荔枝果汁冷冻浓缩结晶速率的研究

研究荔枝果汁冷冻浓缩过程中冷媒温度、果汁可溶性固形物含量对冰晶尺寸大小和冰晶生长速率的影响,以及溶液主体的搅拌速度及溶液的黏度对冰晶生长速率的影响.结果表明:冷冻浓缩初期,果汁冰晶尺寸增长速率较大,是控制果汁冰晶尺寸的关键阶段;冷媒温度越低、可溶性固形物含量越高,冰晶的生长速率越快,但冷媒温度越低,冰晶的最大尺寸越小;果汁主体的搅拌速度越大、果汁主体黏度越低,果汁冰晶生长速率越快.     

西瓜果汁冷冻浓缩结晶速率的研究

研究了西瓜果汁冷冻浓缩过程中冷媒温度、溶液可溶性固形物含量对晶体尺寸大小的影响,并且也研究了冷媒温度、溶液可溶性固形物含量、溶液主体的搅拌速度以及溶液的粘度对晶体生长速率的影响.结果表明,冷冻浓缩初期,晶体尺寸增长速率较大,是控制晶体尺寸的关键阶段.冷媒温度越低、可溶性固形物含量越高,冰晶的生长速率越快,但冷媒温度越低,冰晶的最大尺寸越小.另外,溶液主体的搅拌速度越大、溶液主体粘度越低,晶体生长速率越快.     

生姜在不同低温条件下的冻结规律及品质变化

对子姜在不同低温条件下的冻结曲线进行了测定,分析了以空气作为冷冻介质时子姜片的冻结规律,探讨了漂烫处理、冻结速度对产品质地的影响。实验结果表明,冷冻温度在-40℃以下可达到速冻要求;冻结前漂烫处理造成冰点上升,但在-40℃以下冻结时通过最大冰晶生成带的时间没有明显变化。     

干冰冻结对大黄鱼冻藏期间冰晶及品质的影响

目的:考察冻结方式及冻藏温度对大黄鱼贮藏过程中品质的影响。方法:采用干冰冻结和-40℃空气冻结新鲜大黄鱼鱼片至中心温度-18℃,然后分别置于-40,-18℃冰柜贮藏。测定大黄鱼冻结后和冻藏过程中冻结曲线、冰晶形态、pH值、挥发性盐基氮、K值、Ca²⁺-ATP酶活性、总巯基、羰基、蛋白降解、质构特性等理化指标。结果:干冰冻结通过最大冰晶生成带的时间为40 min,是-40℃空气冻结的1/6,干冰冻结鱼肉样品初始冰晶横截面积和当量直径分别为(96.12±1.61)μm²和(11.06±1.43)μm,显著低于空气冻结的鱼肉样品。结论:冻藏温度对鱼肉肌原纤维蛋白的影响要大于冻结温度，且冻藏温度越低，鱼肉肌原纤维蛋白降解程度越低。干冰冻结后-40℃贮藏有利于保持大黄鱼的鲜度和品质稳定性。     

液氮喷雾速冻及梯度解冻在荔枝品质保鲜上的优势

为探究荔枝的冻融特性,确定其适宜的冻融方式,该研究通过液氮喷雾速冻(-40℃/-60℃/-80℃/-100℃)和梯度解冻(-20℃/0℃/5℃/4℃/25℃)对荔枝冻融特性和品质的影响,并以传统冰柜冻结、浸渍冷冻、室温解冻为对比.结果表明:在-20～-100℃范围内,温度越低,穿过最大冰晶生成带时间越短,对冻结荔枝的保...     

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。     

速冻食品的冰晶形态及辅助冻结方法研究进展

文章简述了食品速冻技术以及不同冻结速度下形成的冰晶形态及观测冰晶的方法,综述了压力辅助冻结、电场辅助冻结以及磁场辅助冻结等技术在近几年的研究进展。直接法能直接观察到冻结过程形成的冰晶,而间接法则是通过观察冻结后冰晶在食品内部留下的间隙来分析冰晶特征。压力辅助冻结能提高过冷度,在压力释放时水分瞬间冻结,使形成的冰晶细小且分布均匀;电场辅助冻结能降低成核温度促使形成更小尺寸的冰晶;磁场辅助冻结能增强氢键抑制冰晶的生长,3种辅助冻结方式有利于提高冷冻食品的品质,具有良好的应用前景。     

西瓜汁冷冻浓缩工艺条件的优化

以西瓜汁为试验材料,探究在冷冻浓缩中,冷媒温度和刮刀转速对冷冻浓缩结晶强度和冰晶纯度的影响。结果表明:冷媒温度必须与果汁冰点达到一定的温度差才能产生冰晶,较理想的冷媒温度范围为-15～-19℃;选择60～105 r/min的刮刀转速,可以获得较多的冰晶,还可以减少果汁的损失。     

赣南脐橙果汁脱苦工艺及对糖、VC和有机酸的影响

研究硅酸镁、大孔径树脂、β-环糊精对赣南脐橙果汁的脱苦工艺条件,并用国标法探讨各种脱苦条件对橙汁中糖、VC、有机酸的变化影响。结果表明,用硅酸镁脱苦时,其较佳的工艺条件为:活化温度120℃,吸附剂用量1.0%,吸附时间1h,吸附温度20℃,此时脱苦率可达64%,而橙汁中的糖、VC、有机酸损失率分别达到11%、4%、61%;用大孔径树脂脱苦时,较好的树脂型号是HP-20,它的较佳工艺条件为:树脂用量1.0%、吸附时间14h、吸附温度20℃时,脱苦率达73%,此时橙汁中的糖、VC、有机酸损失率分别为5%、1%、7%左右;用β-环糊精脱苦时,得到较佳的工艺条件为β-环糊精用量0.6%、包埋温度20℃、包埋时间60min,此时脱苦率达52%,而橙汁中的糖、VC、有机酸损失很少。可为赣南脐橙果汁生产和产品质量监控提供操作参考指导。     

壳聚糖对菠萝汁澄清效果的研究

果汁加工的关键技术是果汁的澄清技术。本实验研究了壳聚糖澄清菠萝汁的工艺参数及条件:通过单因素实验研究壳聚糖用量、澄清时间、果汁温度等对菠萝汁澄清效果的影响,选出较合适的工艺参数;然后又通过正交实验对壳聚糖澄清菠萝汁的工艺条件进行优化。实验结果表明:在壳聚糖添加量为0.7g/L、温度35℃、澄清60min的条件下,菠萝汁澄清透明、色泽自然、香气浓郁。     

真空冷冻干燥过程对脱水胡萝卜品质的影响

为了满足我军对军用食品营养和品质的特殊需求,文中采用真空冷冻干燥技术对营养价值较高的胡萝卜进行加工,并对其冻干工艺参数进行研究。复水性能的好坏和颜色的变化是衡量冻干食品品质最重要的指标,文中研究了干燥过程中对复水性有较大影响的冷冻温度和加热温度。通过对胡萝卜冻干产品的冻干曲线,感官及复水率进行比较得出:冷冻过程决定冻干物料中的冰晶形成速度和大小,胡萝卜所需冷冻温度为—40℃左右,时间大约为2h;加热过程决定冻干物料中冰晶的升华,加热板温度设置为—20℃30min、0℃3h、20℃2 h、50℃3h4个梯度,所得产品品质最佳。     

荔枝冻结规律探讨及速冻加工技术

果皮褐变、裂果和汁液流失多是目前荔枝速冻生产的难题。本文通过测定荔枝在不同冻结温度下的冻结曲线及其结冰率和汁液流失率等情况 ,探讨荔枝冻结规律 ,为提高速冻荔枝商品质量提供参考。试验结果表明 :荔枝冻结过程 3个阶段不明显 ;冻结点约为 -3 0℃ ;最大冰晶生成带约在 - 3～ - 15℃。建议荔枝速冻采用去皮速冻工艺 ,这样既可避免果皮褐变问题 ,又可解决速冻与裂果的矛盾 ,减少汁液流失 ,提高速冻荔枝的商品价值 ,同时方便食用或加工其它制品     

Progressive freeze concentration of orange juice in a pilot plant falling film

In the present study the cryoconcentration of orange juice was investigated, using a pilot plant unit for cryconcentration of liquids using a cold surface. The evolution in time of the concentration of solids in the juice and in the ice was analyzed during the process. It was found that the concentration of solids in the juice showed a linear increase in time at a rate of 0.75 °Brix/h until a final concentration of 28.8 °Brix. The concentration of solutes in the ice showed an exponential increase.Industrial relevanceThe freeze concentration allows dewatering orange juice at temperatures below the water's freezing point, which allows obtaining products of better quality. The freeze concentration is a technology that allows eliminating water from the juices at temperatures below the water's freezing point, which allows obtaining products of better quality. This work has applied this technology to concentrate orange juice, obtaining promissory results.     

鸭梨的冻结特征及影响因素分析

运用自制热镀锡膜铜-康铜热电偶测温方法测定了鸭梨果实不同部位的冻结曲线,对鸭梨果实与汁液的冻结特点作了比较,并对冰点温度与部分品质参数的关系进行了探讨.试验结果表明,鸭梨果实的冻结曲线有3种形式,典型的形式具有过冷点、初始冰点、平衡冰点、终止冰点等关键特征点;果实不同部位的过冷点和冰点温度及其出现的时间顺序存在差异,越靠近果心,冻结速率越小,冰点温度越高;果实与果汁冻结特征的不同点在于果实有“特征小段”而果汁没有,且果汁较果实容易冻结;在一定范围内,鸭梨果实冰点温度与可溶性固形物含量呈极显著负相关,而与单果重、硬度相关性不显著.     

橙汁混浊的稳定性

研究成熟度、制汁工艺、酶处理、贮藏条件对橙汁混浊稳定性影响。结果表明：随着成熟度增加,橙汁混浊度呈上升趋势;胶体磨细微化可以增加果浆中果胶、可溶性果胶的溶出,果胶含量显著增加(P ＜ 0.05);果胶酯酶(PE)活性影响橙汁混浊稳定性,应完全钝化;采用果胶酶酶解会破坏橙汁浑浊稳定性,木瓜蛋白酶酶解橙汁浑浊度的影响不明显;4℃和15℃贮藏对橙汁混浊度的影响不显著(P ＞ 0.05),25℃贮藏对橙汁混浊度降低影响显著(P ＜ 0.05),常温贮藏不利于保持橙汁混浊稳定性。     

Fructooligosaccharide fortification of selected fruit juice beverages: Effect on the quality characteristics

Fortification of selected fruit juice beverages (Pineapple, Mango and Orange juice) with fructooligosaccharides (FOSs), a low calorie prebiotic has been discussed. Results indicated that sucrose which is usually used as a sweetener in fruit juice beverages can be partially substituted with FOS without significantly affecting the overall quality. The fruit juice beverages were evaluated for physicochemical and sensory changes during 6 months storage period at ambient (25 ± 2 °C) and refrigeration temperature (4 °C). The pH, total soluble solids, titratable acidity, and colour did not change significantly (P ≥ 0.05) during storage. The initial FOS content of pineapple, mango and orange juice beverages was 3.79, 3.45, and 3.62 g/100 mL. The FOS content of the fruit juice beverages stored at refrigeration temperature was 2.00-2.39 g/100 mL after 6 months of storage and 2.69-3.32, 1.65-2.08 and 0.38-0.58 g/100 mL at the second, fourth and sixth months of storage at ambient temperature respectively. The sensory analysis showed that the beverages were acceptable up to 4 and 6 months storage at ambient and refrigeration temperature respectively.     

Processing Conditions Affecting the Hygroscopic Behavior of Freeze-Dried Passion Fruit Juice

The effect of freezing rate, freeze drying temperature, added sucrose and anticaking agents, on the water sorption kinetics and hygroscopic equilibrium of freeze-dried passion fruit juice was investigated. Slow frozen samples (-45°C) were prepared in a Harris freezer and fast frozen ones were prepared in liquid nitrogen (- 195.8°C) and a dropping technique. A freeze-drier 12F Pilot Stokes was used to freeze-dry the samples, and the studies of hygroscopicity were conducted in an automatically controlled temperature and relative humidity chamber. The results show the significant influence of the rate of freezing and added sucrose on reducing product hygroscopicity.     

The growth of Propionibacterium cyclohexanicum in fruit juices and its survival following elevated temperature treatments

This study investigated the growth of Propionibacterium cyclohexanicum in orange juice over a temperature range from 4 to 40 degrees C and its ability to multiply in tomato, grapefruit, apple, pineapple and cranberry juices at 30 and 35 degrees C. Survival after 10 min exposure to 50, 60, 70, 80, 85, 90 and 95 degrees C in culture medium and in orange juice was also assessed. In orange juice the organism was able to multiply by 2 logs at temperatures from 4 to 35 degrees C and survived for up to 52 days. However, at 40 degrees C viable counts were reduced after 6 days and no viable cells isolated after 17 days. The optimum growth temperature in orange juice over 6 days was 25 degrees C but over 4 days it was 35 degrees C. The growth of P. cyclohexanicum was monitored in tomato, grapefruit, cranberry, pineapple and apple juices at 30 and 35 degrees C over 29 days. Cranberry, grapefruit and apple juice did not support the growth of P. cyclohexanicum. At 30 degrees C no viable cells were detected after 8 days in cranberry juice or after 22 days in grapefruit juice while at 35 degrees C no viable cells were detected after 5 and 15 days, respectively. However, in apple juice, although a 5 log reduction occurred, viable cells could be detected after 29 days. P. cyclohexanicum was able to multiply in both tomato and pineapple juices. In tomato juice, there was a 2 log increase in viable counts after 8 days at 30 degrees C but no increase at 35 degrees C, while in pineapple juice there was a 1 log increase in numbers over 29 days with no significant difference between numbers of viable cells present at 30 and 35 degrees C. The organism survived at 50 degrees C for 10 min in culture medium without a significant loss of viability while similar treatment at 60, 70 and 80 degrees C resulted in approximately a 3-4 log reduction, with no viable cells detected after treatment at 85 or 90 or 95 degrees C but, when pre-treated at intermediate temperatures before exposure to higher temperatures, some cells survived. However, in orange juice a proportion of cells survived at 95 degrees C for 10 min without pre-treatment and there was no significant difference between numbers surviving with and without pre-treatment. The results from this study demonstrate that P. cyclohexanicum is able to grow in a number of juices, other than orange juice, and able to survive a number of high temperature procedures. Therefore, if initially present in the raw materials P. cyclohexanicum might survive the pasteurization procedures used in the fruit juice industry, contaminate and consequently spoil the final product.     

Estimation of the freezing point of concentrated fruit juices for application in freeze concentration

In freeze concentration operations the fluids remain at temperatures below 0 °C. For a good study of this concentration operation is very important to know the values of freezing point. The aim of this work was to establish a model that predicts the freezing point of fruit juices at various concentrations within the range of interest for freeze concentration (10-40 °Brix). The model proposed relates the freezing point of a juice with the concentrations of main sugars present in the juice: sucrose, glucose and fructose. The freezing point of apple juice, pear juice and peach juice was determined experimentally at various concentrations, and experimental results were well correlated with model calculations.     

菠萝果酒酵母筛选及发酵性能测试

从不同成熟度的菠萝皮中分离酵母菌,通过一级筛选,得到45株产香和产酒较好的菌株,再通过杜氏管法筛选得到发酵速度较快的12株产香和产酒较优良的优势菌,三级筛选是将这12株菌接种到菠萝汁发酵液中,筛选出一株适合菠萝汁发酵的产酒和产香性能较优的菌株。并对该菌株的温度、pH值、初始糖度、SO2及酒精度耐受性进行了测试。结果表明,35℃以上的温度条件下酵母菌酒精产率下降,30℃产酒率最高;pH5.0酵母菌酒精达到最大;初糖浓度超过25°Be就对酵母菌产生抑制;SO2添加量为60mg/L时,酒精产率提高,产酒率随着添加量继续增加而减小;发酵液中酒精体积分数达到5%时,酵母菌的生长受到抑制,当达到8%,抑制效果加剧,超过11%以后,基本达到酵母菌的耐受极限。