Effects of oxidative modification by 13-hydroperoxyoctadecadienoic acid on the structure and functional properties of rice protein

Effects of Packaging Materials on Structural and Simulated Digestive Characteristics of Walnut Protein during Accelerated Storage

Walnuts are rich in fat and proteins that become oxidized during the processing and storage conditions of their kernels. In this study, the effect of three packaging materials (e.g., polyethylene sealed packaging, polyamide/polyethylene vacuum packaging, and polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging) were investigated on the oxidation, structural and digestive properties of walnut kernel proteins. Results showed that the amino acid content gradually decreased and carbonyl derivatives and dityrosine were formed during storage. The protein molecule structure became disordered as the α-helix decreased and the random coil increased. The endogenous fluorescence intensity decreased and the maximum fluorescence value was blue-shifted. After 15 days of storage, surface hydrophobicity decreased, while SDS-PAGE and HPLC indicated the formation of large protein aggregates, leading to a reduction in solubility. By simulating gastrointestinal digestion, we found that oxidation adversely affected the digestive properties of walnut protein isolate and protein digestibility was best for polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging. The degree of protein oxidation in walnuts increased during storage, which showed that except for fat oxidation, the effect of protein oxidation on quality should be considered. The results of the study provided new ideas and methods for walnut quality control.

Solubility and conformational characterization of rice glutelin after high temperature treatment

Enhancing the solubility of rice glutelin in neutral aqueous solution is the prerequisite for the development of rice protein drinks and ingredients. Herein, glutelin was first dissolved in an aqueous solution of pH 12, and then heated at 121 °C for 20 min. The results showed that the solubility of glutelin increased from 2.55 mg/mL to 20.7 mg/mL at pH 7. The size of glutelin aggregates at pH 7 decreased from 900 nm to 400 nm after high temperature treatment (HTT), which was confirmed by atomic force microscopy. The results of small angle X-ray scattering showed that HTT induced the conformational unfolding of glutelin, and the protein in the aggregate was rod like shape as well as the mean square rotation radius decreased from 64.9 to 54.8 Å. Furthermore, Raman spectrum results also agree with the unfolding of glutelin conformation, which was mainly reflected in the changes of tyrosine and tryptophan residues, as well as the decreasing of α-helix content and increasing of β-sheet content. After being freeze-dried, HTT glutelin has a re-solubilization capacity of 15.48 mg/mL in pH 7 aqueous solution, which was superior to that of spray dried glutelin powder (pH 7, 9.19 mg/mL).

Storage Drives Alterations of Proteomic and Protein Structural Properties in Rice (Oryza sativa L.)

Rice quality changes during storage. However, few studies have reported the difference in protein structure between the indica and japonica varieties of rice during storage. The current research characterized the structural properties of the rice protein, and further investigated the proteomic profiles of Jianzhen 2 (indica rice) and Nanjing 9108 (japonica rice) during storage using the TMT labeling method. A significant reduction in free sulfhydryl content and an increase in disulfide bonds content and surface hydrophobicity were observed in both varieties after storage. The results of FTIR indicated that the changes in the protein’s secondary structure of Nanjing 9108 (japonica rice) were more significant than in Jianzhen 2 (indica rice). A total of 4039 proteins in Nanjing 9108 and 4301 proteins in Jianzhen 2 were identified by TMT-labeled proteomics analysis in this study. Significantly, changes were detected in 831 proteins in Nanjing 9108, while only in 60 proteins in Jianzhen 2. Protein processing in endoplasmic reticulum, starch, and sucrose metabolism were both accelerated in both varieties, while oxidative phosphorylation in mitochondria, glycolysis, fatty acid metabolism, and glutathione metabolism were enhanced in Nanjing 9108 (japonica rice). This study provides insight into the proteomic changes and protein structure in rice induced by storage.

Structural Modifications and Strategies for Native Starch for Applications in Advanced Drug Delivery

Pharmaceutical excipients are compounds or substances other than API which are added to a dosage form, these excipients basically act as carriers, binders, bulk forming agents, colorants, and flavouring agents, and few excipients are even used to enhance the activity of active pharmaceutical ingredient (API) and various more properties. However, despite of these properties, there are problems with the synthetic excipients such as the possibility of causing toxicity, inflammation, autoimmune responses, lack of intrinsic bioactivity and biocompatibility, expensive procedures for synthesis, and water solubility. However, starch as an excipient can overcome all these problems in one go. It is inexpensive, there is no toxicity or immune response, and it is biocompatible in nature. It is very less used as an excipient because of its high digestibility and swelling index, high glycemic index, paste clarity, film-forming property, crystalline properties, etc. All these properties of starch can be altered by a few modification processes such as physical modification, genetic modification, and chemical modification, which can be used to reduce its digestibility and glycemic index of starch, improve its film-forming properties, and increase its paste clarity. Changes in some of the molecular bonds which improve its properties such as binding, crystalline structure, and retrogradation make starch perfect to be used as a pharmaceutical excipient. This research work provides the structural modifications of native starch which can be applicable in advanced drug delivery. The major contributions of the paper are advances in the modification of native starch molecules such as physically, chemically, enzymatically, and genetically traditional crop modification to yield a novel molecule with significant potential for use in the pharmaceutical industry for targeted drug delivery systems.

A Narrative Review on Rice Proteins: Current Scenario and Food Industrial Application

Rice, Oryza sativa, is the major staple food that provides a larger share of dietary energy for more of the population than other cereal crops. Moreover, rice has a significant amount of protein including four different fractions such as prolamin, glutelin, globulin, and albumin with different solubility characteristics. However, these proteins exhibit a higher amino acid profile, so they are nutritionally important and possess several functional properties. Compared with many other cereal grains, rice protein is hypoallergic due to the absence of gluten, and therefore it is used to formulate food for infants and gluten-allergic people. Furthermore, the availability makes rice an easily accessible protein source and it exhibits several activities in the human body which discernibly affect total health. Because of these advantages, food industries are currently focusing on the effective application of rice protein as an alternative to animal-based and gluten-containing protein by overcoming limiting factors, such as poor solubility. Hence, it is important to gain an in-depth understanding of the rice protein to expand its application so, the underlined concept of this review is to give a current summary of rice protein, a detailed discussion of the chemistry of rice protein, and extraction techniques, and its functional properties. Furthermore, the impact of rice protein on human health and the current application of rice protein is also mentioned.

Effects of Peroxyl Radicals on the Structural Characteristics and Fatty Acid Composition of High-Density Lipoprotein from Duck Egg Yolk

In this study, high-density lipoprotein (HDL) from duck egg yolk was subjected to oxidation with a system based on 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH)-derived peroxyl radicals. The effects of peroxyl radicals on the protein carbonyl, free sulfhydryl, secondary/tertiary structure, surface hydrophobicity, solubility, particle size distribution, zeta potential and fatty acid composition of HDL were investigated by using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Fourier-transform infrared spectroscopy (FTIR), circular dichroism (CD), fluorescence spectroscopy, dynamic light scattering and ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). The results indicated that the content of protein carbonyl was significantly increased, that of free sulfhydryl was obviously reduced, and the ordered secondary structure was also decreased with increasing AAPH concentration. In addition, the surface hydrophobicity and solubility of HDL showed apparent increases due to the exposure of hydrophobic groups and aggregation of protein caused by oxidation. The fatty acid composition of HDL exhibited pronounced changes due to the disrupted protein–lipid interaction and lipid oxidation by AAPH-derived peroxyl radicals. These results may help to elucidate the molecular mechanism for the effect of lipid oxidation products on the oxidation of duck yolk proteins.

Oxidized Milk Induces Spatial Learning and Memory Impairment by Altering Gut Microbiota in Offspring Mice during Pregnancy and Lactation

Early adverse diet exposures are known to be associated with increased risk of learning and memory injury in offspring, yet whether oxidized milk is involved in such an effect has been largely unknown. Here, we focused on oxidized milk intake in mice during pregnancy and lactation to measure the changes in the learning and memory ability in offspring and also probed into the relevant association with gut microbiota. Milk was oxidized with H₂O₂-Cu or HClO, resulting in different degrees of oxidative damage. KM female mice were fed H₂O₂-Cu, HClO, or normal control diets immediately after caging until their offspring were 3-weeks old. Behavioral tests were then performed to test the learning and memory ability, and 16S rRNA sequencing was completed with harvested fecal contents. As analyzed, fecal microflora in mice with oxidized milk was affected, mainly reflected in decreased mucin-degrading bacteria, Akkermansia and Lactobacillus, and in reversely increased pro-inflammatory bacteria Shigella, pathobiont Mucispirillum, nervous associated bacteria Ruminococcus, Escherichia, and Desulfovibrio. In the meantime, the inflammation developed in mice was aggravated accompanied by increased expression of relevant genes, while the genes and proteins associated with the learning and memory ability were down-regulated. Further behavioral tests proved impairment of the learning and memory ability in offspring. In general, milk of oxidative damage is a risk factor of the impaired transgenerational ability in learning and memory, which is associated with gut microbiota and intestinal mucosa conditions. This finding may help support the potential of early adverse diet as a harmful factor in learning and memory.

Protein structural properties and proteomic analysis of rice during storage at different temperatures

Rice quality changes during storage, but there have been few studies of how rice proteins changes during aging. The present study characterized the structural properties of protein in stored rice and identified the mechanism of quality deterioration using proteomics. Compared with protein from newly harvested rice, the free sulfhydryl content of protein from stored rice was significantly reduced and the disulfide bond content and surface hydrophobicity was higher. Storage resulted in a loss of α-helix and β-sheet structures and increase in β-turn and random coil structures. High-molecular-weight protein subunits decomposed to produce low-molecular-weight subunits at 30 °C, while protein aggregation occurred at 70 °C. At 30 ℃ 157 differential proteins were found and 70 ℃ 395 such proteins occurred. Redox homeostasis, response to oxidative stress, glutathione metabolism, tricarboxylic acid cycle, glycolysis/gluconeogenesis, starch and sucrose metabolism, and fatty acid biosynthesis and degradation led to the different quality of stored rice.

Comparative Study of Oxidative Structural Modifications of Unadsorbed and Adsorbed Proteins in Whey Protein Isolate-Stabilized Oil-in-Water Emulsions under the Stress of Primary and Secondary Lipid Oxidation Products

The impact of typical primary or secondary lipid oxidation (LPO) products, selected as linoleic acid 13-hydroperoxide (13-HPODE) and malondialdehyde (MDA), on the structural modification of unadsorbed or adsorbed proteins in whey protein isolate (WPI)-stabilized oil-in-water (O/W) emulsions during storage up to 48 h at 37 °C in the dark was investigated. The results showed that either 13-HPODE and MDA could lead to structural modifications of unadsorbed or adsorbed proteins with a concentration-dependent manner and time relationship, respectively. Moreover, higher levels of MDA rendered a higher degree of oxidative modifications of WPI than 13-HPODE, indicated by the higher protein carbonyl contents and N'-formyl-L-kynurenine (NFK) and lower fluorescence intensity. Additionally, adsorbed proteins were more easily oxidized by LPO products than unadsorbed proteins. Overall, our results indicated that the formation of secondary LPO products and the protein position were crucial factors to increase the degree of oxidative modifications of WPI in O/W emulsion systems.

Effects of oxidative modification of peroxyl radicals on the structure and foamability of chickpea protein isolates

A chickpea protein isolate (CPI) was oxidized using peroxyl radicals derived from 2,2'-azobis (2-amidopropane) dihydrochloride (AAPH), and the structural and foaming properties of the oxidized CPI were evaluated. The oxidation degree of protein was determined by measuring carbonyl content, dimer tyrosine content, free thiol content, and total thiol content. The structural changes of oxidized protein were evaluated by surface hydrophobicity, endogenous fluorescence intensity, Fourier transform infrared spectroscopy, SDS-PAGE, and amino acid content changes. Compared with the control group (0 mmol/L AAPH), moderate oxidation (0.04 mmol/L AAPH) led to the formation of a soluble protein with flexibility, which could improve the foaming properties of the protein (foaming capacity and stability increased by 25.50% and 6.38%, respectively). Over-oxidized (25 mmol/L AAPH) protein exhibited improved foaming capability, but its foam stability was reduced owing to the formation of insoluble aggregates. The results indicate that oxidation can change protein conformation, and the protein structure can affect the foamability of the CPI. PRACTICAL APPLICATION: CPI is a protein supplement food. Protein oxidation can occur during processing and storage, thereby affecting protein function. In this study, we evaluated how peroxy free radicals affect the structure, solubility and foaming properties of CPI, and clarified the mechanism between them. It has been found that peroxy free radicals can accelerate the oxidation of proteins and have a significant effect on foaming. Therefore, the degree of oxidation should be controlled to improve the quality of CPI.

Animal and Plant Protein Oxidation: Chemical and Functional Property Significance

Protein oxidation, a phenomenon that was not well recognized previously but now better understood, is a complex chemical process occurring ubiquitously in food systems and can be induced by processing treatments as well. While early research concentrated on muscle protein oxidation, later investigations included plant, milk, and egg proteins. The process of protein oxidation involves both radicals and nonradicals, and amino acid side chain groups are usually the site of initial oxidant attack which generates protein carbonyls, disulfide, dityrosine, and protein radicals. The ensuing alteration of protein conformational structures and formation of protein polymers and aggregates can result in significant changes in solubility and functionality, such as gelation, emulsification, foaming, and water-holding. Oxidant dose-dependent effects have been widely reported, i.e., mild-to-moderate oxidation may enhance the functionality while strong oxidation leads to insolubilization and functionality losses. Therefore, controlling the extent of protein oxidation in both animal and plant protein foods through oxidative and antioxidative strategies has been of wide interest in model system as well in in situ studies. This review presents a historical perspective of food protein oxidation research and provides an inclusive discussion of the impact of chemical and enzymatic oxidation on functional properties of meat, legume, cereal, dairy, and egg proteins based on the literature reports published in recent decades.