Characteristics of Oil and Skim in Enzyme‐Assisted Aqueous Extraction of Soybeans

Effects of sucrase enzymatic hydrolysis combined with Maillard reaction on soy protein hydrolysates: Bitterness and functional properties

In this study, sucrase was added to convert non-reducing sugars into reducing sugars in skim obtained by enzyme-assisted aqueous extraction processing (EAEP), then the variation of soy protein hydrolysates (SPH) from the skim under different Maillard reaction times were studied. We conducted one-factor experiment and selected 2 mg/mL sucrase for enzymatic hydrolysis for 2 h. The structure of SPH was investigated by Fourier transform infrared spectroscopy, intrinsic fluorescence spectroscopy, and amino acid composition. Results showed that the Maillard reaction loosened the SPH structure and produced new functional groups. Sensory evaluation, electronic tongue, electronic nose and GC-MS were used to study the sensory characteristics of SPH, we found that the bitterness value was significantly reduced to 1.71 from 4.63 after 2 h of the Maillard reaction. The change of bitterness was related to amino acid composition and the production of pyrazine. Additionally, the iron reduction ability, DPPH free radical scavenging ability, and emulsifying activity reached the highest at 2 h of reaction with 0.80, 73.94 %, and 56.09 %. The solubility, emulsifying stability, and foaming capacity increased and gradually stabilized with the increasing reaction time. Therefore, this paper presents an effective method for generating SPH with low bitterness and high functional properties.

Investigation on the emulsification mechanism in aqueous enzymatic extraction of edible oil from Schizochytrium sp

BACKGROUND

The interaction between emulsified substances and lipids generates an emulsification system during the extraction of microalgae edible oil by aqueous enzymatic method. This study aimed to resolve the dynamics of interfacial protein adsorption during the extraction of microalgae oil at different enzymatic times and the effect on the stability of the interfacial membrane formed by the proteins based on interfacial effects.

RESULTS

At 1.5 h of enzymatic hydrolysis, the molecular weights of the proteins/peptides were all below 35 kD. In addition, the protein-peptide structure was loose, with the lowest number of disulfide bonds, peak surface hydrophobicity, the highest number of residues, and disordered lipid acyl arrangement. At the same time, the physical stability of the emulsion was the lowest, and the interfacial membrane rupture was distinct. On excessive enzymatic hydrolysis (at 3.0 h), a more uniform interfacial membrane was re-formed on the lipid surface.

CONCLUSION

Protein is the main emulsifying substance in the emulsification system. The addition of protease affects the stability of the interfacial membrane formed by proteins. In addition, sufficient enzymatic hydrolysis (1.5 h) inhibited emulsification, while excessive enzymatic hydrolysis (3.0 h) promoted emulsification. © 2023 Society of Chemical Industry.

Leveraging Bioprocessing Strategies to Achieve the Simultaneous Extraction of Full-Fat Chickpea Flour Macronutrients and Enhance Protein and Carbohydrate Functionality

The concurrent extraction of lipids, proteins, and carbohydrates can be achieved by aqueous and enzymatic extraction processes, circumventing the low extractability by mechanical pressing and the use of flammable solvents. The use of alkaline protease, preceded or not by carbohydrase pretreatments, was evaluated on the extractability of oil, protein, and carbohydrates from full-fat chickpea flour and protein functionality. Enzymatic extraction increased oil and protein extractability from 49.8 to 72.0–77.1% and 62.8 to 83.5–86.1%, respectively. Although the carbohydrase pretreatments before the addition of protease did not increase oil and protein extractability, the carbohydrate content of the extracts increased from 7.68 to 9.17−9.33 mg/mL, accompanied by the release of new oligosaccharides in the extracts, as revealed by LC–MS/MS characterization. Enzymatic extraction yielded proteins with significantly higher solubility (25.6 vs. 68.2–73.6%) and digestibility (83.8 vs. 90.79–94.67%). Treatment of the extracts with α-galactosidase completely removed the flatulence-causing oligosaccharides (stachyose and raffinose). This study highlights the effectiveness of environmentally friendly bioprocessing strategies to maximize lipid, protein, and oligosaccharide extractability from full-fat chickpea flour with concurrent improvements in protein solubility and in vitro digestibility, reduction of flatulence related oligosaccharides, and generation of a more diverse pool of oligosaccharides for subsequent prebiotic evaluation.

Graphical abstract

Characteristics of Soy Protein Prepared Using an Aqueous Ethanol Washing Process

Currently, the predominant process for soy protein concentrate (SPC) production is aqueous ethanol washing of hexane-extracted soy meal. However, the use of hexane is less desired, which explains the increased interest in cold pressing for oil removal. In this study, cold-pressed soy meal was used as the starting material, and a range of water/ethanol ratios was applied for the washing process to produce SPCs. Washing enriched the protein content for the SPCs, regardless of the solvent used. However, we conclude that washing with water (0% ethanol) or solvents with a high water/ethanol ratio (60% and above) can be more advantageous. Washing with a high water/ethanol ratio resulted in the highest yield, and SPCs with the highest protein solubility and water holding capacity. The water-only washed SPC showed the highest viscosity, and formed gels with the highest gel strength and hardness among all the SPCs at a similar protein concentration. The variations in the functionality among the SPCs were attributed to protein changes, although the effects of non-protein constituents such as sugar and oil might also be important. Overall, the aqueous ethanol washing process combined with cold-pressed soy meal created SPCs comparable to commercial SPC in terms of composition, but with varied functionalities that are relevant for novel soy-food developments.

Oxidative stability of soy proteins: From ground soybeans to structured products

The production of soy protein-based foods requires multiple-step, intensive processing and storage of soy ingredients, which can increase the product's susceptibility to oxidation. Therefore, we investigated the oxidative stability of soy protein-based products subjected to different relevant conditions or treatments: over storage of soy flours, over fractionation to yield soy protein isolate (SPI), and over subsequent thermomechanical processing to yield a model structured product. Soy flours were stable to lipid and protein oxidation over 250 days storage in chilled or ambient conditions. The fractionation process applied to make SPI did not increase substantially protein carbonylation, but increased surface-exposed hydrophobicity and decreased free thiols, compared to the starting defatted flour. Subsequent processing of hydrated SPI powder at 140 °C further increased protein carbonylation to a high extent. Therefore, we conclude that soy flours can be stable over long storage times, but processing to yield structured foods products promote protein oxidation.

Effects of industrial heat treatments on bovine milk oxylipins and conventional markers of lipid oxidation

The effects of industrial heat treatments of raw bovine milk subjected to Batch Pasteurization (BP), High Temperature Short Time (HTST) and Ultra High Temperature (UHT) on the formation of primary (hydroperoxide content and oxylipins) and secondary lipid oxidation products (thiobarbituric acid reactive species -TBARS) were evaluated. Total fatty acid content, percent of free fatty acids (FFA), and total antioxidant capacity (TAC) were also measured. Except for a 30% reduction in capric acid (C10:0) after UHT compared to BP, no significant differences in total fatty acid concentrations were detected amongst the heat treatments. Compared to raw bovine milk, no statistically significant effects of heat treatment were observed on percent FFA (0.29-0.31%), hydroperoxide concentration (0.0558-0.0624 mmol L^-1), and TBARS values (13.4-18.9 µg MDA kg^-1). HTST and UHT led to significant reductions (50-65%) in linoleic and alpha-linolenic acid oxidized metabolites compared with raw milk and batch pasteurized milk. Compared to raw milk (2943.7 μmol of TEAC L^-1), TAC was significantly reduced by all heat treatments (2245 - 2393 μmol of TEAC L^-1), although no statistically significant differences were observed amongst the treatments. The results demonstrate that heat processing reduces milk oxylipin content and antioxidant capacity and that oxylipin and TAC measurements provide a new sensitive approach to assess the impact of milk processing on lipid oxidation. The nutritional, shelf life and sensory implications of reduced oxylipins in HTST and UHT processed bovine milk merit further investigation.

Aqueous and Enzymatic Extraction of Oil and Protein from Almond Cake: A Comparative Study

The almond cake is a protein- and oil-rich by-product of the mechanical expression of almond oil that has the potential to be used as a source of valuable proteins and lipids for food applications. The objectives of this study were to evaluate the individual and combined effects of solids-to-liquid ratio (SLR), reaction time, and enzyme use on oil and protein extraction yields from almond cake. A central composite rotatable design was employed to maximize the overall extractability and distribution of extracted components among the fractions generated by the aqueous (AEP) and enzyme-assisted aqueous extraction process (EAEP). Simultaneous extraction of oil and protein by the AEP was favored by the use of low SLR (1:12.82) and longer reaction times (2 h), where extraction yields of 48.2% and 70% were achieved, respectively. Increased use of enzyme (0.85%) in the EAEP resulted in higher oil (50%) and protein (75%) extraction yields in a shorter reaction time (1 h), compared with the AEP at the same reaction time (41.6% oil and 70% protein extraction). Overall, extraction conditions that favored oil and protein extraction also favored oil yield in the cream and protein yield in the skim. However, increased oil yield in the skim was observed at conditions where higher oil extraction was achieved. In addition to improving oil and protein extractability, the use of enzyme during the extraction resulted in the production of skim fractions with smaller and more soluble peptides at low pH (5.0), highlighting possible uses of the EAEP skim in food applications involving acidic pH. The implications of the use of enzyme during the extraction regarding the de-emulsification of the EAEP cream warrant further investigation.

Recovery of high value-added protein from enzyme-assisted aqueous extraction (EAE) of soybeans by dead-end ultrafiltration

The skim fraction (SF) obtained from enzyme-assisted aqueous extraction (EAE) of soybeans is a by-product with high protein content of up to 60.67%. As such, it is of great interest to develop an efficient method to recover protein from this fraction. In this study, the potential of dead-end ultrafiltration (UF) in recovering skim protein extracted with different proteases was evaluated. Two polyethersulfone (PES) membranes with molecular weight cutoffs (MWCO) of 3 kDa and 5 kDa were utilized. Results revealed that the membrane with the MWCO of 5 kDa exhibited better filtration efficiency, since higher permeate flux values and lower impurity rejections were observed. Compared with Flavourzyme and Protex 7L, Alcalase 2.4L and Protex 6L exhibited stronger hydrolyzing ability, resulting in higher filtration fluxes but lower protein rejection coefficients. The recovered protein showed comparable amino acid profile to SPC, while with significantly reduced levels of trypsin inhibitors and phytate (p < 0.05), indicating high quality of the recovered protein. Overall, UF can be applicable to recover high value-added protein from EAE of soybeans and remove undesired components from the resulting protein products.

Characterizing the Structural and Functional Properties of Soybean Protein Extracted from Full-Fat Soybean Flakes after Low-Temperature Dry Extrusion

The soy protein isolates (SPI) extracted from different extruded full-fat soybean flakes (FFSF), and their conformational and functional properties were characterized. Overall, the free thiol (SH) content of SPI increased when the extrusion temperature was below 80 °C and decreased at higher temperatures. Soy glycinin (11S) showed higher stability than β-conglycinin (7S) during extrusion. Results also indicated that the increase in some hydrophobic groups was due to the movement of hydrophobic groups from the interior to the surface of the SPI molecules at extrusion temperatures from 60 to 80 °C. However, the aggregation of SPI molecules occurred at extrusion temperatures of 90 and 100 °C, with decreasing levels of hydrophobic groups. The extrusion temperature negatively affected the emulsifying activity index (EAI); on the other side, it positively affected the emulsifying stability index (ESI), compared to unextruded SPI.

Effect of extruding full-fat soy flakes on trans fat content

To evaluate the effects of extrusion process on the trans fatty acids (TFAs) formation in soybean crude oils, three different extrusion parameters, namely, extrusion temperature (80-160 °C), feed moisture (10-26%), and screw speed (100-500 rpm), were carried out. It was found that only five different types of TFAs were detected out using gas chromatography-mass spectrometry. Before the extrusion started, the initial amount of total TFAs was 3.04 g/100 g. However, after extruding under every level of any variable, the total amounts of TFAs were significantly higher than those in the control sample (P < 0.05). For example, taking the effect of extrusion temperature into account, we can find that the highest amount of total of trans fatty acid (TTFA) was 1.62 times the amount of that in the control sample, whereas the lowest amount of TTFA was 1.54 times the amount of that in the control sample. Importantly, it was observed that the amounts of every type of trans fatty acid were not continuously increasing with the increase of the level of any extrusion variable. This phenomenon demonstrated that the formation and diversification were intricate during extruding process and need to be further studied.