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。     

超临界CO2萃取姜挥发油及GC-MS分析

正交试验法时超临界CO2提取生姜挥发油的提取条件进行研究.结果表明,最佳提取条件为:原料粒径为03mm,萃取压力25 MPa,温度40℃,CO2流量30 kg/h,萃取时间100min,所得姜精油呈浅黄色,得率由传统水蒸气蒸馏法的1%左右提高到4.38%.采用气相色谱-质谱联用技术测定最佳提取条件下所得生姜挥发油的化学成分及其相对质量分数,共分离出58种成分并鉴定出其中38种,主体呈香成分为柠檬烯、α-蒎烯、莰烯、金合欢烯、β-水芹烯、β-倍半水芹烯、姜烯等烯类.主体辣味成分为6-姜醇.     

THIN-LAYER DRYING KINETICS OF SESAME HULLS UNDER FORCED CONVECTION AND OPEN SUN DRYING

Sesame hulls are a useful by‐product of the sesame processing industry. The sesame hulls are produced at a high moisture content (68% wet basis) and need further drying to prevent deterioration. In this study, both open sun drying (OSD) and forced convection drying (FCD) at 42, 55, and 76C and 1.2 m/s air velocity were investigated. Six common thin‐layer drying models were fitted to the experimental data. Several statistical parameters were used to evaluate the performance of thin‐layer drying models, including r², x², root mean square error (RMSE) and residuals. Sesame hull drying was found to take place completely in the falling rate region. The modified Page model was found to describe OSD data well, while the Wang and Singh model was the best model for describing FCD. Effective diffusivity was found to be 1.89 × 10^‐8 m²/s and 7.36 × 10^‐10 to 1.20 × 10^‐9 m²/s for OSD and FCD, respectively. Activation energy was also found to be 12.95 kJ/mol for FCD.     

DRYING KINETICS OF RED PEPPER

Desorption isotherms of unblanched and blanched red peppers were experimentally obtained at 30C. The desorption data were exploited to estimate equilibrium moisture contents of the peppers at drying temperatures other than 30C by using a semi-empirical method. Red pepper samples were dried in a tunnel-type drier with an air velocity of 2 m/s at 50C, 60C, 70C, and 80C. The blanched samples dried faster than the unblanched ones. The drying behavior of unblanched and blanched samples was characterized by falling rate period, and constant and falling rate drying periods, respectively. The interphase mass and heat transfer coefficients of the blanched sample during the constant rate period were not affected by temperature and estimated to be 1.94*10⁻³ kg mol/s. m² and 57.3 W/m². K, respectively. Effective moisture diffusivity was estimated between 6.83*10⁻¹⁰−17.4*10⁻¹⁰ m²/s for the unblanched sample and 11.4*10⁻¹⁰−31.0*10⁻¹⁰ m²/s for the blanched sample within the given temperature range. Effect of temperature on the diffusivity was described by an Arrhenius-type equation with an activation energy of 28.4 kJ/mol for the unblanched pepper and 33.3 kJ/mol for the blanched pepper.     

MICROWAVE FINISH DRYING OF POTATO CHIPS

The effect of microwave finish drying of potato chips on their texture, color and oil content was studied. The intermediate moisture content (IMC) of the chips before microwave application and the reducing sugar content of the raw potatoes were the primary variables. The slices were individually submerged in oil at 320° F to various IMC and finish dried with 2500 watts microwave power for 1–3 min. Chip color was rated against PC11 Color Standards. Texture was evaluated subjectively by a panel and objectively by the L.E.E. Kramer Shear Press. Oil determination was made by Soxhlet extraction. The results showed that potato chips removed from the oil at IMC above 13% were unacceptably tough after microwave drying. Potatoes containing more than 0.9% reducing sugar had to be removed from the oil at IMC above 13% in order to obtain acceptable color of the microwave-finished product. Therefore, microwave finishing raises the limiting reducing sugar content from about 0.4 to about 0.9%. Oil content of microwave-finished chips was 90% that of conventional controls     

INFLUENCE OF COMBINED MICROWAVE‐VACUUM DRYING ON DRYING KINETICS AND QUALITY OF DRIED TOMATO SLICES

ABSTRACT

The study investigated the influence of four microwave powers on the drying kinetics and quality of tomato slices in a microwave‐vacuum dryer at vacuum pressures of 0.04, 0.05 and 0.06 MPa. The results showed that increase in microwave‐vacuum drying conditions increased drying rates and resulted in decreased drying time from 84 to 14 min. The nonenzymatic browning index increased with microwave power whereas the overall flavor degradation was between 18.99 and 20.80%. The brightness and the yellowness of the dried tomatoes generally increased but there was a slight reduction in redness when compared with the fresh. The effective moisture diffusivity increased with microwave power and was 7.22 × 10^?9, 9.10 × 10^?9, 14.99 × 10^?9 and 25.19 × 10^?9 m²/s at respective microwave powers of 200, 300, 500 and 700 W.

PRACTICAL APPLICATIONS

Microwave‐vacuum drying is one of the advanced methods with numerous advantages including high thermal efficiency, shorter drying time and improved product quality. Tomato is the second most important vegetable with enormous health benefits, which include reduction of cholesterol, improvement of vision, maintenance of gut, lowering of hypertension, alleviation of diabetes, and prevention of urinary tract infections and gallstones. The quality of dried products obtained using the microwave‐vacuum dryer provides industries with method that can be used to enhance the quality of dried tomatoes. The dried product is a valuable ingredient in the preparation of soups and sauces, as well as in cosmetics and pharmaceutical formulations.

     

微波干燥在亚麻纺织工业的应用

介绍了微波干燥的原理和主要特点,研究了利用微波干燥亚麻纱管的工艺,探讨了微波辐射时间、微波功率对亚麻纱管脱水率的影响,考察了工业微波干燥机的干燥能力,并将实验结果与传统烘房干燥后亚麻纱的色差和断裂强度进行了比较。     

分子包埋法制备姜油树脂微胶囊的研究

以姜为原料，经乙醇直接浸泡和索氏提取法获得的姜油树脂为心材，以β-环糊精和阿拉伯胶为壁材，经乳化、均质、喷雾干燥，制取姜油树脂微胶囊，并对其主要技术参数进行了测定。通过正交试验分析，以姜油树脂的包埋率为指标，确定了心壁材比、包接温度、搅拌时间、阿拉伯胶和β-环糊精比四个因素的最佳值，得出了姜油树脂微胶囊化的最佳工艺条件。     

EVALUATION OF THIN-LAYER DRYING MODELS FOR DESCRIBING DRYING KINETICS OF BARBERRIES (BARBERRIES VULGARIS)

Barberry is known as a medicinal and ornamental plant throughout the world. Edible fruit from the barberry is used in medicine to treat liver, neck and stomach cancer, for purification of the blood and for breath freshness. In order to assess and select a suitable form of the drying curve, six different semitheoretical and/or empirical models were fitted to the experimental data. Experiments were performed at air temperatures of 50, 60 and 70C. At each temperature, three air velocity values were selected: 0.5, 1 and 2 m/s. Consequently, of all the drying models, the Page model was selected as the best mathematical model according to R ², χ ² and root mean square error parameters. Constants related to the Page model are reported and regressed against air condition using multiple regression analysis.

PRACTICAL APPLICATION

All commercial flow dryers are designed on thin-layer drying principles. Thin-layer drying means to dry as one layer of sample particles or slices. In this paper we present a mathematical model for thin-layer drying of barberry fruits (moisture ratio against time). Definition of moisture ratio as a function of time and drying condition has many advantages such as (1) easy control of dryer system, (2) lower energy consumption, (3) less thermal damage to the products and (4) lower investment. It is believed that the present study should be useful to people seeking (1) to optimize the design of drying systems and their components, and (2) to identify appropriate applications and optimal configurations for drying systems.