Effects of acid pretreatments on some physicochemical properties of carrot undergoing hot air drying

Carrot is one of the important root crops cultivated worldwide. In many cases, carrot must be dried prior to its use. Although hot air drying is one of the most common methods for drying carrots, it is well known that hot air drying leads to much quality degradation of a dried product. To alleviate the adverse effect of hot air drying many pretreatment methods have been proposed. In this study, the effects of pretreatments with citric acid, which is used as an anti-darkening agent and a texture-modifier, were investigated. Carrots were soaked in citric acid to pH of either 4 or 5 or blanched in citric acid to pH of either 4 or 5 prior to hot air drying. Untreated carrots, carrots soaked in water and carrots blanched in water were used as control samples. The effects of pretreatments, in combination with hot air drying at 70, 80 and 90 °C, on selected physicochemical properties of dried carrots, namely, color, shrinkage, rehydration ability, β-carotene content and cis–trans isomerization of β-carotene, were evaluated. It was noted that carrots, which were soaked and blanched in citric acid, were redder than the untreated sample. Although shrinkage of pretreated carrots was higher, the rehydration ability of the pretreated carrots was higher than that of the untreated sample. The β-carotene content of carrots with no pretreatment decreased continuously, whereas the contents of β-carotene in citric acid soaked and blanched carrots tended to be unchanged. However, isomerization of β-carotene in all samples was not significantly different.     

Betalain, Acid ascorbic, phenolic contents and antioxidant properties of purple, red, yellow and white cactus pears

Commercialization of cactus pears based on their antioxidant properties can generate competitive advantages, and these can turn into business opportunities and the development of new products and a high-value ingredient for the food industry. This work evaluated the antioxidant activities (1,1-diphenyl-2-picrylhydrazyl radical-scavenging, protection against oxidation of a β-carotene-linoleic acid emulsion, and iron (II) chelation), the content of total phenolic compounds, ascorbic acid, betacyanin, betaxanthin and the stability of betacyanin pigments in presence of Cu (II)-dependent hydroxyl radicals (OH•), in 18 cultivars of purple, red, yellow and white cactus pear from six Mexican states. Our results indicated that the antiradical activities from yellow and white cactus pear cultivars were not significantly different (p < 0.05) and were lower than the average antiradical activities in red and purple cultivars. The red cactus pear from the state of Zacatecas showed the highest antioxidant activity. The free radical scavenging activity for red cactus pears was significantly correlated (p < 0.05) to the concentration of total phenolic compounds (R² = 0.90) and ascorbic acid (R² = 0.86). All 18 cultivars of cactus pears studied showed significant chelating activity of ferrous ions. The red and purple cactus pears showed a great stability when exposed to OH•.     

Effects of air drying properties on drying kinetics and stability of cactus/brewer's grains mixture fermented with lactic acid bacteria

The present work examined the effect of air drying conditions on drying kinetics of cactus/brewer's grains mixture fermented with Lactobacillus plantarum HG328248. The drying kinetics was performed in a convective dryer for three air temperatures (40, 50 and 60 °C) and three air velocities (0.7, 1.0 and 1.3 m/s). Four mathematical models were tested to fit the drying curves. The Page model seemed the most appropriate to describe experimental data. The experimental drying curves showed two periods: that at constant rate and that of falling rate. The air temperature was the main factor in controlling the drying rate. The characteristic drying curve equation was determined.The influence of air drying conditions on color, water activity and microbiological quality of the fermented product was also studied. The temperature affected these parameters more significantly than air velocity. All dehydrated products had a satisfactory microbiological quality and consequently could be introduced in ruminant feed.     

Red pepper (Capsicum annuum L.) drying: Effects of different drying methods on drying kinetics,physicochemical properties,antioxidant capacity,and microstructure

Results of an experimental study are presented and discussed for pulsed vacuum drying (PVD), infrared-assisted hot air-drying (IR-HAD), and hot air-drying (HAD) on drying kinetics, physicochemical properties (surface color, nonenzyme browning index, red pigments, rehydration ratio, water holding capacity, and ascorbic acid), antioxidant capacity (ferric reducing antioxidant power and 2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity), and microstructure of red pepper. As expected, the drying time decreased with an increase in drying air temperature, IR-HAD needed the shortest drying time, followed by HAD and PVD. The effective moisture diffusivity (D_eff) of red pepper under PVD, HAD, and IR-HAD was computed to be in the range 1.33–5.83?×?10^?10, 1.38–6.87?×?10^?10, and 1.75–8.97?×?10^?10 m²/s, respectively. PVD provided superior physicochemical properties of dried red pepper compared to samples dried by HAD and IR-HAD. In detail, PVD yielded higher rehydration ratio, water holding capacity, red pigment and ascorbic acid content, brighter color, lower nonenzyme browning index, and comparable antioxidant capacity compared to samples dried by HAD and IR-HAD at the same drying temperature. Furthermore, PVD promoted the formation of a more porous structure, while HAD and IR-HAD yielded less porous structure. The current findings indicate that PVD drying has the potential to produce high-quality dried red pepper on commercial scale.     

Assessment of the initial moisture content on soybean drying kinetics and transport properties

Several researchers have developed studies to obtain a mathematical model able to describe grain drying kinetics. However, most of these studies neglect the effect of grain initial moisture content on drying curves. In this study, we assessed the dependence of drying curves and mass transfer coefficients on this initial moisture, air temperature, and its velocity by measuring grain mass losses within time on a tray dryer. Mathematical models were adjusted and results indicated that initial grain moisture content has significant influence on drying curves and mass transfer coefficients.     

Effect of outlet drying temperature and milk fat content on the physicochemical characteristics of spray-dried camel milk powder

Abstract

A composite face-centered experimental design was used to investigate the influence of spray drying conditions on the physicochemical characteristics of camel and cow milk powders. Response surface methodology (RSM) was deployed to appraise the effects of these processing parameters (the outlet drying temperature and the milk fat content) on water activity (a_w), glass transition temperature (T_g), bulk density, and free fat quantity. According to RSM analysis, it was noticed that the a_w and the T_g were primarily influenced by the outlet drying temperature instead of by milk fat content. Our results highlighted the negative effects of milk fat content and of the outlet drying temperature on the bulk density as well as on the free fat quantity of camel milk powder. Likewise, our findings underlined the negative effect of the outlet drying temperature on the bulk density of cow milk powder. However, the increase of fat content has led to the overexposure of fat at the free surface of the cow milk powder. Our results suggested a marked similarity of the overall thermodynamic behavior of both milks, during drying. Nevertheless, some differences were highlighted regarding the structuring of the particles of camel milk powder.     

The influence of drying air temperature on the physical properties of dried and rehydrated eggplant

Drying processes generally cause volume and surface change of foodstuffs. Information on the porous structure and the mechanical properties of dried food products is needed for determining food quality, process design and estimating properties such as density and moisture diffusivity.In this work we investigated the structural changes induced in eggplant by convective air drying at four different temperatures (40, 50, 60 and 70 °C) and their effect on the subsequent rehydration process. Drying and rehydration kinetic curves were also measured.The changes in physical properties, such as porosity, pore-size distribution and bulk density were determined by Hg porosimetry, scanning electron microscopy and optical microscopy while their effect on the textural characteristics by dynamometric measurements.As expected, the increase of the drying air temperature causes shorter drying times. The drying temperature influences strongly the microstructure of dried samples: the porosity increases with the air temperature, but the structure is better preserved at intermediate temperature (60 °C) as confirmed by the lower firmness values with respect to the other dehydrated samples (40, 50 and 70 °C). In these latter, the longer drying time and the higher temperature, respectively, causes the development of a wrinkled structure. In particular, at 70 °C the structure of dehydrated samples appears totally broken with a consequent faster water uptake during rehydration.     

Effect of different drying techniques on physicochemical,thermal, and functional properties of seera

Seera produced by different drying techniques was evaluated regarding its various physicochemical properties. The rheological properties of the batter showed a shear thinning behavior and Herschel–Bulkley model was best fitted with R²?=?0.9987. The results revealed that water absorption capacity increased as compared to the wheat flour and maximum absorption was found in freeze-dried seera (1.91?g?g^?1), followed by oven-dried (1.62?g?g^?1) and sun-dried (1.13?g?g^?1). Oil absorption capacity of seera decreased as compared to wheat flour, with minimum values obtained for freeze-dried (0.93?g?g^?1 of seera). Carbohydrate content increased significantly in seera sample to 81.76%, while fat, protein, and moisture content decreased significantly. L* values increased significantly, while as both a* and b* values decreased. Bulk density also showed an increasing trend with maximum value in freeze-dried seera. Transition temperatures changed significantly for the seera samples along with enthalpy of gelatinization. Fourier transform infrared pattern did not change with drying.     

空气纳米气泡的稳定性及理化特性

空气纳米气泡（Air-NBs）的理化特性是其广泛应用的基础。本文利用纳米粒度-zeta电位分析仪研究了水力空化原理产生的Air-NBs的理化特性,即粒径分布和zeta电位,考察了装置运行压力、电解质浓度、pH和温度对Air-NBs理化特性的影响;同时考察了去离子水和CaCl₂溶液中Air-NBs稳定性。结果表明：纳米气泡发生器的压力越大,其产生的Air-NBs的小粒径比例更大,且电解质的加入有助于气泡粒径的缩小。随着溶液中电解质浓度、pH和温度的升高,溶液中Air-NBs的平均粒径逐渐减小,但气泡间的聚结作用会导致其粒径随时间逐渐增大;通过对两种溶液中Air-NBs粒径的实时监测发现其能在溶液中存在5天之久。胶体稳定（DLVO）理论和zeta电位效应可以合理阐释溶液中Air-NBs的稳定性。     

温度、时间和尺寸对市政污泥热风干燥的综合影响

通过单因素实验和正交实验讨论了热风温度、干燥时间和试样尺寸对市政污泥热风干燥的综合影响。实验结果表明：热风温度为140—180℃时,干燥时间为20—40min,热风温度和试样尺寸对污泥热风干燥都有显著的影响,干燥时间的影响不明显。     

Influence of the chestnuts drying temperature on the rheological properties of their doughs

Chestnut flour doughs were prepared using chestnut air-dried at 45, 65, and 85 °C with constant load density (8.0 ± 0.6 kg/m²). Mixing curves of doughs using Mixolab^® device showed that chestnut flour doughs dried at 85 °C needed more water absorption to reach the target consistency, (1.1 ± 0.07 Nm). Thermorheological properties were evaluated by means of a controlled stress rheometer. All tested doughs showed shear-thinning behaviour in the steady-shear tests (0.001–1 s^?1). Oscillatory (1–100 rad s^?1 at 0.1% strain), temperature sweep (30–90 °C) and creep-recovery (loading 50 Pa for 60 s) tests showed that flour doughs from chestnuts dried at 85 °C provide interesting properties, particularly remarkable elasticity that is associated with starch gelatinisation. Experimental data were described using various rheological models.     

温度和相对湿度对褐煤干燥动力学特性的影响

为确定褐煤干燥最佳工艺参数,在恒温恒湿热风干燥实验台上进行了温度为50～90℃,相对湿度为10％～30％条件下的褐煤颗粒热风干燥实验.将实验数据与9种经验、半经验模型进行拟合,利用相关系数、方差、均方根误差3种统计学参数对不同模型进行评价.结果表明:Page模型相比其他模型更适合用于描述干燥过程中褐煤颗粒水分随时间的变...     

Influence of epichlorohydrin content on structure and properties of high‐ortho phenolic epoxy fibers

The high‐ortho phenolic epoxy fibers (HPEFs) were prepared by the crosslinking of heat‐meltable spun filaments derived from melt‐spinning of the novolac epoxy resins copolymerized among phenol, formaldehyde, and epichlorohydrin (ECH) in the presence of zinc acetate and sulfuric acid catalyst, and cured in a combined solution of formaldehyde and hydrochloric acid. The resulting fibers were heat‐treated in N₂ at elevated temperature. Infrared (IR) spectrometer, thermogravimetric analysis (TGA), scanning electron microscope (SEM), and electrical tensile strength apparatus were employed to characterize the change of functional groups, thermal performance, microstructure of fibers, and mechanical properties. The results show that the addition of ECH in the precursor resin can increase the content of long alkyl ether linkage, and gain the peak of thermal stability and mechanical strength. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43375.     

热塑性苯酚甲醛树脂的分子量、游离苯酚含量对胶料加工性能的影响

树脂补强体系下的橡胶硫化实际上是树脂网络和橡胶网络的形成以及相互穿插的过程,热塑性苯酚甲醛树脂的分子量以及游离酚含量势必会对树脂网络的形成产生影响,从而影响橡胶的硫化以及胶料的加工过程。本文就是制备出不同分子量的热塑性苯酚甲醛树脂以及不同游离酚含量的热塑性苯酚甲醛树脂,测试含有这些树脂胶料的加工性能,得出结论,并且用这些结论分析市售的热塑性苯酚甲醛树脂对胶料加工性能的影响。     

Study on quality attributes and drying kinetics of instant parboiled rice fortified with turmeric using hot air and microwave-assisted hot air drying

Abstract

This study investigated the quality and drying kinetics of instant parboiled rice fortified with turmeric (IPRFT) by using hot air (HA) and microwave-assisted hot air (MWHA) drying. The cooked long grain parboiled rice (LGPR) fortified with turmeric was dried with HA at temperatures of 65, 80, 95, and 110?°C. The microwave power density of 0.588 Wg^?1 was incorporated for drying with MWHA. Drying was performed until the dried IPRFT reached 16% (d.b.) of moisture content. The quality of the dried IPRFT was evaluated in terms of color, total phenolics content (TPC), total antioxidant capacity (TAC), rehydration ratio, volume expansion ratio, texture and microstructure. The results showed that the incorporation of microwave power with HA drying helped to reduce the drying time by 50% compared to conventional HA drying. A prediction of the moisture ratio by using the Page model provided the best R² and RMSE in drying kinetics. The drying conditions had small effects on the color, TPC, TAC, and microstructure of the dried IPFRT. The rehydration ratio, volume expansion ratio and texture of the rehydrated IPFRT showed minimal variations from changes in the drying conditions. The TPC and TAC of the dried IPRFT clearly increased compared to the TPC and TAC of the initial LGPR.     

Effect of airflow rate on drying air and moisture content profiles inside a cross-flow drying column

Rice at 20.5 and 16.3% initial moisture contents (IMCs) was dried using 57°C/13% RH air at airflow rates (Qs) of 0.36, 0.46, and 0.56 (m³/s)/m² for 30, 60, and 90?min, respectively, in an experimentally simulated cross-flow drying column. Q significantly affected the drying air and rice moisture content profiles within the drying column; for a particular drying duration, the range of MCs within the column decreased as Q increased. Q also impacted the extents of intra-kernel material state gradients created and thus had potential impacts on kernel fissuring and consequent head rice yield reduction. In addition, the impact of Q on the above-mentioned profiles was dependent on the rice IMC.     

Effect of sonolysis on kinetics and physicochemical properties of treated chitosan

Low molecular weight chitosan with weight‐average molecular weight from 161 to 22,000Da were obtained by sonolysis. Optimal conditions for sonolysis were described. The influence of sonolysis condition and the molecular parameters of initial chitosan on the degradation rate and degradation rate constant were investigated in detail. Weight‐average molecular weight (M_w) and molecular weight dispersion (M_w/M_n) of samples were measured by gel permeation chromatography. The structure of degraded chitosan were characterized by Fourier transform infrared, X‐ray diffraction, and electrospray ionization mass spectrometry. For a given sonolysis time, the decrease in molecular weight has been found to be greatest at lowest reaction temperature and lowest chitosan concentration. Molecular weight of samples decreased exponentially with increasing sonication time at early stages. The action mode of ultrasound on the splitting of molecular chain of chitosan has been discussed. The degree of deacetylation of the main hydrolysis products almost unchanged compared with the initial chitosan. The decrease of molecular weight led to transformation of crystal structure but the chemical structures of residues were not modified. Ultrasonic treatment on chitosan is an alternative, safe method to prepare chitosan having different molecular weights, which are more suitable for biomedical and food applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

温度对毛竹快速热解焦物理化学特性的影响

用固定床反应器制备了热解温度300⁸00℃的毛竹快速热解焦。采用比表面积测试(BET)、扫描电子显微镜(SEM)、傅里叶红外光谱(FTIR)、X射线衍射(XRD)和拉曼光谱(Raman)研究了毛竹热解焦的物理化学特性。结果表明,随着热解温度的升高,热解焦中C=C的含量先增加后减少;热解温度低于700℃时,热解过程中的脱氢作用和芳香环的增长使得芳香碳的含量增加;温度超过700℃时,芳香族化合物发生缩合反应,产生石墨碳。700℃热解焦的比表面积达到最大值233.65 m800℃的毛竹快速热解焦。采用比表面积测试(BET)、扫描电子显微镜(SEM)、傅里叶红外光谱(FTIR)、X射线衍射(XRD)和拉曼光谱(Raman)研究了毛竹热解焦的物理化学特性。结果表明,随着热解温度的升高,热解焦中C=C的含量先增加后减少;热解温度低于700℃时,热解过程中的脱氢作用和芳香环的增长使得芳香碳的含量增加;温度超过700℃时,芳香族化合物发生缩合反应,产生石墨碳。700℃热解焦的比表面积达到最大值233.65 m²/g,并具备良好的吸附特性。800℃热解焦的比表面积下降至170.35 m2/g,并具备良好的吸附特性。800℃热解焦的比表面积下降至170.35 m²/g,这是由于热解焦发生孔坍塌,使得部分孔隙关闭。     

Effect of feed concentration and inlet air temperature on the properties of soymilk powder obtained by spray drying

In this study, soymilk powder was produced by spray drying. The inlet air temperature of spray dryer was varied from 200 to 280°C and the feed concentration was varied from 15 to 25% (w/v). Response surface methodology was used to examine the effects of these independent variables on the detailed characteristics in terms of physical, structural, functional properties of powder. Overall, results show that rising the inlet air temperature caused a decrease in tapped and loose bulk density, true density, filling rate, water holding capacity, and water content of powder; and an increase in compressibility, Hausner ratio, porosity, interstitial air volume, and wettability index. An increase in feed concentration led to an increase in true density, compressibility, Hausner ratio, porosity, interstitial air volume, and wettability index; and a decrease in tapped and loose bulk density, filling rate, water holding capacity, and water content; whereas oil holding capacity might be increased or decreased and it depended almost solely on the feed concentration.     

Stability of carotenoids, phenolic compounds, ascorbic acid and antioxidant capacity of tomatoes during thermal processing

In the present investigation we ascertained the stability of lycopene, beta-carotene, ascorbic acid, polyphenolic compounds and total antioxidant capacity (AC) during the process of concentrating tomatoes into two tomato pastes (10 and 15 degrees Brix). Thermal processing increased the content of lycopene, total phenolic compounds, total flavonoids, and the individual phenolic compounds quercetin, rutin, chlorogenic and cafeic acids, whereas it decreased the other analysed compounds. However, lycopene in the 15 degrees Brix-tomato paste decreased due to the extension of thermal processing, which led to degradation. The AC of aqueous and organic extracts was measured and different AC values were observed depending on the antioxidant profile of the extract and assay used (TEAC and FRAP). AC expressed in dry matter decreased as result of ascorbic acid losses. Overall, thermal processing enhanced the nutritional value of tomatoes, mainly by increasing the lycopene and phenolic antioxidants, but the extension of treatment must be controlled to prevent lycopene degradation.