Continuous Freezer Research Articles

Avaliação do congelamento tradicional e do congelamento assistido por campo eletromagnético nas propriedades físicas e sensoriais do abacate (Persea americana Mill) variedade Hass

Abstract This study evaluated the effect on physical and sensory properties of freezing Halved Avocados (HA) by Traditional Method (TM) in a continuous freezer and by electromagnetic field-assisted method (EM) with CAS (Cells Alive System) freezer, obtaining HATM and HAEM, respectively. Each HA from the same specimen (obtaining 2 HA: one for fresh and the other for frozen-thawed state) was coded and evaluated. The firmness of the upper part of the fresh HA was higher (p < 0.05) than the lower part. The freezing curve showed the crystallization phase in the HAEM (from 14.25 to 20.33 min), thus indicating the formation of ice crystals, as well as affecting the significant decrease (p < 0.05) in more than 60% of firmness in the thawed HA concerning the fresh state. Regarding the color, there were differences (p < 0.05) in saturation (C*) between fresh and thawed avocado (HATM and HAEM); however, there were no differences (p > 0.05) in the tonality (h*). Weight loss of thawed HA was less than 0.5%. The sensory evaluation indicated there were no significant differences (p < 0.05) in firmness between the HATM and HAEM using the triangular test.

Comprehensive Mathematical Model for Freezing Time Prediction of Finite Object

Frozen food sees a continuous increase in consumption thanks to the capability to preserve the organoleptic properties and, at the same time, to increase the shelf-life of the food itself. Therefore, a proper design of the freezing process is crucial and is strictly related to an accurate evaluation of freezing time because this establishes the minimum residence time of the product in a continuous freezer. For this reason, several mathematical models have been proposed and investigated for predicting the freezing time, starting from empirical models (lower accuracy and computational time) up to computational fluid dynamics simulation (higher accuracy and computational time). An excellent compromise between accuracy and computational effort seems to be a model that combines empirical laws for property evaluation and heat diffusion equation solved in one dimension. This model can numerically be solved using the method of lines in which spatial derivatives are discretized by the finite difference method and the resulting system of ordinary differential equations is integrated using an appropriate solver. This work aimed to fill some gaps to develop a comprehensive and more accurate model for freezing time prediction. Indeed, the key idea is to validate a model that could be used to optimize the refrigeration process for energy-saving and be the base for a design of experiment in case of lack of experimental data. The newly developed model includes the evaluation of freezing time for finite food shapes because, in some cases, it is not possible to assume a characteristic direction for heat flux. The property of unfrozen and frozen food (e.g. density, thermal conductivity, apparent specific heat, etc.) are evaluated basing on the principal constituent of food (e.g. water, fiber, protein, etc.), while heat transfer coefficient is evaluated using empirical equations, depending on adimensional numbers. In this way, it is possible to be flexible and not strictly related to the evaluation of the properties of food for each different case. The proposed model was validated with different sets of experimental data related to beef and strawberry pulp freezing. For these cases, the R2 index is equal to 0.982 and 0.996 respectively, showing a good agreement between experimental and predicted data. Finally, a case study of spinach cubes freezing was provided to show the potentiality of the novel model.

Effect of agitation speed on freezing process of ice cream using a batch freezer

AbstractThis study investigates the effect of agitation speed on the freezing process of ice cream using a batch freezer. The temporal change in apparent viscosity during freezing is measured by the Metzner–Otto method. It was found that the apparent viscosity of ice cream after freezing decreased with an increase in the agitation speed. In addition, the number of bubbles incorporated into the ice cream also increased with the increase in the agitation speed. The bubbles were broken down into smaller bubbles by the higher shear force, that is, the higher agitation speed. Furthermore, a narrower distribution of the bubble size was obtained at higher agitation speeds. This indicated that the rheological properties and the microstructure of ice cream can be controlled by the agitation operation.Practical applicationsThis study clarified the effect of agitation speed on ice cream properties such as the apparent viscosity, the overrun and the size distribution of contained bubbles. Especially, the apparent viscosity is important for both industries and consumers. The Metzner–Otto method was used to directly measure the temporal change in the apparent viscosity during freezing. This temporal change has not been investigated so far. It was found that the apparent viscosity decreased with the increase in the agitation speed. In other words, the rheological properties can be controlled by the agitation operation. In industries, the continuous freezer is more preferable than the batch freezer used in this study. Nevertheless, the knowledge would be quite useful for the development of industrial processes of ice cream.

Conventional industrial ice cream freezers and its thermal design: a review.

Freezing is the most important process in any ice cream manufacturing plant. The quality of the end product mainly depends upon the various parameters chosen during freezing process. So far many batch and continuous freezers has been developed and various modifications are made in them in order to achieve more acceptable quality of frozen product. Scraped surface freezers (SSFs) are mainly used for viscous and sticky products. In scraped surface freezers, product come in direct contact with the freezing wall and scraper blades continuously scrapes off the mixture near the wall and mixes it back with product. This action leads to high heat transfer coefficient. Due to the versatility of SSFs in various operations, they are most commonly used. Also design parameters should be properly selected based on the existing models that give least errors. In this review article, various types of ice cream freezers and thermal design involved in SSHE/SSFs are explicitly discussed.

Texture, Oil Adsorption and Safety of the European Style Croquettes Manufactured at Industrial Scale

An European style croquette is like a small breaded patty, but, in its manufacturing, the ingredients (all minced) meat, fish and vegetables are boiled along with wheat flour and milk (or milk powder and water), and then cooled to form a consistent and tied dough. When manufacturing is made at industrial scale, this dough is cooled with cold air, and mechanically extruded, divided and formed, for achieving the required shape and size of the croquettes. Then, in the same manufacturing line, they are coated first by a batter, and secondly with breadcrumbs, and conveyed to the continuous freezer to be packaged later as precooked frozen croquettes, or they are directly conveyed to packaging and cooling for obtaining precooked refrigerated croquettes. Before consumption, at the foodservice sector (for example the kitchen of the restaurant or canteen), or at the home kitchen, this precooked meal is generally deep-fried to create a golden and crunchy outer crust. It is one of the most widespread prepared dishes of the world cuisine and has a continued growth in consumption as a delicacy and as a fast food. However, there is insufficient research devoted specifically to the study of technology and engineering aspects of interest for manufacturing European style croquettes at industrial scale. In addition, the corresponding literature is very scattered when considering the study of croquettes quality, oil absorption during frying, and safety. Therefore, this paper makes a review of the literature analyzing the different technological factors that determine the texture, quality and safety of the croquettes manufactured at industrial scale.

Modeling of the effect of freezer conditions on the hardness of ice cream using response surface methodology

The effect of conventional continuous freezer parameters [mix flow (L/h), overrun (%), drawing temperature (°C), cylinder pressure (kPa), and dasher speed (rpm)] on the hardness of ice cream under varying measured temperatures (−5, −10, and −15°C) was investigated systematically using response surface methodology (central composite face-centered design), and the relationships were expressed as statistical models. The range (maximum and minimum values) of each freezer parameter was set according to the actual capability of the conventional freezer and applicability to the manufacturing process. Hardness was measured using a penetrometer. These models showed that overrun and drawing temperature had significant effects on hardness. The models can be used to optimize freezer conditions to make ice cream of the least possible hardness under the highest overrun (120%) and a drawing temperature of approximately −5.5°C (slightly warmer than the lowest drawing temperature of −6.5°C) within the range of this study. With reference to the structural elements of the ice cream, we suggest that the volume of overrun and ice crystal content, ice crystal size, and fat globule destabilization affect the hardness of ice cream. In addition, the combination of a simple instrumental parameter and response surface methodology allows us to show the relation between freezer conditions and one of the most important properties—hardness—visually and quantitatively on the practical level.

Modeling of the Effect of Freezer Conditions on the Principal Constituent Parameters of Ice Cream by Using Response Surface Methodology

A systematic analysis was carried out by using response surface methodology to create a quantitative model of the synergistic effects of conditions in a continuous freezer [mix flow rate (L/h), overrun (%), cylinder pressure (kPa), drawing temperature (°C), and dasher speed (rpm)] on the principal constituent parameters of ice cream [rate of fat destabilization (%), mean air cell diameter (μm), and mean ice crystal diameter (μm)]. A central composite face-centered design was used for this study. Thirty-one combinations of the 5 above-mentioned freezer conditions were designed (including replicates at the center point), and ice cream samples were manufactured and examined in a continuous freezer under the selected conditions. The responses were the 3 variables given above. A quadratic model was constructed, with the freezer conditions as the independent variables and the ice cream characteristics as the dependent variables. The coefficients of determination (R2) were greater than 0.9 for all 3 responses, but Q2, the index used here for the capability of the model for predicting future observed values of the responses, was negative for both the mean ice crystal diameter and the mean air cell diameter. Therefore, pruned models were constructed by removing terms that had contributed little to the prediction in the original model and by refitting the regression model. It was demonstrated that these pruned models provided good fits to the data in terms of R2, Q2, and ANOVA. The effects of freezer conditions were expressed quantitatively in terms of the 3 responses. The drawing temperature (°C) was found to have a greater effect on ice cream characteristics than any of the other factors.

MANUFACTURE of FROZEN YOGURT WITH ULTRAFILTERED MILK and PROBIOTIC LACTIC ACID BACTERIA

Utilization of ultrafiltered (UF) milk for the manufacture of frozen yogurt was investigated. Three basic frozen yogurt mixes (0, 2, and 4% milk fat) were formulated using ultrafiltered skim milk as a base material and fermented with Lactobacillus acidophilus, Bifidobacterium bifidum, and a mixed yogurt culture of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. the cultured mixes were frozen using a continuous freezer and evaluated for product stability. Results suggest that culture organisms grew well during fermentation and produced acids continuously in the UF mixes, which became excessively viscous at a TA of 0.40% or higher. Therefore, all mixes were fermented to 0.30% TA (±4h) and rapidly cooled to 10C or lower to prevent excessive viscosity development. the finished products contained high levels of protein and calcium as well as good flavor and textural quality. In addition, the culture organisms were stable during six weeks of frozen storage.

A study of fat and air structures in ice cream

Three ice cream mixes of conventional composition with varying emulsifier content (no emulsifier; 0.15% mono- and di-glycerides; 0.15% mono- and di-glycerides plus 0.06% polysorbate 80) were frozen using three different freezing regimes (continuous freezer at low and high back pressure and batch freezer) in order to prepare a series of ice cream samples with varying levels of fat destabilization and foam structures. The hardened samples were viewed by thin-section transmission electron microscopy after freeze-substitution and low-temperature embedding. The images were compared to those obtained by low-temperature scanning electron microscopy. The structures created by increasing levels of fat destabilization were observed as an increasing concentration of discrete fat globules at the air interface and increasing coalescence and clustering of fat globules both at the air interface and within the serum phase. However, air interfaces at the highest levels of fat destabilization were not completely covered by fat globules, nor was there evidence of a surface layer of free fat. Air interfaces from continuous and batch freezing were similar.

Acceptability of Ice Cream Made with Processed Wheys and Sodium Caseinate

Dry sweet whey, whey protein concentrate, and sodium caseinate were used in this study to replace the nonfat dry milk in ice cream. Either whey protein concentrate, a blend of whey protein concentrate and dry sweet whey, or a blend of dry sweet whey and sodium caseinate were used to replace the milk solids-not-fat at 50 or 100%. All the experimental ice creams were compared to control ice creams using nonfat dry milk to increase the milk solids-not-fat.All mixes were manufactured to produce an ice cream having 10.5% fat, 22% total milk solids, 13% sucrose, 3% corn syrup solids, and .3% stabilizer-emulsifier. The ice cream was manufactured in 114-kg batches, the mix being blended, pasteurized (72°C for 30min), homogenized with a two-stage homogenizer (1080 kg/cm2), cooled to 4°C, flavored with pure vanilla extract, and frozen in a continuous freezer. The ice cream was packed in 1-L containers, then stored at −30°C.The final products were evaluated for compositional analyses on two subsamples of each batch of mix; a panel evaluation for flavor, body, and texture by trained panelists; and a 52 family consumer evaluation to determine overall preference. The compositional analyses of ice cream averaged 10.5% fat, 3.9% protein, 5.7% lactose, .94% ash, and total solids of 38.7%. Standard deviations of these analyses were less than 1.00.The panel evaluation showed no significant differences (P>.05) in flavor, body, and texture among the various ice creams. Sandiness was not judged a problem with any of the ice creams.Fifty-two families were randomly selected from the City of Brookings, SD, for consumer evaluation of the ice creams. The 14-wk evaluation was conducted with each family receiving 5L of ice cream as five 1L cartons each week. Each week's ice cream delivery contained one sample from each of three treatment mixes, a control sample, and a duplicate of one of the other four samples. The samples of ice creams were rated on a nine-point hedonic scale (1 best, 9 worst).No significant differences were found in the consumer flavor ratings among the ice creams made with dry sweet whey, whey protein concentrate — dry sweet whey blend (at both the 50% and 100% replacement levels), and the control. The ice cream made with the dry sweet whey-sodium caseinate blend received a significantly higher hedonic rating (P<.01), indicating a poorer quality product.

Changes in Electrical Energy Requirements to Operate an Ice Cream Freezer as a Function of Sweeteners and Gums

Changes in electrical energy required to operate a continuous freezer were monitored for various ice cream formulae. Ice cream formulae consisted of nine different combinations of sucrose, 36 DE corn syrup, and 42 high fructose corn syrup as well as two ratios of guar gum to locust bean gum. Within the same sweetening system, a mix high in locust bean gum tended to have a lower energy demand than mix with large amounts of guar gum. This was especially pronounced in mixes with 50% 42 high fructose corn syrup and/or 50% 36 DE corn syrup solids.

Prepared Milk and Egg Custard with Freeze-Thaw Stability

The concept of a prepared frozen milk and egg custard which upon thawing would resemble the traditional baked custard was investigated. A basic formula was developed consisting of 73.8% whole milk (3.5% fat), 14.6% whole eggs, 10.0% sucrose, 1.0% nonfat dry milk, and 0.6% 300 Bloom gelatin. Processing involved pasteurization (82C for 15min), homogenization, cooling, aging, and freezing in a continuous ice cream freezer followed by storage at −29C. Syneresis which occurred upon thawing when samples were frozen quiescently was absent when the product was frozen in a continuous freezer with the incorporation of air to yield 10 to 15% overrun. Rate of cooling and time of aging the mix greatly influenced consistency of the thawed product. Results of a small-scale project indicated excellent consumer acceptance. Legal aspects of labeling the product are discussed.

Relative Storage Qualities of Frozen and Dried Milk

The storage of both fat and milk solids-not-fat in frozen form is commonly practiced by the dairy industry (9). The destabilizing effect of the continued storage at freezing temperatures upon the normal dispersion of the milk solids is one of the factors limiting the applications of this method to the storage of cream and condensed milk. Sugar sometimes is added to the milk solids to prevent churning of the fat and destabilization of the milk casein. In a series of experiments reported by Babcock et al. (1-7), it was brought out that homogenized milk remained normal when frozen and stored at a constant temperature. Extremely low ( -40 ° F.) temperatures were found best. Homogenized milk frozen and stored in the frozen state was found to have the solids more concentrated in the bottom section. Homogenized milk that had been stored frozen was held at usual fluid milk storage temperatures without any more rapid deterioration than would be expected of regular homogenized milk. The addition of sodium citrate to homogenized milk before freezing and storage improved the storage life of the milk, and added ascorbic acid helped preserve the normal flavor of the milk. Homogenized milk was kept as long as 120 hr. before freezing without adversely affecting the keeping quality of the frozen product. These investigators also found that rotating homogenized milk while it was being frozen prevented a segregation of the milk solids but did not improve the keeping quality of the stored milk. In 1944, Doan and Leeder (8) recommended a procedure for preparation of frozen condensed milk. They proposed a preheating temperature of 180 ° F. for 15 min., a 3 to 1 concentration of the milk, homogenization of at least 3000 lb. before condensing, limiting the air incorporation to 20 to 30 per cent when freezing with a continuous freezer, holding at a temperature not higher than -10 ° F. during freezing, storage and dispensing, and reconstitution in 180 ° F. water. These authors claim the frozen condensed milk can be held for 10 to 12 wk. without effect upon the fat or protein if stored at -15 to -20 ° F.

A Note on Ice Lump Formation in Ice Cream Frozen in Continuous Freezers

A Note on Ice Lump Formation in Ice Cream Frozen in Continuous Freezers

A Note on Ice Lump Formation in Ice Cream Frozen in Continuous Freezers

A Note on Ice Lump Formation in Ice Cream Frozen in Continuous Freezers