Qinchun Rao

Effect of moisture content on selected physicochemical properties of two commercial hen egg white powders

After short-term storage at 23°C, selected physicochemical properties of two hen egg white powders (with and without hydrolysis) were studied. Overall, the effect of moisture content on physicochemical properties of Hydrolysed Egg White powder (HEW) was more severe than those of Dried Egg White powder (DEW). The denaturation temperature (Td) and its enthalpy change (ΔHd) of ovalbumin in DEW followed an exponential model, as well as the Td of HEW. The Gordon-Taylor equation modelled well the glass transition temperatures (Tg) of HEW and DEW. The Guggenheim-Anderson-de Boer (GAB) model fitted well to the type II moisture sorption isotherm. At the critical moisture content (12.0%, dry basis), compared with DEW, the colour of HEW began to darken dramatically and its hardness started to change significantly. These changes were closely related to the inherent characteristics of the two products. The mechanisms relevant to these physicochemical changes were discussed.

Accelerated shelf-life testing of quality loss for a commercial hydrolysed hen egg white powder

In recent years, due to the specific health benefits associated with bioactive peptides and the reduction of protein allergenicity by enzymatic hydrolysis, the utilisation of protein hydrolysates in functional foods and beverages for both protein supplementation and clinical use has significantly increased. However, few studies have explored the moisture-induced effects on food protein hydrolysates, and the resulting changes in the structure and texture of the food matrix as well as the loss in functional properties of bioactive peptides during storage. The main purpose of this study is to determine the influence of water activity (a(w)) on the storage quality of a commercial spray-dried hydrolysed hen egg white powder (HEW). During storage at 45 °C for two months at different a(w)s (0.05-0.79), the selected physicochemical properties of the HEW samples were analysed. Overall, the effect of a(w) on the colour change of HEW at 45 °C for one month was similar to that of HEW after four months at 23 °C due to the presence of a small amount of glucose in HEW. Several structural changes occurred at a(w)s from 0.43 to 0.79 including agglomeration, stickiness and collapse. Kinetic analysis showed a first-order hyperbolic model fit for the change in the L(∗) value, the total colour difference (ΔE(∗)) and the fluorescence intensity (FI). There was a high correlation between colour change and fluorescence, as expected for the Maillard reaction. The reduction in the remaining free amino groups was about 5% at a(w) 0.50 and 6% at a(w) 0.79 after one month storage. In summary, during storage, the Maillard reaction and/or its resulting products could decrease the nutritional value and the quality of HEW.

Storage Stability of Food Protein Hydrolysates—A Review

In recent years, mainly due to the specific health benefits associated with (1) the discovery of bioactive peptides in protein hydrolysates, (2) the reduction of protein allergenicity by protein hydrolysis, and (3) the improved protein digestibility and absorption of protein hydrolysates, the utilization of protein hydrolysates in functional foods and beverages has significantly increased. Although the specific health benefits from different hydrolysates are somewhat proven, the delivery and/or stability of these benefits is debatable during distribution, storage, and consumption. In this review, we discuss (1) the quality changes in different food protein hydrolysates during storage; (2) the resulting changes in the structure and texture of three food matrices, i.e., low moisture foods (LMF, aw < 0.6), intermediate moisture foods (IMF, 0.6 ≤ aw < 0.85), and high moisture foods (HMF, aw ≥ 0.85); and (3) the potential solutions to improve storage stability of food protein hydrolysates. In addition, we note there is a great need for evaluation of biofunction availability of bioactive peptides in food protein hydrolysates during storage.

Moisture-induced Quality Changes of Hen Egg White Proteins in a Protein/Water Model System

In recent years, the intermediate-moisture foods (IMF), such as nutrition and energy bars, are a rapidly growing segment of the global food market. However, due to moisture-induced protein aggregation, commercial high protein nutrition bars generally become harder over time, thus losing product acceptability. In this study, the objectives were to investigate the moisture-induced protein aggregation in a hen egg white proteins/water dough model system (water activity (a(w)): 0.95) and to evaluate its molecular mechanisms and controlling factors. During storage at three different temperatures (23, 35, and 45 °C) for 70 days, four selected physicochemical changes of the dough system were analyzed: the a(w), the color (L* value), the fluorescent Maillard compounds (fluorescence intensity (FI) value), and the remaining free amino groups. Overall, the physicochemical changes of egg white proteins in the dough system are closely related to the glass transition temperature (T(g)). The effect of moisture content on both the L* and FI values occurred as a function of storage time at 45 °C due to the Maillard reaction. The change of the remaining free amino groups at different temperatures was derived from the coaction of both the Maillard reaction and enzymatic hydrolysis from molds. Additionally, through analyzing the buffer-soluble egg white proteins using gel electrophoresis, our results showed that moisture-induced aggregates were produced by two chemical reactions during storage: the disulfide interaction and the Maillard reaction. Furthermore, the effect of two processes during manufacturing, desugarization and dry-heat pasteurization, on the physicochemical changes of the egg white proteins was elucidated. In order to prevent or reduce moisture-induced protein aggregation during product storage and distribution, two potential solutions were also discussed.

Competitive Enzyme-Linked Immunosorbent Assay for Quantitative Detection of Bovine Blood in Heat-Processed Meat and Feed

Animal blood is widely used as a functional additive in food and as a protein supplement in animal feed. Effective analytical methods are therefore needed to enforce labeling regulations for product quality control, as well as to address safety concerns. This study developed a monoclonal antibody (MAb)-based competitive enzyme-linked immunosorbent assay (ELISA) for quantitative detection of ruminant (bovine and ovine) blood in heat-processed meat and feedstuff. MAb BblH9 immunoglobulin G1, which recognizes a 12-kDa, thermostable, ruminant blood protein, was used as the detecting agent in the competitive ELISA. The immunoreactivity of MAb Bb1H9 was confirmed in both an indirect noncompetitive ELISA and a competitive ELISA, in which antigens are presented in immobilized form and free form, respectively. The competitive ELISA was optimized, and three spiked samples adulterated at 0 to 10% were tested to determine the detection limits of the optimized assay. Results showed that MAb Bb1H9 is specific to ruminant blood protein, with no cross-reaction with nonblood samples tested. The optimized competitive ELISA quantitatively detected heat-processed bovine blood over the tested range. The detection limit of the assay for bovine blood in beef (P < 0.001), bovine blood in porcine blood (P < 0.01), and bovine blood meal in soybean meal (P < 0.01) was found to be 0.5% in all cases. This MAb-based competitive ELISA is thus suitable for the sensitive and quantitative detection of ruminant blood proteins in heat processed meat and feed products.

Storage stability of hen egg white powders in three protein/water dough model systems

In recent years, due to the specific health benefits associated with bioactive peptides and the reduction of protein allergenicity by enzymatic hydrolysis, the utilisation of protein hydrolysates in the intermediate-moisture food (IMF) market, such as high protein nutrition bars (HPNB), has significantly increased. Currently, no reported study is related to the storage stability of dried hen egg white (DEW) and its hydrolysates (HEW) in an IMF matrix. Therefore, three DEW/HEW dough model systems (100%HEW+0%DEW, 75%HEW+25%DEW and 50%HEW+50%DEW) were established using two commercial spray-dried egg white powders to study the effect of temperature and fraction of HEW on these IMF models (water activity (a(w)): ∼0.8). During storage at three different temperatures (23, 35 and 45°C) for 70 days, the selected physicochemical properties of the dough systems were compared. Overall, kinetic analysis showed an apparent zero-order model fit for the change in the colour (L(∗)), fluorescence intensity (FI) and hardness, as a function of time, for different dough model systems. As expected, the L(∗), FI and hardness increased as a function of time mainly due to the Maillard reaction. The amount of free amino groups decreased, with an increase in rate of loss, as temperature increased in the 100%HEW+0%DEW model. When DEW was substituted for some HEW, the regeneration of the free amino groups after loss was observed as a function of time. Furthermore, when the percentage of HEW was decreased, the incidence of mouldy samples occurred sooner, which indicates that HEW has some antimicrobial ability, especially in the 100%HEW+0%DEW system where mould growth did not occur.

Storage stability of a commercial hen egg yolk powder in dry and intermediate-moisture food matrices.

Quality loss in intermediate-moisture foods (IMF) such as high-protein nutrition bars (HPNB) in the form of hardening, nonenzymatic browning, and free amino group loss is a general concern for the manufacturers. To measure the extent of quality loss over time in terms of these negative attributes, through changing the ratio by weight between two commercial spray-dried hen egg powders, egg white (DEW) and egg yolk (DEY), the storage stability of 10 IMF systems (water activity (aw) ∼ 0.6) containing 5% glycerol, 10% shortening, 35% protein, and 50% sweetener (either maltitol or 50% high-fructose corn syrup/50% corn syrup (HFCS/CS)) were studied. Additionally, the storage stability of the DEY powder itself was investigated. Overall, during storage at different temperatures (23, 35, and 45 °C), the storage stability of DEY in dry and IMF matrices was mainly controlled by the coaction of three chemical reactions (disulfide bond interaction, Maillard reaction, and lipid oxidation). The results showed that by replacing 25% of DEW in an IMF model system with DEY, the rate of bar hardening was significantly lower than that of the models with only DEW at all temperatures due to the softening effect of the fat in DEY. Furthermore, the use of maltitol instead of HFCS/CS in all bar systems not only resulted in decreased hardness but also drastically decreased the change in the total color difference (ΔE*). Interestingly, there was no significant loss of free amino groups in the maltitol systems at any DEW/DEY ratio.

Immunoassay for the Detection of Animal Central Nervous Tissue in Processed Meat and Feed Products.

An indirect competitive enzyme-linked immunosorbent assay (icELISA) based on the detection of the thermal-stable central nervous tissue (CNT) marker protein, myelin basic protein (MBP), was developed to detect animal CNT in processed meat and feedstuffs. Two meat samples (cooked at 100 °C for 30 min and autoclaved at 133 °C for 20 min) of bovine brain in beef and two feed samples (bovine brain meal in beef meal and in soybean meal) were prepared at levels of 0.0008, 0.0031, 0.0063, 0.0125, 0.025, 0.05, 0.1, 0.2, 0.4, 0.8, and 1.6%. An anti-MBP monoclonal antibody (mAb3E3) was produced using the hybridoma technique and characterized using Western blot. The optimized icELISA was CNT-specific without cross-reactivity with either meat (beef and pork) or soybean meal samples and had low intra-assay (%CV ≤ 3.5) and interassay variability (%CV ≤ 3.3), with low detection limits for bovine MBP (6.4 ppb) and bovine CNT spiked in both meat (0.05%) and feed (0.0125%) samples. This assay is therefore suitable for the quantitative detection of trace amounts of contaminated animal CNT in processed food and feed products.

Matrix effect on food allergen detection – A case study of fish parvalbumin

Two fish parvalbumin models were established to study relationships among matrix effect, extractability, and thermostability during in vitro immunodetection using two parvalbumin-specific monoclonal antibodies (3E1 and PARV19). Our results illustrated that matrix-induced thermal instability of parvalbumin was due mainly to physical (hydrophobic effect) and chemical (thiol-disulfide interchange) interactions. The addition of sodium dodecyl sulfate (SDS, surfactant), β-mercaptoethanol (reducing agent) or ethylenediaminetetraacetic acid (EDTA, metal chelator) during sample preparation could not only increase the extractability of parvalbumin but also enhanced its immunodetection. Our findings demonstrated excess EDTA completely chelated Ca2+ in parvalbumin and rendered it undetectable using PARV19 (a Ca2+-dependent antibody). Overall, our resulted showed that matrix effect on in vitro analyte quantification cannot be underestimated. Any false negative or positive results could lead to severe or life-threatening allergic reactions.

Can Glycation Reduce Food Allergenicity

As a naturally occurring reaction during food processing, glycation, also known as non-enzymatic browning or Maillard reaction, can improve food protein physiochemical properties and functionality. In this perspective, three aspects of glycation (terminology confusion between glycation and glycosylation, its current application, and its impact on immunoreactivity) are elaborated. Overall, the immunoreactivity of glycated proteins may decrease, remain unchanged, or even increase after food glycation. Also, it should be noted that the effect of glycation on the immunoglobulin (Ig)E- or IgG-binding capacity of allergens does not necessarily and correctly predict the allergenicity of the glycated protein in the allergic patient population.