朴素贝叶斯分类模型在中红外光谱测原料奶掺假中的应用研究

现有常规乳与乳制品掺假检测方法主要是利用鲜乳以及所掺入物质的物理化学性质进行测定,每种方法只能检测一种掺假成分,所以比较费时、烦琐。中红外光谱具有分析快速、操作方便、成本低、对样品不造成损伤、无需前处理、再现性好、不污染环境等优点。通过朴素贝叶斯分类模型建立生鲜牛奶和掺假原料奶的判别模型,判断未知样是否属于掺假原料奶。     

脂肪酸指纹判别特种家畜乳真实性的可行性分析

近年来马、骆驼和牦牛等家畜乳得到区域性开发,由于其稀缺、营养价值高且具有一定的保健功能,极易被低价位牛羊乳或植脂末等其他原料掺假或冒充。基于基因和蛋白质物种特异性的鉴别方法,仅适合物种造假,且易受加热、均质和发酵加工等因素的影响。采用化学计量学PCA、SIMCA和PLS等模块对51份牛乳、山羊乳、马乳和驼乳样品,以及42份马乳掺10%、25%和50%牛乳混合样品进行脂肪酸指纹分析和建模。脂肪酸指纹PCA分析显示物种间差异显著,利用脂肪酸指纹建立特种乳真实性鉴别模型是可行的;SIMCA模型判别马乳和牛乳及两者混合样品的正确率为91%;PLS定量模型估计马乳和牛乳混合比例的最大误差为±10%,验证样本计算结果均值的标准差为3.3%。脂肪酸指纹模型也可判别其他化学掺假造成的异常。     

植物油中脂肪酸组成的GC-MS分析

建立几种常见植物油中脂肪酸组成的GC-MS分析方法。并对甲酯化条件进行了优化,甲酯化后待测液经离心过膜后,进入气相色谱-质谱进行测试。通过对谱图进行分析,得到各植物油中主要脂肪酸组成及含量。结果表明,所选几种植物油以16碳脂肪酸和18碳脂肪酸为主,不饱和脂肪酸含量较高,均超过总脂肪酸的70%,平行实验的最大允许偏差均小于10%,各脂肪酸含量均符合国家标准中对食用植物油脂肪酸组成的规定。     

食用植物油中掺混棕榈油的定性与定量分析

目的建立食用植物油中掺混棕榈油的定性与定量分析方法,为植物油掺假提供检测依据。方法植物油样品先经过皂化和甲酯化处理,然后采用气相色谱法对植物油中的各种脂肪酸组成进行检测。以月桂酸为特征指标,直接定性,应用面积归一化法进行定量分析。结果配比实验验证和检测数据分析表明,该方法月桂酸检出限为0.01%,植物油中棕榈油的定量限为5%~100%,最低可以分辨出添加了5%棕榈油的食用植物油样品。结论此方法操作简单、重现性好、精确度高,是一种分析迅速、经济实用的分析方法。     

采用红外光谱分析技术快速鉴别原料乳掺假

针对目前市场上出现的原料乳中掺假的现状,建立了红外光谱技术快速鉴别掺假原料乳的分析方法。收集正常原料乳和掺假乳样品,利用红外光谱技术结合主成分分析方法建立定标识别模型,并通过不同搀假乳的红外光谱检测进行模型验证。结果表明,红外光谱分析技术可以实现原料乳中是否掺假的快速鉴别。     

应用脂肪酸甲酯快速筛选植物油中掺假地沟油

根据植物油和地沟油中脂肪酸酯存在方式的不同,建立植物油中地沟油掺假的快速筛选方法。植物油中脂肪酸是以甘油三酯的形式存在,地沟油中脂肪酸以脂肪酸甲酯的形式存在,利用气相色谱-质谱的全扫描模式,结合NIST 05标准谱库检索功能,对37 种脂肪酸甲酯进行测定。样品采用直接稀释-气相色谱-质谱全扫描分析脂肪酸甲酯,100 个植物油样品中均未检出脂肪酸甲酯;20 个地沟油样品中13 个检出肉豆蔻酸甲酯（C14∶0）、棕榈酸甲酯（C16∶0）和硬脂酸甲酯（C18∶0）等14 种脂肪酸甲酯,检出率为65%,且70%的检出脂肪酸甲酯的地沟油样品中脂肪酸甲酯种类多、含量较高。因此,若植物油样品脂肪酸甲酯种类多、含量高,则可判定为有地沟油掺假;若脂肪酸甲酯含量低或没有脂肪酸甲酯,则可以进一步用其他指标和方法进行检测,脂肪酸甲酯的检测方法可以作为地沟油掺假的快速粗筛方法。     

基于指纹图谱和化学计量分析的鳕鱼肝油软胶囊掺假植物油鉴定

目的 建立一种基于脂肪酸气相色谱(gas chromatography, GC) 指纹图谱技术结合化学计量分析的鳕鱼肝油软胶囊中掺假植物油的鉴定方法。方法 采用GC法测定不同来源鳕鱼肝油软胶囊脂肪酸指纹图谱, 经拟合后构建对照指纹图谱, 并进行样品相似度评价。模拟制备鳕鱼肝油软胶囊中掺入不同种类、不同比例植物油的掺假样品, 以其中14个共有脂肪酸峰的相对峰面积作为数据源, 输入SIMCA-P数据分析软件进行主成分分析(principal component analysis, PCA)及掺假模型建立。结果 获得鳕鱼肝油软胶囊GC对照指纹图谱及三维掺假识别模型, 44批样品经相似度评价发现有2批拟似掺假植物油, 将拟似样品色谱数据标准化后导入SIMCA-P软件, 显示2批样品均掺了大豆油, 掺假比例约为15%和35%。结论 脂肪酸GC指纹图谱结合化学计量分析为鳕鱼肝油软胶囊中掺假植物油的鉴定提供一种可靠准确的检测手段, 可快速有效识别鳕鱼肝油掺假行为。     

气相色谱-质谱联用法测定植物油中脂肪酸组成

建立气相色谱-质谱联用法测定植物油中脂肪酸组成的方法。选用硼化氟-甲醇体系对样品进行甲酯化处理,再通过气相色谱-质谱技术对脂肪酸组成进行分析和鉴定。共分离出11种脂肪酸,结果表明:植物油中的脂肪酸以油酸、亚油酸、棕榈酸、硬脂酸为主,其中油酸和亚油酸含量均达70%以上,不饱和脂肪酸含量与饱和脂肪酸含量的比值:玉米油5.9%,菜籽油17.6%,葵花籽油11.7%,花生油3%,调和油5%。植物油中不饱和脂肪酸含量远远高于饱和脂肪酸含量。     

植物油脂肪酸甲酯化方法比较与含量测定

通过比较不同甲酯化方法、气相色谱升温程序,确定了植物油中脂肪酸成分的气相色谱分析方法,并对5种食用植物油的主要脂肪酸含量进行了分析和比较。结果表明:三氟化硼-甲醇快速甲酯化法具有操作简单、时间短、甲酯化率高的优点。利用CP-Sill 88高极性气相色谱柱,优化的升温程序为:初始温度170℃,保持1 min,以10℃/min升温速率升至200℃,再以1℃/min升温速率升至220℃,保持3 min,20 min内即可有效分离6种脂肪酸。用建立的方法测定5种食用植物油6种脂肪酸的含量,标准曲线的相关性好,相关系数范围为0.999 4~0.999 9,检出限低。     

基于同步荧光光谱的杜仲籽油掺假检测研究

建立基于同步荧光光谱的杜仲籽油掺假判别分析模型及检测方法。以杜仲籽油和7种常见植物油为研究对象,采集激发波长范围为250～700 nm,波长间隔为60 nm的同步荧光光谱,分析杜仲籽油和常见食用油的荧光光谱特性,利用光谱峰面积建立掺假判别模型并对其进行验证。结果表明:杜仲籽油与其他7种植物油的荧光特性存在显著差异;分别利用600～700 nm和300～500nm波长范围同步荧光光谱进行主成分分析,其对杜仲籽油掺假识别准确率高达100%;利用峰面积与掺假比例建立定量判别分析模型,检测限分别为1%和0. 48%。该方法可实现对杜仲籽油掺假的定性和定量分析,且具有较高的灵敏度、简便和快速等特点。     

Sensorial and fatty acid profile of ice cream manufactured with milk of crossbred cows fed palm oil and coconut fat

This work was carried out to study the nutritional quality of milk of cows fed palm oil (PAL) or coconut fat (COC), and the use of that milk as raw material for ice cream production. Three treatments were tested with 23 healthy cows: control (CON), PAL, and COC. The milk was collected at d 21 and 36 of the experimental diet. Proximate composition (moisture, ash, fat, protein, and carbohydrates) and fatty acid composition were evaluated on milk and ice cream, and sensorial analysis, color (lightness, green/red, and blue/yellow), overrun, and texture were evaluated on the ice cream. Fatty acids present in milk and ice cream were determined by gas chromatography. Sensory analysis results showed that the ice cream acceptability index was above 70%. No difference was observed for proximate composition in milk and ice cream. Chromatographic analysis showed an increase in saturated fatty acid concentration in CON and lower levels in PAL; polyunsaturated fatty acid concentration was higher in PAL and lower in CON, in milk and ice cream; monounsaturated fatty acid concentration in milk was higher in PAL and lower in CON but no difference was found in ice cream. Comparing n-3 content in milk and ice cream, we observed that PAL had higher levels than CON and COC. The results indicate that it is feasible to add sources of fat to the animal feed for fatty acid composition modulation of milk and ice cream.     

Determination of bioactive compounds in cream obtained as a by-product during cheese-making: Influence of cows' diet on lipid quality

Bioactive lipid components were determined in cream samples obtained as a by-product of industrial Parmigiano Reggiano cheese-making. Cream samples, produced from raw milk collected after the supplementation of cows' diet with an unsaturated-fat source, i.e., extruded linseed and fresh forage, were collected after cheese production. The addition of an unsaturated fat source into the traditional diet of cows significantly decreased the mean content of saturated fatty acids and significantly increased the mean content of unsaturated fatty acids in cream. In cream from the linseed group, the contents of monounsaturated fatty acids and polyunsaturated fatty acids significantly increased compared to cream from the control group. The total phospholipid content of cream from cows fed with linseed diet was significantly higher than that of cream samples from the control group. Thus, cream from cheese factories supplied by cows fed a linseed diet showed the highest content of bioactive lipids.     

A survey of lipid composition of Khoa samples in relation to possible adulteration

The fatty acid composition of Khoa a heat‐desiccated milk product was determined and compared with those obtained with cow milk, buffalo milk and toned milk. Fatty acid methyl esters were analysed by capillary gas chromatography (GC). Among the Khoa samples analysed, 57% showed fatty acid composition characteristic of milk fat. The ratio of major saturated fatty acids to unsaturated fatty acids (S/U) including 18:1 transfatty acids was calculated for all the fats. The GC profiles of 43% Khoa samples showed the composition of fatty acids not conforming to milk fats. The Khoa samples adulterated with nonmilk fats were further confirmed by cholesterol and triglyceride estimation.     

冰淇淋复合乳化稳定剂流变特性及其应用的研究

本通过对不同溶液表观粘度的测定,研究了冰淇淋用原辅料的流变特性,表明了混合料粘度是控制冰淇淋质量的重要参考指标,并通过对不同复合肥化稳定剂配方所生产的冰淇淋样品的品质检验,发现在主要成分保持一致（含脂量10％,非脂乳固体含量10％,糖含量15％）的情况下,改变乳化稳定剂的配方,可得到不同的产品特点,其中最佳复合乳化稳定剂的配方为：瓜尔事前交0．2％;CMC0．1％;蒸馏单甘脂0．1％;蔗糖酯0．1％。     

β-Casein-phospholipid monolayers as model systems to understand lipid-protein interactions in the milk fat globule membrane

Phospholipid-protein monolayer films were studied as model systems to mimic the structure of the native bovine milk fat globule membrane (MFGM) and to understand lipid-protein interactions at the surface of the globule. Phospholipids extracted from bovine raw milk, raw cream, processed milk and buttermilk powder were spread onto the air-water interface of a Langmuir trough, β-casein was then added to the sub-phase, and Langmuir-Blodgett films were studied by epifluorescence microscopy and atomic force microscopy. In all films, β-casein was responsible for clustering of the sphingomyelin- and cholesterol-rich microdomains into larger platforms. This suggests that the same phenomenon may happen at the surface of the milk fat globule, where specific MFGM proteins may cause aggregation of microdomains.     

Proteolysis of milk fat globule membrane proteins during in vitro gastric digestion of milk

The influence of gastric proteolysis on the physicochemical characteristics of milk fat globules and the proteins of the milk fat globule membrane (MFGM) in raw milk and cream was examined in vitro in simulated gastric fluid (SGF) containing various pepsin concentrations at pH 1.6 for up to 2 h. Apparent flocculation of the milk fat globules occurred in raw milk samples incubated in SGF containing pepsin, but no coalescence was observed in either raw milk samples or cream samples. The changes in the particle size of the fat globules as a result of the flocculation were dependent on the pepsin concentration. Correspondingly, the physical characteristics of the fat globules and the composition of the MFGM proteins in raw milk changed during incubation in SGF containing pepsin. The major MFGM proteins were hydrolyzed at different rates by the pepsin in the SGF; butyrophilin was more resistant than xanthine oxidase, PAS 6, or PAS 7. Peptides with various molecular weights, which altered with the time of incubation and the pepsin concentration, were present at the surfaces of the fat globules.     

Milk lipase and off-flavour development

The origins of milk lipases and free fatty acids are discussed, together with properties of the principal enzyme responsible for lipolysis in raw milk. Variations in milk free fairy acid levels are shown to result from the net effect of several factors which influence overall enzyme activity and the nature of the fat globule surface. Possible forms of damaged fat are described with evidence suggesting that gross damage such as clumping or coalescence does not necessari 1.v give rise to high free fatty acid values. The risks of lipolysis both with types of milking installation and during the handling. storage and processing of milk are assessed. Levels of free fatty acids likely lo produce detectable rancid flavour are given with typical values for milk and cream in the UK     

An Improved Silver Ion HPLC Combined with Capillary Gas Chromatography of cis/trans Fatty Acids in Alimentary Fats and Human Milk Fat

A technique of analysis is described using a silver ion-loaded HPLC (Ag⁺/HPLC) column, gradient elution, and a laser light scattering detector followed by capillary gas chromatography (GC) for the determination of the fatty acid methyl ester (FAME) composition of rapeseed oil, the respective hydrogenated fat, some dietary fats, and human milk fat. With the use of Ag⁺/HPLC, FAMEs were separated into the following classes: saturated, trans-monounsaturated, cis-monounsaturated, trans–trans-di-unsaturated, trans–cis-di-unsaturated, cis–cis-di-unsaturated, and higher unsaturated FAMEs. Within each class, partial separation of positional isomers was also possible. Fractions of the eluate containing trans and cis C18:1 were separately collected and re-analyzed by GC in order to quantitate the positional isomers eight trans and nine cis in rapeseed oil and in human milk fat. The profiles of eight trans positional isomers in human milk fat and in hydrogenated rapeseed oil were alike but entirely different from that of six C18:1 trans isomers in bovine milk fat. Out of nine C18:1 cis isomers found in hydrogenated fat, only C18:1-9c and C18:1-11c were found in both human and bovine milk fat which may indicate some discrimination which occurs for certain isomers in fatty acid metabolism.     

Effect of buttermilk made from creams with different heat treatment histories on properties of rennet gels and model cheeses

Although many studies have reported negative effects on cheese properties resulting from the use of buttermilk in cheese milk, the cause of these effects has not been determined. In this study, buttermilk was manufactured from raw cream and pasteurized cream, as well as from a cream derived from pasteurized whole milk. Skim milks with the same heat treatments were also manufactured to be used as controls. Compositional analysis of the buttermilks revealed a pH 4.6-insoluble protein content approximately 10% lower than that of the skim milk counterparts. Milk fat globule membrane (MFGM) proteins remained soluble at pH 4.6 in raw cream buttermilk; however, when heat was applied to cream or whole milk before butter making, MFGM proteins precipitated with the caseins. Rennet gel characterization showed that MFGM material in the buttermilks decreased the firmness and increased the set-to-cut time of rennet gels, but this effect was amplified when pasteurized cream buttermilk was added to cheese milk. The microstructure of gels was studied, and it was observed that gel appearance was very different when pasteurized cream buttermilk was used, as opposed to raw cream buttermilk. Model cheeses manufactured with buttermilks tended to have a higher moisture content than cheeses made with skim milks, explaining the higher yields obtained with buttermilk. Superior retention of MFGM particles was observed in model cheeses made from pasteurized cream buttermilk compared with raw cream buttermilk. The results from this study show that pasteurization of cream and of whole milk modifies the surface of MFGM particles, and this may explain why buttermilk has poor coagulation properties and therefore yields rennet gels with texture defects.