Passion Fruit Juice Concentration by Ultrafiltration and Evaporation

Passion fruit juice was pretreated with pectinase, centrifugation, and pasteurization. The resulting juice was processed by Ultrafiltration (UF) to 20°Brix. The UF permeate was concentrated by evaporation to 70°Brix and combined with the UF retentate to form the final concentrated product at 40°Brix. The pretreatments caused approximately 20% flavor losses, but accomplished more than 50% flux increases. The UF recovered many important flavor constituents, and improved the rate of evaporation. The final concentrated product contained more than 30% of juice flavor. Results of sensory evaluation indicated that flavor of the reconstituted juice was inferior to fresh juice, but the two juices were not significantly different in overall acceptance.     

Spray evaporation of liquid foods

‘Spray evaporation’ based on the principle of adiabatic humidification was examined as an evaporation technique for the concentration of two types of representative liquid foods, namely, fruit juice and milk. The concentration of apple juice could be increased from 10.0 to 13.0 °Brix by this technique without application of heat utilizing the humidity potential to an extent of 89%. Employing heated process air during processing increased the amount of water evaporation owing to increased saturation humidity level, enabling higher concentrations to be achieved in apple juice (48 °Brix), reconstituted milk (29 °Brix) and single toned milk (22 °Brix). Feed flow rate had an inverse effect on the final concentration under otherwise similar conditions. Evaporative cooling associated with spray evaporation actually delivered the concentrate at a relatively lower temperature. By manipulating the operating conditions, humidity potential could be utilized to the extent of 55% with heated process air. The spray evaporation technique seemed to have a good potential for the concentration of liquid foods.     

The effect of pre-treatment on the anthocyanin and flavonol content of black currant juice (Ribes nigrum L.) in concentration by reverse osmosis

Reverse osmosis process for the concentration of black currant juice was carried using AFC-99 tubular membrane at 30 °C and 45 bar. The contents of selected flavonols and anthocyanins were analyzed after centrifugation; enzyme treatment by Panzym Super E and by Rohapect berry followed by centrifugation; and ultrafiltration black currant juices and juice concentrates. The total soluble solid (TSS) content of the juices increased from the initial 17.6–17.9 °Brix to 24–24.8 °Brix in the case of the centrifuged juice in the concentration process. Similarly, it increased from 14.5–15.5 °Brix to 23.1–23.4 °Brix for the Panzym Super E treated juice, and from 16.1–16.9 °Brix to 22.5–23.1 °Brix for the Rohapect berry treated black currant juices. The ultrafiltered juice had the lowest initial TSS content between 14.1 and 14.9 °Brix and it increased to 22.1–23.1 °Brix. The average permeate fluxes during the concentration process were 7.3 L m⁻² h⁻¹ for the centrifuged juice, 11.9 L m⁻² h⁻¹ for the Panzym Super E treated juice, 9.2 and 13.1 L m⁻² h⁻¹ for the Rohapect berry treated and ultrafiltered juice, respectively. Analysis indicated that the enzymatic treatment resulted in the increase of anthocyanin and flavonol content of the juices. The centrifugation process decreased the amount of anthocyanins and flavonols to some extent. The juice clarified by ultrafiltration had significantly lower concentrations of anthocyanins and flavonols, while the juices treated by Panzym Super E had the highest levels of these flavonoids. This study recommends enzymatic pre-treatment by Panzym Super E, since it improves the permeate flux in reverse osmosis during the concentration process, and results in a juice concentrates highest in anthocyanins and flavonols.     

A new integrated membrane process for the production of concentrated blood orange juice: Effect on bioactive compounds and antioxidant activity

The production of high quality concentrated blood orange juice according to a new integrated membrane process, alternative to thermal evaporation, was evaluated in terms of preservation of the total antioxidant activity and of the bioactive antioxidant components of the juice (ascorbic acid, anthocyanins, hydroxycinnamic acids, flavanones). The process was based on the initial clarification of freshly squeezed juice by ultrafiltration (UF); the clarified juice was successively concentrated by two consecutive processes: first reverse osmosis (RO), used as a pre-concentration technique (up to 25–30 °Bx), then osmotic distillation (OD), up to a final concentration of about 60 °Bx. During the concentration process of the liquid fractions, a slight decrease of total antioxidant activity (TAA) was observed (−15%), which was due to the partial degradation of ascorbic acid (ca. −15%) and anthocyanins (ca. −20%). Nevertheless, this degradation was lower than that observed with thermally concentrated juice: TAA, −26%; ascorbic acid, −30%, anthocyanins, −36%. The possibility to operate at room temperature allowed reduction in thermal damage and energy consumption. On the basis of these results, the integrated membrane process may be proposed as a valuable alternative to obtain high quality concentrated juice, as the final product still showed a very high antioxidant activity and a very high amount of natural bioactive components, showing a brilliant red colour and a pleasant aroma, characteristics that were significantly lost during traditional thermal evaporation.     

Effect of the re-use of the osmotic solution on the stability of osmodehydro-refrigerated grapefruit

Osmotic dehydration (OD) of grapefruit (55°Brix sucrose solution, 30 °C) was carried out to obtain ˜75 g water/100 g sample in the final product. Although the grapefruit was replaced each time, the osmotic solution (OS) was reused for five OD cycles, with or without pasteurization. The samples obtained in cycles 1, 3 and 5, were stored at 10 °C. Changes in °Brix, water content, water activity, pH, total acidity, ascorbic acid content, cation concentration, respiration rate and total microbial counts at different storage times were analyzed and compared to fresh-cut grapefruit stored under the same conditions. During OD, a partial loss of the natural soluble substances present in the fruit was observed. In terms of the dehydration level reached by the fruit, it is possible to reuse the OS in up to 5 OD, without any reconcentration treatment. Nevertheless, it is advisable to pasteurize the OS before each cycle in order to obtain a product with a shelf-life of between 7 and 12 days in refrigeration, depending on the number of cycles.     

Effect of high or low molecular weight of components of feed on transmembrane flux during forward osmosis

The possible mechanism of water transport from feed to osmotic agent side during forward osmosis in situation when feed contains high or low molecular weight compounds and their combination has been presented. The orientation of membrane was found to influence the transmembrane flux. When the feed contains mixture of low and high molecular weight compounds mode I (feed towards the support layer) was found to result in lower flux values as compared to Mode II (feed towards active layer) due to significant external concentration polarization. Forward osmosis resulted in the concentration of betalains content in beetroot juice and anthocyanin content in grape juice from 50.92 mg/L to 2.91 g/L (57.1 fold) and from 104.85 mg/L to 715.6 mg/L (6.8 fold), respectively. Total soluble solids in case of beetroot, grape and pineapple juice were found to increase from 2.3 to 52 °Brix, from 8.0 to 54.6 °Brix from 4.4 to 54 °Brix, respectively.     

Evaluation of hybrid pressure-driven and osmotically-driven membrane process for non-thermal production of apple juice concentrate

This study investigates the potential of hybrid membrane processes including microfiltration (MF), ultrafiltration (UF) and forward osmosis (FO) for non-thermal concentration of apple juice. The process performance and characteristics (physicochemical properties, nutritional and aroma components and microbiological quality) of apple juice were studied. The clarity of apple juice was significantly promoted as pore size of membrane reduced. MF and UF can also ensure microbiological safety in pre-treated apple juice. According to its efficiency of filtration as well as performance of simultaneous clarification and cold-sterilization, 0.22 μm MF membrane was identified as the optimal membrane for the pre-treatment. The pre-treated apple juice can be concentrated up to 65°Brix by subsequent single stage FO. FO retained nutritional and volatile compounds of apple juice while significant reductions were found in the juice concentrated by vacuum evaporation. Hybrid MF-FO can be a promising non-thermal technology to produce apple juice concentrate with high quality.     

Response surface methodological study on HMF and fluorescent accumulation in red and white grape juices and concentrates

White and red grape juices and their concentrates were subjected to thermal treatments at different temperatures ranging from 50 to 70 °C at different times. 5-Hydroxymethylfurfural (5-HMF) and fluorescence relative index (FLRI) were measured. Response surface methodology (RSM) was applied to determine the effect of temperature and time on the HMF and FLRI formation at the different Brix (bx) degrees. An increase in temperature (from 50 to 70 °C) and time (from 12 to 192 h) for 15°, 45° and 65° Brix degrees was associated with an increase in HMF and FLRI development of white and red grape juices. HMF formation was higher in white grape juice and concentrates than in red ones. Optimum conditions were confirmed and these fitted the experimental data well. Thus, regression equations can be used to estimate HMF and FLRI values at various Brix degrees for white and red grape juices and concentrates.     

Degradation behaviour of methamidophos and chlorpyrifos in apple juice treated with pulsed electric fields

Apple juice (13 °Brix) spiked with methamidophos and chlorpyrifos (2–3 mg/l of each compound) was treated by pulsed electric fields (PEF), and pesticide residues were quantified by gas chromatography with flame photometric detection (GC-FPD). Results showed that electric field strength (8–20 kV/cm) and pulse number (6–26 pulses) have significant effects on the degradation of methamidophos and chlorpyrifos. PEF treatment is effective for the degradation of methamidophos and chlorpyrifos residues in apple juice, and chlorpyrifos is much more labile to PEF than methamidophos. An increase in either pulse number or electric field strength could speed the degradation of methamidophos and chlorpyrifos, and the kinetics equations and related parameters quantitatively characterized the degradation behavior of the pesticides. The exponential model better fits the experimental data for all treatments than the linear model.     

Influence of Refractance Window evaporation on quality of juices from small fruits

A new type of evaporator (Refractance Window^® (RW) evaporator) has been developed that operates at atmospheric conditions and uses thermal energy from hot water to concentrate foods. The influence of product temperature and dissolved solids on vitamin C in blueberry juice and color of cranberry juice was evaluated in this new evaporation method in comparison with conventional falling film multi-effect evaporators. During RW evaporation, vitamin C in blueberry juice was reduced by 32% and 48% with product temperatures at 55.5 and 59.0 °C, respectively. Concentration of the same juice from single strength to 65°Brix in an industrial falling film evaporator operating at 68 °C reduced vitamin C content by 70.1%. The color of cranberry juice, defined by the hue angle, was not significantly different between the concentrates from the RW and falling film evaporation methods. Further investigation is needed for complete insights into the mechanism for vitamin C loss in RW evaporation.     

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.     

STUDIES ON THE CLARIFICATION AND CONCENTRATION OF BEETROOT JUICE

Studies on the clarification and subsequent concentration of beetroot juice were carried out. The juice was clarified using enzyme, fining agent (FA), centrifugation and ultrafiltration (UF), while reverse osmosis (RO) and thermovacuum evaporation were used for concentration. The juices were concentrated to 23–25°Brix, and the physicochemical characteristics were evaluated at different stages of processing on the basis of clarity, permeate flux, °Brix, acidity, sugars, pigments and CIE L*, a* and b* (lightness, redness and yellowness, respectively) color values. Average permeate flux during RO was found to be highest (36.08 liters per square meter of membrane per hour [L/m²h]) in the case of enzyme treatment, followed by UF juice, and lowest (30.33 L/m ² h) in the case of enzyme and FA treatments. In terms of clarity of concentrate, the highest value was obtained for juices pretreated with enzyme and UF. Pigment content and L*, a* and b* values showed that pigment loss was higher in the case of RO‐concentrated juice pretreated with enzyme. Comparative evaluation in terms of clarity, color and chemical parameters showed that concentrates obtained using both techniques were comparable.     

Rapid determination of soluble solids content and acidity of Black currant (Ribes nigrum L.) juice by mid-infrared spectroscopy performed in series

Black currant juice quality is a prime importance for growers and industrials. Such quality relies on the empirical and destructive measurements of soluble solids content and acidity. These measurements are time consuming and expensive. The serial analysis of the Black currant juice quality could allow the valuation of the product for the producer and saving of time for the manufacturer. Our objective was to develop predictive models of soluble solids content and acidity based on the mid-infrared spectroscopy performed in series.We showed that infrared spectroscopy allowed determining efficiently the quality of Black currant juices and that such technique could be performed in series. Soluble solids content were determined with a R²-value of 0.97 and an RMSECV of 1.14°Brix for a range of values comprised between 12.9°Brix and 16.42°Brix. Acidity content was determined with a R²-value of 0.96 and an RMSECV of 2.61 g L⁻¹ in a large range of values comprised between 14.87 g L⁻¹ and 36.27 g L⁻¹.These results allow asserting that the soluble solids content and the acidity of Black currant juice can be accurately determined by infrared spectroscopy. Furthermore, a large number of measures can be performed in series, what opens perspectives for a practical application.     

Recovery of bioactive compounds in kiwifruit juice by ultrafiltration

Food quality is not only a function of nutritional values but also of the presence of bioactive compounds exerting a positive effects on human health.This research was undertaken to study the influence of the ultrafiltration (UF) on the composition of some bioactive compounds of the kiwifruit juice in order to develop a natural product which can be used to fortify foods and beverages. At the same time the effect of transmembrane pressure (TMP) and temperature on the permeate flux was also investigated in order to identify the optimal operating conditions for the processing of the juice. An optimal TMP value occurred at 0.6–0.65 bar in different conditions of cross flow velocities. Steady-state permeate fluxes increased linearly with temperature in the range 20–30 °C.The kiwifruit juice was clarified in optimal operating conditions, according to the batch concentration mode, up to a final volume reduction factor (VRF) of 2.76.The analyses of flux decay according to fouling models reported in the literature revealed that the formation of a cake layer covering the entire surface of the membrane is the main cause of the membrane fouling.Most bioactive compounds of the depectinised kiwifruit juice were recovered in the clarified fraction of the UF process. The rejection of the UF membrane towards total phenolics was 13.5%. The recovery of glutamic, folic, ascorbic and citric acids, in the clarified juice, with respect to the initial feed, was dependent on the final VRF of the UF process: an increase of the VRF determines an increase of these compounds in the clarified juice. The rejections of the UF membrane towards these compounds were in the range 0–4.3%.

Industrial relevance

Among different substances contained in the kiwifruit a primary role, in the safeguard of the human health, is carried out by some bioactive compounds such as ascorbic, folic, citric, glutamic acids and polyphenols.This research was undertaken to study the influence of ultrafiltration on the composition of these compounds in order to develop a natural product which can be used to fortify foods and beverages.     

Kinetic and prediction studies of ascorbic acid degradation in normal and concentrate local lemon juice during storage

Kinetics of the loss of ascorbic acid (AA) in local lemon juice of 9° and 50° Brix stored at 25, 35, and 45 °C for 4 months have been investigated. The results indicate that increases of concentrations and temperatures increase the rate of AA degradation. The calculated values of activation energies (E^≠) and frequency factors (A) at different Brix imply that the concentration of juice does not change the mechanism of degradation. Thermodynamic functions of activation (ΔG^≠, ΔH^≠, ΔS^≠ and K^≠) have been determined and considered briefly. A direct equation for estimation of the shelf life of stored juice with respect to first-order losses of AA, at any specific temperature and degradation ratio, has been derived and programmed successfully.     

Effect of PEF and heat pasteurization on the physical-chemical characteristics of blended orange and carrot juice

The effect of different Pulsed Electric Fields (PEF) intensities (25 kV/cm and 280 μs, P1; and 25 kV/cm and 330 μs, P2) and conventional HTST treatment (98 °C, 21 s, T) on quality characteristics (pH, °Brix, total acidity, turbidity, hydroxymethylfurfural (HMF), color, microbial flora, pectinmethylesterase (PME) activity, and sensory analysis) of blended orange and carrot juice were investigated. HMF, L* (luminosity) and C* (saturation or chrome) color parameters did not vary with any of the treatments. Total acidity and turbidity were slightly higher after HTST treatment. Sensory characteristics of the PEF-treated juice were more similar to the untreated juice than the HTST-pasteurized juice. Nevertheless, heat pasteurization (98 °C, 21 s) was more efficient in inactivating microbial flora and PME and preventing the growth of microbial flora and reactivation of PME at 2 and 12 °C for 10 weeks. However, the shelf-life of the PEF-treated juice was established as 4 weeks at 2 °C. This appears to be a reasonable shelf-life for this type of foodstuff.     

Volatile profile of dehydrated cherry tomato: Influences of osmotic pre-treatment and microwave power

Vegetable flavour is a quality characteristic for consumer acceptability. Sun and air are traditionally used for drying tomatoes; however, the optimal combination of techniques such as osmotic dehydration or microwave-assisted air-drying could lead to high quality self-stable products. The aim of this paper was to study the influence of different process variables on the volatile profile of dehydrated cherry tomato halves. The analysed variables were: air-drying temperature (40 and 55 °C), microwave power (0 and 1 W/g) and previous osmotic dehydration with a 55 Brix binary sucrose solution at 30 °C for 120 min (OD1) or ternary solution of 27.5% sucrose + 10% NaCl (w/w) at 40 °C for 60 min (OD2). Twenty major volatile compounds were identified in fresh tomatoes. Among them, 2-isobutylthiazole and 6-methyl-5-hepten-2-one stand out as impact volatile compounds. Dehydration modified the volatile profile, mainly due to the changes induced in some typical fresh-like tomato compounds, but also due to the generation of five new compounds: 1-butanol, 2-methyl-2-butenal, 3-hydroxy-2-butanone, furfural, acetonitrile, related to Maillard reactions, and the catabolism of carotenoids and polyunsaturated fatty acids. Principal component analysis showed the possibility of obtaining dried cherry tomatoes with different volatile profiles, depending on drying conditions.     

Variable selection for partial least squares analysis of soluble solids content in watermelon using near-infrared diffuse transmission technique

This work is focused on the variable selection in building the partial least squares (PLS) regression model of soluble solids content (SSC) that is used to evaluate quality grading of watermelon. The spectra were obtained by the near infrared (NIR) spectrometer with the device designed for on-line quality grading of watermelon and the spectra of 680–950 nm were adopted to analysis. The variable selection was based on Monte-Carlo uninformative variable elimination (MC-UVE) and genetic algorithm (GA). In comparison of the performances of the full-spectra (680–950 nm) PLS regression model and the feature wavelengths PLS regression model showed that the MC-UVE–GA–PLS model with baseline offset correction combined multiplicative scatter correction (MSC) pretreatment was much better and 14 variables in total were selected. The correlation coefficients between the predicted and actual SSC were 0.885 and 0.845, the root mean square errors were 0.562 °Brix and 0.574 °Brix for calibration and prediction set, respectively. This work can make a great contribution to the research of on-line quality grading for watermelon nondestructively.     

Kinetics of amino acid loss in carrot juice concentrate during storage

The loss of total amino acid (TAA) and individual leading amino acids (LAAs) in 20, 40, 60 Brix carrot juice concentrate (CJC) stored at −18 C, 0, 25 and 37 °C is investigated. The LAAs are histidine, proline, serine, aspartic acid, glutamic acid, arginine and alanine in CJC, their summation account for about 86 percent in TAA. As the storage temperature increase and the storage time extend, the loss of TAA and LAAs concentration is significantly increased (P<0.05). The higher the storage temperature such as 37 °C is, the greater the loss of TAA and LAAs concentration is. After 6 month storage, the TAA loss percentage is 72.85, 70.13 and 78.32 in 20, 40, 60 Brix CJC at 37 °C, respectively. The loss kinetics of TAA concentration is well fitted using the first-order reaction and the zero-order reaction. As compared to the zero-order reaction, the first-order reaction provides a perfect fit with better model performance parameters, which included accuracy factor (Af), bias factor (Bf), the sum of the squares of the differences of the natural logarithm of observed and predicted values (SS), and root mean square error (RMSE). Similarly, the loss kinetics of LAAs also followed the first-order reaction. After 6 months storage at 37 °C, the loss percentage of histidine, proline, serine, aspartic acid, glutamic acid, arginine and alanine is 95.46, 93.52, 78.05, 73.14, 70.35, 67.14 and 62.72 in 60 Brix CJC, respectively, the histidine is the most reactive one of LAAs in the study.