稻谷储藏期脂质陈化的研究进展

稻谷陈化是一个复杂的过程,涉及到稻谷籽粒的各项理化性质的变化。淀粉、蛋白质和脂质是稻谷的三大主要成分,直接影响稻谷的食用品质。在储藏过程中,脂质易发生氧化、分解等反应。脂质陈化产生大量游离脂肪酸,使得稻谷品质变差。该文详细论述了稻谷储藏过程中脂质陈化的机理、影响因素,并对稻谷的储藏提出了建议。     

温度及光照对婴幼儿配方乳粉中VA、VD稳定性的影响

为研究不同温度条件下婴幼儿配方乳粉中VA和VD的稳定性,分别考察其在25、40、60℃及80℃储藏条件下乳粉中的含量变化;通过采用透光和避光2种方式储存的乳粉进行光照试验,研究了光照对乳粉中VA和VD稳定性的影响.结果 表明,25℃储藏条件下,乳粉中VA和VD含量均无明显变化;40、60℃和80℃条件下,VA含量有不同...     

稻谷储藏过程中发热霉变研究进展

受外界高温高湿环境条件、含水量等因素的影响,稻谷在储藏过程中易发生发热霉变的现象,严重影响稻谷品质及经济效益。本文详细综述了稻谷发热原因、发热类型以及稻谷霉变成因、霉变过程品质变化、霉变防控,为稻谷的安全储藏提供了依据。     

营养配方食品稳定性及货架期预测研究进展

受温度、光照、氧气等内外界环境因素影响,营养配方食品在长期储藏期间会发生一系列反应,并伴随着化学、物理及感官指标的变化,出现营养价值降低的现象。因此,研究并分析营养配方食品在储藏过程中营养素、化学、物理和感官指标的变化及其影响因素,对确定产品货架期具有重要意义。本文介绍了婴幼儿配方乳粉和特殊医学用途配方食品这两种我国市场上主要存在的营养配方食品的种类及配方特点,概述了营养配方食品稳定性研究现状,讨论了包括不同包装材料等各种影响因素对营养配方食品稳定性的影响,分析了各种货架期预测模型方法的适用性,以期为我国营养配方食品稳定性研究及评价原则制定提供参考。     

糙米保鲜储藏技术试验研究

针对东北气候条件及粳糙米储藏过程中的主要问题,着重研究不同储藏条件与粳糙米品质变化的关系以及储藏条件对粳糙米品质的影响,并寻求较高水分糙米的储藏条件,保持糙米的新鲜.在单因素研究的基础上,采用三因素三水平全因素试验设计方法,研究储藏方式、储藏温度、糙米水分对糙米脂肪酸、黏度的影响,建立了各评价指标与各影响因素的数学模型,并经优化处理找出了最佳参数组合:组合l为充氮储藏、温度12.05℃、水分15.58%;组合2为真空储藏、温度12.3℃、水分15.35%.结果表明:上述储藏方式较常规储粮的安全水分14%提高约2%,可以显著地降低稻谷烘干成本.     

玉米储藏过程中生理代谢与品质变化机理研究进展

玉米是最重要的储粮品种之一。随着粮库玉米存量不断增长,研究储藏过程中玉米生理代谢与品质变化机理和相关指标的变化规律,确保玉米的品质和安全储藏显得尤为重要。玉米的品质在储藏期间更会受到温度、湿度和气候变化等储藏条件的影响。玉米原始含水量对玉米粒和营养成分的影响显著,原始含水量越大,霉变程度越大,呼吸作用越强,脂肪和淀粉含量降低越快。玉米脂质由于呼吸和水解酶的作用,生成大量游离脂肪酸,脂质又是细胞膜的组分,细胞膜也会因氧化而被破坏,导致细胞生理活动紊乱。本文综述了玉米储藏期间生理代谢、营养成分变化机理、理化特性以及主要生物有害物变化规律,以期通过储藏前和储藏过程中品质指标的检测来判别其玉米储藏后品质劣变。     

婴幼儿配方乳粉贮存过程中品质劣变的研究进展

婴幼儿配方乳粉富含脂肪、蛋白质和碳水化合物,在贮存过程中易发生品质劣变,如脂质氧化、非酶褐变和乳糖结晶,而降低其营养价值。文中对婴儿配方乳粉贮存过程中品质劣变的类型、影响因素和研究方法进行了概述,并对婴幼儿配方乳粉劣变反应的研究方向进行了展望。     

多场耦合效应对小麦储藏品质影响的研究

多场耦合理论是近年来粮食储藏领域的热点,研究多场耦合效应对粮食品质的影响,为粮食的智能化管理提供理论依据和实践参考。以生物场和物理场为耦合基础进行研究,以含有不同虫口密度米象(Sitophilus oryzae)的小麦作为生物场,通过粮堆的温度分布云图,运用响应面法和多元回归分析,比较了在不同环境(储藏温度15℃/相对湿度75%、25℃/70%、35℃/65%)中小麦的储藏品质变化,构建了小麦粮堆品质变化的多场耦合模型,分析了影响模型拟合效果的主要因素,提出了小麦品质模型的适用性范围,研究发现干面筋含量、降落值模型在耦合效应下具有较强的拟合度(R²>0.9),而脂肪酸值模型在15℃时拟合效果并不理想,丙二醛含量模型的拟合效果随着储藏时间的延长而降低。在小麦储藏过程中,米象等生物场与其它场强的耦合效应对小麦储藏品质有显著影响,此时粮堆上层小麦的品质相比下层具有更好的稳定性,合理选择参数调整场强大小有利于小麦储藏品质模型的稳定性。     

小麦储藏品质评价指标研究进展

小麦在储藏过程中会发生一系列的物理、化学、生理以及食用品质的变化。综述小麦储藏主要品质评价指标如发芽率、过氧化氢酶活性、脂肪酸值等,及其与储藏条件、储藏时间的关系,旨在为小麦的科学储藏研究提供参考。     

贮藏过程中菠萝浓缩汁非酶褐变原因解析

用带皮的菠萝全果加工的菠萝浓缩汁作为研究对象,分析了贮藏过程中引起菠萝浓缩汁褐变的化学组分,采用通径分析方法,本实验解析了菠萝全果浓缩汁在储藏过程中非酶褐变的主要原因。结果表明,在18℃和37℃储藏条件下,菠萝全果浓缩汁中的总酚、花色苷、抗坏血酸、HMF等成分的变化与浓缩汁的色差值(ΔE)变化密切相关;较高的花色苷初始含量和较快的积累速率直接或间接影响着果汁品质,花色苷是导致菠萝全果浓缩汁品质下降的最重要因素。     

导致乳粉贮藏加工劣变的主要化学反应和物化因素的研究进展

我国乳制品安全日益受到大众的关注,其中乳粉是焦点之一。目前乳粉贮藏加工中引起质量劣变的因素主要为三类化学反应——脂质氧化,美拉德反应和乳糖结晶,它们之间存在相互作用,但机理尚未明确。文中针对乳粉贮藏加工中的重要化学变化和它们的影响因素、测定方法和相互作用的研究进展进行了综述,并对乳粉贮藏中化学反应的研究方向提出了展望,为进一步从机理上研究乳粉劣变并确保乳粉质量安全提供依据。     

The effect of multiwall Kraft paper or plastic bags on physico-chemical changes in milk powder during storage at high temperature and humidity

Plastic bags have recently been introduced as an alternative to multiwall Kraft paper bags in packaging milk powder in 25-kg sizes as it is thought that plastic bags are more durable and would preserve the quality of milk powders during storage better than paper bags. However, there is little scientific information available on the performance of plastic bags for milk powder storage. The aim of this study was to compare the properties of skimmed milk powder (SMP) packaged in plastic or paper bags. Commercially produced and packaged SMP in 25-kg plastic or paper bags was stored at 37°C and 90% relative humidity. Samples were analysed at intervals (0, 45, 90 and 135 days) for moisture, water activity, lactic acid content, pH, insolubility index, bulk density, flowability, dispersibility and particle size. The magnitude of change in the majority of SMP properties measured during storage suggests that plastic bags are similar to paper bags in maintaining milk powder quality during storage.     

Comparative study on the characteristics and oxidation stability of commercial milk powder during storage

The quality of milk powder can decrease during storage. In this study, the characteristics of 12 kinds of commercial milk powder from China were investigated. Changes in various indicators were tracked to comprehensively estimate the oxidation stability of different commercial milk powders. The components of the commercial milk powder were different. The percentages of milk fat, protein, and carbohydrates ranged from 9.8 to 28.5 g/100 g, 15.0 to 24.0 g/100 g, and 32.0 to 67.5 g/100 g, respectively. The water activities ranged from 0.2394 to 0.5286. The diameters of the milk fat globules in different commercial milk powder ranged from 13.99 to 41.09 nm. At the same time, the peroxide value of the control sample was low (≤0.14 mEq/kg). After 3 mo of storage, the peroxide values of some of the commercial milk powder increased significantly. The changes in the thiobarbituric acid values during storage did not follow a common trend. The contents of free fat in the different control samples were 0.21 to 1.67 g/100 g, and these values did not increase during storage. After 3 mo of storage, the hydroxymethyl furfural values and b color values of the different commercial milk powder reached their highest levels. The concentrations of typical oxidized flavor compounds in different commercial milk powder increased greatly with prolonged storage time. The level of hexanal was the highest, and the contents in all the samples ranged from 28.56 to 4,071.28 μg/kg after 6 mo of storage and from 5.91 to 6,281.37 μg/kg after 12 mo of storage. Free radicals were found in some of the stored milk powder, and these were shown as single peaks or multiple peaks. The ratios of the peak areas and masses reached 12.42 × 10⁶ to 14.26 × 10⁸. However, the presence of free radicals in the commercial milk powder was not consistent. The water activities and diameters of the fat globules in the commercial milk powder were highly correlated with their oxidation stabilities during storage.     

原生态与人工添加二十二碳六烯酸羊乳制品贮藏期脂肪酸稳定性比较

通过饲喂奶山羊富含二十二碳六烯酸（docosahexaenoic acid，DHA）的微藻粉，获得原生态DHA羊乳（DHA含量为30 mg/100 g原料乳），然后将其制作成超高温瞬时灭菌（ultra-high temperature instantaneous sterilization，UHT）乳及全脂乳粉，同时设立人工添加富含DHA微胶囊粉的UHT乳及全脂乳粉作为对照组，在常温（25 ℃）和高温（37 ℃）下进行为期28 d的贮藏实验，研究原生态与人工添加DHA羊乳制品贮藏期脂肪酸稳定性。结果表明，与人工添加组相比，贮藏期间原生态UHT乳及全脂乳粉的DHA含量下降速率明显减缓，在UHT乳中，人工添加组乳制品DHA含量降低率在37 ℃下最高达（40.92±3.52）%（贮藏第28天），此时原生态组DHA降低率为（36.70±4.84）%。贮藏期间，原生态与人工添加DHA的UHT乳及全脂乳粉中多不饱和脂肪酸相对含量总体均下降，且与人工添加DHA的乳制品相比，原生态组中多不饱和脂肪酸相对含量更高，更易氧化生成碳链更短的脂肪酸。此外，随着贮藏期的延长，原生态DHA乳制品组中的油脂氧化指标过氧化值和酸价上升速率明显低于人工添加DHA乳制品组。综上，本实验可为制备富含DHA的天然奶制品提供理论参考。     

Stability of retinol in milk during frozen and other storage conditions.

The effect of storage temperature and storage time on the retinol content of four commercial unfortified whole UHT milk samples was studied by HPLC. Significant losses of retinol in these milks were observed after 1 month of storage at 30 degrees C. Losses generally increased with storage time. Increasing the storage temperature from 30 degrees C to 40 degrees C had a variable effect depending on the particular milk. Short periods of frozen storage (up to 60 days) had no effect on the retinol content. However, frozen storage time from 4 to 8 months led to significant (P < 0.05) losses in retinol content. The effect of water activity and temperature conditions during storage of unfortified whole milk powder on the stability of retinol was also studied. Increasing the activity of water and temperature of storage significantly lowered the retinol content in milk powder.     

Storage induced changes to high protein powders: influence on surface properties and solubility

BACKGROUND: MPC 80 is a high‐protein (80%) milk powder commonly used in the food industry as a functional ingredient and valued for its nutritional quality. However, its rehydration properties decline during storage, causing more time to be required for rehydration of the powder by the end user. It is thought that changes at the surface of the powder particles contribute to this reduced solubility during storage. RESULTS: Surface composition and structural changes in milk protein concentrate (MPC) were observed during 90 days of storage at temperatures of 25 and 40 °C and relative humidities of 44, 66 and 84%. No significant changes to the surface composition (fat, protein and lactose) of the MPC powder samples occurred during storage; however, some changes in the microstructure of the powders were observed. Scanning electron microscopy analysis of the powder particles during dissolution showed the formation of a crust, consisting of a thin layer of fused casein micelles, on the surface of the stored powders. An increase in the hydrophobicity at the surface of the particles was evident by X‐ray photoelectron spectroscopy analysis of the bonding state of the elements at or near the surface and by atomic force microscopy measurements of the adherence of particles to the surface of a material. CONCLUSION: The development of this ‘crust’ is thought to contribute to the decrease in the solubility of the powder particles during storage. The increase in the hydrophobicity at the surface and the casein micelle interactions resulting in the surface crust formation appear to contribute to the decrease in the solubility of MPC during storage. Copyright © 2011 Society of Chemical Industry     

Differences in particle characteristics and oxidized flavor as affected by heat-related processes of milk powder

Understanding the formation of oxidized flavor will be highly useful in the improvement of milk powder quality. Effects of preheating, concentration and spray-drying on the particle characteristics and the oxidized flavor stability of milk powder were investigated. The surface composition and free radicals were analyzed using x-ray photoelectron spectroscopy and electron spin resonance spectrometry, respectively. The concentrations of selected oxidized volatiles hexanal and 2-heptanone were determined using solid-phase microextraction gas chromatography-mass spectrometry. Levels of hexanal and 2-heptanone in fresh milk powder were higher than those in raw milk and heated milk, which drastically increased with increasing time of storage. Differences in the morphological observations, free fat, and surface composition of fresh milk powder were found among different heat-related processes. During storage, a radical (g value, a characteristic constant whose value serves to identify any given free radical, was 2.0054) was detected in milk powder. The specific population of the radical increased from 2.99 × 10⁷ at 3 mo to 1.23 × 10⁸ at 6 mo of storage. Addition of ascorbic acid in milk powder changed the type of radicals and reduced the oxidation off-flavor. According to the Pearson correlations, not the surface compositions but the morphological characteristics of milk powder particles should be considered in maintaining the stability of oxidized flavor in storage.     

益生菌冻干保护剂优化及菌粉保存稳定性研究

以嗜酸乳杆菌KLDS AD1和KLDS AD2和双歧杆菌KLDS 2.0604为研究对象,研究冻干保护剂脱脂乳、蔗糖、海藻糖、葡聚糖和Vc钠盐对各菌株冻干存活率的影响,通过单因素、正交实验筛选出优化组合,得出冻干存活率均在87.81%以上。并研究采用优化后的冻干保护剂制备的各菌粉在4℃和25℃下的保存稳定性。保存稳定性实验表明:3株益生菌菌粉在4℃和25℃下保存12个月后,菌粉的活菌数最多下降2个数量级,其活菌数均在1.0×108cfu/g以上。     

保藏温度及时间对UHT 灭菌乳品质的影响

以复合塑料袋装UHT 灭菌乳为研究对象,考察保藏温度和时间对UHT 灭菌乳品质的影响。研究表明,保藏温度和时间对UHT 灭菌乳的蛋白质、乳脂肪、乳糖、滴定酸度及感官指标均有显著影响。具体而言,随保存时间延长,蛋白质、乳脂肪、乳糖含量及感官品质降低,而滴定酸度升高。保藏温度越高,以上变化明显加剧。4℃条件下,保藏时间范围内,样品的感官评分均保持在98 分以上,说明具有优良的感官品质;而保存在22℃和37℃条件下,感官品质下降,且保藏温度越高,感官品质降低越明显。     

Lipid and Cholesterol Oxidation in Whole Milk Powder during Processing and Storage

The influence of animal feed quality on lipid and cholesterol oxidation in whole milk powder was investigated. Powders from a herd receiving a ‘supplemented’ diet showed reduced PV (p < 0.01) and TBARS (p < 0.09) compared to a ‘restricted’ herd, after storage in both vacuum and sachet-packs and less (p < 0.003) cholesterol oxidation products (COPs). High pre-heating temperatures resulted in higher levels of PV, TBARS and COPs in fresh whole milk powders than low pre-heat temperatures, but after storage the reverse occurred. Superior animal feed quality and proper control of processing and storage conditions enhanced oxidative stability of whole milk powder. Lipid and cholesterol oxidation were positively correlated (p < 0.001).