蔗糖含量对牡丹花色苷热稳定性和降解动力学的影响

研究了蔗糖含量对牡丹花色苷热稳定性和降解动力学的影响。结果表明：牡丹花色苷的热降解符合一级反应动力学模型,花色苷半衰期随加热温度升高而缩短;花色苷样品液所含的4 种花色苷中,降解速率依次为矢车菊-3-O- 二葡萄糖＞芍药-3-O- 葡萄糖苷＞矢车菊-3, 5-O- 二葡萄糖苷＞芍药-3, 5-O- 二葡萄糖苷;花色苷样品液的褐变指数随加热温度的升高和加热时间的延长而增大。蔗糖抑制了花色苷的降解,表现为提高了花色苷样品液的吸光度,降低了褐变指数;抑制程度与蔗糖浓度、加热处理的时间和温度有关;但含糖体系花色苷的热降解不符合一级反应动力学。     

Aspects of material science in food processing: changes in plant cell walls of fruits and vegetables

 Foods can be regarded as complex, dispersed systems which are normally metastable. Food processing causes state transitions (second-order transitions) when raw materials, food components or food systems are subjected to external stresses. The state transitions occurring during processing are detectable as changes in structure and properties of the investigated systems. The processing of fruits and vegetables is often connected with changes in cell walls. Cell wall materials in dispersed fruit and vegetable systems can be regarded as a model substrate of the dispersed phase. During processing, cell walls undergo modifications in terms of their physical state, macrostructure, microstructure, and composition, as well as structure-dependent changes in their functional and material properties. The interactions and connections (dependencies) between state transitions, and various changes in structure and properties, are very complex and multivariate and are not well understood as yet. For the evaluation of changing material properties during processing, examination of hydration, rheological (external mechanical stress) and thermal (external thermal stress) characteristics is important. The changes occurring during the processing of fruits and vegetables are determined by external factors (especially various mechanical and thermal stresses) and by internal factors. External stress in many cases causes solubilisation of the cell wall, loss of firmness and favours cell separation. Thermal processing increases pectin degradation by β-elimination. Internal factors such as pH and modified ionic strength, e.g. by applying soak solutions, can have an important influence on the changes in the cell wall during processing. So, calcium ions on the one hand can favour cell wall degradation by β-elimination and, on the other hand, after low temperature blanching and de-esterification of the pectin by activated pectin methyl esterase, can contribute to stabilisation of the texture by formation of a calcium-pectin complex. Knowledge about cell wall degradation mechanisms can be markedly improved by studies using model substrates such as pectin, or cell wall materials like the alcohol-insoluble residue and materials with cellular structure. This knowledge has been used to improve the technology used to process fruits and vegetables and to produce products with better properties. Moreover, testing and applying cell wall materials as ingredients for the production of textured foods and potential health-related foods is suggested.     

Aspects of material science in food processing: changes in plant cell walls of fruits and vegetables

 Foods can be regarded as complex, dispersed systems which are normally metastable. Food processing causes state transitions (second-order transitions) when raw materials, food components or food systems are subjected to external stresses. The state transitions occurring during processing are detectable as changes in structure and properties of the investigated systems. The processing of fruits and vegetables is often connected with changes in cell walls. Cell wall materials in dispersed fruit and vegetable systems can be regarded as a model substrate of the dispersed phase. During processing, cell walls undergo modifications in terms of their physical state, macrostructure, microstructure, and composition, as well as structure-dependent changes in their functional and material properties. The interactions and connections (dependencies) between state transitions, and various changes in structure and properties, are very complex and multivariate and are not well understood as yet. For the evaluation of changing material properties during processing, examination of hydration, rheological (external mechanical stress) and thermal (external thermal stress) characteristics is important. The changes occurring during the processing of fruits and vegetables are determined by external factors (especially various mechanical and thermal stresses) and by internal factors. External stress in many cases causes solubilisation of the cell wall, loss of firmness and favours cell separation. Thermal processing increases pectin degradation by β-elimination. Internal factors such as pH and modified ionic strength, e.g. by applying soak solutions, can have an important influence on the changes in the cell wall during processing. So, calcium ions on the one hand can favour cell wall degradation by β-elimination and, on the other hand, after low temperature blanching and de-esterification of the pectin by activated pectin methyl esterase, can contribute to stabilisation of the texture by formation of a calcium-pectin complex. Knowledge about cell wall degradation mechanisms can be markedly improved by studies using model substrates such as pectin, or cell wall materials like the alcohol-insoluble residue and materials with cellular structure. This knowledge has been used to improve the technology used to process fruits and vegetables and to produce products with better properties. Moreover, testing and applying cell wall materials as ingredients for the production of textured foods and potential health-related foods is suggested. Received: 21 July 1998     

Kinetic model for studying the conversion and degradation of isoflavones during heating

The conversion and degradation of isoflavones during dry or moist heating at 100, 150 and 200 °C, for varied lengths of time, were kinetically studied. Results showed that, at the early stage, all the reaction rates of malonylgenistin (MG), acetylgenistin (AG), genistin (G), and genistein (Ge) increased with increasing temperature and fitted a first-order model, when the concentration changes during heating were analyzed using HPLC. For dry heating, the conversion of MG to G exhibited the highest rate constant (h⁻¹), followed by MG to AG, AG to G, AG to Ge, G to Ge and MG to Ge. Moist heating showed the same phenomenon; however, the last three conversions were not observed. In addition, MG had the highest degradation rate, followed by G, Ge and AG during dry heating, while the reversed trend occurred for moist heating. Moist heating was more susceptible to conversion and degradation of isoflavones than dry heating. The correlation coefficients (r²) ranged from 0.664 to 0.987 for moist heating and 0.688–0.960 for dry heating. The kinetic model developed in this study can be used to predict the concentration changes of isoflavones during dry heating and moist heating.     

MODELLING THE MECHANICAL AND HISTOLOGICAL PROPERTIES OF CARROT TISSUE DURING COOKING IN RELATION TO TEXTURE AND CELL WALL CHANGES

A tensile test was used to measure four mechanical properties of carrot tissue cooked under various time-temperature conditions. A kinetic model describing the changes of these mechanical properties measured during cooking was developed. The histological properties of the rupture surfaces caused by the mechanical testing were investigated. The kinetic model was found capable of predicting the changes in the rupture mechanism of the cell walls. Determining the percentage of cell wall ruptures proved to be an accurate method to assess the textural state of carrot tissue during cooking as compared to the measurement of the mechanical properties.     

Processing and quality characteristics of apple slices processed under simultaneous infrared dry-blanching and dehydration with intermittent heating

This study investigated the effects of three processing parameters, e.g. product surface temperature, slice thickness and processing time, on blanching and dehydration characteristics of apple slices exposed to simultaneous infrared dry-blanching and dehydration (SIRDBD) with intermittent heating. A three-factor factorial experiment design was conducted to determine the influence of processing parameters on product temperature, moisture reduction, drying rate, residual polyphenol oxidase (PPO) and peroxidase (POD) activities and surface color change. Slice thickness had a significant effect on product quality and processing characteristics, as faster inactivation of enzymes and quicker moisture reduction took place in thinner slices. A Page model performed well for describing drying behavior during the treatment, and first-order kinetics and a biphasic model fit well for PPO and POD inactivation, respectively. Surface color changes (ΔE) of apple slices during prolonged heating resulted from non-enzymatic browning with an increase in b value was observed. In order to achieve a 1 log reduction in POD activity, the process resulted in a reduction in moisture from 20% to 59% and in ΔE from 2.27 to 5.59. It is suggested that SIRDBD with intermittent heating could be used as an alternative to manufacture high quality blanched and partially dehydrated fruits and vegetables.     

BETWEEN-SPECIES DIFFERENCES IN FRACTURABILITY LOSS: MICROSCOPIC AND CHEMICAL COMPARISON OF POTATO AND CHINESE WATERCHESTNUT1

Potato and waterchestnut tissue were used as experimental materials for comparing between-species differences in heat softening rate. Scanning electron microscope (SEM) techniques were employed to compare cellular and subcellular changes with corresponding fractur ability losses during cooking of potato and Chinese waterchestnut by four cooking methods. SEM observations strongly suggest that cell wall adhesion and its heat resistance play a major role in fracturability changes during heating. Intracellular substances such as starch and minerals may slightly alter the cell wall strength but do not substantially affect fracturability changes. In addition, differences in the gross chemical composition between species were inadequate for explaining fracturability changes of the two vegetable tissues during heating.     

Changes in lycopene and beta carotene contents in aril and oil of gac fruit during storage

Gac fruits were physically measured and stored under ambient conditions for up to 2 weeks to observe changes in carotenoid contents (lycopene and beta carotene) in its aril. Initial concentrations in the aril of lycopene were from 2.378 mg/g fresh weight (FW) to 3.728 mg/g FW and those of beta carotene were from 0.257 to 0.379 mg/g FW. Carotenoid concentrations in the aril remained stable after 1 week but sharply declined after 2 weeks of storage. Gac oil, pressed from gac aril, has similar concentrations of lycopene and beta carotene (2.436 and 2.592 mg/g, respectively). Oil was treated with 0.02% of butylated hydroxytoluene, or with a stream of nitrogen or untreated then stored in the dark for up to 15 or 19 weeks under different temperatures (5 °C, ambient, 45 and 60 °C). Lycopene and beta carotene in control gac oil degraded following the first-order kinetic model. The degradation rate of lycopene and beta carotene in the treated oil samples were lower than that in the control oil but the first-order kinetic was not always followed. However, both lycopene and beta carotene degraded quickly in gac oil with the first-order kinetic under high temperature conditions (45 and 60 °C) regardless of the treatments used.     

Combined Effects of Baking Conditions and Bacterial α-Amylases on Staling Kinetics of Degassed and Porous Bread Crumb

Enzymes such as ??-amylase are extensively used to retard the staling process. Enzymes are acting both during fermentation and during baking. The objective of this work was to determine the relative action of ??-amylase during fermentation and during baking. The impact of the baking conditions (time, temperature) was also considered. To attain this aim, a degassed bread crumb was baked in a miniaturized system using two programs of baking: heating rates 10.27 and 6.88?°C/min corresponding to 180 and 220?°C baking temperatures, respectively. Mechanical and thermodynamic properties of the degassed crumb were assessed during aging of bread by determining the Young??s modulus E, the amount of freezable water, and the melting enthalpy of retrograded amylopectin. A first-order kinetic model was used to determine the different parameters of staling kinetics. Results showed that the hardening of crumb increased during storage. The kinetics were faster for samples baked with fast heating rate than for those baked with slow heating rates. The use of enzymes decreased the Young??s modulus but did not have any effect on the staling rate. Calorimetric analysis of the starch retrogradation showed a reduction of the amount of freezable water during storage with an increase of retrograded amylopectin. A comparison between mechanical properties of conventional crumb and of the degassed dough confirmed that experimental data fitted correctly the Gibson and Ashby??s model.     

Kinetics of Quality Changes of Shrimp (<Emphasis Type="Italic">Litopenaeus setiferus</Emphasis>) During Pasteurization

Effect of cooking between 1 and 80 min at 60 to 100 °C on several quality attributes of whole peeled shrimp (Litopenaeus setiferus) (80–90 counts/kg) was studied using an isothermal heating method. Cook loss, area shrinkage, and hardness of shrimp increased with increasing heating time and temperature, following a fractional first-order kinetic model with activation energies (E _a ) of 71.0, 53.3, and 29.9 kJ/mol, respectively. Cook loss, area shrinkage, and hardness were positively correlated. The toughness of shrimp muscle increased in the initial period of heating, then decreased in the later period during the treatments. The overall color change (ΔE) increased with increasing treatment time and temperature, and followed a zero kinetic model with an E _a of 37.2 kJ/mol. The kinetic parameters obtained from this study can be applied toward understanding and predicting shrimp-quality changes during pasteurization treatments, and further provides insight into the pasteurization conditions required to achieve safe and high-quality shrimp products and potentially other crustacean shellfish and seafood products.     

A Kinetic Approach to Food Quality Prediction Using Full-History Time-Temperature Indicators

A mathematical model based on the theory of chemical kinetics was derived to predict food quality change from the response of a full-history time-temperature indicator. A first-order kinetic reaction (n = 1) was used to describe both indicator response and changes in food quality. A storage investigation of mature green tomatoes showed that the quality prediction model satisfactorily predicted changes in tomato firmness induced by variable temperature storage. Tomato firmness as predicted from the response of a LifeLines model 57 time-temperature indicator was not significantly different from the observed changes (F = 1.99, p = 0.18) for 28 days of storage. The mathematical derivation was extended to develop a quality-based interpretation of the shelf life of perishable foods.     

Kinetics of thermal softening of potato tissue heated by different methods

The kinetics of thermal softening of potato tissue heated by steaming, steaming+hot air and microwave exposure were evaluated using the rheological properties from four objective methods as firmness indicators. In the three heat treatments, the rate of thermal softening of tissue could be described by two simultaneous first-order kinetic mechanisms. Shear rheological properties were best for studying softening of the tissue with these methods on the basis of chemical kinetic theory. A comparison of kinetic parameters showed that steaming produced a greater degree of softening than the other two heating methods used. The firmness ratios for shear force showed that approximately 16% of the firmness of fresh potato is retained after steaming treatments as compared to 46% and 36%, respectively, for steaming+hot air and microwave. The loss of moisture of samples accounted for the increase in the firmness ratios, especially in steaming+hot air treatments, resulting in a potato with greater firmness but with a texture unacceptable to the consumer. Tension rheological properties and relaxed force detected the loss of moisture to a more significant degree and could therefore be considered very suitable for studying thermal treatments that involve the drying of tissues. With these heating methods, gelatinization contributes less than cell wall structure to potato tissue softening as determined either by kinetic parameters or by microscopic observations.     

MODELING THERMAL SOFTENING KINETICS OF POTATOES USING FRACTIONAL CONVERSION OF RHEOLOGICAL PARAMETERS

Texture degradation in potatoes was investigated during heating of cylindrical test samples, 15 mm diameter and 30 mm long, in water at 60, 70, 80 and 90C by mechanical testing. The rheological parameters obtained from the axial and radial compression, creep and stress relaxation tests decreased exponentially with an increase in heating duration and temperature approaching steady levels corresponding to the remaining texture after prolonged heating. A single first-order kinetic model described the changes in various rheological parameters due to thermal softening of potatoes using fractional conversion technique indicating very high values of the coefficient of determination (R² > 0.97). In general, the visco-elastic test parameters were relatively more sensitive to texture degradation in potatoes in comparison with the quasi-static test parameters. Overall comparison showed that elasticity and viscosity parameters in Kelvin component of the 4-element model (E₂ and η₂) from creep tests and elasticity moduli from axial and radial compression tests (E_a and E_r) best presented the texture degradation kinetics in potatoes with R² ranging from 0.98 to 0.99.     

催化式红外杀青对绿茶热风干燥的影响

以镇江金山翠芽绿茶鲜叶为原料,以蒸汽杀青为对照,研究红外杀青对茶叶品质的影响,对杀青后茶叶进行不同温度热风干燥得到茶叶成品。考察茶叶中多酚氧化酶(polyphenol oxidase,PPO)含量、VC保留率、茶多酚含量以及感官审评分等指标的变化,建立一种催化式红外杀青联合热风干燥的绿茶加工技术。最优杀青干燥工艺条件为:红外辐照距离20 cm杀青150 s,经揉捻作形后,热风干燥温度70℃、干燥40 min。实验结果建立了红外杀青过程中PPO钝化动力学模型和干燥过程中水分干燥动力学模型,可为杀青干燥过程预测提供理论参考。     

Kinetics of tropomyosin denaturation as a predictive model for verifying thermal processing of beef products

An enzyme-linked immunosorbent assay (ELISA) was developed to study thermal denaturation of tropomyosin (Tm) using the time-temperature requirements for cooked beef. The ELISA employed a monoclonal antibody (MAb 2C9) raised against bovine Tm for quantifying residual Tm in muscle extracts. The specificity of MAb 2C9 to bovine Tm was demonstrated by Western blot and the analytical validity of ELISA was confirmed by dot blot. Thermal denaturation of Tm, in the temperature range between 54.4 and 70.0 degrees C, showed first-order dependency. Kinetic parameters of Tm denaturation were derived from isothermal heating of beef muscle extract at 54.4, 57.2, 60.0, and 62.8 degrees C. Temperature dependency of the rate constant (k) was demonstrated by Arrhenius plot; the activation energy (E(a)) of Tm denaturation was determined to be 484 kJ x mol(-1). A mathematic model describing the impact of the heating time-temperature on Tm denaturation was developed. Predicted Tm from the integrated time-temperature model agreed closely with the measured Tm in dynamically heat-processed beef samples. Percent errors between the measured and the predicted values ranged from -5.1 to 5.3%. The kinetic model provides an accurate and reproducible prediction of the impact of actual heating time-temperature on residual Tm in cooked beef. The MAb-based ELISA and kinetic model developed in this study have the potential to be adapted by the meat industry as a quality control tool.     

Fruit load or fruit position alters response to temperature and subsequently cherry tomato quality

Changes in fruit–source ratio during the growth and maturation of cherry tomato fruits were studied in combination with increased fruit temperature. Six treatments were compared: the presence or absence of local heating combined with different fruit origins (7P, fruit from trusses pruned to seven flowers; 14P, proximal fruits; 14D, distal fruits from trusses pruned to 14 flowers). 7P were less sensitive to heating whereas 14P and 14D showed greater reduction in water and dry matter (DM) content. Distal fruits had the lowest structural DM (sDM), which could be due to a lower fruit cell number. Heating further decreased the sDM, so that fruit sink size was the lowest for distal fruits subjected to heating. Under low competition (7P), heating had a beneficial effect on sugar and lycopene content, whereas acids, β‐carotene and vitamin C content were reduced. Under high competition (14P, 14D), heating increased the ratio sDM–DM. This was mainly due to the reduced content of sugars and acids, but also to the reduced accumulation of secondary metabolites such as vitamin C, β‐carotene and lycopene. This study underlines the interactions between fruit temperature and the fruit–source ratio and the consequences for fruit composition and nutritional quality. Copyright © 2005 Society of Chemical Industry     

非热加工技术对果蔬类胡萝卜素生物利用度的影响研究进展

类胡萝卜素是一类广泛存在于果蔬食品中的脂溶性天然色素,具有多种生理功能.通常果蔬中类胡萝卜素的生物利用度较低,不同加工方式对类胡萝素的释放和生物利用度会有不同的影响,通过科学的手段提高果蔬中类胡萝卜素的生物利用度成为果蔬加工领域研究的热点.本文简述了不同非热加工技术(高压均质技术,超高压技术,超声波技术,高压脉冲电场技...     

Uncertainty in thermal process calculations due to variability in first-order and Weibull kinetic parameters

ABSTRACT:  Alternatives to first-order model of death kinetics of microorganisms have been proposed as improvements in the calculation of lethality for a thermal process. Although such models can potentially improve predictions for many situations, this article tries to answer the question of whether the added complexities of these models are a worthwhile investment once we include the effect of uncertainties in various microbiological and process parameters. Monte Carlo technique is used to include variability in kinetic parameters in lethality calculation for a number of heating processes, for both first-order and Weibull kinetics models. It is shown that uncertainties represented by coefficient of variation in kinetic parameters lead to a wide range of final log-reduction prediction. With the same percent variability in kinetic parameters, uncertainty in the final log reduction for Weibull kinetics was smaller or equal to that for first-order kinetics. Due to the large effect of variability in the input parameters on the final log reduction, the effort to move toward more accurate kinetic models needs to be weighed against inclusion of variability.     

Multiscale Biomechanics of Tomato Fruits: A Review

Bruising and other mechanical damage to fruit caused by external forces during and postharvesting is manifested at the macroscale but is ultimately the result of failure of cells at the microscale. However, fruits have internal structures and cells from different tissue types react differently to application of an external force. Not much is known about the effects of such forces on single cells within tissues and one reason for this is the lack of multiscale models linking macro- (organ or whole fruit), meso- (tissue), and micro- (cell) mechanics. This review concerns tomato fruits specifically as this is an important crop and is an excellent exemplar of past and proposed research in this field. The first consideration is the multiscale anatomy of tomato fruits that provides the basis for mechanical modeling. The literature on experimental methods for studying multiscale mechanics of fruit is then reviewed, as are recent results from using those methods. Finally, future research directions are discussed, in particular the combination of work over all scales. It is clear that a bottom-up approach incorporating single-cell mechanics in finite element models of whole fruit assumed to have internal structures is a promising way forward for tomato fruits but further method developments may be needed for these and other fruits and vegetables, in particular recovery of representative single cells from tissues for mechanical characterization.