Maturity effects on dielectric properties of apples from 10 to 4500 MHz

Dielectric properties of external surface, internal tissue and juice of Fuji apples during the last two months of tree-ripening were measured with an open-ended coaxial-line probe and a network analyzer at 24 °C from 10 to 4500 MHz. The firmness, soluble solids content (SSC), pH, moisture content and electrical conductivity were also measured to determine whether permittivity is related to apple quality. During the tree-ripening period, the permittivity and electrical conductivity did not reveal obvious trends. Moisture content and SSC remained essentially constant, while the firmness decreased and pH increased with maturity. No obvious correlations were found between permittivity and firmness, moisture content or pH. The linear relationship between surface permittivity and SSC was poor (R² < 0.2). The best R² for linear regression between loss tangent of tissue and SSC and between dielectric constant of juice and SSC was 0.61 and 0.67, respectively, at 4500 MHz. Further studies are needed to assess the potential usefulness of dielectric properties for sensing apple maturity or internal quality.     

蛋清粉凝胶特性改性研究进展

蛋清粉作为一类干燥的蛋制品,既保有了蛋清蛋白优良的功能特性,同时规避了液蛋制品难贮藏、难运输的固有弊端,因而用途十分广泛。为了进一步满足市场对高凝胶性蛋清粉的需求,国内外研究者对此做了大量的工作。本文从蛋清蛋白的组成着手,阐述了蛋清蛋白凝胶性能的影响机理,着重对蛋清粉凝胶特性的改性研究进展进行了综述,以期为丰富食品蛋白质凝胶化理论研究以及拓展蛋清粉高效应用提供参考。      

915MHz和2450MHz下扇贝柱介电特性的研究

利用介电网络分析仪测量温度20~100℃,频率0.3~3GHz下扇贝柱介电常数和介电损耗因数,从而得出扇贝柱在微波加热过程中温度和频率对介电特性的影响。结果表明,温度一定时,介电常数和介电损失因数都是先随着频率增加而降低,随后变化不显著;频率915MHz和2450MHz时,介电常数与温度成负相关,介电损耗因数与温度成正相关。且915MHz和2450MHz下,穿透深度随温度的升高而减小。扇贝柱介电特性的研究为微波杀菌技术的研究提供了理论基础。      

全脂乳粉和脱脂乳粉在1kHz～10MHz下的介电特征研究

分别研究了各4种不同品种的全脂乳粉和脱脂乳粉在1kHz～10MHz波段的介电特性。结果发现:随着频率的增加,全脂乳粉和脱脂乳粉的ξ’和ξ″值呈单调递减趋势;全脂乳粉的ξ’和ξ″值都高于脱脂乳粉,相同类型乳粉各品种间的ξ’和ξ″差异不大;全脂乳粉的ξ″值在103～105Hz频率段减小趋势明显,且ξ″值的对数与频率的对数成线性反比关系,而脱脂乳粉无此规律;全脂乳粉和脱脂乳粉的穿透深度Dp随频率的提高而减小,两类乳粉的介电特性差异可能与它们各自的脂肪和乳糖含量有关。     

915MHz和2450MHz频率下温度和盐溶液浸渍对青鱼介电特性的影响

采用同轴探针法测定了频率915、2450MHz,温度范围10～90℃下,经浓度1%、2%、3%、4%食盐溶液浸渍的生鲜青鱼鱼片和预加热青鱼鱼片的介电特性值,并应用DSC测定了样品肌动蛋白和肌球蛋白的热变性温度。考察了温度、频率、水分含量、食盐溶液浸渍和蛋白质热变性对样品介电常数、介电损失率和穿透深度的影响。结果显示,浸渍盐溶液的渗透使得样品介电行为在一定程度上接近于相应盐浓度的浸渍溶液。浸渍对样品介电常数影响较小,而对介电损失率变化较大。随温度的上升,因加热过程中蛋白质的热变性引起样品水分的流失,导致生鲜样品的介电常数值的减小趋势明显大于预加热样品。而经浸渍的生鲜样品的介电损失率增大趋势明显大于预加热样品,并随浸渍溶液含盐量增大而增大。应用二项式方程得出介电特性的回归预测方程。      

Functional Properties of Milk-Egg Mixtures

We used an experimental design (Scheffe simplex-centroid design) to examine ingredient interactions in food protein mixtures and their effects on functional properties. A defined and limited number of milk, albumen, and egg yolk blends were made and evaluated for heat gelation properties and for emulsifying and foaming capacity and stability. The method accounted for nonlinear interactions between the ingredients. Synergistic effects were revealed on heat gelation and emulsifying properties but antagonistic effects for foaming properties were noted.     

Effect of various refrigeration temperatures on quality of shell eggs

BACKGROUND: The objective of this study was to evaluate the effects of low storage temperatures on shell egg quality. RESULTS: Approximately 2100 shell eggs were collected and stored at ? 1.1, 0.6, 2.2, 3.9, 5.6 and 7.2 °C for up to 4 weeks. Eighteen eggs at each storage temperature were evaluated after 0, 2, 7, 14, 21 and 28 days of storage. Haugh units (HU), yolk index (YI), albumen pH (pHA), yolk pH (pHY) and angel food cake density (CD) were measured. Shell egg quality tended to be preserved better at below 2.2 °C, as high HU and YI values relative to eggs stored at 7.2 °C were determined on day 28. However, storage at ? 1.1 °C tended to cause the opposite effect, especially highly declined HU values over time. Significantly different HU values of shell eggs were measured after 14 days of storage, with eggs stored at 0.6 and 2.2 °C having the highest HU values, 80.42 and 77.97 respectively. CONCLUSION: A lower temperature limit for shell egg storage could be established between 0.6 and 2.2 °C, as both temperatures showed the highest HU values, 77.88 and 77.60 respectively, after 28 days of storage. Copyright © 2011 Society of Chemical Industry     

基于低场核磁共振技术的咸鸭蛋腌制过程水分及质构特性变化

运用低场核磁技术测定腌制过程中蛋清和蛋黄中水分的横向弛豫时间(T_2)和信号强度,并表征蛋清和蛋黄中水分的迁移过程,同时结合蛋清和蛋黄的含水率、含盐量和质构特性分析了盐离子对咸鸭蛋品质的影响。结果显示:在腌制过程中,蛋清和蛋黄中的水分不断向外迁移,水分含量显著降低(P0.05),蛋清中水分的T_2显著增加(P0.05),表明蛋清中不同类型水分受到的束缚力降低,水分的自由度增大,其中T_(22)相对降低,T_(23)相对增加,质构指标(硬度、弹性、内聚性和咀嚼性)显著降低(P0.05),持水力前期显著降低(P0.05),后期略有增加;随着鸭蛋内盐分含量的显著增加(P0.05),蛋黄中不同类型的水分的T_2显著降低(P0.05),蛋黄中的成分结合的更加紧密,硬度、内聚性和咀嚼性显著增加(P0.05),而弹性却显著降低(P0.05)。应用低场核共振磁技术对咸鸭蛋状态及水分含量的测定可以作为预测咸鸭蛋成熟度和品质的参考指标。     

储藏条件对大豆籽粒力学特性的影响

选取黑龙江大豆,使其储藏60、90、120、150 d,储藏温度分别为20、25、30℃,储藏籽粒的含水率分别为12.0%、13.5%、15.0%,使用Brookfield质构仪测定了不同储藏温度、不同含水率、不同储藏时间的大豆籽粒的最大破坏力、最大破坏力能、最大破坏应变。试验结果表明:储藏60 d,储藏温度为20~30℃,储藏籽粒的含水率为12.0%~15.0%,大豆籽粒压缩最大破坏力、最大破坏能、最大破坏应变的变化范围分别为:106.85~90.19 N、160.80~108.92 mJ、0.356~0.412;储藏150 d,储藏温度为20~30℃,储藏籽粒的含水率为12.0%~15.0%,大豆籽粒压缩最大破坏力、最大破坏能、最大破坏应变的变化范围分别为:99.19~81.50N、113.01~90.52 mJ、0.439~0.472;在相同的储藏温度、储藏时间条件下,大豆籽粒的压缩最大破坏力、最大破坏能随着含水率的增加而减小,最大破坏应变随着含水率的增加而增加;在相同的含水率、储藏时间条件下,大豆籽粒的压缩最大破坏力、最大破坏能随着储藏温度的增加而减小,最大破坏应变随着储藏温度的增加而增加;在相同的储藏温度、含水率条件下,大豆籽粒的压缩最大破坏力、最大破坏能随着储藏时间的增加而减小,最大破坏应变随着储藏时间的增加而增加。     

糙米储藏水分对糊化特性的影响

对13.5%、14.5%、15.5%、16.5%水分条件下储藏的糙米进行定期的RVA测定,糙米放入温度设定为25℃的恒温箱中储藏,储藏时间为6个月,每30d检测一次。结果表明：不同水分储藏样品的峰值粘度随着储藏时间延长不断增加,储藏水分越高,峰值粘度上升越快;水分、时间对峰值粘度影响极显著（p〈0.01）;峰值粘度与储藏时间、水分呈极显著二元线性关系。储藏样品的最低粘度随着储藏时间延长不断增加,水分含量越高最低粘度越高;水分、时间影响极显著;最低粘度与储藏时间、水分呈极显著二元线性关系。不同水分储藏样品的崩解值随着储藏时间延长变化不同;水分、时间影响显著性分别为0.029、0.000;回归方程显示,低水分储藏崩解值随着储藏时间延长而升高,高水分储藏崩解值与时间则成显著一元二次方程的关系。水分、时间对最终粘度影响显著性为0.000;最终粘度随时间、水分变化经曲线拟合呈显著二元线性关系,回归方程显著。储藏期间,糙米回生值随时间延长显著上升,储藏后期趋于下降;方差分析显示时间对回生值影响极显著,水分影响不显著,不同水分样品与储藏时间均呈极显著一元二次方程关系。含水率越高,糙米食味品质保持越好。     

Effect of Antioxidants on Cholesterol Oxidation in Spray-dried Egg Yolk during Extended Ambient Storage

ABSTRACT: Equimolar amounts of butylated hydroxyanisole, ascorbyl palmitate or a tocopherol blend were added to liquid yolk and spray-dried. One-g samples were stored in the dark at ambient temperature for 36 mo, then evaluated using gas chromatography. The tocopherol blend and BHA inhibited 7-ketocholesterol production. No significant differences were observed between the control and the various antioxidant treatments for the production of other cholesterol oxides. In contrast to the results of a previously conducted accelerated study, the added antioxidant levels were insufficient to significantly reduce cholesterol oxidation in spray-dried egg yolk held for an extended period of time, and additional means of inhibition may be required.     

蛋黄组成成分的性质研究

蛋黄用0.17mol/L氯化钠1∶1等重稀释后,进行冷冻离心可得到上清和沉淀两部分,对其进行了组成、蛋白质溶解度和乳化性质及颗粒形态的分析研究。电泳分析表明,上清部分主要为低密度脂蛋白和卵黄蛋白,沉淀部分主要为高密度脂蛋白和卵黄高磷蛋白。这三部分随着氯化钠浓度的增大,蛋白质溶解度逐渐增大,在氯化钠浓度为0.5mol/L时,蛋黄、上清、沉淀三部分的溶解度在90%以上。在蛋白质溶解度在90%以上时,测定三部分的乳化性质,得出上清部分的乳化活性最好,沉淀部分的乳化稳定性最好。     

蛋白质量浓度对鸡蛋热诱导凝胶特性的影响

以蛋清、蛋黄和全蛋液为原料,研究蛋清、蛋黄和全蛋蛋白热诱导凝胶的形成能力以及蛋白质量浓度对蛋清、蛋黄和全蛋蛋白热诱导凝胶特性的影响。结果表明：蛋清、蛋黄和全蛋形成热诱导凝胶的最低蛋白质量浓度分别为50、55、50mg/mL;在50～135mg/mL范围内,随蛋白质量浓度的增加,蛋清、蛋黄和全蛋蛋白的凝胶强度和保水性不断增大,蒸煮损失整体呈下降趋势;蛋白质量浓度对蛋清、蛋黄和全蛋凝胶的弹性也有显著影响。     

Influence of pH on surface properties of aqueous egg albumen solutions in relation to foaming behaviour

The surface properties of aqueous egg albumen protein solutions (0.1 g litre⁻¹) were studied at pH values of 4.8, 7.0, 9.2 and 10.7 and related to foaming behaviour such as bubble size distribution, overrun and drainage. By measurements far from equilibrium of dynamic steady state surface dilation using the overflowing cylinder technique, egg albumen showed ability to slow down surface expansion and to lower the dynamic surface tension. The pH‐effect was small, but at pH 4.8 the film length, at which a motionless surface was created, was longer than at higher pH indicating a somewhat more rigid surface at low pH. Near equilibrium sinusoidal surface area deformation resulted in relatively high moduli of egg albumen, with a significant effect of pH. The surface modulus E showed at pH 4.8 an increase in the course of time, but at higher pH it was constant. Large deformation of egg albumen surface was not destructive, and for all pH values the surface behaved viscoelastic, with highest loss modulus E″ and tan θ values at pH 4.8. Surface deformation frequency sweeps revealed the relaxation processes to be relatively slow at pH 4.8 and faster at pH 7.0–10.7. Foamability measured as overrun of foam as a result of shaking and stirring was highest at pH 4.8 and lowest at pH 10.7. Foam stability against drainage was best at pH 7.0 after 30 min, but at a long‐term scale foam at pH 4.8 was most resistant to drainage. Foam samples were subjected to microscopy and image analysis. The smallest bubbles were found at pH 4.8 (mean diameter 142 µm) and the largest at pH 7.0 (mean diameter 328 µm). In conclusion, the foaming behaviour of an aqueous egg albumen solution at pH 4.8 can be related to dynamic surface properties as follows: the more rigid behaviour of the surface at this pH favours a small bubble size and slow drainage of liquid from the foam. The high overrun at this pH can be explained by a lower dynamic surface tension, but also here film stability during foam making can be promoted by a more rigid liquid surface. © 1999 Society of Chemical Industry     

热处理对鸡蛋蛋黄性质的影响

研究了不同强度的热处理(处理温度59、62、65、68℃,处理时间0～9 min)对鸡蛋蛋黄上清和颗粒的蛋白质组成、溶解性、乳化性和游离巯基含量的影响。结果表明:蛋黄上清中的γ-卵黄蛋白和蛋黄颗粒中的部分高密度脂蛋白在加热处理过程中发生变性形成大分子聚集体,加热处理对蛋黄上清蛋白质溶解度的影响大于对蛋黄颗粒的影响,温和的热处理对蛋黄上清与颗粒的乳化性质均没有显著影响,68℃处理较长时间会使蛋黄上清与颗粒的乳化活力下降,乳化稳定性提高。热处理过程中蛋黄上清和颗粒的游离巯基含量变化均未表现出明显的规律性。     

Moisture dependence of some electrical and dielectric properties of cassava

The electrical resistance and the 1.0 kHz dielectric properties of cassava were measured at different moisture content values with the Kiethley digital multimeter and GR 1608-A impedence bridge respectively. The resistance increased linearly with decreasing moisture content while the Naperian logarithm of the a.c. conductivity decreased linearly with decreasing moisture content. Regression constants were obtained in both cases. The dielectric constant decreased with decreasing moisture content.     

壳聚糖涂膜对鸡蛋品质的影响

通过对新鲜鸡蛋涂擦不同质量浓度的壳聚糖溶液,旨在研究壳聚糖对鸡蛋品质的影响。试验将300 枚新鲜鸡蛋随机分成6 组,分别涂上0、0.5、1.0、1.5、2.0g/100mL 和2.5g/100mL 壳聚糖溶液,25℃条件下贮存5周。每周从每个处理中取10 枚鸡蛋测定鸡蛋失重率、哈夫单位、蛋黄指数和蛋清pH 值。结果表明,第5 周与第1 周相比,不涂壳聚糖的鸡蛋失重率和蛋清pH 值显著升高(P ＜ 0.05)、哈夫单位和蛋黄指数显著低(P ＜ 0.05) 。5 周时,与不涂壳聚糖的鸡蛋相比,所有涂壳聚糖的鸡蛋失重率显著降低(P ＜ 0.05),蛋黄指数显著升高(P ＜ 0.05);涂1.0、1.5、2.0g/100mL 和2.5g/100mL 壳聚糖的鸡蛋哈夫单位显著升高(P ＜ 0.05),蛋清pH 值显著降低(P ＜ 0.05);涂1.5、2.0g/100mL 和2.5g/100mL 壳聚糖的鸡蛋间比较,蛋质量损失率、哈夫单位、蛋黄指数和蛋清pH 值差异均不显著(P ＞ 0.05)。用0.5g/100mL 壳聚糖涂擦的鸡蛋5 周时降到C 级,相当于不涂壳聚糖的鸡蛋3 周时的级别;用1.0、1.5、2.0g/100mL 和2.5g/100mL 壳聚糖处理的鸡蛋5 周时降到B 级,相当于不用壳聚糖处理的鸡蛋2 周时的级别。该实验证明壳聚糖能够延长鸡蛋货架期。     

不同品种鲜蛋品质差异分析

目的探究褐壳蛋、粉壳蛋和白壳蛋3种类型鸡蛋的品质差异以及对于蛋粉加工的潜在影响。方法选用京红1号、京粉1号和京白1号所产的褐壳蛋、粉壳蛋和白壳蛋作为试验对象,对37周龄和51周龄蛋鸡所产3种类型鸡蛋的蛋品质进行分析比较。结果 37周龄和51周龄的白壳蛋蛋壳厚度、蛋壳比例和蛋壳强度均显著低于其他2个类型鸡蛋(P0.05);37周龄时3种类型鸡蛋的蛋黄水分含量没有显著性差异(P0.05);白壳蛋蛋清水分含量以及总水分含量均较其他2个类型鸡蛋要低。37周龄时褐壳蛋的蛋黄蛋白质和脂肪含量均显著高于其他2个品种,白壳蛋次之,粉壳蛋最低。37周龄时白壳蛋的蛋清蛋白质含量显著低于其他2个品种。由于蛋清中脂肪含量极少,本试验不予考虑。结论褐壳蛋加工成蛋粉后具有更好的营养价值,而白壳蛋可以提高蛋粉加工的产量。     

储藏温度对鸡蛋蛋黄乳化性的影响

本研究通过测定鸡蛋在不同温度(4℃、25℃和37℃)储藏15 d后蛋黄的表面疏水性(H0)、乳化活性(EA)和乳化稳定性(ES)、Zeta电位、粒径分布、蛋白质溶解度、圆二色谱(CD)等指标变化,评估储藏温度对蛋黄蛋白质结构和乳化性的影响。结果表明,随着储藏温度的降低,H0、Zeta电位绝对值和EA均显著降低(p0.05),粒径显著升高(p0.05),相比对照组(3.22±0.03),在4℃储藏15 d后的蛋黄H0下降至1.09±0.04;ES的变化受温度的影响不显著,而蛋白质溶解度仅在低温条件下显著下降(p0.05);CD的结果显示随着储藏温度的升高,α-螺旋和β-折叠含量逐渐降低,无规卷曲含量逐渐升高。本研究发现储藏温度显著影响着蛋黄的乳化性(p0.05),虽然高温储藏会加速鸡蛋品质劣化,高温储藏蛋黄乳化活性(0.63±0.01)优于低温储藏蛋黄乳化活性(0.42±0.02),这为鸡蛋在不同温度储藏条件下蛋黄产品的开发提供理论参考。