食品射频灭菌过程加热均匀性调控研究进展

作为一种新型物理灭菌技术,射频(radio frequency, RF)加热具有穿透深度大、传热效率高、无化学残留、适合批量处理等特点,可有效杀灭食品中的致病菌。然而,受物料本身特性参数、射频系统结构、物料周围介质等因素影响,非均匀加热一直是射频灭菌规模化应用面临的主要挑战之一。为进一步明确食品射频灭菌过程均匀性调控的最新研究进展,本文基于射频杀菌的机制及特点,对调控射频加热均匀性的具体措施进行了梳理,包括调控物料介电参数、改变环境介质、优化射频加热系统等,为加热均匀性调控的进一步研究及射频灭菌技术的进一步应用奠定基础。     

不同形状尺寸冷冻牛肉的射频解冻均匀性探究

分别选取不同形状、厚度、底面积和放置方式的8种冷冻牛肉样品,采用频率为40.68 MHz的小型射频解冻炉进行解冻试验;基于试验数据,建立并求解计算机模型,预测样品的解冻升温速率和温度分布,并计算其解冻均匀性系数。结果表明,模拟计算得到的温度值与试验值契合度较高;所有牛肉样品的解冻速率整体上呈线性上升的趋势(相变温度区上升较缓慢)。厚度大的样品解冻速度快,但解冻均匀性较差;相同厚度的样品,底面积越大,解冻速度越慢,解冻均匀性较好;当样品垂直放置时,长方体样品出现严重过热现象,最高温度达到了55.2℃,解冻均匀性较差,而圆柱体样品的最高温度为36.6℃,解冻均匀性相对较好。     

狭鳕鱼糜射频解冻均匀性优化

射频加热时物料的介电特性随着温度变化会导致冷热点部位吸收能量不同,致使温度分布产生差异。提高加热均匀性是射频解冻中最为关注的问题。研究射频功率、电极板间距、间歇加热时间等因素对冷冻鱼糜解冻均匀性的影响,并采用正交试验设计对解冻工艺进行优化。由正交试验结果可知,对狭鳕鱼糜解冻后温度的标准偏差的影响的主次顺序为:射频功率(A)>极板间距(B)>间歇时间(C);对狭鳕鱼糜解冻所需时间影响的主次顺序为:极板间距(B)>射频功率(A)>间歇时间(C)。根据综合平衡法取狭鳕鱼糜最佳解冻参数A1B3C3,即射频功率1.5k W、极板间距15 cm、间歇时间2.0 min。验证试验结果表明,鱼糜上表面平均温差15.2℃,温度标准偏差2.5℃,解冻均匀性较好,平均解冻所需时间8.2 min,验证试验结果与优化预期结果较为相符。     

微波加工过程中食品温度分布规律及其均匀性研究

微波加热因其加热速度快、操作简便等特点,已成为食品加工业的研究热点之一。虽然微波加热技术在过去几十年里发展快速,但加热不均匀仍是微波加工过程中存在的主要问题,许多学者对其温度分布规律、加热均匀性改善等方面做了大量研究。该文首先介绍了微波加热技术在食品行业中的发展过程及应用优势,并阐述了微波加热的基本原理、介电特性及穿透深度的含义,在此基础上按照食品种类,对微波加工过程中发现的温度分布不均的现象进行归纳,并对现有改善均匀性的方法进行总结,改善方法包括提高电场分布均匀性、改善食品组分及几何尺寸、优化环境媒介及包装形式,最后对改善食品微波加热的均匀性研究提出几点展望。     

射频加热技术在食品工业中的应用

射频加热技术作为一种新型热加工技术,其在食品干燥、杀菌、杀虫、解冻等领域的潜力被广泛开发,并且在这些领域已有部分工业应用。文章综述了射频加热技术机理、在食品领域的应用以及射频加热过程的数学建模方法,指出了射频加热技术目前存在的加热不均匀性等问题及解决方案,并对未来研究的方向进行了展望。     

射频加热技术在农产品和食品加工中的应用

射频加热技术是近年来广受关注的一种加热方式,因其具有加热迅速、均匀性好、节约能源、维护成本低等特点,被广泛应用于食品和农产品的加工之中。该文首先对射频加热技术的工作原理和特点进行探讨,提出可以通过使用COMSOL软件的模拟实现来改善射频加热的均匀性;然后,通过分析近年来射频加热技术的应用文献,综述了射频加热技术在解冻、干燥、灭菌和杀虫等领域的研究进展;最后,提出了射频加热技术尚存的问题,并对未来研究方向进行展望。     

超声波处理对畜肉解冻过程与解冻后品质影响的研究进展

冷冻是食品保藏的重要方法,部分冷冻食品在消费前仍需进行独立的解冻处理。传统解冻方法存在升温不均匀、处理时间长且汁液损耗大的问题。作为新的解冻技术,物理场解冻受到了广泛的研究和关注。本文综述了近年来物理场解冻在冷冻食品加工中的研究进展,阐述了超声波、介电和电场等技术在解冻过程中的作用机理和应用效果。相对于传统解冻,物理场解冻更好地保持食材的营养成分、维持感官品质,减少汁液流失,同时提高解冻效率。不同种类的食品原料和解冻方法可能会引起差异性的效果,需要分析实际原料对物理场的响应规律和特征理化指标,如介电常数、电导率和脂肪含量等,从而得到最佳的解冻条件。未来的研究应聚焦于探究高效稳定且低能耗的物理场辅助技术,继续深入研究对食材品质和解冻效果的影响,以更好地满足消费者对冷冻食品的高效处理需求。

     

冷冻猪肉欧姆加热解冻电势梯度与尺寸对解冻效果的影响

欧姆加热解冻是一种潜力很大的解冻方法。试验中研究冻结物料的尺寸、电势梯度对解冻时间、解冻速率、失水率、解冻均匀性和能量利用率的影响。选用尺寸不同的冻猪肉进行了解冻试验,尺寸分别为直径3、4、5 cm,长度为6 cm。解冻时从中心温度-18～5℃。试验过程中,变换解冻材料中的电势梯度,分别为20、30、40V/cm。结果表明:电势梯度和尺寸对解冻均匀性、失水率、能量利用率的影响不大。电势梯度和样品尺寸对解冻时间的影响较明显,电势梯度变大,解冻时间变小,尺寸增大,解冻时间变长。电势梯度和尺寸对解冻速率的影响分为两个阶段。电势梯度和尺寸对内部冻结温度以下的解冻速率影响不明显。在内部冻结温度以上,电势梯度增大,解冻速率变大,解冻加快,样品尺寸变大,解冻速率降低。欧姆加热解冻较传统解冻中的水解冻具有很大的优势。     

微波加热过程中圆柱型包装食品的温度分布研究

从实验和理论上考察介电特性(介电常数、介电损失率)对圆柱型食品温度分布形态形成的影响。实验中以凝胶琼脂为实验样品,通过对样品添加NaCl来改变样品的介电特性,采用液晶感温片测得样品直径面的温度分布。结果表明,添加NaCl可提高样品的表面加热性,使样品的温度分布高温区由中心部向着项角部转移。为了从理论上对该现象加以描述,采用数学模型对样品中的温度分布进行了计算,结果表明,计算值与实验值有着良好的一致性。     

通电加热技术在食品加工中的应用

从通电加热技术的发展历史入手.阐述了该技术的原理和特点;并从电场、频率、物料本身等方面讨论了通电加热的各种影响因素及其作用机理;介绍了目前对该技术的研究成果,以及该技术在食品加工中的应用和广阔的发展前景.     

Recent developments in applications of radio frequency heating for improving safety and quality of food grains and their products: A review

Abstract

Food grains constitute a vital part of the daily diet of the population worldwide, and are generally considered as safe products with high storage stability due to their low moisture contents. However, post-harvest losses (PHL) caused by insects, fungi, food-borne pathogens, and undesirable enzymes remain a major concern for the grain industry. Thermal treatments are commonly used to reduce the PHL of grains and their products without any chemical residues. Among which, radio frequency (RF) technology has been regarded as a promising alternative to traditional heating methods for improving safety and quality of food grains due to its fast, volumetric, and deep penetration heating characteristics. This review provided comprehensive information about principles of RF technology and its main applications including disinfestation, pasteurization, enzyme inactivation, drying, and roasting for processing food grains and their products. The methods to improve the RF heating uniformity and effects of RF heating on product quality were also reviewed. Finally, the current problems and recommendations for future work related to RF processing of grains and their products were discussed. This review would improve the understanding of RF heating for food grains and their products and promote the application of RF technology in the food grain industry.     

Computer simulation for improving radio frequency (RF) heating uniformity of food products: A review

Radio frequency (RF) heating has great potential for achieving rapid and volumetric heating in foods, providing safe and high-quality food products due to deep penetration depth, moisture self-balance effects, and leaving no chemical residues. However, the nonuniform heating problem (usually resulting in hot and cold spots in the heated product) needs to be resolved. The inhomogeneous temperature distribution not only affects the quality of the food but also raises the issue of food safety when the microorganisms or insects may not be controlled in the cold spots. The mathematical modeling for RF heating processes has been extensively studied in a wide variety of agricultural products recently. This paper presents a comprehensive review of recent progresses in computer simulation for RF heating uniformity improvement and the offered solutions to reduce the heating nonuniformity. It provides a brief introduction on the basic principle of RF heating technology, analyzes the applications of numerical simulation, and discusses the factors influencing the RF heating uniformity and the possible methods to improve heating uniformity. Mathematical modeling improves the understanding of RF heating of food and is essential to optimize the RF treatment protocol for pasteurization and disinfestation applications. Recommendations for future research have been proposed to further improve the accuracy of numerical models, by covering both heat and mass transfers in the model, validating these models with sample movement and mixing, and identifying the important model parameters by sensitivity analysis.     

Analysis of radio frequency (RF) power distribution in dry food materials

The objectives of this research were to investigate the influence of various factors on radio frequency (RF) power distribution in dry food materials, placed in a 12 kW, 27.12 MHz parallel plate RF system, using a validated finite element computer model. The factors investigated were sample size, shape, relative position between the RF electrodes, and dielectric properties (DPs) of the sample and the surrounding medium. Effects of electrode gap and top electrode configuration on the RF power distribution behavior of the sample were also studied. The RF power uniformity in the samples was compared using RF power density uniformity index (PUI). Simulated results showed that the RF power uniformity in cuboid shaped samples, placed on the bottom electrode, first decreased and then increased with the increase in sample size. The sample shape and its vertical position between the fixed gap parallel plate electrodes also affected the RF power distribution and uniformity. A cuboid sample had higher RF power densities at the edges, while an ellipsoid had higher power densities in the center parts. Simulated results showed that the smaller values of DPs resulted in better RF power uniformities in the samples. Reducing the electrode gap improved the RF power uniformity of the sample. While studying the influence of the top electrode configuration on the RF power distribution and uniformity, the results showed that optimum RF power uniformity in a particular sample size could be achieved with a particular top electrode bending position and angle. The results are useful in understanding complex RF heating, designing and scaling up of efficient RF systems.     

A microwave and ohmic combination heater for uniform heating of liquid-particle food mixtures

Microwave and ohmic combination heating was proposed to improve the uniformity of thermal processing of particulate foods. Thermal patterns of a liquid-particle mixture in a small test cell were studied using both experimental and simulation approaches. Carrot cubes (10 mm × 10 mm × 10 mm) and 0.1% NaCl salt solution were used as model foods. The temperature distribution of solid and liquid phases was examined using individual and combination heating methods. Under ohmic heating, the liquid was heated faster by 18.9 °C after 250 s. The heating rate of a carrot cube was faster than liquid under microwave heating and temperature rise of carrot was approximately 11.2 °C higher than that of solution after heating of 70 s. Samples experienced different heating patterns over time during the combination heating. Carrot samples showed a thermal lead initially when heated under microwave and the trend reversed during the second stage when ohmic heating was applied. Liquid-particle temperature difference was reduced as the combination heating proceeded, and came to be less than 2 °C at the end. Results obtained from simulation showed similar patterns and all prediction data agreed well with the experimental data. The prediction errors for sample temperatures ranged from 5.7% to 11.6%. The results provided better understanding for designing a continuous flow combination heater that can produce uniform temperature of solid-liquid mixtures. PRACTICAL APPLICATION: If successful, this combination heating technique will find its way to effective aseptic or sterile processing of low acid multiphase foods containing large particulates (such as soups with meatballs or vegetables) that has not been a commercial reality in the United States.     

微波技术在食品解冻中的研究进展

随着冷冻食品消费量的不断增加,快速有效的解冻方式也日益受到重视,其中微波解冻技术由于其独特优势在冷冻行业得到快速发展与应用。本文就微波解冻的基本原理与特点及其在食品解冻中的应用作一介绍,并对存在的问题及研究趋势进行了总结和展望。