Influence of Low-temperature Blanching Combined with High-pressure Shift Freezing on the Texture of Frozen Carrots

ABSTRACT: Freezing causes texture loss of tissue-based systems such as fruits and vegetables. To evaluate the potentials of high-pressure freezing for minimizing freezing damage, the effects of high-pressure shift freezing and regular freezing conditions on the texture of carrot cylinders were investigated. To improve the strength of the plant material by a pectin-based network, carrot cylinders were submitted to different pretreatment conditions before freezing. The reduced freezing time of high-pressure shift freezing compared with conventional freezing results in a limited positive effect on the hardness of non-pretreated carrots. A pronounced hardness improvement was obtained when calcium soaking followed by thermal (30 min at 60°C) or high-pressure (15 min at 60°C and 300 MPa) pretreatment was combined with high-pressure shift freezing. During subsequent frozen storage at -18°C, the increased hardness values of pretreated, high-pressure frozen carrots could not be maintained.     

速冻白芦笋在冻结物冷藏间脱水的研究

模拟冻结物冷藏间稳定温度场和周期波动的非稳定温度场,在其中对半解冻和未解冻的速冻白芦笋分别进行脱水实验。理论分析和实验结果证实,温度场的存在是造成冻藏局部小环境水分浓度不平衡而引发速冻白芦笋脱水危害的根本原因。     

Pecan Texture as Affected by Freezing Rates, Storage Temperature, and Thawing Rates

Pecan texture was measured by texture profile analysis (TPA) at 80% compression before and after being frozen at 6 controlled rates, to 3 minimum temperatures and thawed at 2 rates. Freezing and thawing rates had more influence than storage temperature on pecan texture. Certain TPA parameters (i.e., hardness, area 1, fracturability and slope of linear segment of force vs. deformation curve) were more affected than others by freezing and thawing rates. Freezing and thawing at high rates had the least effect on pecan texture.     

Frozen Carrots Texture and Pectic Compotients as Affected by Low-Temperature-Blanching and Quick Freezing

Carrots preheated for 2 hr at 60°C and then cooked became firmer than raw or cooked carrots. After preheating, the amount of high methoxyl pectin decreased, and low methoxyl pectin increased. Firmness of carrots decreased through freezing then thawing, but preheated carrots retained firmer texture than those blanched in boiling water. Quick-freezing resulted in better texture than slow-freezing. Loss in texture was accompanied by release of pectin. Slow-freezing accelerated release of pectin as compared to quick-freezing. Preheated carrots were slower in release of pectin. The degree of esterification of pectin substances in raw carrots decreased during preheating, freezing and thawing. Cell damage in quick frozen carrots was slight. Optimum preheating occurred with 30 min at 60°C or 5 min at 70°C. Preheating and then quick freezing were effective in improving texture of frozen carrots.     

Optimization of Low Temperature Blanching of Frozen Jalapeño Pepper (Capsicum annuum) using Response Surface Methodology

The effects of low-temperature long-time blanching of diced jalapeño pepper prior to freezing on extrusion force, color and pH of the product were evaluated and optimized by response surface methodology. The blanch temperature was the most important factor, while hold time had no significant effect on product quality. Maximum extrusion force and color parameter a*(green-red) correlated with temperature. The pH and the color parameters L*(brightness) and b*(blue-yellow) showed no significant variation with the experimental variables. The recommended blanch temperature of 55°C produced a firmness value of 779N and a color value of –10.55 of parameter a* in frozen jalapeño peppers.     

Texture and Rehydration of Dehydrated Carrots as Affected by Low Temperature Blanching

Whole carrots were blanched at four temperatures for five time periods, then blanched again for 6 min at 100°C. A control sample was blanched 8 min at 100°C. All samples were then dehydrated. Very slight differences in rehydration ratios between treatments were observed. The 50°C blanch gave a firmness equal to or less than the control for all blanch times. The carrots blanched at 55°C for 15, 30 and 45 min were less firm than the control while the 60 and 90 min blanched samples were firmer than the control. The 60 and 65°C blanched samples had significantly firmer texture than the control when blanch time was > 30 min. Blanching carrots for 45 min at 65°C increased firmness of the rehydrated product by 51% for uncooked and 27% for cooked.     

Gluconic Acid Influences Texture and Color of Canned Asparagus

The color and texture of canned asparagus spears were measured using a shear-press and a Gardner color difference meter. Canning spears with 1% gluconic acid reduced pH of asparagus tissue to = 4.1 within 24 hr. After 5 mo storage, the 1% acidified pasteurized spears were lighter, less green, and more yellow than nonacidified retorted spears. Acidification with a milder thermal process almost doubled firmness of the acidified spears.     

不冻液冻结乌鳢块冻藏过程中品质变化

为了研究不冻液冻结对乌鳢块冻藏过程中冰晶及品质的影响,采用不同冻结温度（－20、－30、－40 ℃）的不冻液和空气冻结乌鳢块,以冰晶大小、盐溶性蛋白含量、pH值、挥发性盐基氮（total volatile basic nitrogen,TVB-N）含量、硫代巴比妥酸（thiobarbituric acid,TBA）值和持水性等为指标,考察了乌鳢块冻藏（－18 ℃）过程中的品质变化。结果表明：采用－20、－30、－40 ℃不冻液冻结的乌鳢块通过最大冰晶生成带的时间分别为310、226 s和125 s,生成冰晶的面积分别为308.8、142.4 μm2和86.5 μm2,分别显著短于和小于空气冻结方式下乌鳢块通过最大冰晶生成带的时间（3 412 s）和生成冰晶的面积（939.6 μm2 ）（P＜0.05）。另外,在－18 ℃冻藏过程中,经不冻液冻结的乌鳢块的盐溶性蛋白含量均明显高于空气冻结组,而形成冰晶大小、pH值、TBA值、TVB-N含量、汁液流失率和蒸煮损失率均明显低于空气冻结组,其中－40 ℃不冻液冻结后的乌鳢块在冻藏过程中品质变化最小。综合以上结果,不冻液冻结比空气冻结能够更好地保持冻藏过程中乌鳢块的品质,且不冻液的冻结温度越低,冻结速率越高,形成冰晶越小,越有利于鱼肉品质的保持。     

不同贮藏方式对芦笋黄酮类物质含量的影响

采用普通冷藏、气调贮藏、化学试剂前处理后冷藏等几种方式保存绿芦笋,研究不同贮藏方式对芦笋中黄酮类物质含量的影响。结果表明,各贮藏方式黄酮含量整体均呈下降趋势,至28 d,各组黄酮含量保存率为35.4%～53.1%。100%O2气调包装和200μmol/L的CaCl2溶液浸泡2 h后冷藏可延缓整个贮藏过程中黄酮类物质含量的下降。     

速冻黄瓜、藕的烫漂处理

将新鲜黄瓜、藕通过几种不同的烫漂处理，速冻后冻藏1个月，期间定时对样品进行检测，以确认最佳烫漂处理方式。试验结果表明：黄瓜烫漂30S、藕烫漂35S时冻藏效果最好，可保持黄瓜和藕的色泽、风味、质地，以及VC等营养成分。     

豆薯软罐头质地变化及贮藏动力学研究

为考察豆薯罐头加工适应性、丰富豆薯产品种类,以豆薯为原料,探讨了热烫、杀菌、贮藏对其质构特性的影响。结果显示:热烫处理4 min后豆薯的硬度、凝聚性、咀嚼性、回复性、弹性分别为新鲜豆薯的63.2%、43.9%、17.7%、51.4%、69.8%;预煮和杀菌阶段豆薯质地变软,其硬度、凝聚性、咀嚼性、回复性、弹性分别为处理前的79.5%与74.64%、54.7%与105.33%、18.0%与98.73%、73.0%与105.18%、44.8%与98.19%;在常温或低温下贮藏180 d,豆薯的各项质构指标均较未处理豆薯有所下降。因此通过适当控制上述加工方式和采用低温贮藏可延缓豆薯罐头的软化;此外,将各质构参数进行贮藏动力学分析发现:一级动力学模型能很好的反映其质构变化。     

Freezing Rate and Frozen Storage Effects on Color and Sensory Characteristics of Pineapple Fruit Slices

This study was carried out to evaluate the influence of freezing process (cold room –18°C and air-blast freezer –50°C) and frozen storage (–18°C for 0 to 12 mo) on color and sensory quality of pineapple fruit slices (Smooth Cayenne and Red Spanish cultivars). L, –a and +b color parameters showed differences (P ≦ 0.05) with cultivar, but not with freezing rate. No differences (P ≥ 0.05) were found in sensory analysis (color and appearance) between the cultivars, frozen at different rates, compared to fresh product, or after 1 yr frozen storage. The two cultivars are suitable for freezing.     

Frozen Mushrooms Quality as Affected by Strain, Flush, Treatment Before Freezing, and Time of Storage

ABSTRACT: Four strains of mushrooms ( Agaricus bisporus )—U3, hybrids of U3 (3/1, M-300), and in-between strain No. 200—were treated before freezing: washed in water, washed in water containing sodium metabisulfite (3g·L^-1), and washed in water containing sodium metabisulfite (5g·L^-1) then immersed in boiling water for 20 s. Appearance and whiteness of frozen mushrooms were most affected by the washing in water containing sodium metabisulfite. The residue of sulfur dioxide changed from 52 mg·kg^-1 after 1 d to 27 mg·kg^-1 after 90 d of storage. The whitest mushrooms (fresh and frozen) were for No. 200 strain. Short-time immersion in boiling water markedly increased toughness of stored frozen mushrooms.     

液体浸渍冷冻对鲟鱼贮藏过程中品质的影响

研究新兴低温冻结技术液体浸渍冷冻对鲟鱼贮藏期品质的影响,分析比较液体浸渍冷冻和传统空气冷冻处理后的鲟鱼在贮藏期的品质变化,并对多个指标进行了检测分析。结果表明,液体浸渍冷冻处理的鲟鱼冷冻速率是传统空气冷冻的12.47倍,经过液体浸渍冷冻的鲟鱼其肌纤维受到的破坏较空气冷冻小,贮藏过程中鲟鱼的回复性与L*值均较空气冷冻高(P0.05),二者挥发性盐基氮值和过氧化值的变化趋势也具有显著性差异(P0.05)。因此,液体浸渍冷冻能够更好地保持鲟鱼原有的品质,可在鲟鱼贮藏保鲜过程中加以利用。     

Effect of Freezing and Frozen Storage on Chemical and Microbiological Characteristics in Sheep Milk Cheese

ABSTRACT: Most chemical components and water activity of an the Los Pedroches' brand ewes' milk cheese were not altered by frozen storage. Lactic acid concentration and pH were significantly different (p < 0.05) in control cheeses and those kept in frozen storage for 3 and 6 months from those stored for 9 months. Proteolysis continued slowly during frozen storage, with significantly higher rates of non protein nitrogen and amino acid nitrogen (p < 0.05) present at the end of the storage period. Counts of microorganisms, except for enterococci, tended to decrease during frozen storage. Freezing rates did not affect the chemical and microbiological characteristics studied.     

Textural and Ultrastructural Changes in Carrot Tissue as Affected by Blanching and Freezing

ABSTRACT: The impact of blanching and freezing conditions on firmness retention and ultrastructural changes in the cell wall and middle lamella of carrot tissues were studied. Freezing caused extensive degradation of cell wall pectins as evident from the rapid loss in tissue firmness. High-temperature short-time blanching (100°C, 0.58 min.; 90°C, 2.12 min.) retained firmer texture than low temperature long time blanching (80°C, 11.64 min.; 70°C, 71.1 min.). Freezing at rapid rates of -4.5°C/min and -2.4°C/min showed less softening than slow rates of -0.19°C/min and -0.05°C/min. Softening was further enhanced in blanched-frozen carrots. Severe structural damage due to growing ice crystals and substantial loss of pectic material were seen at slower freezing rates.     

浸渍冻结对凡纳滨对虾冻藏过程中肌肉组织的影响

本文以肌纤维轮廓、细胞间隙、肌丝、肌节以及肌纤维间隙等为指标,研究浸渍冻结和静止空气冻结对凡纳滨对虾冻藏过程中肌肉组织结构的影响。结果发现,浸渍冻结对虾的肌纤维排列更加致密,形成的冰晶间隙更加细小,分布均匀,肌原纤维直径变短的程度比静止空气冻结的小;而静止空气冻结的肌纤维排列疏松,形成的冰晶间隙宽大。随着贮藏时间的增加,浸渍冻结对虾的冰晶逐渐增大,间隙逐渐变大,细胞核也逐渐分解变少。冻藏90 d后,静止空气冻结对虾中很难发现细胞核的存在,肌丝结构大部分消失,明暗带难分辨,肌节长度变短程度严重,肌节消失,且没有完整结构的线粒体。但是浸渍冻结对虾中肌丝结构及明暗带依然存在,肌节长度变短程度比静止空气冻结的小,部分线粒体结构完整。结果表明,浸渍冻结更有利于对虾的肌肉结构的保持,能更好地保持对虾的品质。     

烫漂工艺对白对虾品质的影响

研究了白对虾烫漂预处理中的品质变化。采用NaCl溶液对白对虾进行烫漂,探讨在100℃条件下,烫漂溶液浓度和烫漂时间对白对虾失重率、色泽、质构和烫漂残液的影响。试验表明:2%NaCl、烫漂1 min为合理参数,在此条件下,白对虾失重率达10.34%,烫漂液浊度94NTU,每克白对虾流失蛋白质<0.1g,硬度和弹性分别为1 813g、0.842g,彩度为28.07,模糊综合评价等级为优,失重率高,营养损失少,色泽、组织状态均较理想。     

冻结及冻藏温度对小龙虾冻藏过程中脂质氧化的影响

本研究将小龙虾热烫后置于真空包装盒内,灌水并抽真空,分别于3 种冻结温度（－20、－40 ℃和－55 ℃）的冰柜内冻结至中心温度为－15 ℃,再于2 种冻藏温度（－20 ℃和－40 ℃）的冰柜中冻藏24 周,测定不同温度冻结和冻藏小龙虾肉的脂肪质量分数、游离脂肪酸（free fatty acids,FFAs）含量以及脂肪酸组成、过氧化值（peroxide value,POV）和硫代巴比妥酸反应物（thiobarbituric acid reactive substances,TBARS）值,探讨冻结及冻藏温度对小龙虾脂质氧化的影响。结果表明：随着冻藏时间的延长,6 组小龙虾的脂肪质量分数、不饱和脂肪酸（unsaturated fatty acids,UFAs）和多不饱和脂肪酸（polyunsaturated fatty acids,PUFAs）相对含量显著下降（P＜0.05）,FFAs含量和饱和脂肪酸（saturated fatty acids,SFAs）相对含量、POV、TBARS值总体显著上升（P＜0.05）。冻藏温度相同时,－20 ℃冻结的小龙虾肉的POV、TBARS值高于－40 ℃和－55 ℃,而FFAs含量和脂肪酸组成无明显差异;冻结温度相同时,－20 ℃冻藏小龙虾肉脂肪和FFAs含量、POV、TBARS值均明显高于－40 ℃冻藏组,UFAs和PUFAs含量低于－40 ℃冻藏组,SFAs含量高于－40 ℃冻藏组。结论：冻结温度－40、－55 ℃和冻藏温度－40 ℃均减轻了小龙虾肉脂质的水解和氧化程度。     

芦笋保鲜技术研究及脂氧合酶抑制剂的保鲜应用初探

在冷藏加湿的基础上,通过对于芦笋贮藏过程中的失重率、叶绿素的含量,以及芦笋的木质化、散尖程度等感官指标的测定,比较了不同的处理方式对于芦笋的保鲜效果。在保持环境气体组成O210%、5%CO2的基础上,采用脱除乙烯和脂氧合酶抑制剂处理,可以有效保持芦笋的品质,延长货架期。