Effects of the Roasting-Assisted Aqueous Ethanol Extraction of Peanut Oil on the Structure and Functional Properties of Dreg Proteins.

The effects of the roasting-assisted aqueous ethanol extraction of peanut oil on the structure and functional properties of dreg proteins were investigated to interpret the high free oil yield and provide a basis for the full utilization of peanut protein resources. The roasting-assisted aqueous ethanol extraction of peanut oil obtained a free oil yield of 97.74% and a protein retention rate of 75.80% in the dreg. The water-holding capacity of dreg proteins increased significantly, and the oil-holding capacity and surface hydrophobicity decreased significantly, reducing the binding ability with oil and thus facilitating the release of oil. Although the relative crystallinity and denaturation enthalpy of the dreg proteins decreased slightly, the denaturation temperatures remained unchanged. Infrared and Raman spectra identified decreases in the C-H stretching vibration, Fermi resonance and α-helix, and increases in random coil, ß-sheet and ß-turn, showing a slight decrease in the overall ordering of proteins. After the roasting treatment, 62.57-135.33% of the protein functional properties were still preserved. Therefore, the roasting-assisted aqueous ethanol extraction of peanut oil is beneficial for fully utilizing the oil and protein resources in peanuts.

The underlying reasons for the efficient extraction of peanut oil by aqueous ethanol combined with roasting conditioning pretreatment.

To overcome the disadvantages of severe emulsification and difficulty in obtaining free oil during aqueous extraction of peanut oil, the effect of roasting assisted aqueous ethanol extraction on free oil recovery was investigated. When peanut kernels were roasted at 180 °C for 10 min, free oil recovery increased from 57% to 96%, and the acid and peroxide values of the peanut oil met the requirements of good quality. The degree of hydration swelling of proteins in the extract increased, and soluble solids were easier to aggregate, resulting in reduced emulsification and significantly higher free oil recovery. The roasting conditions selected were found to significantly promote protein hydrophilicity, aggregation and fusion of oil bodies, as well as cell rupture, which facilitated the release of free oil but with a lower degree of protein denaturation. This study may promote the practical application of aqueous extraction technology for peanut oil.

Eating Quality and In Vitro Digestibility of Brown Rice Improved by Ascorbic Acid Treatments.

The effects of ascorbic acid treatment alone and in combination with degreasing or hydrothermal treatment on eating quality and in vitro digestibility of brown rice were explored for improving poor mouthfeel and low digestibility, and the improvement mechanism was investigated. The results indicated that the texture of cooked brown rice was significantly improved by degreasing combined with ascorbic acid hydrothermal treatment; the hardness and chewiness decreased to the level of polished rice; the stickiness increased three times of the cooked untreated brown rice; and the sensory score and in vitro digestibility were significantly enhanced from 68.20 and 61.37% to 83.70 and 79.53%, respectively. In addition, the relative crystallinity and water contact angle of treated brown rice were respectively reduced from 32.74% and 113.39° to 22.55% and 64.93°, and normal temperature water uptake significantly increased. Scanning electron microscope showed that the separation of starch granules occurred inside cooked brown rice grain obviously. The improvement of eating quality and in vitro digestibility of brown rice is conducive to enhancing the consumers acceptance and human health.

Revealing the reasons for the pasting property changes of rice during aging from the perspective of starch granule disaggregation.

BACKGROUND: The pasting properties of rice change markedly after aging, although the mechanism for this still remains unknown. Aged and fresh rice grains were ground and the flours were fractionated by particle size, and then the pasting properties, particle size distribution and microscopic morphology of the heated flour fractions were evaluated. RESULTS: Compared to the corresponding fresh flour fractions with the same particle size, a lower peak viscosity for those aged flour fractions from 80 µm to 450 µm and a higher peak viscosity for those aged flour fractions from 20 µm to 60 µm were observed. The amounts of smaller particles disaggregated from the aged flour fractions were significantly less and the separated entities were always larger than the corresponding fresh rice fractions. CONCLUSION: Disaggregation difficulty of starch granules was the reason for the changes in the pasting properties of rice after aging. This finding is helpful for understanding rice aging mechanisms and regulating eating quality of rice flour as an ingredient. © 2022 Society of Chemical Industry.

Improving the eating quality of brown rice by defatting combined with hydrothermal treatment.

Aiming at consumer acceptability of brown rice such as cooking difficulty and coarse taste, the effects of defatting and hydrothermal treatment alone or in combination on the texture and sensory score of cooked brown rice were studied, and the improvement mechanism was explored through cooking quality and microscopic morphology. The results showed that defatting combined with hydrothermal treatment could significantly improve the quality of brown rice, the hardness and chewiness of treated cooked brown rice decreased respectively from 20.385 N and 10.221 N to 14.494 N and 6.886 N, and the sensory score increased from 68.90 to 83.50. The room temperature water absorption rate of the treated brown rice increased from 10.72 % to 29.71 %, which was much higher than that of polished rice. The cooking quality of the treated brown rice was obviously improved, the optimal cooking time decreased from 30.33 min to 22.67 min, and the heating water absorption, volume expansion rate and solid loss increased from 147.32 %, 255.20 % and 13.35 mg/g to 219.15 %, 400.39 % and 22.49 mg/g, respectively. Scanning electron microscope showed that defatting combined with hydrothermal treatment significantly increased cracks and micropores of brown rice grains, which may be the intrinsic reason for the improvement in room temperature water absorption rate and cooking quality of brown rice and thus eating quality of cooked brown rice. The results are of great significance for promoting the staple consumption of whole-grain brown rice with broad application prospects.

Restoring fresh texture in cooked aged rice with reducing agents.

Effects of ascorbic acid and sodium sulfite on texture of cooked aged rice were researched in this study. Hardness increase and stickiness reduction are common for cooked aged rice. The texture of cooked aged rice was significantly changed approaching to fresh rice by both reducing agents despite of sulfur-containing or not (p < 0.05), and the values of hardness, stickiness and stickiness/hardness ratio could be completely restored to the levels of the corresponding fresh rice. Moreover, this effect showed a dose-effect relationship. Morphology examination suggested that ascorbic acid made starch granules swelling adequately and full of larger dents in the interior of cooked aged rice, while sodium sulfite only made starch granules displayed relatively smaller dents. Particle size analysis indicated that ascorbic acid enhanced the swelling and separation of starch granules, but sodium sulfite only promoted the granule separation due to deagglomeration. Therefore, the two reducing agents are useful in restoring texture of aged rice to fresh rice through changing gelatinization behavior and can be as a key probe to disclose aging mechanisms of rice.

Infrared and Raman spectroscopic characterization of structural changes in albumin, globulin, glutelin, and prolamin during rice aging.

Structural changes in albumin, globulin, glutelin, and prolamin from fresh and aged rice were characterized in this study. Infrared and Raman spectroscopies revealed changes in interactions between protein and starch, and the occurrence of structural changes involving secondary and tertiary structures of protein induced by rice aging. The α-helical structure was reduced, and aliphatic amino-acid side chains became more buried in albumin after rice aging. Oxidation of the sulfhydryl group in globulin was evident. The unordered coil in glutelin decreased, and a characteristic frequency of the free sulfhydryl group appeared. The antiparallel ß-sheet in prolamin increased, the conformation of disulfide bonds changed, and tyrosine residues became exposed to a polar environment. The association between globulin and starch strengthened, whereas that between glutelin and starch diminished. These differences in structure and interactions with starch might be responsible for the dissimilar pasting properties between fresh and aged rice.