A new microwave-assisted extraction method for melatonin determination in rice grains

A new microwave-assisted extraction (MAE) method has been developed for the extraction of melatonin from rice grains. The stability of melatonin under MAE conditions was studied in order to define the working range. The studied analytical conditions for the MAE were temperature (125−175 °C), microwave power (500−1000 W), time (5−15 min), solvent (10−90% EtOAc in MeOH), and ratio of solvent to sample (10:1–20:1). Extraction variables were optimized by Response Surface Methodology (RSM). Extraction temperature was found to have a highly significant effect on the response value (p < 0.0001) and the solvent and quadratic of time also had significant effects (p < 0.1). The optimized MAE conditions were as follows: extraction temperature 195 °C, microwave power 1000 W, extraction time 20 min, solvent 100% MeOH, and ratio of solvent to sample 10:1. The developed method showed high precision (in terms of CV: 4.97% for repeatability and 4.34% for intermediate precision). Finally, the new method was applied to real samples in order to investigate the presence of melatonin in a wide variety of rice grains.     

Effects of visible light irradiation on the oxidative stability in rice bran

Raw rice bran was treated with or without visible light exposure at room temperature or stored at 40 °C in the dark for 10 days and rice bran oil (RBO) was recovered from each rice bran. Headspace oxygen content from rice bran and conjugated dienoic acid (CDA) value, acid value, content of γ-oryzanol, and fluorescence intensity in RBO were analyzed to determine the effects of visible light on the oxidative stability in rice bran. Headspace oxygen content in visible light irradiated rice bran (RBL) decreased by 12.8% for 10 days while those in the dark (RBD) and stored at 40 °C (RBT) decreased by 5.87 and 5.35%, respectively, implying visible light irradiation accelerates the consumption of oxygen. CDA values in RBO from RBL were significantly higher than those in RBO from RBD and RBT (p < 0.05). However, acid values in RBO were not significantly different among samples (p > 0.05). Both γ-oryzanol content and fluorescence intensity in RBO from RBL were significantly lower than those in RBO from RBD and RBT (p < 0.05). Fluorescence intensity, which is related to the content of chlorophylls, decreased in samples under light only, implying that chlorophyll photosensitization may play important roles in the acceleration of lipid oxidation in rice bran.     

Young rice protein as a new source of low allergenic plant-base protein

New plant-based milk protein substitutes that do not exhibit immune-mediated adverse effects are in high demand. In-vitro digestibility (oral, gastric and duodenal) of rice was investigated at flowery, milky, dough and mature stages using SDS-PAGE and band densitometry. Possible allergenic proteins found were 13–14, 22–23, 37–39, and 52 kDa. Protein content in young rice at flowery-to-milky stage (9.19–11.48%) was higher than rice bran (8.90%). Possible allergens of young rice rapidly decreased and completely disappeared after digestion. Digestibility of dough-to-mature stage was much slower especially for colored rice. Proteins at 13–14, 52 kDa and 13–14, 37–39 kDa were indigestible in the mature stage of PT1 and RB respectively. High protein content and low allergic potential of young rice supported its possible use as a new plant-based protein alternative.     

Profiling the effects of microwave-assisted and soxhlet extraction techniques on the physicochemical attributes of Moringa oleifera seed oil and proteins

There is a constant search for biomaterials from natural products like plants for food and industrial applications. The work embodied in this report aimed at investigating the effects of microwave-assisted and soxhlet extraction (MAE and SE) techniques on the functional physicochemical quality characteristics of Moringa oleifera seed oil and proteins extracts. M. oleifera ​seeds were ground to fine powders and oil was extracted by microwave-assisted and soxhlet extraction techniques using petroleum ether. Quality attributes including yield percent, moisture content, iodine, saponification, specific gravity, viscosity, pH, thiobarbituric acid, acid and peroxide values were measured. Mineral and vitamin contents, chemical/functional groups, fatty acid (FA) composition, and reducing power of the oil were evaluated. Metabolomics of protein extracted from the defatted powders were analyzed by nuclear magnetic resonance (NMR). M. oleifera ​oil from MAE and SE methods had good yield (34.25 ​± ​0.0%, 28.75 ​± ​0.0%), low moisture content (0.008 ​± ​0.0%, 0.011 ​± ​0.0%), non-drying and unsaturated, moderately saponified, less dense (0.91 ​± ​0.01, 0.92 ​± ​0.02 g mL⁻¹), had Newtonian flow, were weakly acidic, showed good content of FAs, recorded strong potential for long shelf-life, showed stability against oxidative rancidity and enzymatic hydrolysis, had very rich deposits of micro- and macro-nutrients as well as water-soluble and lipid-soluble vitamins, and functional groups in the oil were reflective of its content of long- and medium-chain triglycerides (LCT and MCT). Monounsaturated and saturated fatty acids (MUFA and SFA) were detected and the oil has excellent ferric ion reducing power. NMR metabolomic assay revealed the presence of nine essential amino acids (EAAs) in the protein extract. MAE technique is a feasible and acceptable alternative for high throughput extraction of ​M. oleifera ​oil with high yield and excellent quality attributes. The study revealed that MAE did not impart any remarkable advantage(s) on the physicochemical properties of ​M. oleifera ​seed oil and protein compared to SE technique.     

Functional characterization of extruded rice noodles with corn bran: Xanthophyll content and rheology

The rheological changes in rice noodles by the substitution of corn bran and the effect of temperature on the xanthophyll content (lutein and zeaxanthin) of the corn bran-rice flour noodles were evaluated. The use of corn bran increased the water holding capacity of rice flour at room temperature while the opposite results were observed after heating. The pasting parameters of rice flour-corn bran mixture were reduced with increasing levels of corn bran and the mixture paste exhibited more dominant liquid-like behavior. The noodles containing corn bran exhibited lower expansion ratio and softer textural properties. The levels of lutein and zeaxanthin in raw corn bran were 336.9 and 123.1 μg/100 g, respectively and were significantly reduced (P < 0.05) by heating. While lutein and zeaxanthin were not detected in the control noodles without corn bran, their levels in corn bran-incorporated noodles ranged from 56.2 to 137.3 μg/100 g and from 37.9 to 61.9 μg/100 g, respectively and were significantly reduced by 37.7–45.4% (P < 0.05) after cooking. Thus, the heat-labile characteristics of two xanthophylls were clearly observed. This study provides useful information on the processing performance and xanthophyll content of corn bran, possibly extending its use in a wider variety of foods.     

Effect of various heat treatments on rancidity and some bioactive compounds of rice bran

Rice bran contains natural phytochemicals but unstable against hydrolytic and oxidative rancidity. Various heat treatments, such as dry-heating (DH), freeze-drying followed by dry-heating (FDDH), microwave heating (MH), autoclaving (AC), and ethanol vapor (EV) treatment were applied to rice bran and their effects on the storage stability at room temperature were evaluated. The free fatty acid (FFA) content of untreated rice bran gradually increased from 2.14 to 19.81% during 24 weeks, whereas those of the treated rice brans were not or marginally changed. The FFA content in DH samples was greater than that in FDDH samples, indicating the positive effect of freeze-drying prior to DH. Among the treatments, autoclaving was most effective in retarding the FFA formation. The tocol content in the rice brans varied with the treatments, ranging from 181.4 mg/kg (EV) to 310.6 mg/kg (AC), whereas that in untreated rice bran was 216.3 mg/kg. Amounts of other bio-functional components such as phytosterols and policosanols were either unchanged or increased by the treatments. Policosanol level was increased by all the heat treatments, but not affected by EV treatment, indicating that the thermal treatments induced the release of free policosanols.     

Differences in functional properties and biochemical characteristics of congenetic rice proteins

Proteins in brown rice (BR), white rice (WR) and rice bran (RB) were extracted from the same paddy rice and investigated for their components, functional properties and chemical characteristics by SDS-PAGE methodology. BR and WR proteins possessed a poor solubility under weak acid conditions due to a high content of glutenin and richness in higher molecular-weight (MW) protein fractions. Rice bran protein contained significantly lower molecular-weight components (MWs < 50 kDa) than those in WR and BR. Nitrogen solubility, foaming and emulsification properties of their rice protein preparations were affected not only by pH (3–11), but also by the concentrations of NaCl (0.4–2.0%) and sucrose (4.0–20.0%). All of them, particularly rice bran protein, had favorable functional properties in the medium with a high salt or sugar concentration. Therefore, they have a good potential for development in the food industry.     

β-Glucan extraction from bran of hull-less barley by accelerated solvent extraction combined with response surface methodology

The objective of this study was to explore optimal extraction technology of β-glucan from bran of hull-less barley (Qingke in Chinese), and provide scientific basis for industrialization of β-glucan extraction from a commodity waste which is rich in β-glucan. β-Glucan extraction from bran of hull-less barley was performed with an accelerated solvent extraction (ASE) technique and compared with ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), and reflux extraction. The best combination of extraction parameters was obtained through response surface methodology (RSM) with a three-variable-three-level Box-Behnken design (BBD). The optimum extraction parameters were as follow: extraction time for 9 min, extraction temperature at 70 °C, number of cycles at 4, and extraction pressure at 10 MPa. Under these conditions, the experimental extraction yield of β-glucan was 16.39 ± 0.3%, which agreed closely with the predicted value (16.33%). Compared with other extraction methods, ASE produced much higher β-glucan and more environmentally friendly extraction and solvent systems, less extraction discrimination and shorter time, and could be useful to the development of industrial extraction processes.     

Extraction and characterization of water-extractable and water-unextractable arabinoxylans from spelt bran: Study of the hydrolysis conditions for monosaccharides analysis

Monosaccharide analyses were performed, statistically treated and adopted for spelt bran fractions; with regard to the arabinoxylan content. The AX content of the initial spelt bran reached 9.2% with an A/X ratio of 0.39. The initial spelt bran was rich in starch (41.2%) and protein (18.9%). WE- and WU-AXs from micronised spelt bran were extracted after improved enzymic destarching and deproteinisation treatments. WU-AXs were obtained by two successive extractions with 2% alkaline hydrogen peroxide at 60 °C during 4 h. 55% of the AX present in spelt bran was extracted by using the three extraction steps (WE- and WU-AXs), among AX, 13% were WE and 87% were WU. A/X ratios were different depending on the extraction process. WE-AXs were less rich in arabinose than WU-AXs. Each fraction contained two populations of AX. The first one consisted of low MW AX (7–8 kDa). The second population had a higher MW, 310–415 kDa for WU-AXs and 28 kDa for WE-AXs. The extracts had to be purified in order to improve the AX content. Results were compared to those obtained with wheat bran in the literature. This research was, to the best of our knowledge, the first study on AX extraction from spelt bran.     

Isolation and antioxidative properties of phenolics-saponins rich fraction from defatted rice bran

The study presents a protocol for the preparation of phenolics-saponins rich fraction (PSRF), a new active nutraceutical from defatted rice bran followed by the determination of its antioxidant properties. PSRF was prepared by employing a simple alcoholic fractionation procedure on the crude alcoholic extract (CAE) of defatted rice bran. PSRF was found to be significantly higher in the contents of total phenolic, saponin, and steroidal saponin than CAE and its counterpart, aqueous fraction (AqF) (p < 0.05). Except for iron chelating activity, PSRF exhibited notably higher activity than CAE and AqF in all antioxidant activity assays performed (p < 0.05). HPLC-DAD analysis revealed that PSRF contained substantially higher amounts of gallic acid, 4-hydroxybenzoic acid, caffeic acid, p-coumaric acid, and ferulic acid than CAE and AqF (p < 0.05). In conclusion, alcoholic fractionation of CAE simultaneously concentrated the phenolic compounds and saponins into PSRF, thus contributed to its higher antioxidant activity. Due to its elevated antioxidant properties, PSRF may be recommended for investigation as an active ingredient in the nutraceutical, functional food, and natural food preservative formulations. This is also the first report suggesting defatted rice bran as a potential and sustainable source of saponins.     

Enzymatic modification and particle size reduction of wheat bran improves the mechanical properties and structure of bran-enriched expanded extrudates

The aim of this study was to examine enzymatic modification of wheat bran, performed in a low-moisture process, and the reduction of bran particle size as means of improving the technological performance of wheat bran in expanded extrudates. Modification of bran by hydrolytic enzymes increased the crispiness and decreased the hardness and piece density of extrudates containing wheat bran and endosperm rye flour in 20:80 ratio. These improvements correlated (P < 0.01 or 0.05) with an increased content of water extractable arabinoxylan and decreased water holding capacity of the bran, as well as with increased longitudinal expansion of the extrudates. Furthermore, bran with a fine average particle size (84 μm) produced extrudates with improved mechanical properties and higher radial expansion than coarse bran (particle size 702 μm). The impact of bran particle size was also observed in the cellular structure of the extrudates as differences in cell size and homogeneity. The bran drying method, oven or freeze drying after enzymatic modification, did not have a major impact on the properties of the extrudates. The study showed that the functionality of wheat bran in extrusion can be improved by enzymatic modification using a low-water process and by reduction of bran particle size.     

The effect of infrared stabilized rice bran substitution on B vitamins,minerals and phytic acid content of pan breads: Part II

The effect of replacing wheat flour by infrared stabilized rice bran (SRB) at the levels of 2.5, 5.0 and 10.0% on the content of thiamine, riboflavin, niacin, pyridoxamine, pyridoxine, minerals and phytic acid in white wheat, wheat bran, and whole grain wheat breads was investigated. The incorporation of SRB significantly increased the amount of the noted B vitamins, especially niacin, in all bread types (p < 0.05). Zinc, iron, potassium and phosphorus levels of the breads increased gradually and significantly with the inclusion of SRB (p < 0.05). Moreover, phytic acid content of the breads increased proportional to the SRB substitution dose (p < 0.05).     

Effect of steam explosion on enzymatic hydrolysis and baking quality of wheat bran

In this study, the effect of steam explosion (SE) treatment on microstructure, enzymatic hydrolysis and baking quality of wheat bran was investigated. Coarse and fine bran were treated at different steam temperatures (120–160 °C) and residence times (5 or 10 min) and then hydrolysed with carbohydrase enzymes. The SE treatment increased water extractable arabinoxylan (WEAX) content from 0.75 to 2.06% and reducing sugars from 0.92 to 2.41% for fine bran. The effect was more pronounced with increased SE temperature and residence time. The highest carbohydrate solubilisation was observed in fine bran at SE treatment of 160 °C, 5 min. WEAX content increased to 3.13% when this bran was incubated without enzyme, while WEAX content increased to 9.14% with enzyme addition. Microscopic analysis indicated that cell wall structure of wheat bran was disrupted by severe SE conditions. Supplementation of SE treated (150 °C, 10 min) bran at 20% replacement level decreased the baking quality of bread. However SE followed by enzymatic hydrolysis increased specific volume and decreased crumb hardness (on the day of baking and after three days of storage). Phytic acid content of bread supplemented with SE treated bran was lower than the one supplemented with untreated bran.     

The effect of different extraction techniques on extraction yield, total phenolic, and anti-radical capacity of extracts from Pinus radiata Bark

The performance of four techniques, conventional maceration, Soxhlet extraction, microwave assisted extraction (MAE), and ultrasound assisted extraction (UAE), for extraction of Pinus radiata bark, in one and several stages, were evaluated. For each technique, the mass extracted (g extract/g bark), total phenols (by Folin-Cicalteau), and tannin (by precipitation) concentration and anti-radical capacity (diphenyl-picrylhydrazyl, DPPH) were quantified. In one stage, the extracted mass increased in the following order: maceration < UAE < MAE < Soxhlet (p < 0.05). The total phenols and tannin levels were also higher with the Soxhlet technique. With additional extraction stages, only the samples produced with MAE and UAE techniques improved their parameters. Additionally, MAE extracts presented a higher anti-radical capacity than does Soxhlet and Pycnogenol^® extracts. Therefore, MAE was a simple and rapid method that was useful for extraction of P. radiata bark. Scanning electron micrographs (SEM) provided evidence of the mechanical effects on cell walls, mainly evidenced by cell destruction produced by Soxhlet, MAE, and UAE on the bark. In contrast, maceration only results in slightly ruptured cell pores, which could explain its low extraction yield.     

Changes in bran structure by bioprocessing with enzymes and yeast modifies the in vitro digestibility and fermentability of bran protein and dietary fibre complex

Bran is a good source of dietary fibre, phytochemicals, and also protein, but highly insoluble and recalcitrant structure of bran hinders accessibility of these components for gastrointestinal digestion. In the present work, influence of bioprocessing on the microstructure and chemical properties of rye bran and wheat bread fortified with the rye bran were studied. In vitro protein digestibility, and release of short chain fatty acids (SCFA) and ferulic acid in a gut model were studied. Bioprocessing of rye bran was performed with subsequent treatments with cell-wall hydrolysing enzymes (40 °C, 4 h) and yeast fermentation (20 °C, 20 h). Bioprocessing of rye bran resulted in reduced total dietary fibre content, caused mainly by degradation of fructan and β-glucan, and increased soluble fibre content, caused mainly by solubilisation of arabinoxylans. Microscopic analysis revealed degradation of aleurone cell wall structure of the bioprocessed rye bran. Bioprocessing caused release of protein from aleurone cells, assessed as a larger content of soluble protein in bran and a higher hydrolysis rate in vitro. Bioprocessed bran had also faster SCFA formation and ferulic acid release in the colon fermentation in vitro as compared to native bran.     

Direct measurement of rice bran lipase activity for inactivation kinetics and storage stability prediction

Rice bran is a rich source of valuable nutrients and has potential for high-value applications. Endogenous lipases catalyze the hydrolysis of rice bran oil to free fatty acids, which initiates lipid oxidation. The evaluation of the success of rice bran stabilization processes in terms of the degree of lipid oxidation and shelf-life has so far relied on the measurement of free fatty acid content over a storage period of 3–6 months. In the present study, a photometric and a titrimetric pH-stat method for direct lipase activity measurement immediately after debranning were adapted to rice bran. The photometric method was further applied to determine rice bran lipase/esterase inactivation kinetics, which are useful to optimize stabilization treatments in order to prevent overprocessing and retain maximum level of nutrients. Rice bran was heat-treated in a specialized, hermetically sealable reactor at controlled holding times (5–40 min), temperatures (70–145 °C) and moisture contents (10–20%). Temperature dependency of the lipase/esterase inactivation rate could be described by the Arrhenius equation. Empirical findings on the importance of moisture content for effective rice bran stabilization could be quantified. Furthermore, the results demonstrate the great potential of the method to predict the shelf-life of stabilized rice bran without time-consuming storage tests.     

Optimization of the ultrasound-assisted extraction of tryptophan and its derivatives from rice (Oryza sativa) grains through a response surface methodology

An analytical ultrasound-assisted extraction (UAE) technique has been optimized and validated for the extraction of tryptophan and its derivatives from rice grains. A Box–Behnken design in conjunction with a response surface methodology based on six factors and three levels was used to evaluate the effects of the studied factors prior to optimizing the UAE conditions. The significant (p < 0.05) response surface models with high coefficients of determination were fitted to the experimental data. The most significant (p < 0.0001) effect is the solvent-to-sample ratio while quadratic effects caused by temperature and solvent-to-sample ratio were of moderate importance (p < 0.05). The optimal UAE conditions were as follows: extraction time of 5 min, ultrasound amplitude of 30%, cycle of 0.7 s⁻¹, extraction temperature of 30 °C, 8% methanol in water as the extraction solvent at pH 3 and a solvent/solid ratio 5:1. The method validation ensured that appropriate values were obtained for the LOD, LOQ, precision and recovery. Furthermore, the method was successfully applied to the analysis of a number of rice samples of different varieties. It was demonstrated that this particular UAE method is an interesting tool for the determination of tryptophan and tryptophan derivatives in rice grain samples.     

Evaluation of rice flour modified by extrusion cooking

Flour from long-grain, high-amylose, milled rice was extruded in a double screw extruder. Response surface methodology (RSM) using a face-centered cube design was used to evaluate the effects of operating variables, namely the screw speed (200–300 rpm), barrel temperature (100–160 °C), and feed moisture content (16–22%) on some functional, physical, pasting, and digestibility characteristics of the extrudates. Regression analyses showed that water absorption index (WAI) was significantly (P<0.05) affected by all linear, quadratic, and interaction terms. Viscosity values of extruded rice flours were far less than those of their corresponding unprocessed rice flour dispersed in the Micro Visco Amylo Graph (MVAG) indicating that the starches had been partially pregelatinized by extrusion process. Peak viscosity indicated a high positive correlation with hot paste viscosity (HPV) and cold paste viscosity (CPV) with r>0.700 (P<0.01). The effects of processing on the in vitro digestibility of starch fractions in rice extrudates was tested using controlled enzymatic hydrolysis with alpha-amylase and glucoamylase. The starch-digestion rate depended mainly on processing conditions. Rapidly digestible starch (RDS) was found to correlate negatively with slowly digestible starch (SDS) (r=−0.964, P<0.01) and with resistant starch (RS) (r=0.793, P<0.01), respectively. Whereas SDS correlated positively with RS (r=0.712, P<0.01).     

Identification of a GDSL-motif carboxylester hydrolase from rice bran (Oryza sativa L.)

A major esterase (designated OsEST1) showing high activity using 1-naphthyl acetate as a substrate was identified from rice bran and purified approximately 239-fold to near-homogeniety. The purified enzyme migrated as a single polypeptide band on native and SDS-polyacrylamide gels and had a molecular mass of 25 kDa under denaturing conditions. Analysis of its tryptic peptides by MALDI-TOF-MS and subsequent data mining identified a corresponding cDNA OsEST1 consisting of 714 nucleotides and encoding a 238 amino acid protein. Analysis of its primary sequence indicated that OsEST1 is a GDSL-motif carboxylester hydrolase belonging to the SGNH protein subfamily in containing the putative catalytic triad of Ser¹¹, Asp¹⁸⁷, and His¹⁹⁰. OsEST1 showed the highest catalytic activity at approximately pH 8.0–8.5 and at 45 °C with K_m and V_max values for 1-naphthyl acetate of 172 μM and 63.7 μmol/min/mg protein, respectively. However, OsEST1 showed no activity with triacylglycerol. Alignment of the primary sequence of OsEST1 and other rice GDSL-motif esterases/lipases showed that OsEST1 aligns with a specific family of plant SGNH esterases involved in response to dehydration and cuticle formation. These results suggest that OsEST1 is not a lipase but an esterase activity which has some other function in rice, especially during seed development.     

Effect of preparation conditions on composition and sensory aroma characteristics of acid hydrolyzed rice bran protein concentrate

Hydrolysates were prepared from rice bran protein concentrate (RBPc) in paste form (P-RBPc), or as spray-dried (S-RBPc) or freeze-dried (F-RBPc) powder by acid hydrolysis with aqueous 0.5N HCl at 95 °C for 12 or 36 h. The forms of the protein raw material had only a slight influence over the sensory aroma characteristics of the liquid hydrolysates. The liquid hydrolysate (S-H-RBPc-12) prepared from S-RBPc with hydrolysis time of only 12 h could produce the desirable aromas as to a similar extent as that of 36 h. In order to demonstrate the effect of drying method on the composition and aroma characteristics, a representative S-H-RBPc-12 was converted into a powder by freeze- and spray-drying techniques. Sensory analysis indicated that the spray-dried powder had higher cracker-like and salty aroma intensities and received a higher overall liking score compared to the freeze-dried hydrolysate powder.