山楂气体射流冲击干燥特性及干燥模型

研究不同干燥温度、风速、物料盒宽度和喷嘴高度对山楂气体射流冲击干燥特性及有效水分扩散系数的影响,采用7 种数学模型拟合实验数据,得到了用于描述山楂气体射流冲击干燥的最适数学模型。结果表明：山楂的气体射流冲击干燥主要属于降率干燥。干燥温度对山楂的干燥曲线和干燥速率曲线均具有显著影响,而风速、物料盒宽度以及喷嘴高度对山楂的干燥曲线和干燥速率曲线的影响均不显著。山楂的气体射流冲击干燥有效水分扩散系数随着风温和风速的增加而增加,随着物料盒宽度和喷嘴高度的增加而降低,且最高有效水分扩散系数为9.271×10-8 m2/s。在实验范围内最适宜于描述山楂在气体射流冲击干燥过程中含水率变化规律的数学模型是Page和Modified Page模型。     

冻融处理对甘薯变温压差膨化干燥动力学的影响

为探索冻融处理对甘薯变温压差膨化干燥特性的影响,研究了不同冻融次数和抽真空干燥温度条件下甘薯膨化干燥特性,建立了甘薯变温压差膨化干燥动力学模型。结果表明:冻融甘薯变温压差膨化干燥过程存在加速、等速和降速干燥3个阶段。抽真空干燥温度为85℃时,冻融1、2、3次甘薯膨化干燥需要225、175、250 min;冻融2次,抽真空干燥温度为75、85、95℃时,甘薯膨化干燥分别需要265、175、242 min。冻融甘薯在不同干燥条件下的干燥过程均满足Henderson and Pabis方程,其中待定系数A、k与冻融次数呈立方关系,相关系数R~2为0.999;冻融甘薯在不同干燥条件下的有效水分扩散系数(D_(eff))在3.45×10~(-8)~5.41×10~(-8)m~2/s之间。     

冻融-热泵干燥机的设计与试验优化

为探究冻融处理对香菇热泵干燥特性的影响,设计了一种冻融-热泵干燥机。依据自制冻融-热泵干燥机的结构特点,在干燥箱内的5个不同位置布置9个干燥床架,并在每个床架上均匀布置若干料盘。根据冷冻与融化速率对香菇物理性质的影响,设计快冻慢融的冻融干燥方法。重点考察新鲜香菇干燥品质的变化情况,主要指标有干基含水率、水分比、复水性、色差、干燥速率、有效水分扩散系数等,并结合4种典型薄层干燥模型,利用水分比进行数据拟合,从而建立干燥数学模型。结果表明:冻融香菇在干燥箱不同位置有效水分扩散系数在1.98×10-7～2.36×10-7m2/s之间,色差、复水性差异性小,干燥后感官性较好,且复水值总体与色差L值呈正比;香菇冻融干燥各位置水分比和干燥速率变化情况基本一致,均匀性好。经过4次冻融处理,每次冻融后干燥速率短时间内有一定提高,随后下降,且随着冻融次数的增加,其对水分迁移速率的影响呈下降趋势,第4次冻融后干燥速率无明显变化,说明随着香菇含水率的下降,冻融处理对水分的剥离能力逐渐减弱。在20 h进入单纯热泵干燥阶段,在30 h基本达到平衡含水率,单纯热泵干燥过程存在加速与降速阶段,无明显恒速干燥阶段。冻融香菇在不同干燥条件下的干燥过程均满足Henderson and Pabis方程,其中待定系数a,b,c,k,g,h与层架之间呈5次方关系,相关系数R2为0.998。本文为冻融-热泵干燥机的设计及香菇冻融干燥提供参考。     

龙眼热泵干燥特性及数学模型的研究

以整果龙眼为原料,研究高温热泵干燥不同工艺条件对龙眼干燥特性的影响,并建立相应的数学模型.结果表明:与干燥风速相比,干燥温度对龙眼整果干燥速率影响较大,干燥温度越高,干燥用时越短;风速对龙眼干制加工时间的影响随干燥温度的减小而增大;干燥过程分为三个阶段,加速期、恒速期和降速期,降速期为干燥的主要阶段;除65℃、1.0m/s干燥条件外,有效水分扩散系数随干燥温度的增加而增加;整果龙眼热泵干燥的活化能为25.12K J/mol;采用10种薄层模型拟合龙眼整果的热泵干燥曲线,发现Midilli模型模拟效果最优,该模型能根据热泵干燥的时间、温度和风速为整果龙眼的干燥过程提供可靠的分析和预测.     

杏子红外辐射干燥特性及数学模型

为了改善杏子在传统干燥过程中卫生条件差、能耗大、干燥后品质不高、环境污染等问题,将红外辐射干燥应用到杏子干燥。研究了杏子在不同干燥条件下的干燥特性曲线,求出不同条件下有效水分扩散系数并建立了数学模型。结果表明:随着辐射温度和辐射距离减少,物料的有效水分扩散系数不断增加,且辐射温度对杏子红外辐射干燥影响更明显;在干燥过程中杏子水分比的变化规律符合以Page模型为基础的数学模型。     

大果山楂片热风干燥特性及其动力学模型

为了解大果山楂片在热风干燥条件下的干燥特性,试验以大果山楂为原料,大果山楂片干基含水率和干燥速率为考察指标,研究不同大果山楂片厚度、装料量和热风温度对干燥速率的影响,并建立大果山楂片热风干燥的动力学模型。结果表明,不同大果山楂片厚度、装料量和热风温度均对大果山楂片热风干燥特性影响较大,随着热风温度的升高,干燥速率增大;随着山楂片厚度和装料量的增加,干燥速率降低。不同条件下的干燥均可分为加速和降速干燥2个阶段。根据试验数据建立数学模型,大果山楂片热风干燥的动力学符合Page模型,此模型适合对大果山楂片热风干燥过程进行预测和描述。该研究结果可为预测热风干燥过程中大果山楂片水分含量和干燥时间提供理论依据。     

渗透-中短波红外联合干燥对猕猴桃切片干燥特性及动力学模型的影响

采用不同含量果葡糖浆与不同中短波红外干燥温度进行联合干燥,研究不同条件下猕猴桃切片的干燥特性、有效水分扩散系数,建立渗透与中短波红外联合干燥动力学数学模型。试验结果表明:猕猴桃切片的渗透-中短波红外联合干燥的过程属于降速干燥,有2个阶段的降速过程,二者的水分转换范围为0.300~0.900(d.b)。在试验条件下,水分有效扩散系数在1.08×10-10~2.38×10-9m2/s范围内变化。所用6个模型均能较好地描述猕猴桃切片联合干燥过程中的水分变化规律,其中"Two-term"模型对整个过程的拟合性最好,其R2的均值达0.99958,χ2和RSME的均值分别为3.90000×10-5,5.01000×10-4。     

番木瓜热风干燥特性分析

探讨不同干燥温度和不同切片厚度条件下番木瓜的热风干燥特性。通过9种数学模型对番木瓜热风干燥试验数据进行拟合,结果表明:同大多数农产品干燥一样,番木瓜热风干燥主要为降速过程。不同干燥温度和物料厚度番木瓜热风干燥的水分有效扩散系数Deff的变化范围分别是1.798 4×10-8~3.323 3×10-8,0.579 3×10-8~2.852 2×10-8 m2/s,由此可以看出番木瓜热风干燥的水分有效扩散系数随着干燥温度和物料厚度的增大而增大;Page模型是番木瓜热风干燥过程的最适模型,平均R2值、SSE值、RMSE值和X2值分别为0.998 1,0.003 3,0.012 4,0.000 2。经回归分析,得到温度、厚度与有效水分扩散系数Deff的关系表达式。研究结果可以为生产实践中预测番木瓜热风干燥的水分变化提供参考。     

黄秋葵热风与远红外干燥特性、动力学及品质的比较

为获得黄秋葵干燥工艺条件,选取不同干燥方式、干燥温度对黄秋葵进行干燥,研究不同干燥工艺条件对干燥特性、动力学和品质的影响。结果表明：热风干燥速率受干基含水率的影响大,远红外干燥速率受干基含水率的影响小。Midilli 模型能准确描述黄秋葵热风和远红外干燥过程。在相同温度下,热风干燥的有效水分扩散系数比远红外干燥的大0.52～1.10 倍,热风干燥所需活化能比远红外干燥所需活化能低5 481.76 J/mol。干制品的VC 降解、复水比和硬度受温度和时间累积效应的影响。以干燥特性、动力学和干制品品质为指标,基于主成分分析获得黄秋葵干燥条件,热风温度70 ℃,干燥时间为300min,有效水分扩散系数为1.36×10-9m2/s,所得干制品VC 含量7.71mg/100g、复水比6.03、硬度3.25 N。     

甘蓝型油菜籽热风干燥特性及其数学模型

油菜籽的干燥和储存直接影响种用油菜籽的生理特性和作物产量以及加工用油菜籽的加工特性和制油品质,为了给油菜籽热风干燥装置设计、工艺和过程控制优化提供基础依据,本文研究了不同初始含水率、热风温度和风速条件下甘蓝型油菜籽的热风干燥特性,比较了10种数学模型在甘蓝型油菜籽热风干燥中的适用性。结果表明:油菜籽热风干燥过程没有出现明显的恒速干燥阶段,干燥主要发生在降速干燥阶段;Page模型是描述油菜籽干燥特性的最佳数学模型,由模型预测的干燥特性曲线与实验所得的干燥曲线一致性好;热风温度是影响油菜籽热风干燥的主要因素,随着热风温度的升高,油菜籽的有效水分扩散系数增大,当热风温度从45℃增加到65℃时,其有效水分扩散系数由3.835×10-10 m2/s增加到7.666×10-10 m2/s,油菜籽的干燥活化能为29.26 kJ/mol。     

大果山楂发酵液改善高脂饮食小鼠肥胖指标和肠道菌群多样性

研究大果山楂发酵液对高脂饮食小鼠体质量、体脂肪、血脂及肠道菌群的影响。将32只C57BL/6雄性小鼠随机分为4组：正常组、高脂饮食组、低浓度大果山楂发酵液组和高浓度大果山楂发酵液组,处理12周,测定相关肥胖指标和肠道菌群。结果表明,大果山楂发酵液可抑制由高脂饮食导致的体质量、内脏脂肪指数和肝脏指数增加;降低高脂饮食小鼠总胆固醇（TC）、肝甘油三酯（TG）和低密度脂蛋白（LDL）含量;增加高脂饮食小鼠肠道菌群丰度和多样性,提高拟杆菌门（Bacteroidetes）相对丰度,降低厚壁菌门（Firmicutes）相对丰度;8种菌的相对丰度在高脂饮食组和大果山楂发酵液组差异显著（P＜0.05）。     

Ethanol pre-treatment to ultrasound-assisted convective drying of apple

For the first time, the ethanol as pre-treatment to the ultrasound-assisted convective drying of food was evaluated. Pre-treatments were performed by immersion of apple slices in ethanol (0–30 min). Pre-treated samples were convectively dried (50 °C, 1 m s⁻¹), without/with ultrasound (21.77 kHz, 20.5 kW/m³). As results, if both technologies were considered, conventional drying time reduction reached 70 ± 2%. From drying kinetics modelling, it was identified that ethanol pre-treatments mainly reduced the external resistance to mass transfer, while ultrasound had a greater influence on the internal one. In dried samples, as the ethanol pre-treatment time increased, the shrinkage decreased, and their rehydration capacity was greater. After rehydration, samples showed a decrease of >85% in viscoelastic characteristics. The antioxidant capacity and total phenolic content were better retained with ultrasound application. The obtained results corroborate that the proposed technologies are complementary significantly accelerating the drying without negative effects on physical properties.     

Effects of high hydrostatic pressure or high intensity electrical field pulse pre-treatment on dehydration characteristics of red paprika

The effects of various pre-treatments (hot water blanching, skin treatments, high pressure and high intensity electric field pulse treatment) on the dehydration characteristics of red paprika (Capsicum annuum L.) were evaluated and compared with untreated samples. Hot water blanching (100°C, 3 min) prior to dehydration (fluidised bed dryer at 60°C, 6 h and 1 m/s) resulted in the permeabilisation of 88% of the cell membranes in paprika, which in turn resulted in a higher mass and heat transfer. Skin treatments (such as lye peeling and acid treatment), as practised conventionally, increased dehydration rates but affected only the skin permeability. The application of high hydrostatic pressure (HHP, 400 MPa for 10 min at 25°C) or high intensity electric field pulses (HELP, 2.4 kV/cm, pulse width 300 μs, 10 pulses, pulse frequency 1 Hz) pre-treatments resulted in cell disintegration indexes of 0.58 and 0.61, respectively. Cell permeabilisation of these physical treatments resulted in higher drying rates, as well as higher mass and heat transfer coefficients, as compared to conventional pre-treatments.     

Gelling properties of duck albumen powder as affected by desugarization and drying conditions

The effects of desugarization using glucose oxidase/catalase and spray‐drying conditions on gelling properties of duck albumen powder were studied. Gelling temperatures increased as spray‐drying inlet temperatures (140–180C) were increased (p < .05). ΔE*, a*‐, and b*‐ values of gel increased but L* and whiteness decreased when higher spray‐drying temperatures were used (p < .05). However, whiteness and lightness of albumen gel were drastically increased after desugarization (p < .05). Texture profile analysis showed that hardness, springiness, gumminess, and chewiness of gel decreased with increasing spray‐drying temperatures. Moreover, gel of freeze‐dried desugarized albumen powder had higher hardness, springiness, gumminess, and chewiness than that of spray‐dried nondesugarized counterpart (p < .05). Albumen gel prepared from desugarized albumen powder showed the compact network with more connectivity and smaller voids than that from nondesugarized one as visualized by scanning electron microscopy, regardless of drying conditions. Prior desugarization could lower browning and increased gelling properties of duck albumen powder. Higher spray drying inlet temperature generally exhibited the adverse effect on properties of resulting albumen powder. Both desugarization and drying conditions had the profound influence on characteristics and textural property of duck egg albumen.     

Effect of processing on the texture and structure of raspberry (cv. Heritage) and blackberry (cv. Thornfree)

This paper reports separate studies of the effect of pre-treatments (CaCl₂, low methoxyl pectin (LMP), and combined solutions) and the effect of freezing method (at four different rates) and thawing mode (at two different rates) on objective parameters, structure and sensory characteristics of fresh raspberries and blackberries. After that, the effect of a complete freezing process combining the best pre-treatments with the best freezing/thawing conditions found for each fruit was investigated. Kramer Shear Cell (KSC), back extrusion, compression and multiple penetration tests were used to measure fruit texture objectively. For calcium and LMP pre-treatments, which were applied separately, texture parameters were significantly higher in samples treated at the highest concentrations (100 mM of CaCl₂ for both fruits and 0.3 and 3% of LMP for raspberry and blackberry, respectively) compared to fresh controls. Blackberry structure was more susceptible than raspberry structure to the effect of pre-treatments. For the combined pre-treatments, the highest texture parameters were found in the samples treated with CaCl₂ (100 mM) and LMP (0.1%) in the case of raspberries and CaCl₂ (100 mM) and LMP (3%) in the case of blackberries. Combined pre-treatment did not increase firmness with respect to that of samples treated only with calcium, which indicates that CaCl₂ preserved the raspberry structure more efficiently during processing. Fruits frozen by forced convection with liquid nitrogen vapour at –40 °C were significantly firmer. Raspberries should be thawed at 5 °C, whereas blackberries may be thawed at room temperature. Sensory analysis showed that the blackberry structure was more resistant to freezing. In both fruits, over the complete process parameter values were again highest in the samples treated with 100 mM CaCl₂, applied either separately or in combination with LMP. In raspberry, panellists detected no significant differences between sensory texture parameters of the different samples, and in blackberry, panellists found no significant differences between any of the sensory characteristics. Multiple penetration maximum force (F _MP) was the parameter that best expressed product firmness for both fresh and frozen raspberries, whereas compression slope (S _C) best reflected changes in blackberries. SEM mainly corroborated results from objective texture parameters.     

Effect of temperature on the drying characteristics,colour, antioxidant and beta‐carotene contents of two apricot varieties

In this study, the drying characteristics, colour, oxygen reactive antioxidant capacity (ORAC) and beta‐carotene contents of two apricot varieties dried at different temperatures were compared. The hot air drying of apricot slices for both varieties consisted of a constant rate period (CRP) and two of falling rate periods (FRP). The CRP drying rate and the first and second FRP drying coefficients increased with drying temperature for both apricot varieties. The first and second FRP of both apricot varieties gave activation energies of 23.5–28.7 and 25.6–29.3 kJ mole^?1, respectively. The colour values (L*, a* and b*) of both dried apricot varieties decreased with increasing temperature, while the total colour change of both dried apricot varieties increased with temperature. The chroma, hue angle and browning index values of both dried apricot varieties decreased with increasing temperature, and the hydrophilic ORAC and beta‐carotene contents increased with drying temperature.     

Structural and Chemical Characteristics of Sisal Fiber and Its Components: Effect of Washing and Grinding

This work covers the study of microstructural changes of natural sisal fibers induced by different conditioning pre-treatments: mechanical grinding, cryogenic grinding, and hot water washing. The aim of the work is to clarify the effects of the pre-treatments on crystallinity and infrared spectra of sisal. Scanning electron microscopy results allowed to identify morphological changes on the fiber surface. Deeper changes of chemical origin were studied by attenuated total reflectance/Fourier transform infrared spectroscopy (FTIR) and focused on the main components of cellular walls: cellulose, lignin, and xylan. The work was complemented with crystallinity index (I_c) data determined by two very different methods: the widely used for lignocellulosic fibers Segal equation based on X-ray diffraction measurements, and the other based on FTIR through the 1430/900 cm^?1 band intensity ratio, which is mostly used with cellulosic samples.     

Quality improvement of non-sulphited mango slices by drying at high temperatures

An optimum drying routine for producing non-sulphited mango slices has been developed. The interaction of essential drying parameters (air temperature, air velocity, dew point, slice thickness and drying time) on water activity (a_W) and browning was determined. Microbiological stability of the dried product was achieved at a moisture content of 17% wet base (w.b.) corresponding to a_W = 0.6. Browning was monitored by the red colour shade of the product (CIE-Lab chromaticity coordinate a*). Drying air temperature and drying time were shown to be the primary factors influencing product colour and a_W. In contrast to common practice, drying for about 6 h at elevated air temperature (80 °C), instead of 50 or 60 °C for a longer time, was optimal, since significant colour changes of the mango slices were not observed even without the use of any chemical or thermal pre-treatment. Moreover, at increased temperature, drying time was considerably shortened from about 9 h to 6 h, resulting in significant extension of the drying capacity.

Industrial Relevance

The suggested process concept for dried mango slices based on high-temperature drying is of utmost significance for the international marketing of dried fruit products. Chemical pre-treatments such as sulphitation often used to minimise quality deficiencies could be avoided. Sulphitation has been recently under critical consideration with respect to allergen labelling of foodstuffs implemented by EU-Member States in November 2004 (Directive 2003/89/EC) [Directive 2003/89/EC. Official Journal of the European Union, 25.11.2003, pp. L308/15–18 (http://europa.eu.int/eur-lex/pri/en/oj/dat/2003/l_308/l_30820031125en00150018.pdf)]. Export quality was improved and the drying process simplified, improving the utilisation of drying capacities. Particularly referring to an application of the technology in small- and medium-sized enterprises with limited investment possibilities, the suggested novel drying procedure in mango processing aimed at the optimisation of well-established simple drying methods instead of choosing technically more sophisticated technologies.     

不同组合渗透与冷冻前处理对蓝莓干燥品质的影响

为研究渗透、冷冻前处理对食品干燥品质的影响,同时为改善产品品质提供理论支撑和技术指导,以蓝莓为研究对象,在对样品进行相同干燥处理(热风,30 h,60℃)前,进行不同组合模式的渗透(海藻糖、氯化钙、蔗糖)和冷冻-解冻(液氮-80℃,室温)前处理,以干果的脱水速率、含水量、色泽、质构、总糖、抗氧化活性物质等作为评价指标进行分析。研究显示:不同组合渗透、冷冻-解冻前处理对蓝莓物化品质影响显著,冷冻-解冻-渗透-干燥组为最优,较单一渗透处理组、单一冷冻-解冻处理组、未前处理组脱水速率分别提高5.55%、6.39%、36.91%;硬度分别提高8.59%、39.80%、909.00%;总糖含量保持率分别提高1.10、1.44、2.70倍,抗氧化活性(总酚、花色苷、ORAC)提高了16%以上。结果表明:冷冻-解冻处理可以促进渗透效果,渗透与冷冻-解冻前处理模式结合对干燥速率的加快和干燥品质的提升具有显著协同作用。     

Application of PEF- and OD-assisted drying for kiwifruit waste valorisation

The production of dried snacks with high nutritional value represents a valid alternative to use the kiwifruit waste as undersized fruits, with a positive economic impact on the entire production chain. Therefore, this work aimed to evaluate the effect of pulsed electric field - PEF (200 V/cm) and/or osmotic dehydration – OD pre-treatments on drying kinetics (50, 60, 70 °C), texture, colour, and sensorial properties of yellow kiwifruit snacks. The drying kinetics were significantly influenced both by applied treatment and drying temperature. The firmness of the kiwifruit snacks was improved by the combination of PEF/OD pre-treatments. In general, drying temperature of 70 °C and the use of combined pre-treatments seem to be a good compromise to reduce drying time and obtain products with high quality in terms of colour, firmness, and overall acceptability.