• Title, Summary, Keyword: freeze drying

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Influence of Freezing Process on the Change of Ice Crystal Size and Freeze-Drying Rate in a Model System (모델 시스템에서 동결속도에 따른 얼음 결정체의 크기 및 동결건조속도의 변화)

  • Byun, Myung-Hee;Choi, Mi-Jung;Lee, Sung;Min, Sang-Gi
    • Food Science of Animal Resources
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    • v.18 no.2
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    • pp.164-175
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    • 1998
  • The objective of this study was to investigate the effects of freezing rate on ice crystal size and freeze-drying rate. Our experiments were carried out with self-manufactured freeze-dryer. Gelatin gels (2% w / w, 80$\times$20mm) were frozen unidirectionally (Neumann's model) from the bottom at -45, -30, -20, and -15$^{\circ}C$ and followed with freeze-drying. Under the upper conditions we measured freezing rate and the change of temperature and pressure during freeze drying. Freeze-dried gelatins were cut horizontally into 5 mm thickness from the bottom and measured their pore sizes. Also freeze-drying rate(primary drying) is estimated by measuring the temperature of sample and pressure of vacuum chamber. During freeze-drying, profiles of pressure and temperature were shown constant tendency regardless of freezing temperature and we could expect the end-point of freeze drying by considering pressure and temperature together. In temperature profiles, the point which temperature increased significantly was observed during freeze-drying. There is no relationship between freeze temperature and drying rate of primary drying in our model system. As freezing temperature increased, ice crystal size(X*) which correspond to 63.2% of cumulative frequency was increased and at the same freezing temperature ice crystal size(X*) was decreased with distance from the bottom of the sample. Freezing conditions have a strong influence on the quality of the final freeze-dried products in freeze-drying system.

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Application of Fixatives to Freeze Dried Rose Petals

  • Jo, Myung-Hwan;Kim, Tae-Yun;Hong, Jung-Hee
    • Journal of Environmental Science International
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    • v.17 no.11
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    • pp.1227-1233
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    • 2008
  • The effect of freeze drying and fixatives in post-treating freeze drying on the morphological properties of the rose (Rosa hybrida L.) petal were investigated for the production of high quality of freeze dried rose. The morphology including form and color of the dried flowers of cut rose were depended on the drying methods. The drying time was extended due to their density and water content, and was shorter in the freeze drying than that in the natural and hot air drying. Freeze dried process for dried flowers took 2 days in a freeze dryer and did not cause shrinkage or toughening of rose petal being dried, preserving its natural shape and color. The diameter of freeze dried flowers showed little reduction compared to fresh flowers. In Hunter color values of petals of freeze dried flowers, L and a values were high and showed little variations in comparison to fresh petals. Freeze drying led to a noticeable increase in anthocyanin contents in petals, suggesting that anthocyanin contents play an important role in the acquisition of freezing tolerance. Exposure of flowers to freeze drying was accompanied by an increase in the carotenoid content. In the post-treating freeze drying, epoxy resin, a fixative, applied alone or in combination to petals of freeze dried flowers showed efficient coating for the protection from humidity and sunlight. Combined application of epoxy and acetone to freeze dried petals permitted maintenance of natural color and excellent tissue morphology, showing color stability and shiny texture in surface of petals. These findings suggest that application of fixatives to freeze dried rose petals improves the floral preservation and epoxy coating provides good quality in the freeze dried flower product.

A Fixed Grid Finite Volume Analysis of Multi-Dimensional Freeze Drying Process under Vacuum Condition (고정격자계에서 유한체적법을 이용한 진공동결건조 과정의 열 및 물질전달에 대한 연구)

  • Chi-Sung, Song
    • Journal of the Korean Society of Marine Engineering
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    • v.28 no.6
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    • pp.981-992
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    • 2004
  • Freeze drying under vacuum condition is a complex process that involves simultaneous heat and mass transfer, sublimation of ice, and motion of sublimation front. Proper treatment of the motion of sublimation interface is crucial for an accurate prediction of the freeze drying process. Based on the enthalpy formulation that has been successfully used in liquid/solid phase change problems. a fixed grid method. streamlined for the freeze drying analysis. was developed in this study. The accuracy of the fixed grid method was checked by solving a one-dimensional tray freeze drying and a two-dimensional vial freeze drying problem and then comparing the results with those by the moving grid method. Finally. the freeze drying characteristics of two-dimensional slab and axis-symmetric cylinder was investigated using the fixed grid method.

A Study on the Freeze Drying Rate with Frozen Layer (동결층소멸을 이용한 동결건조 속도에 관한 연구)

  • Hong, S.S.;Lee, H.M.;Oh, C.S.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.2 no.2
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    • pp.105-111
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    • 1990
  • The drying rate in freeze drying was obtained by experiment of garlic moisture contents depending on the drying time. Freeze drying experiment of garlic juice was carried out in vaccum freeze drier of laboratory scale by backface heating, and a mathematical model is also used to simulate the process of simultaneous heat and mass transfer in freeze drying to compare with experimental data.

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Development of Freeze Drying Analysis Program using Fixed Grid (고정격자를 이용한 동결건조 해석프로그램의 개발)

  • Nam Jin Hyun;Song Chi Sung;Kim Charn-Jung
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.10
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    • pp.923-931
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    • 2004
  • A multi-dimensional freeze drying analysis program, which took simultaneous heat and mass transfer, sublimation of ice and motion of sublimation front into full account, was developed using finite volume method with fixed grid. The effect due to the motion of sublimation interface was modeled by an enthalpy formulation streamlined for the freeze drying problems. The efficiency and accuracy of the program was validated by solving one- and two-dimensional freeze drying problems frequently encountered in industrial processes. Finally, the freeze drying processes of cylinder and slab objects with permeable side surfaces were simulated, which demonstrated the capability of the present analysis program in solving multi-dimensional freeze drying problems with complex sublimation interface configurations.

Comparative Evaluation of Physicochemical Properties of Pine Needle Powders Prepared by Different Drying Methods

  • Chung, Ha-Sook;Lee, Jun Ho
    • Preventive Nutrition and Food Science
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    • v.20 no.2
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    • pp.143-147
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    • 2015
  • Systematic study of how different drying methods, namely hot-air drying, vacuum-drying, and freeze-drying, affect color, browning index, degree of rehydration, water solubility, and vitamin C content is critical for utilizing pine needle powders (PNP) as a novel ingredient in functional foods. Samples prepared by vacuum-drying showed a significantly higher $L^*$-value, whereas higher $a^*$- and $b^*$-values were detected in the hot-air dried samples (P<0.05). The browning index was significantly higher in samples prepared by vacuum-drying compared to samples prepared by freeze-drying (P<0.05). Freeze-dried PNP exhibited a significantly higher degree of rehydration than hot-air dried samples (P<0.05). Water solubilities of freeze-dried and hot-air dried samples were significantly higher than that of vacuum-dried sample (P<0.05). Vitamin C was less destroyed during freeze-drying compared to hot-air or vacuum-drying (P<0.05). Freeze-dried samples displayed a clear porous structure and appeared to have a bigger space, whereas hot-air dried samples showed lower porosity than vacuum and freeze-dried samples.

Quality Change of Cinnamon Extract Prepared with Various Drying Methods (건조 방법에 따른 계피 Extract의 품질 변화)

  • 김나미;김동희
    • The Korean Journal of Food And Nutrition
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    • v.13 no.2
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    • pp.152-157
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    • 2000
  • In order to select the optimum drying method for the production of cinnamon extract, water extract and 70% ethanol extract of cinnamon were prepared. And then several drying method of oven drying, vacuum evaporation, spray drying and freeze drying were performed. Content of cinnamic acid, cinnamic aldehyde, eugenol, tannin and free sugar, and antioxidant activity, degree of browning, pH, color value, turbity and solubility were compared. In water extract, contents of cinnamic acid, cinnamic aldehyde, eugenol were 29.45mg/100g, 94.86mg/100g, 120.75mg/100g and decreased to 4.76%∼44.21%, 5.30%∼48.05%, 3.66%∼21.83% by oven dyring, vaccum drying, spray drying respectively, but freeze drying showed a little decrease of those components. In 70% ethanol extract, effectual components decreased to 76.05%∼88.38% and 26.86%∼78.76% by freeze drying and vacuum evaporation respectively. Antioxidant activity decreased by drying and decreasing rate in 70% ethanol extract was lower than water extract. Degree of browning increased as the drying temperature increased. Tannin and free sugars were little affected by drying temperature. Solubility decreased in oven drying and 70% ethanol extract. Overall data suggested that optimum drying methods of cinnamon extract were freeze drying in case of water extract and freeze drying and vaccum drying in case of 70% ethanol extract.

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Physicochemical Properties of Chaga (Inonotus obliquus) Mushroom Powder as Influenced by Drying Methods

  • Lee, Min-Ji;Seog, Eun-Ju;Lee, Jun-Ho
    • Preventive Nutrition and Food Science
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    • v.12 no.1
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    • pp.40-45
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    • 2007
  • The effects of drying methods on the physicochemical properties of chaga (Inonotus obliquus) mushroom powder were investigated. Scanning electron micrograph revealed that freeze drying produced smaller particle- sized samples which in turn resulted in higher porosity than did vacuum and hot-air drying. Samples prepared by freeze drying showed a significantly higher L*-value as compared with those prepared by hot-air drying and vacuum drying (p<0.05). The lightness (L*-value) significantly decreased with increasing relative humidity and storage temperature regardless of drying method (p<0.05). The yellowness (b*-value) increased significantly with increasing relative humidity (p<0.05). Browning index was significantly lower in samples prepared by freeze drying (p<0.05) but not significantly different between samples dried by hot-air and vacuum drying. Freeze dried sample exhibited a significantly higher degree of rehydration than other samples (p<0.05) probably due to the small particle size. Water solubility of the freeze dried sample was higher than those of the other methods while swelling ratio of the same sample appeared to be lower than those of others. Freeze dried chaga mushroom powder contained significantly lower amount of total phenolics and total sugar as compared to other samples (p<0.05).

Volatile Retention during Freeze Drying of Fruit Juices (과실쥬스의 동결건조 중 휘발성분 보유력)

  • 심기환;최진상;주옥수;강갑석
    • Journal of the Korean Society of Food Science and Nutrition
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    • v.19 no.6
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    • pp.555-564
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    • 1990
  • The headspace gas chromatographic(analytical) technique was used to evaluate the retention of volatiles in fruit juices during freeze drying as a function of freezing rate, the content of initial solid and chamber pressure. The effects of freezing rate and drying time on the volatile retention under the experimental conditions were marked, particulary at long freezing time. The retention of volatiles in the freeze dried was largely affected by the freezing rate. The highest volatile loss under the freeze drying conditions was observed during the first stage of drying. The behavior during freeze drying of the volatile substances was affected by high content of initial solid. The volatile retention was higher in quick freeze drying than slow freeze drying and low pressure than high.

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Effects of Drying Methods on Content of Active Components, Antioxidant Activity, and Color Values of Saururus chinensis Bail (건조방법에 따른 삼백초의 유효성분 함량, 항산화능 및 색도)

  • Kim, Min-Ja;Kim, In-Jae;Nam, Sang-Young;Lee, Cheol-Hee;Yun, Tae;Song, Beom-Heon
    • Korean Journal of Medicinal Crop Science
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    • v.14 no.1
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    • pp.8-13
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    • 2006
  • This study was carried out to investigate drying methods for keeping freshness and active components of aerial part of Saururus chinensis. Chopped samples were prepared using hot air drying, hot air drying + roasting, presteamed + hot air drying, freeze drying, and sun drying. Drying time was shorter $88{\sim}93%$ in hot air drying and freeze drying than in sun drying. Percentage of dry matter was higher in the order of freeze drying > sun drying > hot air drying, and moisture content in the order of sun drying > hot air drying > freeze drying. The contents of total phenolics and quercetin related substances were greater in the order of freeze drying > hot air drying > sun drying, while were decreased due to treatments before or after hot air drying. Electron donating ability (EDA) was highest in freeze drying, and showed a little difference between hot air drying and sun drying, but was increased because of treatments before or after hot air drying. In color values, the a value was lower in the order of freeze drying < hot air drying < sun drying. The contents of active components of plant parts of hot air dried were higher in the order of flower >leaf > chopped sample > stem. EDA showed similar tendency with those. The a value was lower in the order of leaf < chopped sample < flower < stem. As a result, freeze drying of chopped samples or hot air drying of leaf and flower were effective to maintain qualities of aerial part of Saururus chinensis.