Modelling of heat transfer in a climbing-film evaporator: Part II

The equation developed theoretically in part I for the liquid zone is validated from experimental data obtained with a pilot size single tube glass climbing-film evaporator.From experiments with the feed entering at the boiling temperature the heat transfer coefficient in the boiling zone is calculated.The validity of the proposed model is demonstrated for sucrose solutions of different concentrations and for tomato juice.     

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.     

DILUTION AND SOLIDS ADULTERATION OF APPLE JUICE

The adulteration of apple juice with pear juice and corn drived syrups has been practiced in many countries. The sorbitol/sucrose ratios and the sorbitol/total sugar ratios were determined for the juices of 14 apple varieties and 3 pear varieties. A multivariate normal test was applied to develop an equation for the detection of apple juice adulteration with sugar solutions or pear juice. Adulteration of apple juice with more than 10% sugar solution or pear juice were detectable with this method.     

Engineering factors in the production of concentrated fruit juices 1. Fluid physical properties of orange juices

This study presents the essential physical properties (boiling-point rise, viscosity, density, specific heat) of orange juices, necessary for the optimization of processing units for concentrated orange juices.
When these physical properties were correlated with the sucrose content of juice, expressed as degrees Brix, in the range 10–65° Brix and compared with those of aqueous sucrose solutions, significant differences were observed in respect of viscosity, specific heat and elevation of boiling point.     

Effect of ultrafiltration on concentrated apple juice colour and turbidity

Colour and turbidity of conventional bentonite-gelatin clarified apple juice was compared with 30,000–50,000 and 100,000DA hollow fibre ultrafiltered apple juice, with and without pectinolytic enzyme treatment. Results indicated that objective quality of ultrafiltered apple juice compared favourably with conventionally clarified apple juice over 30 weeks of storage at 37.5°C. However, treatment with pectinolytic enzymes before ultrafiltration increased both the initial colour and the browning rate. No significant differences were found in the values of the transmission haze after storage.     

Sensory Characteristics of Apple Juice Evaluated by Consumer and Trained Panels

ABSTRACT: To identify sensory characteristics of unclarified apple juice and to compare unclarified and clarified types, 140 consumers and 10 trained panelists evaluated 16 commercial apple juice samples (4 clarified and 12 unclarified). Unclarified and clarified juices were clearly separated by the first principal component (PC1), whose main factor was fresh, green, and sweet aroma. It was difficult to predict consumer preference by regression models using trained panel preference and analytical attributes. Mapping consumers' overall preferences on a sensory profile made by PC1 and PC2, the consumer panel preferred apple juice with moderately increased fresh and green aroma and thoroughly decreased sour and astringent.     

Sugar composition of apple juices

Fifty-one samples from 12 geographic growing regions of Turkey and 3 varieties common for production of apple juice concentrate were processed to apple juice and analysed for their sugar composition. Enzymatic analyses was used to determine soluble sugars of apple juice. Glucose, fructose, sucrose, total sugar concentrations (g/l) and total soluble solids (%) of apple juices were ranged, respectively, as follows: 9.30-32.2, 66.10-96.00, 8.5-55.10, 110.90-164.40, 11.80-18.60. Cultivar significantly influenced the content of all the sugar analysed. Significant differences in fructose and sucrose concentrations have also been found between some growing areas.     

Compressibility and density of select liquid and solid foods under pressures up to 700 MPa

Compressibility and density were measured at 25 °C and pressures up to 700 MPa with a variable volume piezometer for sucrose solutions (2.5–50%), soy protein solutions (2.5–10%), soybean oil, chicken fat, clarified butter, chicken breast, ham, cheddar cheese, carrot, guacamole, apple juice, and honey. Compressibility of sucrose and soy protein solutions decreased as a function of concentration (p < 0.01). For equal mass concentrations, protein solutions were less compressible (p < 0.04) than sucrose solutions at pressures greater than 200 MPa. Relative to water, fats showed high compressibility to 100 MPa, similar compressibility from 100 to 300 MPa, and less compressibility from 300 to 700 MPa. Chicken breast, ham, cheddar cheese, carrot and guacamole showed relatively large compressibility from 0.1 to 100 MPa. Honey showed the smallest volume decrease over 700 MPa. Density of all samples increased with pressure, at a decreasing rate.     

Temperature dependence of water activity in aqueous solutions of sucrose

A comprehensive experimental data analysis was performed to evaluate the effect of temperature on the water activity coefficient and selected excess thermodynamic functions for aqueous solutions of sucrose. A four-suffix Margules equation with temperature-dependent parameters was used to fit thermodynamic data such as the vapor pressure, boiling point, osmotic coefficient, freezing point, sucrose solubility, heat of dilution and specific heat of solution. The proposed equation gives an adequate representation of the available literature data on sucrose solutions for temperatures from −15 to +150 °C and sucrose concentrations up to 98% wt. The isotherms of water activity coefficient exhibit a characteristic minimum at about 96% wt. sucrose which is then followed by a dramatic increase to values well exceeding 1, as it was suggested before by some theoretical models [Starzak, M., & Mathlouthi, M. (2002). Water activity in concentrated sucrose solutions and its consequences for the availability of water in the film of syrup surrounding the sugar crystal. Zuckerindustrie, 127, 175–185; Van Hook, A. (1987). The thermodynamic activity of concentrated sugar solutions. Zuckerindustrie, 112, 597–600]. The effect of temperature on water activity, almost negligible for dilute solutions, was found significant for very concentrated solutions (above 80% wt. sucrose). The new water activity equation should find numerous applications in the food technology and sugar industry.     

Prebiotic effect of fermented cashew apple (Anacardium occidentale L) juice

Leuconostc mesenteroides B-512F and L. mesenteroides B-742 were cultivated in clarified cashew apple juice to produce prebiotic oligosaccharides. Yeast extract (20 g/L); K₂HPO₄ (g/L) and sucrose (50 g/L) were added to the juice to promote the microbial growth and dextransucrase production. Initial pH was adjusted to 6.5 with H₃PO₄. Fermentations were carried out at 30 °C and 150 rpm for 24 h. The prebiotic effect of the fermented cashew apple juice, containing oligosaccharides, was evaluated through the Lactobacillus johnsonii B-2178 growth. L. johnsonii was incubated for 48 h using fermented cashew apple juice as substrate. Lactobacillus growth was compared to the microbial growth in non-fermented juice and in MRS broth. L. johnsonii growth in the fermented cashew apple juice was threefolds the observed growth in the non-fermented juice.     

苹果汁复合澄清法和壳聚糖澄清法的优化研究

研究了果胶酶复合澄清法和壳聚糖澄清法对苹果汁的澄清效果,确定了最佳工艺条件,采用优化的澄清方法,苹果汁的透光率可达98％以上。论文对不同成熟期的苹果制汁的澄清工艺进行了调整,还探讨了澄清工艺对苹果汁主要成分的影响。     

膜技术在苹果汁加工中的应用

应用平板式超滤技术对苹果浊汁进行了过滤澄清和除菌。研究了巴式杀菌酶解或未酶解的苹果浊汁、未巴式杀菌未酶解的苹果浊汁、温度对膜通量的影响,超滤组件形式、操作参数对3种不同预处理料液的滤液质量的影响及反渗透系统的浓缩效果。结果表明:平板式超滤膜通量能满足工业需求且大于管式超滤膜,操作温度宜为50℃,当加水倍数0.09倍时,可使浓缩倍数达到20倍。苹果汁超滤液的透光率在97%以上、色值在50%以上、浊度指标小于0.3,pH值、总酸、糖度、氨基态氮等却未发生明显的变化。苹果汁超滤液质量指标和耐热细菌检查结果比较表明,平板式超滤可代替对苹果汁巴式杀菌及酶解。反渗透系统对苹果汁超滤液进行浓缩,浓缩倍数为2～2.3倍,糖截留率为100%。     

富γ-氨基丁酸乳酸菌发酵功能饮料的研制

以糙米汁、黄豆芽汁和牛奶酶解液为培养基生产的富含γ-氨基丁酸乳酸菌发酵液为原料,进行功能饮料研制。优化得到的GABA功能饮料配方为:乳酸菌发酵液5%、枸杞汁40%、苹果汁40%、复合甜味剂3%、柠檬酸0.10%。经0.25%(w/v)的明胶和0.25%(w/v)的单宁澄清后,饮料于室温放置60d未出现浑浊和沉淀等现象。模糊综合评价表明,GABA功能饮料符合消费者的饮用要求。     

Concentration of apple and pear juices in a multi-plate freeze concentrator

In this article we will examine the process for concentration of apple and pear juices as well as concentration of sugar solutions modelling pear juice (simulation fluid) using a descending film multi-plate freeze concentrator. It has been determined in advance the freezing point of those fluids in the working concentration and temperature intervals. In addition, different parameters were studied to allow tracking of the process of freeze concentration, such as ice accumulation, variation of the content of soluble solids in the solution and in the ice removed, ice production and energy consumption. The apple and pear juices tested showed similar behaviour, while the mixture of sugars used for simulation showed better behaviour, due perhaps to the absence of foam in the process and to the quicker formation of ice. It has been obtained concentrations of 30.2 and 30.8 °Bx with the apple and pear juices, respectively, and up to 32.7 °Bx with the simulation fluid.Industrial relevanceThe clarified juices usually are concentrated on an evaporation stage. In this stage the juice is subjected to high temperatures that cause undesirable reactions, such as non enzymatic browning and destruction of nutritive compounds. The freeze concentration is a technology that allows eliminating water from the juices at temperatures below the water’s freezing point, what allows obtaining products of better quality. In this work has been applied this technology to concentrate apple and pear juices, obtaining promissory results.     

Determination of Oxygen Solubility in Liquid Foods Using a Dissolved Oxygen Electrode

A rapid method for determining oxygen solubility in foods was introduced. Fructose, glucose, sucrose, orange juice, apple juice, grape juice, grapefruit juice, lemonade, and tomato juice had similar oxygen solubilities at comparable °Brix readings. The equation: In [ppm O₂] = 2.63 ? 0.0179 (°Brix) ? 0.0190 (°C) estimated to within 5% the oxygen solubility of sugar solutions and fruit juices at temperatures between 4°C and 40°C. At likely food concentrations, citric acid, ascorbic acid, and NaCl reduced oxygen solubility by less than 10%. Tests for component interactions were also conducted. There was no measurable synergism or antagonism between fructose, glucose, and sucrose with or without organic acids.     

树脂法生产无色浓缩苹果汁的初步研究

采用吸附树脂除去苹果汁中的色素,脱去果汁的颜色,同时用离子交换树脂除去苹果汁中的氨基酸,从而基本控制了果汁的褐变,保持了果汁高的色值。     

On the production of glucose and fructose syrups from cashew apple juice derivatives

The cashew crop is an important agro-economic activity in many equatorial areas, although less than 10% of the cashew apple production is exploited industrially. This work focuses on two aspects: obtaining food-grade syrups from cashew apple juice and studying fixed bed adsorption dynamics to separate fructose from glucose. Syrups obtained by concentrating clarified cashew apple juice under vacuum showed similar characteristics to a reference food-grade syrup, with a higher content in fructose, which may contribute to a higher sweetening power with less caloric intake. Adsorption equilibrium studies were performed with synthetic solutions of fructose and glucose by frontal analysis under the concentration range found in the syrups (10-120 g/L) at 30, 40 and 60 °C, using the cation exchange resin Dowex MTO 99Ca. Fructose was more strongly adsorbed than glucose, with measured selectivities ranging from 1.50 to 2.25. Resistance to mass transfer was significant and thought to be due to resin crosslinkage. Glucose and fructose breakthrough curves using cashew apple syrup as feed were practically identical to those measured with synthetic solutions, which leads us to believe that high-fructose syrups may be readily obtained by using current continuous chromatographic units, such as SMB.     

Impact of Ionizing Radiation and Thermal Treatments on Furan Levels in Fruit Juice

The formation of furan in freshly prepared apple and orange juices as affected by ionizing radiation and thermal treatments was studied using a newly developed solid‐phase microextraction method coupled with gas chromatography‐mass spectrometry (GC‐MS). Results show that furan levels increased linearly as radiation dose increased from 0 to 5 kGy. Irradiation induced more furan in apple juice than in orange juice. During post‐irradiation storage at 4 °C, furan levels increased in both apple and orange juices, particularly in the 1st 3 d. On the other hand, irradiation degraded deuterated furan (d₄‐furan) spiked in water and fruit juices. The rate of degradation as a function of radiation dose was the highest in water and the lowest in orange juice. Submerging the juice samples in boiling water for 5 min induced higher amounts of furan in orange juice than in apple juice, but autoclaving (121 °C, 25 min) resulted in more furan formation in apple juice than in orange juice. Results reported here suggest that both ionizing radiation and thermal treatments induce furan formation in fruit juices.     

Flavour losses in apple juice manufacture

Flavour losses occurring in apple juice manufacture were investigated by gas chromatography and sensory analysis in two factories A and B using different technologies and equipment. Samples were taken at different intervals during the processing season from the raw material, the pressed juice, the clarified and filtered juice, the apple juice concentrate and the apple flavour concentrate produced in plant A. The chromatograms of the pressed juice showed changes in volatile composition as compared to the raw material: the number of components was slightly reduced, although some new components could be detected, probably owing to enzymatic processes. The enzyme preparation and method used for clarification did not affect volatile composition to the extent expected. The volatile abstracting effect of vacuum evaporation for flavour recovery as performed in plant A seems to be compensated by flavour formation from precursors during pectolytic enzyme treatment. The greatest losses in both factories were encountered during evaporation concentration of the clarified and filtered juice. Chromatographically established volatile composition was distinctly different in the concentrated apple juice samples from the two plants, however, this difference was perceived by the sensory test panel only towards the end of the processing season. The apple flavour concentrate contained less than half of the volatile components present in the raw material. The gas chromatograms of the flavour concentrates produced at different times did not reflect the fluctuations observed in the volatile composition of the raw material and the intermediate and end products, however, sensory tests showed the samples from the beginning of the processing season to be superior to those from its end.     

Thermophysical Properties of Clarified Apple Juice as a Function of Concentration and Temperature

Effect of concentration and temperature on thermophysical properties of clarified apple juice was studied. Density, viscosity, specific heat, and thermal conductivity were measured at different conditions, ranging from 20 to 90^oC and 12 to 70^oBrix. Experimental data were related to the corresponding properties of water and compared with the behavior of sugar solutions. The results obtained were used to derive mathematical models and correlations for predicting these properties as a function of both concentration and temperature.