Spray Drying: Retention of Volatile Compounds Revisited

ABSTRACT

Retention or loss of trace volatile compounds during spray drying can be vital for product quality. Examples of cases where loss or retentions of volatile substances are important include retention of balanced flavor and aroma in food products, removal of odiferous substances, and control of the release of volatile organic compounds to the atmosphere. Factors and mechanisms determining losses of these substances are reviewed. Losses can occur during atomization, from undisturbed drops and as a result of morphological development. On the basis of this insight, several avenues for controlling the retention of volatile substances are identified and analyzed. These include control of atomizer pressure or rotation speed, choice of spray angle, configuration of air input, lteration of the air temperature profile, feed concentration, the presence of an oil phase and/or suspended solids, foaming of the feed, feed composition, and steam blanketing of the atomizer.

The quality of a spray-dried product can be strongly affected by the presence or absence of volatile compounds that were present in the feed to the spray dryer. For example, spray-dried coffee and tea have suffered from a air and thereby avoid bubble formation, expansion and bursting for deaerated feeds (20). This approach produces a product with high bulk density. If that result is cceptable, then it should also be a way of precluding volatiles loss due to morphological development.     

Influence of heat pump drying on tomato flavor

ABSTRACT

Tomato flavor from a heat pump dehumidifier dryer was characterized and compared to fresh and freeze-dried tomato samples for the retention of fresh flavor compounds. The monitored quality parameters were nonvolatile, volatile, and odor intensity. There were no differences in nonvolatile profiles; however, significant changes in key odor-impact volatiles were observed. Commercial spray-dried tomato was also evaluated to examine thermally induced volatile changes. The volatile and sensory profiles of heat pump dried tomato were comparable to freeze-dried tomato, with good retention of fresh aroma. In contrast, loss of compounds contributing to fresh green aroma ((E)-2-hexenal, 1-penten-3-one, 1-hexanol) and presence of heat-induced compounds (dimethyl sulfide, furfural, pyrrole derivatives) were detected in the spray-dried tomato.     

Characterization of a Spray Drying System for Soymilk

Soymilk slurries were spray dried at various combinations of inlet air temperature (1255. 265, and 275°C), feed rate (0.38 and 0.57 Lpm), and atomizer speed (119,300 and 26,800 rpm). Monitored dryer parameters included dry and wet bulb temperaturea of ambient and exhaust air, drying chamber's inlet and outlet air temperatures, product and feed temperatures, velocity pressure at exhaust pipe, atomizer speed, and feed rate. Weather data was included in the analysis.

Collected data was used to estimate the state of the outlet air using psychrometrics and assuming adiabatic saturation. Equations to predict outlet and product temperatures were developed. Average thermal and eveporative efficiencies were 65.9 and 78.4%. respectively.     

Spray Drying of Tomato Pulp: Effect of Feed Concentration

The effect of feed concentration on spray drying of tomato pulp preconcentrated to 78, 82, and 86% wet basis is investigated in two spray drying systems: a pilot scale spray dryer (Buchi, B-191) with cocurrent regime and a two-fluid nozzle atomizer, and the same connected with an absorption air dryer (Ultrapac 2000). Data for the residue on the chamber and cyclone walls were gathered and two types of efficiencies were calculated as an indication of the spray dryer performance. Tomato powders were analyzed for moisture, particle size, and bulk density. In both spray drying systems, with increases in tomato pulp concentration overall thermal efficiency, evaporative efficiency, material loss in the cyclone, powder moisture content, and bulk density decreased, whereas powder particle size increased. On the contrary, the effect of feed solids content on residue formation and product recovery was dependent on the drying medium. In the standard dryer, the higher the feed concentration, the higher was the residue accumulation, and the lower the product recovery, whereas in the modified system increases in pulp concentration resulted in lower residue formations and higher product yields.     

Characterization of a Spray Drying System for Soymilk

ABSTRACT

Soymilk slurries were spray dried at various combinations of inlet air temperature (1255. 265, and 275°C), feed rate (0.38 and 0.57 Lpm), and atomizer speed (119,300 and 26,800 rpm). Monitored dryer parameters included dry and wet bulb temperaturea of ambient and exhaust air, drying chamber's inlet and outlet air temperatures, product and feed temperatures, velocity pressure at exhaust pipe, atomizer speed, and feed rate. Weather data was included in the analysis.

Collected data was used to estimate the state of the outlet air using psychrometrics and assuming adiabatic saturation. Equations to predict outlet and product temperatures were developed. Average thermal and eveporative efficiencies were 65.9 and 78.4%. respectively.     

白炭黑的喷雾干燥现状及节能措施

介绍了白炭黑的喷雾干燥现状,包括旋转雾化器和压力式雾化器喷雾干燥的基本流程、热空气分布器和改进的二次热空气分布器的结构以及典型的喷雾干燥的操作参数等。还介绍了相关的节能措施,即在二级干燥塔底设置流化床或增加干燥塔高度、增加料液固含量、提高热空气进口温度、料液预热、回收烟道气及干燥塔气体的废热等。为白炭黑喷雾干燥工艺的改进提供了参考。     

MANUFACTURING PARAMETERS AND QUALITY CHARACTERISTICS OF SPRAY DRIED JAMEED

Spray drying of jameed - a dried fermented dairy product, is investigated. The study covers the effects of the operating variables upon the physical and chemical characteristics of the dried product. The investigated variables were: feed total solids, feed flow rate, inlet air temperature, air flow rate and atomizer pressure. The product characteristics measured were: total solids, bulk density, average particle size, wettability, dipersibility, color, ash content, salt content, fat content and pH. Best overall results were obtained for a feed total solids of 17%, feed flow rate of 36.5 ml/min, inlet air temperature of 100 /C, air flow rate of 632 cm₃/s, and atomizer pressure of 1.5 bar.     

Effect of Pretreatments and Drying Methods on the Properties and Fishy Odor/Flavor of Gelatin from Seabass (Lates calcarifer) skin

Effects of different pretreatments of seabass skin and various drying methods on properties and fishy odor/flavor of resulting gelatin were evaluated. All gelatins contained α- and β-chains as the predominant components. Generally, a higher gel strength was found in the freeze-dried gelatin, compared with spray-dried counterpart (p < 0.05). Gel strength of gelatin decreased as the inlet temperature for spray drying increased (p < 0.05). All gelatin samples had creamy whitish color but became more yellow as the inlet temperature for spray drying increased. All gelatin gels were sponge- or coral-like in structure. Gelatin from skin pretreated with citric acid had lower fishy odor/flavor than that from skin pretreated using acetic acid. The lower fishy odor/flavor with coincidentally lower abundance of volatile compounds, including aldehydes, ketones, and alcohols, etc., was found in gelatin obtained by spray drying, in comparison with its freeze-dried counterpart. The lower fishy odor/flavor in spray-dried gelatin was in accordance with the lower thiobarbituric acid reactive substances and peroxide values. Thus, spray drying in conjunction with an appropriated pretreatment could be an effective method for production of gelatin with negligible undesirable fishy odor and flavor.     

MICROENCAPSULATION OF EMULSIFIED HYDROPHOBIC FLAVORS BY SPRAY DRYING

The retention of emulsified flavor during spray drying was investigated under various compositions of feed liquid. Drying of the emulsion solution was carried out in a spray dryer, equipped with a centrifugal atomizer. The retention of d-limonene during spray dying was nearly hundred percent independent of the composition of the feed liquid, whereas the retention of ethyl butyrate emulsified by gum arabic (GA) was much lower (0-20%). The retention of ethyl butyrate was markedly dependent on the concentration of maltodextrin and the type of emulsifier, indicating that the stability of emulsion is a controlling factor for flavor retention. The use of mixing emulsifiers, adjusting of density of ethyl butyrate, and the addition of 1% gelatin were quite effective procedures to improve the retention of ethyl butyrate, particularly when emulsified by GA.     

Spray Drying Performance of a Laboratory Spray Dryer for Tomato Powder Preparation

This work investigates the performance of a spray dryer for tomato powder preparation by spray drying of tomato pulp. Samples of tomato pulp with a 14% constant total solids concentration were used, and a pilot scale spray dryer (Buchi, B-191) with cocurrent operation and a two-fluid nozzle atomizer was employed for the spray drying process. Twenty-four different experiments were conducted keeping constant the feed rate, the feed temperature, and the atomizer pressure, and varying the compressed air flow rate, the flow rate of drying rate, and the air inlet temperature. In each experiment the air outlet temperature was recorded. Data for the residue remaining in the chamber and cyclone walls was gathered and two types of efficiencies were calculated as an indication of the spray dryer performance. Analysis of experimental data yielded correlations between residue accumulation and the variable operating conditions. The same operating parameters had a great influence on the air outlet temperature whereas temperature deviations were observed comparing measured air outlet temperatures with corresponding outlet adiabatic saturation temperatures.     

MANUFACTURING PARAMETERS AND QUALITY CHARACTERISTICS OF SPRAY DRIED JAMEED

ABSTRACT

Spray drying of jameed - a dried fermented dairy product, is investigated. The study covers the effects of the operating variables upon the physical and chemical characteristics of the dried product. The investigated variables were: feed total solids, feed flow rate, inlet air temperature, air flow rate and atomizer pressure. The product characteristics measured were: total solids, bulk density, average particle size, wettability, dipersibility, color, ash content, salt content, fat content and pH. Best overall results were obtained for a feed total solids of 17%, feed flow rate of 36.5 ml/min, inlet air temperature of 100 /C, air flow rate of 632 cm₃/s, and atomizer pressure of 1.5 bar.     

Spray Drying Performance of a Laboratory Spray Dryer for Tomato Powder Preparation

Abstract

This work investigates the performance of a spray dryer for tomato powder preparation by spray drying of tomato pulp. Samples of tomato pulp with a 14% constant total solids concentration were used, and a pilot scale spray dryer (Buchi, B-191) with cocurrent operation and a two-fluid nozzle atomizer was employed for the spray drying process. Twenty-four different experiments were conducted keeping constant the feed rate, the feed temperature, and the atomizer pressure, and varying the compressed air flow rate, the flow rate of drying rate, and the air inlet temperature. In each experiment the air outlet temperature was recorded. Data for the residue remaining in the chamber and cyclone walls was gathered and two types of efficiencies were calculated as an indication of the spray dryer performance. Analysis of experimental data yielded correlations between residue accumulation and the variable operating conditions. The same operating parameters had a great influence on the air outlet temperature whereas temperature deviations were observed comparing measured air outlet temperatures with corresponding outlet adiabatic saturation temperatures.     

Narrow tube spray drying

Spray drying conventionally necessitates relatively large or elongated drying chambers. The present study examined the possibility in shrinking the spray drying chamber into narrow tube-like geometry. The key was in utilizing fine droplets which had low transport response time. A narrow copper/steel tube spray dryer (internal diameters between 12.7 and 48.0 mm) was constructed and was fitted with a two-fluid atomizer producing droplets in the size range smaller than 10 µm. Maltodextrin, lactose, and sucrose were spray-dried. The narrow tube approach allowed direct manipulation of the drying conditions via heating or cooling along the wall of the tube. This form of manipulation in the drying conditions, surprisingly, resulted in very distinctly crystalline spray-dried sucrose particles. The tube spray dryer was further modified with a long coiled-up tube, extending the particle residence time with minimal space requirements. Endoscopic analysis revealed that particle deposition within the tube resembled loosely attached particle and granules. The tube spray drying concept can potentially be used to provide precise control of the particle drying history along the length of the drying chamber, not limited to the control of the drying conditions at the inlet or outlet of a spray dryer.     

Manufacturing Better Quality Food Powders from Spray Drying and Subsequent Treatments

In this article three major aspects of spray-dried food powders are discussed. We first address several practical problems involved during spray drying that may greatly influence product quality. The second issue identifies how an accurate drying kinetics model can form a useful tool to predict changes in the physical and biological quality aspects and the microstructure of the particle during processing. Dryer-wide simulations using the accurate drying kinetics model can significantly reduce the number of experimental trials for optimizing the process. To date, such success has been restricted to production runs for pilot-scale or small-scale industrial operations. The final issue addresses some of the challenges encountered when evaluating the functionality of the spray-dried powders during their reconstitution. The superior functionality of the spray-dried food product needs to be established more scientifically, which can help commercial operations to achieve high-quality reconstitution.     

MICROENCAPSULATION OF EMULSIFIED HYDROPHOBIC FLAVORS BY SPRAY DRYING

The retention of emulsified flavor during spray drying was investigated under various compositions of feed liquid. Drying of the emulsion solution was carried out in a spray dryer, equipped with a centrifugal atomizer. The retention of d-limonene during spray dying was nearly hundred percent independent of the composition of the feed liquid, whereas the retention of ethyl butyrate emulsified by gum arabic (GA) was much lower (0–20%). The retention of ethyl butyrate was markedly dependent on the concentration of maltodextrin and the type of emulsifier, indicating that the stability of emulsion is a controlling factor for flavor retention. The use of mixing emulsifiers, adjusting of density of ethyl butyrate, and the addition of 1% gelatin were quite effective procedures to improve the retention of ethyl butyrate, particularly when emulsified by GA.     

Effect of Additives on Quality of Spray-Dried Fructooligosaccharide Powder

Fructooligosaccharide (FOS) finds its applications as an alternative sweetener in powder form. The effect of different process parameters (feed concentration, feed flow rate, inlet air temperature), different additives (maltodextrin, gums, starch), and anticaking agents (in different combinations and concentrations) during spray drying were investigated. FOS solution with 2% magnesium oxide as an additive gave a maximum powder yield (43% w/w), and the spray-dried powder size was fine and the texture was like talcum powder. Flow properties and microbial analysis were found to be satisfactory. The addition of anticaking agents did not have a significant effect either on the color of the powder or on FOS content, indicating good quality of the powder with respect to flowability, microbial load, and texture.     

Drying of Herbal Product in Closed System

A new product from a low temperature drying method that reduces the loss of highly volatile essential oils is presented. The proposed drying method consists of evaporation/sublimation of water and aromatic substances in a dryer with a closed drying agent cycle. In parallel, the evaporated compounds are continuously condensed in a heat exchanger. As a result of the drying process, high-quality dried plants and Fluidolat as liquid phase containing water and volatile organic compounds are obtained. The aim of presented investigations was to optimize the developed technology for the herb lavender.     

THEORETICAL AND PRACTICAL ASPECTS OF AROMA RETENTION IN SPRAY DRYING AND FREEZE DRYING

For many food products the presence of volatile aroma components is a prime quality feature. Upon drying part of these components may be lost, leading to unbalanced flavour patterns in the reconstituted product. The mechanisms of aroma loss in most drying processes are well understood by now. For homogeneously dissolved aroma components this can be described succesfully by Thijssen's selective diffusion theory. Somewhat more complicated is the loss of aroma components which are present in the form of a dispersion.

An extensive overview is given of theory and experimental work on aroma loss in slab drying, spray drying and freeze drying. Practical processing rules following from the basic insights are discussed. It is the intention to present a broad coverage of the subject.     

COMBINED CONVECTIVE AND INFRARED DRYING OF A CAPILLARP POROUS BODY

Abstract

This work investigates the effect of spray drying conditions on some properties of tomato powder prepared by spray drying of tomato pulp. A pilot scale spray dryer (Buchi, B-191) with cocurrent regime and a two-fluid nozzle atomizer was employed. Sixty-four different experiments were conducted keeping constant the feed rate, the feed temperature, and the atomizer pressure, and varying the compressed air flow rate, the flow rate of drying air, and the air inlet temperature. Tomato powders were analyzed for moisture, solubility, density (bulk and packed), and hygroscopicity. Analysis of experimental data yielded correlations between powder properties and the above-mentioned variable operating conditions. Regression analysis was used to fit a full second order polynomial, reduced second order polynomials and linear models to the data of each of the properties evaluated. F values for all reduced and linear models with an R ² ≥ 0.70 were calculated to determine if the models could be used in place of full second order polynomials.     

Spray Drying and Agglomeration of Instant Bayberry Powder

Optimum technology of spray-dried bayberry powder was studied using D-optimal experimental design. The operating conditions were varied within the following ranges: inlet air temperature 140–160°C, outlet air temperature 65–85°C, maltodextrin DE values 12 and 19, and feed concentrations of 7–17°B. The spray-dried bayberry powder was analyzed for moisture content and color. Moisture content of spray-dried powder was determined mainly by the inlet and outlet air temperatures, DE value, and the feed concentration. The inlet and outlet temperature had important effects on powder color. Finally, instant bayberry powder for beverages was produced by agglomeration of the spray-dried product.