Browsing by Subject "Soy protein"

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    Hypoallergenization of soy protein using a combination of limited enzymatic hydroylsis and controlled Maillard-induced glycosylation
    (2014-05) Walter, Jordan Kay
    Emerging interest among consumers as to the health benefits of soy and a shifting preference toward more economical sources of protein has led to the increased global interest in soy protein. However, the main drawback to the expanded use of soy protein is its allergenicity, as soy is listed among the "Big 8" food allergens by the Food and Drug Administration (FDA). Therefore, in order to prevent a decrease in the momentum behind the usage of soy protein ingredients, different protein modification techniques must be explored in order to reduce the allergenicity of soy. Extensive enzymatic hydrolysis can reduce the allergenicity of a protein. However, this technique has negative consequences such as decreased protein functionality and bitter flavor. In order to limit enzymatic hydrolysis, response surface methodology (RSM) can be used to determine the optimized combination of factors, such as time, temperature and enzyme to substrate ratio, that results in the maximum reduction in immunoreactivity of the modified protein, while maintaining quality. Enzymatic hydrolysis, however, when limited, may only reduce the immunoreactivity to a certain extent. Thus a second technique, such as Maillard-induced glycosylation may further reduce the allergenicity of the minimally hydrolyzed soy protein. The first objective was to determine optimal hydrolysis conditions for a maximum reduction of soy protein allergenicity using response surface methodology. The second objective was therefore to determine the effect of limited and controlled Maillard-induced glycosylation on the allergenicity of soy protein hydrolysate produced under optimized conditions from objective 1. A central composite design (CCD) was used to produce different soy protein hydrolysate (SPH) samples using Alcalase 2.4L with 3 independent variables; temperature (x1), time (x2), and enzyme to substrate ratio (E:S) (x3), with the degree of hydrolysis (DH) and the % reduction in immunoreactivity as the response variables. Western blots and ELISA were used to evaluate the immunoreactivity of the different hydroylsates using sera from different soy allergenic individuals. The design included 20 experimental units with 6 center points to assess experimental variability, 8 factorial points, and 8 alpha points to assess potential curvature in the data. The effects of the different independent variables on the responses were assessed by fitting the data to the appropriate model. Once a model was selected, 3D plots were generated. Once all of the responses were fit to the appropriate models, constraints were then added onto the levels of the variables that resulted in a DH greater than 8%. The predicted % reductions in immunoreactivity were then determined for each individual sera with the added constraints. Due to overlap in the predicted optimum response among the sera, one set of conditions was chosen to produce one optimized hydrolysate. Maillard-induced glycosylation of the optimized hydrolysate was conducted using conditions that were carefully selected to control the reaction. Several different measurements were done to assess the progression of the reaction, including Amadori compound formation, browning, lysine blockage, and fluorescence, all of which confirmed limited progression of the reaction. The immunoreactivity of SPH, partially glycosylated soy protein hydrolysate (PGSPH), and partially glycosylated soy protein (PGSP) was determined using ELISA and Western blots. Significant reductions in immunoreactivity (up to 58%) were observed for the different hydrolysates produced using RSM. Variability among sera was observed for the different hydrolysates, which was attributed to the resulting protein and protein/peptide profile upon hydrolysis. Different hydrolysis conditions may have resulted in the exposure or elimination of IgE binding regions (epitopes). Using RSM modeling, the optimized hydrolysis conditions were determined and the resulting SPH had a DH of 7.8% and a % reduction in immunoreactivity ranging from 20-52%. When the produced SPH was subjected to controlled Maillard-induced glycosylation, a significantly (P ≤ 0.05) higher % reduction in immunoreactivity (up to 83%) was observed when using serum that had the highest soy specific IgE (45.30 kU/L). Results from this work, for the first time, showed that two different protein modification techniques can be utilized in combination to substantially reduce the allergenicity of soy protein while maintaining quality. Therefore, limited enzymatic hydrolysis combined with controlled Maillard-induced glycosylation has great potential for the development of hypoallergenic protein ingredients.
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    The impact of moisture-induced aggregation of soy protein isolate and hydrolysate during storage on product and nutritional quality
    (2014-05) Gillman, Lauren Elizabeth
    With the increased interest in protein-based foods in the United States, soy protein isolate (SPI) and hydrolysate (SPH) have become widely used in the food industry. However, during processing and distribution proteins/peptides tend to aggregate when introduced to increased temperatures and relative humidity. When aggregation occurs in a dry protein powder, there is a decrease in processability, product quality, and consumer acceptability. It is therefore necessary to characterize the covalent and non-covalent interactions involved in moisture-induced aggregation as well as their reaction kinetics to aid in the development of technologies to limit aggregation.The objectives of this study were twofold: (1) to characterize the physicochemical changes of moisture-induced protein/peptide aggregation in SPI and SPH powders during storage as a function of water activity (aw) and temperature and (2) to determine the nutritional and physiological changes of SPI and SPH during storage when subjected to various aw and temperatures.The effects of aw and temperature during the storage of SPI, SPH, and a 50:50 mixture on several physicochemical characteristics were investigated. Three temperatures (25, 35, and 45°C) and 8 aw (ranging from 0.05 to 0.79) were employed for the storage study. Prior to storage, intrinsic properties as well as moisture sorption isotherms were determined for each protein powder. Over time, the color change was assessed in a non-destructive manner; also, samples were collected at predetermined time points to monitor the aggregation and resulting changes. Change in color, % solubility, protein/peptide profile, loss of free amino groups, formation of fluorescent Maillard compounds, and denaturation were monitored using well-established methods of analysis. Reaction kinetics were used when possible to better understand the effects of storage parameters and sample types, while also allowing for better predictions at other storage parameters. Lastly, changes in in vitro digestibility and angiotensin-converting enzyme (ACE) inhibitory activity were assessed to determine protein aggregation's effects on nutritional and physiological changes.Storage at aw above the monolayer moisture value of the soy protein ingredients resulted in the formation of insoluble aggregates. Hydrophobic interactions, disulfide bonds, and covalent linkages induced by the Maillard reaction lead to the observed aggregation; these interactions were most pronounced at 45°C and aw>0.59. Even though there was a minimal amount of reducing sugars in the protein powders, the development of fluorescent compounds, change in color, and loss of free amino groups indicated that the Maillard reaction occurred. Soy protein hydrolysate was the most susceptible to the Maillard reaction, but SPI and 50/50 had larger decreases in % solubility over time at aw>0.33 and 45°C. The aggregates formed during storage, however, did not have a significant effect on the % digestibility and ACE inhibitory activity of soy proteins/peptides. These findings can be used to help predict changes in food matrices with similar aw during storage for optimal utilization of soy protein ingredients.