EFFECT OF DIFFERENT DRYERS AND DRYING CONDITIONS ON ACCEPTABILITY AND PHYSICO-CHEMICAL CHARACTERISTICS OF DURIAN LEATHER

Optimization study on drying condition ofdurian leather was carried out using Response Surface Methodology (RSM). The optimization was conducted for two different dryers, oven dryer and forced-air cabinet dryer, with temperature and time of drying as independent variables. It was shown that both variables significantly affected most of the sensory properties. For both dryers, the optimum points for 5 sensory attributes evaluated including taste, aroma, texture, appearance and overall acceptability, were at temperatures ranged from 47–55 C for 10–14 h. Based on the overall acceptability, the optimum condition for oven-dried leather was achieved at temperature 50C for 12.6 h, while for cabinet-dried leather at 52.5C for 10 h. Results showed that panelist preferred product dried with low temperature-long time compared with high temperature-short time. Except for Hunter color b value of cabinet-dried product, results also indicated that drying condition was significantly influencing the physico-chemical properties such as moisture, A_w, nonenzymatic browning, texture, vitamin C and color of durian leather.     

THE EFFECT OF PROCESSING METHOD ON THE CHARACTERISTICS OF CARROT JUICE

ABSTRACT

The production of carrot juice using different technologies is the main subject of this investigation. Although the production and preservation of the carrot juice technology have not been improved and are not prevalent, an intensive study has been carried out on this subject recently. In this study, the effects on the yield and quality of carrot juice produced with and without total enzymatic liquefaction (Pectinex Ultra SP‐L, Novo Nordisk Ferment, Dittingen, Switzerland) as well as lactofermentation or citric acid addition have been investigated. Generally, enzymatic liquefaction of mash increased the juice yield (89.32 ± 1.17 and 90.43 ± 0.47% for lactofermented and citric‐acid‐added samples, respectively), while the control sample juice yield was found to be 59.90 ± 0.81%. Lactofermented and acid‐added samples demonstrated lower pH value. In enzyme‐treated samples, the total acidity increments were also determined. Accordingly, galacturonic acid formed after enzymatic breakdown of pectin in the raw material increased the total acidity of the samples. Magnesium contents of lactofermented juices were found to be low because lactic acid bacteria require magnesium for their growth. β‐Carotene contents have been found to be higher in both lactofermented and in nonenzyme‐treated samples.

PRACTICAL APPLICATIONS

This article describes the effects of different processing methods on the characteristics of carrot juice. It is difficult to preserve vegetable juices such as carrot juice because of their low acidity. The acidity of carrot juice (pH ～6.2) can be adjusted by the addition of citric acid or the lactofermentation method to pH 4.5. With these processes carrot juice can be preserved by pasteurization as occurs for low pH fruit juices, increasing shelf life. According to the results of this study, increasing the acidity of mash with lactofermentation or citric acid addition also increases the juice yield.

     

胡萝卜木瓜南瓜复合保健饮料的研制

以胡萝卜、木瓜、南瓜为主要原料,采用正交试验设计方法、单因素试验设计及感官评定研究胡萝卜、木瓜、南瓜复合果蔬饮料的最佳配方.试验结果表明,最佳配方为:胡萝卜木瓜南瓜体积比为10:30:20,白糖12%,柠檬酸0.26%,琼脂0.1%.     

果蔬片微波干燥特性及最佳工艺研究

通过对利用微波干燥香蕉片的研究，揭示了微波干燥果蔬片的失水特性。同时，进行四因素三水平的正交实验以及二因素三指标的二次正交回归实验，得出各指标的回归方程，并进行参数优化，从而得到最佳工艺条件：前期发射功率为900W、前期时间2min、后期发射功率397W、后期时间11．3min。     

CONVECTIVE DRYING OF PUMPKIN: INFLUENCE OF PRETREATMENT AND DRYING TEMPERATURE

The aim of this research was to study the influence of blanching as a pretreatment on the drying rate, color and rehydration rate of pumpkin slices ( Cucurbita maxima ) dried in a convective dryer at 50, 60 and 70C.
The different pretreatments did not modify drying time. The diffusion coefficient depended on temperature and moisture content, but not on pretreatments. It varied between 1.6 and 2.9  ×  10⁻⁹ m²/s and activation energy was approximately 35.6 kJ/mol. The rehydration rate of the dried sample, which was found to be influenced by drying temperature but not by the pretreatments, reached about 2 kg water/kg dry solid in about 150 s in boiling water. Color parameters " L " and " b " were influenced by drying temperature and pretreatments. Parameter L varied between 36 and 53 and parameter b varied between 20 and 31. Samples dried at 70C without pretreatments presented color parameter values very similar to those of the fresh sample.

PRACTICAL APPLICATIONS

This work evaluates the pretreatment and drying conditions of pumpkin. Five parameters of the optimal product are considered: pretreatment time, drying time, temperature, color and rehydration rate of the product. With these results, drying of pumpkin can be carried out in industrial convective dryers and the dried product may be used in the preparation of soups, premixed foods, snacks, etc.     

酸碱挤压联合作用对膳食纤维组成的影响

研究了酸碱预处理与挤压联合对大豆纤维进行加工的作用，结果表明：酸的浓度和强度以及碱浓度和水的数量对可溶性纤维（SDF）的转化都有利。变化主要发生在半纤维素部分，而纤维素所受影响很小。     

不同生产工艺对罗非鱼片的物理化学特性的影响研究

通过空气、真空和冷冻干燥等方法生产的罗非鱼,分析了样本的密度、多孔性以及毛孔大小分布,新鲜罗非鱼片的密度是1127kg／m^2,而分别通过空气、真空和冷冻干燥等方法生产罗非鱼肉的密度,依次是986,735and343kg／m^3冷冻干燥样本的多孔性比空气和真空干燥样本的高出很多。研究了罗非鱼片的过氧化值和颜色。     

STUDIES ON THE EFFECT OF SURFACTANT, BLANCHING AND OSMOTIC PRETREATMENTS ON THE CONVECTIVE DRYING OF POTATOES

Moisture removal from solids is an integral part of food processing. To approach the drying process of a given product it is necessary to have a knowledge of the drying kinetics. However, foodstuffs are often subjected to certain chemical and physical treatments, such as surfactant impregnation, osmotic dehydration or blanching, prior to convective drying. The drying behavior of potatoes was monitored within an experimental air tunnel dryer, with the mechanism of internal moisture migration being identified as diffusion. This was subsequently evaluated on the basis of the liquid diffusion theory. Experimental data revealed osmotic concentration as a favorable process. A 29±2% reduction in diffusion coefficient was observed following osmotic dehydration with a salt/sugar solution, however, this provided a 63±3% reduction in drying time. Structural modifications were induced by blanching, with this rendering a 10±1 and 27±2% lowering of the moisture transfer rate during drying at 30 and 60C, respectively.     

PHYSICO-CHEMICAL AND STORAGE CHARACTERISTICS OF GARLIC PASTE

A processed paste with a total solids and pH value of 33% and 4.1, respectively was prepared from fresh garlic by addition of 10% sodium chloride (w/w) and citric acid. Appearance of green pigment (in terms of the Hunter color -a* value) was noticed in the product during preparation. Paste was thermally processed at 70, 80 or 90C, respectively for 15 min. Greening of paste decreased with increase in temperature. Rheological data revealed that garlic paste behaved as a psuedo-plastic fluid with a flow behavior and consistency index of 0.14 and 279 Pa.sⁿ, respectively. The paste was analyzed periodically for color and microbiological counts. The product was found to be shelf stable at 25C for a period of at least 6 months. The green coloration decreased significantly (p<0.05) during storage.     

SUPERHEATED STEAM-DRYING OF MATE LEAVES AND EFFECT OF DRYING CONDITIONS ON THE PHENOL CONTENT

Four drying experiments of mate leaves (Ilex paraguariensis St. Hilaire) were carried out in a packed bed superheated steam dryer by varying outlet steam temperature from 120 to 140C and equivalent particle diameter from 4.7 × 10^?3 to 6.95 × 10^?3 m. The influence of these variables on the drying coefficient calculated by assuming a simplified drying kinetic model was investigated. A classical statistical approach revealed the significant effect of both factors on this parameter. Two additional drying runs were performed at identical conditions with conventional hot air and low pressure superheated steam, respectively. The influence of drying atmosphere on the total content of phenols was evaluated. A conventional process of extraction by using an aqueous methanol solution was adopted. Analyses for total phenols were performed by spectrophotometry at 715 nm by applying Folin‐Denis assay. The leaves dried with superheated steam had approximately 47% higher retention of these compounds.     

EFFECT OF SONIC ENERGY ON THE AIR DRYING OF APPLE AND SWEET POTATO CUBES

Cubes (2 cc) of apple and sweet potato were dried with and without sound energy in air at velocities of 5 – 20 fps and temperatures of 125 – 175°F. A stem jet or electronic whistle provided sound energy at 9,800 and 13,000 Hz with an intensity up to 135 dB. Results indicated that sonic energy had no effect on drying rate under all experimental conditions.     

喷雾干燥法制备南瓜粉的工艺参数研究

采用喷雾干燥法制备南瓜粉，通过对均质压力、料液温度、喷雾干燥进风温度3个因素进行单因素和正交实验分析，得出料液温度为40℃，均质压力为25MPa，喷雾干燥进风温度为160℃时制得的南瓜粉质量最佳，该南瓜粉的复水性、冲调稳定性及分散性较好。     

胡萝卜纸生产工艺及配方研究

开发可食性包装纸是减少白色污染，实现绿色包装的有效途径之一。本文以胡萝卜为基料，添加适当的增稠剂、增塑剂、抗水荆，利用胡萝卜的天然色泽，研究出胡萝卜纸的生产工艺参数及配方。得出胶粘剂的最佳配方是由海藻酸钠、羧甲基纤维素钠和琼脂三种增稠剂复合而成，复合胶粘剂的最佳比例是1：2：1，增塑剂的用量为3％；胡萝卜纸干燥的最佳温度是60℃～65℃。胡萝卜纸含水率的最佳值是12％～14％。胡萝卜纸可用于食品的内包装实现包装功能，还可直接用作方便食品食用，即能减少环境污染，又能增强食品美感，具有良好的市场应用前景。     

蓝莓花青素的提取及理化性质的研究

以蓝莓果为原料采用乙醇浸提法提取花青素,确定的最佳提取条件为pH 3.5、浸提温度50℃、浸提60min,浸提剂乙醇浓度为50%,提取1次,该条件下提取率为5.8%.对蓝莓花青素的理化性质研究结果表明,蓝莓花青素热稳定性较好:蔗糖和柠檬酸使蓝莓花青素的稳定性增强;还原荆Vc在低浓度下对蓝莓花青素的影响不大;Cu2 、Sn4 、Al3 、Fe3 对蓝莓花青素有稳定作用.     

DRYING RATE EFFECT ON THE PROPERTIES OF WHEY PROTEIN FILMS

The effects of drying temperature, drying relative humidity and film thickness on the drying characteristics, water vapor permeability, and tensile properties of glycerol (Gly)-plasticized whey protein isolate (WPI) films were investigated. 50%WPI:50%Gly and 60%WPI:40%Gly (dry basis) films were studied. Constant rate periods were compared among films. A higher temperature (95C) and lower relative humidity (30%RH) increased the slope of the weight versus time plot during the constant rate period, indicating shorter drying times to reach the falling rate period. Water vapor permeabilities were significantly lower for films dried at 95C and 30%RH than for films dried at 21C and 50%RH. Films dried at 95C and 30%RH were generally thinner, stiffer, stronger, and less extendable than films dried at 21C and 50%RH.