基于LF-NMR弛豫特性的煎炸油总极性化合物含量定量建模方法

将低场核磁共振（low field nuclear magnetic resonance,LF-NMR）分析技术应用于煎炸油脂总极性化合物（total polar compounds,TPC）含量的预测。采用柱层析方法测定油脂样品的TPC含量作为测定值,采集油脂样品的LF-NMR弛豫特性（峰起始时间T21、T22、T23相应的峰面积比例S21、S22、S23、单组分弛豫时间T2W）,分别利用向后筛选多元回归分析、主成分回归分析和偏最小二乘回归分析建立LF-NMR弛豫特性与TPC含量的回归方程,比较3 种模型的校正集和预测集的决定系数与均方根误差,最终确定最优模型为偏最小二乘回归模型。应用此模型预测预测集样品TPC含量,决定系数R2可达0.928,预测集均方根误差为0.568%,模型稳定。     

基于LF-NMR技术下3种猪肉水分含量预测模型的建立与比较

本文研究低场核磁共振技术与肉中水分测量的预测模型,选取新鲜猪肉样品利用MesoMR23低场核磁分析实验仪器测定T₂弛豫特性,同时应用直接干燥法测定肉中实际水分含量,分别利用最小二乘法(LSE)、偏最小二乘法(PLSR)和主成分回归法(PCR)建立预测模型比较。结果表明:三种预测模型的决定系数R2均大于0.9。LSE、PLSR和PCR的预测集中,样品水分含量的预测值与参考值之间的决定系数分别为0.960、0.969和0.941,预测均方根偏差分别为0.048、0.048和0.104。因而,PLSR模型具有更好的预测结果。     

注胶肉糜的低场核磁弛豫特性及与近红外光谱技术判别效果的比较

研究了注入亲水胶体种类及比例对肉糜低场核磁共振技术(low fielcl nuclear magnetic resonance,LFNMR)特性的影响,探索了基于LF-NMR数据判别肉糜注胶程度的可行性,并与近红外光谱技术(NIR)的预测效果进行了比较。结果表明:随温度升高,肉糜的LF-NMR多组分弛豫图谱中代表不易流动水的T22峰及对应的S22减小;添加黄原胶或卡拉胶可使样品体系的持水性增加,表现为S22显著增大。基于样品LF-NMR弛豫特性的判别分析可实现对肉糜注胶程度的分段预测,分组正确率为90.5%~100%,交叉验证正确率为81.0%~100%。对NIR而言,应用偏最小二乘回归法(PLS)所建预测模型对注胶肉糜的预测效果相对较优(Rc为0.9886)且模型较为稳健(RPD=6.63)。与LF-NMR方法相比,NIR法可实现对肉糜注胶比例更为准确的预测。     

基于LF-NMR及主成分回归分析的油脂煎炸品质预测

以大豆油和玉米油为研究对象,研究薯条煎炸过程(温度(180±5)℃,36 h)中低场核磁(LF-NMR)弛豫特性及理化指标(酸价、黏度、吸光值及总极性化合物含量)的变化规律。应用主成分回归分析建立通过LF-NMR弛豫特性预测理化指标的相关性模型。结果表明:随煎炸时间的延长,油样的LF-NMR弛豫特性中,峰起时间(T21、T22)及单组份弛豫时间(T2w)线性减小,T21特征峰的峰面积比例(S21)线性增大;油样的酸价、总极性化合物(TPC)均随煎炸时间的延长而线性增大,黏度、吸光值则呈二项式增大。与大豆油相比,玉米油的酸价、黏度、吸光值、S21等虽变化幅度较大,但TPC,T21,T22,T2w变化幅度较小。通过主成分回归分析可建立酸价、黏度及总极性化合物含量与LF-NMR弛豫特性间的相关性模型(R20.90),模型验证良好,说明可利用油脂煎炸过程中LF-NMR弛豫特性的变化,快速、有效地预测其理化指标的改变程度,从而有效监控煎炸油脂及食品的质量。     

低场核磁共振无损检测技术在水产品加工贮藏方面的应用

水分的含量及分布状态对于水产品的品质有重要的影响。低场核磁共振技术因其能快速、无损地检测食品水分含量和及其分布与迁移状况,在水产品加工和贮藏的品质分析方面有巨大应用潜力。核磁弛豫技术可对水产品加工过程水分进行检测、区分和对理化指标进行预测;核磁成像技术可对水产品进行内部水分的可视化观测。本文总结了最近低场核磁共振技术在水产品加工贮藏中的应用,对低场核磁共振作为无损、快速的检测技术在水产品加工和贮藏领域的应用前景进行了展望。     

低温环境下滩羊肉制品贮藏时间的研究

采用低场核磁共振(LF-NMR)技术对滩羊肉制品中的水分进行测定,根据其弛豫特性的变化,可反映出不同滩羊肉制品的贮藏终点。结果表明:低场核磁共振技术研究滩羊肉制品在低温贮藏过程中水分分布情况及水分迁移变化规律,能够准确判断肉制品的贮藏时间。通过低场核磁共振技术并结合主成分分析快速检测出清蒸羊羔肉的贮藏终点为60天,羊肉臊子的贮藏终点为70天,羊棒骨的贮藏终点为70天,白水羊肉的贮藏终点为40天,手抓羊肉的贮藏终点为60天。     

基于LF-NMR及判别分析的葵花籽油过氧化值定性分析

为实现利用低场核磁共振(LF-NMR)技术快速检测葵花籽油过氧化值是否超标,收集了乐惠(LH)、金龙鱼(JLY)、福临门(FLM)、日清(RQ)、海狮(HS)、葵王(KW)、多力(DL)和融氏(RS)8品牌,共计162个不同氧化程度的葵花籽油LF-NMR弛豫特性(T21、S21、T22、S22、T23、S23、T2W),其中过氧化值超标样品数为74,并结合判别分析建立了葵花籽油过氧化值是否超标的定性判别模型。结果表明,葵花籽油LF-NMR弛豫信号随氧化时间变化存在一定的规律性,借助于判别分析进一步提取有效信息,发现模型总体判别准确率可达85.8%,其中RQ和RS葵花籽油判别准确率均达到90%以上,除HS仅为77.27%外,其余品牌判别准确率均在80%以上,判别效果良好。说明可以利用葵花籽油的LF-NMR弛豫特性对其过氧化值进行快速有效的定性分析,省时省力,具有重要实践意义。     

无花果热风干燥过程中水分变化及其品质研究

为探究不同温度热风干燥过程中水分含量变化情况及对无花果品质的影响,该研究采用不同温度热风干燥（50、60、70、80℃）对无花果进行干燥处理后,运用低场核磁共振（low-field nuclear magnetic resonance,LF-NMR）技术检测各温度干燥过程中无花果的水分迁移规律,采用色差计测定不同干燥温度的无花果色泽变化,并对其总酚含量及抗氧化活性进行考察。结果表明,随干燥温度的升高,无花果的干燥速率显著提高,达到平衡的时间明显缩短。低场核磁共振信号显示,随干燥时间的延长,核磁共振横向弛豫T2峰向左移动,说明随着干燥时间的延长无花果中水分自由度降低。T2峰横向弛豫时间、峰面积（A）与水分比相关性分析结果显示,干燥过程中无花果的水分比（moisture ratio,MR）与T21、T23的横向弛豫时间以及A23、A总呈显著相关。低场核磁共振成像（low-field magnetic resonance imaging,LF-MRI）图谱显示,新鲜无花果内部水分分布较为均匀,随干燥时间的延长,水分由内向外周扩散。不同温度烘干样品的品质分析显示低温烘干（50℃或60℃）能更好地保持无花果的色泽,而高温烘干（80℃）样品中多酚类成分含量最高,其抗氧化活性最好。以上研究表明低场核磁共振技术可用于热风干燥过程中无花果水分含量、分布及其状态变化的无损检测。     

低场核磁共振分析在果蔬干燥中的应用进展

低场核磁共振分析与成像(LF-NMR/MRI)是一种利用氢质子的弛豫时间分析水分的流动状态和分布状态的快速检测手段,广泛应用在果蔬干燥领域。文章在阐述低场核磁共振应用原理的基础上,总结了LF-NMR/MRI在葡萄、香菇、生姜等果蔬原材料干燥前处理、干燥过程和干燥终点水分状态上的研究进展。重点介绍了LF-NMR/MRI在微波真空干燥中在线应用的案例,文章对LF-NMR/MRI在果蔬干燥领域的高效应用提供参考。     

基于低场核磁共振技术的大米水分含量及活度快速预测

以直接干燥法和水分活度仪测定的结果作为参考值,采用低场核磁共振仪对大米样品进行测量,获取样品的横向弛豫数据,结合化学计量学算法建立多元校正模型,实现对大米水分含量及活度的快速测定。采用偏最小二乘方法(PLS)和误差反向传播人工神经网络方法(BP-ANN)对160个校正集样品进行训练后,建立多元校正模型,并对90个预测集样本进行预测。结果显示,PLS与BP-ANN 2种方法中预测集样品的水分含量预测值和参考值之间的相关系数分别为0.937 6和0.955 5,预测均方根偏差分别为0.005 8和0.004 6,水分活度预测值和参考值之间的相关系数分别为0.983 0和0.993 4,预测均方根偏差分别为0.009 2和0.006 2,表明2种方法能够快速而准确地对大米的水分含量及活度进行预测。     

响应面-主成分分析法优化山药韧性饼干配方

为拓宽山药应用领域,以低筋小麦粉与山药粉为原料,开发山药韧性饼干。以感官评分与质构作为综合评价指标,进行单因素实验探究山药粉添加量对韧性饼干的影响。在此基础上,响应面结合主成分分析法优化山药韧性饼干配方。结果表明:以粉(低筋面粉+山药粉)100%计,山药粉添加量28%,水添加量26.76%,橄榄油添加量13.30%,磷脂添加量0.76%,糖添加量20%,食盐1.0%,小苏打1.0%,碳酸氢铵0.5%;烘烤温度:上火170 ℃,下火150 ℃,时间:12 min。此条件下,测得饼干硬度:(697.01±20.83) g,柔韧性:(0.292±0.018) mm,感官评分:81.80±3.63,饼干质构特性优于空白饼干,口感松脆、色泽均匀,具有独山药风味。     

Mechanical and fracture properties for predicting cracking in semi-sweet biscuits

Mechanical and fracture properties required for predicting crack development in semi‐sweet (‘rich tea’) biscuits have been experimentally determined. Pilot‐scale biscuits of different fat concentrations were prepared and studied with commercial biscuits at different moisture contents. Bending modulus, fracture stress and strain were measured using three‐point bending tests. All biscuit types showed considerable dependence on moisture content over a range of 4–12%. Young's modulus and failure stress showed a uniform decrease and failure strain showed an increase with increasing moisture content. For pilot‐scale biscuits of different fat concentrations, an increase in fat level caused a decrease in modulus and failure stress values; however, the failure strains were very similar for all the fat types. The testing of the samples with top surface up and top surface down revealed that the sample orientation does not affect the measured parameters. The measured parameters also did not show any directional dependence within the plane, thus assuring that the assumption of an isotropic material would be valid for modelling. The mechanical and fracture properties measured in this study will serve as a very useful set of data to predict the stress state and cracking of the checked biscuits.     

Biscuit making properties of flours from hard and soft milling single variety wheats

Bench scale baking tests for two types of biscuits,¹ a hard sweet (HS) and a short sweet (SS), have been used to examine the biscuit making properties of a large number of flour samples from wheats grown in four consecutive years (1980–1983). Multiple regression models for prediction of biscuit properties using a range of standard cereal laboratory tests as independent variables on results from 1980–1981 harvest wheats confirmed earlier observations that such tests are of limited commercial value for biscuit flour specification. However the results of baking tests, with both types of biscuit, from single wheat varieties grown during 1981–1983 showed that flours from soft milling wheats (SMW) required less water to give biscuit doughs of standard consistency (measured instrumentally) than did flours from hard milling wheats (HMW). In addition biscuit doughs made with SMW flours gave greater oven spring, i.e. biscuits of lower bulk density, than doughs made from HMW flours. In each season the difference in the mean values of both parameters for flours milled from SMW and HMW was highly significant (P<0.001). With one exception the variability of the measured parameters within seasons was not significantly different between SMW and HMW. However within both SMW and HMW varieties highly significant differences (P<0.001) were observed between seasons for the mean values of both measured biscuit parameters. The effect of flour particle size on the biscuits was studied by regrinding a number of flours. With flours from both SMW and HMW reduction in particle size resulted in HS biscuits of higher density but SS biscuits of lower density.     

Textural attributes of commercial biscuits. Effect of relative humidity on their quality

Two commercial biscuits of semi‐sweet type, ‘Marie’ and ‘Petit Beurre’ were used for investigating: (i) their texture variability as a function of the location and the side of puncturing and (ii) the influence of storage under different relative humidity on their texture, porosity and colour. Significant texture differences were found as a function of the location of puncturing (centre or periphery of biscuit area), as well as between the upper and the opposite side of a biscuit. At small relative humidity changes (11–32%) a distinct relationship between texture and moisture content was not noticed. In ‘Petit Beurre’ at a_w 0.32 a peak was observed in the puncture force values. In both biscuits porosity increased with their moisture content, accompanied by an area expansion. Significant differences in colour were mainly noticed between the upper and opposite side of the biscuits. Colour was less influenced by relative humidity changes.     

基于太赫兹时域光谱技术的饼干水分定量分析

目的探究太赫兹时域光谱(THz-TDS)技术无损检测饼干中水分含量的可行性,为在线设备研发提供理论基础。方法选取表面平整的薄片饼干样品,利用透射模式,通过对测得的时域谱、频域谱以及菲涅尔公式计算得到的折射率和吸收谱与饼干水分含量的化学值建立线性关系及模型,进而对饼干中的水分含量进行了测定。结果吸收系数谱的偏最小二乘(PLS)模型相关系数为0.97518,预测均方根误差为0.00595,优于其他谱图的建模效果。结论该技术可以用于测定饼干中的水分含量。     

利用低场核磁共振技术分析冬瓜真空干燥过程中的内部水分变化

为研究冬瓜真空干燥过程中内部水分的含量、分布及状态变化,应用低场核磁共振（low-field nuclearmagnetic resonance,LF-NMR）技术,测定不同干燥条件下冬瓜真空干燥过程中的横向弛豫时间T2反演谱,进而分析冬瓜样品内部的水分状态及其变化规律。结果表明：在真空干燥过程中,冬瓜干基含水率与NMR信号幅值之间呈显著的线性关系;真空干燥过程改变了样品的横向弛豫时间T2,增加了冬瓜内部不易流动水的含量、降低了水分的流动性;不同干燥温度条件下,结合水所占比例、自由水所占比例随着干燥时间的变化分别呈指数模型、多项式模型,且拟合方程的决定系数均大于0.95,拟合精度较高。该研究为进一步研究产品的保藏提供技术指导,为冬瓜的真空干燥实际产业化生产控制提供理论依据。     

Use of healthier fats in biscuits (olive and sunflower oil): changing sensory features and their relation with consumers' liking

The aim of this study was to evaluate consumer acceptability of biscuits when saturated fat was replaced by olive or sunflower oil and to determine the sensory characteristics responsible for changes in acceptability. Ninety seven consumers evaluated the acceptability of six biscuit samples varying in the fat source (dairy shortening, olive oil and sunflower oil) and fat content (10.6% and 15.6%). Using a Check All That Apply question (CATA), consumers also evaluated sensory properties of biscuits. Results indicated that the replacement of saturated fat (dairy shortening) by vegetable oils had an effect on biscuit acceptability which depended on biscuit fat content. According to biscuits' acceptability data, three different clusters of consumers were identified. By using a multiple factor analysis, the relationship among sensory CATA data and acceptability of each cluster explained the different acceptability patterns of consumers. For most of consumers acceptability was related to attributes “crispy”, “easy to chew” and “biscuit flavour” which, for one group were perceived in shortening biscuits and, for another in both olive and shortening biscuits. However, for the third group of consumers, acceptability was only related to flavour attributes like “roasted flavour” or “biscuit flavour” that were perceived in vegetable oil biscuits which were the preferred biscuits while, shortening biscuits were disliked and perceived as having an “off flavour”.     

Flour properties and the manufacture of semi sweet biscuits

The results of laboratory and baking tests applied to 48 commercial flour samples, produced during six growing seasons, have been examined in an attempt to determine methods of predicting the behaviour of flour in making semi sweet biscuits from the results of the laboratory tests. The laboratory tests examined were found to be of limited value for this purpose. The most important single property was the protein content of the flour, which should be within the range 7.5 to 10%, if biscuits of acceptable appearance and eating quality are to be obtained. Comparison of the results of the present investigation with those published some 20 years ago^{1, 2} shows that marked changes have occurred during the intervening years in the properties of flours considered suitable for the manufacture of semi sweet biscuits. It is suggested that, within the range of flour protein content mentioned above, process control is more important than flour properties in the manufacture of this type of biscuit.     

Protein nutritive quality during production and storage of dietetic biscuits

A comparative investigation of the changes in available lysine content during industrial production of two dietetic hard biscuits based on whole grain wheat flour/grits and a standard hard biscuit based on white wheat flour was performed. Dough preparation did not significantly affect the available lysine content. However, after baking, a significant loss (27–47%) of available lysine was found in all three types of biscuit. The average relative decrease in available lysine in proteins of each type of biscuit correlated highly significantly with technological parameters, mainly with the interaction between baking temperature and baking time (r = 0.980, p = 0.001). Physical characteristics of the biscuits, such as thickness, surface area, weight and density, also contributed considerably to the extent of damage to available lysine. The two dietetic biscuits were characterised by a higher available lysine content than the standard biscuit, and accordingly by a higher protein nutritive quality, with average chemical scores (calculated for adults) of 97 and 105 as against 60 for the standard biscuit. Storage for a long time (1 year) had no significant influence on the chemical scores. © 2002 Society of Chemical Industry