Effect of Temperature (−5 to 130 °C) and Fiber Direction on the Dielectric Properties of Beef Semitendinosus at Radio Frequency and Microwave Frequencies

ABSTRACT:  The dielectric properties must be defined to design efficient radio frequency (RF) and microwave (MW) processes by the food manufacturers. The objective of this study was to understand how frequency, temperature, and muscle fiber orientation influence the dielectric properties. The eye of round ( Semitendinosus ) muscle was selected because it contains large, relatively uniform muscle cells with similar muscle fiber orientation and relatively uniform chemical composition throughout the tissue. Dielectric properties were measured using an open-ended coaxial probe technique at 27, 915, and 1800 MHz and temperatures between −5 and 130 °C. Power penetration depth was calculated. Since many commercially prepared, thermally processed, ready-to-eat entrees are made with frozen meat, dielectric property measurements were started from −5 °C. The dielectric constant and dielectric loss factors were often higher for muscle with the muscle fiber measured in a parallel orientation to the probe compared to samples of the same treatment (for example, fresh or frozen) in a perpendicular tissue orientation at the same frequency and temperature. Dielectric constant and loss values for frozen beef tended to be higher than fresh beef at the same temperature and frequency. Tissue orientation appeared to have a greater effect on dielectric loss values at lower frequencies. Penetration depth tended to be greater when the direction of propagation was perpendicular to the muscle fiber.     

NaCl添加量及pH对马铃薯泥品质特性的影响

该试验以蒸制熟化的马铃薯泥为对象,利用电子眼、应变控制流变仪、物性测试仪、扫描电子显微镜、激光共聚焦显微镜、X-射线衍射仪、核磁共振分析系统等,研究NaCl添加量（0%、0.5%、1.0%,m/m,以薯泥计）及pH（6、7、8）对马铃薯泥色泽、流变学特性、质构特性及微观结构等的影响规律。结果表明：随NaCl添加量的增加,马铃薯泥弹性由81.86%减小到79.40%、硬度由551.72 g增大到784.28 g,网络结构受到一定的破坏。随pH的增加,与pH为6时相比,马铃薯泥的弹性由81.44%减小到75.96%、硬度呈先降低后升高的趋势,稳定性减弱;当pH为6时,马铃薯泥弹性最大（81.44%）,硬度较小（528.84 g）,形成了致密的凝胶网络结构。综上所述,在不添加NaCl、pH为6时,马铃薯泥具有最佳的加工特性。该研究可为采用NaCl及调节pH制备适用于主食及休闲食品加工的高品质马铃薯泥提供理论依据。     

响应面法优化马铃薯泥面条工艺配方

为加快马铃薯主食化进程,降低马铃薯全粉面条的成本,有效利用马铃薯中的营养成分,以马铃薯泥为原料,对马铃薯泥面条的工艺配方进行研究。在单因素试验的基础上,利用响应面法优化马铃薯泥面条工艺配方,研究面条中马铃薯泥添加量、盐添加量、水添加量对感官得分和断条率的影响,得出回归方程预测模型。结果表明:马铃薯泥、盐和水的添加量分别为40.65%、0.40%、17.13%时,感官得分最高为98.13,面条的断条率最低为6.15%。该研究为马铃薯泥面条的进一步研究提供理论依据。     

肉品的消毒灭菌方法

本文综述了肉品消毒灭菌的控制方法。     

Electrochemical Impedance Spectroscopy as an Alternative to Determine Dielectric Constant of Potatoes at Various Moisture Contents

The dielectric (DE) properties, specifically the DE constant (ε′) and loss factor (ε′′), were measured for vacuum‐dried and freeze‐dried potato samples at a microwave frequency of 2.45 GHz over a range of different moisture contents (MCs) using a DE probe and also a 2‐probe electrochemical impedance spectroscopy (EIS). Third‐order polynomial models (ε′ = f₁(MC); and ε′′ = f₂(MC)) at room temperature were developed for regression analysis. Additionally, at various temperatures (T), biphasic 3rd‐order polynomial models (ε′ = f₁(MC, T); and ε′′ = f₂(MC, T)) were obtained to determine ε′ and ε′′ as a function of MC and T using measured data. The vacuum‐dried potato sample showed a good fitness of ε′ and ε′′ (R² = 0.95 and 0.96, respectively) to the regression model with the range of MCs from 18% to 80% (w/w), while the freeze‐dried potato sample showed a good fitness of ε′ and ε′′ to the 1st‐phase regression model with MC < 50% w/w (R² = 0.95 and 0.96, respectively) and the 2nd‐phase regression model with MC > 50% w/w (R² = 0.94 to 0.96). EIS measurements were also used to obtain correlation impedances for ε′ and ε′′ determined by the DE probe method. The resulted regression analysis meets the demands for simple, rapid, and accurate assessment for transient values of ε′ and ε′′ of food products during dehydration/drying processes. The EIS method was verified to be a successful alternative to direct measurements of ε′ and ε′′.     

Dielectric Properties of Cloudy Apple Juices Relevant to Microwave Pasteurization

Continuous flow microwave heating is an emerging technology that brings advantages to the pasteurization of food products such as fruit juices. In order to correctly design the microwave cavity and applicator tube, knowing the dielectric properties of the product is important. The relative electrical permittivity describes the capacity to store electrical energy, while the dielectric loss factor describes the ability to dissipate energy as heat. The penetration depth of microwaves depends on these properties and on the field frequency. In this work, the dielectric properties and electrical conductivity of cloudy apple juices, obtained from different varieties of apples (Gala, Fuji, Granny Smith, and Red Delicious) and from an industrial plant (Gala), were determined from 500 to 3000 MHz and temperatures between 10 and 90 °C. Penetration depth was also calculated, and all results were correlated with temperature for commercial frequencies of 915 and 2450 MHz. At these frequencies, apple variety showed little influence and the permittivity decreased almost linearly with temperature. The loss factor curves showed a minimum around 40 °C at 915 MHz and were slightly smaller for juices with lower conductivity. At 2450 MHz, the loss factor varied between 7 and 18 with a negative temperature effect, which indicates that thermal runaway should not be a problem. The penetration depth ranged from 33 to 58 mm at 915 MHz and from 9 to 23 mm at 2450 MHz, depending on temperature and variety, which is useful information for the design of applicator tubes.     

响应面法优化包装型马铃薯泥营养餐的加工工艺

以马铃薯泥为主要原材料,制做包装型马铃薯泥营养餐。以感官评分和菌落总数为指标,在单因素试验的基础上,采用响应面试验对包装型马铃薯泥营养餐的加工工艺进行优化。结果表明,包装型马铃薯泥营养餐的最佳加工工艺为:蒸煮时间10 min、灭菌温度117℃、灭菌时间8 min。在该工艺条件下制得的包装型马铃薯泥易于储藏、消费者接受程度高,菌落总数为2 CFU/g。     

黑胡椒颗粒的介电特性混合方程研究

通过介电混合方程对黑胡椒颗粒的介电特性进行推算,对比模拟值与实验值以验证介电特性混合方程的适用性。以黑胡椒颗粒为研究对象,测定压缩黑胡椒粉的介电特性,并运用介电特性混合方程-CRIME方程、LLLE方程、BE方程计算获得胡椒颗粒的介电特性,随后运用COMSOL Multiphysics软件建立静电场-热传导双向耦合模型对射频加热仿真,并通过27.12MHz,12 k W的平行极板式射频系统进行加热实验验证。采用CRIME方程获得的胡椒颗粒介电特性运用在仿真中与试验结果温度分布为最接近。作者证明了通过压缩胡椒粉末介电特性代入CRIME方程能够有效获得黑胡椒颗粒的介电特性,这有助于工业生产中颗粒物料射频加热工艺的研发。     

微波杀菌对卤猪肝品质特性的影响

为了研究微波杀菌技术对卤猪肝品质特性的影响,以卤猪肝为研究对象,采用微波等杀菌方式对酱卤猪肝进行杀菌,研究微波杀菌对卤猪肝杀菌效果及含水率、质构、色泽、维生素等理化指标的影响。结果表明:微波杀菌后卤猪肝水分含量降低,嫩度下降,韧性增强,在表面温度达到70℃时,其杀菌效果与高温杀菌接近,且微波杀菌后,卤猪肝的色泽变暗、VA含量减少,但与高温杀菌相比,品质变化较小。