动物性食品中胆固醇氧化产物的研究进展

动物性食品中的胆固醇氧化产物(Cholesterol Oxidation Products,COPs)的健康效应受到广泛关注。其水平在新鲜动物性食材中均很低,但在储藏加工和家庭烹调中可能有显著增加。文章介绍了水产品、畜产品、蛋制品及乳制品4类食品中影响胆固醇氧化产物形成的因素。研究表明长时间储藏、高温、非适宜的水分活度、与光线和氧气接触等因素均会促进胆固醇氧化产物的形成。烹调中加入油脂的饱和程度和所含抗氧化物质也影响动物性食物烹调后COPs的形成。加入适量的天然抗氧化物质可能有利于减少COPs的生成。     

Fatty acids and cholesterol oxidation in salted and dried shrimp

The aim of this work was to evaluate the occurrence of cholesterol oxidation products and to analyze the lipidic profile in salted–dried shrimp. Fifty samples of salted–dried shrimp were evaluated, and the cholesterol oxides (7β-OH, 7α-OH, 7-Keto and 25-OH) were quantified by high-performance liquid chromatography. The cholesterol oxides: 7β-OH (34.63–72.56 μg/g), 7α-OH (5.02–12.12μg/g), 7-Keto (7.44–32.68 μg/g) and 25-OH (2.37–22.88 μg/g) were determined in all samples analyzed. Regarding to the total cholesterol content and the average thiobarbituric acid reactive substances (TBARS) content, the results ranged from 73.88 to 247.69 mg/100 g, and 0.02 to 1.30 mgMA/kg, respectively. The fatty acids profile was: 27.48% saturated, 43.90% monounsaturated and 28.61% polyunsaturated. The presence of cholesterol oxidation products and the values of TBARS indicate the degree of oxidation of this product, which was probably initiated by inadequate conditions of processing and storage.     

Effect of electron-beam irradiation on cholesterol oxide formation in different ready-to-eat foods

A study of the formation of ¹cholesterol oxidation products (COPs) has been carried out in four ²ready-to-eat (RTE) foods (cooked ham, Spanish Serrano ham, minced beef, and soft cheese). The samples were previously treated with electron-beam irradiation between 1 and 8 kGy. Three COPs, 25-hydroxycholesterol, 7-ketocholesterol and 6-ketocholestanol, were extracted together with the lipid fraction using chloroform. Then, COPs were isolated by sample clean up using ³solid phase extraction (SPE) and were analyzed by ⁴high performance liquid chromatography with ultraviolet detection (HPLC-UV). Method validation was established by precision and recovery studies. Results showed that non-irradiated cheese and cooked ham samples did not contain COPs. In general, an increase in COP content was observed in all cases when the irradiation dose increased, although this increase was not linear. The 6-keto COP was not detected in any of the RTE food samples studied regardless of the irradiation dose.

Industrial relevance

Nowadays, changes in dietary habits have produced an important increase in consumption of prepared foods thus increasing microbiological contamination risks; consequently, it is necessary to apply easy methods, able to be implanted in industrial production lines, and which eliminate potential contaminants and enhance shelf life. The application of E-beam irradiation to vacuum packed ready-to-eat (RTE) food of animal origin could be a useful technique for sanitization purposes; besides, it is a clean, rapid and environmentally friendly treatment. During this treatment cholesterol oxide products (COPs) may be formed. They have received considerable attention in recent years because of their biological activity which has been associated with human diseases, such as the inhibition of cholesterol biosynthesis, atherosclerosis, changes in membrane properties, cytotoxicity, mutagenesis and carcinogenesis. Therefore, COP analysis in food samples of animal origin is of great interest.In this work, an increase in the 25-OH and 7-keto COP content has been detected after E-beam irradiation with doses from 1 to 8 kGy, which is in the upper accepted limit in other foods, but final COP concentrations found in the foodstuffs studied here were at least one order of magnitude lower than those which produce toxic effects in in vivo and in vitro experiments. Analysis was made by HPLC with UV detection; so, two COPs with absorption properties were used as targets.     

Effect of irradiation and packaging conditions after cooking on the formation of cholesterol and lipid oxidation products in meats during storage

The effect of irradiation and packaging conditions on the content of cholesterol oxidation products (COPs) and lipid oxidation in cooked turkey, beef, and pork during storage was studied. Ground turkey leg, beef, and pork were cooked, packaged either in oxygen-permeable or oxygen-impermeable bags, and irradiated at 0 or 4.5 kGy. Lipid oxidation and COPs were determined after 0 and 7 days of storage at 4°C. Packaging of cooked meat was more important than irradiation in developing COPs and lipid oxidation in cooked meats during storage. 7-Hydroxycholesterol, 7β-hydroxycholesterol, β-epoxide, and 7-ketocholesterol were among the major COPs formed in cooked turkey, beef, and pork after storage, and their amounts increased dramatically during the 7-day storage in aerobic conditions. Irradiation had no significant effect on the amounts of any of the COPs found in cooked turkey and beef, but increased (P<0.05) the amounts of - plus 7β-hydroxycholesterol, β-epoxide, 7-ketocholesterol, and total COPs in aerobically packaged cooked pork. The amounts of COPs and lipid oxidation products (TBARS) closely related to the proportion of polyunsaturated fatty acids in meat. The results indicated that the composition of fats in meat is important on the oxidation rates of lipids and cholesterol, and packaging is far more important than irradiation in the formation of COPs and lipid oxidation in cooked meat.     

Cholesterol oxide, cholesterol, total lipid and fatty acid contents in processed meat products during storage

The effects of storage time on the formation of cholesterol oxides and on alterations in the fatty acid composition of processed meat products manufactured by Brazilian industries were investigated in this study. Cholesterol oxides and cholesterol were determined by HPLC using photodiode array and refractive index detectors. Samples of jerked beef, Italian-type salami, chicken mortadella and Chester mortadella were analysed at 30 day intervals starting at zero time, for 90 days for the mortadella and 120 days for the jerked beef and salami. The mortadellas were stored under refrigeration at 6 °C and the jerked beef and salami at room temperature, but protected from the light. No cholesterol oxides were formed during the storage time in any of the samples. The cholesterol content, the fatty acid composition and total lipid contents showed no significant differences during storage with the exception of the total lipid content of the jerked beef, which varied from 3.5 at zero time to 2.4 g/100 g after 120 days storage.     

Analysis of furan in heat-processed foods consumed in Korea using solid phase microextraction–gas chromatography/mass spectrometry (SPME–GC/MS)

Furan (C₄H₄O) is a volatile compound formed during the Maillard reaction and was recently classified as a possible human carcinogen (group 2B) by the International Agency for Research on Cancer. It has been reported to occur in various canned and jarred foods that undergo heat treatment. The aim of the present study was to optimise the sample preparation for furan analysis using solid phase microextraction–gas chromatography/mass spectrometry (SPME–GC/MS), according to the food matrix. We also performed the monitoring and risk assessment of furan in various food products. The optimised fibre exposure temperatures, time and amount of sample of liquid, semi solid and paste state foods were 5 g (ml), 50 °C, and 20 min, respectively. The level of furan in canned meat (32.16 ng/g) was the highest among the samples studied. The furan levels in canned fish, canned vegetable, nutritional/diet drinks, canned soups and jarred sauces were 29.40, 22.86, 7.28, 18.54 and 21.52 ng/g, respectively. Furan concentrations in baby food products were between 3.43 and 97.21 ng/g. Exposure estimates (14.59 ng/kg bw/day) of baby foods was the highest among all the tested food samples. However, the exposure estimate of baby foods was lower than that prescribed by the US FDA.     

Steroidal glycoalkaloids in potato foods as affected by cooking methods

Potato and its products have become indispensable foods and snacks for most people. Steroidal glycoalkaloids (SGAs) occur in all tissues of the potato, and consuming potatoes with a high SGA content harms human health. Therefore, the effects of different cooking methods on the SGA content in potato foods were investigated in this study. The results indicated that adding food-grade acetic acid during the manufacturing process did not affect the SGA content in stir-fried shredded potatoes or fresh mashed potatoes. However, the SGA content in potato food after peeling was significantly lower than that in non-peeled food, and the volume ratio of potato skin to flesh decreased with the increase of the potato tuber volume. Therefore, potato breeders and farmers should make the most hard to increase the proportion of commodity potato via corresponding science and technology. In addition, frying significantly reduced the SGA content in potato chips. Further research indicated that SGAs degraded slowly at 150°C, while they degraded rapidly at 190°C within 30 min. The temperature of rapeseed oil in the frying process can be as high above 200°C. Thus, frying significantly decreased the SGA content in potato chips, which could be attributed to temperature. These results will provide a theoretical basis and practical guidance for potato breeding and cooking.     

Evaluation of cholesterol and lipid oxidation in raw and cooked minced beef stored under oxygen-enriched atmosphere

Oxygen-enriched modified atmosphere packaging (MAP) represents an important means to stabilize meat colour but may lead to an increase in lipid oxidation, influencing the acceptability and safety of the product. In this work, the effect on cholesterol and lipid susceptibility to oxidation was investigated in commercial minced beef held under MAP (80% O(2)/20% CO(2)). Cholesterol oxidation products (COPs), peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) were determined, before and after pan frying, at 1, 8 and 15 days since packaging under refrigerated storage (3-4°C). 7α-Hydroxycholesterol, 7β-hydroxycholesterol and 7-ketocholesterol were the more abundant COPs identified. COPs significantly increased in raw beef during storage: after 1, 8 and 15 days since packaging COPs were at the levels of 10.4, 30.7 and 60.5μg/g of fat, respectively. Cooking did not affect cholesterol oxidation in freshly packaged minced beef but led to a rise in COPs amount with respect to raw muscle after 8 and 15 days of storage. The trend in cholesterol oxidation reflected the progressive increase in lipid peroxidation rate brought by MAP conditions.     

Phytosterol oxidation products in enriched foods: Occurrence,exposure, and biological effects

Hypercholesterolemia is an important risk factor for the development of cardiovascular diseases. Dietary intake of phytosterols/phytostanols and their fatty acid esters results in a reduction of the LDL and total plasma cholesterol levels. Therefore, these constituents are added to a broad spectrum of foods. As in the case of cholesterol, thermo‐oxidative treatment of phytosterols may result in the formation of phytosterol oxidation products (POPs), i.e. keto‐, hydroxy‐, and epoxy‐derivatives. This review summarizes and evaluates the current knowledge regarding POPs in the light of the potentially increasing dietary exposure to these constituents via the consumption of foods enriched with phytosterols/phytostanols and their esters. Data on the occurrence of POPs and approaches to assess the potential intake of POPs resulting from the consumption of enriched foods are described. The knowledge on the uptake of POPs and the presently available data on the impact of the consumption of enriched foods on the levels of POPs in humans are discussed. Biological effects of POPs, such as potential proatherogenic properties or the loss of the cholesterol‐lowering effects compared to nonoxidized phytosterols, are discussed. Finally, knowledge gaps are outlined and recommendations for further research needed for a safety assessment of POPs are presented.     

乳化食品中油脂氧化分析及其货架期评价方法的研究进展

油脂氧化是导致乳化食品变质的主要原因。油脂中的不饱和脂肪酸发生氧化,不仅会降低乳化食品的营养价值,还会产生不良风味、有害成分,进而影响乳化食品货架期和食用安全。相对于纯油体系,以乳化形式存在的油脂在高油-水界面比下极易发生氧化,缩短乳化食品的货架期。为明确乳化食品中油脂氧化分析以及其货架期评价方法,在介绍乳化食品中油脂氧化的基本过程的基础上,综述了乳化食品中油脂氧化分析方法(过氧化值、共轭二烯值、硫代巴比妥酸值、茴香胺值、挥发性物质含量)以及货架期的评价方法,为乳化食品中油脂氧化程度分析及其货架期预测提供参考。     

Volatile profile of mango (Mangifera indica L.), as affected by osmotic dehydration

The effect of osmotic dehydration on the volatile fraction of mango fruit was studied. Osmotic treatments were carried out at atmospheric pressure (OD) and by applying a vacuum pulse (PVOD). Sucrose at 35, 45, 55 and 65 °Brix was used as osmotic solution until reaching 20 or 30 °Brix in the liquid phase of dehydrated mango. Volatile compounds of fresh and dehydrated samples were obtained by simultaneous distillation–extraction, and analyzed by GC–MS. In general, osmotic dehydration provoked changes in the concentration of analyzed compounds to different extents, depending on process conditions. The use of highly concentrated osmotic solutions, and the high level of sample osmodehydration, induced losses of volatiles with respect to the fresh samples. On the other hand, more heavily diluted solutions and shorter treatment times (lower osmodehydration level) could give rise to the enhancement of volatile production. In these cases, sample mass loss was reduced during treatment since sugar gain was promoted against water loss.     

Antioxidant and antiacetylcholinesterase activities of five plants used as Portuguese food spices

In the present work, we report the results of a study aimed at evaluating the antiradical activity, the antioxidant activity and the acetylcholinesterase (E.C. 3.1.1.7.) inhibitory capacity of essential oils, ethanol and boiling water extracts from five aromatic herbs growing wild in Portugal and used in traditional food preparations: fennel (Foeniculum vulgare), mint (Mentha spicata), pennyroyal (Mentha pulegium), rosemary (Rosmarinus officinalis) and wild thyme (Thymus serpyllum). The water extracts of M. spicata and M. pulegium showed the highest radical-scavenging activity (DPPH test) values (IC₅₀ = 5.7 ± 0.4 and 8.9 ± 0.2 μg ml⁻¹ respectively). This activity was higher than that found with the standard antioxidant BHT. The ethanol extracts of M. spicata, T. serpyllum and F. vulgare showed the highest antioxidant activities measured by the β-carotene/linoleic acid assay, IC₅₀ = 36.9 ± 0.1, 41.2 ± 0.1 and 68.7 ± 0.1 μg ml⁻¹, respectively. The inhibition of AChE was higher in the essential oil fraction. The highest activity was found for R. officinalis with an IC₅₀ = 69.8 ± 0.1 μg ml⁻¹.     

毛细管气相色谱法测定食品中的酚类抗氧化剂

建立了同时测定食品中BHA、BHr、TBHQ和PG等四种酚类抗氧化剂的测定方法.采用HP-1毛细管色谱柱分离,氢火焰离子化检测器外标法定量,样品加标回收率为96.3%～104.2%,相对标准偏差为0.63%～1.53%,检出限分别为BHA为0.72mg/L、BHT为0.62mg/L、TB-HQ为0.68mg/L、PG为1.2mg/L.该方法具有快速、灵敏度高、重现性好、预处理简单等优点.     

Presence of synthetic antioxidants in organic and conventional milk

Samples of conventional (n = 11) and organic (n = 81) milk, both raw and heat-treated, were analysed for the presence of synthetic antioxidants (butylated hydroxytoluene, butylated hydroxyanisole, dodecyl gallate, propyl gallate and octyl gallate) to verify whether those labelled as “organic” corresponded to EU Regulations on the use of additives in such products. The analysis detected only the antioxidant BHT and its aldehyde BHT–CHO in all 11 conventional milk and in 18 of 81 organic milk samples. The investigation highlights the importance of strict control of organic dairy production, since synthetic antioxidants added to feedstuff to prevent rancidity can be transferred to milk.     

Effect of processing conditions on the oxidation of cholesterol in ghee

The cholesterol oxidation products (COP) in fat-rich dairy products were identified and quantified. Fresh cream contained no COP whereas fresh butter contained trace levels of 7β-hydroxy- and 5,6α-epoxycholesterol. Low levels of various major COP were present in ghee (clarified butter fat). Intermittent heating and frying of ghee induced severe oxidation of cholesterol and a number of COP were detected by GC and TLC. Most atherogenic COP. viz 25-hydroxycholesterol and cholestantriol, were formed more in intermittently heated ghee (8.1-9.2% of the total COP) than in fried ghee samples (7.1 %).     

Inhibition of protein and lipid oxidation by rapeseed, camelina and soy meal in cooked pork meat patties

In this study protein-containing by-products of deoiling processes rich in phenolics were applied to meat to be used as potential food ingredients in developing meat products with antioxidant effect. The effect of rapeseed meal (Brassica rapa L.), camelina meal (Camelina sativa), soy meal and soy flour (from soybean, Glycene max L.), in inhibiting oxidation of lipids and proteins was tested in cooked pork meat patties. A commercial CO₂ extract from rosemary (Rosmarinus officinalis) was used as a reference material alone and in combination with the other plant materials. The cooked pork meat with added plant materials was oxidized for 10 days at 5 °C under light. The oxidation was followed by measuring the formation of hexanal, pentanal and propanal by headspace gas chromatography and the formation of protein carbonyls by converting them to 2,4-dinitrophenylhydrazones (DNPH). Rapeseed meal (0.5 and 0.7 g/100 g meat) and camelina meal (0.7 g/100 g meat) as such and their combination (addition of 0.5 g/100 g) with rosemary extract (0.04 g/100 g) were effective antioxidants toward both protein and lipid oxidation while soy meal and flour were effective only in combination with rosemary extract.     

Occurrence of furan in commercial processed foods in Brazil

Selected commercial processed foods available in the Brazilian market (306 samples) were analysed for furan content using a validated gas chromatography-mass spectrometry method preceded by headspace solid phase micro-extraction (HS-SPME-GC/MS). Canned and jarred foods, including vegetable, meat, fruit and sweet products, showed levels up to 32.8?µg?kg^?1, with the highest concentrations observed in vegetables and meats. For coffee, furan content ranged from 253.0 to 5021.4?µg?kg^?1 in the roasted ground coffee and from not detected to 156.6?µg?kg^?1 in the beverage. For sauces, levels up to 138.1?µg?kg^?1 were found. In cereal-based products, the highest concentrations (up to 191.3?µg?kg^?1) were observed in breakfast cereal (corn flakes), cracker (cream crackers) and biscuit (wafer). In general, these results are comparable with those reported in other countries and will be useful for a preliminary estimate of the furan dietary intake in Brazil.     

Determination of ethylenethiourea (ETU) and propylenethiourea (PTU) in foods by high performance liquid chromatography-atmospheric pressure chemical ionisation-medium-resolution mass spectrometry

A robust and sensitive method for the determination of ethylenethiourea (ETU) and iso-propylenethiourea (i-PTU) in foods is reported. ETU and i-PTU were extracted by blending with dichloromethane (DCM) in the presence of sodium sulphate, sodium carbonate, thiourea and ascorbic acid. ²H₄-ETU and n-PTU were used as internal standards. After filtration the DCM was removed by rotary evaporation and the extract re-dissolved in water before analysis by reversed-phase liquid chromatography with detection by atmospheric pressure chemical ionization-mass spectrometry using a double focusing mass spectrometer at a resolution of 5000. Mean recoveries of ETU and i-PTU from fruit-based, cereal-based and meat-based infant foods, potato chips and tinned potatos at 0.01 mg kg^-1 and from pizza and yoghurt at 0.02-0.1 mg kg^-1 were 95% and 97% respectively. Precision, including both repeatability and internal reproducibility, was in the range of 3.1-13.1%.     

Essential and trace elements content of commercial infant foods in the UK

There is a paucity of data in respect of the nutritional quality of complementary foods for infants and young children aged between 6 and 12 months. The primary objective of this study was to examine nutritive values of such complementary infant food on the UK market in order to ascertain their suitability relative to dietary guidelines for the 6–9 months age group. Quantitative analyses were conducted on eight different products representing four popular brands (meat and vegetable based) currently on sale in the UK. Eight major mineral and trace elements, namely: calcium, copper, magnesium, iron, zinc, potassium, sodium and selenium were measured by ICP–OES and ICP–MS. The results of these studies were referenced to the Recommended Nutrient Intake (RNI) values for 6–9 months old children, and a menu of entire daily intake of minerals and trace elements was composed taking into consideration the nutrient and energy intake from milk consumption. Based on these comparisons, all the food samples studied in this work contained less essential minerals than expected from the RNI values except for potassium in meat and vegetable based recipes. These results suggest that commercial complementary infant foods on the UK market may not contain the minimum levels of minerals required for the labelling declaration of micronutrient content (Commission Directive 2006/125/EC). This provides opportunities and scope for product optimisation to improve their nutritive value.