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.     

Texture of Pecans Measured by Sensory and Instrumental Means

The texture of pecans (Carya illinoensis) from four cuhivars (Barton, Mahan, Western and Wichita) was analyzed using sensory and instrumental methods. Sensory hardness, flexibility and crispness were rated by trained panelists. Ranking of hardness and crispness was also carried out. A Texture Analyser TAXT2 was used for 50% compression, texture profile analysis (TPA), puncture and bending. Puncture and 50% compression gave best reproducibility, least variability and agreement with sensory data. The most relevant TPA parameters were cohesiveness, elasticity and fracturabihty. Parameters from the bending test did not indicate texture of the pecans suitably.     

Blanching, Freezing and Frozen Storage Influence Texture of White Asparagus

We studied effects of three methods of blanching in conjunction with freezing, on texture of white asparagus as defined by three measures: maximum shear force, cutting energy, and total fiber content. We also assessed shelf life of asparagus kept in frozen storage at -22°C. Methods of blanching were total immersion in hot water, progressive immersion in hot water and steam. An increase in total fiber content was found throughout frozen storage. This increase correlated with lignification of vascular bundles in the basal segment of spears, even during frozen storage. This was reflected in an increase in maximum shear force and cutting energy required. The shelf life of frozen asparagus was 12 mo using total fiber content as a criterion.     

葡萄贮藏期间果肉质地参数变化规律的TPA表征

采用3种常用保鲜膜对巨峰葡萄进行气调包装,放于-0.3℃的冰温保鲜库中贮藏,分别在0、5、10、15、20、25、30 d利用质构仪质地多面分析(TPA)法测定葡萄果肉,得到葡萄贮藏期间果肉质地参数变化规律.结果表明:TPA测试反映了3种保鲜膜内的葡萄果内各项质地参数变化规律总体均呈现下降趋势;果肉硬度与黏着性、咀嚼性呈较好的正相关性,而与凝聚性呈负相关;果肉咀嚼性与硬度、黏着性、弹性呈较好的正相关性;果内弹性与凝聚性、咀嚼性、回复性呈较好的正相关性,而回复性与弹性、凝聚性以外的质地参数相关性较差;葡萄好果率与贮藏时间在一定范围内呈良好线性关系,提出一个经验公式将好果率与果肉硬度进行关联.     

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.     

Changes in Temperature, Texture, and Structure of Konnyaku (Konjac Glucomannan Gel) During High-pressure-freezing

To determine the effects of high-pressure-freezing, changes in temperature, texture, and structure of konnyaku (a gel with high water content) were measured during freezing for 60 min at 0.1 to 700 MPa and -20 °C. During freezing at 0.1, 100, 500, 600, and 700 MPa, exothermic peaks were detected (konnyaku froze). However, at 200 to 400 MPa, exothermic peak was not detected and temperature rose when pressure was released at -20 °C; the supercooled konnyaku froze by pressure-shift-freezing. The coarse gel network observed in unfrozen konnyaku was compressed by freezing due to formation of ice crystals. The rupture stress increased and strain decreased in all frozen konnyaku. High-pressure-freezing was ineffective in improving the texture of frozen-then-thawed konnyaku.     

Effect of Freezing Rate and Microwave Thawing on Texture and Microstructural Properties of Potato (Solanum tuberosum)

Food freezing is a preservation process that works by lowering temperature while simultaneously decreasing water activity. It is accepted that although freezing preserves foods, it generally has a negative effect on textural quality. This research investigated the texture response of potatoes (Solanum tuberosum) as a function of time to freeze (defined as the time for the center temperature to reach ?20 °C) and thawing process. Potatoes slices (6 mm) were blanched then frozen in an ethanol/carbon dioxide bath, a pilot scale high velocity air freezer (HVAF) and a still air freezer to achieve various times to freeze. Slices were stabilized at –20 °C and thawed by 2 methods; room temperature air and microwave. Afterwards, samples were allowed to come to room temperature prior to texture profile analysis (TPA). Results indicate a maximum texture loss of the potato was reached at a time to freeze of approximately 8 min (corresponding to the HVAF). The texture difference between room temperature and microwave thawing methods was not shown to be significant (P = 0.05). SEM images showed the cellular structure of the potato in a HVAF to be similar to that of the still air freezer, validating that the matrix was maximally damaged in both conditions. This work created a continuous quality loss model for the potato as a function of time to freeze and showed no textural benefit to high velocity over still air freezing.     

Physicochemical Properties of Pacific Whiting Surimi as Affected by Various Freezing and Storage Conditions

ABSTRACT: Effects of various freezing methods of surimi on the biochemical and physical properties, were examined. Stress values increased up to 3 mo and then decreased. Strain values significantly decreased over time, except freeze-dried surimi stored at -18 °C. Yellowness (b*) of the freeze-dried surimi stored at 22 °C increased significantly during storage. In addition, salt-extractable proteins (SEP) decreased while dimethylamine (DMA) increased. Freeze-dried surimi showed the highest SEP and the lowest DMA values after 9 mo storage. Electrophoretic patterns did not show any apparent damages to the MHC until 6 mo. At 6 and 9 mo, development of proteins with smaller molecular weights was observed, indicating proteolytic degradation during frozen storage.     

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.     

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.     

反复冻融对泰州芋头淀粉品质特性的影响

本文以泰州地区三种芋头为原料,采用氨水提取芋头淀粉,研究-18 ℃冷冻24 h,25 ℃解冻1 h(反复冻融0、5、10次)对其体系性质、微观结构的影响,探讨冻融过程中淀粉品质的变化规律。结果表明,三种芋头淀粉颗粒表面形态的破坏程度随着冻融次数的增加而增大;冻融次数越多,其稳定性越差,三种品种相比,冻融稳定效果:靖江香沙芋 > 泰兴香荷芋 > 兴化龙香芋。冻融处理使淀粉凝胶硬度、弹性、咀嚼性增加,最后趋于稳定,黏性随冻融次数的增加呈递减趋势。随着样品冻融次数的增加,兴化龙香芋的起始糊化温度、峰值糊化温度、终点糊化温度比同等条件下的泰兴香荷芋、靖江香沙芋高。三种芋头淀粉的膨润力随着温度的升高而逐渐增大,随着冻融次数的增加,每种芋头淀粉的膨润力和凝沉性呈现下降的趋势。因此,随着冻融次数的增加,芋头淀粉品质下降。     

Mushroom Texture, Cell Wall Composition, Color, and Ultrastructure as Affected by pH and Temperature

Pasteurized mushrooms had firmer texture and lighter color compared with those that were retorted. Addition of acid and retorting temperature resulted in extensive softening of mushrooms and solubilization of proteins and polysaccharides that diffused into brine. Total chitin was not affected by applied treatments and did not appear to be related to texture alteration of processed mushrooms. Extensive solubilization caused by acidification and retortion resulted in reduction of cell diameter and enlarged intercellular space within the cap tissue. Mild acidification of sterilized samples reduced discoloration compared with the control, but further acidification resulted in considerable darkening. In contrast, tissue and color of pasteurized mushrooms seemed to be unaffected.     

Pecan Kernel Breakage and Oil Extracted by Supercritical CO2 as Affected by Moisture Content

During supercritical CO₂ extraction of oil from pecans, kernel breakage frequently occurs when the depressurization time is short. The purpose of this study was to investigate the effects of initial moisture content of pecan kernels and moisture equilibration time on pecan breakage and oil recovery when extracting with supercritical CO₂. Initial pecan moisture content, adjusted to 3.5% to 11.0%, had a significant effect on breakage when using a short depressurization time. With higher pecan moisture, less kernel breakage occurred. Increasing moisture equilibration time from 1 to 48 h reduced kernel breakage and produced an average of 30% more oil during extraction. Moisture content did not significantly affect the amount of oil extracted.     

猕猴桃冷冻破壁离心取汁工艺

根据缓慢冻结破坏细胞壁的原理,采用冻融离心取汁新工艺制取猕猴桃果汁,对冷冻破壁和离心工艺参数进行单因素和正交试验分析。结果表明：冷冻破壁离心取汁工艺所制备的果汁在出汁率、VC 含量、透光率及色泽方面都明显优于传统榨汁工艺,最佳工艺条件为切片厚度0.6cm、－ 14℃冷冻10h、30℃解冻30min、3000r/min 离心20min、100 目过滤。     

反复冻融法辅助提取油菜花粉多糖的研究

通过对加水量、冻结时间、解冻温度、冻融次数等进行单因素试验及正交试验,验证反复冻融法对油菜花粉中多糖的辅助提取效果,确定最佳处理条件为:加水量40 mL/100 g,冻结时间4 h,解冻温度80℃,冻融次数2次,在此条件下,油菜花粉可溶性多糖溶出率可达到21.79%。     

速冻肉馅在冻融过程中细菌动态变化研究

为了确定速冻饺子在冻融过程中影响其品质变化的关键因素,本实验按一定的工艺进行速冻肉馅加工,于-18℃冻藏,在冻融条件下研究速冻肉馅冻融过程中的细菌的动态变化。结果表明,乳酸菌、肠杆菌和假单孢菌均能在冻融条件下很好的生长,乳酸菌数一直明显高于肠杆菌和假单孢菌总数;速冻肉馅在第16d即第三次冻融时感官品质发生明显变化,此时细菌总数和乳酸菌总数增加极显著,分别为4.1332lgCFU/g和3.9529lgCFU/g,是产品中主要的优势菌,为保证肉馅正常的货架期,其冻融次数不宜超过3次。     

Thawing, Refreezing and Frozen Storage Effects on Muscle Functionality and Sensory Attributes of Frozen Cod (Gadus morhua)

Thawing and re-freezing of cod fillet blocks did not necessarily result in greater deterioration (relative to a ‘once frozen’ control) of cooked fish sensory attributes after 9 months frozen storage at –22°C. Thawed and refrozen fish muscle displayed a faster decline in myofibril protein solubility than once frozen controls and had reduced water-holding capacity but analysis of proton spin-spin relaxation times indicated no change in water location. The decline in protein solubility was not caused by complete protein unfolding. Long thawing times (30 hr) before re-freezing and storage resulted in cooked fish with more gray appearance and more stale flavor. Changes in fish muscle functionality did not enable direct inference of sensory attributes.     

食用胶和解冻方式对速冻乳化香肠品质的影响

研究速冻技术条件下,沙蒿胶和卡拉胶对乳化香肠品质的影响,探讨不同解冻技术的优缺点.结果表明:速冻过程会引起产品析水率上升、硬度下降、弹性变小等变化,沙蒿胶和卡拉胶的添加可有效降低速冻对产品的不利作用,当二者的添加量分别为0.5g/kg和8g/kg时,可有效降低速冻引起的析水率上升、弹性变小和硬度降低等变化;从解冻方式来看,微波解冻既可以节约大量时间,同时感官评分较高,可行性较高.