased lipid hydroperoxide and hexanal formation at free fatty acid concentrations as low as 0.1% of the lipid. The prooxidant effect of free fatty acids was dependent on fatty acid type with lipid oxidation rates being in the order of linolenic < linoleic < oleic. There were no significant differences in lipid oxidation rates when free fatty acid isomers with cis or trans double bonds were compared. The prooxidant activity of the free fatty acids was postulated to be due to their ability to attract prooxidant metals as well as co-oxidise the triacylglycerol in the oil. Overall, these results show that the oxidative stability of oil-in-water emulsions is strongly linked to both the concentration and type of free fatty acids present.     

鲈鱼风干成熟过程中脂质分解氧化规律

以鲈鱼(perch)为原料进行腌制风干成熟,通过分析测定加工过程中鲈鱼肌肉脂肪组成、脂肪酶及脂肪氧合酶(LOX)活力、硫代巴比妥酸值(TBARS)和过氧化值(POV)变化情况,探究其脂质分解氧化规律。结果表明:鲈鱼肌肉风干过程中总脂肪含量显著降低(P<0.05),中性脂质、磷脂含量在加工过程中显著下降(P<0.05),游离脂肪酸(FFA)含量显著上升(P<0.05),棕榈酸(C16:0)、硬脂酸(C18:0)、油酸(C18:1)、二十碳五烯酸(C20:5)和二十二碳六烯酸(C2 2:6)是FFA的主体成分;酸性脂肪酶、中性脂肪酶和磷脂酶活力在加工过程中总体上都呈显著下降趋势(P<0.05),且磷脂酶活力下降幅度最大,中性脂肪酶活力始终显著高于其他两种酶(P<0.05);而LOX活力持续下降,POV和TBARS值在整个加工过程中都呈现先增大后减小的变化趋势,说明风干成熟后期较高的温度能促进脂质氧化产物进一步分解,加速风味物质的形成。     

Mechanisms by which flavonol aglycones inhibit lipid oxidation better than glycosylated flavonols in comminuted muscle tissue

The effect of glycosylation on the ability of flavonoids to inhibit lipid oxidation in comminuted muscle tissue has not been previously examined. This work examined the ability of quercetin and quercetin-β-d-glucoside to inhibit lipid oxidation in mechanically separated turkey (MST). Quercetin inhibited formation of lipid peroxides and thiobarbituric acid reactive substances (TBARS) more effectively compared to quercetin-β-d-glucoside during frozen storage (p < 0.05). The possible mechanisms that cause glycosylation to decrease inhibition of lipid oxidation were also examined. Hydroxyl radical scavenging activity was similar when comparing quercetin and quercetin-β-d-glucoside, which indicated that the free hydroxyl group in 3 position of C ring in quercetin did not enhance its hydroxyl radical scavenging ability. Since muscle membrane lipids are susceptible to lipid oxidation, the ability of quercetin and quercetin-β-d-glucoside to incorporate into cellular membranes was studied. After adding quercetin and quercetin-β-d-glucoside to minced chicken muscle, flavonol content in the membrane fraction was determined. Around 32% of added quercetin partitioned into the membranes whereas quercetin-β-d-glucoside was not detected in the membranes. Similar trends were observed when each flavonol was added to isolated membranes. These studies suggest that glycosylation of flavonols weakens their ability to inhibit lipid oxidation in muscle tissue partly by decreasing the amount of flavonols in the membrane phase. In order to understand whether metal chelation by flavonols is a likely mechanism involved in the inhibition of lipid oxidation in MST, the role of endogenous metals in promoting lipid oxidation was examined. Addition of the metal chelators ethylenediamine tetraacetic acid (EDTA) and tetrakis(2-pyridylmethyl) ethylenediamine (TPEN) to MST did not inhibit lipid oxidation, which suggests that endogenous metals present in MST were not promoters of lipid oxidation. Hence it seems unlikely that the mechanism of inhibition by flavonols involved metal chelation in the comminuted muscle.     

Lipid Peroxidation by Microsomal Fractions Isolated from Light and Dark Muscles of Herring (Clupea harengus)

Enzymic lipid peroxidation by light and dark muscle microsomes of herring (Clupea harengus) required ATP or ADP, NADH and Fe. NADPH could not effectively replace NADH. Inhibition was observed at high concentrations of ADP and NADH but not Fe. The optimal pH for the reaction of both types of microsomes was between 6 and 7. The average peroxidation rate was 362 and 1143 nmoles MDA per mg protein per hr at 6°C for the light and dark muscle microsomes, respectively. The energy of activation for the light and dark muscle microsomes was similar. The light muscle microsomes lost activity faster than the dark muscle microsomes when exposed to 35°C. Ferrous ion stimulated enzymic lipid peroxidation of light and dark muscle microsomes over that observed with ferric ion.     

Changes in lipids and proteins of marine catfish (Tachysurus dussumieri) during frozen storage

Changes in lipids and protein of marine catfish ( Tachysurus dussumieri ) were followed over a period of 300 days storage at –20°C. Phospholipids decreased and free fatty acids (FFA) and peroxide value (PV) increased. A linear relationship between the decrease in phospholipid and increase in FFA was observed, suggesting that FFA were formed by hydrolysis of phospholipid. Fatty acid analysis showed that polyunsaturated fatty acids (PUFA) increased in the neutral lipid fraction and decreased in the phospholipid fractions; this also suggests hydrolysis of the latter and release of free PUFA into the neutral fraction.
A decrease in water soluble protein (WSP) and salt soluble protein (SSP) indicated denaturation of proteins on prolonged frozen storage; both changes were strongly associated with the changes in peroxide value and free fatty acids.     

Effects of the addition of exogenous lipase on lipolysis and lipid oxidation during wet-curing and dry-ripening of silver carp inoculated with mixed starter cultures

Lipid degradation caused by lipolysis and oxidation plays an important role in the evolution of final product quality of cured silver carp. This study aimed to determine the impact of exogenous lipase (ExL) on lipolysis and lipid oxidation during the wet-curing and dry-ripening of silver carp inoculated with mixed starter cultures. The addition of ExL to silver carp increased the hydrolysis of total lipids and phospholipids. The free fatty acids (FFAs) content during wet-curing was significantly higher in the ExL-treated group compared with the control. Increased FFA accumulation contributed to a high level of conjugated dienes, peroxides and thiobarbituric acid-reactive substances in the ExL-treated group, indicating that the lipid oxidation was improved by the addition of ExL. Increased neutral lipase, acid lipase and phospholipase activities during the wet-curing stage might explain the more extensive release of FFAs in the presence of ExL. The addition of ExL promotes the hydrolysis and oxidation of lipids in cured silver carp.     

Effect of high-pressure treatment on the fatty acid composition of intramuscular lipid in pork

To investigate the effect of high-pressure (HP) treatment on lipid oxidation and fatty acid composition of intramuscular lipid in pork, the longissimus muscles from Rongchang (RC) pig were pressurized at 200, 350 and 500 MPa for 20 min at 20 °C prior to 7 days storage at 4 °C. The changes in TBARS number, lipid content and fatty acid composition of total intramuscular lipids, phospholipids, triglycerides and free fatty acids in untreated and HP treated samples were analyzed. HP treatment had no significant effect on the content and fatty acid composition of total lipids and triglycerides in the samples, but treatment at 350 MPa and above led to marked increases in TBARS values and lipolysis of partial phospholipids causing a correlative increase of free fatty acid content. A preferential hydrolysis for polyunsaturated fatty acids (PUFA) in phospholipids was observed, which resulted in the percentage of PUFA in phospholipids decreasing markedly and thereby that in free fatty acids increasing significantly.     

Differential lipid damage in various muscle zones of frozen hake (Merluccius merluccius)

 A comparison of the lipid damage produced in different hake zones was carried out during frozen storage at –11 and –18  °C. Three light muscle zones and the dark muscle were considered. Lipid oxidation [conjugated dienes; thiobarbituric acid index (TBA-i); fluorescence formation] and hydrolysis (free fatty acids, FFA) were determined. The most predominant lipid damage in all zones was hydrolysis, at the end of storage reaching values of about 40% (for the light muscle zones) and 12% (for the dark muscle) of the total lipids at –11  °C. Significant (P<0.05) correlation value (r=0.67–0.85) relationships between the frozen storage time and the FFA content were obtained for the four muscle zones at both temperatures. A comparison of the regression lines slopes in the different zones showed that a lower (P<0.05) lipolitic activity was produced in the dark muscle compared to the three light zones at both temperatures. A low lipid oxidation development was produced in the three light muscle parts, so that no significant differences between them could be assessed. However, the dark muscle showed a higher oxidation development (TBA-i and fluorescence formation) as a result of a higher lipid content and the presence of prooxidant constituents.     

Differential lipid damage in various muscle zones of frozen hake (Merluccius merluccius)

 A comparison of the lipid damage produced in different hake zones was carried out during frozen storage at –11 and –18  °C. Three light muscle zones and the dark muscle were considered. Lipid oxidation [conjugated dienes; thiobarbituric acid index (TBA-i); fluorescence formation] and hydrolysis (free fatty acids, FFA) were determined. The most predominant lipid damage in all zones was hydrolysis, at the end of storage reaching values of about 40% (for the light muscle zones) and 12% (for the dark muscle) of the total lipids at –11  °C. Significant (P<0.05) correlation value (r=0.67–0.85) relationships between the frozen storage time and the FFA content were obtained for the four muscle zones at both temperatures. A comparison of the regression lines slopes in the different zones showed that a lower (P<0.05) lipolitic activity was produced in the dark muscle compared to the three light zones at both temperatures. A low lipid oxidation development was produced in the three light muscle parts, so that no significant differences between them could be assessed. However, the dark muscle showed a higher oxidation development (TBA-i and fluorescence formation) as a result of a higher lipid content and the presence of prooxidant constituents. Received: 16 June 1998     

Effects of some technologies of curing uncomminuted meat products on their flavour Part 1. Changes in the contents of fatty acids as meat flavour precursors

A study was made of the fatty-acid composition of phospholipids and the fraction of free fatty acids in two uncomminuted pork products, loin and neck, manufactured by three technologies: I, brine curing; 11, dry curing; 111, dry curing using%.6% honey. A higher phospholipid content was found in the loin products. Brine curing caused a more intensive lipid hydrolysis in both types of meat products. The free fatty-acid fraction in the meat products manufactured by technologies II and III was richer in unsaturated fatty acids, which are some of the most important meatflavour precursors.     

Lipid Hydrolysis in Frozen Baltic Herring

SUMMARY— The lipid composition of Baltic herring ( Clupea harengus var . membranus) muscle and the hydrolysis during freeze storage was studied with thin-layer chromatography. The concentrations of the various lipid classes were initially 2–5 times as high in dark muscle as in white muscle. Storage for up to 12 weeks at –15°C resulted in an increase of the free fatty acid content from 50 to 1000 mg/100 g in the dark muscle, and from 17 to 280 mg/100 g in white muscle. The increase was due to hydrolysis of lecithin, cephalin and to a varying extent also of triglycerides. According to indirect estimations, roughly 45 and 75% of the free fatty acid formed in dark and white muscle respectively was a result of phospholipid hydrolysis; the remainder of triglyceride hydrolysis. The hydrolysis of lecithin was faster than that of cephalin in both types of muscles. The enzymatic attack showed no preference for anyone of the different fatty acids in the phospholipids.