الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Microencapsulation is an excellent method to maintain quality and avoid flavor or essential oil changes caused by oxidation, heating, volatilization or chemical interactions. Furthermore, microencapsulation is a novel way to overcome hydrophobicity and make active or core components more stable. This study focuses on the microencapsulation of characteristic flavorings such as linalool, citral, limonene and isoamyl acetate, which are widely used in food, fragrance and pharmaceutical industries. The economic and environmental issues associated with the valorization of agro-industrial waste such as orange peel, led to its inclusion in the current study as a flavoring source. Spray-drying (physical approach) and coacervation (chemical method) were used to compare the effect of energy and procedures on the microencapsulated flavorings’ physicochemical properties. Traditional wall materials such as gum arabic (GA), maltodextrin (MD) and sodium caseinate (SC) were used in different proportions during spray-drying of key flavorings to evaluate the effects of varying wall materials on the properties of the flavor microcapsules before and after storage. Physical properties such as encapsulation efficiency, viscosity, emulsion stability and moisture were investigated before and after spray-drying process. A scanning electron microscope (SEM) and a chromameter were also used to examine the morphology and amount of nonenzymatic browning (NEB) in powder particles. The influence of encapsulation process on flavor retention and chemical composition was investigated by Gas chromatography-Mass Spectrometry (GC-MS).
Investigation of prepared emulsions prior to spray-drying process showed the following results:
1- A constant trend could be observed in all samples, where the increase of GA from 5 – 15% provided higher viscosity in examined emulsions A1-A3, B1-B3, C1-C3, E1-E3 and F1-F3. Whereas, the presence of MD in the maximum concentration, in the absence of GA led to the lowest viscosity, as shown in A4, B4, C4, E4 and F4 emulsions.
2- Increasing of GA concentration causes decreasing in creaming index (CI%), which means more stable emulsion against separation or creaming. Conversely, the poor emulsifying properties of MD were proven by forming a small separation layer with low emulsion stability and higher CI% as shown in A4, B4, C4, E4 and F4 samples.
In the same context, the physicochemical parameters of spray-dried flavorings were examined with the following findings:
1- The measured bulk densities were ranged from 0.27 to 0.33g/cm3, where A1(0.30g/cm3) - A3(0.32g/cm3), B1(0.29g/cm3) - B3(0.31g/cm3) and E1(0.29g/cm3) - E3(0.31g/cm3). The previous findings showed an increase with the rise of GA concentration with a DROP on A4 (0.28g/cm3), B4 (0.30g/cm3) and E4(0.29g/cm3) samples with the absence of GA. On the other hand, a different trend was observed for limonene (C) and orange peel oil (F) samples, where the presence of MD as a prominent in-wall mixture resulted in higher bulk density which could be related to the higher moisture detected in the same samples compared to others.
2- The samples: A1, A4, B1, B4, C1, C4, E1, E4, F1 and F4, which have the lowest or no GA dissolved faster than those which have higher or maximum concentration of GA like A3, B3, C3, E3 and F3. Samples with MD as a predominant in the wall mixture (A4-F4) took up more than two times faster to dissolve in water than those of the maximum GA concentration (A3-F3). Therefore, use of GA as a carrier increased the dissolution time.
3- Moisture content of the formulated spray-dried capsules at zero time was found to be 2.97-5.17%. A common trend could be observed in A1(4.09%)-A3(4.47%), B1(4.27%)-B3(4.90%) and E1(3.28%)-E3(3.97%) samples; as the concentration of GA increased in the wall material, the moisture of powders was raised and a DROP was noted in A4(4.16%), B4(3.87%) and E4(3.27%) samples; i.e., on the absence of GA. In contrast, a decrease in moisture content observed in C1(3.40%)-C3(3.04%) samples with a higher increase in C4 (3.39%) and lack of GA in F4 (3.62%) does not seem to affect the moisture, which still rises. Moisture content of 3 months stored microcapsules was ranged from 3.55 - 5.41%, while moisture in 6 months stored samples was 3.59 – 5.68%. A fixed trend was observed in 3 and 6 months stored samples of A1-A3, B1-B3 and E1-E3, where an increase in moisture content was recorded with the rise in GA concentration and a DROP was detected in A4, B4 and E4 associated with the absence of GA and presence of MD in a maximum concentration. At the same time, comparable and close results were obtained for limonene (C) and orange peel oil (F) samples. Generally, an increase in moisture content is noted in stored samples compared to zero-time ones, but the differences among samples are unique.
4- The oil retention % was maximum for A4 (94.10%), B4 (86.77%), C4 (92.22%), E3(69.99%) and F4 (86.97%) compared to other samples in corresponding classes with a significant difference. A4, B4, C4 and F4 sample are associated with predominant MD as a wall material, while E3 is characterized by a ternary wall system including the highest concentration of GA. On the other hand, isoamyl acetate (E-samples) have shown the lowest oil retention% among the investigated flavorings (64.44-69.99%). The variation in wall blend used in the encapsulation process showed a significant effect on the oil retention% among samples at zero time. Compared to zero-time, stored B, C, E and F samples for 3 and 6 months showed significant changes in oil retention% compared to zero-time with few exceptions. There were no significant differences between zero-time and 3 months storage for E2 and F2 and non-significance between 3 and 6 months for C3 and F4 samples. On the contrary, storage for 3 and 6 months did not show any significant differences for A-samples containing linalool, except for the A4 sample, which exhibited a significant difference between zero-time and 3-months of storage.
5- Encapsulation efficiency (EE%) at zero-time was positively influenced by 10% GA concentration as shown in A2 (87.68%), B2 (83.45%), C2 (85.35%), E2 (67.89%) and F2 (85.77%) samples. The previous values constitute nearly the maximum peak in EE% line-trend in all samples, where the concentration of GA in wall mixture of these samples seems to be the optimum infeed solids for flavor retention based on solubility and viscosity in solution. The non-significant differences between C2-C3 and E2-E3 lead simply because the optimum GA concentration in the limonene (C) and isoamyl acetate (E) samples could be between 10-15% in the wall blend. The remarkable increase of A4 and B4 EE% values (87.87 and 82.77%, respectively) could be associated with their chemical structure and MD as predominant carrier material, while the lowest EE% recorded for E4 (59.87%) may be attributed to the higher volatility, vapor pressure, lower molecular weight of isoamyl acetate and the quality of capsules, which discussed later. A-samples (linalool) did not show significant changes in EE% during 3-months storage for A1, A2, A3 and A4. Non-significant differences were detected during storage between 3 and 6-months in A1, A2, A3 and A4. For the remaining samples; B, C, E and F significant differences were noted for EE% during storage time, after 3 or 6-months. In general, the values of EE% for investigated spray-dried flavorings, even after 6 months of storage, are promising compared to values described in the references reported in the current section where encapsulation process of the current study effectively delayed the release of flavorings under the same storage conditions.
6- All spray-dried flavorings underwent significant changes in color, especially in b* during storage. However, such changes in color parameters during storage are not dramatic and are believed not effectively to change final products’ sensory properties or quality. For example, by focusing on ∆b*, changes in spray-dried samples during storage were 0 (F4) to 1.74 (C1) and from -1.24 (C3) to 0.57 (E2) for the 6 months stored samples. The changes in b* found to be negative in many samples, i.e., absence of browning or oxidation. In contrast, a* values changed during 3 or 6 months of storage remain in the negative value.
7- A spherical shape with a smoother surface for particles could be demonstrated in A1 sample, with some deflated capsules and adherence of small particles to the surface of larger ones. The microparticles obtained with more concentration of GA (A2 and A3 samples) showed similar structure to A1 beside other larger agglomerates of irregular shapes. The predominate of MD in-wall mixture (A4-sample) led to more uniform, spherical and smooth particles with a bit of adherence for small ones in some capsules; meanwhile, some tiny bubbles or craters on particles’ skin along with small agglomeration were observed at wider extensions. Generally, no porous cracks were detected in the SEM microstructure of the samples. Both limonene (C) and orange oil (F) series samples resembled linalool (A-series) samples in their behavior, where increasing the GA concentration affects the morphology of particles with more agglomeration, while the predominant MD leads to more spherical and smooth particles. However, small bulbs with semispherical particles were shown in F1 samples on a wide scale. On the contrary, wrinkles could be observed on the surfaces of B1 sample, which disappeared on B2, B3 and B4 samples. It seems that MD in B4 sample did not enhance the microstructure, where the majority of the formed particles exhibited irregular, semispherical structure. It is noteworthy that, the propagation of concavities in E-samples, despite the spherical, bubbles and smooth surfaces observed. In general, neither cracks nor porous were found in the microstructure of samples. The previous note is essential for the shelf life of the spray-dried flavorings because porous surfaces tend to lose volatiles quickly during storage and allow the permeability of oxygen into microcapsule, causing undesirable reactions or deterioration. The same phenomena detected in zero-time microstructures are found in stored samples with some modifications. Semispherical particles with adherence for the little ones, wrinkles on the surfaces and some agglomerations were observed in the microstructure of A1. Meanwhile, A2 and A3 exhibited spherical particles with adherence and major structures of agglomerations. The absence of GA in-wall combination accompanies the unique deflated particles with surface concavities observed in the A4 microstructure. Samples B1-B3 are similar to A2-A4 samples, while B4 showed semispherical structures with wrinkles on the surface like the A1 sample. C1-C3 and F1-F3 microstructures showed spherical particles as a major fraction, semispherical particles as a minor fraction, adherence for small particles to a bigger one and concavities on the surfaces. Both C4 and F4 have the major spherical identical particles, with respect to the MD as a predominant in the wall blind. Rare agglomeration is noted in both series of samples. Deflated particles and smooth with concavities on surfaces characterized E1-E3 samples, while E4 showed mostly a single particle with a few agglomerations.
8- Overall, compared to control sample, the retention is based on the type of carriers and the nature of core or flavoring. For example, A (linalool) and B (citral) samples showed the highest retention with the predominant MD (A4 and B4) in the wall combination due to H-bonding formation. In contrast, limonene and isoamyl acetate showed the highest retention during use GA in a maximum concentration in the wall combinations (C3 and E3). The molecular weight and high vapor pressure of isoamyl acetate (E samples) compared to the other flavorings used in this study are the main reasons for the loss in aroma compound in the presence of MD. On the other hand, orange peel oil (F samples) showed both trends, where F3 and F4 represent the highest retention due to both polar and non-polar constituents in oil. It is noteworthy spray-drying and storage processes did not lead to any changes in the chemical structure of single flavorings, but in orange peel oil samples. A total number of 3 compounds were identified in orange peel oil, where limonene (97.43%), α-myrcene (2.13%) and α-pinene (0.44%) were the dominant compounds in oil. The GC–MS analysis of the spray-dried orange peel oil showed a remarkable difference compared to the control; however, the same trend was observed in all samples, where limonene was still the predominant compound with 71.01-95.06% for F1-F4. Only 13, 12, 10 and 4 compounds were identified in spray-dried samples (F1-F4). Some of the oxygenated terpenes like limonene oxide, 4-terpineol, trans-carveol, carvone and linalyl acetate were presented in F1 sample with a higher concentration than other samples of spray-dried orange peel oil. The lower the limonene and the non-oxygenated content, the higher the oxygenated compounds generated during spray drying process. Increasing the GA concentration from F1 to F3 seems to avoid limonene from interaction or converted to others by the environmental conditions during spray-drying. At the same time, the fast-drying of F4 due to the predominance of MD in the wall combinations did not allow any interaction with limonene during drying process. Again, the stability and retention of spray-dried flavors during storage was assessed by using GC-MS. The retention reflected the overall loss, while changes in structure due to reactivity with the environment during storage represent an important factor that reveals the encapsulation efficiency. Generally, no changes could be observed in the chemical form of single spray-dried flavorings (A, B, C and E) stored for 6 months, except for F samples. However, the loss is small and not remarkable in many cases, reflecting the successful encapsulation process. For example, the loss in A4, B4, C4 and E4, where the MD is predominant in the wall combinations, could be expressed as the smallest due to spherical, homogenous, non-porous and non-cracked particles formed by MD and SC as a wall mix. Eighteen compounds were detected in spray-dried orange peel oil (F samples). At the same time, only 14 components were identified where limonene is the predominant (67.95-88.59%), followed by the oxygenated constituents like limonene oxide (2.12-4.34%), 4-terpineol (1.01-5.03%), carvone (1.07-8.28%) and linalyl acetate (2.12-4.63%). In contrast to MD and GA concentrations seem to be very effective in the retention of limonene and non-oxygenated part.
On the other hand, microencapsulation of flavorings by simple coacervation technique (chemical method) showed the following results:
1- The total percentage of encapsulated flavoring’s retention ranged from 99.07 to 99.73%. The high percentage of the retention flavorings indicates a near absence of loss among the volatiles encapsulated by simple coacervation technique during study.
2- No significant differences were recorded among the encapsulated flavorings concerning the encapsulation efficiency. The efficiency percentages were found between 96.40 to 97.07%, which revealed excellent encapsulation of the core content despite the difference in physicochemical properties. The non-significant differences are related to the total retention content, where the highest efficiency percent was for isoamyl acetate (97.07%), which showed the highest retention percentage and the lowest was for limonene (96.40%).
3- The microcapsules had a spherical to elongated ellipsoids morphology, with few or no dents on the surface. Neither holes nor cracks were found on the surface of microcapsules. Consequently, the complete and sealed capsules shown in the SEM micrographs assured the effective protection of the flavoring or the core material. Irregular morphology was observed but with a mononuclear structure, entirely sealed without agglomeration. The particle size was not homogeneous for different microcapsules according to the SEM. The average particle size was lower than 1000µm for linalool, limonene, citral and isoamyl acetate coacervated flavorings, except for encapsulated orange oil, which exceeded 1000 µm.
4- Since the coacervation technique is low or no energy method compared to the spray drying protocol that discussed before, it is expected to have more retention in coacervated flavorings than spray-dried ones. The percentage of flavorings retained after simple coacervation ranges between 97-99.3%, which revealed an efficient encapsulation technique. Limonene, α-myrcene and α-pinene were the major components in microencapsulated orange peel oil. Other components, namely linalool (0.79%) and linalyl acetate (0.25%), presented in encapsulated sample, may be due to the processing steps, especially the magnetic stirring (500 rpm/1 hr). Generally, the previous results showed excellent retention capability of oil encapsulated using a simple coacervation technique.
5- Alginate spectrum (control) offers broadband at 3200-3400 cm–1 related to OH stretching with strong hydrogen bonding. The peak at 2924 cm–1 is ascribed to the overlapping symmetrical and asymmetrical C-H stretching vibration of aliphatic chains (-CH2-, -CH3). The asymmetric and symmetric vibrational modes of carboxylate ions (O-C-O) were recorded at 1633 and 1414 cm–1, respectively. The vibrational mode at 1093 cm–1 was attributable to the pyranose ring’s C–O stretching vibration. Due to its polysaccharide structure, sodium alginate’s (C-O-C) stretching vibration was manifested at 1035 cm–1. C-H stretching was also identified for both uronic acid (982 cm-1) and mannuronic acid (878 cm-1). The spectra of microencapsulated flavorings were related strongly to the control but, of course, slight shifts suggesting fundamental structure changes due to simple coacervation. For example, narrower and more intense bands in the 3200-3400 cm-1 region reflect new hydrogen bonds between alginate and flavorings for A, B, E and F but not the C-sample due to the nature of flavoring. The O-C-O signal is more intense in the alginate (control) than in the microencapsulated samples, except for the C-sample, which revealed weaker ionic bonds between flavorings and carboxyl groups of alginate to the absence of efficient functional groups in aroma compounds.
6- The flavor attributes for spray-dried flavorings were evaluated, where A4, B4, C4, E4 and F4 recorded the highest scores with significant differences for flavor and color attributes, except for C4 in color. Therefore, they were chosen to fortify sponge cake and jelly as food product examples. On the other hand, conservative samples prepared using the same flavorings were applied in sponge cake and jelly. Higher color scores were shown for the sponge cake samples fortified with spray-dried limonene or orange peel oil (C or F) than the control but without significant differences. Samples fortified with spray-dried and coacervated limonene and isoamyl acetate (C, c, E and e) were the most preferred in odor, taste and softness, with respect to encapsulation orange peel oil which also showed a higher softness score. As an overall preference, sponge cakes fortified with spray-dried isoamyl acetate and limonene (E and C) were significantly the highest, followed by fortified samples with the same coacervated flavorings (e and c). Fortification of jelly with encapsulated flavorings does not affect the texture, which showed no significant differences. Encapsulated isoamyl acetate, linalool and orange peel oil samples were the highest in odor, taste and overall preference among examined jelly samples.
from the collected results, it could be concluded that: Microencapsulation of key flavorings, namely; linalool, citral, limonene, isoamyl acetate and the agro-industrial waste like orange peel, using two main encapsulation techniques: i.e., spray-drying (physical method) and coacervation (chemical method) were effective methods to keep the quality and avoid changes in flavors or essential oils due to environmental conditions. The increase of GA provided higher viscosity and lower CI% in prepared emulsions before spray-drying. Meanwhile, the rise of GA increases the bulk density, wettability and moisture content of spray-dried flavorings. The same trend was observed in stored samples for 3 and 6 months with differences compared to zero-time samples. The predominance of MD showed the highest oil retention %, in contrast to encapsulation efficiency, which expressed the maximum with the GA. No significant differences were detected in stored samples compared to zero-time. All spray-dried flavorings underwent significant changes in color, especially in b*, during storage. The predominate MD in-wall mixture led to more uniform, spherical and smooth particles with a bit of adherence for small ones in some capsules. The GC-MS analysis of linalool and citral spray-dried microcapsules showed the highest retention with the predominant MD in the wall combination, in contrast to limonene and isoamyl acetate, which presented the highest retention during use of GA in a maximum concentration in the wall combinations. Generally, no changes could be observed in the chemical form of single spray-dried flavorings stored for 6 months, except for orange peel oil powder. The nutritional data and biochemical parameters showed non-significant results without adverse effects in all groups fortified with spray-dried flavorings compared to control. The simple coacervation technique showed superior retention for the flavorings proved by measuring encapsulation efficiency and GC-MS, with no significant (p ≥ 0.05) differences concerning the encapsulation efficiency. Compared to control samples, sponge cakes fortified with encapsulated isoamyl acetate and limonene prepared by both techniques (spray drying and simple coacervation) were significantly the highest in overall preference, while encapsulated isoamyl acetate, linalool and orange peel oil samples were the highest in odor, taste and overall preference among the examined jelly samples. According to the present study’s findings, applying of such encapsulated flavorings in food products proved as safe.
Recommendations
1- Microencapsulation of key flavorings, namely; linalool, citral, limonene, isoamyl acetate and the agro-industrial waste like orange peel, by using two main methods of encapsulation techniques: spray-drying (physical method) and coacervation (chemical method) were an effective method to keep the quality and avoid changes in flavors or essential oils due to environmental conditions.
2- The simple coacervation technique showed superior retention for the flavorings with no significant differences concerning the encapsulation efficiency.
3- Compared to control samples, sponge cakes fortified with encapsulated isoamyl acetate and limonene prepared in both techniques (spray drying and simple coacervation) were significantly the highest an overall preference.
4- Encapsulated isoamyl acetate, linalool and orange peel oil samples were the highest in odor, taste and overall preference among the examined jelly.
5- According to the present study’s findings, applying such encapsulated flavorings in food products proved safe.
6- Current study recommending to use spray drying method for encapsulated flavor compounds and obtained in powdered form, which facilitates the marketing, using and application in the field of different food industries.