Development of a robotic-HPLC determination of riboflavin vitamers in food

The need for laboratory automation is fuelled by the demands for better nutrient composition values based on large numbers of representative food samples. A fully automated method for the simultaneous analysis of the individual riboflavin vitamers in foods has been developed. It combines robotic extraction with HPLC quantitation. The robotic method was compared with a similar manual extraction using a variety of unfortified foods that are significant dietary sources of total riboflavin (TRF). The polymer-based columns used in the HPLC separation were found to be sensitive to the total organic carbon (TOC) content of ‘HPLC-grade’ water. Several procedures of varying complexity were successfully applied in order to remove interfering artifacts from the water.     

Leaching of toluene-neoprene adhesive wastes

This work consists of the study of the extraction of solvent (toluene) from a polymeric (neoprene) substrate during a leaching process. Total organic carbon (TOC) is the main contaminant parameter in the leaching of these systems due to the solution of the toluene and the dispersion of the polymer. The toxicity of the extracts was measured with a Microtox equipment, using Photobacteria phosphoreum, deducing that the toxicity of the extracts is low due to the low solubility of toluene but that the toxicity of toluene is high. On the basis of the experimental results, the amount of toluene diffused vs time in plane sheet systems was studied. A kinetic model has been developed considering two stages: In the first stage, the toluene diffuses into the system across the neoprene chains at a constant rate, not depending on the initial toluene concentration. This fact is explained by considering that there is a constant difference of the toluene concentration between the interface with the water and the inner part of the sample. In the second stage, the dispersion of the polymer with the corresponding amount of toluene takes place. The diffusion of toluene in the leaching process is compared and analyzed considering the diffusion of toluene in a desorption process in air so that the difference of toluene concentration between the interface and the interior can be estimated. A mathematical model is also proposed for considering the leaching process in other operating conditions.     

WATER ABSORPTION, LEACHING and COLOR CHANGES DURING the SOAKING FOR PRODUCTION of SOY-BULGUR

In this study, the soaking process, which is the first step of soy‐bulgur production to develop a new type food product, was investigated. the soaking operation was conducted at 30, 50 and 70C for 120 min and samples were taken from the soybean and soaking water at 10 min intervals. Moisture content and color (L, a, b and YI values) of soybean were measured, as well as soluble solids content and color (L, a, b and YI values) of soaking water during the soaking process. the results were analyzed by using ANOVA and Duncan test. Soaking time and temperature were significantly effective (P < 0.05) on all variables, except the time effect on the YI‐value. During the soaking, moisture content, lightness (L) and yellowness (b) increased and, redness (a) and yellowness index (YI) of soybean decreased. Soluble solids content, yellowness and yellowness index increased in contrast to a decrease in the lightness and greenness of the soaking water. As a result, soluble solids content in the soaking water increased, which illustrated the leaching of soluble solids from soybean to water. Color of soybean turned to lights, in contrast to darkening and opaqueness of water during soaking. Results showed that the moisture content, soluble solid content, L, a, b and YI values can be successfully modeled using polynomial equations, which can be used to estimate their changes during the soaking operation.     

Effect of Rehydration Temperature on Functional Properties,Antioxidant Capacity and Structural Characteristics of Apple (Granny Smith) Slices in Relation to Mass Transfer Kinetics

Apple slices dried at 60C were rehydrated at 20, 40 and 60C to analyze the influence of processing temperature on quality attributes and rehydration kinetics. Diffusion coefficient increased with process temperature from 1.36 to 2.37 × 10^?9 m²/s. The Weibull model obtained the best fit quality for the experimental data based on statistical test, chi square. Color was not recovered during rehydration and the results indicated that the use of low temperatures is more adequate. Water‐holding capacity decreased, while rehydration ratio increased with increasing rehydration temperature, indicating structural modifications. Increasing rehydration temperatures led to a reduction in the glass transition temperature and hardness values of samples. The radical‐scavenging activity showed higher antioxidant activity at higher rehydration temperatures rather than at lower temperatures. It was found that rehydration temperature modifies the cell structure and antioxidant capacity of final product.     

Organic matter in central California radiation fogs

Organic matter was studied in radiation fogs in the San Joaquin Valley of California during the California Regional Particulate Air Quality Study (CRPAQS). Total organic carbon (TOC) concentrations ranged from 2 to 40 ppm of C. While most organic carbon was found in solution as dissolved organic carbon (DOC), 23% on average was not dissolved inside the fog drops. We observe a clear variation of organic matter concentration with droplet size. TOC concentrations in small fog drops (<17 microm) were a factor of 3, on average, higher than TOC concentrations in larger drops. As much as half of the dissolved organic matter was determined to have a molecular weight higher than 500 Da. Deposition fluxes of organic matter in fog drops were high (0.5-4.3 microg of C m(-2) min(-1)), indicating the importance of fog processing as a vector for removal of organic matter from the atmosphere. Deposition velocities of organic matter, however, were usually found to be lower than deposition velocities for fogwater, consistent with the enrichment of the organic matter in smaller fog drops with lower terminal settling velocities.     

Improving predictability of sediment-porewater partitioning models using trends observed with PCB-contaminated field sediments

More than 1900 sediment-water partitioning coefficients were measured for 58 polychlorinated biphenyl (PCB) congeners in 53 historically contaminated sediments collected from 10 urban and rural waterways in the United States and Canada. Freely dissolved porewater concentrations were determined using passive sampling with polyoxymethylene. Measured total organic carbon (TOC)/water partitioning coefficients, K(TOC), ranged from one to nearly three orders-of-magnitude higher than typical literature values based on spiking experiments and model predictions. Although total PCB concentrations ranged from 0.08 to 194 mg/kg, the more highly contaminated sediments showed only slightly lower K(TOC) values than less-contaminated sediments. No correlation was observed between log K(TOC) values and sediment TOC, black carbon (BC), or BC/TOC fractions (r(2) typically <0.1). Utilizing a two-carbon model incorporating anthropogenic BC did not improve predictions over a one-carbon TOC model. A comparison of models recently validated for field data showed that a coal-tar poly parameter linear-free energy relationship (PP-LFER) and a Raoult's Law model were successful at predicting average log K(TOC) values, without the need for any calibration or fitting (within a factor of 10 more than 90% of the time, and within a factor of 30 more than 99% of the time). Predictions were further improved by the introduction of a Weathering Factor (WF) that accounts for the relative depletion of lower molecular weight congeners due to weathering. Highly weathered sediments (with a WF near 1) tended to follow the coal-tar PP-LFER and Raoult's Law model the closest. Less-weathered sediments (with WF ? 1) sorbed less than predicted by these models. Noncalibrated WF inclusive coal-tar PP-LFER and Raoult's Law models performed as well or better than a quantitative-structure activity relationship (QSAR) model calibrated specifically to the data. These recommended partitioning models here can readily be used for all 209-PCB congeners.     

Chemical pathway and kinetics of phenol oxidation by Fenton's reagent

Phenol oxidation by Fenton's reagent (H2O2 + Fe2+) in aqueous solution has been studied in depth for the purpose of learning more about the reactions involved and the extent of the oxidation process, under various operating conditions. An initial phenol concentration of 100 mg/L was used as representative of a phenolic industrial wastewater. Working temperatures of 25 and 50 degrees C were tested, and the initial pH was set at 3. The H2O2 and the Fe2+ doses were varied in the range of 500-5000 and 1-100 mg/L, respectively, corresponding to 1-10 times the stoichiometric ratio. A series of intermediates were identified, corresponding mainly to ring compounds and short-chain organic acids. Most significant among the former were catechol, hydroquinone, and p-benzoquinone; the main organic acids were maleic, acetic, oxalic, and formic, with substantially lower amounts of muconic, fumaric, and malonic acids. Under milder operating conditions (H2O2 and Fe2+ at lower concentrations), a great difference was found between the measured total organic carbon (TOC) and the amount of carbon in all analyzed species in the reaction medium. This difference decreased as the doses of H2O2 and Fe2+ increased, indicating that the unidentified compounds must correspond to oxidation intermediates between phenol and the organic acids. To establish a complete oxidation pathway, experiments were carried out using each of the identified intermediates as starting compounds. Dihydroxybenzenes were identified in the earlier oxidation stages. Muconic acid was detected in catechol but not in the hydroquinone and p-benzoquinone oxidation runs; the last two compounds were oxidized to maleic acid. Oxalic and acetic acid appeared to be fairly refractory to this oxidation treatment. A detailed knowledge of the time evolution of the oxidation intermediates is of environmental interest particularly in the case of hydroquinone and p-benzoquinone because their toxicities are several orders of magnitudes higher than that of phenol itself. The time evolution of the intermediates and TOC was fitted to a simple second-order kinetic equation, and the values of the kinetic constants were determined. This provides a simplified approach useful for design purposes.     

Milk composition and yield of the black Bedouin goat during dehydration and rehydration

Milk composition and yield were measured in the black Bedouin goat during 4 d of dehydration followed by 2 d of rehydration. During this time the goats were exposed to strong solar radiation with no access to shade; all of these conditions occur commonly in the desert. Milk yield, initially similar to that found in the desert, was maintained during the first 2 d of dehydration, fell to 35% of the initial value over the third and fourth days and recovered fully during 2 d of rehydration. As yield fell, milk osmolality, and milk fat and protein concentrations rose. During rehydration all 3 fell once more, but whereas osmolality finished below initial values the concentrations of fat and protein remained higher than before dehydration. The milk remained isosmolar with plasma throughout. Total yields of milk solids and milk water during the whole experimental period were 70 and 67% of normal respectively and normal growth of the young was not disturbed.     

Rehydration Capacity of Chilean Papaya (Vasconcellea pubescens): Effect of Process Temperature on Kinetic Parameters and Functional Properties

Slabs of Chilean papaya hot air-dried at 60 °C were rehydrated at 20, 40, 60, and 80 °C to study the influence of process temperature on mass transfer kinetics during rehydration. Diffusive and empirical models were selected to simulate the experimental rehydration curves. All models parameters showed dependence with temperature, thus activation energy could be estimated according to an Arrhenius-type equation. Among the applied models, Weibull provided the best fit for each rehydration curve based on the statistical tests RMSE, SSE, and chi-square. According to these results, this model could be used to estimate the rehydration time of Chilean papaya. In addition, rehydration ratio and water-holding capacity were analyzed. Both indices showed a decrease with increasing rehydration temperature indicating modification of the papaya cell structure due to thermal treatment which resulted in a reduction of the rehydration ability, in particular at high rehydration temperatures.     

Viscoelastic behaviour of dehydrated products during rehydration

Viscoelastic behaviour of dehydrated products during rehydration of apple, banana, carrot and potato was examined under uniaxial compression tests. Samples were dehydrated with four different drying methods: conventional, vacuum, freeze and osmotic-freeze drying and after that they were rehydrated in an air dryer at 50°C and 80% air humidity. Compression tests were performed during rehydration for various moisture contents, ranging from 0.01 to 1.5 kg/kg dry basis. The viscoelastic behaviour of dehydrated products during rehydration were examined comparing the values of the four parameters incorporated into the stress–strain model, during rehydration with those of dehydrated products. The four examined parameters: maximum stress, maximum strain, elastic parameter and viscoelastic exponent seem to show a hysteresis phenomenon. It can be concluded that dehydrated product do not keep their viscoelastic behaviour after rehydration due to structural damages that occur during drying. More specifically, freeze dried materials present the highest hysteresis after rehydration, losing their elasticity and becoming more viscous. Osmotic pretreatment seems to help freeze dried materials to keep their elastic nature, probably due to solids gain. Air and vacuum dried materials showed the smallest hysteresis tendency, keeping their viscoelastic characteristics during rehydration close to those of dried materials.     

Effect of temperature and pretreatment on water diffusion during rehydration of dehydrated mangoes

The kinetics associated with rehydrating dehydrated mangoes was studied at three temperatures: 25, 40, and 60 °C. Besides, we studied how rehydration was affected by pretreating the fruit with osmodehydration in either sucrose or glucose before it was thermally dehydrated. We show that rehydration can be interpreted by Fickian diffusion and that the effective water diffusion coefficient is larger at 40 °C than at either 25 or 60 °C. Consequently, during rehydration of untreated samples at 40 °C, the weight gain, water gain, and loss of solids attain optimal values. We found that the rehydration kinetics of mango was not affected by osmodehydration pretreatments in sucrose. However, pretreatment in glucose significantly improved rehydration; for example, the effective diffusion coefficients of the glucose-treated samples were about twice as large as those of the untreated samples.     

Kinetics of water absorption and soluble‐solid loss of hot‐air‐dried carrots during rehydration

Cubes of carrots dried at 60, 70, 80 and 90 °C were rehydrated at 20 and 95 °C. Kinetics of water gain and soluble‐solid loss were monitored and described by Peleg model. Dry matter holding capacity, water absorption capacity and rehydration ability were derived to assess the rehydration process. It was found that leaching flow was higher for the samples dried at higher temperatures. Rehydration ability and dry matter holding capacity of the samples rehydrated at 95 °C were higher than those observed for the samples soaked at 20 °C. Swelling of carrots during rehydration neither depended on temperature of drying nor on the temperature of the water. The results indicate that the use of low drying temperatures is suitable for preserving the quality attributes of carrots after rehydration.     

热泵式长豇豆干燥工艺优化

为保证热泵干燥后长豇豆产品的复水性和色泽等品质参数良好,同时降低豇豆干燥过程中的能量消耗,提高豇豆干燥生产的效率,采用Box-Behnken试验设计,分析干燥温度、漂烫时间和铺料密度3 个因素对豇豆产品的复水率、色差、单位耗能量和耗时4 个参数的影响,建立多元回归模型,并对干燥工艺参数进行优化,得到热泵式长豇豆干燥工艺的最佳条件为漂烫时间3 min、铺料密度2 kg/m2、干燥温度50 ℃。在该工艺条件下,实际测得长豇豆复水率1.15,色差值22.39,单位耗能量14.31（kW·h）/kg,耗时7 h,与预测值误差极小,为豇豆在实际热泵式干燥设备生产加工中的应用提供一定的理论依据。     

Survival and growth of Pseudomonas aeruginosa in natural mineral water: a 5-year study

A 5-year study was carried out on the growth curve of two strains of P. aeruginosa inoculated at a density of 10(2) cfu/ml into samples of natural mineral water with different levels of dissolved solids (TDS at 180 degrees C: 72.5 and 382 mg/l) and low organic content (TOC: 0.17 and 0.35 mg/l). The resulting growth curves were similar for both strains, with only slight differences depending on the different amounts of dissolved solids in the water. After 4-5 days counts were increased by 3 log units. This level was maintained until 70-100 days from inoculation, after which a slow decrease began, culminating in the death of one of the strains after 5 years. No difference in recovery was observed between the method using direct inoculation on Cetrimide Agar and the resuscitation technique (preincubation in Tryptone Soya Agar followed by inoculation on Cetrimide Agar) in the exponential phase of the growth curve. During the stationary and death phases, however, the enrichment technique gave statistically slightly higher counts than the selective technique, indicating the presence of damaged P. aeruginosa cells. The use of a resuscitation step when using Cetrimide Agar to assess bottled water quality is recommended.     

毛肚涨发工艺优化及其水分分布和组织结构变化研究

为更安全有效地使盐渍毛肚复水涨发,本实验研究了碳酸钠涨发毛肚的工艺条件。采用单因素和响应面试验,对碳酸钠浓度、碳酸钠处理时间、温度进行优化。以增重率和破碎力为响应值,确定碳酸钠涨发毛肚的最优工艺条件。结果表明,毛肚的最优工艺条件为碳酸钠浓度1.03%(w/v),碳酸钠处理时间2.3 h,温度43℃,此时毛肚的增重率达185.25%±3.61%,破碎力为2333.31±99.12 g,脆度高,感官评价良好。碳酸钠处理后毛肚不易流动水和自由水含量明显增加,肌纤维断裂、肌细胞膨润饱满。本研究表明该碳酸钠涨发盐渍毛肚工艺可靠,增重率高,嫩化效果好。     

Dairy powder rehydration: influence of protein state, incorporation mode, and agglomeration

A simplified method to study rehydration was used on different dairy powders. The method involved dispersing powder in a stirred vessel equipped with a turbidity sensor. The changes of turbidity occurring during powder rehydration highlighted the rehydration stage, and the influence of the proteins’ state on rehydration was clarified. Casein powders had a quick wetting time but very slow dispersion, making the total rehydration process time-consuming. On the other hand, whey powders were found to have poor wettability but demonstrated immediate dispersion after wetting. Mixing casein (80%) and whey (20%) before spray drying greatly improved rehydration time compared with casein powder; whereas mixing whey powder with casein powder at the same ratio after spray drying caused a dramatic deterioration in the rehydration properties. Moreover, agglomeration was found to significantly improve the rehydration time of whey protein powder and to slow down the rehydration time of casein powder. These opposite effects were related to the rate-controlling stage (i.e., wetting stage for whey protein and dispersion stage for casein).     

Including spatial variability in Monte Carlo simulations of pesticide leaching

A methodology is developed to quantify the uncertainty in a pesticide leaching assessment arising from the spatial variability of non-georeferenced parameters. A Monte Carlo analysis of atrazine leaching is performed in the Dyle river catchment (Belgium) with pesticide half-life (DT50) and topsoil organic matter (OM) content as uncertain input parameters. Atrazine DT50 is taken as a non-georeferenced parameter, so that DT50 values sampled from the input distribution are randomly allocated in the study area for every simulation. Organic matter content is a georeferenced parameter, so that a fixed uncertainty distribution is given at each location. Spatially variable DT50 values are found to have a significant influence on the amount of simulated leaching. In the stochastic simulation, concentrations exist above the regulatory level of 0.1 microg L(-1), but virtually no leaching occurs in the deterministic simulation. It is axiomatic that substance parameters (DT50, sorption coefficient, etc.) are spatially variable, but pesticide registration procedures currently ignore this fact. Including this spatial variability in future registration policies would have significant consequences on the amount and pattern of leaching simulated, especially if risk assessments are implemented in a spatially distributed way.     

STUDY OF SOLIDS LEACHED DURING RICE COOKING USING THE TRANSMITTANCE AT 650 NM

The objective of this research was to develop a method to predict the amount of total solids leached during rice cooking using light transmittance at 650 nm with an ultraviolet-visible spectrometer. Rice was cooked in excess water for different durations, the transmittance was measured, and the solids were determined gravimetrically after evaporation of the water. Results of leached solids obtained gravimetrically showed a good correlation with the logarithm of the transmittance ( R ²  =  0.9731), thus indicating the feasibility of the method. As a result, calibration curves were developed using rice starch and rice flour as standards. Calibration curves generated with rice starch has shown to overpredict the amount of solids leached. When rice flour was used, the method predicted that the solids leached with an average error of 2.3%, with a minor tendency towards underprediction.

PRACTICAL APPLICATIONS

During the industrial production of instant rice, important amounts of solids leach out from the rice, producing yield loss and high biochemical oxygen demand (BOD) waste streams. A quick method to estimate the leaching potential of different rice varieties would be important to adjust processing parameters and minimize leaching. The results presented in this study show that the transmittance at 650 nm can be used to estimate the solids leached during rice cooking. Still, the successful implementation of this method depends on the finding of suitable standards.     

八角热风干燥水分变化及品质分析

为了探究八角的干燥特性及内部水分扩散机理,本研究以热风温度（50、60和70 ℃）和预处理方式（杀青和不杀青）为实验变量,对八角进行了热风干燥实验,同时进行低场核磁共振检测和品质分析。结果表明,八角干燥过程基本处于降速干燥阶段,且干燥时间与热风温度呈负相关关系,杀青处理可以降低干燥时间。经低场核磁共振T₂谱检测,发现新鲜八角含有3个波峰,经干燥加工处理,不易流动水峰会分离出来1~2种波峰,这部分增加的波峰为大分子有机物。通过对八角干燥过程中的各峰面积和各组分占比进行研究,发现干燥加工主要除去的水分为不易流动水,而结合水、大分子有机物和小分子有机物的质量变化很小。杀青预处理对干燥过程八角的波峰分布影响甚微,但增加了八角的干燥速率。通过对八角品质的分析可以得到:经杀青预处理,干燥后的八角色泽更好,复水能力更强,但皱缩率更大,且热风温度越高,八角的复水能力越大,但会导致皱缩率也增大。     

Slow desorption mechanisms of volatile organic chemical mixtures in soil and sediment micropores

Desorption profiles of trichloroethylene (TCE), tetrachloroethylene (PCE), and a TCE-PCE mixture were measured for three natural solids and four zeolites. Initial sorbed mass (Mi) in slow desorbing sites of natural solids and in micropores of zeolites were obtained from desorption profiles. In natural solids, Mi increases with recalcitrant organic matter content. In zeolites, Mi generally increases with decreasing micropore width and increasing micropore hydrophobicity, but the effect of hydrophobicity is stronger. In both natural solids and zeolites, competition between TCE and PCE causes Mi for each sorbate in the mixture to be less than or similar to that for each sorbate alone. Zeolite results indicate that micropore width affects this competition more than micropore hydrophobicity for the solids examined. Desorption in all solids was simulated with the radial diffusion model, either alone or coupled with the advection-dispersion equation when necessary; diffusion rate constants (D/R2) were obtained. In natural solids, mean values of D/R2 increase with decreasing recalcitrant organic matter content. In zeolites, values of D/R2 generally increase with increasing micropore width, while they are a weak function of hydrophobicity. In both natural solids and zeolites, competition between TCE and PCE causes D/R2 for each sorbate in the mixture to generally be larger than that for each sorbate alone. Zeolite results indicate that the effects of competition on D/R2 generally decrease with decreasing micropore width for the solids examined; a trend with micropore hydrophobicity is not apparent. For the three natural solids and four zeolites examined in this study, the similar effects of competition between TCE and PCE on values of Mi and D/R2 and the overlapping range of D/R2 values support the hypothesis that diffusion through hydrophobic micropores affects and may control slow mass transfer processes in the recalcitrant organic matter of natural solids. These results contribute to the fundamental understanding of slow mass transfer processes in natural solids, and they indicate that characterization of micropore width and polarity may be necessary to predict organic chemical transport and fate.