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.     

Demethylation of Pectic Substances: Relationship to Methylesterase Activity during Brine Storage of Cherries

Residual pectin methylesterase activity (60% of initial activity) was present in cherry fruit stored 12 mo in brine. The specific activity of pectin methylesterase increased during the first 4 mo (195% of initial specific activity) but remained relatively stable thereafter. Methanol concentration increased (+144.5%) indicating that pectic substances underwent continuous demethylation during 12 mo storage. Pectin deesterification was probably of enzymatic origin since notable chemical deesterification occurred only at a pH lower than that found in fruit during storage. Residual pectin methylesterase activity introduces the possibility of improving fruit texture by manipulating physico-chemical conditions prior to blanching and candying.     

苯乳酸-海藻酸钠涂膜保鲜剂的制备及其在甜樱桃保鲜中的应用

利用苯乳酸的抑菌能力和海藻酸钠的成膜性制备苯乳酸-海藻酸钠涂膜保鲜剂,并应用该保鲜剂对甜樱桃 进行涂膜保鲜。通过测试保鲜剂成膜的性能,确定保鲜剂中海藻酸钠的适宜添加量;通过测定甜樱桃生理指标和品 质指标的变化,研究保鲜剂对甜樱桃的冷藏保鲜效果。结果表明：在6 g/L苯乳酸、5 g/L甘油、5 g/L黄原胶存在的 情况下,海藻酸钠添加量为12 g/L时制备的保鲜剂有较好的成膜性能。应用该保鲜剂保鲜甜樱桃,能较好地抑制甜 樱桃的腐烂,减少水分散失,降低呼吸强度,保持贮藏甜樱桃的色泽和硬度,延缓可溶性固形物和可滴定酸质量分 数的下降,从而有利于降低甜樱桃代谢强度,保持果实品质,延长甜樱桃的保鲜期。     

Programmed Freezing Affects Texture, Pectic Composition and Electron Microscopic Structures of Carrots

Raw and blanched carrots (3 min, boiling water) were frozen at ?2°C, ?3°C, ?4°C or ?5°C/min (final ?20°C or ?50°C) then thawed at 20°C or 100°C. Firmness of thawed raw carrots was: ?5°C > ?4°C > ?3°C > ?2°C/min. Effect of freezing rate on blanched carrots was less than that on raw carrots, but firmness of thawed carrots was not affected by final temperature of freezing. When raw carrots were thawed at 20°C, high methoxyl pectin decreased. Pectin decrease in blanched carrots caused by freezing was greater than that in frozen raw carrots. Effects of slow-freezing, programmed-freezing (slow + quick + slow) and quick-freezing showed quick freezing (—5°C/min) best for texture. As freezing rate decreased, drip increased. A wide difference among experimental samples in fine structure was revealed by cryo-scanning electron microscopy.     

Texture and Pectic Composition Differences in Raw, Cooked and Frozen-Thawed Chinese Cabbages due to Leaf Position

Differences in texture of raw, cooked and blanched-frozen-then-thawed Chinese Cabbages and their leaf positions (10, 20, 30, 40, or 50th midribs from the outside) were investigated. Firmness and rupture strain of raw midribs were low, but increased after short cooking time. Crispness of tissues decreased and elasticity increased. The 20–30th midribs were slowest to soften during cooking, while the inner midribs from the 40th were more readily softened. The 40th contained more high methoxyl pectin than did the 20th. Therefore, they were more quickly softened because of pectic release by transelimination. After freezing-thawing, firmness decreased and rupture strain increased. Midribs with firmer texture contained more pectin. After freezing-thawing, amounts of pectin in midribs decreased.     

Pectinesterase Activity and Proximate Analyses of Sea Buckthorn Juices

Three varieties of sea buckthorn fruit were harvested and pressed to obtain juices. These were analyzed for pectin methylesterase activity, moisture, nitrogen, oil, pH, total acid, and °Brix. Yields of press juice for Hippophae rhamnoides ssp. rhamnoides L. varieties Luchistaya, Prozrachnaya, and ssp. mongolica Rousi cv. Indian Summer were 68%, 69%, and 66% w/w, respectively. Differences in juice composition were found to be in moisture content, °Brix, pH, and in total acid with the Luchistaya variety having the highest acid levels and lowest pH. Pectin methylesterase (PME) was present in all sea buckthorn juices with initial activity levels of 6.8 to 14.0 μ equivalents per min per 100 g of juice at pH 8 and 23 °C. Activity was pH‐dependent with little PME activity at pH 3 to 5 and the highest activity at pH 8. The cream, pellet, and serum layers of centrifuged juices all contained PME. Heat treatment reduced PME activity in the juices by 1 decimal reduction or less.     

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.     

Relationship between Pectic Substances and Strand Separation of Cooked Spaghetti Squash--Part 2. Changes in Firmness,Histological Structure and Pectic Substances during Soaking in Pectin Extractants

The flesh of spaghetti squash separates into strands when cooked. The purpose of this paper is to investigate the cause of strand separation （during cooking） by soaking for 24 h at 35 ℃ in solutions with three kinds of pectin extractant. The changes in strand separation, firmness, histological structure and the pectin of flesh during soaking in 0.01 N HCI solution （pH 2.0）, 0.035 M ammonium oxalate solution （pH 4.0） or 2% sodium hexametaphosphate solution （pH 4.0） were investigated. When flesh was soaked in the HCI solution, the separation into strands and removal of calcium and magnesium were greater than that soaked in other pectin extractants. High methoxyl pectin was extracted by soaking in HC1 solution （pH 2.0） due to removal of polyvalent cations. This result shows that high methoxyl pectin glues strands together in the flesh of spaghetti squash. The shape of the cells which constituted strands was round; on the other hand, that of cells surrounded strands was elongated. When cooked in boiling water or soaked at pH 2.0, the shape of the former cells was maintained, but the latter cells, which contributed to adhesion between strands, broke down. Thus, the flesh separated into strands. When flesh was boiled for 15-30 min, pectin degraded and dissolved in the cooking solution; consequently, the flesh separated into strands and also the middle lamella of cell walls of strands separated. However, pectin remaining in strands maintained their crispness.     

甜樱桃采后腐烂病原菌的分离与鉴定

为了研究山西省甜樱桃果实采后贮藏过程中的病原菌,本文对低温贮藏过程中发生腐烂的甜樱桃果实的病原菌进行分离纯化。在形态学基础上,结合基因序列分析,对分离获得的2株病原真菌YTA、YTB进行鉴定。YTA和YTB利用真菌通用引物ITS序列进行PCR扩增,将测序所得的基因序列与NCBI的GenBank进行同源序列比对,确定甜樱桃病原菌的生物学分类。结果表明:病原菌YTA为草酸青霉(Penicillium oxalicum),YTB为葡萄孢属(Botrytis sp.),将其重新回接到甜樱桃上,均能引起甜樱桃腐烂。草酸青霉(Penicillium oxalicum),葡萄孢属(Botrytis sp.)均是造成山西省甜樱桃采后腐烂的病原菌。     

真空油炸紫薯片预处理工艺的优化

研究了真空油炸紫薯片的预处理工艺.应用单因素试验及正交试验设计方法,对切片厚度、漂烫条件、冷冻时间等真空油炸紫薯片质量的预处理因素进行了系统研究,确定了真空油炸紫薯片的最佳预处理工艺:切片厚度3.0 mm;漂烫温度95℃,漂烫时间3.5 min;在-20℃条件下,冷冻18 h;在-0.094～-0.098 MPa真空度条件下,90℃真空油炸15 min.真空油炸紫薯片最大程度地保存了紫薯的营养价值,花青素含量为1.54 mg/g,脂肪质量分数为17.40％,破碎力为468.9 N.产品带有清晰的纹理,口感酥脆,无油腻感.     

烟台地区引起甜樱桃采后腐烂霉菌的分离鉴定

为明确引起烟台地区甜樱桃采后腐烂的主要霉菌,对烟台采后腐烂甜樱桃中的霉菌进行分离,应用内部转录间隔区序列分析方法和形态学观察将分离的霉菌进行鉴定。选出代表性霉菌菌株回接樱桃,进行致腐性检测。结果表明:从烟台不同区县收集的腐烂樱桃中分离出的60株霉菌分属于6个种:燕麦赤霉菌(Gibberella avenacea)、总状毛霉菌(Mucor racemosus)、三线镰刀菌(Fusarium tricinctum)、互生链格孢菌(Alternaria alternate)、奥桑青霉菌(Penicillium polonicum)和烟曲霉菌(Aspergillus fumigatus),其中互生链格孢菌和总状毛霉数量较多,分别为14株和15株。将这些霉菌中的代表菌株重新接回到甜樱桃,均能引起甜樱桃的腐烂。     

Pectic Substance Degradation and Texture of Carrots as Affected by Pressurization

Heated pectin was degraded by transelimination (β-elimination) above pH 5 and by hydrolysis below pH 2, but pressurized pectin did not degrade. Thus cooked carrots decreased in firmness, but pressurized carrots did not. Pressurizing above 200 MPa slightly increased rupture strain. Galacturonic acid levels decreased in carrots cooked for 30 min. Total pectin in pressurized carrots was the same as in cooked for 3 min. However, with increased pressure, the amount of high methoxyl pectin in carrots decreased while low methoxyl pectin increased. Thus, the effects of pressurization on pectin degradation (transelimination) and texture of carrots were different from those of heating.     

雪里蕻腌菜的质构与果胶组分含量的关系

对雪里蕻腌菜中果胶组分的含量与质构变化进行了检测分析,雪里蕻腌菜在正常腌渍过程中总果胶含量趋于稳定,而水溶性果胶增加至一稳定值,六偏磷酸钠溶解性果胶下降至一稳定值.在腐烂过程中,总果胶含量显著下降,同时水溶性果胶组分增加和六偏磷酸钠溶解性果胶下降明显.研究结果表明,可用检测雪里蕻腌菜醇不溶物中果胶组分含量的变化来监测腌菜质构变化.     

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.     

紫薯果胶类多糖的成分分析及稳定性研究

以超声波辅助酶法提取及纯化紫薯果胶类多糖,并对其主要成分及稳定性进行分析.结果表明:所得紫薯果胶类多糖的干燥减量、酸不溶灰分、pH值、总半乳糖醛酸、酯化度、总糖、蛋白质含量分别为4.32％、0.32％、4.22、65.24％、31％、65％、1.02％,符合相关标准.测出所得紫薯果胶类多糖的重均分子量为70745 Da...     

Effects of High Pressure and Heat Treatment on Pectic Substances and Related Characteristics in Guava Juice

Effects of high pressure treatment on guava juice pectic substances and related juice characteristics were investigated and compared with heat treatment. The viscosity and turbidity of guava juice pressurized at 600 MPa and 25°C for 10 min increased slightly; whereas the viscosity of juice heated at 95°C for 5 min decreased while turbidity increased. There were no apparent changes in water soluble, oxalate soluble and alkali soluble pectin in pressurized juice. However, heat treatment of juice decreased water and alkali soluble pectins and slightly increased oxalate soluble pectin. High pressure treatment resulted in no marked changes in pectic and cloud substances of guava juice, and maintained the natural viscous of the juice.     

Effects of High-Pressure Pretreatment and Calcium Soaking on the Texture Degradation Kinetics of Carrots during Thermal Processing

ABSTRACT: Carrots ( Daucus carota ) pretreated under different high-pressure conditions were thermally processed at temperatures in the range of 90°C to 110°C. Texture degradation (hardness) was monitored objectively using a texture analyzer. For a given thermal treatment, the rate constant (k-value) decreased with increasing pretreatment pressure. A high-pressure pretreatment (200 to 500 MPa) at 60°C for 15 min resulted in a more pronounced texture improvement compared with the same pretreatment at 20°C and 40°C, respectively. Calcium impregnation conferred more beneficial effects when applied immediately after the high-pressure pretreat-ment. The observed changes in texture characteristics were associated with the degree of methylation of carrot pectins, which is dependent on pectinmethylesterase (PME) activity.     

The Use of Potato and Sweet Potato Starches Affects White Salted Noodle Quality

ABSTRACT Potato and sweet potato starches and derivatives thereof were used to substitute part of the wheat flour in white salted noodle (WSN) manufacture. The quality of the WSN obtained was compared with the quality of WSN made from wheat flour only. When up to 20% of wheat flour was replaced by acetylated potato starch and acetylated sweet potato starches, the cooking loss of WSN decreased, while the softness, stretchability, and slipperiness increased significantly. Native and hydroxypropylated starches did not exhibit these effects. It can be concluded that the substitution of part of wheat flour with acetylated starches strongly affects noodle-making and final noodle quality, and starch substitution can be used to change the performance of a given wheat flour for noodle making in a desired way.     

微生物发酵法提取甘薯渣果胶及其对凝固型酸奶稳定性的研究

采用微生物发酵法提取甘薯渣果胶,并研究其作为稳定剂对凝固型酸奶稳定性的影响。结果表明:微生物发酵法提取甘薯渣果胶的最佳提取条件:发酵温度35℃,pH 5.0,发酵时间48 h,接种量15%,优化条件下的果胶提取率为6.55%;同时研究表明,果胶对凝固型酸奶的稳定性有一定影响,结果表明,果胶的最佳添加量为0.2%。     

Ultrastructural and Changes in Pectin Composition of Sweet Cherry from the Application of Prefreezing Treatments

ABSTRACT: Thermal and calcium pretreatments applied to preserve the sweet cherry texture by the freezing/thawing process produced biochemical changes in the pectic substances and ultrastructural alterations to the cells and tissues, which were visible under scanning electron microscopy. Partial dehydration of the epidermic tissue caused by calcium (100 m M CaCl₂) and thermal (50 °C/10 min) pretreatment attenuated the surface damage produced by freezing. However, pretreatment at 70 °C/2 min caused partial destruction of the epidermic tissue and plasmolysis of the parenchymatic cells. After freezing, the cell walls in the parenchymatic tissue of the fruits pretreated with 100 m M CaCl₂ exhibited swelling as a result of gelling of the cell-wall pectic material. Thermal pretreatments increased the ethylenediaminetetraacetic acid (EDTA)-soluble pectin fraction and reduced the degree of pectin esterification. Thermal treatments at 70 °C, without immersion in calcium, reduced the water- and pectinase-soluble pectin fractions, whereas immersion in calcium prevented depolymerization of these fractions. Immersion in 100 m M CaCl₂ increased the water-soluble pectin fraction.