Abstract
ABSTRACT: Rice bran is a by-product of the rice milling process, found worldwide in abundance and highlighted due its protein content. This study optimized the conditions for ultrasonic-assisted extraction of protein from defatted rice bran (DRB) and characterized the rice bran protein concentrate (RBPC). A sequential strategy of experimental design was employed; the effect of pH, temperature, ultrasound exposure time, and amplitude were evaluated regarding the percentage of protein extraction by a Full factorial design (FFD) with a fixed frequencies (FFD-A: 37 kHz; FFD-B: 80 kHz). Subsequently, the percentage of protein extracted was optimized employing a Central composite rotatable design (variables: pH and ultrasound exposure time) and RBPC obtained was characterized regarding chemical and functional properties. The pH and ultrasound exposure time had positive effect (P ≤ 0.05) on percentage of protein extraction; moreover, 37 kHz frequency was more effective in protein extraction. The optimized condition (frequency: 37 kHz; temperature: 30 °C; pH: 10; ultrasound exposure time: 30 min; and amplitude: 100%) allowed 15.07% of protein recovery and the RBPC presented 84.76 g 100 g-1 of protein. Magnesium and copper were the main mineral in RBPC (34.4 and 25.5 µg g-1, respectively), while leucine was the limiting amino acid (0.42) and threonine presented the highest chemical score (1.0). The RBPC solubility was minimal at pH 4 and higher at pHs 6-10; the water and oil absorption capacity were higher than bovine serum albumin (BSA) and the emulsifying capacity was comparable to BSA, with a suitable stability. It was possible to obtain a higher purity RBPC than described in the literature, due to the optimization in the extraction process steps, with functional properties suitable for application in food products, especially emulsified ones.
Highlights
Rice bran is a by-product from rice nutritionally rich, especially due its protein composition, drawing as an alternative source in contribution of this nutrient (ROMERO, 2015)
Rice bran proteins have different degrees of hydrogen, disulfide bonds that keep the polypeptides strongly bonded and different degrees of hydrophobicity may difficult the protein extraction process; the conventional method in isolating rice bran proteins is alkali extraction followed by precipitation at the isoelectric pH (ROMERO, 2015)
The ultrasonic waves is a physical technique highlighted as an alternative to reduce the extraction time and efficiency of rice bran protein extraction (CHITTAPALO et al, 2009; PHONGTHAI et al, 2016a)
Summary
Rice bran is a by-product from rice nutritionally rich, especially due its protein composition (approximately 15%), drawing as an alternative source in contribution of this nutrient (ROMERO, 2015). V.50, n.12, supplying important nutritional and functional properties, such as foaming, emulsifying and gelation capacity (PHONGTHAI et al, 2016a; HOU et al, 2017) In this context, it is evident the improvement on studies of rice bran protein functional properties, such as, the application of this protein on different food formulations. Rice bran proteins have different degrees of hydrogen, disulfide bonds that keep the polypeptides strongly bonded and different degrees of hydrophobicity may difficult the protein extraction process; the conventional method in isolating rice bran proteins is alkali extraction followed by precipitation at the isoelectric pH (ROMERO, 2015) In this context, physical, enzymatic, and mechanical treatments may be associated in order to the release rice protein from cells. The ultrasonic waves is a physical technique highlighted as an alternative to reduce the extraction time and efficiency of rice bran protein extraction (CHITTAPALO et al, 2009; PHONGTHAI et al, 2016a)
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