Production of rice bran protein concentrate and its application in gluten-free products

Name: Suphat Phongthai

Organization : Mae Fah Luang University

keyword: Rice bran

LCSH: Rice bran

Classification :.LCCS: TX558.R5

LCSH: Gluten-free foods

Abstract: Plenty of rice bran is produced as by-product during rice milling process in each year. It has increasingly gained much interest from the industry sector to utilize as an alternative and economic source of plant-based protein, since it consists of 10-15% hypoallergenic and high quality proteins. Alkaline extraction is the most popular and simple method that has been used to recover protein from plant materials, even though it provides a low yield, takes long extraction time, and consumes a lot of solvent. Due to the complexity of rice bran fraction, the other techniques have to be combined in order to assist the conventional extraction of protein, and also invent the simple, rapid, organic, and environmental friendly method for protein recovery. Accordingly, the objectives of this study were to optimize the conditions of ultrasonic-, microwave-, and enzyme-assisted extractions of protein from organic rice bran for improving the extraction efficiency. In addition, the obtained rice bran protein concentrate and the hydrolysates prepared by several enzymes with different degrees of hydrolysis were determined for their bioactivity, chemical, physical, and functional properties. The possibility of using rice bran protein concentrate in gluten-free (GF) products, such as bread and pasta, was also studied. Rice bran was used for isolating protein through ultrasonic-assisted extraction (UAE). The variables affecting the extraction efficiency included the sonication amplitude and extraction time. The optimal condition consisted of 76% sonication amplitude, 18 min extraction time, and 0.99 g/10 mL solid-liquid ratio, which gave protein yield of 4.73 ± 0.03%. The degree of hydrolysis (DH) for the rice bran protein by Subtilisin A (SPH), Actinase E (APH), and Neutrase 0.8L (NPH) were 20.03 ± 0.24%, 13.84 ± 0.04%, and 5.54 ± 0.07%, respectively. The molecular weight (MW) of the isolated proteins ranged between < 11 to 75 kDa. The NPH exhibited greater scavenging activity on DPPH radical and ACE-inhibitory activities. The SPH was efficient in reducing power and metal chelating activities. In addition, NPH displayed the highest positive effect for foaming activity (66.25%) (p < 0.05), and then followed by APH (57.50%) and SPH (52.50%). Microwave-assisted extraction (MAE) was applied for extracting rice bran protein with a response surface methodology (RSM). The extraction time and solid-liquid ratio affected to the extraction efficiency. The optimal condition was 1000 W of microwave power, 90 sec of extraction time, and a solid to liquid ratio of 0.89 g rice bran/10 mL of distilled water. The protein yield of MAE was higher than that of alkaline extraction (ALK) by about 1.54-fold (p < 0.05), while the protein digestibility was similar. The protein hydrolysates (PHs) with different degrees of hydrolysis (DH) (5.04, 10.37 and 15.04%) were produced by Alcalase. The MW of the rice bran protein concentrates (RBPC) and the PHs ranged between < 11 kDa and 100 kDa. The excessive enzymatic hydrolysis resulted in a negative effect on water and oil absorption capacities. The PHs with DH 15.04% acted as the strongest DPPH radical scavenger, ferric reducing agent, and also metal ion chelator (p < 0.05). However, the DH of 5.04% was sufficient for improving the functional properties of RBPC, especially foam ability and the emulsion activity index. In case of enzyme-assisted extraction, the optimal condition was 1:10 solid-liquid ratio, 4 h of extraction time, and 10,000U of α-amylase. The protein recovery and protein yield were 16.80 ± 0.29% and 3.72 ± 0.12%, respectively. The hydrolysis of protein concentrate under in vitro gastrointestinal tract (pepsin-trypsin) greatly improved the antioxidant properties (DPPH & ABTS radicals scavenging activities, ferric reducing antioxidant power, and metal chelating activity). Rice bran protein hydrolysate was further fractionated by membrane ultrafiltration (UF, F1: MW <3 kDa, F2: MW 3-5 kDa, and F3: MW 5-10 kDa). Peptides with smaller MW possessed higher antioxidant activities (p < 0.05). UF showed a great efficacy to selectively separate the metal-chelating peptides. Tyrosine and phenylalanine had positive correlations with their DPPH & ABTS radicals scavenging activities and ferric reducing antioxidant power (r > 0.831). A major peptide fragment was detected at m/z 1,088 by a MALDI-TOF mass spectrometry. In the application study, RBPC was prepared using a pilot-scale extraction. The obtained RBPC was composed of 68.07 ± 0.54% protein (dry basis). For baking trials, the addition of RBPC had strongly influenced on the rheological properties, especially elastic modulus (G') of gluten-free batters during oscillation, and the relative elasticity of final gluten-free breads. Breads enriched with 2% RBPC, and a combination of 1% egg albumen and 1% RBPC had the highest specific volume (p < 0.05). Additionally, crumb porosity and sensory attributes were improved. RBPC also showed higher efficacy to inhibit bread staling than egg albumen. On the other hand, RBPC caused some negative effects of rice flour-based gluten-free pasta, such as increases the cooking loss, and lessens the firmness of pasta. Whey protein concentrate enriched pasta demonstrated the shortest optimal cooking time at 4.3 min (p < 0.05). The enrichment of 9% egg albumen (w/w) displayed the greatest capacity for preventing structure disintegration with the lowest cooking loss of 4.38 to 4.63% (p < 0.05). Enrichment with 6% soy protein concentrate provided similar L* values to a commercial one. Moreover, the 9% egg albumen enrichment clearly affected to pasta structure as the improved pasta firmness for up to 72.25%. The protein networks around the starch granules were observed to be enriched with egg albumen and whey protein concentrate, whereas the pasta enriched with RBPC produced a cracked and non-continuous surface. Based on the results, it can be concluded that the ultrasonic-assisted extraction has the highest potential for industrial process scale-up. The desirable properties of rice bran protein could be controlled by enzymatic modification. The bioactive peptides from rice bran might be a useful active ingredient to be incorporated in nutraceutical products. Moreover, RBPC was successfully used as a quality improver for rice flour-based gluten-free bread.

Mae Fah Luang University

Address: CHIANG RAI

Email: library@mfu.ac.th

Name: Saroat Rawdkuen

Role: Advisor

Name: Regine Schönlechner

Role: Co-Advisor

Created: 2016

Issued: 2560

Modified: 2020-04-29

Issued: 2017-08-17

วิทยานิพนธ์/Thesis

application/pdf

CallNumber: Thesis TX558.R5 S959p 2016

eng

DegreeName: Dotor of Philosophy

Level: Doctoral Degree

Descipline: Food Technology

Grantor: Mae Fah Luang University

©copyrights Mae Fah Luang University

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