Nonenzymatic Browning in Apple Juice Concentrate during Storage

Rate of browning in Red Delicious and Granny Smith apple juice concentrates during storage was investigated. Color development at 65°, 70° and 75°Brix and storage temperatures of 5°, 20° and 37°C were compared over 120 days. Color deterioration occured at a faster rate in Red Delicious. Reaction at different concentration and storage conditions was exponential, following an Arrhenius-type dependence with temperature. Activation energy for a solids content of 65 - 75°Brix ranged from 16.4 - 19.3 Kcal/mole. Influence of juice variety on activation energy was negligible. Water activity results are in general agreement with those reported by other investigators. A satisfactory correlation to predict commercial concentrate browning has been obtained. All other things being equal, thermal history is a critical factor to obtain a lighter color concentrate.     

Storage Stability of Orange Juice Concentrate Packaged Aseptically

Orange juice concentrates were packaged aseptically by a “Dole” aseptic canning machine using 6 oz metal cans. The final juice products (11°, 34°, 44°, 58° Brix) were stored between ?18° and 36°C and tested periodically for nonenzymatic browning, ascorbic acid destruction, furfural and sensory changes. Nonenzymatic browning, the main deterioration phenomena in these products, was satisfactorily retarded at 12°C or lower. Ascorbic acid destruction rate constant was dependent on temperatures between 5 and 25°C, and was affected by degree of juice concentration. Furfural accumulation in juice was higher than that in 58° Brix concentrate. Orange juice concentrate of 58° Brix did not show flavor changes after storage at 5°C or 12°C for 17 or 10 months, respectively, when evaluated after reconstitution to 11° Brix.     

Effect of Storage Temperature on the Stability of Aseptically Packaged Concentrated Orange Juice and Concentrated Orange Drink

Commercial orange drink concentrate and two orange juice concentrates were aseptically packed in flexible bags and stored at 4°, 15°, 22°, and 30°C for 6 months. Ascorbic acid, nonenzymatic browning and sensory quality were measured monthly. Sensory characteristics for drink concentrate deteriorated after 3 and 4 months at 30°C and 22°C, respectively. Juice concentrates were unacceptable after 2 and 5 months at 30°C and 22°C, respectively. Drink concentrate ascorbic acid loss was greater than juice concentrates at 4°, 15°, and 22°C. Changes in nonenzymatic browning as measured by Hunter color and by absorbance at 420 nm were similar to changes in other containers. The quality of refrigerated aseptic drink (15°C) and juice (4°C) was similar to frozen concentrates (?18°C).     

Influence of Water Activity on the Nonenzymatic Browning of Apple Juice Concentrate during Storage

Highly concentrated clarified apple juice was kept in storage at 37°C over a period of 100 days. The soluble solids content ranged from 65–90.5°Brix. Color development was monitored as O.D. at 420 nm. A maximum nonenzymatic browning rate (NEB_r) was found to occur between water activities 0.53 and 0.55. It was assumed that (1) dilution of reactants was responsible for the browning rate reduction at high water contents white (2) viscosity inhibited the color formation at low water activities. Viscosity ranged from 48 to 1.3 × 10⁶ cp and increased sharply when the commercial levels of concentration (70–72°Brix) were exceeded.     

苹果浓缩汁非酶褐变动力学及影响因素

通过检测苹果汁的色值(T440nm)、褐变指数(A420nnm)、氨基态氮、5- 羟甲基糠醛含量等指标研究加工过程对苹果汁褐变的影响以及在不同贮藏温度(5、20℃和37℃)下苹果浓缩汁(70.5°Brix)的非酶褐变速率。3 个贮藏温度下的苹果浓缩汁褐变速率均符合一级反应动力学模式,而且高温情况下褐变更明显。随着贮藏时间的延长,氨基态氮含量明显下降而5- 羟甲基糠醛含量上升,尤其是贮藏在37℃的苹果汁这一变化更明显。5- 羟甲基糠醛与果汁褐变效应呈指数关系,可以说明苹果汁在贮存中的褐变主因是发生美拉德反应,而且氨基态氮含量与果汁褐变效应的线性关系也验证了这一结论。在果汁的初始加工过程中,破碎、压榨、酶解、超滤、前巴氏杀菌等单元操作中美拉德反应并不明显;吸附操作可以去除果汁中的氨基态氮以及其他色素物质;而其他操作过程如浓缩和后巴氏杀菌则促进了美拉德反应,导致果汁氨基态氮含量明显下降。     

Heat Induced Browning of Clarified Apple Juice at High Temperatures

A procedure to determine deterioration reaction kinetics of fluid foods at elevated temperatures is described. With this method the nonenzymatic browning (NEB) measured as O.D. at 420 nm of Red Delicious (RD) and Granny Smith (GS) apple juices was examined. Color development at 15°, 30°, 50°, and 70° Brix and temperatures ranging from 90–108°C were compared over 60 min. Results indicated an apparent first order reaction rate depending on temperature, apple juice composition and soluble solids. Browning occurred at a more rapid rate in GS juice. NEB reaction rate was shown to depend critically on the total amino acid content. Temperature dependence followed the Arrenhius equation and the activation energy (E_a) ranged from 22.0–24.8 Kcal/mole.     

Kinetics of haze formation and factors influencing the development of haze in clarified apple juice

The rate of haze formation in commercial clarified apple juice stored at 4, 25 and 37°C was monitored over a 16 to 35-week storage period. Changes in turbidity, tannin content and browning index were evaluated. The juice appeared virtually clear and had very little colloidal particles during the initial stages of storage. After 24 weeks, an increase in turbidity of 2.32 NTU was observed for juice samples stored at 37°C. An increase of 0.58 and 0.95 NTU was observed for samples stored at 25 and 4°C, respectively. There was a general decrease in tannin content and an increase in browning index with storage; this effect was most pronounced for samples stored at 37°C. The rate of haze formation and tannin depletion in juice samples followed first-order reaction kinetics. Light and headspace did not affect haze formation. NaCl and CaCl₂ increased haze development while sucrose (up to 60%), urea (0.5 M), and EDTA (up to 0.01 M) had little effect. Addition of sodium dodecyl sulfate retarded haze formation.     

Molecular Weight Cut-off of Ultrafiltration Membranes and the Quality and Stability of Apple Juice

The quality and stability of apple juice clarified using 10,000 (10K), 50K, 100K, and 500K daltons molecular weight cut-off (MWCO) hollow fiber membranes were examined . Ultrafiltered juice was tested for initial stability, starch presence, pH, total acidity, total solids, soluble solids, turbidity, browning, Hunter color, total phenols, and sensory attributes. Turbidity, browning, total phenols, and sensory color were different depending upon the MWCO used. Samples were stored at 18°C and 43°C for 6 months and evaluated monthly. At 18°C, there were no significant changes but initial differences due to membranes remained. At 43°C, the increase in turbidity, browning, and chroma, as well as the decrease in lightness and hue with time, were significant. Reaction rates were all the same independent of the MWCO except for chroma.     

Influence of Storage on the Composition of Clarified Apple Juice Concentrate

The effect of storage on apple juice concentrate was determined by following changes in composition during a period of 111 days at 37°C. Results showed that storage caused an 87% loss in the total free amino acids, which was mostly due to decreases in glutamic acid, asparagine and aspartic acid. The forml titration method was inadequate for determining the amino compounds involved in Maillard-type reactions. Sucrose was hydrolyzed under these conditions at a rate corresponding to a fist order process. The reducing sugars increased at a rate determined by the inversion of sucrose; no consumption attributable to browning reaction was detected. Reduction of organic acids was 9% while apparent phenolic compounds increased from 0.149 to 0.215 g/100g. A maximum accumulation of HMF was observed after 100 days of storage.     

浓缩苹果汁酶促褐变及其控制

酶促褐变是引起苹果浓缩汁色值降低、品质劣变的主要原因之一 ,本文介绍了浓缩苹果汁酶促褐变的三个必要生化条件 :酚类物质、多酚氧化酶 (PPO)和氧气 ,并综述了浓缩苹果汁生产中酶促褐变的控制方法 ,如加热钝化酶、调节pH值、添加酶或底物的抑制剂、使用膜技术、添加漆酶等 ,均能有效控制浓缩苹果汁的酶促褐变 ,提高果汁的品质     

Physical-Chemical Characteristics of Partially Clarified Guava Juice and Concentrate

Partially clarified guava juice concentrate was prepared from single strength guava puree (5.5°Brix) by treatment with pectinase (2 hr at 50°C), extraction of juice with a rack-and-cloth press, and vacuum concentration to 23°Brix. The concentrate had the following characteristics: density, 1.10; pH, 3.16; total acids, 4.67%; ash, 1.51%; moisture, 72.4%; ascorbic acid, 867 mg%; viscosity, 4.4 cp; and CIE L* 39.2, CIE a* 10.33, CIE b* 27.11.     

Non-enzymatic browning of peach juice concentrate during storage

The effect of storage temperature and soluble solids concentration (Brix) on non-enzymatic browning of peach juice concentrate was studied by measuring absorbance at a 420-nm wavelength. The light absorbance of 70°Brix concentrate stored at 3 and 37°C was measured. Comparing the results with literature data for other fruit juices stored at 37°C, it was found that PJC browning rate is noticeably higher. Samples stored at 3, 15 and 30°C in the range of 12°Brix to 89°Brix followed a browning kinetics that can be satisfactorily fitted by means of a parabolic model. The maximum browning rates were found at high solids concentration. Lowering the storage temperature provoked those maximum to shift towards lower concentrations, probably due to the viscosity effect on reacting ions mobility. The browning rate followed an Arrhenius type of dependence upon temperature. It was found that PJC stored at 3°C underwent almost no colour changes, which suggests that it is a good storage option instead of the −20°C adopted by some manufacturers.     

Nonenzymatic Browning in Pear Juice Concentrate at Elevated Temperatures

The effect of temperature and soluble solids (°Brix) on nonenzymatic browning in pear juice concentrate was determined by following absorbance at 420 nm (A₄₂₀) over the temperature range of 50–80°C. Browning could be modeled as a zero order rate process with rates of 22.2 × 10⁻⁴ (45.2 °Brix), 36.9 × 10⁻⁴ (55.4 °Brix), 53.5 × 10⁻⁴ (65.1 °Brix) and 107 × 10⁻⁴ (72.5 °Brix) A₄₂₀· min⁻¹ at 80°C. Temperature dependence was described by the Arrhenius relationship with an average activation energy of 21.9 kcal · mole⁻¹. Formol titration indicated a 20% loss of amino acids during heating 4.4 hr at 80°C and no loss of carbohydrates was observed after any heating period.     

Effect of Ultrafiltration Combined with High-Pressure Processing on Safety and Quality Features of Fresh Apple Juice

Ultrafiltration (UF, 0.05 μm) with a ceramic membrane was combined with high-pressure processing (HPP) at 500 MPa/6 min and high-temperature short time (HTST) at 110 °C/8.6 s to process fresh apple juice. The aim of this study was to compare the effect of UF + HPP and UF + HTST on quality features of fresh apple juice and analyze the quality changes of the juice treated by UF + HPP and stored during 60 days at 4 °C. Applying UF, total plate count (TPC) and yeasts and molds (Y&M) significantly decreased by 0.29 and 0.28 log cycle, total phenols and ascorbic acid decreased by 33.50 and 26.52 %, and antioxidant capacity, using the DPPH and FRAP assay, significantly decreased by 26.40 and 25.37 %. Meanwhile, the juice clarity was 99.75?±?0.07 % and seven aroma compounds were changed. TPC and Y&M in juices treated by UF + HPP and UF + HTST were <1 log cycle. When compared to the juice treated by UF + HTST, the juice treated by UF + HPP showed lower browning degree and higher total phenols and clarity, and retained seven main volatile aroma compounds. Fresh apple juice processed by UF + HPP was microbiologically safe (TPC <1.8 log cycles and Y&M <1 log cycle) during 60 days of storage at 4 °C. The first-order model was a suitable model for all quality parameters of refrigerated fresh apple juice; however, rate constant k of first-order model was between ?0.0157 and 0.0350, showing the quality features of the refrigerated juice was stable.     

Enzymatic Browning Inhibition in Cloudy Apple Juice by Electrodialysis

Cloudy apple juice (pH 3.8) was acidified to pH 2.7, at 16–24°C and at a constant current density of 40 mA/cm², in an electrodialysis (ED) unit composed of an AB electrocell with three compartments, a bipolar membrane (Neosepta BP-1) and two ion-exchange membranes (anion- and cation-exchange). The treatment inhibited 81% of the activity of polyphenoloxidase and slowed enzymatic browning, indicated by a decrease in indice “a” and an increase in “L” on the Hunter Lab colorimeter scale. During ED treatments, conductivity and K⁺ concentration in apple juice decreased by, respectively, 21% and 86%.     

Effects of pH on Nonenzymic Browning during Storage in Apple Juice Concentrate Prepared from Bramley's Seedling Apples

In Bramley's Seedling, adjustment of juice pH affected darkening in apple juice concentrate during storage in the order pH 2.0 > pH 3.0 > pH 4.0. Darkening was also greater in model systems corresponding to juice at pH 3.0 compared with pH 4.0. The rapid darkening in concentrate of this cultivar appeared to be due to high rates of Maillard browning reactions rather than to other forms of nonenzymic browning.     

Changes in Muscadine Grape Juice Quality During Cold Stabilization and Storage of Bottled Juice

Muscadine grapes (Vitis rotundifolia, Michx.) of two cultivars (Noble and Carlos) were washed and extracted. The resulting juice was cold stabilized for 0, 7 and 60 days at 2°C, then treated, bottled, pasteurized and stored at 2°C and 24°C for 0, 4, 8, and 12 months. Carlos juice was lower in phenols and pH and higher in acidity than Noble. The high total anthocyanins and phenols in the Noble juice caused a significant loss in pigment during cold stabilization. Dilution of juice with 40% water and adjustment of the sugars was beneficial to flavor and color of Carlos, yet 40% dilution was too high for Noble juice. Treatment of either juice with CaCO₃ increased pH and decreased acidity. During 12 months storage, the Carlos juice became darker due to browning, while the Noble juice became lighter by losing pigment, especially at 24°C.     

Color and Cloud Stabilization in Cloudy Apple Juice by Steam Heating During Crushing

Steam heating of crushed apples in the range 65–70°C for 15 to 20 sec controlled enzymatic browning and effectively stabilized cloudiness. Particles in fresh pressed cloudy apple juice were 3 mm but after 15 min of centrifugation at 4200 × g almost all particles had a diameter of 1 mm, and cloud could be considered stable. Median and modal diameters were virtually coincident, suggesting a symmetrical distribution. The specific surface area of the cloudy juice particles was 50 mm²/g and no agglomeration occurred.     

Optimization and Modeling of Apple Juice Cross-flow Microfiltration with a Ceramic Membrane

The performance of a 0.2 μm ceramic membrane for clarification of depectinized apple juice was studied. The results showed that the flux was higher at high feed velocities (14.6 m/seC) and high temperatures (50°C), and the transmembrane pressure was a positive factor only at high temperatures. The juice flux at optimal conditions was between 400–500 kg/hr.m². Filtration of juice with pectin resulted in flux decreases of 40–50% compared to deoectinized juice. Periodic back-flushing during processing at optimal conditions, i.e., high temperature, high feed velocity and low pressure, did not significantly increase the juice flux.     

Production of Apple Juice by Single Pass Metallic Membrane Ultrafiltration

A new process utilizing single pass metallic membrane ultrafiltration (UF) was developed to produce apple juice. Pureed whole apples were treated with cellulase and pectinase at 50°C for 2 hr, resulting in a 60% decrease in viscosity. To obtain clarified juice, enzyme treated puree was pumped through a single-pass, tubular membrane system consisting of a metallic oxide membrane formed-in-place on the porous structure of sintered stainless steel tubes. Juice yields of 80–85% were obtained with a single pass, and gas chromatographic profiles of ultrafiltered juice were nearly identical to that of the original apple puree. Permeabilities and sugar rejection characteristics of the UF system were dependent on tube diameter.