Fermentation pH and temperature influence the cryotolerance of Lactobacillus acidophilus RD758

The effects of 3 fermentation temperatures (30, 37, and 42°C) and 3 fermentation pH (4.5, 5, and 6) on the cryotolerance of Lactobacillus acidophilus RD758 were studied in relation to their fatty acid composition. Cryotolerance was defined as the ability of the cells to recover their acidification activity after freezing and frozen storage at −20°C. Better cryotolerance was obtained in cells grown at 30°C or at pH 5; these cells showed no loss in acidification activity during freezing and a low rate of loss in acidification activity during frozen storage. On the other hand, cells grown at 42°C or at pH 4.5 displayed poor cryotolerance. The membrane fatty acid composition was analyzed and related to the cryotolerance using principal component analysis. The improved cryotolerance observed during the freezing step was associated with a high ratio of unsaturated to saturated fatty acids, a low C18:0 content, and high C16:0 and cyclic C19:0 relative concentrations. High resistance during frozen storage was related to a high cycC19:0 concentration. Finally, the low cryotolerance observed after fermentation at pH 4.5 was explained by a low C18:2 content.     

Cryotolerance of Lactobacillus delbrueckii subsp. bulgaricus CFL1 is influenced by the physiological state during fermentation

To better understand the effects of freezing and frozen storage on different characteristics of the cell state, the influence of the physiological state, as defined by fermentation pH and harvesting time, and the freezing medium on the cryotolerance of Lactobacillus bulgaricus CFL1 was investigated. Esterase activity, membrane integrity, cultivability and acidification activity were quantified during culture with and without pH control, and during freezing and frozen storage at ?20 °C. The preservation of esterase activity and membrane integrity was not related to starter functionalities such as cultivability and acidification activity. Cell cryotolerance increased with fermentation time or when cells were harvested during culture at pH 5 and frozen, as compared with fermentations at pH 6 or without pH control. Long-term cell cryotolerance could be predicted by determining an early physiological parameter such as a low initial acidification activity when the cells are harvested.     

Method of quantifying the loss of acidification activity of lactic acid starters during freezing and frozen storage

We have developed a method to quantify the resistance to freezing and frozen storage of lactic acid starters, based on measuring the time necessary to reach the maximum acidification rate in milk (tm) using the Cinac system. Depending on the operating conditions, tm increased during the freezing step and storage. The loss of acidification activity during freezing was quantified by the difference (delta tm) between the tm values of the concentrated cell suspension before and after freezing. During storage at -20 degrees C, linear relationships between tm and the storage time were established. Their slope, k, allowed the quantitation of the decrease in acidification activity during 9-14 weeks of frozen storage. The method was applied to determine the resistance to freezing and frozen storage of four strains of lactic acid bacteria and to quantify the cryoprotective effect of glycerol.     

Improvement of cryopreservation of Lactobacillus delbrueckii subsp. bulgaricus CFL1 with additives displaying different protective effects

In order to improve the acidification activity of frozen suspensions of Lactobacillus delbrueckii subsp. bulgaricus CFL1, the protective effect of nine additives, in binary and multicomponent solutions, was quantified during freezing and storage at –20°C.The best protective media were those containing sodium ascorbate and betaine or sodium glutamate, greatly improving the acidification activity recovery after freezing (+70%) and frozen storage (+90%) when compared to a control medium. However, the effect of each additive was different before than after freezing or during frozen storage. The presence of an antioxidant in the protective media appeared essential to maintain the acidification activity of L. bulgaricus during the cryoprotection stage and frozen storage. Betaine and sodium glutamate provided the highest resistance to freezing, while leading to the greatest reduction of the cryoscopic point of the medium. Their cryoprotective effect was explained by a decrease in the number of ice crystals formed during freezing and frozen storage.     

Changes in the fatty acid composition of dietetic ready-to-cook chicken meat products during frozen storage

A study was made on the fatty acid composition of dietetic ready-to-cook products of boneless chicken legs or breasts prepared by curing using several curing mixtures during frozen storage. Leg muscles were found to be richer in unsaturated fatty acids than breast muscles, substantial differences having been found in the contents of palmitoleic and linolenic acids. During frozen storage, the contents of unsaturated fatty acids were reduced, especially intensively in the leg muscle ready-to-cook products. The fastest changes occurred in linolenic and linolic acids and partly in palmitic acid. The level of oleic acid remained substantially unchanged throughout the storage period. Irrespective of the changes found, the ratio of unsaturated and saturated fatty acids in all the groups studied remained greater than 1 for both types of meat. The application of citrate in the curing mixture had a favourable effect on the changes, in that a minimum alteration in the contents of unsaturated fatty acids was achieved.     

冻藏条件对人乳脂质及挥发性风味物质的影响

以新鲜人乳为对照(0d),设置-18、-60℃和-60℃快速冷冻(-60℃(Q))3种冻藏条件分别冻藏60 d与180 d,通过测定脂质含量、非酯化脂肪酸(non-esterified fatty acids,NEFA)含量、脂质过氧化物(lipid peroxide,LPO)含量、脂肪酸组成、乳脂肪球微观结构及挥发性...     

Modifications in membrane fatty acid composition of Salmonella typhimurium in response to growth conditions and their effect on heat resistance

The effects of growth temperature (in the range 10-45 degrees C) and acidification up to pH 4.5 of the culture medium (Brain Heart Infusion, BHI) with different organic acids (acetic, citric and lactic) and hydrochloric acid on membrane fatty acid composition and heat resistance of Salmonella typhimurium CECT 443 were studied. The heat resistance was maximal in cells grown at 45 degrees C (cells grown in non-acidified BHI showed a D58-value of 0.90 min) and decreased with decreasing growth temperature up to 10 degrees C (D58-value of 0.09 min). The growth of cells in acidified media caused an increase in their heat resistance. In general, acid adapted cells showed D-values of between 1.5 and 2 times higher than the corresponding for non-acid adapted control cells. This cross-protection response, which has important implications in food processing, was not dependent on the pH value and the acid used to acidify the growth medium. A membrane adaptation corresponding to an increase in the unsaturated to saturated fatty acids ratio (UFA/SFA) and membrane fluidity was observed at low growth temperature. Moreover, the acidification of the growth medium caused a decrease in UFA/SFA ratio and in the C18:1 relative concentration, and an increase in cyclopropane fatty acids (CFA) content mainly due to the increase in cyc19 relative concentration. Thus, acid adapted cells showed CFA levels 1.5 times higher than non-acid adapted control cells. A significant proportion of unsaturated fatty acids were converted to their cyclopropane derivatives during acid adaptation. These changes in membrane fatty acid composition result in cells with decreased membrane fluidity. A clear relation between membrane fatty acid composition and heat resistance was observed. In general, D-values were maximum for cells with low UFA/SFA ratio, and, consequently, with low membrane fluidity. Moreover, CFA formation played a major role in protecting acid adapted cells from heat inactivation. However, changes observed in membrane fatty acid composition are not enough to explain the great thermotolerance of cells grown at 45 degrees C. Thus, other mechanisms, such as the synthesis of Heat Shock Proteins, could be responsible for this increase in the bacterial heat resistance.     

Comparative study of physiological adaptation to salt stress in the genome shuffled Candida versatilis and a wild-type salt-tolerant yeast strain

Candida versatilis is a yeast with a complex salt-tolerant system. It can maintain normal physiological activities and metabolic fermentation under a high-salt environment. The cellular mechanisms of adaptation to salt stress in strains of a wild type of C. versatilis (WT) and S3–5, genome shuffling strains of C. versatilis with improved tolerance to salt, were investigated. The content of intra- and extra-cellular glycerol, intra-cellular Na⁺, as well as membrane fluidity and permeability, were determined under salt-stressed yeast growth conditions. The results showed that Na⁺/H⁺-antiporter played a primary role in Na⁺ extrusion and H⁺-ATPase has been associated with yeast survival under salt stress. Considerable amounts of glycerol were produced and secreted by the yeast to outside the cell under this salt stress. Changes in the portion of membrane saturated and unsaturated fatty acid composition of C. versatilis in response to osmotic stress lead to membrane permeability and fluidity decreases. They could restrict the influx of Na⁺, enhance H⁺-ATPase activity, and prevent leakage of glycerol across the cell membrane under osmotic stress. The salt tolerance of genome shuffled strain S3–5 was higher than WT. It could be correlated with a higher level of intra-cellular accumulation of glycerol and sodium ions in cells of S3–5 than WT as well as a higher portion of oleic fatty acid (C18: 1) and a lower level of linoleic acid (C18: 2) in cell membranes of the studied yeast mutant. It can be concluded that S3–5 improved physiological regulatory mechanisms of response to salt stress, such as decreased membrane fluidity and a permeability that rapidly adjusted to osmotic stress.     

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。     

Hake natural actomyosin interaction with free fatty acids during frozen storage

The interaction of hake muscle actomyosin with free fatty acids in 0.6 M KCl pH 7 during frozen storage has been studied up to 280 days. ATPase activity, protein solubility and relative viscosity measurements were performed. Oleic and myristic acid had a detrimental effect on these properties during frozen storage. Oleic acid was bound to the protein from the beginning, mainly to the insoluble fraction. The diminishment of functionality following addition of oleic acid is not due to aggregation caused by covalent-type bonds, since it occurs well before the electrophoretic change is appreciable.     

热水处理对近冰温贮藏鲜枣品质提高与膜脂代谢的相关性分析

以采后临泽小枣（Zizyphus jujuba Mill. cv. Linzexiaozao）为实验材料,探讨热水处理对近冰温贮藏鲜枣果实耐冷性与膜脂脂肪酸组分变化的影响。采后果实用60 ℃热水浸泡1 min,自然干燥后,装入带有若干小孔(孔径为2 mm)的聚乙烯塑料饭盒,置于(?1.5~?2)℃的冷库中贮藏,定期测定果实冷害指数、细胞膜透性、丙二醛(MDA)、脂氧合酶(LOX)活性及膜脂脂肪酸组分变化。与对照相比,贮藏50 d时,热水处理果实的冷害指数、相对电导率、MDA和LOX活性分别降低了7.56、17.93%、17.93 μmol/g·FW和15.84 U/g·FW,不饱和脂肪酸油酸(C_18:1)、亚油酸(C_18:2)和亚麻酸(C_18:3)的相对含量及膜脂脂肪酸不饱和指数(IUFA)、脂肪酸不饱和度(UFA/FA)分别增加了11.10%、9.13%、8.60%和55.17、0.65,饱和脂肪酸肉豆蔻酸(C_14:0)、棕榈酸(C_16:0)、硬脂酸(C_18:0)和花生酸(C_20:0)的相对含量也分别降低了54.10%、18.66%、17.93%和3.37%,且差异显著(P<0.05)。尤其是对照LOX活性与亚麻酸(C_18:3)的相对百分含量变化有极显著(P<0.01)的负相关性(r=?0.931)。结果表明,鲜枣在近冰温冷藏下发生冷害的程度与膜脂中亚麻酸（C_18:3）的相对含量变化存在相关性。热水处理抑制了鲜枣膜脂脂肪酸不饱和指数(IUFA)和脂肪酸不饱和度(UFA/FA)的下降,诱导膜脂中不饱和脂肪酸的降解速率减缓,从而维持较高的膜脂稳定性,使采后鲜枣近冰温贮藏的耐冷性增强。     

基于代谢组学和转录组学分析工业面包酵母（Saccharomyces cerevisiae）ABY3冷冻胁迫应答机制

为研究面包酵母（Saccharomyces cerevisiae）响应冷冻胁迫的机理，对面包酵母－20 ℃处理7 d前后的发酵菌液进行胞内的代谢组学和转录组学分析。在－20 ℃、7 d的环境胁迫下，面包酵母不加糖模拟面团发酵后的存活率为43%，发酵力下降42%。冷冻胁迫下，面包酵母胞内24 种代谢物的变化与494 种基因的表达差异与应答机制相关。通过差异代谢通路分析得出：冷冻胁迫下，胞内氨基酸的匮乏与质膜僵硬化可能是影响细胞生长和发酵性能的主要原因，而胞内不饱和脂肪酸相对含量的增加和海藻糖的积累并不能消除低温对细胞的损伤。研究结果可完善酵母冷冻胁迫应答机理，为耐性调节机制的研究提供思路，对冷冻面团的优化和技术发展具有重要意义。     

鲐鱼低温冻藏过程中脂肪氧化特性

鲐鱼组氨酸含量较高,在低温贮藏中品质易发生劣变,影响其食用安全性.以-18℃冻藏的鲐鱼为研究对象,在贮藏0、10、20、40、60、80、100 d后分别取样,测定鲐鱼风味、过氧化值、酸价、硫代巴比妥酸反应物(thiobarbituric acid reactive substances,TBARs)值和脂肪酸成分的变...     

营养胁迫植物乳杆菌KLDS 1.0328的生理特性及其冷冻干燥菌粉贮存稳定性分析

为探究冷冻干燥植物乳杆菌KLDS 1.0328的贮存稳定性受初始营养条件调控的差异性,分析葡萄糖胁迫、吐温80胁迫以及葡萄糖和吐温80复合胁迫对该菌株生长、产酸、细菌素抑菌活性、形态、细胞膜脂肪酸和菌粉贮藏过程中存活率的影响。研究发现,葡萄糖和吐温80胁迫对菌体的生长、产酸和细菌素的产生有不同程度的影响。扫描电镜结果显示,吐温80胁迫或葡萄糖和吐温80复合营养胁迫环境下,菌体由短杆状转变为长棒状或卵圆形,尺寸也随之增大或减小。经多种营养胁迫处理后,各处理组中菌体细胞膜的不饱和脂肪酸与饱和脂肪酸含量比值均有所提高。此外,葡萄糖胁迫可显著提高冷冻干燥植物乳杆菌KLDS 1.0328在－18 ℃贮存42 d期间的稳定性和存活率。     

Survival of Bifidobacterium strains in organic fermented milk is improved as a result of membrane fatty acid composition

Survival of three Bifidobacterium strains in organic and conventional fermented milks in relation to their membrane fatty acid composition was studied during chilled storage. Survival of Bifidobacterium lactis BB12 and BL04 over 21 days at 4 °C was improved in organic fermented milks, whereas these parameters were less effective for Bifidobacterium infantis ATCC15697. These different behaviours were linked to acidification activity, oxidoreduction potential and relative fatty acid composition, which differed among the strains and the types of milk used. The higher relative unsaturated fatty acid content in organic products, including trans-vaccenic, conjugated linoleic and α-linolenic acids, resulted in an increase in the linoleic and α-linolenic acid content in the cell membranes of B. lactis BB12 and BL04. The study showed that the membrane fatty acid composition, which depended on the strain and on the milk fatty acid composition, affected the survival of bifidobacteria during chilled storage in fermented milk products.     

降温方法对不同成熟度鸭梨果肉脂氧合酶活性和膜脂脂肪酸的影响

为了探讨缓慢降温抑制采后鸭梨果实褐变的机理,研究了不同降温方法对不同成熟度鸭梨果肉脂氧合酶(LOX)活性及膜脂脂肪酸组分和含量的影响。结果表明:在贮藏期间,LOX活性缓慢上升,晚采果活性较高;缓慢降温抑制了LOX活性的升高和果肉褐变,对早采果影响明显。鸭梨果肉中含有月桂酸、豆蔻酸、棕榈酸、棕榈油酸、珠光酸、硬脂酸、油酸、亚油酸、亚麻酸,其中含量较多的是亚油酸、棕榈酸和油酸。推迟采收和缓慢降温提高了果肉的U/S值,缓慢降温提高了鸭梨果肉的亚麻酸及前期的亚油酸含量,在贮藏后期,随着LOX活性的升高,亚油酸、亚麻酸的含量减少,二者可能是LOX的反应底物。适当早采结合缓慢降温可提高鸭梨果肉膜脂不饱和脂肪酸含量和U/S值,抑制果肉褐变。     

Production and Stability of (E, Z)-2, 6-Nonadienal, the Major Flavor Volatile of Cucumbers

ABSTRACT: Factors affecting the production and stability of (E, Z) -2, 6-nonadienal (NDE) from pickling cucumbers were examined. Production capability was rapidly destroyed in tissues exposed to freezing, fermentation or processing conditions. Lower concentrations were produced by exocarp tissues than mesocarp or endocarp tissues, which probably accounted for an almost linear relationship between fruit size and NDE production. NDE production was reduced by acidification, enhanced by linolenic acid, and unaffected by other unsaturated fatty acids NaCl or CaCl2. E-2-nonenal production was suppressed when NDE production was increased by linolenic acid. NDE was unstable in filtrates of homogenized tissues. Its stability was substantially improved by acidifying to pH 2 and unaffected by CaNa2EDTA. Extraction and concentration by vacuum distillation further enhanced stability. Loss of NDE in distillates averaged 0.3%/d during storage at 5 °C.     

Changes in fatty acid composition and electrolyte leakage of ‘Hayward’ kiwifruit during storage at different temperatures

Exposure to low storage temperature induces changes in electrolyte leakage and fatty acids composition, in a way depending on the plant tissue. Those changes alter the response of the fruit to storage conditions. The influence of storage temperature on ripening, fatty acids composition and electrolyte leakage of ‘Hayward’ kiwifruit were investigated. Harvested fruit were stored at 0, 5, 10, 15 and 20 °C for 5, 12 and 17 days. Measurements of SSC, firmness, flesh colour, fatty acid composition and electrolyte leakage were performed during the experiment. Kiwifruit did not fully ripen during the 17 days storage at any temperature. The major fatty acid component in ‘Hayward’ kiwifruit consisted of linolenic, followed by oleic, palmitic, linoleic and stearic acid. Membrane permeability and unsaturated/saturated fatty acid ratio increased during storage in all treatments. The highest increase was during the first 5 days and at the lowest temperatures. The increase in unsaturated/saturated fatty acid ratio was caused mainly by a decrease in palmitic and an increase in oleic acids. Stearic, linoleic and linolenic acids had insignificant changes during storage. The main increase in electrolyte leakage and unsaturated/saturated fatty acid ratio occurred during the first storage days and at lower temperatures, probably as a response of the tissue to an adaptation to the new stress storage conditions.     

Effect of fermentation,processing and storage on lipid composition of sauerkraut

The changes in lipid composition and fatty acid distribution of sauerkraut during fermentation, canning, processing and storage were investigated organoleptically and chemically. Treatments were significant throughout the experiment. pH, lactic acid, and moisture content did not reveal any substantial changes. Total lipids, neutral lipids, and glycolipids increased, whereas phospholipids were unaltered during fermentation and processing. Quantitative changes in nonpolar and polar lipids during storage were in opposite directions, and net lipid content did not change. The changes in fatty acid composition were primarily in the distribution of palmitic, stearic, oleic, linoleic and linolenic acids during fermentation, processing and storage. Total lipids did not relate to organoleptic evaluation. However, polar lipids, specifically phospholipids, were directly related to storage stability and increased amounts of general acceptability. The formation of phospholipids may be catalysed by a reaction between tin from the cans and polar lipids at the expense of neutral lipids.     

酸奶制品发生后酸化主要发酵剂菌确定及性质研究

将培养物中保加利亚乳杆菌与嗜热链球菌调节为相同 pH值 ( 4 .5 0 )、起始相同菌数7.4× 1 0 7个 /mL后 ,分别贮存 ( 2 5℃ ) ,贮存第 1 1d ,嗜热链球菌的 pH值为 4.5 7,保加利亚乳杆菌的为 3.85。将保加利亚乳杆菌确定为导致后酸化发生的主要发酵剂菌 ,是其细胞壁或细胞膜的性质保护了乳糖酶活性