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The solubilization of peanut protein isolate (PPI) powders modified by atmospheric pressure cold plasma (ACP) treatment was studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), low-field nuclear magnetic resonance (low-field NMR) spectroscopy, and FTIR spectroscopy. Significant improvements in both the solubility and water holding capacity (WHC) of the PPI gel were observed after treatment with ACP. The PPI solubility reached a maximum value after 7 min of treatment, with a 12.17% increase over the values observed for the untreated samples. In addition, the WHC increased by 17.90% after 3 min of treatment. The SEM and EDS data revealed that following the 7-min treatment, the PPI surface was rougher and more loosely bound than that of the untreated sample. This indicated an increase in the PPI specific surface area and exposed protein–water binding sites on the treated PPI surface as well as a marked increase in its oxygen content, suggesting an increase in the hydrophilic groups on the PPI surface. The low-filed NMR measurements revealed that the trend in the T21 peak area of the relaxation time was consistent with the data observed for the WHC. The FTIR results revealed a decrease in the proportion of β-sheets and an increase in that of the β-turns within 3 min of treatment, suggesting that the polarity and hydrophilicity of the protein surface were enhanced. The protein structure changed from a compact folding to a loose unfolding configuration after ACP treatment. [ABSTRACT FROM AUTHOR]

The structural modification and gelation properties of sweet potato protein (SPP) affected by sulfur-containing amino acids (L-cysteine or L-cystine) and high hydrostatic pressure (HHP) were investigated. Additives altered the denaturation temperature and reduced the denaturation enthalpy of SPP. Higher α-helical contents were observed in untreated or HHP-treated SPP with L-cysteine or L-cystine, while β-sheet and random coil structure unit were decreased. FTIR spectra showed a weak absorbance in HHP-treated SPP with L-cysteine and L-cystine. Storage modulus (G′) of untreated or HHP-treated SPP was enhanced by L-cysteine and L-cystine. Textural properties of SPP gels were improved by sulfur-containing amino acids and HHP, especially for L-cysteine. Decrease in T2b relaxation time and increase in A21 proportion peak area by low-field NMR suggested that water bound more closely to SPP molecules in the presence of L-cysteine and L-cystine, and more immobilized water fraction was trapped in SPP gel matrix. [ABSTRACT FROM AUTHOR]

Sweet potato is one of cheap sources for starch industries worldwide, and exploiting starch wastewater as an alternative protein source is mainly environmental and economic concerns. In this study, the effects of high hydrostatic pressure (HHP; 250, 400, and 550 MPa) on chemical forces, structure, and gelation properties of sweet potato protein (SPP) at pH 3.0, 6.0, and 9.0 were investigated. The values of surface hydrophobicity (Ho) and absolute value of zeta potential of SPP significantly increased from 250 to 550 MPa (p < 0.05) at all three pH conditions. The total amount of sulfhydryl (-SH-) groups in SPP decreased after HHP at pH 9.0, whereas the amount of free -SH- increased. High molecular mass aggregates (> 180 kDa) were observed in SPP after HHP at pH 6.0 and 9.0 by SDS-PAGE. Regarding elastic rheological behaviors, storage modulus (G′) values of SPP were significantly strengthened after HHP treatment. In addition, textural properties and water-holding capacity of gels made from SPP after 250 and 400 MPa at pH 9.0 were significantly improved, and the gels showed a compact and uniform gel network with the contribution of immobilized water fractions. The gel properties exhibited by SPP after HHP treatment at different pH levels, in particular after 400 MPa at pH 9.0, suggested that it could be potential protein resources as new gelling reagent in the food system. [ABSTRACT FROM AUTHOR]

Peanut protein isolate (PPI) solutions were modified by dielectric barrier discharge (DBD) cold plasma (CP) treatment. Effects of CP treatment on the solubility, emulsion stability, and water holding capacity (WHC) of peanut protein were studied. The results showed a significant improvement in solubility, emulsion stability, and WHC following CP treatment. CP treatment resulted in the unfolding of PPI structure, thereby increasing the β-sheet and random coil content and decreasing the α-helix and β-turn content, as analyzed by Fourier-transform infrared spectroscopy. Low-field nuclear magnetic resonance showed an increase in the peak area of T relaxation time by CP treatment and the change in T peak area was in agreement with the result of WHC. This study demonstrated that CP may be successfully applied as a method to modify the functionality of PPI. [ABSTRACT FROM AUTHOR]

The thermal, dynamic, and structural properties of wheat starch-water systems with different levels of water content (11, 35, 40, 42, 45, and 50%, wet basis) were investigated. H time domain nuclear magnetic resonance (TD-NMR) spectroscopy was used to interpret and quantify the water transfer and starch transformations in terms of water uptake, granule swelling, amylose leaching, and melting of starch polymers in relation to the different levels of water content. Complementary differential scanning calorimetry (DSC) experiments were performed to study the effects of water content on the degree of starch gelatinization. In particular, this twofold approach was applied to the first endotherm to study the mechanisms of gelatinization with a common heating range both in NMR and DSC. It was shown that the trend of the enthalpy changes in the first phase transition in starch-water (SW) mixtures was strongly correlated with the loss of solid content measured by NMR in the corresponding temperature range (55-70 °C). Based on the evolution of the relative amplitudes of T , structural transformations of starch were shown to occur in both crystalline and amorphous regions within SW samples, supporting the fact that the amorphous phase of starch also plays a significant role in the phase transition of granules during gelatinization. This dynamic and hydrothermal approach provided the first NMR-based interpretation of the first endotherm measured by DSC. [ABSTRACT FROM AUTHOR]

Wheat starch-based model systems and wheat flour dough with the same water content (close to 45 %) were investigated upon heating (20-90 °C) using time-domain H NMR spectroscopy with the aim of assigning each spin-spin relaxation time ( T) measured to a specific proton fraction. On the basis of the signal evolution according to Curie's law for pure starch and pure water, temperature-associated changes for each T value and their mass intensity were interpreted and assigned to water and/or biopolymer proton fractions related to the reversible swelling of starch or its gelatinization. The addition of 2 % ( w/ w) salt to model samples and dough induced few changes during the reversible swelling process but impacted on the measurements performed above 60 °C. Finally, studies performed on starch-based model systems improved understanding of the complex thermal processing of starch in dough by taking into account phenomena other than the starch swelling and gelatinization, such as gluten denaturation and changes in water-biopolymer interactions. [ABSTRACT FROM AUTHOR]

Water characteristics and prediction of unfrozen water in sweet corn treated with different blanching temperatures (20, 40, 50, 60, 70, 80, 90, and 100 °C/10 min) were investigated by low-field nuclear magnetic resonance (LF-NMR). Transverse relaxation analysis was firstly used to study the changes of water characteristics and distribution. Then, a chemometric method using partial least squares (PLS) method was employed to predict unfrozen water. Four relaxation components were discerned and pertained to vacuolar, cytoplasmic, and extracellular water, and cell wall protons, respectively. The intracellular water in sweet corn was transported to extracellular space after treatment and the loss of intracellular water increased with blanching temperature. Three groups of blanching temperatures were discriminated by principal component analysis. The PLS regression model based on LF-NMR data accurately predicted unfrozen water in blanched sweet corn with an adjusted determination coefficient of 0.97. [ABSTRACT FROM AUTHOR]