酱油中铅含量测定的前处理方法探讨

分别采用直接稀释法、干灰化法、过硫酸铵灰化法、湿式消解法和微波消解法对酱油样品进行前处理,以石墨炉原子吸收光谱法对处理好的样品中铅含量进行测定;通过对各前处理方法和检测结果的精密度、回收率进行分析、讨论,以期达到在实际检测工作中更好应用的目的.     

The physicochemical and microbiological characteristics of pork jerky in comparison to beef jerky

This study was carried out to compare the physicochemical and microbiological characteristics of beef and pork jerky, prepared from whole muscle of beef semimembranosus (BSM), pork semimembranosus (PSM), pork longissimus dorsi (PLD), and pork psoas major (PPM). The BSM and PSM jerky had higher moisture content, and PPM jerky had lower water activity than other jerky samples during 30 days of storage at 25 °C (P < 0.05). Pork jerky samples had higher lightness value than beef jerky, while PSM jerky had higher pH value than other jerky samples (P < 0.05). The shear force and TBARS values of PPM jerky were higher than those of other jerky samples (P < 0.05). Saturated fatty acid (SFA, %) was significantly higher in the BSM jerky than others, while unsaturated fatty acid (UFA, %) was significantly higher in the PSM and PLD than BSM and PPM jerky samples (P < 0.05). The PPM jerky showed a significant increase in UFA (%) during storage, and a significantly decrease in microbial count after storage of 30 days (P < 0.05).     

Comparison of various methods for determination of water in white yoghurts

Water content was determined in 11 samples of white yoghurts. Several techniques, namely Karl Fischer (KF) volumetric titration, near and middle infrared spectroscopy (MIR), oven drying and moisture analyser were used. Optimisations of solvent, titration temperature and extraction time were carried out for the KF titration. Methanol at room temperature with 5 min extraction period was used as final conditions. For the infrared spectroscopy (FTIR) the suitable solvent and the appropriate wavenumbers for water analysis were chosen. The measurement in the near infrared (NIR) region at the wavenumber 10270 cm⁻¹ using acetonitrile as solvent and transmission method was evaluated as the best of the FTIR methods. Based on the comparison of individual methods the oven drying at 105 °C seems to be the most suitable, but it is the most time consuming. However, KF volumetric titration and especially FTIR methods appear to be good alternatives to the drying methods.     

Prediction of water activity in vegetables creams: Note 1

A study on empirical models for a _w value prediction, directly correlated to humectant substances concentration, was carried out in model systems and vegetables food. The test, performed for different a _w values predicted on aqueous solution, aqueous extract and vegetables creams of mushroom (Cv. Champignon), showed a high accuracy of proposed model. In fact the values of correlation coefficient (r), were always greater than 0.985, and the maximum pure error was 0.014.     

A novel approach for color degradation kinetics of paprika as a function of water activity

The influence of temperature and water activity on color degradation in paprika powders was investigated. The Hunter color parameters (L, a, b), hue angle (h), and total color difference (TCD) were used to estimate the color changes of paprika during thermal treatment at different temperatures (60, 80 and 99 °C) and water activities (0.459, 0.582 and 0.703). The changes in L, a, b and TCD values were significantly influenced by the processing time, temperature and water activity. The color changes during processing and storage were described by a first order kinetic model. The temperature dependence of the degradation followed the Arrhenius relation. Samples with a high water activity exhibited a high rate constant of the color degradation. The effect of water activity on activation energy was not significant. A linear relationship between the water activity and rate constant of the color parameters was found. By incorporating the linear relationship k_refa_w into the Arrhenius equation, a modified Arrhenius equation was proposed which was used to predict paprika color changes as influenced by temperature and water activity.     

Effect of water activity on carotenoid degradation in dehydrated carrots

The effect of water activity on the stability of carotenoids in dehydrated carrots was studied.     

Effect of water activity on oxidative deterioration of freeze-dried beef

The effect of water activity on lipid oxidation in freeze-dried beef was studied. Analytical indices of the extent of oxidation (thiobarbituric acid (TBA) number and Ex 350Ee320 fluorescence ratio) showed that samples of water activity 0.270 underwent less oxidation during 84 days storage in oxygen at 50°C than samples of lower water activity. Samples stored under nitrogen, irrespective of water activity, did not show any oxidation.     

Sorting for beef tenderness using high performance liquid chromatography and capillary electrophoresis: A research note

This study utilized two sampling methods to examine changes in sarcoplasmic proteins during aging of beef and their relation to tenderness. Water-soluble proteins either obtained by manually expressing exudates from the meat (drip) or by an extraction procedure using homogenization and centrifugation (ext) were analyzed for longissimus lumborum muscle using HPLC and capillary electrophoresis (CE) on days 2, 7, 10 and 14 postmortem. A peak that consistently increased with aging was identified using HPLC. Among nine peaks detected in the CE analysis, peak 9 (100kDa) that increased and peak 4 (30kDa) that decreased with aging were correlated (P<0.05) to tenderness as determined by Warner-Bratzler shear force (WBSF). For pooled data of all aging periods, drip sample explained the most variability (49%) in shear force compared to ext sample (25%) using HPLC analyses. At 2 days postmortem, a multiple linear regression model explained 83% of the variation in WBSF using CE-ext or HPLC-drip samples. Sixty percent of the variability in shear force was explained by CE-ext samples for day 7 data. The variability in shear force as explained by either drip or ext sample was less than 51 percent for 10 and 14 days postmortem data. The drip samples were comparable to ext samples in predicting WBSF values for both tough (>46N WBSF on day 2) and tender (<46N WBSF on day 2) strip loins using CE and HPLC procedure. Results suggest that a simple drip sampling may have a potential for use with either HPLC or CE analyses on day 2 postmortem for sorting carcasses into tenderness groups.     

Acrylamide kinetic in plantain during heating process: Precursors and effect of water activity

Almost two thirds of plantain world production is processed by means of deep frying which place it in the same occurrence as potatoes-based food in some tropical regions (Latin America, Central Africa and Southeast Asia). Asparagine content and effect of water activity on acrylamide kinetic in a plantain matrix was surprisingly investigated for the first time. Asparagine content was analyzed in ten edible Musa L., and “Cooking bananas” were found (maximum of 70 mg/100 g db) to be less concentrated than “dessert bananas” (maximum of 321 mg/100 g db). Moreover, asparagine content decreased by 75% after 11 days of post-harvest ripening. Acrylamide formation/elimination kinetics were determined in plantain paste at three different initial water activity values (0.972, 0.904, and 0.430) measured at 25 °C and heated at high temperatures (140-200 °C) in a closed reactor. Acrylamide in plantain was formed at the same magnitude as for potatoes, rye and wheat-based products (max ~ 0.9 ppm, wb). Kinetic parameter estimation was performed using a single response modeling. The reaction kinetic and the estimated kinetic parameters revealed an increase in acrylamide formation and elimination reaction rates with decreasing water activity. The corresponding activation energies of the rate constants remained unaffected.     

变温压差干燥技术在牛肉干生产中的应用

采用变温压差干燥技术研制牛肉干的生产工艺和技术条件。通过对影响牛肉干复水率的因素进行研究,初步得出影响产品复水率的各因子（干燥前水分含量、干燥温度、干燥压差、干燥时间）最佳取值范围。结论如下：干燥前水分含量为30％,干燥温度为65℃,干燥压差为0．28MPa,干燥时间5h。     

测定稻谷中α-淀粉酶活性的两种方法的比较

采用碘比色法和降落数值法分别测定稻谷中α-淀粉酶活性,对测定结果进行了比较分析。实验结果表明：两种方法都可以测定α-淀粉酶活性,两者的测定结果差异显著,但两者测定结果呈显著直线相关性,说明降落数值的高低能间接的反映α-淀粉酶活性的大小;从变异系数来看,后者的变异程度较低,其精密度较高,前者引起的误差因素较后者多;后者较前者简便快速,重复性好等优点。通过分析研究比较,降落数值法是分析测定大量样品α-淀粉酶活性的最佳方法。     

Moisture sorption isotherm of fresh lean beef and external beef fat

The moisture sorption isotherm (MSI) of lean beef and fat beef was experimentally determined. The experimental procedure used was that of the COST 90 project with some modifications to accelerate equilibration. The procedure was validated with the standard reference material microcrystalline cellulose. The MSI of the beef at the highest humidity range was obtained by accelerating equilibration with changes of salts, using a low water activity salt for some time. This procedure was reliable for beef samples but not for the fat samples. No significant changes were found for lean beef in the temperature range 5–40 °C. Three models, GAB, Peleg and Lewicki, were used to fit the experimental data. The best fit was obtained with the GAB equation. The fat MSI was determined at 5, 15 and 25 °C and it was best fitted with the Lewicki model.     

Influence of water activity and molecular mobility on peroxidase activity in salt and sorbitol-maltodextrin systems

Solvent composition, system mobility and viscosity play a central role in the regulation of enzymatic activity.The aim of this study was to investigate the individual and combined effect of water activity (a_w), bulk viscosity and glass transition temperature () on the activity of horseradish peroxidase (HRP) in buffered solutions. For this purpose, the water activity of the solutions was modulated using both a ionic (sodium chloride) and a non-ionic (sorbitol) ligand and viscosity changed upon the addition of maltodextrin.In viscous solutions characterized by different compositions, the effectiveness of a solute in the inhibition of the HRP activity was dependent both on the chemical properties of the solution, as described by a_w, and on the mobility of the system, as described by the inverse of viscosity and T − . Viscosity was the most important factor in the inhibition of HRP activity in solutions characterized by the same value, but when was changed, due to changes in the solutes composition, the latter became a key factor in the regulation of the enzyme activity.In salt-maltodextrin systems the water activity reduction limited HRP activity with higher efficiency at low viscosities whilst in sorbitol-maltodextrin systems, characterised by different values, the a_w lowering by sorbitol addition resulted in the increase of HRP activity depending on its effect on .     

Evaluation of spectrophotometric and fluorometric methods for alkaline phosphatase activity determination in ewe's milk

The alkaline phosphatase (ALP) activity test has been used since 1935 to assess the effectiveness of pasteurization. Different analytical methods exist for detecting ALP in milk. Unfortunately, there is little information about ALP activity in ewe's milk. The aim of this study was to assess and compare the official European method (spectrophotometric method) and the Fluorophos method (fluorometric method) regarding their use in ewe's milk. Bulk ewe's milk samples were taken from a flock and from three different dairies. A portion of the original sample was pasteurized at 63 degrees C for 30 min in a circulating bath; another portion was heated to and kept at 95 degrees C for about 2 min, and 0.1% (vol/vol) of raw milk was added. The samples obtained were analyzed in duplicate using the spectrophotometric and fluorometric methods. The relation between ALP activity determined by the two methods was characterized by the following equation: Y = 1.34 + 0.0039X (where Y = ALP in microg of phenol per ml of milk and X = ALP in mU/liter; R2 = 91.5%). Precision parameters (repeatability [r], standard deviation of repeatability [s(r)], and relative standard deviation of repeatability [RSDr]) for both methods were calculated. The values of RSDr for the Fluorophos method were 4.30 for pasteurized milk and 2.96 for 0.1% raw milk, close to the value indicated by Rocco in whole cow's milk (RSDr = 4.4). The repeatability for the official method (r = 2.16) was close to that indicated for whole cow's milk (r = 2).     

可食用膜制备及在酱牛肉保鲜中应用的研究

分别以大豆蛋白和牛骨胶原蛋白为原料制成复合可食膜Ⅰ、Ⅱ对酱卤肉制品进行杀菌、真空包装等处理,通过测定TBA值、TVB-N值、菌落总数、感官指标,研究其在不同温度(35、20、4℃)下的保质期。实验结果:在35℃条件下,Ⅰ、Ⅱ组的保质期分别为40、50d,对照组为30d;在20℃条件下,Ⅰ、Ⅱ组的保质期分别为120、140d,对照组为80d;4℃条件下,Ⅰ、Ⅱ组的保质期分别为200、210d,对照组为140d。实验结果表明,经过大豆蛋白复合可食膜、牛骨胶原蛋白复合可食膜处理后,酱卤肉的保质期均优于对照组,牛骨胶原蛋白可食膜的保质、保鲜效果优于大豆蛋白可食膜。     

Conservation of water for washing beef heads at harvest

The objective of this research was to develop methods to conserve water necessary to cleanse beef heads prior to USDA–FSIS inspection. This was to be accomplished by establishing a baseline for the minimum amount of water necessary to adequately wash a head and application of image analysis to provide an objective measure of head cleaning. Twenty-one beef heads were manually washed during the harvest process. An average 18.75 L (2.49 SD) and a maximum of 23.88 L were required to cleanse the heads to USDA–FSIS standards. Digital images were captured before and after manual washing then evaluated for percentage red saturation using commercially available image analysis software. A decaying exponential curve extracted from these data indicated that as wash water increased beyond 20 L the impact on red saturation decreased. At 4σ from the mean of 18.75 L, red saturation is 16.0 percent, at which logistic regression analysis indicates 99.994 percent of heads would be accepted for inspection, or less than 1 head in 15,000 would be rejected. Reducing to 3σ would increase red saturation to 27.6 percent, for which 99.730 percent of heads likely would be accepted (less than 1 in 370 would be rejected).     

Veterinary drugs residues: a review of the latest analytical research on sample preparation and LC-MS based methods

ABSTRACT

The world population is increasing and there is a growing demand for food, leading to intensification of farming methods and a requirement for more coadjuvants. Potential high profits sometimes lead to fraudulent use of drugs and pesticides. Veterinary drugs in particular can pose a real risk to human health if their residues are allowed to enter the food chain. Parent drugs and their metabolites can occur in foodstuffs individually or as multicomponent mixtures with enhanced adverse effects. In order to protect consumer safety, the European Union has established lists of forbidden substances, maximum residue limits for authorised drugs and precise criteria for confirmation analyses and interpretation of the results. Due to their nature and potential danger, the ‘best available technique’ should always be applied. Following this principle, this review examines the procedures and techniques applied to monitoring pharmaceutical products of major concern (e.g. anthelmintics, NSAIDs, corticosteroids, coccidiostats) in foods of animal origin, discussing advances over the past five years and future trends in the field of food safety. Our goal was both to focus attention on this important topic and to provide a selection of the most relevant recent papers on drug residues in foodstuffs.     

The effect of water activity on cholesterol oxidation in spray- and freeze-dried egg powders

The aim of the paper was to estimate the effect of water activity in spray- and freeze-dried whole egg and egg yolk powders on cholesterol oxidation during 3-months of storage at room temperature.     

Influence of type and state of crystallisation on the water activity of honey

In total, 249 samples of different honey types were analysed concerning water content and water activity. The samples were identified by using physico-chemical parameters and melissopalynological methods.