Browsing by Author "Kalaydzhiev, Hristo"
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- Comparative biochemical profile of protein-rich products obtained from industrial rapeseed mealPublication . Ivanova, Petya; Kalaydzhiev, Hristo; Rustad, Turid; Silva, Cristina L. M.; Chalova, Vesela I.Protein-rich products, prepared from industrial rapeseed meal, have the potential for versatile applications in the food-, feed-, and nutraceutical industries. The aim of study was to characterize the biochemical composition of two protein-rich products obtained from industrially produced rapeseed meal. Protein isolate (PI) and acid soluble protein (ASP) were prepared by alkaline extraction (pH 12.0) followed by isoelectric precipitation (pH 4.5). Biochemical analyses revealed that PI contained a high protein amount (86.9%), while ASP had 28.8% protein and a relatively high level of non- protein compounds including ash (20.6%) and fiber (30.0%). Results showed that neither protein products contained glucosinolates. They were rich in microelements; the most abundant were Cu (64.3 mg kg-1) and Fe (133 mg kg-1) in PI and Mn (39.7 mg kg-1) and Zn (84.2 mg kg-1) in ASP. PI and ASP were also a good source of Se (1.1 mg kg-1 and 0.9 mg kg-1, respectively). Lysine was the most abundant essential amino acid in PI with amino acid score of 100.7% followed by leucine (98.3%) and valine (95.8%). Both protein products were mainly composed of low molecular weight fractions (5 to 33 kDa) but in different ratio. The PI contained two fractions with molecular weights 53 and 235 kDa which were not found in ASP. In conclusion, PI and ASP exhibited different biochemical characteristics which make them suitable for different applications.
- Enhanced solubility of rapeseed meal protein isolates prepared by sequential isoelectric precipitationPublication . Kalaydzhiev, Hristo; Georgiev, Radoslav; Ivanova, Petya; Stoyanova, Magdalena; Silva, Cristina L. M.; Chalova, Vesela I.The solubility of plant protein isolates is a key determinant of their potential application. Two protein isolates (PI) from ethanol-treated industrial rapeseed meal, PI10.5–2.5 and PI2.5–8.5, were prepared by sequential isoelectric precipitation of alkali-extracted proteins (pH 12) starting from pH 10.5 to 2.5 or from pH 2.5 to 8.5, respectively. Biochemical analyses revealed that PI2.5–8.5 contained a higher amount of crude protein (72.84%) than PI10.5–2.5 (68.67%). In the same protein isolate, the level of total phenols (0.71%) was almost two-fold higher than that in PI10.5–2.5 (0.42%). No glucosinolates were established in both protein isolates. SDS-PAGE analysis demonstrated that PI10.5–2.5 contained 10 to 15 kDa protein fractions in a relatively higher amount, while PI2.5–8.5 was enriched in 18 to 29 kDa protein fractions. PI10.5–2.5 exhibited high solubility, varying from 41.74% at pH 4.5 to 65.13% at pH 6.5, while PI2.5–8.5 was almost two-fold less soluble under the same conditions. Up to pH 5.5, the addition of NaCl at 0.03 and 0.25 M diminished the solubility of PI2.5–8.5, while the solubility of PI10.5–2.5 was increased. The supplementation of PI10.5–2.5 with 0.25 M NaCl enhanced the protein solubility to 56.11% at pH 4.5 and 94.26% at pH 6.5. The addition of 0.03 M NaCl also increased the solubility of this protein isolate but to a lower extent. Overall, the approach for sequential precipitation of proteins influenced the biochemical characteristics, protein fractional profile and solubility of prepared protein isolates.
- Foaming properties of acid-soluble protein-rich ingredient obtained from industrial rapeseed mealPublication . Ivanova, Petya; Kalaydzhiev, Hristo; Dessev, Tzvetelin T.; Silva, Cristina L.M.; Rustad, Turid; Chalova, Vesela I.The use of the rapeseed meal as a source for preparation of protein-rich ingredients for the food industry is an alternative to the current limited application as a feed additive. The aim of this study was to evaluate foaming properties of an acid-soluble protein-rich ingredient (ASP) obtained from industrial rapeseed meal as a co-product of a protein isolate. Foam capacity and stability over a period of 60 min were evaluated by using volumetric and image analyzing methods. The influence of NaCl at two boundary concentrations (0.03 and 0.25 M) was studied over a pH range from 2 to 10. The ASP exhibited high foamability ([90%), not influenced by pH or salt addition. In contrast, foam stability, measured over a 60 min period, was pH and NaCl dependent. By the end of the observation period, the addition of 0.25 M NaCl reduced the foam volume by more than 70% at all pH values. After 30 min at pH values 4, 6 and 8, which are the most common for food products, the foams without NaCl retained 51, 38 and 41% of the initial foam volume, respectively. The results were in agreement with image analysis observations where microstructure ofthe foams with NaCl was more heterogeneous than that of the foams without salt addition. The high foamability and relatively high foam stability at pH from 4 to 8 without NaCl addition shows that ASP could be a potential alternative to plant proteins currently used as foaming agents in the food industry.
- Functional properties of protein isolate and acid soluble protein-rich ingredient co-produced from ethanol-treated industrial rapeseed mealPublication . Kalaydzhiev, Hristo; Ivanova, Petya; Silva, Cristina L. M.; Chalova, Vesela I.Rapeseed meal is produced in large quantities as a by-product of vegetable oil production. To enhance the utility and profi tability of the rapeseed meal, it was treated with ethanol and used for concomitant preparation of two protein-rich ingredients, namely protein isolate (PI) and acid soluble protein (ASP). Their functional properties were evaluated in response to two boundary concentrations of NaCl (0.03 and 0.25 mol/L) in a wide pH range (2 to 10). The PI exhibited the lowest protein solubility at isolectric point (pH 4.5) which increased both at lower and higher pH. In contrast, ASP exhibited high protein solubility (>70%) which was negligibly influenced by pH. The addition of 0.03 mol/L NaCl increased its protein solubility to almost 100% at acidic pH. The water holding capacity of PI was positively influenced by the addition of 0.25 mol/L NaCl. The ASP did not exhibit any capacity to hold water but demonstrated higher ability to absorb oil compared to the PI. Both ingredients exhibited different thermal stability in response to salt addition at pH 7 and 8. PI and ASP exhibited completely different pattern of emulsion stability as influenced by pH. While the stability of PI emulsions was close to 100% and only negligibly affected by pH, the ASP emulsion stability significantly varied in response to pH variation. The concomitant production of PI and ASP resulted in products with distinctive techno-functional properties, which makes them suitable for different applications as additives in the formulation of new food products.
- Multifunctionality of rapeseed meal protein isolates prepared by sequential isoelectric precipitationPublication . Georgiev, Radoslav; Kalaydzhiev, Hristo; Ivanova, Petya; Silva, Cristina L. M.; Chalova, Vesela I.Rapeseed meal is a by-product of the oil-producing industry with a currently underesti-mated application. Two protein isolates, PI2.5–8.5 or PI10.5–2.5, were obtained from industrial rapeseed meal after treatment with an aqueous ethanol solution. The alkaline-extracted proteins were sequen-tially precipitated by two different modes, from pH 10.5 to 2.5, and vice versa, from 2.5 to 8.5, with a step of 1 pH unit. The preparation approach influenced both the functional and antioxidant properties of the isolates. The PI10.5–2.5 exhibited higher water and oil absorption capacities than PI2.5–8.5, reaching 2.68 g H2O/g sample and 2.36 g oil/g sample, respectively. The emulsion stability of the PI2.5–8.5, evaluated after heating at 80 °C, was either 100% or close to 100% for all pH values studied (from 2 to 10), except for pH 6 where it reached 93.87%. For the PI10.5–2.5, decreases in the emulsion stability were observed at pH 8 (85.71%) and pH 10 (53.15%). In the entire concentration range, the PI10.5–2.5 exhibited a higher scavenging ability on 2,2-diphenyl-1-picryl hydrazyl (DPPH) and hydroxyl radicals than PI2.5–8.5 as evaluated by DPPH and 2-deoxyribose assays, respectively. At the highest concentration studied, 1.0%, the neutralization of DPPH radicals by PI10.5–2 reached half of that exhibited by synthetic antioxidant butylhydroxytoluene (82.65%). At the same concentration, the inhibition of hydroxyl radicals by PI10.5–2 (71.25%) was close to that achieved by mannitol (75.62%), which was used as a positive control. Established antioxidant capacities add value to the protein isolates that can thus be used as both emulsifiers and antioxidants.
- Multifunctionality of rapeseed meal protein isolates prepared by sequential isoelectric precipitationPublication . Georgiev, Radoslav; Kalaydzhiev, Hristo; Ivanova, Petya; Silva, Cristina L. M.; Chalova, Vesela I.Rapeseed meal is a byproduct of the oil-producing industry with an underestimated application. Mainly, it is used as an inexpensive protein-rich ingredient in feed formulation but in limited quantity. Alternatively, it could be used as a source for the preparation of protein isolates for the food industry. Most plant protein isolates are prepared by isoelectric precipitation at a single pH point in the acidic pH area, where they exhibit the lowest solubility, limiting their functionality and subsequent application. In the current study, two protein isolates, PI2.5-8.5 or PI10.5-2.5, were obtained from industrial rapeseed meal after treatment with aqueous ethanol solution. The alkaline-extracted proteins were sequentially precipitated by two different modes, from pH 10.5 to 2.5, and vise-versa, from 2.5 to 8.5, with an increment of 1 pH unit. The protein isolates, comprised of a mixture of proteins, differed by biochemical composition, protein profile, and solubility, which was evaluated at two levels of NaCl concentrations, 0.03 and 0.25 M, and a broad pH range from 2 to 8.5. The supplementation of PI10.5-2.5 with 0.25M NaCl enhanced the protein solubility to 56.11% at pH 4.5 and 94.26% at pH 6.5. The solubility of PI2.5–8.5 was lower but still almost 10-fold higher than the negligible solubility (2.80%) of the rapeseed meal protein isolate prepared by isoelectric precipitation at pH 4.5. The preparation approach influenced both the functional and antioxidant properties of the isolates. The PI10.5-2.5 exhibited higher water and oil-absorption capacities than PI2.5-8.5 reaching 2.68 g H2O/g sample and 2.36 g oil/g sample, respectively. The emulsion stability of the PI2.5-8.5, evaluated after heating at 80 °C, was either 100 or close to 100% for all pH values studied (from 2 to 10) except for pH 6, which reached 93.87%. For the PI10.5-2.5, decreases in the emulsion stability were observed at pH 8 (85.71%) and pH 10 (53.15%). In the entire concentration range, 0.2% to 1.0%, the PI10.5-2.5 exhibited a higher scavenging ability on 2,2‑diphenyl‑1‑picryl hydrazyl (DPPH) and hydroxyl radicals than PI2.5-8.5 as evaluated by DPPH and 2-deoxyribose assays, respectively. At the highest concentration studied, 1.0%, the neutralization of DPPH radicals by PI10.5-2 reached half of that exhibited by synthetic antioxidant butylhydroxytoluene (82.65%). At the same concentration, the inhibition of hydroxyl radicals by PI10.5-2 (71.25%) was close to that achieved by mannitol (75.62%) which was used as a positive control. Being fairly soluble in water and with good emulsifying properties, the PI2.5-8.5 and PI10.5-2.5 would have a broader scope of application as multifunctional ingredients with antioxidant properties as an add.
- Stability of sunflower and rapeseed oil-in-water emulsions supplemented with ethanol-treated rapeseed meal protein isolatePublication . Kalaydzhiev, Hristo; Gandova, Vanya D.; Ivanova, Petya; Brandão, Teresa R. S.; Dessev, Tzvetelin T.; Silva, Cristina L. M.; Chalova, Vesela I.A protein isolate (ERPI) was prepared from ethanol-treated rapeseed meal and used as a stabilizing agent in sunflower and rapeseed oil-in-water emulsions. The aim of the current study was to explore the influence of protein and oil concentrations on initial stability of sunflower and rapeseed oil-in-water emulsions by evaluating Gibbs free energy (ΔG) and particle size distribution. The 7-day dynamics of emulsion stability was investigated by turbidity measurement as well. A 32 factorial design was applied to assess the significance of oil (5%, 10% and 15% w/w) and ERPI protein (0.25%, 0.5% and 1.0% w/w) addition on stability of the emulsions. The results demonstrated that the increase of oil concentrations from 5 to 15% positively influenced the initial stability of sunflower and rapeseed oil-in-water emulsions. In both oil types, ERPI protein supplementation at all levels resulted in significant differences in the stability of 5% and 10% oil emulsions but did not alter the initial stability of the emulsions prepared with either 15% sunflower or rapeseed oil. With a few exceptions, there was a good agreement between Gibbs free energy data and microstructural profiles of the emulsions. Overall, emulsions with all sunflower oil concentrations and 1.0% ERPI protein exhibited better initial and a 7-day stability dynamics compared to all rapeseed oil-based emulsions. The study demonstrated the potential of ethanol-treated rapeseed meal protein isolate to serve as an emulsifying agent in sunflower and rapeseed oil containing emulsions.
- Valorization of rapeseed meal: influence of ethanol antinutrients removal on protein extractability, amino acid composition and fractional profilePublication . Kalaydzhiev, Hristo; Ivanova, Petya; Stoyanova, Magdalena; Pavlov, Atanas; Rustad, Turid; Silva, Cristina L. M.; Chalova, Vesela I.The production of rapeseed oil leads to generation of large quantities of rapeseed meal as a by-product. To increase the applicability of the rapeseed meal in feed and food industries, the content of antinutrient compounds is often reduced by treatment with ethanol. The aim of the study was to evaluate the influence of ethanol pre-treatment of the rapeseed meal on protein extractability, amino acid composition and fractional profile. The ethanol treatment of the rapeseed meal significantly increased the protein content from 37.4 to 42.3% and reduced the lipid concentration from 1.9 to 1.1%. Approximately 4- and 14-fold reductions of the phenols and glucosinolate contents were achieved respectively. Protein yield, however, was diminished from 26.4 to 23.6%. A stronger decrease of the protein yield, from 47.8 to 26.4%, was caused by processing of the rape seeds to rapeseed meal. The process resulted in the reduction of lysine content, while further ethanol treatment of the rapeseed meal affected more amino acids, both essential (threonine, phenylalanine) and non-essential (alanine, tyrosine, arginine, histidine). Comparative fractional protein profiles of rape seeds, rapeseed meal and ethanol treated rapeseed meal exhibited differences in both composition of the fractions and the relative quantity of the proteins. Data suggested that the treatment of the rapeseed meal with ethanol impacted protein solubility, amino acid composition and protein fractional profile. This knowledge is valuable when ethanol treated rapeseed meal is used either as a protein feed additive or as a source for generation of protein-rich ingredients with specific nutritive value and functionality.