Effect of freezing rate on quality parameters of freeze dried soursop fruit pulp

The effect of freezing rate on the final moisture and ascorbic acid content, water solubility, wettability and color of freeze dried soursop fruit pulp treated with maltodextrin was studied. Different size ice crystals derived from distinct freezing rates origins diversity of product specific surface area that influence both water desorption and water dissolution, but in opposite manners. After a constant drying time of 6 h the moisture content of the dried samples was in the range of 8.68–13.09% being higher for higher values of freezing rate. An inverse linear dependence between initial freezing rate and final water solubility (85.75–81.51%) of freeze dried samples was also found. Faster freezing rates also affected the wetting time (0.36–1.26 min) because they produced decreasing in pore size and simultaneously increasing in capillary tortuosity of the final micro-structure of the dried samples. Freeze-dried powders were much brighter in color compared to the maltodextrin treated pulp. Among the freeze dried samples, those prepared with higher freezing rates were lighter in color.     

Behaviour of aroma volatiles during the evaporative concentration of some tropical fruit juices and pulps

The dynamics of aroma separation from some tropical fruit juices and pulps was studied using a thin film evaporator. In the case of mango (Mangifera indica Linn, Alphonso and Totapuri varieties) and guava (Psidium guajava Linn) pulps, 90% of each of the volatile fraction, esters, carbonyls and alcohols, was removed at 30–35% evaporation of the water in a single pass. In the case of pineapple (Ananas sativa Schult F) juice, 90% separation of esters and carbonyls required about 80% and 47% evaporation, respectively. However, the behaviour of alcohols in pineapple juice was found to be similar to that of mango and guava. Mango pulp from Alphonso and Totapuri varieties on 60% evaporation showed a loss in oxygenated terpenes of 80% and 63%, respectively, while guava pulp lost about 58% oxygenated terpenes on 60% concentration. The dynamics of the total aroma volatiles separation from the fruit juices and pulps showed that, in a single pass evaporation, 85–90% volatiles were removed at a juice evaporation degree of 60% water, while the same extent of aroma removal occurred at 32–35% total evaporation by multiple pass.     

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.     

Calculation method for designing a multi-plate freeze-concentrator for concentration of fruit juices

The aim of this work is to establish a calculation method for designing and sizing of equipment for film freeze-concentration of fruit juices. The various steps are outlined of an algorithm that uses the characteristics of the juice as inputs.The calculation method assumes that the amount of fruit juice, its concentration (^°Brix), and its sugar composition (% of fructose, glucose and sucrose) are known. Using pre-set (constant) values for the flow of concentrated juice and for the heat flow, the algorithm predicts the values of the main unknowns: the concentration of impurities in the ice, the concentration of sugars in the final concentrate, the heat-exchange surface needed, the amount of ice obtained, and the duration of the concentration step.Using this calculation method, one can estimate the size of the equipment and its operational costs, which can be used to analyse the economic viability compared to alternative processes.     

一种连续冷冻浓缩装置及其应用分析

介绍了一种基于界面渐进原理的新型连续式冷冻浓缩装置。该装置通过将制冷过程和浓缩过程有机结合,具有结构简单、调控性强、适用料液广、能源效率高等优点。初步分析表明该装置从料液中除去1t水的电能消耗低于5kW·h,在果蔬汁浓缩、海水淡化等领域均具较强的市场竞争力。     

冷冻处理对果蔬的影响及其应用

讨论了冷冻处理对果蔬中蛋白质、糖分、维生素等营养成分以及颜色、风味、微观结构等方面的影响，阐述了其在果蔬产业中，尤其是热敏类成分含量较高果品的榨汁、浓缩等工艺中的应用现状及前景，强调了冷冻处理在果蔬产业中的应用依然存在很大的挖掘空间。     

Freeze concentration of whey in a falling-film based pilot plant: Process and characterization

Falling-film freeze concentration is a technique for concentration of liquids by freezing the available water in the form of a layer of ice on a refrigerated surface. Processing at low temperatures keeps the organoleptic properties of the initial product. In this study the freeze concentration of whey was investigated as an technological alternative for the use of this byproduct of the dairy industry. Freeze concentration tests were carried out in pilot-scale equipment and the increase in soluble solids content of the whey and the amount and purity of the ice formed were analysed. Electrical conductivity, viscosity and freezing point of the concentrated whey were determined. The concentrate obtained had a solid concentration of up to 21.8 °Brix. The ice formed in the last stage of the freeze-concentration process had a lactose content of 11.3 g/L and protein content of 3.45%. The electrical conductivity of the ice formed increased exponentially to a value of 29.40 mS/cm. Freeze-concentrated whey of 10, 15, and 20 °Brix behaves as a Newtonian fluid in the temperature range of −4 °C-4 °C.     

国产三效板式蒸发器在浓缩果汁生产中的应用

介绍了国产三效板式蒸发器成功替代进口蒸发器及其在浓缩果汁生产中的应用     

Production of concentrated cherry and apricot juices by cryoconcentration technology

In this study, apricot and cherry juices were successfully cryoconcentrated. Two freezing temperatures −10 ± 1 °C, −20 ± 1 °C, and three cryoconcentration stages were studied. Freezing temperature did not show any affect on total dry matter content of the concentrated juices, as well as on their physico-chemical properties. At the same time, the cryoconcentration stage effect was highly significant on total dry matter content and juice qualities. Total dry matter of the apricot juice increased from 14.50 ± 1.12 g/100 g up to 35.50 ± 2.09 g/100 g in three cryoconcentration stages. Cherry juice total dry matter increased from 15.50 ± 1.26 g/100 g up to 45.50 ± 2.47 g/100 g. Concentrated juices had high aroma numbers and high content of ascorbic acid compared to the same juices obtained by the conventional method. The present study demonstrated that cryoconcentration as an environmentally friendly technology is a promising and highly effective food processing technique in the juice industry. Aroma number increased from 3.55 up to 8.38 and from 5.23 up to 15.75 for apricot and cherry juices, respectively. The juices obtained by cryoconcentration technology were compared to the same juices obtained by the conventional method of evaporation.     

Vacuum-assisted freeze concentration of sucrose solutions

Freeze concentration in a one-step configuration has emerged as an interesting alternative to conventional processes in terms of both the construction and operation of the equipment. For vacuum-assisted freeze concentration reported in this study, vacuum was used as the driving force to remove the concentrated solution from the ice matrix. By applying a vacuum (80 kPa), the efficiency of the freeze concentration was significantly improved over atmospheric conditions showing an evident advantage in terms of the process time (which was one-third of the time required for atmospheric treatments), and a higher recovery of solute, approximately 0.5 kg of sucrose obtained per 1 kg of initial sucrose compared to recovery values ranging from 0.16 to 0.3 kg/kg for atmospheric treatments. A better performance of vacuum-assisted freeze concentration may be attributed to the structure of the frozen phase which acted as a porous solid matrix allowing the flow of the concentrated solution.     

Behavior of functional compounds during freeze concentration of tofu whey

The liquid waste generated from tofu production, denominated as Tofu Whey (TW), contains important amounts of isoflavones that can be evaluated by various separation techniques. In this work TW was concentrated by falling-film freeze concentration from 1.9 to 15.5 °Brix, up to levels of 208 mg of isoflavones per 100 g solids. The levels of isoflavones, proteins, sugars, calcium and magnesium were determined both in the ice and in the concentrate obtained. It was found by rheological characterization that TW shows a Newtonian behavior at concentrations between 1.9 and 15.5 °Brix with freezing points of −0.6 to −2.7 °C.     

Bergamot: A source of natural antioxidants for functionalized fruit juices

Bergamot is a common Italian citrus fruit, cultivated almost exclusively to produce essential oils; the juice is considered a waste product, which represents a serious environmental and economic problem for the industries. The aim of this study was to re-evaluate bergamot juice through its chemical characterization and its use to enrich and fortify fruit juices. To investigate this, apples and apricots were used for the laboratory-scale production of fruit juice, following both the traditional industrial recipe and those with the addition of bergamot juice at 10% or 20%, together with or in order to replace the synthetic additives normally used in the industrial process (ascorbic acid and citric acid). The ascorbic acid content and the antioxidant activity were measured during the different steps of juice production and after storage at 37 °C for 15 days to evaluate juice shelf-life. Apricot and apple juices fortified with bergamot juice showed a significant increase in their antioxidant properties and a decreased reduction in ascorbic acid content after the typical production steps. All of the results obtained support the hypothesis that the addition of bergamot juice to juices preserves their ascorbic acid content from thermal degradation and contributes to enhance the antioxidant activity, ensuring a product much richer in antioxidants and ascorbic acid. A preliminary consumer test encouraged the production of bergamot fortified fruit juices. Finally, this is the first time that isorhoifolin and rutin have been detected in bergamot juice.     

State transitions and freeze concentration in trehalose-protein-cornstarch mixtures

State transitions of solutions of mixtures of trehalose, albumen, gelatin, and cornstarch were studied and state diagrams were established. Maximum freeze concentration was achieved by annealing of solutions at a temperature −1 °C. The onset temperatures of glass transitions of maximally freeze-concentrated solutes, , were lower and onset temperatures of ice melting, , were higher for mixtures of trehalose, proteins and cornstarch when compared with those of pure trehalose. Solute concentration in the maximally freeze-concentrated phase, , was 79% for trehalose, trehalose/albumin (1:1), and trehalose/cornstarch (1:1). The of trehalose/gelatin (1:1), and trehalose/cornstarch/gelatin (1:1:1) was 74% and 75%, respectively. The state diagrams established with experimental and predicted T_g values are useful for characterization of thermal phenomena and physical state of carbohydrate-protein-polysaccharide mixtures at various water contents.     

The correlation between freezing point and soluble solids of fruits

The freezing points of 11 breeds of fruits were measured using a HP34970A data collector and soluble solids were measured using a PR101 (0–45%) refractometer. The results show that there is a high negative correlation between soluble solids and freezing point. The mathematical model is Y(Freezing point)=0.146694–0.19555X. All the breeds have typical freezing curves. The freezing point of Ya pear is 0.26 °C lower than that of Ya pear juice. Grape freezing point is 1.2 °C lower than that of grape juice.     

Fast and reliable analyses of sulphite in fruit juices using a supramolecular amperometric detector encompassing in flow gas diffusion unit

A new compact system encompassing in flow gas diffusion unit and a wall-jet amperometric FIA detector, coated with a supramolecular porphyrin film, was specially designed as an alternative to the time-consuming Monier-Williams method, allowing fast, reproducible and accurate analyses of free sulphite species in fruit juices. In fact, a linear response between 0.64 and 6.4 ppm of sodium sulphite, LOD = 0.043 ppm, relative standard deviation of ±1.5% (n = 10) and analytical frequency of 85 analyses/h were obtained utilising optimised conditions. That superior analytical performance allows the precise evaluation of the amount of free sulphite present in foods, providing an important comparison between the standard addition and the standard injection methods. Although the first one is most frequently used, it was strongly influenced by matrix effects because of the unexpected reactivity of sulphite ions with the juice matrixes, leading to its partial consumption soon after addition. In contrast, the last method was not susceptible to matrix effects yielding accurate results, being more reliable for analytical purposes.     

Application of a commercial immunoassay to the direct determination of insecticide imidacloprid in fruit juices

An ELISA was used to directly determine residual imidacloprid in fruit juices. Imidacloprid could be determined by only diluting samples without any pre-treatments such as filtration, centrifugation, and clean-up procedures. The ELISA enabled imidacloprid to accurately determine down to about 5 μg/L in apple and grape juice samples and down to about 20 μg/L in orange juice sample. Recovery and precision of the ELISA were evaluated by spiking fruit juice samples with imidacloprid in the 10–400 μg/L ranges. Coefficients of variation were lower than 20% in all cases, and average recoveries were 94.2%, 113.2%, and 104.2% for apple, grape, and orange juice samples, respectively. No false positive results were found. The results obtained with the proposed ELISA well correlated with the reference HPLC for each fruit juice sample (r > 0.99).     

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。     

The initial freezing point temperature of beef rises with the rise in pH: A short communication

This study tested the hypothesis that the initial freezing point temperature of meat is affected by pH. Sixty four bovine M. longissimus thoracis et lumborum were classified into two ultimate pH groups: low (< 5.8) and high pH (> 6.2) and their cooling and freezing point temperatures were determined. The initial freezing temperatures for beef ranged from − 0.9 to − 1.5 °C (? = 0.6 °C) with the higher and lower temperatures associated with high and low ultimate pH respectively. There was a significant correlation (r = + 0.73, P < 0.01) between beef pH and freezing point temperature in the present study. The outcome of this study has implications for the meat industry where evidence of freezing (ice formation) in a shipment as a result of high pH meat could result in a container load of valuable chilled product being downgraded to a lower value frozen product.     

反渗透技术在果蔬汁浓缩中的应用研究

利用反渗透技术对几种果蔬汁（ 黄瓜、芹菜、胡萝卜、枸杞子、红杏） 的浓缩处理进行实验与分析。结果表明在一定条件下, 通过反渗透方法可对果胶含量低的果蔬汁直接进行浓缩处理, 并且浓宿倍数超过１０ 倍以上。而果胶含量较高的果汁则需要预先进行酶解脱胶后再进行浓缩。实验中发现果胶的含量直接影响浓缩的程度与效果。结果分析认为反渗透在果蔬汁的浓缩加工方面确实可行。还对各类果蔬汁的制取、脱胶、浓缩加工处理模式做了分析探讨。     

果汁冷冻浓缩中生物冰核的成冰作用及初步应用

介绍了冰核细菌促进成冰的机制,并结合国外有关报道和我们的研究结果,论述了冰核细菌在食品冷冻浓缩中导致冰晶形成的结构、冷冻效率、应用前的预处理及食用级冰核细菌在果汁中的应用情况,最后展望了未来的研究方向。