Total and Thermostable Pectinesterases in Citrus Juices

Grapefruits, tangerines and several orange cultivars were evaluated for total and thermostable pectinesterase (TS-PE) activity. Juices were extracted with a Fresh'n Squeeze^TM Multi Fruit Juicer. Variation in total pectinesterase (PE) and TS-PE was not significantly different between cultivars. No significant contribution by traditional quality control parameters (%pulp, °Brix, % acid, pH), to total PE or TS-PE was observed. Positive correlations were observed between TS-PE and total PE, when expressed on a pulp (0.669) or soluble solids (0.624) basis.     

Thermal Pasteurization Effects on Color of Red Grapefruit Juices

Changes in color due to thermal pasteurization of two cultivars of red grapefruit juice were studied. Juices were pasteurized at 91°C using a plate heat exchanger. Apparently, thermal pasteurization changed all three color parameters (CIE L*, a*, b*) in the juice, causing a slight color shift towards lighter and brighter. Thermal pasteurization especially affected CIE b* value and chroma in juice. The reflectance spectrum in the visible region (400 nm to 700 nm) clearly showed changes in spectral distribution of light reflected from juice after pasteurization. There were no changes (P>0.05) in major carotenoid pigments (β-carotene and lycopene) in the juices after pasteurization.     

High Pressure Inactivation Kinetics of Saccharomyces cerevisiae Ascospores in Orange and Apple Juices

High pressure inactivation kinetics (D and z values) of Saccharomyces cerevisiae ascospores were determined in fruit juices and a model juice buffer at pH 3.5 to 5.0. Approximately 0.5 to 1.0 × 10⁶ ascospores/mL were pressurized at 300 to 500 MPa in juice or buffer. D-values ranged from 8 sec to 10.8 min at 500 and 300 MPa, respectively. The range for z-values was 115 to 121 MPa. No differences (P≥0.05) in D (at constant pressure) or z-values among buffers or juices at any pH were determined, indicating little influence of pH in this range and absence of protective or detrimental effects of juice constituents.     

Portable, low-cost equipment for small-scale fruit juice processing

Simple, low-cost portable equipment to extract citrus juice, and pasteurize it and other fruit juices by passing through a coil of stainless steel tube in boiling water was designed, constructed and tested. Temperature reached was varied by altering the hydrostatic feed height, and the product was directly hot-bottled and capped. Pasteurization was microbiologically effective, and had little effect on ascorbic acid, furfural and colour of freshly prepared pineapple orange, Valencia orange and apple juices, and an orange squash drink, and only the expected changes occurred on storage at 21°C for periods up to 6 months, although with no indication of microbial activity. Taste panel ratings showed a loss of liking for treated orange juice, but not for apple. The equipment is suitable for improved utilization of crops by community technology in less-developed areas.     

Physicochemical Characteristics and Quality of Refrigerated Spanish Orange-Carrot Juices and Influence of Storage Conditions

ABSTRACT: The effects of the physicochemical and quality characteristics of various refrigerated mixed orange and carrot juices, and their changes with storage time and temperature were investigated. Density, dry extract, Brix values, acidity, turbidity, formol index, pectinmethylesterase, hydroxymethylfurfural, essential oils, ascorbic acid, and color varied with storage time and temperature. Some of the parameters could be used as indicators of quality loss or spoilage of the juices. The degradation of ascorbic acid corresponded to 1st-order kinetics. The shelf life of the juices was established at 4 °C and 50-d storage or at 10 °C and 32-d storage.     

蜜柑鲜汁与巴氏灭菌汁香气成分比较研究

采用顶空-固相微萃取法提取蜜柑鲜果汁与巴氏灭菌果汁的香气成分,用气相色谱-质谱进行分离鉴定,应用色谱峰面积归一化法测定各成分的相对含量。实验结果显示:鲜果汁与巴氏灭菌果汁分别鉴定出78和79个香气成分。蜜柑鲜汁中的主要香气成分是D-柠檬烯(69.82%)、芳樟醇(3.35%)、γ-松油烯(1.61%)、4-松油醇(1.01%)和α-松油醇(0.81%)等;灭菌后的蜜柑汁中的主要香气成分为D-柠檬烯(58.20%)、α-松油醇(8.02%)、γ-松油烯(1.65%)、4-蒈烯(1.29%)、β-松油醇(1.11%)。灭菌后,果汁原有的愉悦的香气成分如丁酸乙酯未检出;α-松油醇、癸醛的含量增加使果汁风味变劣;产生的二甲基硫醚、糠醛、p-乙烯基愈疮木酚也影响果汁品质。     

Effect on Orange Juice of Batch Pasteurization in an Improved Pilot-Scale Microwave Oven

ABSTRACT:  The effects on orange juice batch pasteurization in an improved pilot-scale microwave (MW) oven was evaluated by monitoring pectin methyl-esterase (PME) activity, color, carotenoid compounds and vitamin C content. Trials were performed on stirred orange juice heated at different temperatures (60, 70, 75, and 85 °C) during batch process. MW pilot plant allowed real-time temperature control of samples using proportional integrative derivative (PID) techniques based on the infrared thermography temperature read-out. The inactivation of heat sensitive fraction of PME, that verifies orange juice pasteurization, showed a  z -value of 22.1 °C. Carotenoid content, responsible for sensorial and nutritional quality in fresh juices, decreased by about 13% after MW pasteurization at 70 °C for 1 min. Total of 7 carotenoid compounds were quantified during MW heating: zeaxanthin and β-carotene content decreased by about 26%, while no differences ( P  < 0.05) were found for β-cryptoxanthin in the same trial. A slight decrease in vitamin C content was monitored after MW heating. Results showed that MW heating with a fine temperature control could result in promising stabilization treatments.     

Effect of pulp reduction and pasteurization on the release of aroma compounds in industrial orange juice

ABSTRACT:  Release of aroma compounds in orange juice according to pulp content and pasteurization was performed by headspace-solid phase microextraction (HS-SPME), HS-SPME-GC-olfactometry, and by the determination of partition coefficients of aroma compounds between the juice and the headspace. Orange juices with 12% and 6% pulp contents were collected from a processing line before and after pasteurization. HS-SPME revealed that the 6% pulp juice was the most affected by pasteurization, with an increase in the release of several aroma compounds that are generated by heat treatment (that is, α- and β-terpinéol) and a decrease in the release of compounds sensitive to pasteurization (that is, neral and geranial). Principal component analysis of olfactometric data allowed discriminating fresh and pasteurized juices, regardless of the pulp content. The determination of the gas/liquid partition coefficients by the phase ratio variation method was possible for 7 aroma compounds. For the most hydrophobic ones, the release of aroma compounds in fresh juices was higher in the 6% pulp juice than in the 12% pulp juice. However, in pasteurized juices, the difference between their partition coefficients was less marked. Potential interactions between cloud proteins and hydrophobic aroma compounds may explain this phenomenon.     

Thermal Stability of Ricin in Orange and Apple Juices

ABSTRACT: Ricin is a potent protein toxin that could be exploited for bioterrorism. Although ricin may be detoxified using heat, inactivation conditions in foods are not well characterized. Two brands of pulp-free orange juice and 2 brands of single-strength apple juice (one clarified and the other unclarified) containing 100 μg/mL added ricin were heated at 60 to 90 °C for up to 2 h. With increasing heating times and temperatures the heat-treated juices exhibited decreasing detectability of ricin by enzyme-linked immunosorbent assay (ELISA) and cytotoxicity to cultured cells. Z-values for ricin inactivation in orange juices were 14.4 ± 0.8 °C and 17 ± 4 °C using cytotoxicity assays, compared to 13.4 ± 1.5 °C and 14 ± 2 °C determined by ELISA. Although insignificant differences were apparent for z-values measured for the 2 orange juice brands, significant differences were found in the z-values for the 2 brands of apple juice. The z-values for ricin inactivation in the clarified and unclarified apple juices were 21 ± 4 °C and 9.5 ± 1.1 °C, determined by cytotoxicity assays, and 20 ± 2 °C and 11.6 ± 0.7 °C, respectively, using ELISA. Overall, there were no significant differences between results measured with ELISA and cytotoxicity assays. Ricin stability in orange juice and buffer was evaluated at 25 °C. Half-lives of 10 ± 3 d and 4.9 ± 0.4 d, respectively, indicated that active ricin in juice could reach consumers. These results indicate that ricin in apple and orange juices can remain toxic under some processing and product storage conditions. Practical Application: Ricin is a potent toxin that is abundant in castor beans and is present in the castor bean mash by-product after cold-press extraction of castor oil. U.S. Health and Human Services recognizes that ricin could be used for bioterrorism. This study reports the stability of ricin in apple and orange fruit juices at temperatures ranging from 60 to 90 °C (140 to 194 °F).     

Thermal Inactivation of Salmonella on Cantaloupes Using Hot Water

The inactivation of Salmonella on cantaloupes using hot water was investigated. Whole melons, inoculated with a cocktail of Salmonella isolates, were subjected to thermal treatments of various lengths in water at 65 °C, 75 °C, and 85 °C. Treatment with water at 85 °C for 60 and 90 s resulted in reductions of up to 4.7 log colony forming units (CFU) per square centimeter of rind. However, the rind of melons treated at 85 °C for 90 s were noticeably softer than the rind of melons treated for 60 s. Thermal penetration profiles were measured and computer simulations were conducted to verify the effect of hot water treatment conditions on the internal temperatures of cantaloupe melons. Experimental and simulation data indicated that the internal temperature of melons treated with hot water did not increase rapidly compared with the rind temperature. Regardless of the process temperature used, the temperature of the edible flesh, 10 mm from the surface of the rind, remained at least 40 °C cooler than the surface temperature of cantaloupe melons. These results demonstrate the utility of hot water for the inactivation of Salmonella on cantaloupes and provide a framework to producers of fresh‐cut melon for the potential use of hot water as an intervention treatment.     

Recovery of Limonoid Glucosides from Citrus Molasses

ABSTRACT: A method to recover multi-gram quantities of limonoid glucosides from citrus molasses using ion-exchange and styrene/divinylbenzene resins has been developed. A cation exchange resin is used to decolorize the molasses, while an anion exchanger is used to separate limonoid glucosides from other negatively charged compounds. Styrene/divinylbenzene resins are used to bind limonoid glucosides and remove water-soluble materials. The method affords approximately 5 grams of a water-soluble powder containing over 60% by weight limonoid glucosides per liter of molasses. An analysis of the efficiency of the method shows that less than 10% of the total limonoid glucosides are lost during recovery.     

Suitability of Bifidobacterium spp. and Lactobacillus plantarum as Probiotics Intended for Fruit Juices Containing Citrus Extracts

A strain of Lactobacillus plantarum and 4 strains of bifidobacteria were inoculated in apple juice and in a commercial beverage labeled as “red‐fruit juice,” containing citrus extracts as natural preservatives; the suitability of the probiotics was evaluated in relation to their resistance to 2 kinds of citrus extracts (biocitro and lemon extract), survival in juices at 4 and 37 °C, and inhibition of Zygosaccharomyces bailii. Cell count of L. plantarum and bifidobacteria over time was fitted through the Weibull equation, for the evaluation of the first reduction time (δ), death time, and microbiological shelf life (the break‐point was set to 7 log cfu/mL). Bifidobacterium animalis subsp. lactis experienced the highest δ‐value (23.21 d) and death time (96.59 d) in the red‐fruit juice at 4 °C, whereas L. plantarum was the most promising strain in apple juice at 37 °C. Biocitro and lemon extract did not exert a biocidal effect toward probiotics; moreover, the probiotics controlled the growth of Z. bailii and the combination of L. plantarum with 40 ppm of biocitro reduced the level of the yeast after 18 d by 2 log cfu/mL.     

Microbial, Enzymatic, and Chemical Changes During Storage of Fresh and Processed Orange Juice

Microbial, enzymatic, and chemical comparisons were made on orange juice stored at 4°C without pasteurization, with light pasteurization (66°C, 10 sec) directed at vegetative microorganisms, and with full pasteurization (90°C, 60 sec) directed at the heat stable isozyme of pectinesterase. Effects of oxygen-barrier and nonbarrier packaging were also examined. Oxygen-barrier packaging did not benefit unpasteurized juice. However, lightly and fully pasteurized juices in barrier cartons exhibited lower microbial counts, greater ascorbic acid retention, and apparent slowing of cloud loss by the third week of storage. During the first 22 days storage, microbial, cloud, sugar, and ascorbic acid values for lightly pasteurized juice were similar to those of juice receiving full pasteurization.     

柱前衍生- 气相色谱法同时测定不同柑橘汁中的糖和肌醇

为建立柱前衍生-气相色谱技术同时测定不同柑橘汁(宽皮柑橘、甜橙、柚子、柠檬和金柑)中3种肌醇(肌肌醇、鲨肌醇、手性肌醇)和3种可溶性糖(果糖、葡萄糖、蔗糖)的方法,以内标物(甲基-α-D-葡萄糖苷)定量,标准物质的保留时间定性。结果表明：在两个添加水平下,6种成分的平均回收率为98.1%～106.9%,相对标准偏差为0.6%～6.1%,检测限在0.29×10-3～0.41×10-3μg/L(RSN＝3)。本方法简便快速,结果准确可靠。     

高静压对桃汁的杀菌效果及动力学模型

为了描述及预测高静压对桃汁的杀菌效果,研究了压力300,400,500,600MPa条件下保压3,5,10,15,20,25min的高压处理对桃汁中菌落总数、霉菌、酵母数的影响,并对不同压力条件下的杀菌效果进行动力学分析。研究结果表明,压力越高,保压时间越长,杀菌效果越好。霉菌、酵母对压力较为敏感,500 MPa以上的压力即可将其完全杀灭。Weibull模型在压力300～600 MPa时具有很好的拟合性(相关系数R~2>0.9)。尺度参数b随压力增大而增大,形状参数n则随压力的增大而减小。     

Pasteurization of Fresh Orange Juice Using Low-Energy Pulsed Electrical Field

ABSTRACT: Using the hurdle approach, temperature, acidity, and number of pulses were varied to maximize microbial inactivation in orange juice. The effect of PEF combined with the addition of nisin, lysozyme, or a combination of both to orange juice was also investigated. Optimal conditions consisting of 20 pulses of an electric field of 80 kV/ cm, at pH 3.5, and a temperature of 44 °C with 100 U nisin/ml resulted in over a 6-log cycle reduction in the microbial population. The process was most influenced by a change in temperature (p < 0.0001). Following treatment, there was a 97.5% retention of vitamin C, along with a 92.7% reduction in pectinmethylesterase activity. The microbial shelf-life of the orange juice was also improved and determined to be at least 28 d when stored at 4 °C without aseptic packaging. Gas chromatography revealed no significant differences in aroma compounds before and after pulsing.     

High-Pressure Processing of Orange Juice: Kinetics of Pectinmethylesterase Inactivation

ABSTRACT: A kinetic study of pectinmethylesterase (PME) inactivation in orange juice was conducted. Juice samples were subjected to combinations of high pressure (400, 500, 600 MPa) and thermal (25, 37.5, 50 °C) treatments for various time periods. PME inactivation followed a first-order kinetic model with a residual activity of pressure-resistant enzyme remaining. Calculated D-values ranged from 4.6 min to 117.5 min at 600 MPa/50 °C and 400 MPa/25 °C, respectively. Pressures in excess of 500 MPa resulted in sufficiently fast inactivation rates for economic viability of the process.     

Pasteurization of Fresh Orange Juice Using Gamma Irradiation: Microbiological, Flavor, and Sensory Analyses

Recent concern about the presence of disease‐causing bacteria in unpasteurized juice has highlighted the need to develop alternative means of pathogen control that preserve sensory properties and nutrient content. The objectives of this study were to determine the effects of different doses of gamma irradiation on reducing the microbial pathogens L. monocytogenes and Salmonella enterica in fresh orange juice, and to determine whether significant reduction could be achieved without compromising sensory qualities. While irradiation was effective in destroying pathogens, the development of off flavors precludes its use as an alternative processing technology.     

Thermal Inactivation of Yeasts in Fruit Juices Supplemented with Food Preservatives and Sucrose

Thermal inactivation of five yeasts (Candida krusei, Hansenula anomala, Saccharomyces bailii, S. cerevisiae and Torulopsis magnoliae) suspended in five fruit juices (apple, apricot, grape, orange and pineapple) as affected by potassium sorbate, sodium benzoate and sucrose was investigated. Yeasts were most sensitive to heat when suspended in orange juice. Both preservatives, at a concentration as low as 100 ppm, enhanced the rate of inactivation in juices containing no added sucrose. Supplementation of juices with sucrose (30 and 50%) resulted in protection against death of yeasts. The detrimental effects of potassium sorbate and sodium benzoate were reduced in the presence of high concentrations of sucrose. While neither preservative exhibited a consistent superior lethal effect compared with the other, overall, sodium benzoate was generally more effective than was potassium sorbate.