Microwave heating is a convenient way to heat materials; it is considered to be a fast, clean, and easy to use technology. The use of microwaves for industrial food unit operations is the subject of research since several years ago. However, the application of microwaves depends, among other variables, on the dielectric properties of the material to be heated; otherwise, the efficiency of the process and the quality of the final product cannot be guaranteed. This paper reviews basic concepts related to microwaves and dielectric properties, and then it presents reported dielectric properties data for selected fluid foods and microwaveheating processes that have been recently studied. These processes are focused mainly on microbial inactivation, enzyme inactivation, chemical, physical, or sensory changes evaluation, or for reheating. The temperature uniformity is also discussed as a key issue for successful application of microwave heating, which is now applied by some companies.

100 g -1 of calyces. The total monomeric anthocyanin content (209±21 mg . 100 g -1 ) was similar to that obtained using the HPLC technique (215±31 mg . 100 g -1 ) when extracting the calyces with the 50:50% (v/v) ethanol:water solution. The deepest red-purple (Hue = 62.50±0.34) colored solution was observed when extracting the calyces with ethanol. The antioxidant and color properties of Roselle calyces make the extracts ideal for use in foods as a natural extract, concentrate, or powder.

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Bee pollen is a hive product, resulting from floral pollen agglutination by worker bees and it is characterized by its excellent bioactive and nutritional composition. Currently, research is focused on bee pollen applications on food industry, because this product has been considered an excellent source of compounds for human nutrition. It is also important in some industries, where color and particle size are important characteristics for production. Due to the granular nature of bee pollen, conventional colorimetry does not allow describing color correctly; thus, digital image analysis is a better alternative. This technique could also allow classifying bee pollen according to its appearance beyond the color. Consequently, the aim of this work was to develop a novel methodology for image data processing to classify bee pollen as ingredient in food industry. Seven color groups in samples were established regarding harvest month and particle size.It was possible to calculate the percentage of each color group in all samples. This methodology also allowed selecting each fraction for different applications in food industry using colorimetry, granulometry and the 2 relationship between both of them.

This study compared the stability of extracts of calyces microencapsulated with different concentrations of mesquite gum during storage. Dry Roselle calyces were mixed with 50:50 (v/v) ethanol:water solution to obtain 18°Bx concentrate. This Roselle extract concentrate was mixed with purified mesquite gum (100:1-100:5 v/w). The Roselle extract concentrate-gum (RECG) was spray dried at inlet and outlet temperatures of 180 ± 2 and 104 ± 2.3 °C, respectively, at an air flow rate of 38 m/h. Encapsulated Roselle powders (ERP) were analyzed for moisture content, total monomeric anthocyanins (differential pH), phenolic compounds (Folin and Ciocalteu method), antioxidant capacity (ABTS), and color parameters ([Formula: see text], and [Formula: see text]) after 5 weeks and 1 year of storage. Sorption properties (isotherms) and micrographs of powders were also obtained. The average yield of RECG powders was 15.27 ± 0.81 g/100 mL. During storage, ERP showed average values of phenolic compounds, antioxidant capacity, and anthocyanins of 3.43 ± 0.25 g gallic acid equivalents/100 g, 9.34 ± 1.4 g Trolox equivalents/100 g, and 318.7 ± 20.6 mg cyanidin--glycoside/100 g, respectively. Color parameters remained constant along the storage time.

Microwave technology for the pasteurization of fruit juices offers advantages over conventional processing methods due to volumetric heating and fast rates that result in shorter processing times. In this study, guava nectar was pasteurized by microwave heating (2450 MHz) to 90°C using 500 or 950 W. For comparison, nectar pasteurization at 90oC was performed using a plate heat exchanger (PHE) at 400 or 200 mL/min for holding times 3.1 and 12.5 s respectively. After thermal treatments, nectars were stored at 4°C and analyzed over a storage period of 12 days. Results showed a significant pectinmethylesterase inactivation. 94% of vitamin C was retained in microwave pasteurized nectar at 12th day storage for samples treated at 500 W. Rheological properties for nectar remained without significant variations during storage. Color was better preserved after microwave treatments (ΔE*= 0.69-0.75) as compared to samples processed by PHE (ΔE*= 1.84-2.75). Microbial counts remained below detectable levels throughout storage.

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