Chemical and microbial evaluation of Egyptian dried egg white prepared by different techniques

Egg white was dehydrated (pan drying, spray drying) without and with glucose removal (using bacteria, yeast and enzyme). Although, moisture, protein and ether extract percentage in spray dried samples were, in general, in the same range as the imported Swiss made spray dried sample (as standard), yet the least moisture percentage was found in samples in which sugar was removed by yeast. The standard sample had the best solubility (99.79%). followed by the spray dried sample desugarized by yeast (99.67%). Samples in which Streptococcus lactis was used gave the highest percentage of insoluble matter (4.24%). Pan dried and spray dried samples were similar in solubility. The total microbial counts were found to decrease in egg white after drying (max. 4.9 × 10 org. in prepared samples, zero in the standard). Salmonella was absent in all dried samples. There are variations in the type of protein fractions of liquid egg white when the enzyme treatment or controlled bacterial fermentation were used. When yeast fermentation was used a decrease in some protein fractions was noticed in comparison with the nondesugarized sample. The dehydrated egg white proteins indicate that there was no difference between the different techniques applied for glucose removal, between drying methods and between prepared samples and imported one; 5 fractions were obtained in each sample.     

Effect of moderate spray drying conditions on functionality of dried egg white and whole egg

ABSTRACT:  Dried egg and egg-derived proteins have a range of applications in baking, dressings, and confectionery products. Egg powder was produced under high time–temperature scales (approximately 160 °C), which led to many changes in egg components, resulting in different functional properties of eggs after reconstitution. In this study, moderate operating conditions were selected to dry egg white and whole egg using a pilot-scale spray dryer. Functional properties changes were evaluated with an appropriate statistical technique. Major finding supports that spray drying of egg white at moderate conditions (air inlet temperature ranged from 110 to 125 °C) resulted in a product that enhanced considerably the water holding capacity of produced gels. Moreover, gel prepared with the dried samples was firmer than that of the fresh samples. Drying at a moderate scale allowed not only the increasing of the foaming capacity and the stability of foam but also an increase in their emulsifying capacity and stability of the emulsions.     

干燥方式对蛋清蛋白理化性质和功能特性的影响

为探究干燥方式对蛋清蛋白（egg white protein,EWP）功能特性的影响及其内在机理,分别通过喷雾干燥与真空冷冻干燥制备蛋清蛋白粉,并对其蛋白结构、理化性质与功能特性进行研究。结果表明,与蛋清液（EWP-C）相比,喷雾干燥使蛋清蛋白（EWP-P）的内源性荧光强度降低,表面疏水性和表面游离巯基含量增大。傅里叶变换红外光谱分析显示,EWP-P的α-螺旋、β-折叠和β-转角分别为16.30%、25.72%和40.23%,冷冻干燥蛋清蛋白（EWP-D）分别为20.43%、24.32%和35.69%。不同pH下,EWP-D的溶解度均高于EWP-P,表面张力小于EWP-P。此外,EWP-P的接触角为99.62°,高于EWP-D（接触角为65.97°）,表明喷雾干燥能显著提高蛋白的疏水性（P<0.05）。EWP-D在不同pH下的乳化性、乳化稳定性以及起泡性均大于EWP-P,但起泡稳定性更小,这与EWP-D较高的溶解性与较低的表明疏水性有关。荧光倒置显微镜及激光共聚焦扫描显微镜分析表明EWP-D乳液的微粒更小,分布更均匀,其稳定性高于EWP-P。综上,喷雾干燥蛋清蛋白的β-折叠结构较多,表面游离巯基含量和表面疏水性较高,具有较好的凝胶性;冷冻干燥蛋清蛋白的表面疏水性较小,且表面张力小、溶解度大,具有更好的乳化能力与起泡性。     

Foam-mat drying technology: A review

This article reviews various aspects of foam-mat drying such as foam-mat drying processing technique, main additives used for foam-mat drying, foam-mat drying of liquid and solid foods, quality characteristics of foam-mat dried foods, and economic and technical benefits for employing foam-mat drying. Foam-mat drying process is an alternative method that allows the removal of water from liquid materials and pureed materials. In this drying process, a liquid material is converted into foam that is stable by being whipped after adding an edible foaming agent. The stable foam is then spread out in sheet or mat and dried by using hot air (40–90°C) at atmospheric pressure. Methyl cellulose (0.25–2%), egg white (3–20%), maltodextrin (0.5–05%), and gum Arabic (2–9%) are the commonly utilized additives for the foam-mat drying process at the given range, either combined together for their effectiveness or individual effect. The foam-mat drying process is suitable for heat sensitive, viscous, and sticky products that cannot be dried using other forms of drying methods such as spray drying because of the state of product. More interest has developed for foam-mat drying because of the simplicity, cost effectiveness, high speed drying, and improved product quality it provides.     

EFFECT of DRYING TYPE and DRYING CONDITIONS OVER FERMENTATIVE ABILITY of BREWER'S YEAST

In this work the growth and glucose consumption as well as alcohol production kinetics of fresh and rehydrated brewer's yeast were evaluated. Dried yeast was obtained by fluidized bed and spray drying. Based on fermentation trials, there was no difference between the number of viable cells determined at the end of the stationary phase, however differences in growth velocity between the dehydrated yeast and the fresh yeast cream were found. Regarding alcohol production, no differences were found in most of the treatments (F2, F3, F4*, A1, A2. A3 and A4) with respect to the fresh yeast. the brewery dried yeast with an efficient viability and fermentative ability can be stored at least 4 months and used when required. Therefore the need of conventional propagation and fresh yeast transport may be eliminated.     

超声处理对蛋清粉速溶性的影响

以新鲜蛋清液为原料,采用超声处理对其进行改性后,喷雾干燥制成蛋清粉,以期改善蛋清粉的溶解性,制备速溶性蛋清粉。选择超声时间、超声功率、超声时蛋清液体积分数3 个因素,以分散性、溶解度和稳定系数作为速溶性评价指标,通过单因素试验和正交试验对超声处理条件进行优化,得出最优的超声处理条件为：超声时间10 min、超声功率120 W、超声时蛋清液体积分数50%。在此条件下制备的蛋清粉的平均分散时间为56.67 s、平均溶解度为93.56 g/100 g、平均稳定系数为97.29%,具有较好的速溶性。通过对未超声喷雾干燥和冷冻干燥蛋清粉进行十二烷基硫酸钠-聚丙烯酰胺凝胶电泳、扫描电子显微镜观察和粒径分析,发现超声之后喷雾干燥得到的蛋清粉的颗粒更小、更均匀。圆二色光谱和表面疏水性结果显示,超声后喷雾干燥蛋清粉的蛋白质结构发生了改变,超声后其蛋白质结构趋于无序,表面疏水性增加,这些结构上的变化都有助于提高速溶性。本研究结果为超声波在新型蛋制品领域的应用提供了参考。     

Quality of fresh and stored foam mat dried Mandarin powder

Foam mat drying is a lucrative process of mandarin (kinnow) pulp preservation in the form of powder. Foam mat drying of mandarin pulp experiments were carried out at 65, 75 and 85 °C drying air temperatures using carboxy methyl cellulose, milk and egg white as foaming agents at different concentrations levels to get dried mandarin powder. Quality of the reconstituted dried Mandarin pulp‐powder was evaluated for 6 month storage studies at an interval of 2 months for total sugars (%), ascorbic acid (mg 100 mL^?1), total acid (%), pH and microbial load (fungal and bacterial) using standard procedures. It was observed that total sugars, ascorbic acid and total acid were decreased whereas pH was slightly higher than the fresh pulp. There was minor bacterial growth noticed in all the treatments, which is within the permissible limit, furthermore no fungal growth was noticed during storage period.     

接触脱水膜干燥对南美白对虾干复水特性的影响

接触脱水膜（contact dehydrating sheet,CDS）是一种适用于鱼肉等富含蛋白质食品干燥的新型冷脱水技术。为研究低温脱水对南美白对虾干复水特性的改善作用及其内在原因,本实验研究了CDS脱水至不同水分质量分数虾干的蛋白质结构变化及复水过程中复原率、持水力和水分状态的分布情况,并和热风干燥（hot air drying,HAD）的虾干进行比较。结果表明：采用CDS脱水法制备的不同水分质量分数（60%、45%、30%,以湿基计）虾干复原率、持水力均高于相对应的HAD脱水虾干组,其中水分质量分数为30%时,CDS脱水虾干的复原率、持水力分别为85.22%、69.17%,明显高于HAD脱水虾干（62.55%、65.73%）。低场核磁共振分析表明CDS脱水处理的水分质量分数为30%的虾干复水后虾仁的结合水、不易流动水、自由水比例均比HAD处理组更接近鲜虾。表面疏水性和蛋白质结构分析表明CDS脱水虾干蛋白的表面疏水性变化程度比HAD脱水低,蛋白质二级结构变化比HAD脱水虾干小。因此,CDS脱水法能维持蛋白质结构的完整性,复水后的虾干有更好的复原率、持水力,使产品品质更接近鲜虾,可以作为对虾及其他高值水产品的脱水干燥新途径。     

Effect of Dehydration on Raspberries: Polyphenol and Anthocyanin Retention, Antioxidant Capacity, and Antiadipogenic Activity

ABSTRACT:  Fresh and dried raspberries prepared by freeze drying (FD), microwave-vacuum (MIVAC), hot-air drying (HAD), and a combination of hot-air drying and microwave-vacuum (HAD/MIVAC) drying methods were evaluated for polyphenol retention, total polyphenol and anthocyanin contents, total antioxidant capacity, and antiadipogenic activity (the inhibition of fat cell development). Ellagic acid and quercetin were present in the largest concentrations in fresh and dehydrated raspberries. Dehydration led to a loss of polyphenols and anthocyanins and antioxidant capacity. Polyphenols (aglycone form) were retained in the greatest amount: 20% (freeze dried) to 30% (HAD/MIVAC) (fresh = 100%). A total of 30% of polyphenols (glycoside form) were retained in raspberries dried by the HAD/MIVAC methods with 5% of retention observed for raspberries dried by FD, HAD, or MIVAC. FD and MIVAC resulted in higher retention of anthocyanins (aglycone form) than other drying methods. It was also observed that antioxidant activity was reduced by dehydration. Adipogenesis was inhibited by polyphenolic glycosides (30%) and aglycones (30% to 40%) in fresh and HAD/MIVAC raspberries. Extracts from dried raspberries by HAD/MIVAC methods were relatively more effective at inhibiting adipogenesis compared to HAD and FD dried raspberries.     

Influence of spray drying conditions on functionality of dried whole egg

Instead of traditional liquid eggs, more and more dried whole egg products are being used in the manufacture of fine bakery goods, since dried semi‐finished products have some advantages regarding storage, handling and microbiological safety. However, the spray drying process leads to changes in sensitive egg components, eg proteins, and affects the functional properties of whole egg after reconstitution. Knowledge of the influence of drying conditions on the resulting functionality is necessary to enable the production of dried egg with tailor‐made properties for applications in different food products. Some of these relationships were determined using a pilot spray dryer for drying experiments and an appropriate statistical evaluation of the results. It could be demonstrated that higher temperatures during spray drying lead to a considerable decrease in the foaming properties of whole egg powder but increase the capability of emulsion stabilisation. Additionally, a simplified example demonstrates the use of these relationships for the selection of optimal drying conditions of whole egg with respect to its application in a cake with higher fat content. © 2002 Society of Chemical Industry     

Pulse Combustion Spray Drying of Egg White: Energy Efficiency and Product Quality

A new technique for spray drying of egg white was developed and termed as pulse combustion spray drying (PCSD) which uses high-temperature pulsating jets generated by the pulse combustor to atomize and dry the liquid feed simultaneously. The pilot-scale PCSD testing of egg white was conducted and the drying energy efficiency was evaluated. Selected product properties of the PCSD egg white powders were measured. It was found that compared with traditional spray drying, the PCSD process achieved a higher energy efficiency of 2,604 kJ/kg water evaporated and the PCSD powders had a superior surface characteristics, smaller mean particle diameter, and more homogeneous size distribution. Additionally, the egg white proteins and their foaming and gelling properties were protected well in the PCSD process. Experimental results showed that the PCSD technique is promising for drying of egg white and even other heat-sensitive food feeds.     

干燥方式对不同接枝度的大豆分离蛋白-麦芽糊精聚合物性质影响

以大豆分离蛋白(SPI)和麦芽糊精(MD)为原料制备不同接枝度的SPI-MD聚合物,研究比较喷雾干燥和冷冻干燥两种处理方式对不同接枝度下的SPI-MD聚合物性质的影响,如溶解度、疏水性、持水性、乳化性、乳化稳定性及起泡性、泡沫稳定性等的影响。实验表明,喷雾干燥样品的溶解性,表面疏水性和乳化性高于冷冻干燥样品;冷冻干燥样品则具有较好的持水性。另外,两种干燥样品的乳化稳定性非常接近。不同接枝度的两种干燥样品起泡性差异较大,且泡沫稳定性都相对较差。     

Studies on freezing of partially dehydrated spinach

Spinach (Spinacea oleracea) was dehydrated at 70 °C, partially dehydrated frozen (dried to its critical moisture ratio and frozen at ?20 °C) and frozen at ?20 °C. Results indicated that the time required for spinach dehydration was 7 h. Thus, the moisture ratio was 10.1 and 0.054 for the fresh and dried spinach, respectively. The critical moisture ratio during dehydration process was 2.20 after 2.65 h of drying time. Reducing sugars, free amino nitrogen, ash, iron and magnesium were slightly decreased in the partially dehydrated frozen spinach relative to the fresh samples. Dehydration markedly degraded the total chlorophyll, chlorophyll a, chlorophyll b, carotenoides and ascorbic acid whereas the freezing of partially-dehydrated spinach and freezing process were less effective. On the other hand, freezing of partially dehydrated spinach increased phaeophytin. There were no changes in pH-values of studied preserved samples. Freezing of partially dehydrated spinach improved the reconstitution of product at 100 °C and at room temperature (25 °C) comparing to dehydration. The drip loss of frozen spinach was 16.4% after 105 min of thawing time. Cooked fresh and frozen spinach were better in colour, flavour, texture, appearance and shape and over-all acceptability than that of dehydrated cooked one. Moreover, freezing of partially dehydrated spinach improved the aforementioned properties.     

Trehalose improves flavour retention in dehydrated apricot puree

The influence of the addition of two sugars (trehalose and sucrose) on the retention of volatiles responsible for the characteristic aroma in dehydrated apricot puree was studied. Aroma compounds of fresh and both freeze‐dried and foam‐mat‐dried apricot puree were analysed by manual headspace solid‐phase microextraction coupled with gas chromatography (GC‐FID and GC‐MS). The best retention of aroma compounds in dehydrated apricot puree was obtained when trehalose was added, regardless of the dehydration process used (freeze drying or foam‐mat drying), although, generally, a much higher retention of flavour volatiles was obtained in freeze‐dried purees. Principal Component Analysis and Cluster Analysis were applied to all the apricot purees studied to obtain a simplified view of the relationship among the aroma compounds in dehydrated apricot purees. This study gives further insights into the mechanisms that occur when trehalose is applied as an additive and will enable the development of new processes to maximize this effect and to produce superior dried products.     

Effects of Ultrasound Assistance on Dehydration Processes and Bioactive Component Retention of Osmo‐Dried Sour Cherries

Despite having numerous health benefits, dried sour cherries have proven to be more acceptable to consumers when infused with sugar or other sweeteners to enhance their flavor, which, in turn, leads to serious anthocyanin losses. For this reason, a consideration was made for the application of ultrasound to accelerate solid gain and shorten drying time, thus favoring bioactive component retention. To determine the usefulness of ultrasound as a tool for sour cherry osmotic infusion enhancement, the effect of sonication time on dehydration effectiveness, as well as the stability of bioactive components during osmotic treatment and consecutive convective drying, was investigated. Fruits were osmo‐dehydrated using a 60% sucrose solution for 120 min (40 °C), during which, ultrasound of 25 kHz (0.4 W/cm²), was applied for 0, 30, 60, 90, and 120 min, after which, the fruits were convectively dried. In the range of the applied ultrasound energy no significant effect of sonication on mass transfer intensification was observed; moreover, longer acoustic treatment seemed to retard moisture removal during subsequent convective drying, which can be related to the breakdown of the parenchyma cell walls caused by the prolonged ultrasound (US) action. It was concluded that although US assistance could be considered neutral for bioactive component retention, excessive sonication time can lead to some anthocyanin deterioration. According to high‐performance liquid chromatography analysis, the particular anthocyanin alterations, both during dehydration and final drying, occurred in a similar way. Sonication time prolongation caused approximately 10% more bioactive compound deterioration, than earlier, shorter trials.     

Improving functionality of whole egg powder by the addition of gelatine, lactose, and pullulan

The addition of gelatine (G), lactose (L), pullulan (P), and their mixtures at equal ratios (gelatine + lactose [GL] and gelatin + pullulan [GP]) to whole egg prior to drying was studied. Their effects on the functional properties (emulsion and gelling ability, water holding capacity of gel, foaming, color) and soluble protein content of spray dried egg powder during the 6 mo of storage at 20 °C and 50% relative humidity were investigated. It was demonstrated that the emulsion and foaming stability, water holding capacity of gel, and color change were significantly affected by the storage time, whereas storage time did not affect the strength of gel texture prepared by egg powders. Gelatine and pullulan improved the foaming stability and water holding capacity. Lactose caused a decrease in emulsion and foaming stability values. The maximum color change was observed for the plain egg powder, showing that mixing whole egg with carbohydrate- and/or protein-based additives before the drying process preserved the color of egg powder. Adding carbohydrate and/or protein caused significant changes in functional properties of egg powder.     

Vergleichende Untersuchungen an Trockeneiprodukten

Zusammenfassung Das Schaumbildungsvermögen und die Schaumstabilität erleidet in Trockeneiklar-Handelsprodukten keine Beeinträchtigung. Das Schaumbildungsvermögen zeigte sich gegenüber Bezugsproben sogar verbessert. Analog den Befunden bei Schaleneiern nach unterschiedlicher Vorbehandlung zur Salmonellenabtötung kann man auch bei Trockeneiprodukten die quantitativen Veränderungen im Gehalt an freien Aminosäuren als Indiz für solche Vorbehandlung (z. B. Hitzepasteurisierung) ansehen. Auch bei Trockeneiklar ergab sich eine Zunahme der freien Aminosäuren gegenüber den Bezugsproben, die teilweise im Größenbereich der Werte von pasteurisiertem Flüssigeiklar bei ähnlichen Pasteurisierungsbedingungen lagen. In anderen Fällen wurden einerseits niedrigere, andererseits wesentlich höhere Werte als in Flüssigei gefunden. Bei diesen Handelsprodukten waren die Bedingungen des Trocknungsverfahrens nicht bekannt. Auch im Trockeneigelb zeigten sich divergierende Tendenzen: einerseits Zunahmen der neutralen und sauren, bzw. Abnahmen der basischen Aminosäuren, andererseits Abnahme sämtlicher Aminosäuren gegenüber den Bezugswerten. Eine thermische Belastung (37°C) von Eiklar vor der Gefriertrocknung führt zu geringfügigem Anstieg der freien Aminosäuren. Unterschiede im Gehalt an freien SH-Gruppen traten in den untersuchten Proben untereinander und gegenüber den Bezugsproben nicht auf.[/p]

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Comparative studies on dry egg productsI. Influence of pasteurisation and manufacturing methods on the content of free amino acids and SIT groups

Summary The quantitative changes of free amino acids in dry egg products may be considered as an evidence for different methods of preliminary treatment (e. g. heat pasteurisation) for the elimination of salmonella analogous to the findings in shell eggs after such treatment. Increase of free amino acids could be observed also in dry egg white compared to freeze dried egg white (reference sample). The increase lies partly on a level with the values of liquid egg white at similar pasteurisation conditions. In other cases both lower values and much higher values were found than in liquid egg. The conditions of drying were unknown at the most commercial products. Also in the dry egg yolk diverging tendencies were observed: on the one side an increase of the neutral and acid amino acids and a decrease of the basic amino acids, on the other side a decrease of all amino acids in relation to the freeze dried egg yolk (reference sample). A thermic influence (37°C) on egg white before freeze drying leads to a small increase of free amino acids. Differences in the free SH groups of commercial dry egg white were found neither between the investigated samples nor with regard to the freeze dried egg white. Foam power and foam stability of dry egg products were found in similar level with the freeze dried egg white. Foam power was even improved.

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Wir danken dem Bundesministerium für Wirtschaft und dem Forschungskreis der Ernährungsindustrie für die Förderung dieser Arbeit.     

Screening of Proteolytic Enzymes to Enhance Foaming of Whey Protein Isolates

Whey protein isolate (WPI) was modified to enhance foaming characteristics by controlled hydrolysis using proteolytic enzymes. Alcalase, acid fungal protease, chymotrypsin, pepsin and trypsin were used to hydrolyze 5% rehydrated WPI. Decree of hydrolvsis was estimated by freezing point depression and terminated at 2.5 to 3% by heating or pH adjustment. Controls were treated under similar conditions but without enzymes. Hydrolysates were separated into permeate and retentate by ultrafiltration and concentrated by reverse osmosis before freeze drying. Foam capacity, stability and surface tension of hydrolysates were measured. Permeate from Alcalase exhibited the best foaming characteristics, comparable to egg white.     

Preparation of High‐Grade Powders from Tomato Paste Using a Vacuum Foam Drying Method

We present a rapid and gentle drying method for the production of high‐grade tomato powders from double concentrated tomato paste, comparing results with powders obtained by foam mat air drying and freeze dried powders. The principle of this method consists of drying tomato paste in foamed state at low temperatures in vacuum. The formulations were dried at temperatures of 50, 60, and 70 °C and vacuum of 200 mbar. Foam stability was affected by low serum viscosity and the presence of solid particles in tomato paste. Consequently, serum viscosity was increased by maltodextrin addition, yielding optimum stability at tomato paste:maltodextrin ratio of 2.4:1 (w/w) in dry matter. Material foamability was improved by addition of 0.5% (w/w, fresh weight) egg white. Because of solid particles in tomato paste, foam air filling had to be limited to critical air volume fraction of Φ = 0.7. The paste was first pre‐foamed to Φ = 0.2 and subsequently expanded in vacuo. After drying to a moisture content of 5.6% to 7.5% wet base (w.b.), the materials obtained were in glassy state. Qualities of the resulting powders were compared with those produced by freeze and air drying. Total color changes were the least after vacuum drying, whereas air drying resulted in noticeable color changes. Vacuum foam drying at 50 °C led to insignificant carotenoid losses, being equivalent to the time‐consuming freeze drying method. In contrast, air drying caused lycopene and β‐carotene losses of 18% to 33% and 14% to 19% respectively. Thus, vacuum foam drying enables production of high‐grade tomato powders being qualitatively similar to powders obtained by freeze drying.     

The significance of critical processing steps in the production of dried egg albumen powder on gel textural and foaming properties

The purpose of the present work was to study the variation in egg albumen functional properties as a function of seven selected processing steps from the initially raw liquid albumen to the final dried egg albumen powder. Albumen samples in six replicates were analysed for dry matter, pH, glucose, triglycerides, albumen gel properties (ie textural stress and Hencky strain, water‐ and protein‐binding capacity and gel colour L*, a*, b*), foaming properties (ie overrun, stability against drainage and bubble breakdown) and surface tension. The gel texture and water‐holding capacity significantly decreased during the processing steps from raw albumen through storage, centrifugation and ion exchange, whereas the final dry‐pasteurisation resulted in increased gel properties. Covalently linked protein polymers formed during the dry‐pasteurisation, as revealed by SDS‐PAGE, may explain this improvement. The foam overrun increased twofold during the three final steps of ultrafiltration, spray‐drying and dry‐pasteurisation compared with the raw albumen; however, the foam stability decreased, ie drainage and foam volume breakdown rates increased. The surface pressure increase was positively correlated with the foam overrun. This paper reveals at which processing steps the control of functional properties of egg albumen powder can take place. Copyright © 2004 Society of Chemical Industry