活性硅酸镁对柑桔汁中柠檬苦素吸附的研究

研究了活性硅酸镁吸附橙汁和柠檬汁中的柠檬苦素。实验表明,只加入1.5%和2%的650℃活化的硅酸镁,当摇床频率为150 r/min、振荡温度为10℃、振荡1.5h经7000 r/min高速离心5min,可将柠檬苦素的脱除率达到97%以上,且对其品质影响较小。     

Removal of limonin from bitter orange juice

Polyamides are shown to be effective adsorbents for removal of the bitter principle, limonin, from pasteurised Washington Navel orange juice. The extent of limonin removal varies with different juices, but sufficient can be removed by one or two treatments to bring the concentration below the organoleptically detectable level. The commercial use of polyamides to prepare non-bitter juices from Navel oranges is discussed.     

Effect of some citrus juice constituents on taste thresholds for limonin and naringin bitterness

A panel of 20 to 27 screened judges was used to determine the threshold of pure limonin and naringin in distilled water, sucrose solutions, citric acid solutions adjusted to various pH values and in citrus juice model systems. Thresholds in distilled water were 1 and 20 mg/l for limonin and naringin, respectively. Sucrose, citric acid and combinations of these constituents in a model system increased the threshold of limonin and naringin several fold. The highest thresholds were obtained at low pH values in the absence of sugar. In a 1.2% citric acid solution containing 5% sucrose, 2.5% dextrose and 2.5% fructose the maximum limonin threshold of 11 mg/kg was obtained at pH 3.8. The maximum difference threshold for limonin in orange juice was 6.5 mg/kg and also occurred at pH 3.8. The optimum pH for limonin bitterness suppression (maximum threshold) was 3.8 in both model systems and natural orange juice. Thresholds on either side of this value were lower and limonin bitterness was more noticeable. No pH optimum was observed for naringin threshold in model systems. Individual thresholds showed a wide range of sensitivity to both limonin and naringin bitterness.     

The solubility of limonin,the bitter principle of orange juice

Limonin analyses were made on solutions obtained by equilibrating water at pH 6.3 and pH 3.2 with limonin at temperatures ranging from 0 to 100°C. The results indicated that the increase in the limonin assay with increasing temperature was due to the effect of heat on both the direct solubilisation of limonin and the hydrolysis of limonin to the related hydroxyacid. On storing these solutions at 25°C for several months, the assays from the acidified solutions fell to about the solubility of limonin in unheated solutions equilibrated at 25°C, but the four-fold higher analyses recorded for the neutral solutions indicated that they still contained considerable amounts of the hydroxyacid due to the maintenance of the lactone-hydroxyacid equilibrium. Although sugars and pectins had no detectable effect on the solubilisation of limonin at 25°C, they markedly increased the amount of limonin passing into solution on heating. In addition, they affected both the position of the equilibrium in these solutions on cooling and the rate at which the equilibrium was reached. Moreover, the equilibrium in supersaturated solutions of limonin and its rate of establishment also depended on the methods used for their preparation. These findings are discussed in relation to studies on bitterness in orange juice.     

Cellulose acetate as a selective sorbent for limonin in orange juice

Cellulose acetate as flake or powder is an efficient and selective sorbent for removing the bitter principle limonin from orange juice. Treatment of orange juice serum with powder (10 g/litre) removed 44–70% of the limonin content in less than an hour, at the same time removing relatively negligible amounts of hesperidin and ascorbic acid. Similar amounts of limonin could be removed by agitating the whole juice with cellulose acetate flakes held in open mesh bags which allowed contact between the enclosed flakes and the juice. Other materials, including related carbohydrate derivatives and polymers, were tested but only cellulose acetate butyrate shared the unusual sorptive properties of cellulose acetate.     

不同甜橙品种果汁中柠檬苦素含量的变化

为了减少柠檬苦素对橙汁品质的影响,为橙汁加工的原料品种和加工时间选择提供参考,对20个甜橙品种的鲜榨果汁与巴氏灭菌果汁,在7个不同成熟期,采用高效液相色谱法检测了柠檬苦素和诺米林含量。结果表明:各成熟阶段的所有测试甜橙品种的鲜榨果汁与巴氏灭菌果汁均能检测到柠檬苦素,巴氏灭菌果汁中柠檬苦素含量更高,平均是鲜汁的约2倍;随着果实的成熟,柠檬苦素含量总体逐步降低,到11月中旬时,试验甜橙品种的鲜榨果汁与巴氏灭菌果汁的柠檬苦素含量已低于人的苦味阈值,适于橙汁加工;不同甜橙品种甚至不同脐橙品种之间,柠檬苦素的含量存在明显差异;诺米林含量与柠檬苦素含量呈现类似变化,但含量更低,不是导致橙汁苦味的主要因素。此外,短期的冷冻贮藏对柠檬苦素的含量影响不大。     

Quantitation of limonin in Iranian orange juice concentrates using high-performance liquid chromatography and spectrophotometric methods

Bitterness is a major problem in the citrus industry worldwide, and is mostly due to the presence of limonoid compounds, especially limonin. In this study, the limonin content of orange juice concentrates from three active factories in west Mazandaran province, after reconstitution, was assayed using high-performance liquid chromatography (HPLC) and spectrophotometric methods. With HPLC, employing acetonitrile/water (v/v) (32:68) with a flow rate of 0.9 ml/min at =207 nm, the limonin content was in the range 11.7–23.3 g/ml with a mean ± standard deviation (SD) of 18.5±3.6 g/ml. Spectrophotometric measurement of limonin at 503 nm with Burnham reagent gave a range of 9.9–21.8 g/ml with a mean ± SD of 17.16±4.1 g/ml. The correlation coefficients of the detector linear response for the limonin standard (0–50 g/ml) for HPLC and spectrophotometry were 0.995 and 0.989, respectively. The percentages of limonin recovery with and without sample addition were 101.02–111.40 and 93.0–100.8, respectively, for HPLC. The percentages of limonin recovery for the spectrophotometric method resulted in 95.6–101.8 for limonin-added samples. The precision factors for the two assay methods were ±2.10% and ±1.69, respectively. The correlation coefficient of the two methods was 0.84. Sensory evaluation of the reconstituted samples from the view point of bitterness confirmed 85% of the results of the analytical methods. This study recommends spectrophotometric analysis as a useful and suitable method for quantitation of limonin in the quality control laboratories of orange juice plants.     

Effect of pectic enzymes on cloud stability and soluble limonin concentration in stored orange juice

Attempts to use pectic enzymes to stabilise the cloud and reduce the limonin content simultaneously in citrus juices were unsuccessful but led to several significant findings. Acid-catalysed reactions and residual effects of inactivated enzymes were shown to play a more important role in cloud stability than had been generally recognised. The maintenance of resuspended cloud, sometimes used as a measure of cloud stability during storage, was not always related to the actual retention of cloud; and although it was directly related to water-soluble pectin content, cloud retention was not. Factors controlling the solubility of limonin in orange juice appeared more complicated than previously thought and varied in their relative contribution from juice to juice. Other chemical reactions were involved besides the conversion of a non-bitter precursor to limonin, and the changes induced by endogenous pectic enzymes in unpasteurized juice had a more important effect on limonin solubility than the changes following the addition of fungal pectic enzymes to pasteurised juice. Finally, the separation of micro-crystalline limonin complicated limonin analysis of stored juices.     

Clarification of reconstituted frozen orange juice concentrate by continuous flow centrifugation for limonin glucoside solid phase extraction

BACKGROUND: The suitability of continuous flow centrifugation for the clarification of reconstituted frozen orange juice concentrate prior to its application to a solid phase extraction column for the isolation of limonin glucoside was evaluated. Clarification experiments spanning three flow rates (325, 588 and 875 mL min^?1) and three rotor speeds (equivalent to 2130, 8521 and 19 172 × g) were conducted in a simple factorial design. RESULTS: With increasing rotor speed or decreasing flow rate the average particle size, colour parameters (CIE L*, a*, b*) and residual solids in the resulting centrifugates were found to decrease, whereas juice characteristics including pH, conductivity, °Brix and limonin glucoside content were unchanged by the clarification process. Mean particle size in the resulting centrifugates ranged from 1.14 to 79.31 µm. The most effective clarification was obtained using a 325 mL min^?1 flow rate in conjunction with the maximum rotor speed. Suitability of the centrifugates for processing by solid phase extraction was tested through a two‐step process, in which the centrifugates were first screened using small columns, followed by application of the centrifugate to a larger self‐packed column (6.5 cm × 20 cm) containing SP‐70 Sepabeads. CONCLUSION: Centrifugates from two conditions (325 and 588 mL min^?1 at the maximum rotor speed) were suitable for direct application to both columns. It was found that up to 19 L of these centrifugates could be applied to the 6.5 cm × 20 cm column without clogging or experiencing a decrease in flow rate. Analysis of the column effluent revealed that 11 L of centrifugate was sufficient to saturate this column. Published in 2008 by John Wiley & Sons, Ltd.     

Some factors affecting sensory thresholds and relative bitterness of limonin and naringin

Equivalent sweetness to varying levels of sucrose was determined for naringin dihydrochalcone (ND), neohesperidin dihydrochalcone (NHD), hesperetin dihydrochalcone glucoside (HDG) and aspartylphenylalanine methyl ester (AP). The effect of sucrose and these compounds at equivalent sweetness levels on thresholds of limonin and naringin was determined. HDG was the most effective compound and sucrose the least effective in raising the threshold or suppressing bitterness of both limonin and naringin. At 1% sucrose equivalence, limonin thresholds were increased 0,40, 150 and 220% for sucrose, NHD, AP and HDG, respectively. At 5% sucrose equivalence, naringin thresholds were increased 80, 90, 145 and 180% by AP, sucrose, NHD and HDG, respectively.     

Combined use of ultrasound and natural antimicrobials to inactivate Listeria monocytogenes in orange juice

The presence of Listeria monocytogenes could seriously affect the safety of nonpasteurized fruit juices. High-intensity ultrasound combined with mild heat treatment and natural antimicrobials may be an alternative technology for fruit juice preservation. The response of L. monocytogenes in orange juice to combined treatments involving moderate temperature (45 degrees C), high-intensity ultrasound (600 W, 20 kHz, 95.2 microM wave amplitude), and the addition of different levels of vanillin (0, 1,000, 1,500, and 2,000 ppm), citral (0, 75, and 100 ppm), or both was investigated to find the most effective inactivation treatment. Nonlinear semilogarithmic survival curves were successfully fitted by the Weibull model. The presence of vanillin or citral greatly increased the bactericidal effect of thermosonication and changed the distribution of inactivation times. When both antimicrobials were added together and ultrasound was applied, narrowest frequency shapes, skewed to the right, with low ariances and death time means between 1.6 and 2.6 min, were obtained. Orange juices with 1,500 or 1,000 ppm of vanillin and 100 ppm of citral were pleasant for the consumers.     

柑桔类果汁中柠碱的脱苦方法

就柑桔中苦味物质的分布及其主要成分进行了论述，并介绍了几种柑桔类果汁中柠碱的脱苦方法。     

新会柑果汁柚皮苷脱除技术的研究

用戴维斯(Davis)法测定柚皮苷的含量,研究β-环糊精(β-cyclodextnn,β-CD)、温度和作用时间对新会柑果汁的脱苦效果的影响.结果表明:β-CD的添加量为0.8%,在45～50℃之间作用时间45 min柚皮苷的脱苦效果最好.     

Effect of subthreshold concentrations of limonin,naringin and sweeteners on bitterness perception

A sensory panel of experienced judges was used to determine taste thresholds of mixtures of limonin and naringin and various sweeteners. Data from these experiments showed that within the 95% confidence interval, subthreshold interactions between limonin and naringin were additive, indicating that less than threshold amounts of these compounds contributed to bitterness of a mixture. Mixtures of hesperetin dihydrochalcone glucoside (HDG), neohesperidin dihydrochalcone (NHD), naringin dihydrochalcone (ND), sucrose and naringin were neither additive nor synergistic at subthreshold concentrations. At suprathreshold levels, sucrose, (HDG) and (NHD) were effective in suppressing naringin bitterness, but (ND) was not.     

柑桔类果汁苦味物质的脱除研究

柠碱和柚苷是柑桔汁和柑桔其他制品中的主要苦味成分,采用吸附脱苦法、酶脱苦法、β-环糊精脱苦法、乙烯利代谢脱苦法及其他脱苦法可将它们除去,文中还提出了采用综合脱苦法应用于生产实际的观点。     

Use of pectinesterase for detection of hydrocolloids addition in natural orange juice

In natural orange juice, pectin is the major constituent responsible for cloud stability. In adulterated and imitation orange juices, for technical reasons, cloud stability is effected by different natural or synthetic hydrocolloids. Pectinesterase, an enzyme specific for pectin hydrolysis, was used to detect substitution of natural pectin of orange juice by other hydrocolloids. Natural orange juice, imitation orange juice and mixtures of them were used in this study. In pasteurized orange juice samples, pectinesterase was added at 20 mg/100 ml of juice. Mixtures were heated at 50°C in a water bath for 24 h and the percentage of clarification, as well as the amount of precipitate formed after centrifugation were measured. A linear correlation was found to exist between natural orange juice percentage in the natural–imitation orange juice mixtures and precipitate formed. A second order relation was found to exist between the percentage of the natural orange juice in the natural–imitation orange juice mixtures and the degree of clarification of orange juice. The method was used successfully for the detection of addition of extraneous hydrocolloids in orange juice for adulteration purposes.     

High-pressure homogenization of orange juice to inactivate pectinmethylesterase

A homogenizer was used to treat orange juice at five pressures (0–250 MPa) and three initial temperatures (22, 35 and 45 °C). A maximum of five passes for the selected conditions were used to process orange juice. Pectinmethylesterase (PME) activity, microbial load, cloudy appearance, and vitamin C were evaluated in just squeezed and homogenized orange juices. A reduction of 50.4, 49.4 and 37.8% of PME activity was observed in juice homogenized by one pass at 250 MPa at the initial temperatures of 22, 35, and 45 °C, respectively. Pectinmethylesterase activity in orange juice was reduced as passes number was increased. The final temperature of the five times homogenized orange juice was not beyond 28 and 37 °C after being treated at 100 and 250 MPa, respectively. More than 30 and 80% of enzyme activity was reduced after five passes at 100 and 250 MPa, respectively. Less that 8.7 × 10² and 1.85 × 10³ CFU/mL of mesophiles and yeasts plus molds, respectively, were counted in orange juice treated five times at 100 MPa. The cloudy appearance of the homogenized orange juice was maintained for 12 days under low temperature conditions.

Industrial relevance

“Cold pasteurization” of orange juice, using a homogenizer as a high-pressure procedure, could be an alternative to thermal processing to avoid sensory, nutritional and physiochemical changes in juice. This process may deliver a pasteurized orange juice with characteristics similar to just squeezed orange juice. In addition to reduce the microbial load, homogenization may reduce pectinmethylesterase enzyme, which may cause phase-separation in juice and consequently give an unwanted appearance that consumers dislike. Additionally, homogenized orange juice appearance could be stable during several days before being brought to the consumers' daily eating table.     

Ultraviolet treatment of orange juice

Ultraviolet (UV) with a wavelength of 254 nm tends to inactivate most types of microorganisms. Most juices are opaque to UV due to the high-suspended solids in them and hence the conventional UV treatment, usually used for water treatment, cannot be used for treating juices. In order to make the process efficient, a thin film reactor was designed and constructed from glass with the juice flowing along the inner surface of a vertical glass tube as a thin film. The decimal reduction doses required for the reconstitute orange juices (OJ; 10.5° Brix) were 87±7 and 119±17 mJ/cm² for the standard aerobic plate count (APC) and yeast and moulds, respectively. The shelf life of fresh squeezed orange juice was extended to 5 days with a limited exposure of UV (73.8 mJ/cm²). The effect of UV on the concentration of Vitamin C was investigated using both HPLC and titration methods of measurements. The degradation of Vitamin C was 17% under high UV exposure of 100 mJ/cm², which was similar to that usually found in thermal sterilization. Enzyme pectin methylesterase (PME) activity, which is the major cause of cloud loss of juices, was also measured. In contrast to the heat treatment, UV processing does not inactivate enzyme pectin methylesterase. The energy required for UV treatment of orange juice (2.0 kW h/m³) was much smaller than that required in thermal treatment (82 kW h/m³). The color and pH of the juice were not significantly influenced by the treatment.

Industrial relevance

This paper is of interest since it suggest—despite the low UV transmittance in orange juices—the use of a thin film UV reactor. The data suggest that shelf life extension from 2 to more than 5 days could be achieved with less energy requirements than for thermal processing. However, it seems unlikely that such thin film reactors could provide a real alternative to current conventional or new (e.g. high pressure pulsed electric field) processing.     

Factors controlling the accumulation of limonin and soluble constituents within orange fruits

A study was made of the differences in the quality and chemical constituents of the juice and albedo from Washington Navel and Valencia Late oranges grown at one orchard location on trifoliata orange and rough lemon rootstocks and harvested over a period of 40 weeks. Variety was the most significant factor in determining limonin contents, with rootstock an important subsidiary factor. Although limonin contents decreased absolutely as the season progressed, the maturity factor was important only in fruit of high initial limonin content. Differences in limonin contents were due to greater accumulation of limonin during fruit development and not to more rapid disappearance of limonin as the season progressed. An unknown factor controlled the distribution of limonin and soluble solids within the fruit, leading to the accumulation of these constituents in the blossom end. This “distribution factor” was so important that the differences in the limonin contents of albedo from the two halves of the same fruit were greater than the differences arising from the rootstock factor. For both limonin and soluble solids contents, the distribution factor operated uniformly throughout the season, irrespective of variety or rootstock. There was a direct relation between the chemical compositions of fruits picked at the same time from trees grown on different rootstocks, suggesting that relatively few picks could provide a basis for comparison of rootstock/scion combinations. The fact that such relations held irrespective of variety indicates an environmental effect on chemical composition which overrides varietal differences, whereas differences in variety and rootstock were more important in determining the physical characteristics of the fruit. Besides providing a basis for selecting fruit to give juice of optimum quality, these findings carry at least equal importance for the new light they throw on the physiological origins of variations in fruit quality.