超声波对不同孔隙率水果冻结特性的影响

为研究超声波对不同孔隙率水果冻结特性的影响,以苹果、梨、哈密瓜为对象,在相同超声频率下,用不同强度超声波辅助浸渍冷冻,用温度记录仪测定冻结时间,分析冻结过程中的温度变化,并对冻融后样品进行滴水损失率、质构、色泽、水分分布以及抗坏血酸含量测定。结果表明：苹果、梨、哈密瓜在0.145 W/cm2的超声强度下浸渍冷冻相变阶段时间分别为21.67、21.33、16.67 s,样品较直接浸渍冷冻处理相变时间显著缩短（P＜0.05）。经不同强度超声辅助浸渍冷冻后的3 种水果与直接浸渍冷冻组相比,滴水损失率均下降,其中苹果因孔隙率小,下降显著（P＜0.05）,3 种水果硬度均提高,但与鲜样相比,抗坏血酸含量显著下降（P＜0.05）。相比未超声处理的样品,对孔隙率小的水果进行超声处理更有利于保持产品的品质。     

Evaluation of the effects of different thawing methods on texture,colour and ascorbic acid retention of frozen hami melon (Cucumis melo var. saccharinus)

The effects of different thawing methods (room temperature thawing, running water thawing, microwave thawing at 300 W, 500 W, 700 W and high‐pressure thawing at 100 MPa, 150 MPa, 200 MPa) on quality (drip loss, texture, colour, ascorbic acid contents and sensory quality) of frozen hami melon were investigated. The results showed that different thawing treatments affected the quality of hami melon significantly (P < 0.05). Samples thawed by microwave at 500 W best preserved ascorbic acid for nearly half of fresh hami melon. Less drip loss, texture damage and discolouring were observed for the samples thawed by microwave at 700 W than other thawed samples; however, serious ascorbic acid loss was detected. High‐pressure‐thawed samples exhibited shorter thawing time but severe quality losses. The results suggested that microwave thawing at 500 W was an appropriate method to thaw frozen hami melon with the highest sensory score (6.7).     

不同解冻技术对冷冻香菇(L.edodes)品质的影响

本文研究常温空气、冷藏、微波(119、259和280 W)以及超高压(100、150和200 MPa)解冻对香菇品质(色泽、汁液流失率、硬度、离子渗透率以及总酚含量)和解冻时间的影响。结果表明:与常温空气和冷藏解冻相比,微波和超高压解冻能够显著缩短香菇的解冻时间,并且随着微波功率和压强的增大,解冻时间逐渐缩短。但超高压解冻后香菇色泽与硬度显著下降,离子渗透率显著上升,从而使得香菇品质显著降低;而微波解冻在色泽(总色差降低19.9~44.1%)、硬度(升高18.9~38.0%)、汁液流失率(降低45.7~42.0%)、总酚含量(升高21.1~25.2%)和其他生理指标方面都优于常温空气解冻技术。其中,259 W的微波功率是香菇解冻的最优条件,同时该条件的感官评价分值最高(7.1)。本文表明微波解冻能够显著提高香菇的解冻速率和品质,这对香菇加工具有一定意义。     

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.     

超声波对毛豆浸渍冷冻过程的影响

研究超声波功率、超声波作用时间、超声波脉冲值对提高毛豆仁浸渍冷冻速率的影响.通过响应面分析可知在载冷剂温度为-20℃下超声波辅助浸渍冷冻的最佳工艺参数:超声波功率为58 W,超声波作用模式为50%,超声波作用时间为0.7 min,解冻后毛豆仁质构(硬度)和持水力分别为6.05 kg/cm~2和92%.     

Dehydrofreezing of pineapple

Dehydrofreezing technique involves one step of partial dehydration before freezing, in order to diminish the tissue damage by removing part of water from vegetable tissue prior to freezing. The objective of the present study was to evaluate the effect of osmotic dehydration and hot air-drying, applied previous to the freezing process, on the end quality of pineapple slices. Quality loss was quantified through drip loss, ascorbic acid content and mechanical properties changes of tissue. Freezing was carried out in a conventional air-blast tunnel at −31.5 ± 2 °C. Mechanical properties of fresh and dehydrated fruit, with and without the later process of freezing, were evaluated through compression tests. Ascorbic acid content was quantified by liquid chromatography. Osmotic dehydration and hot air-drying have the beneficial effect of reducing the time necessary for pineapple samples freezing. The freezing–thawing process affects the values of pineapple samples mechanical properties. Ascorbic acid losses were somewhat greater during the osmotic dehydration than with air dehydration.     

Minimizing texture loss of frozen strawberries: effect of infusion with pectinmethylesterase and calcium combined with different freezing conditions and effect of subsequent storage/thawing conditions

Vacuum infusion (VI), freezing, frozen storage and thawing conditions were optimized in order to minimize the texture loss of frozen strawberries. Slow freezing caused severe loss in textural quality of the strawberries. This quality loss could not be prevented by the application of VI prior to slow freezing, or by the application of rapid, cryogenic or high-pressure shift freezing conditions on non-infused fruits. A remarkable texture improvement was noticed when infusion of pectinmethylesterase (PME) and calcium was combined with rapid or cryogenic freezing. The highly beneficial effect of PME/Ca-infusion followed by HPSF on the hardness retention of frozen strawberries was ascribed to the combined effect of the infused PME (53% reduction in degree of esterification (DE) of the strawberry pectin) and the high degree of supercooling during HPSF. During frozen storage, textural quality of PME/Ca-infused high-pressure frozen strawberries was maintained at temperatures below −8 °C, whereas the texture of PME/Ca-infused strawberries frozen under cryogenic freezing conditions was only preserved at temperatures below −18 °C. Thawing at room temperature seemed to be an appropriate method to thaw strawberries. Fast thawing by high-pressure induced thawing (HPIT) did not prevent textural quality loss of frozenstrawberries.     

复合护色剂预处理及不同冻融条件对冷冻双孢蘑菇品质的影响

本实验针对冷冻双孢蘑菇在冻融过程中的品质劣变问题,研究了柠檬酸、L-半胱氨酸、抗坏血酸、异抗坏血酸钠等护色剂对双孢蘑菇褐变的影响,进一步分析了不同冷冻温度（－80、－40、－20 ℃）和解冻温度（25、4 ℃）对双孢蘑菇的汁液流失率、质构特征、微观结构、水分含量与分布及过氧化物酶活力等指标的影响。结果表明,复合护色剂配比为3.0 g/L异抗坏血酸钠、1.5 g/L L-半胱氨酸、0.4 g/L抗坏血酸、10 g/L柠檬酸时具有最佳护色效果;－80 ℃冷冻、4 ℃解冻的冻融条件下,双孢蘑菇汁液流失率为1.98%,显著低于其他各处理组;水分含量、质构特征值均高于其他冻融条件处理的双孢蘑菇;因此,－80 ℃冷冻、4 ℃解冻的冻融条件是较合理的冻融处理方式。本研究为冷冻双孢蘑菇产品的开发及冻融技术提供了参考。     

Effect of high-pressure versus conventional thawing on color, drip loss and texture of Atlantic salmon frozen by different methods

Atlantic salmon (Salmo salar) samples were frozen by conventional air freezing, plate freezing and liquid nitrogen (LN) freezing, and subjected to different thawing treatments: water immersion thawing (WIT) (4°C and 20°C) and high-pressure thawing (HPT) at 100, 150 and 200 MPa with water (containing 2 g oil/100 g) as pressure medium at 20°C. Temperature and phase change behavior of fish samples were monitored during freezing and thawing. The phase change point of frozen salmon was lowered to −14°C, −19°C and −25°C for the HPT processes at 100, 150 and 200 MPa, respectively. These phase change temperatures were lower than for pure ice at the same pressures possibly due to the presence of solutes in salmon. The HPT times were 22.6±1.4, 18.1±1.4 and 17.0±1.3 min at 100, 150 and 200 MPa, respectively, as compared with 26.6±2.1 and 94.3±3.4 min for the WIT process at 20°C and 4°C, respectively. Employing pressures above 150 MPa caused noticeable color changes in salmon during the HPT process and the product texture was significantly modified during HPT at 200 MPa. Different freezing rates prior to thawing resulted in differences in drip loss in salmon samples, but they did not induce specific color and texture changes. A significant (P<0.05) reduction of drip loss by the HPT process was observed only for the LN frozen samples in which mechanical cracking occurred and much of the drip appeared after WIT process. Drip loss formed during pressure thawing seems to be a complicated process, for which further studies are needed.     

EFFECT OF THAWING METHODS ON TEXTURAL QUALITY OF SOUS-VIDE STEWED BEEF ASSESSED BY SENSORY AND INSTRUMENTAL ANALYSES

This study compared four different thawing methods using sensory test with magnitude estimation, preference test with hedonic scale and physical analyses. The four methods were tap‐water, refrigeration, microwave reheating, and boiling‐water reheating. For physical analyses, there were differences (p≤0.001) among treatments in drip loss and expressible juice. For drip loss, the microwave reheated samples were the highest and the refrigeration and tap‐water treated samples were the lowest. For expressible juice, tap‐water and refrigerated samples were higher (p≤0.01) than the microwave and boiling‐water reheated samples. Microwave and boiling‐water reheated samples had higher hardness and cheviness and lower juiciness and fiber‐looseness. The refrigerated and tap‐water thawed samples had reverse sensory properties. Naive panelists preferred the refrigerated and tap‐water treated samples to the microwave and boiling‐water reheated samples for juiciness, tenderness, and overall preference. Physical parameters from textural profile analysis were not different among the thawing methods. Expressible juice was the best indicator for sensory hardness, juiciness, fiber‐looseness and chewiness among the physical parameters. Usually a quadratic regression model fit best when expressible juice was used to predict sensory textural properties.     

不同解冻方法对速冻桑葚汁液流失率、理化品质及抗氧化活性的影响

为减少速冻桑葚在解冻过程中的汁液流失率、缩短解冻时间和减少其色泽的变化,增加解冻桑葚的营养物质和抗氧化活性的保留量,采用微波功率500 W解冻、微波功率550 W解冻、超声波解冻、冷藏解冻、室温解冻进行速冻桑葚的解冻实验。结果表明:微波功率500 W解冻和微波功率550 W解冻的解冻时间较短,分别为0.58 min和0.35 min,冷藏解冻的解冻时间最长为305 min。不同解冻方法的汁液流失率存在显著差异,微波功率500 W解冻的汁液流失率最低,为1.34%;超声波解冻的汁液流失率最高,为9.24%。微波功率500 W解冻桑葚的总酚含量(151.66 mg/100 g)、花色苷含量(矢车菊素-3-O-葡萄糖苷2.27 mg/g、矢车菊素-3-O-芸香糖苷0.69 mg/g、天竺葵素-3-葡萄糖苷0.047 mg/g)及抗氧化活性((2,2’-联氨-(3-乙基苯并噻唑啉-6-磺酸)二氨盐)自由基清除能力21.87μmol Trolox/g、1,1-二苯基-2-三硝基苯肼自由基清除能力35.70μmol Trolox/g、铁离子还原能力27.85μmol Trolox/g)均显著高于其他4种解冻方法。综合考虑,微波功率500 W解冻优于其他4种解冻方法。     

Freezing and thawing rate effects on drip loss from samples of pork

The effects of six freezing rates, two storage times and three thawing rates on the drip loss from small samples (approximately 6 g) of pork were studied. Drip was collected by centrifugal extraction. Protein denaturation of the meat sample was analysed by differential scanning calorimetry. At fast freezing rates, drip losses obtained were not significantly different from that of fresh samples. At the slower freezing rates studied, drip losses were greater than that from fresh samples. After four weeks storage, drip losses were significantly greater at the slow freezing rates compared to the samples without storage. However, for the stored samples, there were no differences in drip losses with respect to the initial freezing rates. Furthermore, the drip losses from stored samples were not significantly different from drip losses of samples at the slow freezing rates without storage. No differences in denaturation profiles of the meat samples, composition of drip or total protein concentrations in the drip samples were observed.     

低压静电场辅助冷冻对竹笋品质的影响

为研究低压静电场辅助冷冻对竹笋冻结特性的影响,以冻结曲线、硬度、水分损失率、水分迁移、冰晶形态和组织微观结构为指标,探究低压静电场辅助冷冻（－35 ℃）和普通冷冻（－35 ℃）条件下竹笋品质的变化规律。结果表明：低压静电场辅助冷冻提高了冻结效率,改变了冰晶形态及分布,减轻了组织微观结构破损程度,改善了解冻汁液流失情况。与静电板间距10、20、30、40 cm处的冷冻竹笋解冻后水分损失率分别为14.16%、12.58%、9.73%、10.44%,显著低于对照组（21.01%）（P＜0.05）,硬度分别为461.19、507.48、496.65 g和455.31 g,显著高于对照组（350.70 g）（P＜0.05）。低场核磁共振分析结果表明,在低压静电场辅助冷冻下竹笋解冻后汁液流失减少,扫描电子显微镜观察结果显示,竹笋纤维排列整齐,组织微观结构保持较好。低压静电场辅助冷冻可有效改善竹笋品质,可为利用低压静电场进行果蔬的冷冻贮藏和冷链运输提供参考。     

Effect of Cultivar and Ripening Stage on Quality and Microstructure of Frozen Mangoes (Mangifera indica Linn.)

The aim of this work was to investigate the quality and microstructure of different frozen mango cultivars. Since freezing can cause severe textural damage to fruit, the proper selection of a ripening stage and cultivar can reduce such damage. Two mango cultivars (Nam Dok Mai and Chok Anan) were allowed to ripen for four ripening stages. During ripening, titratable acidity, alcohol-insoluble residues, and firmness significantly decreased while total soluble solids, total pectin, and water-soluble pectin levels increased. Mangoes from the three final ripening stages were frozen until the temperature of the samples reached –25°C. After thawing, the partially ripe mango samples exhibited the highest firmness, lowest drip loss, lowest water-soluble pectin, and the highest sensory firmness scores. The microstructure found using light microscopy and transmission electron microscopy showed that all frozen-thawed mangoes exhibited a swelling and folding of the cell wall due to freezing damage. The cell walls of fully ripe mangoes were dramatically damaged, which explained the low firmness values. Tissue and cell wall damage in Nam Dok Mai were the greatest, which contributed to the large drip loss. The cheaper Chok Anan cultivar was more resistant to freezing damage than Nam Dok Mai.     

Effects of freezing and thawing processes on the quality of Atlantic salmon (Salmo salar) fillets

ABSTRACT:  High-pressure processing is finding a growing interest in the food industry. Among the advantages of this emerging process is the ability to favorably freeze and thaw food. This study aims at comparing the effect of different freezing and thawing processes on the quality of Atlantic salmon fillets. Atlantic salmon ( Salmo salar ) samples were frozen by Pressure-Shift Freezing (PSF, 200 MPa, −18 °C) and Air-Blast Freezing (ABF, −30 °C, 4 m/s). Samples were stored 1 mo at −20 °C and then subjected to different thawing treatments: Air-Blast Thawing (ABT, 4 °C, 4 m/s), Immersion Thawing (IMT, 20 °C), and Pressure-Assisted Thawing (PAT, 200 MPa, 20 °C). Changes in texture, color, and drip loss were investigated. The toughness of the PSF samples was higher than that of the ABF sample. The modification of color was more important during high-pressure process than during the conventional process. The PSF process reduced thawing drip compared with ABF. The presence of small ice crystals in the pressure-shift frozen sample is probably the major reason leading to the reduced drip volumes. The freezing process was generally much more influent on quality parameters than the thawing process. These results show the interaction between freezing and thawing processes on selected quality parameters.     

Physicochemical properties of thawed chicken breast as affected by microwave power levels

The main objective of this study was to determine the effect of microwave thawing at different power levels on the physicochemical properties of chicken breast. Each frozen chicken breast samples were thawed in microwave oven at microwave power levels of 125, 250, and 375W. To compare the effect of microwave thawing on meat quality, refrigerator thawing was used as a control. As the microwave power level increased, the thawing rate increased and temperature differences between the edge position and center position of the samples also increased. Treatment at a power level of 250 W resulted in a lower thawing loss and a higher moisture content, water holding capacity, and tenderness than the other treatments (p<0.05). However, there were no significantly differences of proximate composition excluding moisture content, pH, lightness, and yellowness. The use of excessive input energy during microwave thawing (higher microwave power level) damaged the physicochemical properties of the thawed chicken breast; therefore, the microwave power level of 250 W is the best thawing method on the frozen chicken breast to minimize the changes in meat quality in this study.     

不同预处理方式对速冻草莓品质的影响

确定了速冻草莓的最佳冻结时间,并研究了用不同预处理方式处理速冻草莓在冻藏期间的VC含量、pH值的变化,硬度与汁液流失率.速冻预处理溶液采用蔗糖和氯化钙溶液,通过改变浸蘸溶液的浓度和浸蘸时间来改变处理方式.经实验最终确定,最佳速冻时间为5 h,速冻草莓冻藏期间的VC含量逐渐降低,pH值呈上升趋势,经20%糖液处理的草莓色泽较好,用CaCl2溶液预处理草莓的方式可明显提高草莓硬度,减少其汁液流失率.     

Use of pectinmethylesterase and calcium in osmotic dehydration and osmodehydrofreezing of strawberries

Strawberry samples of two varieties (Camarosa and Elsanta) were dehydrated using different osmotic solutions (60% glucose, fructose, sucrose and raftilose) and subsequently frozen by rapid and high-pressure shift freezing (HPSF). The effect of pectinmethylesterase (PME) and calcium (Ca⁺⁺) added to the osmotic solutions on several compositional parameters and the textural/structural quality of dehydrated and osmodehydrofrozen-then-thawed samples was studied. Due to the presence of PME and Ca⁺⁺ in the osmotic solutions, weight reduction upon dehydration was slightly decreased, which was correlated to a small positive effect on the net uptake of sugars and depression of the initial freezing point. Except for the Camarosa samples treated with sucrose, PME and Ca⁺⁺ in osmotic sugar solutions positively affected the relative hardness of dehydrated fruits, which was ascribed to the effect of PME and Ca⁺⁺ on the cell wall strength of the tissue. No cell wall damage and tissue particle alterations were observed upon dehydration. The effect of osmotic dehydration (OD) using different sugar solutions without PME and Ca⁺⁺ on the texture and structure of frozen-then-thawed samples was limited and sometimes negative. The added PME and Ca⁺⁺ however positively influenced the volume and shape of the thawed samples, which could be related to slightly higher relative hardness values and, for the Elsanta strawberry fruits, also to the reduced (up to 81%) drip loss upon thawing. Upon freezing the dehydrated fruits, no cell wall disruption was observed. Tissue distortion caused by freezing and indicated by a decrease in particle size, convexity and roundness, was compensated by the use of PME and Ca⁺⁺ during OD.     

A preliminary investigation of the effects of frozen storage on samples of pork

The effects of combinations of freezing, thawing and frozen storage on the drip loss and ultrastructure of small samples (approximately 6 g) of pork were studied. Samples were stored for up to 12 weeks at -20°C or for up to 4 weeks at temperatures fluctuating between -10 and -3°C. Drip was collected by centrifugal extraction. Cryo-scanning electron microscopy was used to study the ultrastructure of the meat. Sizes of cavities created after sublimation of the ice crystals were quantitatively analysed using an image analysis software package. Freezing rate by storage time interactions were observed in drip loss analyses. No differences were observed in the drip protein concentration or electrophoretic patterns. Ultrastructural differences were only observed after thawing samples stored at the higher temperatures. The effects being investigated were subtle.     

Effect of steaming,freezing, and re-steaming on the texture properties of non-glutinous rice cakes

The effects of steaming time (6, 8, and 10 min), freezing storage period, and re-steaming for thawing on the textural properties of non-glutinous rice cakes (baekseolgi) were investigated. As the steaming time increased, the rice cakes softened. In particular, the sample that was steamed for 10 min showed lower hardness than those steamed for shorter periods. A short period of steaming was insufficient for water bound to the surface of the starch granules to penetrate the granules in the dough. During the re-steaming process of the frozen non-glutinous rice cake samples, the retrogradation of starch and water syneresis contributed to the increased hardness of non-glutinous rice cakes.