On quantifying nonthermal effects on the lethality of pressure-assisted heat preservation processes

Direct experimental identification and quantification of the pressure contribution to a pressure-assisted sterilization process efficacy is difficult. However, dynamic kinetic models of thermal inactivation can be used to assess the lethality of a purely thermal process having the same temperature profile. Thus, a pressure-assisted process' temperature record can be used to generate a corresponding purely thermal survival curve with parameters determined in conventional heating experiments. Comparison of the actual final survival ratio with that calculated for the purely thermal process would reveal whether the hydrostatic pressure had synergistic or antagonistic effect on bacterial spores survival. The effect would be manifested in the number of log cycles subtracted or added to the survival ratio, and in the length of time at the holding temperature needed to produce the final survival ratio of the combined process. A set of combined treatments would reveal how the temperature and pressure profiles affect the pressure's influence on the process' lethality to either vegetative cells or spores. The need to withdraw samples during the thermal and combined processes would be avoided if the thermal survival parameters could be calculated by the "three endpoints method," which does not require the entire survival curve determination. Currently however, this method is limited to thermal inactivation patterns characterized by up to 3 survival parameters, the Weibull-Log logistic (WeLL) model, for example.     

Estimation of the survival curve of Listeria monocytogenes during non-isothermal heat treatments

Published survival curves of Listeria monocytogenes under several constant temperatures in the range of 50–65°C could be described by the model Log₁₀[S(t)]=−b(T)t^n(T), where S(t) is the momentary survival ratio, and b(T) and n(T) coefficients whose temperature dependence was expressed by empirical models. When the temperature history T(t) is also expressed algebraically, b(T) and n(T) are transformed into time dependent terms, b[T(t)] and n[T(t)] respectively. If there is no growth and damage repair during the heating process, and the momentary inactivation rate only depends on the momentary temperature and survival ratio, then the solution of the differential equation dLog₁₀[S(t)]/dt=−b[T(t)]*n[T(t)]*{−Log₁₀[S(t)]/b[T(t)]}^∧{(n[T(t)]−1)/n[T(t)]} provides the survival curve under the specified non-isothermal conditions. The validity of this model is demonstrated by the agreement of its predictions, calculated numerically using Mathematica®, to reported survival data of Listeria during heating at a constant and varying rates. Unlike in the traditional calculation methods of microbial survival, the one employed here does not require that microbial mortality be a process following a first or any other order kinetics model.     

对流热处理在生鲜湿面保鲜中的应用

该文研究了对流热处理方法对生鲜湿面保鲜效果和色泽的影响。实验表明,最佳的对流热处理条件为热处理温度90℃,热处理时间25 min。在不使用任何防腐剂的情况下,通过此方法能够使生鲜湿面在36℃下安全储藏49 h。     

Modeling non-isothermal heat inactivation of microorganisms having biphasic isothermal survival curves

Biphasic isothermal inactivation constitutes a special case of non-linear mortality kinetics. It can be modeled with a primary model that contains an 'If' statement and three temperature dependent survival parameters: the first and second logarithmic inactivation rate constants and the time of the transition from one phase to the other. The temperature dependence of the two inactivation rates of Salmonella enteritidis and that of the transition time determined from published data could be described by empirical logistic terms. These were used to construct an inactivation rate equation for non-isothermal heating and cooling regimes. The resulting differential equation, despite having an 'If' statement in its formulation, could be easily solved numerically for simple as well elaborate temperature profiles. The solutions for a variety of realistic heat treatment histories indicated that when the heating or cooling rate is high enough, the biphasic character of the inactivation disappears. This is true regardless of whether the rate at the first phase is higher than at the second, the most common scenario, or vice versa. Theoretically, the same will happen with inactivation caused by a non thermal agent whose intensity increases or diminishes, in biphasic growth under rapidly varying conditions and in enzymatic activity or inactivation.     

Simple model for estimating heat and mass transfer in regular-shaped foods

In this paper a simplified model is presented, which describes the cooling of high-moisture cylindrical food with evaporation at the surface. This simplified model is derived from the observation of simulation results of a detailed finite volume method, that the average temperature has a fixed location. The simplified model can be represented by an electrical network analogue, comprising of one or two heat capacities, heat resistances and a heat flow source (for the evaporation). By dividing the food body in a shell and a core, one can predict the average temperature and surface temperature with comparable accuracy as the finite volume model for any Biot number and moderate to large time scales.     

通过接枝改性提高羽绒纤维保暖性能的探究

通过接枝金属锆离子来提高羽绒的保暖性,采用红外分析、ICP测定、蓬松度、保暖率分析以及电镜观察对其接枝效果、保暖性能及其表面形貌变化进行探究。结果表明:经过单宁酸改性的羽绒纤维能明显增加对锆离子的吸附量,经过接枝金属锆离子,羽绒纤维的保暖率提高了5%左右,蓬松度也有所提升。另外,通过对改性前后扫描电镜图片的比较发现:改性前后羽绒纤维的表面形态并未有明显变化,色泽上有略微变化。     

藤稔葡萄先促成后避雨栽培技术

藤稔葡萄采取措施,提早上市是提高经济效益的有效途径。大棚栽培的藤稔葡萄,能提早30天发芽,提早7～15天开花,但成熟期提早效果不明显。本人经过多年实践,总结出藤稔葡萄先保温促成栽培,后避雨,采前去膜技术,使藤稔葡萄比露地提早10～15天成熟,因此市场价格高达10元/kg以上,取得了较好的经济效益。1 架式安排与种植密度大棚采用连栋式结构,每栋棚宽6～8m,高3m,棚长根据田块安排,拱片用毛竹或钢管,立柱用粗10×8cm水泥柱,用0.05mm无滴长寿大棚膜,地面盖地膜。每栋棚种3行葡萄,株距1.2～1.5m,双十字“V”形篱架。2 石灰氮处理12月底修剪后,…     

热处理对鸡蛋保鲜效果的影响

在含有0.08%的活性钙水溶液中,采用加热的办法对鸡蛋进行处理,然后将其在30℃高温下贮藏,以新鲜度中的哈夫单位和感官评定等为指标,研究加热处理对其保鲜效果的影响.试验结果表明:加热处理的最适条件是加热温度50℃、加热时间20min,此外蛋清透明度、表面色泽、光亮度等感官指标均好于对照组.经温水处理的鸡蛋,在30℃下贮藏,其保藏期可延长至少一个月以上.     

Modelling the cooling phase of heat sterilization processes, using heat transfer coefficients

A mathematical model based on finite differences was presented, which improved the accuracy of current modelling techniques during the cooling period for conduction heating foods undergoing thermal processing. The surface heat transfer coefficient between can and cooling fluid was incorporated into the finite difference equations, with a value of 600 W m⁻² K⁻¹ chosen from literature and confirmed by calculations from surface temperature measurements and a correlation of the form Nu = f(GrxPr)ⁿ.
Experimental results were obtained for a cylinder of Sylgard 184 elastomer (length 62mm, diameter 57mm) and a polypropylene block (26x91x141 mm). At the end of cooling the heat transfer coefficient model predicted a centre temperature just 2.5°C above the measured value for polypropylene, and for Sylgard 184 this difference was 2.7°C.
This model will improve both real-time process control via the 'derived-value' technique, and the use of controlled pressure cooling with less damage to containers. Optimization of quality factors will also be improved with increased knowledge of in-container temperatures.     

采后黄皮果实热处理保鲜

研究采用45℃、1 min,45℃、5 min,50 ℃、1 min和50 ℃、5 min对采后黄皮进行热处理,并贮藏于6℃观察其保鲜品质的变化,对其贮藏期间的苯丙氨酸解氨酶(PAL)活性,多酚氧化酶(PPO)活性,过氧化物酶(POD)活性和细胞膜透性变化进行了检测.研究结果显示,45℃、5 min和50℃、1 min处理均能有效地延长采后黄皮果实保鲜寿命,其中尤以50℃、1 min处理效果最好.其生理生化指标变化也明显不同于对照和其他处理.     

高温高压下珍珠岩保温性能的研究

在合成金刚石过程中,白云石套管的使用在一定程度上阻止了叶蜡石相变层的发生,而且白云石在高温高压下具有比较好的保温性。采用在常温常压下具有低热导率的物质珍珠岩替换白云石套管,试图进一步提高腔体温度。通过腔体温度测定的实验,结果发现,珍珠岩在高温高压下的保温性能并不如白云石,不适宜作为合成金刚石用的传压、保温材料。     

Use of potassium sorbate, diethylpyrocarbonate and heat for the preservation of prunes at high moisture levels

Normal mould and yeast growth causing spoilage in prunes containing 69% moisture could be prevented by heat processing. At 57% moisture, a dip in 10% potassium sorbate solution was effective for 40–50 days. At 43% moisture, a 5% potassium sorbate dip provided protection and at 34% even a 2% potassium sorbate dip or 550 ppm diethylpyrocarbonate was adequate to inhibit the mould and yeast growth during the 90 day duration of this study.     

Ability of some food preservation processes to modify the overall nutritional value of food

The impact of food transformations on final nutritional quality of food products is a major question that has been studied only partially. This paper propose an assessment of different preservation processes with the light of two overall nutritional scores, positive (SAIN) and negative (LIM), developed in 2008, in response to a European regulation made to improve nutritional information on processed food. With the example of two different products, apple and pork meat, the objective is to monitor the nutritional scores as a function of the preservation operation chosen, isolated or combined, traditional or innovative. The results show that nutritional scores are very different as a function of the mass transfers involved during the preservation operation. The results give insights in the ability of a technological choice to modify the nutritional quality of a food item and potentially orientate a food label. This work also shows the limitations of using global nutritional scores as a tool to evaluate a food process.     

米饭保温时间与品质变化的动态关系

目的研究米饭的保存时间和温度与米饭品质之间的动态关系,探寻最佳的食用时间。方法利用电饭煲蒸煮米饭,保温焖制2 h后收集其温度、水分的关键性指标,分析其变化规律幵通过这些指标探究米饭保温的时间、温度与米饭品质之间的具体关系。记录内米饭水分含量、食味值、硬度、粘度、弹性、平衡度等相关品质指标的动态变化规律。结果在电饭煲的保存过程中,水分含量随温度的下降而不断下降,在0~30 min时,米饭硬度上升,粘度下降;30~45 min时,粘度上升,硬度下降;45~60 min以后,硬度持续增高,粘度持续下降。而米饭的食味值也呈现先上升,再下降现象,在保温约15~30 min时,米饭食味品质最佳。结论温度变化对米饭的品质指标有一定影响,不同保存时间对米饭的品质影响呈现显著差异。     

大跨度主动蓄能型温室温湿环境监测及节能保温性能评价

针对日光温室土地利用率低,单体小不能进行立体栽培果树种植,不利于机械化操作等问题。该文提出一种大跨度主动蓄能型温室,该温室南北走向,双屋面拱形钢骨架结构,并采用主动蓄放热系统进行能量的蓄积与释放。该试验以传统砖墙日光温室作为对照,对大跨度主动蓄能型温室室内外温湿度以及主动蓄放热系统的能量收支进行分析,并对比2种温室的建造成本,综合分析了试验温室保温节能效果及经济效益。结果表明:大跨度主动蓄能型温室土地利用率高达87.4%。温室夜间平均气温高于10 ℃,无极端低温,晴天夜间平均气温比对照温室高1.5~3.1 ℃,比室外高13.9~19.3 ℃;阴天夜间平均气温比对照温室高1.2~2.8 ℃,比室外高12.5~18.9 ℃。夜间室内相对湿度平均比对照温室低7%~10%。主动蓄放热系统性能系数COP(coefficient of performance)为3.4~4.2,平均每天能耗0.013 kWh/m2,与传统燃煤锅炉加温系统相比,平均节能率为47%。大跨度主动蓄能型温室建造成本每平米307.2元,比传统砖墙日光温室低144.5元。大跨度主动蓄能型温室是一种土地利用率高,单体大,保温性能良好,能进行冬季果菜生产的新型温室类型,且投入少,综合其经济环境效益,值得推广应用。     

国内外果蔬热处理保鲜技术研究进展

综述了近年来国内外热处理果蔬保鲜技术的研究及应用进展。介绍了热处理对果蔬采后生理生化、采后品质及采后腐烂控制的研究及应用现状