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The present study aimed to assess the drying kinetics of black rice and fit different mathematical models (empirical and diffusive) to the experimental data, and evaluate the effect of drying air temperature on the physical-chemical and bioactive compounds quality of black rice. Drying air temperatures ranged from 40 to 80 ºC and the drying air speed was 1.5 m/s. Physical-chemical characterization of the product was based on the following parameters: moisture, water activity, ashes, total protein content, pH, total acidity, lipids, total carbohydrates, total anthocyanins, flavonoids, total phenolic compounds and antioxidant activity. Among the empirical models, Page showed the lowest mean squared deviations (MSD) and highest coefficients of determination (R2). For the diffusion model, the values of effective mass diffusivity and convective heat transfer coefficient increased with increasing drying air temperature, and the Biot number indicated that the first-type boundary condition would also describe well the drying process. Physical-chemical parameters and bioactive compounds differed between the temperatures used, and the temperature of 60 ºC led to the best relationship between drying time and preservation of product characteristics.

The effects of different hydrothermal pretreatments on the physical chemical characteristics and drying kinetics of red rice starch (Oryza sativa L.) were investigated.The hydrothermal pretreatments chosen include the cooking, autoclave, and steam explosion processes. To obtain the starch in powder form, the pastes were dried at a temperature of 50°C with an air speed of 1.0 m/s. The mathematical models (empirical and diffusive) were adjusted to the experimental data. The starches were submitted to extraction yield, color, water binding capacity, and proanthocyanidins. The values for the diffusivity are between 3.08 × 10 −7 and 2.74 × 10 −6 m 2 /min for treatments. The pretreatments of cooking in the grain and autoclave in the starch gave better results than the other studied treatments (formulations), presenting shorter drying time (450 and 510 min) and higher yield (48.60% and 53.54%), respectively. With the application of pretreatments, it is possible to save energy and reduce thermal damage. Novelty impact statement:The results obtained in this study reveals the application autoclave pre-treatment in red rice starch effectively saves energy and reduces thermal damage as the drying time is shortened. In addition, the drying process information can be used when designing future new equipments. Highlights• The effects of different hydrothermal pre-treatments on the physical chemical characteristics and drying kinetics of red rice starch (Oryza sativa L.) were investigated.• The hydrothermal pre-treatments included the cooking, autoclave and steam explosion processes.• The pre-treatments of cooking (grain) and autoclave (starch) gave the best results, presenting shorter drying time (510 and 450 min) and higher yield (53.54% and 48.60%), respectively. | INTRODUC TI ONRice is a staple food consumed in many countries around the world due to its nutritional composition (Pereira-Caro et al., 2013). Presenting a series of pigmented varieties, among which red rice has attractive characteristics such as high content of proteins, minerals, vitamins, starch, and bioactive compounds (anthocyanins, proanthocyanidins, and carotenoids) (Sumczynski et al., 2016;Butardo et al., 2019).One of the carbohydrates most found in rice is starch, a polysaccharide that exhibits interesting properties because of its biodegradability, biocompatibility, and nontoxicity (Afolabi et al., 2012).

The aim of this study was to evaluate the effect of temperature on the drying kinetics of achachairu peels. Empirical and diffusive models were used to describe the drying kinetics and the thermodynamic properties of the process. Both fresh and dehydrated samples were characterized according to their bioactive compounds and antioxidant activity. The drying was carried out in an air circulation oven at a speed of 1.5 m s−1 at temperatures ranging from 40 to 80°C. Parameters of the effective diffusivity and activation energy were calculated considering the first six terms of Fick's model, and the thermodynamic properties are as follows: enthalpy, entropy and Gibbs free energy. Total phenolic compounds, antioxidant activity by ABTS•+ and DPPH•, and total tannins using aqueous and hydroalcoholic extracts were analysed for both fresh peels and the dehydrated. Page's model was considered to be the most appropriate for describing the drying process that occurred at a decreasing rate from the initial phases until the end of the process; Fick's model showed a higher diffusivity value at a temperature of 80°C. The activation energy of the process ranged from 27.773 to 27.569 kJ mol−1 depending on the number of terms used in Fick's model. The thermodynamic properties indicated that the process is endothermic and not spontaneous. The extraction process using solvents with different polarities (water and ethanol) enabled the extraction of phenolic compounds; however, the extraction by 'AE' revealed superior results for AA‐ABTS•+, TT and AA‐DPPH•, the latter not being capable of identifying differences in the fresh sample.

This study aimed to develop red rice flours in order to provide alternatives to replace conventional flours in the production of gluten-free foods for people who suffers from celiac disease. To obtain the flour, red rice grains were dried at temperatures of 40, 50, 60, 70, and 80 C and air velocity of 1.5 m/s. Mathematical models (empirical and diffusive) were fitted to the experimental data obtained and, subsequently, the dehydrated grains were ground to obtain the flour, which was subjected to physicochemical and bioactive characterization to verify the impact of the applied temperatures on the final product quality. It was found that the Page model is more reliable to describe the drying kinetics of red rice, since it showed higher coefficients of determination (R 2) and lower chi-square (χ 2). The diffusion model showed satisfactory fit, with coefficient of determination (R 2) higher than 0.99 and chi-square (χ 2) lower than 0.0146659. Higher drying rate was found at the temperature of 80 C, but cracks were observed in the grains and there was greater degradation of anthocyanins. The pH, total titratable acidity, and flavonoids did not differ between the temperatures applied. Lower values of moisture content, water activity, total phenolic compounds, and antioxidant activity were obtained in the grains subjected to temperature of 80 C. Therefore, the temperature of 40 C was the one that ensured greatest conservation of all bioactive compounds analyzed and greater antioxidant activity for all three methods. Practical applications: The diffusion model provides a realistic and physical interpretation of the drying operation, stimulating the correct time needed to reduce the moisture content of the material, of initial value at the equilibrium value. In this way, it is possible to save energy and reduce the degradation of bioactive compounds promoted by thermal damage, which material is submitted, in addition to aiming at the optimization of drying equipment projects. 1 | INTRODUCTION Rice (Oryza sativa L.) has several types of cultivars and is a widely consumed food in the world, with different colors, such as white, black, red, and brown. Red rice is thus called because of the reddish color of the pericarp of the grains, which in turn is due to the accumulation of tannins and anthocyanins (Agostineto, Fleck, Rizzardi,

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Properties of modified starch and its interaction with functional raw materials are of great interest to the food industry. Thus, this study aimed to evaluate the rheological and technological characterization of starches modified by the action of the enzymes α-amylase and amyloglucosidase and their mixtures with jaboticaba peel powder. The parameters of firmness, gumminess, and final viscosity of starches paste increased, and the tendency to setback was reduced with the addition of jaboticaba peel powder. Starches and mixtures presented shear-thinning behavior. The addition of jaboticaba peel powder to starches increased water, oil, and milk absorption capacity, while syneresis remained stable over the storage period. The addition of jaboticaba peel powder had a positive effect on native and modified starches' rheological and technological properties, qualifying it as an alternative for developing new functional food products.