Kinetics of freshly squeezed orange juice quality changes during ozone processing

Freshly squeezed orange juice samples were ozonated with control variables of gas flow rate (0-0.25 L min (-1)), ozone concentration (0.6-10.0%w/w), and treatment time (0-10 min). Effects of ozone processing variables on orange juice quality parameters of pH, degrees Brix, titratable acidity (TA), cloud value, nonenzymatic browning (NEB), color values ( L*, a*, and b*), and ascorbic acid content were determined. No significant changes in pH, degrees Brix, TA, cloud value, and NEB ( p < 0.05) were found. L*, a*, and b* color values were significantly affected by gas flow rate, ozone concentration, and treatment time. The changes in lightness ( L*) values and total color difference (TCD) values were fitted well to zero-order kinetics, whereas a*, b*, and ascorbic acid degradation followed first-order kinetics. The rate constants for a*, b*, and TCD were linearly correlated with ozone concentration ( R (2) = 0.88-0.99), whereas the rate constants for L* and ascorbic acid were exponentially correlated ( R (2) = 0.94-0.98).     

Characterization of polyphenol oxidase and peroxidase and influence on browning of cold stored strawberry fruit

Polyphenol oxidase and peroxidase were extracted from two different varieties of strawberry fruit (Fragaria x ananassa D, cv. 'Elsanta' and Fragaria vesca L, cv. 'Madame Moutot') and characterized using reliable spectrophotometric methods. In all cases, the enzymes followed Michaelis-Menten kinetics, showing different values of peroxidase kinetics parameters between the two cultivars: Km = 50.68 +/- 2.42 mM ('Elsanta') and 18.18 +/- 8.79 mM ('Madame Moutot') mM and Vmax = 0.14 +/- 0.03 U/g ('Elsanta') and 0.05 +/- 0.01 U/g ('Madame Moutot'). The physiological pH of fruit at the red ripe stage negatively affected the expression of both oxidases, except polyphenol oxidase from 'Madame Moutot' that showed the highest residual activity (68% of the maximum). Peroxidase from both cultivars was much more thermolable as compared with PPO, losing over 60% of relative activity already after 60 min of incubation at 40 degrees C. The POD activation energy was much lower than the PPO activation energy (DeltaE = 97.5 and 57.8 kJ mol-1 for 'Elsanta' and 'Madame Moutot', respectively). Results obtained from d-glucose and d-fructose inhibition tests evidenced a decreasing course of PPO and POD activities from both cultivars as the sugar concentration in the assay medium increased. Changes in CIE L*, a*, b*, chroma, and hue angle values were taken as a browning index of the samples during storage at 4 degrees C. A decrease in L* was evident in both cultivars but more marked in 'Elsanta'. PPO and POD activities from cv. 'Elsanta' were very well-correlated with the parameter L* (r2=0.86 and 0.89, respectively) and hue angle (r2=0.85 and 0.93, respectively). According to these results, the browning of the fruit seemed to be in relation to both oxidase activities.     

Characterization and role of polyphenol oxidase and peroxidase in browning of fresh-cut melon

Polyphenol oxidase (PPO) and peroxidase (POD) were extracted from two different varieties of melon ( Cucumis melo L. cantalupensis cv. Charentais and C. melo L. inodorus cv. Amarillo) and characterized using reliable spectrophotometric methods. In both cases the enzymes followed Michaelis-Menten kinetics, showing different values of kinetics parameters between the two cultivars: K m = 7.18 +/- 0.70 mM ('Charentais') and 6.66 +/- 0.20 mM ('Amarillo') mM; V max = 7.93 +/- 0.35 units/min ('Charentais') and 13.82 +/- 0.37 units/min ('Amarillo'), relative to PPO; K m = 24.0 +/- 2.10 mM ('Charentais') and 5.05 +/- 0.19 mM ('Amarillo') mM; V max = 344.83 +/- 10.32 units/min ('Charentais') and 80.64 +/- 2.01 units/min ('Amarillo'), relative to POD. Optimum pH for PPO was 7.0 for 'Charentais' and 7.5 for 'Amarillo, whereas it was 4.5 for both cultivars relative to POD. Melon PPO had maximum activity at 60 degrees C in both 'Charentais' and 'Amarillo' cultivars, whereas POD maximum activity was found at 45 degrees C in 'Charentais' and at 25 degrees C in 'Amarillo'. POD from both cultivars showed higher thermolability compared with PPO, losing >90% of relative activity after only 5 min of incubation at 70 degrees C. POD's activation energy was much higher than that of PPO (Delta E (#) = 86.3 and 160.6 kJ mol (-1) for 'Charentais' and 'Amarillo', respectively). PPO and POD activities from both cultivars showed a decreasing pattern as sugar concentration in the assay medium increased, except in POD extract from 'Charentais', which maintained its activity in the presence of high d-glucose concentration (up to 5 M). Changes in L*, a*, b*, chroma, and hue angle values were chosen to describe the browning development in the samples during storage at 5 degrees C. A slight decrease in L* value and a more marked reduction of a* value were noted in both cultivars above all at the end of storage period. POD activity during storage at 5 degrees C was highly correlated with changes of parameters a*, b*, chroma, and hue angle ( r (2) from 0.82 to 0.97) for cultivar 'Charentais'. According to these results, only POD activity seemed to be involved in browning of minimally processed melon.     

Characterization of color fade during frozen storage of red grapefruit juice concentrates

Color changes in red grapefruit juice concentrates during storage at -23 degrees C for 12 months were studied. Concentrate (38 degrees Brix) was packed in both plastic (16 oz) and metal (6 oz) cans. Decrease in red intensity (CIE a) in juice color and slight increases in CIE L*, b*, and hue values from analysis of reconstituted juices were the characteristic color changes in concentrate during frozen storage. With respect to fresh concentrate, juice color in stored concentrate shifted toward the direction between negative DeltaC* and positive DeltaL*, indicating the color became slightly paler. A color difference seems to exist between the two containers, especially for the magnitude of DeltaE*; color changes were more pronounced in concentrates packed in plastic. There are significant changes (P < 0.05) in major carotenoid pigments (beta-carotene and lycopene) in the concentrates. More than 20% loss of lycopene and about 7% loss of beta-carotene occurred with plastic containers after a 12-month period. Regression analysis showed that the rate of decline was about 0.291 ppm per month (r = 0.990) for lycopene compared to 0.045 ppm (r = 0.817) for beta-carotene in concentrate stored in plastic. In the metal can, the same trends were observed but pigment losses were slightly smaller than those with plastic. An estimated shelf life for lycopene was 26.1 months in the metal can compared to 18 months in plastic. Shelf life for beta-carotene was more than 39 months, more than twice that of lycopene in plastic container.     

高压CO2处理保持非还原桃汁的品质

采用高压CO2（high pressure carbon dioxide,HPCD）处理非还原（not from concentrate,NFC）桃汁,分析HPCD处理后NFC桃汁pH值、可溶性固形物、色泽、酚类和抗氧化活性等品质特性的变化,讨论HPCD对NFC桃汁品质的影响。NFC桃汁的pH值和可溶性固形物含量分别为3.82和10.3°Brix,HPCD处理后没有显著变化;HPCD处理后NFC桃汁颜色变暗,色泽参数L、a、b值显著降低,对应的褐变度提高;NFC桃汁中的主要酚类物质有儿茶素、绿原酸、新绿原酸和阿魏酸,HPCD处理后酚类物质含量没有显著变化;采用FRAP和1,1-二苯基苦基苯肼（1,1-diphenyl-picrylhydrazyl,DPPH）清除率2种方法测定NFC桃汁的抗氧化活性,2种方法的测定结果都表明 HPCD 处理后 NFC 桃汁的抗氧化活性提高,并且随着处理时间的延长而逐渐提高。以上结果表明HPCD能较好的保持NFC桃汁的品质,为非热加工技术应用于果蔬加工提供理论基础。     

Effect of thermal treatment on the quality of cloudy apple juice

Apple juice from eight different varieties of apples was heated at high-temperature (60-90 degrees C) and short-time (20-100 s) (HTST) combinations. To determine the effect of heating conditions on enzymatic browning and cloud stability in apple juices, the activity of polyphenol oxidase and pectinesterase was analyzed and correlated with the thermal treatment conditions and the quality of the juice. Additional investigations included the measurement of pH value, soluble solid content, titratable acidity, color, and turbidity after 3 and 6 months. The results showed that HTST treatment at 80 degrees C already inactivated polyphenol oxidase, whereas pectinesterase activity was reduced to half and could even at 90 degrees C not be inactivated completely. In fact, highest residual pectinesterase activity was found at 60 degrees C. Heating at 70 degrees C caused stable pectinesterase activity and even a slight increase for 50 and 100 s heating times. Turbidity and lightness increased after HTST treatment. In particular, differences in cloud stability between the varieties were measured. HTST parameters did not correlate with the residual cloud stability after 6 months. The sensory evaluation revealed that only a few combinations were distinguishable. The best stability of cloud and color in relation to heat impact was achieved by HTST treatment between 70 degrees C/100 s and 80 degrees C/20 s.     

Use of Chromameter‐Measured Color Parameters in Estimating Color‐Related Soil Variables

Abstract

Soil color is a soil property that may be used as an interpreting index in estimating processes and properties. Quantifying color allows one to obtain information for rapidly estimating the related processes in soils. CIELAB color parameters L*, a*, and b* of ground (air‐dried and sieved) soil samples and aggregate surfaces of four soil profiles formed in calcareous colluviums in northern Turkey were analyzed. Values of color parameters measured in ground and intact soils were compared and related to soil properties by the regression technique. Results revealed that the L* value obtained with a ground soil sample was a significant predictor of organic matter in A horizons (p < 0.001). Although calcic horizons yielded the highest L* values, no significant relationship was obtained between calcium carbonate contents and lightness of soils in any of horizons studied. The parameters of b* could adequately be used to quantify dithionite‐extractable iron oxide contents in soils studied. The results further showed that the CIELAB color parameters obtained with ground samples were more informative than that of aggrevated samples in relating color parameters to soil properties.     

Effects of pulsed electric fields on the quality of orange juice and comparison with heat pasteurization

Effects of pulsed electric fields (PEF) at 35 kV/cm for 59 micros on the quality of orange juice were investigated and compared with those of heat pasteurization at 94.6 degrees C for 30 s. The PEF treatment prevented the growth of microorganisms at 4, 22, and 37 degrees C for 112 days and inactivated 88% of pectin methyl esterase (PME) activity. The PEF-treated orange juice retained greater amounts of vitamin C and the five representative flavor compounds than the heat-pasteurized orange juice during storage at 4 degrees C (p < 0.05). The PEF-treated orange juice had lower browning index, higher whiteness (L), and higher hue angle (theta) values than the heat-pasteurized orange juice during storage at 4 degrees C (p < 0. 05). The PEF-treated orange juice had a smaller particle size than the heat-pasteurized orange juice (p < 0.05). degrees Brix and pH values were not significantly affected by processing methods (p > 0. 05).     

便携式生鲜猪肉多品质参数同时检测装置研发

针对农畜产品检测现场的需求,基于可见/近红外光谱检测技术和嵌入式系统,开发了灵活方便的猪肉品质无损检测装置。该装置利用卤素灯作为光源,新型光导探头和微型光谱仪采集肉样光谱信息,通过ARM(advanced RISC machines)控制处理器进行集中控制和数据的处理;在内嵌linux操作系统上,采用Qt开发工具,设计出人性化的交互界面,并将猪肉品质的检测结果输出到装置触摸屏上。为了建立多品质无损检测数学模型,获取了猪肉里脊在400~1 000 nm波长范围内的光谱数据,通过国标方法测得猪肉里脊主要品质参数颜色(L*、a*、b*)和p H值,采用标准正态变量变换(standard normalized variate,SNV)和Savitzky-Golay(S-G)平滑对光谱数据进行预处理,并结合理化数据建立偏最小二乘(partial least squares regression,PLSR)模型。用全交叉验证法选取PLSR建模的主成分数。p H值、L*、a*和b*的预测相关系数为0.88、0.90、0.97和0.97,预测标准差为0.19、1.77、1.17和0.63。通过现场试验表明,轻便式多品质无损检测装置具有较高的检测精度,满足于猪肉的颜色和p H值等品质参数检测的要求。     

超高压加工鲜切苹果片的色变动态特性

以红富士和冰糖心2种苹果为试材,研究0、200、300、400和500MPa超高压处理对鲜切苹果片的色变动态特性。结果表明,超高压处理能显著抑制鲜切苹果片在空气中的色变速率。采用4种三色值组合(ΔL*a*/b* 、ΔL*a*b*、Δ(ΔE)和ΔW.I.)作为色变指标研究鲜切苹果片的色变动态特性,结果表明,超高压处理和未处理的鲜切苹果片的各色变指标均随时间呈线性变化,鲜切苹果片的色变符合零级动力学反应。通过对三色值组合的优选,色变指标ΔL*a*/b*被选作反应压力对色变影响的最佳指标,并在此基础上建立了色变指标(ΔL*a*/b*)与压力(P)的关系模型。模型表明,400MPa为超高压加工鲜切水果片的较优压力。     

Multivariate approach to the measurement of tomato maturity and gustatory attributes and their rapid assessment by Vis-NIR spectroscopy

Standard methods for determining quality and maturity are time- and labor-consuming and generally measure individual criteria at a specific time, without considering relationships among quality parameters. To propose a rapid and nondestructive analysis method describing multidimensional quality variables, an experiment was undertaken with mature green to overripe tomato fruits found on the North American retail markets. Factor analysis was used to analyze results. Four factors were considered, representing 81% of total variance. The first one, tomato maturity stage (TMS), is related to color, lycopene content, firmness, titratable acidity (TA), pH, and soluble solids (SS). Nondestructive rapid assessment by vis-NIR spectroscopy can predict TMS (r(2)=0.93). Factors 2 and 3 are both related to taste and should be considered simultaneously. Factor 2, called the gustatory index, is linked to electrical conductivity (EC), SS, TA, and pH. Factor 3, defined by SS, can be directly measured by a refractometer. Four categories of taste are proposed; the most desirable one ranks high both in soluble solids (above 4.5 degrees Brix) and in gustatory index (above 0). It was not possible to measure the gustatory index by vis-NIR spectroscopy (r(2)=0.17), but it can be estimated by EC, using a simple formula. The proposed limit between high and low gustatory index then corresponds to an EC of 5.4 mS/cm. Factor 4, variety, mostly discriminates the pink tomato type and field-grown samples from other varieties.     

Nonenzymatic browning reaction of essential amino acids: effect of pH on caramelization and Maillard reaction kinetics.

The interaction between glucose and essential amino acids at 100 degrees C at pH values ranging from 4.0 to 12.0 was investigated by monitoring the disappearance of glucose and amino acids as well as the appearance of brown color. Lysine was the most strongly destroyed amino acid, followed by threonine which induced very little additional browning as compared with that undergone by glucose. Around neutrality, the nonenzymatic browning followed pseudo-zero-order kinetics after a lag time, while the glucose and amino acid losses did not follow first-order kinetics at any of the pH values tested. Glucose was more strongly destroyed than all of the essential amino acids, the losses of which are really small at pH values lower than 9.0. However, glucose was less susceptible to thermal degradation in the presence of amino acids, especially at pH 8.0 with threonine and at pH 10.0 with lysine. The contribution of the caramelization reaction to the overall nonenzymatic browning above neutrality should lead to an overestimation of the Maillard reaction in foods.     

Fluorescence, browning index, and color in infant formulas during storage

Free and total fluorescent compounds, browning index, and color formation were measured in milk-based powdered infant formulas (IF) during 2 years of storage at 20 and 37 degrees C. The excitation spectra from 415 nm emission show three peaks (ex lambda1 = 270 nm, lambda2 = 325/315 nm, lambda3 = 350 nm) and from 347 nm excitation two emission peaks (415 and 520 nm), and no wavelength shifts were observed. Temperature and time of storage exert in general no significant effect on the development of fluorescence emission intensity and browning index. However, an important increase in pentodilysine was recorded-probably because of the iron and ascorbic acid contents of the samples-as well as in browning index in adapted IF. In both IF a color increase (deltaE) throughout storage was observed, this increase being greater in samples stored at 37 degrees C than in those stored at 20 degrees C. The increase in color with time fitted a linear regression model. Color appeared to be an indicator of sufficient sensitivity to measure the effect of temperature or storage time.     

Polyphenol oxidase from Dominga table grape

Dominga grape polyphenol oxidase (PPO) was extracted using phase partitioning with Triton X-114. The enzyme was obtained in latent state and could be optimally activated by the presence of 0.2% sodium dodecyl sulfate (SDS) at pH 6.0. In the absence of SDS, the enzyme showed maximum activity at acid pH. The kinetic parameters of the enzyme at pH 3.0 and 6.0 in the presence of SDS were calculated. The effect of several inhibitors was studied, tropolone being the most effective with a K(i) value of 18 muM. The effect of cyclodextrins was also studied, and the complexation constant K(c) between G(2)-beta-cyclodextrins and 4-tert-butylcatechol was calculated using the enzymatic method (K(c) = 13960 M(-)(1)). The evolution of the color parameters (L, a, b) of liquefied grape berries was inhibited by inhibitors of PPO activity, such as diethyldithiocarbamate, metabisulfite, and G(2)-beta-cyclodextrins, indicating that enzymatic browning by PPO is the main process involved in the browning of Dominga grape juice at room temperature.     

Estimation of Chlorophyll Contents by Correlations between SPAD‐502 Meter and Chroma Meter in Butterhead Lettuce

Abstract

Chlorophyll content of butterhead lettuce leaves was estimated by correlations between the Minolta SPAD‐502 and Minolta chroma meter CR 300. The SPAD‐502 readings and extractable chlorophyll (Chl a, Chl b, and total Chlorophyll) contents were related. High linear correlations were obtained for chlorophyll a (R²=0.90), chlorophyll b (R²=0.85), and total chlorophyll (R²=0.92). After that, during the growth cycle of butterhead lettuce grown in soilless culture, leaves were selected and SPAD‐502 and chroma meter readings were made. Finally, correlations between SPAD‐502 readings and leaf color (L*, a*, b*, C*, and hue angle) determined by the chroma meter were calculated. Hue angle (H°; R²=0.75) and lightness index (L*; R²=0.68) were the parameters that better relate with SPAD‐502 readings, so these parameters can also be used for rapid and nondestructive estimates of leaf chlorophyll in situ.     

Biochemical and microbial changes during the storage of minimally processed cantaloupe

The effect of storage time on pH, titratable acidity, degrees Brix, organic acids, sugars, amino acids, and color of minimally processed cantaloupe melon (Cucumis melo L. var. reticulatus Naud. cv. Mission) was determined at 4 degrees C and 20 degrees C. Changes in most of the biochemical parameters with storage time were relatively slow at the lower temperature. At 20 degrees C, a 17% loss in soluble solids and a 2-fold increase in acidity occurred after 2 days. Organic acid content also increased considerably with time at this temperature as a result of the production of lactic acid. Oxalic, citric, malic, and succinic acids were the organic acids, and glucose, fructose, and sucrose were the sugars present in the freshly cut cantaloupe. Malic acid concentration decreased concurrently with lactic acid production indicating the possible involvement of anaerobic malo-lactic fermentation along with sugar utilization by lactic acid bacteria. The effect of storage on microbial growth was determined at 4, 10, and 20 degrees C. Gram-negative stained rods grew at a slower rate at 4 degrees C and 10 degrees C than the Gram-positive mesophilic bacteria that dominated microorganism growth at 20 degrees C. Eighteen amino acids were identified in fresh cantaloupe: aspartic acid, glutamic acid, asparagine, serine, glutamine, glycine, histidine, arginine, threonine, alanine, proline, tyrosine, valine, methionine, isoleucine, leucine, phenyl alanine, and lysine. The dominant amino acids were aspartic acid, glutamic acid, arginine, and alanine. Total amino acid content decreased rapidly at 20 degrees C, but only a slight decrease occurred at 4 degrees C after prolonged storage. Changes in lightness (L), chroma, and hue at both temperatures indicate the absence of browning reactions. The results indicate the potential use of lactic acid and lactic acid bacteria as quality control markers in minimally processed fruits.     

Application of tristimulus colorimetry to estimate the carotenoids content in ultrafrozen orange juices

Tristimulus Colorimetry was applied to characterize the color of Valencia late orange juices. Color measurements were made against white background and black background. The profile of the main carotenoids related to the color of the juices was determined by HPLC. Significant correlations (p < 0.05) between b*, Cab* and h(ab) and the content of beta-cryptoxanthin, lutein + zeaxanthin and beta-carotene were found. The correlations between the color parameters L*, a*, b*, Cab* and h(ab) and the carotenoids content were also explored by partial least squares. The results obtained have shown that it is possible to obtain equations, by means of multiple regression models, which allow the determination of the individual carotenoid levels from the CIELAB color parameters, with R2 values always over 0.9. In this sense, equations have been proposed to calculate the retinol equivalents (1 RE = 1 microgram retinol = 12 micrograms beta-carotene = 24 micrograms alpha-carotene = 24 micrograms beta-cryptoxanthin) of the orange juice analyzed as a function of the color parameters calculated from measurement made against white and black backgrounds. The average RE per liter of juice obtained by HPLC was 51.07 +/- 18.89, whereas employing these equations, average RE values obtained were 51.16 +/- 1.36 and 51.21 +/- 1.70 for white background and black background, respectively.     

猕猴桃果浆中叶绿素和颜色的热降解动力学

为了研究猕猴桃果浆加工中叶绿素和绿色的热降解规律,测定了不同温度(70、80、90℃)和pH值(pH值3.3、6.0、8.0)对猕猴桃果浆叶绿素含量和色差的影响。结果表明,猕猴桃叶绿素a、b和绿色值(-a*)的热降解属一级动力学反应;在相同pH值条件下,随温度升高,叶绿素a、b和绿色值(-a*)的反应速率常数(k)降低,半衰期(t1/2)缩短;随pH值增加,叶绿素a的活化能(Ea)变化范围为14.69～66.02kJ/mol,叶绿素b为40.88～54.64kJ/mol,绿色值(-a*)为48.55～64.14kJ/mol;pH值3.3时叶绿素a、b的降解和绿色值(-a*)相关性较好。猕猴桃果浆加工中适量提高pH值可减少叶绿素和绿色的损失。     

Lipid-oxidation-induced carboxymyoglobin oxidation

We evaluated the usefulness of the ratio A503/A581 as a browning index (BI) for estimating brown color formation in solutions containing oxymyoglobin (OxyMb) and carboxymyoglobin (COMb). In split-chamber cuvette analyses with different proportions of metmyoglobin (MetMb), COMb and OxyMb, BI was highly correlated (r = 0.93-0.94) with direct estimation of MetMb. Moreover, A503/A581 was not influenced by different COMb-OxyMb proportions. Second, we investigated 4-hydroxy-2-nonenal (HNE)-induced spectral changes in OxyMb and COMb solutions. At pH 7.4 and 37 degrees C, BI was greater in HNE-treated OxyMb and COMb samples than in aldehyde-free controls (P < 0.05). However, at pH 5.6 and 4 degrees C, HNE-induced browning was more pronounced in COMb than in OxyMb. These results indicated that COMb is susceptible to lipid-oxidation-induced browning in a pH- and temperature-dependent manner.     

Properties of low moisture composite materials consisting of oil droplets dispersed in a protein-carbohydrate-glycerol matrix: effect of continuous phase composition

The influence of continuous phase composition on the properties of low moisture (<3% water) composite materials consisting of oil droplets dispersed in a protein-carbohydrate-glycerol matrix was investigated. These composites were produced by blending canola oil (62.3%), whey protein concentrate (1.7%, WPC), and corn syrup and glycerol together (36.0% combined) using a high speed mixer equipped with a whisk. The polyol composition was varied by changing the ratio of corn syrup to glycerol in the system while keeping the total concentration of these two polyol components constant. Some composites were analyzed directly after preparation ("unbaked"), while others were analyzed after heating at 176 degrees C for 10 min to simulate baking of a food product ("baked"). The "lightness" of the composites was greater before baking (higher L value), but the color intensity of the composites was greater after baking (higher b value), which was attributed to Maillard browning reactions. The brownness of the baked composites increased with increasing corn syrup concentration, which was attributed to Maillard browning reactions. Squeezing flow viscometry indicated that the consistency and yield stress of the composites increased with baking, which was attributed to whey protein unfolding and aggregation. These rheological parameters also increased with increasing corn syrup concentration, which was attributed to its influence on the continuous phase rheology and on the interactions between the whey proteins. This study shows that the continuous phase composition and thermal history of low moisture composite materials have a large impact on their final physicochemical properties.