Application of glycerol to freezing bovine pancreas. Part 2. Effects of glycerol and grinding on frozen pancreas quality

Effects of glycerol on the quality of ground and whole pancreas stored frozen at -30 degrees C were studied. The quality was assessed from quantitative changes in soluble proteins, proteolytic enzyme activity, and insulin content. Grinding was found to enhance the effects of the cryoprotector due to its uniform distribution in the tissue. A relationship between proteolytic enzyme activity and protein solubility was demonstrated.     

Application of glycerol to freezing bovine pancreas. Part 3. Effects of freezing rate and glycerol addition on changes in pancreas proteins

Changes in protein solubility, amino nitrogen and activity of proteases in bovine pancreas frozen at ?70 and ?18°C after soaking in various aqueous glycerol solutions were studied. Reduction of freezing temperature causes decrease of value in all studied parameters. Additionally, an inhibitory effect of glycerol on protease activity was demonstrated.     

Application of glycerol to freezing bovine pancreas. Part 3. Effects of freezing rate and glycerol addition on changes in pancreas proteins.

Changes in protein solubility, amino nitrogen and activity of proteases in bovine pancreas frozen at -70 and -18 degrees C after soaking in various aqueous glycerol solutions were studied. Reduction of freezing temperature causes decrease of value in all studied parameters. Additionally, an inhibitory effect of glycerol on protease activity was demonstrated.     

Application of glycerol to freezing bovine pancreas. Part 1. Effect of cryoprotector on activity of certain enzymes in frozen minced pancreas.

Effects of different concentrations of glycerol on the activity of amylase, lipase, and proteases in frozen minced pancreas were studied. A 15% glycerol addition was found to decrease the proteolytic enzyme activity and to increase the activity of amylase. Moreover, accelerated freezing was shown to enhance the activity of all the enzymes studied.     

不同冻结方式对大菱鲆鱼片冻藏过程中品质变化的影响

该文以鲜活大菱鲆为原料,研究了5种冻结方式处理对大菱鲆鱼片贮藏过程中品质变化的影响。对5种冻结方式(-20℃冰箱冻结、-20℃平板速冻、-30℃冰箱冻结、-30℃平板速冻、-90℃液氮速冻)处理的大菱鲆鱼片在-18℃冷库冻藏15周内的理化指标、质构特性和微观结构进行测定。结果表明,随着冻藏时间的延长,不同冻结方式处理的大菱鲆鱼片持水力、肌原纤维蛋白含量、活性巯基含量、Ca~(2+)-ATPase活性及质构特性均呈下降趋势;白度值、TBA值呈上升的趋势;pH呈先下降后上升趋势;微观组织结构不同程度劣化。经-90℃液氮速冻和平板速冻处理的大菱鲆鱼片品质劣化趋势显著低于或迟缓于冰箱冻结组,低温速冻在大菱鲆品质保鲜方面具有广阔的应用前景。     

冻结温度对速冻方竹笋品质特性的影响

为评价速冻方竹笋的品质特性,实验以金佛山方竹笋为原料,研究不同冻结温度对速冻方竹笋的品质特性影响。结果表明:-23℃和-40℃冻结温度的速冻方竹笋水分含量分别为91.62%、90.49%,与对照组比较显著下降（p<0.05）;硬度分别为628.50±55.72、（746.67±30.2）g,剪切力分别为2286.03、2851.13 g（p<0.05）,但均与对照组呈显著性下降（p<0.05）;L*值分别为70.73±0.26、68.52±0.54,a*值分别为-1.50±0.08、-2.03±0.20,显著下降（p<0.05）;b*值分别为24.06±0.15、25.20±0.19,显著增加（p<0.05）。说明速冻对方竹笋的品质特性有显著影响,但-40℃冻结更有利于保持方竹笋的质地。      

Effect of freezing method and frozen storage duration on lamb sensory quality

This study assessed the effect of three freezing methods with three frozen storage durations (1, 3, and 6 months) on the sensory quality of lamb. Methods were: air blast freezer, freezing tunnel + air blast freezer, and nitrogen chamber + air blast freezer. Meat was frozen after 48 h of ageing (0-4 °C). Fresh meat (72 h ageing at 2-4 °C) was used as control. Sensory analyses (trained panel and consumer tests) were performed on loin chops (Longissimus lumborum) after 24 h of thawing. Results from the trained panel test showed that freezing (method and/or storage duration) had no significant effect. Consumers found that freezing affected sensory quality. Cluster analysis for overall acceptability divided the population into four classes with different preference patterns, and none of them showed a significant preference for fresh meat. The small differences between fresh and thawed meat shown in this study should not give consumers concerns about buying frozen meat or consuming thawed meat.     

液氮冻结对冻藏雷竹笋品质的影响

目的 研究液氮的3种冻结温度和冻结至3种中心温度对冻藏雷竹笋品质的影响。方法 测定不同液氮冻结温度和中心温度的冻藏雷竹笋的汁液流失率、可溶性固形物和粗纤维含量、硬度、色差、挥发性风味物质和感官评分。结果 液氮冻结温度组中,-60℃组冻结雷竹笋的感官评分、硬度显著低于-90、-120℃组（p<0.05）,而汁液流失率、粗纤维含量、a*值显著高于-90、-120℃组（p<0.05）;雷竹笋原有挥发性风味物质的信号强度为：-120℃>-90℃>-60℃,冻藏过程中产生的挥发性风味物质的信号强度为：-120℃<-90℃<-60℃。中心温度组中,-6℃组冻结雷竹笋的感官评分、硬度显著低于-12、-18℃组（p<0.05）,而汁液流失率、粗纤维含量、a*值、b*值显著高于-12、-18℃组（p<0.05）;雷竹笋原有挥发性风味物质的信号强度为：-18℃>-12℃>-6℃,冻藏过程中产生的挥发性风味物质的信号强度为：-18℃<-12℃<-6℃。-12℃和-18℃组冻藏雷竹笋品质差异不显著。结论 降低液氮冻结温度加快了冻结速率,维持了冻藏雷竹笋较好的感官品质;冻结至中心温度-12℃时,雷竹笋内部大部分水分已完成冻结,此时转移至-18℃冰柜中对雷竹笋组织内部影响不显著（p>0.05）。     

冻结速率对冻鸭品质特性的影响

鲜鸭分别于-35℃浸渍冷冻液和风冷冷库中冻至-18℃,然后在-18℃保藏库中贮藏5个月,以解冻汁液流失、蒸煮损失、肌肉剪切力、色泽、pH、TVB-N和微生物为指标,研究冻结速率不同对鸭在冷冻和贮藏过程中品质变化的影响,采用回归分析预测其贮藏期。结果表明:鸭体中心温度降到-18℃,浸渍式冷冻处理组用时仅仅52min,显著短于风冷组的738min;除pH值无显著差异外,浸渍式冷冻组的其他各项品质指标显著优于风冷冷冻组。     

南极磷虾肉冻融循环过程水分的迁移及微观结构变化

为解决新零售预制烤鱼经冷冻复热后口感下降的问题,选取草鱼为研究对象,以水分含量、持水力、水分分布及组成和微观结构等为指标,探究鱼肉油炸、冷冻、复热不同阶段的品质变化规律。结果表明,随冻融循环次数增加,鱼肉肌纤维破坏程度增加,水分含量显著降低（P<0.05）,持水性变差,脂肪氧化和蛋白降解程度显著增加（P<0.05）,风味发生改变。复热后,冻融1次鱼肉仍能保持较好口感,但冻融2次后鱼肉感官评分较低,且肌原纤维小片化指数、TBARS和TCA-可溶性肽含量较冷冻前样品分别增加了24.44%、225.84%和52.85%。综上,当油炸预制鱼产品在贮运流通过程中发生冻融次数超过2次时明显降低产品食用品质和消费者接受度。

     

Influence of freezing process and frozen storage on the quality of fruits and fruit products

The effects of freezing and frozen storage on bioactive compounds in fruit products have not been completely elucidated, and the outcomes are often contradictory. Given the wide range of results, the aim of this review is to explore the effects of freezing, thawing, and storage conditions on the physicochemical quality of fruit products, including the phytochemical content. We also discuss how growing and environmental conditions can affect the freezing process and product quality. Studies show that cultivar selection, preharvest factors, and ripening stage are important factors that contribute to the freezing performance and the quality of fruit products.     

浓缩与冻结方式对牛乳品质的影响

通过膜分离将鲜牛乳浓缩成不同总固形物含量的乳样(11. 83%、14. 94%、17. 61%、23. 01%),采用4种冻结方式(冰箱冻结、冷库冻结、螺旋冻结、平板冻结)对乳样进行冻结处理。测定乳样的色度、p H值、酸度、粒度、乙醇稳定性和热稳定性,并结合共聚焦显微镜和十二烷基硫酸钠-聚丙烯酰胺凝胶电泳进行对比分析。结果表明,随着总固形物含量的升高,牛乳的p H值、酸度、乙醇稳定性和热稳定性降低,总色差值、平均粒径增大。经冻结处理后乳样中β-乳球蛋白含量均降低。在4种冻结方式中,平板冻结速率最快,乳样的乙醇稳定性和热稳定性均最高;冰箱冻结的乳样平均粒径和乳脂肪球粒径均最大。综上,推荐将鲜牛乳浓缩至总固形物含量为23. 01%,然后采用平板冻结的工艺,可以更好地维持冻结乳样的品质。     

Effect of freezing method and frozen storage duration on instrumental quality of lamb throughout display

This study evaluated the effect of freezing method (FM) (air blast freezer, freezing tunnel, or nitrogen chamber) and frozen storage duration (FSD) (1, 3, or 6 months) on the instrumental measurements of quality of thawed lamb, aged for a total of 72 h, throughout a 10-d display period, compared to the quality of fresh meat. pH, colour, lipid oxidation, thawing, and cooking losses in Longissimus thoracis and lumborum muscle, were determined following standard methods. FM affected yellowness, FSD redness and thawing losses, and both affected oxidation (increased as freezing rate decreased and/or as storage duration increased). When compared with fresh meat, the main differences appeared on oxidation (where a significant interaction between treatment (3FM × 3FSD + fresh meat) with display duration was detected), and on total losses (thaw + cook losses). Oxidation was lower in fresh meat, but values were not significantly different from those stored frozen for 1 month. Fresh meat had smaller total losses than did thawed meat, but losses were not significantly different from meat frozen in the freezing tunnel and stored frozen for 1 month. Display duration had a greater effect on instrumental quality parameters than did FM or FSD. pH, b*, and oxidation increased, and L* and a* decreased with an increase in the number of days on display. In conclusion, neither freezing method nor frozen storage up to 6 months influenced extensively the properties of lamb when instrumental measurements of quality were measured in meat that had been displayed for 1 d after thawing. The small deterioration shown in this study should not give consumers concerns about frozen meat.     

Effects of four multi-compound freezing medium on the quality of red drum (Sciaenops ocellatus) during frozen storage

Taking air freezing (AF) as the reference, the effects of four types of multi-compound freezing medium for cryogenic liquid quick-freezing (immersion freezing, IF) on the freezing rate, quality and myofibrillar protein (MP) denaturation of red drum (Sciaenops ocellatus) fillets during frozen storage (−18°C) from days 0 to 90 were studied. Samples were gathered on days 0, 15, 30, 45, 60 and 90 for analysis. The results showed that IF groups (IF-1: 20% ethanol, 30% propylene glycol, 10% sodium chloride aqueous solution; IF-2: 20% ethanol, 20% propylene glycol, 10% glycerol, 10% sodium chloride aqueous solution; IF-3: 20% ethanol, 20% propylene glycol, 10% polyethylene glycol, 10% sodium chloride aqueous solution; IF-4: 20% ethanol, 20% propylene glycol, 5% glycerol, 5% polyethylene glycol, 10% sodium chloride aqueous solution) significantly shortened the time to cross the formation zone of maximum ice crystals while the freezing rate was 6.13 times higher than the AF group after adding 30% propylene glycol as the freezing medium. Furthermore, compared with the AF group, the IF groups significantly reduced losses in the water-holding capacity, the myofibrillar fragmentation index, microstructure damage, texture characteristics, drip loss and water migration (P < 0.05). In addition, the MP of IF groups had higher maximum transition temperatures (T_max1 and T_max2), total sulfhydryl content, Ca²⁺-ATPase activity and relative α-helix content compared with the AF group. In conclusion, IF could significantly increase the freezing rate of red drum fillets, and slow down quality deterioration and denaturation of MP during frozen storage for 90 days (−18°C). In particular, IF-2 (20% ethanol, 20% propylene glycol, 10% glycerol, 10% sodium chloride aqueous solution) was found to be more suitable for the immersion freezing of marine fish among the four multi-compound freezing medium.     

Studies on thermal treatment of hake. Part 2. Effects of thermal treatment and frozen storage on volatile ammonium bases content

Dynamics of volatile ammonium bases (VAB) in minced meat of the Pacific hake (Merluccius productus) in function of heating temperature (40, 60, 80, 100, 120 and 130 degrees C) and of storage duration (3-8 months at -28 degrees C) was followed. A gradual increase in the VAB content was found with increasing temperature and frozen storage time; the increase proved statistically significant when compared to the VAB content in the control.     

不同冻结和解冻方式对猪肉品质的影响

为探究冻结和解冻方式对猪肉品质的影响,以解冻汁液流失率,p H,脂类氧化（TBARS）值,蛋白质溶解度,滋味及微观结构的变化作为猪肉品质的评定指标。采用-18、-27、-70℃三种冻结温度进行冻结,冻结后-18℃冻藏3 d,每个冻结组解冻时均分别采用4℃低温空气、25℃静水、25℃空气三种方式进行解冻。结果表明:冻结方式与解冻方式对猪肉品质均有不同程度的影响。通过多因素方差分析可以得出,解冻汁液流失、蛋白质溶解度同时受冻结、解冻方式影响显著（p<0.05）。p H受冻结、解冻方式影响不显著（p>0.05）;TBARS受解冻方式影响显著（p<0.05）,受冻结方式影响不显著（p>0.05）;解冻方式是影响滋味变化主要因素;-70℃冻结和4℃低温解冻能够较好地保持猪肉品质。      

冻结温度对冷冻全麦馒头复蒸品质及组分性质的影响

分析不同冻结温度（–20、–40、–80℃）对不同全麦粉替代率（30%、50%、100%）冷冻全麦馒头复蒸品质及组分性质的影响,结果表明：冻结温度越低,冷冻速度越快,复蒸全麦馒头比容保持越好,对复蒸全麦馒头的质构品质影响越小。冻结温度对不同全麦粉替代率冷冻馒头的高径比无显著影响。–20℃下,不同全麦粉替代率冷冻馒头复蒸后硬度均显著高于新鲜馒头;–80℃下,复蒸后馒头硬度最接近新鲜馒头。冻结温度越低,冷冻全麦馒头淀粉的糊化焓值越低,100%全麦馒头淀粉糊化特性指标值越接近新鲜馒头;–40℃下,30%和50%全麦馒头淀粉糊化特性指标值与新鲜馒头更接近。较低的冻结温度下冷冻馒头中面筋蛋白的可萃取率较低,面筋蛋白二级结构破坏较小。冻结温度越低,全麦馒头内部的微观结构受损越小,复蒸后,其品质越接近新鲜馒头。综上,较低的冻结温度有利于保持全麦馒头较好的品质。     

Effects of freezing and frozen storage on the microstructure and texture of ewe's milk cheese

Semi-hard ewe's milk cheeses, frozen immediately after manufacture either slowly at –35 °C or rapidly at –80 °C and stored at –20 °C for 4 months were studied for microstructural and textural characteristics during subsequent ripening. Two control groups were used to establish the effect of freezing: the fresh unfrozen cheese and cheese thawed immediately after freezing. Freezing proper did not result in any marked changes in the textural parameters of the cheeses, but considerable changes were found in slowly frozen cheeses after 4 months of frozen storage. Shear strength values were lower in all frozen and stored cheeses, particularly in cheese samples frozen slowly compared to those in the unfrozen control batch. This parameter and firmness values were significantly lower in both slowly and rapidly frozen cheeses at the completion of ripening. Ripening tended to offset differences in elasticity, noticeable in the cheeses during the first 30 days of ripening. Light microscopy and electron microscopy revealed small cracks and ruptures in the cheeses which could not be observed by the naked eye. More extensive damage to the cheese microstructure was found in slowly frozen cheese samples stored frozen for 4 months.     

冻结方式对油条品质特性的影响

探究冻结方式对油条水分分布及品质特性的影响。采用液氮浸渍冻结(liquid nitrogen freeze, LF)、螺旋隧道冻结(spiral tunnel freeze, SF)及低温冰箱冻结(refrigerator freeze, RF)3种方式分别对油条进行冻结,测定冻结后油条水分含量、T_2弛豫时间、复炸后油条的色泽及比容、质构特性和感官品质。冻结方式对油条水分含量有显著影响(P<0.05),对L~*值、a~*值、色差△E有极显著影响(P<0.01);LF和SF处理油条内瓤结合水含量极显著高于RF(P<0.01),自由水含量显著低于RF(P<0.05);LF处理油条组织水分迁移最少,复炸后比容最大,表皮色泽、组织酥软性较好,组织孔隙较均匀,质构特性较优,最接近新鲜油条感官品质。液氮冻结处理油条品质较优,有望成为工业生产油条的新型冻结技术,为速冻油条生产提供了科学参考。