Shuntang Guo

Identification and Characteristics of Iron-Chelating Peptides from Soybean Protein Hydrolysates Using IMAC-Fe3+

The iron-chelating peptides from soybean protein hydrolysates (SPH) were investigated using immobilized metal affinity chromatography (IMAC). The results demonstrated that SPH could absorb on the IMAC-Fe(3+) column, while the capability of the binding iron was different in SPH (10-30 kDa), SPH (3-10 kDa), and SPH (1-3 kDa). The highest binding amount on the column occurred with SPH (10-30 kDa). With the IMAC method, the iron-chelating peptides were shown to be formed at pH lower than 5.5, and they were not affected by NaCL with the concentration between 0.1 mol/L and 1 mol/L, while the iron-chelating peptides could be partially disrupted by 0.02 mol/L Na(2)HPO(4) at pH 8.0. Furthermore, the iron-chelating peptides were identified with reversed phase (RP)-HPLC, SDS-PAGE, and MALDI-TOF MS/MS. The binding characteristics of the SPH on IMAC-Fe(3+) and the sequences of the iron-chelating peptides revealed that binding sites between SPH and iron might be the carboxyl groups of Glu and Asp residues.

A study of the soluble complexes formed during calcium binding by soybean protein hydrolysates.

The soluble complexes formed between hydrolyzed soybean protein and calcium at pH 7.4 were investigated using dialysis, gel chromatography, and Fourier transform infrared spectrometry (FTIR). The results demonstrate that the amount of calcium bound was significantly different for soybean protein hydrolysates obtained using the proteases neutrase, flavourzyme, protease M, and pepsin. Maximum levels of calcium binding (66.9 mg/g) occurred with hydrolysates produced using protease M. Peptide fragments exhibiting high calcium binding capacity had molecular weights of either 14.4 kDa or 8 to 9 kDa, and the calcium binding capacity was linearly correlated with carboxyl group content (R(2)= 0.8204). FTIR experiments revealed that upon binding calcium, the amide I band underwent a shift to lower wave numbers. A wide, intense Ca-O absorption band also appeared between 400 and 100 cm(-1) in the far-infrared spectrum. The width and intensity of this band increased after treatment of samples with glutaminase. The amount of bound calcium was related to both the molecular weight of the peptides and to the carboxyl group content, and the most likely sites for calcium binding are the carboxyl groups of Asp and Glu.

Effect of Soluble Soybean Protein Hydrolysate‐Calcium Complexes on Calcium Uptake by Caco‐2 Cells

Soybean protein hydrolysates (SPHs) bind with calcium, forming soluble SPH-calcium complexes via the carboxyl groups of glutamic and aspartic acid residues. However, their effect on calcium uptake is still unclear. In this study, Caco-2 cells were used to estimate the effect of SPH-calcium complexes with different molecular weights on calcium uptake in vitro. The changes in intracellular calcium ion concentration were measured by Fura-2 loading and expressed in fluorescence intensity. SPH-calcium complexes could promote calcium uptake. Improved fluorescence intensity was significantly different in SPH-calcium complexes (10 to 30 kDa), SPH-calcium complexes (3 to 10 kDa), and SPH-calcium complexes (1 to 3 kDa). The maximum levels of relative fluorescence intensity (18.3) occurred with SPH-calcium complexes (10 to 30 kDa). The effect of SPH-calcium complexes (10 to 30 kDa) on Ca(2+) increase was determined to be concentration dependent in the range of 0.5 to 4 mg/mL. Our results indicate that soybean protein itself might be responsible for promoting calcium absorption.

Purification and characterization of caclium-binding soybean protein hydrolysates by Ca2+/Fe3+ immobilized metal affinity chromatography (IMAC)

Soybean protein hydrolysates (SPHs) can bind calcium in order to form soluble peptide-calcium complexes. However, amino acid composition and structural characteristics of the calcium chelating SPHs are still unclear. This study separated SPHs with calcium and iron immobilized metal affinity chromatography (IMAC), and examined the effects of SPHs with different amino acid composition on calcium binding capacity. Three fractions (FFe-1, FFe-2 and FFe-3) isolated with IMAC-Fe(3+) were shown possessing increased Glu, Gln, Lys and Pro content from FFe-1 to FFe-3, and improved amount of bound calcium. Furthermore, the fractions adsorbed on IMAC-Ca(2+) (Fe(3+)) were separated and identified with reverse-phase (RP)-HPLC and MALDI-TOF MS/MS. The results showed that the sequence of peptides from FCa-2 and FFe-3 fractions was DEGEQPRPFPFP.

Characterization of the Volatile Substances and Aroma Components from Traditional Soypaste

In this study, the flavor substances of soypaste were extracted by a simultaneous distillation method and identified by GC-MS. The characteristic aroma components of soypaste were determined by the GC-O technique and the FD value of the characteristic aroma components was determined by AEDA method. It could be inferred that the aroma of the soypaste should be attributed to the presence of heterocyclic compounds and organic acids, with the heterocyclic compounds playing a prominent role.

Off-flavor related volatiles in soymilk as affected by soybean variety, grinding, and heat-processing methods.

Off-flavor of soymilk is a barrier to the acceptance of consumers. The objectionable soy odor can be reduced through inhibition of their formation or through removal after being formed. In this study, soymilk was prepared by three grinding methods (ambient, cold, and hot grinding) from two varieties (yellow Prosoy and a black soybean) before undergoing three heating processes: stove cooking, one-phase UHT (ultrahigh temperature), and two-phase UHT process using a Microthermics direct injection processor, which was equipped with a vacuuming step to remove injected water and volatiles. Eight typical soy odor compounds, generated from lipid oxidation, were extracted by a solid-phase microextraction method and analyzed by gas chromatography. The results showed that hot grinding and cold grinding significantly reduced off-flavor as compared with ambient grinding, and hot grinding achieved the best result. The UHT methods, especially the two-phase UHT method, were effective to reduce soy odor. Different odor compounds showed distinct concentration patterns because of different formation mechanisms. The two varieties behaved differently in odor formation during the soymilk-making process. Most odor compounds could be reduced to below the detection limit through a combination of hot grinding and two-phase UHT processing. However, hot grinding gave lower solid and protein recoveries in soymilk.

Evaluation of the aroma quality of Chinese traditional soy paste during storage based on principal component analysis.

Soy paste, a fermented soybean product, is widely used for flavouring in East and Southeast Asian countries. The characteristic aroma of soy paste is important throughout its shelf life. This study extracted volatile compounds via headspace solid-phase microextraction and conducted a quantitative analysis of 15 key volatile compounds using gas chromatography and gas chromatography-mass spectrum analysis. Changes in aroma content during storage time were analyzed using an acceleration model (40 °C, 28 days). In the 28 days of storage, results showed that among key soy paste volatile compounds, alcohol and aldehyde contents decreased by 35% and 26%, respectively. By contrast, acid, ester, and heterocycle contents increased by 130%, 242%, and 15%, respectively. The overall odour type transformed from a floral to a roasting aroma. According to sample clustering in the principal component analysis, the storage life of soy paste could be divided into three periods. These three periods represent the floral, roasting, and pungent aroma types of soy paste.

Inhibitory Action of Soybean β-Conglycinin Hydrolysates on Salmonella typhimurium Translocation in Caco-2 Epithelial Cell Monolayers

Soybean protein hydrolysates are widely used as functional foods as they have antioxidative properties able to enhance immune responses in humans. The alcalase enzymatic hydrolysates of beta-conglycinin were fractionated by ultrafiltration, and two main fractions, SP1 (<10 kDa) and SP2 (10-20 kDa), were obtained. The effects of these two fractions on the growth, development of epithelial cells, and formation of intercellular tight junctions were tested on an in vitro Caco-2 cell culture system. The inhibitory effects of SP1 and SP2 on the penetration of Salmonella typhimurium into Caco-2 epithelial cells were also examined. The results showed that the addition of >0.05 g/L of SP2 improved epithelial cell growth and that a concentration of 0.5 g/L of SP2 increased intercellular tight junction formation, which resulted in increased of transepithelial monolayer resistance (TER) values. Moreover, a lower S. typhimurium count compared to control was obtained when Caco-2 cells were grown in 0.05 and 0.5 g/L of SP2. These results show that beta-conglycinin hydrolysates play an important role in resisting S. typhimurium penetration into intestinal epithelial cells and that high molecular mass peptides (10-20 kDa) were more effective overall than low molecular mass peptides.

Aroma Stability of Millet Powder During Storage and Effects of Cooking Methods and Antioxidant Treatment

ABSTRACT Foxtail millet is a cereal crop that contains high levels of unsaturated fatty acids, so that processed food such as instant millet powder is susceptible to lipid oxidation, which gradually leads to deteriorated flavor and quality. In this work, volatiles of millet powder samples with or without storage at room temperature for 12 months were extracted and analyzed by gas chromatography–olfactometry/mass spectrometry. In fresh steamed millet powder, hexanal, 2-pentylfuran, and 3-octen-2-one might be dominant odorants, whereas in deteriorated steamed millet powder, volatiles such as 1-octen-3-ol, (E)-2-octen-1-ol, (E)-2-octenal, 3-nonen-2-one, (E)-2-nonenal, decanal, 2-undecanone, and 2-methylnaphthalene emerged or increased over time, among which 1-octen-3-ol and (E)-2-nonenal were highly responsible for its rancid flavor. We also compared millet powder prepared with two different processing methods, steaming and extrusion. Compared with steaming, extrusion was a cooking method of millet that help...

Yield and textural properties of tofu as affected by soymilk coagulation prepared by a high-temperature pressure cooking process.

The cooking of raw soymilk is a necessary procedure prior to the production of tofu. The effects of the high-temperature pressure cooking (HTPC) and traditional cooking methods on the yield and textural properties of tofu products were investigated. Results showed that when HTPC was applied, the content of protein particles increased, thereby contributing to the formation of a dense network of tofu gel. Thus, significant improvement of textural properties, including hardness, chewiness and springiness, was observed. Moreover, HTPC contributes to the change in the composition of the particulate protein, whereas the proportion of β-conglycinin in the non-particulate protein increased. The start and end points of the protein coagulation induced by Ca(2+) moved backward, and slowed the coagulation process, which was conducive to the incorporation of water or dry matter into the gel.