In this study some effects of the alkaline treatment on the rice starch rich and protein rich fractions were observed during a fast extraction method using rice flour as raw material. The rice flour was selected with a view of reducing the contact time between the raw material and the solvent during the extraction operation (compared to the traditional process, which requires a soaking step of 24 h in NaOH solution prior to wet grinding due to use of broken rice as raw material) since the changes caused by the alkaline treatment are time-dependent. Additionally, performing the extraction in a shorter time reduces process costs. Using the rice flour it was possible to perform the extraction operation with 30 min of contact time between the raw material and the solvent. Furthermore, as the rice flour contained 7.00 ± 0.06% of protein and starchy residue showed 1.30 ± 0.03% of protein, was observed a protein extraction yield of 81.4%. This is a high yield since according to Zhou et al. (2002) the rice endosperm contains approximately 70–88% of glutelin, an alkali soluble rice protein. With this method it was possible to obtain a rice protein concentrate with 79% protein and a starchy residue with a low residual protein content. However, the products presented high levels of sodium, which suggests the need for washings. The amino acid content of the protein concentrate obtained was practically unchanged compared to the rice flour. The proteins of the protein concentrate were denatured during extraction due to the alkaline treatment. Moreover, some of the starch suffered gelatinization. Because the rice flour used as a raw material had a high damaged starch level, these granules were possibly more susceptible to leaching promoted by NaOH, easily enduring the cold gelation phenomenon. Thus, it is strongly suggested that the two fractions obtained in the starchy residue (upper layer and lower layer) needs to be separated during the extraction process. In this way, three products will be obtained: a rice protein concentrate, a fraction containing pre-gelatinized starch plus other polysaccharides from the cell wall, and a fraction rich in rice starch. The rice protein concentrate, even with their tertiary structure altered, can be used as a food supplement. Furthermore, with the application of specific proteases, the rice protein can be used to obtain protein hydrolyzates and bioactive peptides. The pre-gelatinized fraction may be employed in the processing of starch-based adhesives, or even to obtain rice syrups. The fraction rich in starch with preserved granular structure needs further studies to identify their best applications as food ingredient, since its lipid content is higher than other rice starches already on the market. Therefore, it is understood that the fast alkaline method for rice starch and protein extraction is interesting in a technological point of view as it enables the process cost reduction and useful ingredients obtention to the food and chemical industries.
In this study some effects of the alkaline treatment on the rice starch rich and protein rich fractions were observed during a fast extraction method using rice flour as raw material. The rice flour was selected with a view of reducing the contact time between the raw material and the solvent during the extraction operation (compared to the traditional process, which requires a soaking step of 24 h in NaOH solution prior to wet grinding due to use of broken rice as raw material) since the changes caused by the alkaline treatment are time-dependent. Additionally, performing the extraction in a shorter time reduces process costs. Using the rice flour it was possible to perform the extraction operation with 30 min of contact time between the raw material and the solvent. Furthermore, as the rice flour contained 7.00 ± 0.06% of protein and starchy residue showed 1.30 ± 0.03% of protein, was observed a protein extraction yield of 81.4%. This is a high yield since according to Zhou et al. (2002) the rice endosperm contains approximately 70–88% of glutelin, an alkali soluble rice protein. With this method it was possible to obtain a rice protein concentrate with 79% protein and a starchy residue with a low residual protein content. However, the products presented high levels of sodium, which suggests the need for washings. The amino acid content of the protein concentrate obtained was practically unchanged compared to the rice flour. The proteins of the protein concentrate were denatured during extraction due to the alkaline treatment. Moreover, some of the starch suffered gelatinization. Because the rice flour used as a raw material had a high damaged starch level, these granules were possibly more susceptible to leaching promoted by NaOH, easily enduring the cold gelation phenomenon. Thus, it is strongly suggested that the two fractions obtained in the starchy residue (upper layer and lower layer) needs to be separated during the extraction process. In this way, three products will be obtained: a rice protein concentrate, a fraction containing pre-gelatinized starch plus other polysaccharides from the cell wall, and a fraction rich in rice starch. The rice protein concentrate, even with their tertiary structure altered, can be used as a food supplement. Furthermore, with the application of specific proteases, the rice protein can be used to obtain protein hydrolyzates and bioactive peptides. The pre-gelatinized fraction may be employed in the processing of starch-based adhesives, or even to obtain rice syrups. The fraction rich in starch with preserved granular structure needs further studies to identify their best applications as food ingredient, since its lipid content is higher than other rice starches already on the market. Therefore, it is understood that the fast alkaline method for rice starch and protein extraction is interesting in a technological point of view as it enables the process cost reduction and useful ingredients obtention to the food and chemical industries.
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