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This work described the hydration kinetics of several grains from the legumes and cereal families, which many of them were studied for the first time. In addition, some comparisons among the different hydration kinetics were performed to corroborate some hypothesis about this process. By comparing the hydration kinetics of the studied grains and fitting their data to suitable equations, the idea that this process is very complex was reinforced. It is difficult to say how intrinsic properties of the grains (color, size, specie, family, structure or composition) affect the hydration process. Some reported hypothesis about the hydration process were argued. For instance, it was demonstrated that some hypotheses about the grains hydration are not completely true: the grains with darker color seed coat do not always hydrate slower than the lighter color ones; the grains with sigmoidal behavior can hydrate faster than the grains with downward concave shape behavior; the bigger size grains sometimes hydrate slower than the smaller ones. It was concluded that the hydration process behavior and velocity are affected by many intrinsic properties of the grains (composition and structure, in a complex interaction) acting together to give the representative hydration kinetics behavior of each curve. Practical applications From the academic point of view, the results of this work will help to avoid misunderstandings during the study of the grains hydration process, as many hypotheses were reanalyzed and argued. Furthermore, it provides new data, in special for sigmoidal behavior grains, which is very scarce in the literature. From the industrial point of view, this work provides data about the hydration kinetics of several grains, which is very useful for the process design.

The present work studied, for the first time, the effect of two technologies on the hydration and germination process of beans: ionizing irradiation and ultrasound. In addition, this work proposed a possible biological effect of ultrasound to describe its effect on grain hydration. Carioca beans were irradiated at doses of 2.3 and 3.8 kGy using γ‐rays, establishing different metabolic activities for the beans. Then, they were hydrated with and without the ultrasound technology (91 W/L and 25 kHz) at 25 °C. Both the hydration and germination kinetics were evaluated considering the application of both technologies alone and in combination. As results, irradiation did not significantly affect (P > 0.05) the hydration rate, the equilibrium moisture, or the lag phase time, but ultrasound affected them, reducing 50% of the processing time. On the other hand, only the equilibrium moisture was slightly reduced by the interactive effect of irradiation and ultrasound technology, which was discussed based on different metabolism levels. Furthermore, the germination process of carioca bean was hindered by both the studied variables, reducing its germination capacity to 0% in some cases. Therefore, by studying the effect of ultrasound on beans with different active metabolism (due to different irradiation doses), it was suggested that both physical and biological mechanisms are involved during hydration process and that both can be affected by ultrasound. Further, irradiation could be used on carioca beans with objectives such as avoid germination, insects, and microorganism's growth, without an important effect on the hydration kinetics. Practical Application Ultrasound technology has demonstrated to accelerate the soaking process of several legume grains. However, sometimes, grains are irradiated for disinfestation purpose to improve their shelf life. Indeed, irradiation can change the grain properties as the cooking time, hydration time, and germination capacity. Therefore, this work verified if irradiation changes the desirable effect of ultrasound on grain processing: soaking and germination. Moreover, this work novelty is also based on describing the phenomena: by proposing a possible biological effect, further approaches to improve the grain processing can be achieved.

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The cooking process of grains consists of a hydrothermal treatment in order to convert the raw seed into a product ready to be eaten. The chemical and physical changes during cooking result in palatability and digestibility through the inactivation of antinutritional factors, leaching of polyphenols, gelatinization of starch, solubilization of some polysaccharides, denaturation of proteins, and creation of flavor (Sefa-Dedeh & Stanley, 1979; Siddiq & Uebersax, 2012). According to Wood (2016), cooking time can be simply defined as the time from the start of cooking until the grains are ready to be eaten, when nearly all the grains are sufficiently soft and pleasant to chew. In fact, cooking time is an important property to characterize commercial grains, influencing their price and being an important target on genetic improvement. Consequently, many works have determined the cooking time of grains using different methods based on the softening of the grains, including sensory analysis (Garruti & Bourne, 1985), tactile (forefinger and thumb) method