Changes in texture,microstructure and nutritional quality of carrot slices during blanching and freezing

Thermal processing of vegetables has pronounced effects on the cell structure, often lowering the final textural properties of the product. In order to investigate the effect of thermal processing on carrot, slices were subjected to different blanching and freezing treatments before frozen storage. Microwave-, steam- or water-blanched material was frozen and then stored at −24 °C. Steam-blanched carrots were subjected to blast freezing or cryogenic freezing at different temperatures before frozen storage. The influence of these process conditions on the texture (maximum load and slope), microstructure, dry matter, sugars, carotene and drip loss was investigated. Microwave blanching differed from the other blanching methods by resulting in a heterogenic cell structure. The content of dry matter, carotene and sucrose was higher following microwave blanching. Blast freezing resulted in low maximum load which seemed to be caused by major tissue damage. Concerning cryogenic freezing, lowering the temperature from −30 °C to −70 °C resulted in better preservation of the native microstructure together with an increase in maximum load, which was most pronounced after one month of storage. No significant effect was observed when lowering the temperature from −30 °C to −70 °C for any of the other measured parameters. © 1999 Society of Chemical Industry     

The influence of formulation and cooling rate on the rheological properties of chocolate

Rheological properties of chocolate play a relevant role either in process design or texture definition. Nevertheless, only flow properties of molten product or mechanical properties of samples cooled at fixed temperature (usually 20 °C) are measured, whilst testing conditions close to the industrial applications (temperature close to 30 °C) are less common to be used. In this work, chocolate samples (cooled at 1 and 5 °C min⁻¹) were characterised at 30 °C by using small-amplitude oscillations and low-stress creep tests, aiming at establishing how material properties are related to the chocolate microstructure. The effects of either 3 anhydrous milk fats (AMF), having different melting points, or sugar particle size were evaluated. It was found that addition of AMFs, owing to their solid content, can yield an increase in consistency; however, this effect is less relevant when coarse sugar is used, because of the broader particle size distribution, and it depends on the thermal history because of the different fat crystallisation time. Finally, creep tests resulted to be very sensitive in detecting changes in chocolate rheological properties.     

Characterisation of dairy emulsions by NMR and rheological techniques

Droplet size distribution strongly affects macroscopic properties of emulsions. In this work rheological and NMR (nuclear magnetic resonance) analyses were performed to evaluate material properties as well as droplet size distribution and possible flow-induced alteration. The investigated materials were commercial dairy emulsions, based on milk, vegetable fats, a mixture of sugars, emulsifiers (hydrophilic or lipophilic) and natural stabilizers (carrageenan and guar gum). Rheological properties of three different dairy emulsions were related to the droplet size distribution obtained by NMR and dynamic light scattering (DLS) techniques. NMR seems to be a particularly useful technique because no previous sample treatment is necessary, whereas DLS requires a significant emulsion dilution that could change the droplet size distribution. Obtained results evidence the effect of two relevant ingredients (surfactants and fats) on rheological properties and droplet size distribution of tested emulsions. For sample containing sunflower oil and a hydrophilic emulsifier, rheo-NMR evidenced mechanical instabilities also confirmed by rheological tests. Comparison of results about the droplet size distribution evaluated by NMR and DLS evidenced that in this case sample dilution could affect size distribution. Finally, rheo-NMR was confirmed to be a powerful instrument capable of determining the material structure and alterations induced by the flow.     

Processing Conditions Affecting the Hygroscopic Behavior of Freeze-Dried Passion Fruit Juice

The effect of freezing rate, freeze drying temperature, added sucrose and anticaking agents, on the water sorption kinetics and hygroscopic equilibrium of freeze-dried passion fruit juice was investigated. Slow frozen samples (-45°C) were prepared in a Harris freezer and fast frozen ones were prepared in liquid nitrogen (- 195.8°C) and a dropping technique. A freeze-drier 12F Pilot Stokes was used to freeze-dry the samples, and the studies of hygroscopicity were conducted in an automatically controlled temperature and relative humidity chamber. The results show the significant influence of the rate of freezing and added sucrose on reducing product hygroscopicity.     

PREDICTION OF FREEZING TIMES FOR FOODS AS INFLUENCED BY PRODUCT PROPERTIES

This investigation utilizes a computer simulation technique to predict the freezing times and temperature history curves for food products. The input information consists of the product properties for temperatures above the initial freezing point, freezing medium conditions and the initial product temperature. It has been established that food products with lower initial freezing points, higher initial water contents and higher initial product densities will have longer freezing times. The prediction of freezing time is most sensitive to the accuracy of the measurement of the product density and the initial freezing point if the freezing point is above ?0.5°C. The influence of the accuracy of unfrozen product thermal conductivity data on the freezing time is not important in the range of 0.45 to 0.55 W/m°K investigated. The combined influence of inaccuracy in measuring these product properties on the freezing time prediction will be significant even if the influence of an individual product property is small.     

The Effects of Applying Oscillating Magnetic Fields During the Freezing of Apple and Potato

The use of Oscillating Magnetic Fields (OMF) during freezing has been advocated by some for preserving the intrinsic ‘fresh’ qualities of the subsequently thawed food. This paper describes studies to investigate the effects of a range of different OMF freezing settings using an ABI Cells Alive System (CAS) freezer on characteristics of the freezing process and food-quality parameters. The effects of short-term frozen storage on sample properties were also evaluated. Apple and potato samples were frozen at ??30 or ??45 °C with a range of OMF settings whilst measuring sample temperatures. Samples were then either immediately thawed or stored frozen for 1 month. Effects of OMF on freezing temperature curve texture parameters, sample dimensions, sample weights and sample texture parameters of thawed samples were determined. Overall, results showed no statistically significant continuum of effect in these trials that prevails across all CAS settings and/or temperatures for apple and potato for any parameter measured. However, significant effects were seen at some settings for some parameters for each product, and this may suggest that OMF may possibly be tuneable for specific situations. Where significant changes did occur, these only appeared at isolated settings, temperatures or storage periods. This suggests that OMF may not affect all foods in an equal manner and that any effect depends on an interrelationship of food type, freezing rate, magnetic field frequency and storage conditions. We conclude that there is no major effect of OMF on freezing parameters and there is no overall pattern of OMF on freezing processes.     

Microwave assisted freezing part 2: Impact of microwave energy and duty cycle on ice crystal size distribution

Among innovative freezing processes, electromagnetic wave assistance during freezing has received great attention in recent years. The literature provides interesting studies indicating that smaller ice crystals may be obtained during freezing with the assistance of microwaves. In the companion paper, we designed a laboratory scale prototype to perform experiments of this type in well controlled conditions at 2.45 GHz. In the current study, we performed freezing experiments using this prototype and developed a protocol to measure ice crystal sizes using X-ray micro-tomography. The methodology was first validated by measuring ice crystal distribution in unidirectional conventional freezing. Then several microwave assisted freezing modalities were studied. Experiments were conducted with pulsed and continuously applied microwaves. The impact of microwave irradiation time was studied at a constant incident microwave power, and then at constant energy supplied to the system. We observed a significant reduction of up to 25% in ice crystal size when microwave assistance was used during freezing with both pulsed and continuously applied microwaves. These observations tend to disconfirm the hypothesis in the literature according to which ice crystal size reduction is due to temperature oscillations. The only remaining hypothesis in the literature is that ice crystal size reduction may be due to the perturbation of the H-bond network in water, which could be a precursor to crystalline structure. It appeared that at constant incident microwave power, the increase in irradiation time tended to decrease ice crystal size. No significant difference in ice crystal size reduction was observed for a constant energy supplied to the system. The amount of energy supplied by microwaves seems to be a factor influencing ice crystal size.Industrial relevanceMicrowave assisted freezing is an emerging process which permits reducing ice crystal size, and thus improving frozen product quality. The measurement of ice crystals in samples frozen in controlled conditions of both freezing and microwave irradiation allows studying the main parameters that induce the reduction of their size. Better understanding of the relevant factors influencing nucleation and/or crystal growth can help to optimize the process.     

冻藏温度对玉米醇溶蛋白膜的影响

冻藏温度对玉米醇溶蛋白膜特性有一定影响。结果表明:蛋白膜的机械特性、平衡水分含量和水蒸气透过率随冻藏温度的变化而发生变化。随着冻藏温度的降低,蛋白膜的抗拉强度和延伸率都呈下降的趋势;蛋白膜的平衡水分含量随冻藏温度的降低先上升,而后又略有下降;水蒸气透过率随冻藏温度的降低而上升。     

Technology Allowing Baby Spinach Leaves to Acquire Freezing Tolerance

This study focuses on improving the freezing tolerance of spinach leaves when applying vacuum impregnation (VI) and pulsed electric fields (PEF) as pre-treatments. Changing the cultivation conditions of the spinach plants was tested for improved freezing tolerance of the harvested leaves. Spinach plants were initially cultivated at 20 °C for 5 weeks and harvested at the beginning of week 6 before the cultivation conditions were changed to 5 °C. After exposing the plants to cold stress, leaves were harvested on day 1, 8, and 20. The leaves from different cultivation temperatures were treated with VI with 30% (w/v) trehalose solution and PEF prior freezing at ??22 °C in a blast freezer. After freezing and thawing, the viability of harvested spinach leaves was 50% for the plants cultivated at 20 °C for 5 weeks. When the cultivation conditions were changed, the viability of the harvested leaves increased to 82% on day 1, 89% on day 8, and without a significant further increase on day 20. During cold cultivation, sucrose accumulated in the leaves, which might have contributed to the increased survival. The influence of impregnating the accumulated sugars instead of changing the cultivation conditions on the survival of the leaves was tested. The viability of the leaves was 75%, which was higher than the survival of the control (50%). The results indicate that it is possible to increase leaf survival after freezing and thawing by applying VI and PEF in combination with either by changing the cultivation conditions of spinach plants or by externally impregnating additional sugars to the harvested leaves.     

Physical properties of tempered mixtures of cocoa butter,CBR and CBS fats

Physical characteristics of precrystallised binary mixtures of cocoa butter (CB) and 5, 10, 15, 20, 25 and 30% (w/w) cocoa butter replacer (CBR) or cocoa butter substitute (CBS) were determined. The lipid composition was obtained by chromatography and the solid fat content (SFC) by nuclear magnetic resonance. Tempering was carried out using a lab‐scale agitated jacket vessel reactor. Bars made with tempered samples were submitted to X‐ray diffraction and rupture tests. Snap values of crystallised mixtures decrease with an increase in the amount of alternative fat. X‐ray diffraction patterns confirmed the predominant formation of the beta polymorph habit for CB and beta prime form for CBR and CBS. Mixtures of CB and CBR exhibit chemical compatibility. The knowledge of the snap values and of the variation of SFC with temperature proved to suffice to adequately anticipate the influence of the addition of alternative fats on chocolates physical attributes.     

A Microscopical Study of the Structure of Meat Emulsions and Its Relationship to Thermal Stability

Meat emulsions were examined by light microscopy to determine the relationships between structure and emulsion stability. Beef-meat based emulsions were prepared either by varying chopping temperature or by adding soy plastic fats of different hardness. Formation of fat channels was observed in uncooked emulsions prepared either at a chopping temperature of 26°C or with soft plastic fat of 0.25cm^?1 hardness index. Such fat channel formations caused discontinuity of protein matrix, leading to fat separation during cooking and weakening of textural strength of products. Changes in fat globule size and distribution as affected by melting properties or hardness of fats were clearly reflected by changes in emulsion stability. Results suggest that emulsion stability is determined largely by the physical properties of protein matrix and fat incorporated. Stable emulsions were obtained with fats of appropriate melting properties and hardness and relatively cohesive protein matrix under given comminution conditions which allowed uniform fat distribution.     

传统食醋浓缩醋膏工艺条件优化

以传统食醋为原料,依次采用冷冻浓缩和蒸馏浓缩技术制备醋膏,并通过单因素试验及响应面试验优化醋膏工艺条件。结果表明,最佳工艺条件为预处理温度4 ℃,冷冻温度-10 ℃,蒸馏温度55 ℃,酵母抽提物3.5 g/L,白砂糖125 g/L。利用该优化工艺得到的醋膏产品膏体浓稠,风味怡人,是一款新型的食醋衍生产品。     

Improvement of the oral bioavailability of coenzyme Q10 by emulsification with fats and emulsifiers used in the food industry

Coenzyme Q₁₀ (CoQ₁₀) was emulsified with fats and emulsifiers commonly used in the food industry, and the oral bioavailability of the emulsified product was compared with that of a standard commercial product. Five commonly used fats (olive oil, safflower oil, coconut oil, butter, and cocoa butter), four types of emulsifier (lecithin, monoglycerides, calcium stearoyl-2-lactate (CSL), and diacetyl tartaric acid esters of monoglycerides), and two types of aqueous phase (distilled water with or without 8 g/100 g w/w skim milk) were employed in this study. It was found that CoQ₁₀ was more soluble in coconut and safflower oils than in the other fats. In addition, it was demonstrated that emulsion with coconut oil, skim milk aqueous solution, and CSL produced an optimal formulation. Based on the results, a model emulsified CoQ₁₀ product was prepared. Its oral bioavailability was confirmed to be slightly greater than that of a standard commercial CoQ₁₀ product.     

Sources of energy values and contribution of various products to maintenance of chemical contents of the diet of an unorganized population of Moscow

With use of a method of daily reproduction at representative sample of an unorganized population of inhabitants of Moscow the sources of energy value and contribution of various products to supply organism by the basic food substances (protein, fats, carbohydrates and cholesterol) are investigated. Is established that the nutrition structure is obviously debalanced. More quarters of daily diet energy is provided for consumption of animal fats and simple sugars. Is shown that the main part of fat (2/3) enters in organism as the "latent" fats of animal products, the fats "in the pure form" half consist from butters. The main source of the saturated fats and cholesterol for men are meat, and for women--the dairy products. 12% researched refuse purified sugars.     

PREDICTING DRYING BEHAVIOR OF SPAGHETTI IN A CONTINUOUS INDUSTRIAL DRYER WITH THE MODELS DETERMINED IN A LAB SCALE BATCH SYSTEM

In the first stage of this study experimental data were obtained by using a lab scale batch type dryer, operating under various constant temperature/constant relative humidity combinations; then a mathematical model was determined for the effective diffusivity of moisture in spaghetti. In the second stage of the study the model obtained in the lab scale batch type dryer was used to calculate the moisture content of the spaghetti leaving continuous industrial scale dryer, and its success was tested by comparing with the experimentally determined moisture content of the product. The model was not found successful and corrected. Mathematical models based on experimental data obtained in a bench-top laboratory dryer underestimated the apparent equilibrium moisture content and over estimated the effective diffusivity of water in spaghetti in industrial scale continuous drying equipment. The structural differences in the product, extrapolation of the data beyond the range of the original experiments, variations in mode (batch versus continuous), surface-to-volume ratios, flow patterns, and geometry associated with each drying system were anticipated as the cause of the scale up problem.     

Chemical, Physical, and Sensory Properties of a Sweet Potato French-Fry Type Product During Frozen Storage

Chemical, physical, and sensory properties of a sweet potato Frenchfry type product were determined after 0, 3, 6, 9, and 12 months frozen storage. Analyses included measurements of dry matter, sugars, alcohol insoluble solids, carotene, vitamin C, color, texture and sensory panel scores for color, flavor and texture. Few changes were observed except for an appreciable loss (58%) in vitamin C and an apparent increase in carotene (27%). A partial drying treatment before freezing increased the rate of ascorbic acid loss. For the fried product, no appreciable storage-induced changes were noted in the sensory scores for color, flavor and texture thus indicating that the product had good stability in frozen storage.     

Dispersibility of freeze-dried poly(epsilon-caprolactone) nanocapsules stabilized by gelatin and the effect of freezing

A nanocapsule (NC)-gelatin suspension was freeze-dried to produce a sample of dry food. The obtained dried product was rehydrated, and the dispersibility of the nanocapsules was investigated. It was found that the prepared freeze-dried food had different dispersion characteristics at different positions in the dried bulk sample, and this heterogeneity was dependent on the cooling program used during the processing. A model mathematical calculation was carried out in order to obtain the thermal profiles of the sample during freezing. The freezing front velocity and the viscosity of the solution at/around the freezing front were estimated by using the simulated thermal profiles. The dispersibility of the prepared dry food was found to correlate with these values. This suggested that the gel network formation of NC-gelatin would be advantageous for producing excellent NC dispersion characteristics after drying. A slow cooling condition is favourable for promoting sol-gel transition in the solution. However, the large scale of ices formed during slow freezing would damage the gel networks, leading to poor dispersibility. The present work discusses key processing factors for controlling the dispersion characteristics of nanocapsules stabilized in a freeze-dried food sample.     

Freeze-Thaw Stability of Illinois Soybean Beverage

The objective of this work was to study the effects of freezing conditions, processing and formulation variables on freeze-thaw (F-T) stability of Illinois soybean beverage. Objective and subjective evaluations were made on a sample before and after freezing. Total solids content of the supernatant from a centrifuged sample was used to calculate a F-T stability index. This index was below 35% for both plain base and plain beverage. The freeze-thaw stability was affected by freezing temperature, holding time before freezing, changing of temperature during frozen storage and desludging. However, length of frozen storage and homogenization pressure had no apparent effect. Addition of sugars and salt resulted in a beneficial effect on the stability. In order to prevent visible freeze damage, approximately 7% sucrose or 5% dextrose hydrate were required in a beverage containing 0.2% salt.     

Is lowering reducing sugars concentration in French fries an effective measure to reduce acrylamide concentration in food service establishments?

The objective of this study was to obtain insight into the actual effectiveness of lowering reducing sugars concentration in par-fried potato strips on the concentration and variation of acrylamide in French fries prepared in real-life situations in food service establishments. Acrylamide, frying time, frying temperature, and reducing sugars were measured and characteristics of fryers were recorded. Data showed that the use of par-fried potato strips with lower concentrations of reducing sugars than the commonly used potato strips was an effective measure to reduce acrylamide concentrations in French fries prepared under standardised frying conditions. However, there was still large variation in the acrylamide concentrations in French fries, although the variation in reducing sugars concentrations in low and normal types of par-fried potato strips was very small and the frying conditions were similar. Factors that could affect the temperature-time profile of frying oil were discussed, such as setting a lower frying temperature at the end than at the start of frying, product/oil ratio and thawing practice. These need to be controlled in daily practice to reduce variation in acrylamide.     

Effect of blanching in water and sugar solutions on texture and microstructure of sliced carrots

Thermal processing of vegetables has pronounced effects on the cell structure, often negatively affecting the final textural properties of the product. In order to study the effect of thermal processing and the protective effect of sugars on the tissue, sliced carrots were subjected to blanching treatments under different time and temperature combinations both in water and in 4% sugar solutions made of trehalose or maltose. The influence of these process conditions on mass transfer, texture, and microstructure (Cryo-scanning electron microscopy) was thus investigated. The total mass loss of all the samples blanched in water was associated to their cook value (C(100)(18)) except for the overprocessed one (90 °C, 10 min) that showed a total mass change significantly lower due to water uptake. The use of trehalose and maltose in the blanching solution reduced the solute loss while increasing the water loss. Microstructural analysis of the differently blanched carrots showed detachments between adjacent cell walls as well as plasmolysis phenomena as the time and temperature of the thermal treatment were increased. A protective effect of both sugars on cell structures was observed mostly in the sample treated at 90 °C. At macroscopic level, textural changes upon blanching were observed by a penetration test. As blanching time was increased, samples processed at 75 °C showed a hardness increase, while those processed at 90 °C showed a hardness decrease. However, both trehalose and maltose did not exert significant effects on the textural properties of blanched carrots when compared with those blanched in water. Practical Application: The results of this study could offer interesting perspectives in the optimization of the heat treatments in order to preserve the quality of semi-finished processed vegetables. Furthermore, the microstructural analysis is nowadays an important investigation tool that could contribute to a deeper understanding of both the effects of processing and ingredients on the vegetable microstructure and its relationship with the changes occurring on the quality properties at macroscopic level.