Bioacessibilidade de compostos fenólicos após a digestibilidade de amido de arroz de pericarpo preto e vermelho submetidos a diferentes métodos de pré-cocção, cocção e pós-cocção

Abstract

When consumed, rice undergoes the cooking process, which induces sensory and chemical changes in the starch and other components, such as phenolic compounds. Studies on the effects of cooking and digestion on rice phenolic compounds yield inconsistent results, emphasizing the necessity for comprehensive research. This study examined these effects on black and red rice grains, with variations in their preparation concerning pre-cooking (hydration and washing), cooking (method, time, and water quantity), and post-cooking (cooling and freezing) parameters, as well as subsequent digestion. The findings demonstrate that red rice exhibited the most substantial reductions in phenolic compounds during cooking (-39% total, -64% free, and -22% bound), while black rice showed a moderate decrease in free phenolics (- 17%), alongside an increase in complexed (+20%) and total (+4%). The microwave method displayed superior preservation of free phenolics. The water quantity used in cooking directly influenced the free phenolic content, while the cooking duration had a notable impact. Irrespective of the cooking time, black rice manifested an increase in the bound fraction of phenolics, whereas red rice exhibited an upsurge in the complexed fraction with extended cooking periods. Moreover, in vitro digestion led to reductions in the levels of bioaccessible phenolics in both types of rice, approximately 57% in black rice and 61% in red rice in comparison to the total levels before cooking. The water quantity during cooking and cooking time influenced bioaccessibility, while storage had no significant effect on phenolic content. The grains remaining after digestion demonstrated a significant increase primarily in the free fraction, averaging 325% in black rice and 589% in red rice. No significant correlations were found between the presence of phenolic compounds and starch hydrolysis during in vitro digestion, but the existence of bioaccessible phenolic compounds exhibited a robust association with the free phenolic fraction after cooking. These results underscore the complexity of the interplay among cooking, digestion, and phenolic compounds in rice, underscoring the significance of considering the bioaccessibility of these compounds when preparing more nourishing foods. Additionally, the study evaluated how different cooking methods affect starch hydrolysis, revealing that the pressure method led to lower hydrolysis rates, highlighting the integrity of the grain matrix as a critical factor in starch digestibility. These findings provide pertinent data to address diverse dietary requirements and to comprehend the effects of cooking and digestion processes on phenolic compounds and starch in rice.