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Keywords:

  • Functional ingredient;
  • Linseed oil;
  • Microencapsulation;
  • Spray dryer

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgements
  7. References

The main objective of this study was to develop an optimized formulation of soup powder enriched with omega-3 fatty acids. For this purpose, the process conditions for optimizing the microencapsulation efficiency (ME) of linseed oil by spray drying were determined using the Taguchi methodology with an orthogonal array L4(23). The effect of the variables on the ME, such as wall material concentration (25 and 30%), linseed oil concentration (14 and 20%), and wall material type (gum arabic GA; and a mixture maltodextrin/GA), was evaluated. The oxidative stability of the microcapsules obtained were determined by the Rancimat method, and a morphological and size characterization of microcapsules was performed by scanning electronic microscopy, confocal microscopy, and laser diffraction. The optimization of the soup formulation was reached by means of RSM, using the central composite design, two control factors (salty taste and consistency), and 11 design points. The hedonic test was applied to measure the acceptability of the optimized formulation. Chemical characterization of optimized soup and its oxidative stability were also evaluated. This study resulted in a healthy soup enriched with omega-3 which was highly acceptable to consumers.

Practical applications: Linseed oil is a healthy and nutritive oil, very rich in unsaturated fatty acids such as omega-3. In addition to protecting the oil against oxidative damage, the microencapsulation of oils in a polymeric matrix (mainly polysaccharides and proteins) also offers the possibility of controlled release of the lipophilic functional ingredient and can be useful for the supplementation of foods with PUFA. The soup powder enriched with microencapsulated linseed oil as a source of omega-3 formulated in this study will contribute to the development of foods according to the functionality requirements of current consumers and markets.

Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgements
  7. References

In recent decades consumer demands in the field of functional food production have increased considerably. Functional foods play an outstanding role in promoting health, increasing longevity, and preventing the onset of chronic diseases.

Public health organizations such as the USDA in its Dietary Reference Intakes of macronutrients, and the WHO/FAO 1 in a report about diet, nutrition, and the prevention of chronic diseases, have recommended daily amounts for each type of fatty acid, saturated, monounsaturated, polyunsaturated, and long-chain PUFA. Among the PUFA, the most important families are the well-known n-3 and n-6 fatty acids. These two families are similar in that they both comprise a precursor, namely ALA for the n-3 and linoleic acid for the n-6 families and terminal products obtained by a succession of elongations and desaturations during metabolism; the two groups of fatty acids share the same long-chain converting enzymes. These precursor compounds are essential because the human body is unable to synthesize them, although, it can metabolize them to longer-chain derivatives. Furthermore, the diet must cover the body's needs for these fatty acids 2. The absence of EFA in a normal diet has been described as being responsible for the development of a wide variety of diseases, such as cardiovascular disorders, inflammatory processes, viral infections, certain types of cancer, and autoimmune disorders 3. The administration of oils rich in EFA has proved effective in the prevention and treatment of these health issues 4. Potential mechanisms for the cardioprotective effect of n-3 PUFAs include anti-arrhythmic, anti-inflammatory, hypotriglyceridemic effects, lowered blood pressure, and improved endothelial function 5.These potential health benefits have gained the interest of the food industry, the medical community and consumers, and have promoted increased numbers of products containing n-3 fatty acids 6.

Linseed oil is named as functional ingredient due to its being an excellent dietary source of the ALA (C18:3n-3). Linseed oil is highly unsaturated (90% of total fatty acids), and particularly rich in ALA (55.0%), oleic acid (21.2%), and linoleic acid (13.8%) 7.

One technological process aimed at protecting polyunsaturated oils against oxidation is microencapsulation. This process is useful for masking or preserving flavors and aromas, enhancing stability, and transferring bioactive liquid lipids into easily handled powdery solids for food fortification purposes 8. Microencapsulated oils are essentially powdery food products or ingredients comprising oil globules dispersed in a continuous matrix of saccharides and/or proteins. The process of oil microencapsulation consists basically in the preparation of an oil-in-water emulsion containing the matrix components in the aqueous phase, which is then dried 9. Microencapsulation by spray drying has been found effective for retarding or suppressing the oxidation of unsaturated fatty acids 8, 10–14.

In this study, the process conditions for optimizing the microencapsulation efficiency (ME) of linseed oil by spray drying were determined in order to obtain an edible oil as a powder ingredient, with an enhanced stability for oxidation useful to food formulation. A soup powder enriched with microencapsulated linseed oil (MLO) as a source of omega-3 was formulated to contribute to the development of foods according to the functionality requirements of current consumers and markets.

Materials and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgements
  7. References

Materials

Gum arabic (GA) and maltodextrin (MD; Sigma–Aldrich), and solvents (chloroform, petroleum ether, hexane, and methanol) were purchased from Merck. Corn, wheat flour, basil, onion, pepper powder, reduced-sodium salt, skim milk, monosodium glutamate, corn starch, sodium caseinate, and tricalcium phosphate were used for the soup formulation. Linseed oil was obtained from the company Terrasol located in Pucon, Chile, showing an initial peroxide value of 3.45 meq/Kg determined according to AOAC methods. The frozen corn was dried for 9 h at 45°C, then ground and sieved to a fine powder with a particle size between 0.0117 and 0.0165 in. (mesh Nos. 40 and 50). The yield of the sieved corn was 98%.

Linseed oil microencapsulation process

Experimental design for linseed oil microencapsulation

To optimize the linseed oil microencapsulation an experimental Taguchi design was applied using the criterion bigger is better and utilizing a matrix L4(23) with three-independent variables: concentration of wall material (Factor A, 25 and 30%, i.e., g of polysaccharides in 100 g emulsion), oil concentration (Factor B, 14 and 20%), and type of wall material (Factor C, GA and GA/MD; Table 1). The ratio of GA/MD used was 3:2 15, 16. The average for the level of each factor and analyses of variance were calculated using the software Qualitek-4. The optimized theoretical equation (OTE) was determined considering the averages of response with the greatest impact, identifying the most important factors, and levels of work. Table 1 shows the orthogonal matrix and the orthogonal array used with the design factors.

Table 1. Efficiency of linseed oil microencapsulation using the orthogonal array L4(23)
Design pointOrthogonal matrix L4(23)Microencapsulation efficiency (%)
ABCABCAverage
  1. Coded variables and non-coded variables A, wall concentration (%); B, oil concentration (%); C, wall type (GA: gum arabic; MD/GA: maltodextrin/gum arabic).

11112514GA66.0 ± 9.21
21222520MD/GA54.6 ± 6.46
32123014MD/GA90.7 ± 1.19
42213020GA69.1 ± 5.20
Microencapsulation by spray dryer

In keeping with the experimental design, the linseed oil was added to the encapsulating solution and then the mixture was emulsified using a model 400DS Benchtop homogenizer at 18 000 rpm × g for 2 min.

The spray drying process was carried out in a LabPlant SD-05 dryer (Huddersfield, England) on a laboratory scale, with a 1.5 mm nozzle diameter and a spray chamber of 500 mm × 215 mm. Emulsions were fed into the main chamber through a peristaltic pump. An air input temperature of 140°C and an outlet temperature of 95°C were used, with a drying air flow of 73 m3/h and a feed rate of 5.3 g/min following the microencapsulation process conditions set out by preliminary assays for spray drying.

Prior to its characterization, the microencapsulated oil (powder product) was stored at −20°C in sealed plastic bags under vacuum according to Imagi et al. 17.

Determination of microencapsulation efficiency

For the determination of ME, it was necessary to quantify the total oil in the microcapsule and the free oil (non-encapsulated oil fraction).

The total oil of microcapsules was determined according to the Association of Official Analytical Chemists 18. The Soxhlet extraction was accomplished in cellulose thimbles containing 1 g of dried sample. Extractions were carried out using 150 mL of petroleum ether for 5 h. The oil was concentrated using vacuum rotary evaporation of the solvent; further lipid content was dried at 105°C until constant weight.

According to Velasco et al. 9, the fraction of free oil was determined by adding 100 mL of light petroleum ether (60–80°C) to 1 g of microencapsulated powder, and stirring at RT for 15 min. After filtering and evaporating the solvent in a rotary evaporator, the extracted oil was dried until constant weight.

The ME was calculated as reported by Velasco et al. 9 as follows:

  • equation image

The microencapsulated oil amount was calculated from the difference between total oil and free oil amounts.

Characterization of microparticles
Determination of the oxidative stability of oil from microcapsules

For these analyses, the extraction of oil from the optimized product (microcapsule obtained from the design point with the highest ME) was carried out as described by Bligh and Dyer 19. Oil from 15 g of microcapsules was extracted with 15 mL of chloroform and 30 mL of methanol stirring for 2 min and 30 s. A second extraction was performed where 10 mL of chloroform were added to the mixture and homogenized for 30 s. Then the solution was diluted with water and homogenized for 30 s. The mixture was centrifuged at 8872 × g for 10 min at 4°C to separate the phases. The solvent was evaporated in a rotary evaporator at 40°C and afterward with a N2 flow. The remaining residue was weighed and the oil content was determined. The Rancimat (model 743, Metrohm) was used to determine the oxidative stability of oil extracted from microcapsules. Consistent with Kobus et al. 20, 3.5 g of oil sample previously extracted from the microcapsule was used, and the temperature was fixed at 100°C in order to obtain the induction time (IT) and oxidative stability index (OSI) at an air flow of 20 L/h.

Microcapsule morphology

The microcapsule morphology of design points 1 and 3 was observed by means of scanning electronic microscopy (SEM) and confocal microscopy. For SEM, the dried particles were coated with carbon and then pure gold by an Edwars S150 Sputter Coater, and observed in a JEOL JSM – 6380 LV scanning electronic microscope. For confocal microscopy, the linseed oil was stained with Nile red prior to microencapsulation by spray dryer. The microcapsules were examined in a confocal microscope with a 488-nm argon laser, 40 and 100× (oil immersion) objectives and the software FV-ASW 1.7. All the settings for the confocal microscope and the imaging of capsules were computer controlled.

Particle size distributions for microcapsules obtained from design points 1 and 3 were measured by laser diffraction (Malvern Mastersizer X, Malvern, UK). Samples were prepared by suspending the particles in cyclohexane. On the basis of the volume share distribution, a granulometric composition was determined using the characteristic parameters D10 and D90, which are the equivalent volume diameters at 10 and 90% cumulative volume, respectively. The absorption coefficient used was 0.1.

Fatty acid composition

Fatty acid composition of microcapsules obtained from the design point with the highest ME, was obtained by GC analyses. The fatty acid composition were determined with a Clarus 500 chromatograph (Perkin Elmer) equipped with a FID and Fused Silica Capillary Column TVSS 2380 (60 m × 0.25 mm × 0.2 µm film thickness, Supelco). The FAME were identified with a standard 37-component FAME Mix (Supelco) and using methyl nonadecanoate (Sigma) as the internal standard. Nitrogen was used as the carrier gas. An aliquot of the sample was injected under the following GC conditions: the oven temperature was programmed at 150°C for 1 min, increasing to 168°C at a rate of 1°C/min, holding for 11 min, then increasing to 230°C at 6°C/min, which was maintained for 8 min. The temperature of the injector and detector were 250°C.

Development of a corn soup powder enriched with microencapsulated linseed oil

Soup formulation

The soup was prepared containing 20% MLO as follows: wheat flour (3.0 g), skim milk 0% fat (3.0 g), dehydrated basil powder (0.1 g), dehydrated onion powder (0.3 g), dehydrated pepper powder (0.2 g), corn (14 g: 8.0 g powder of 0.00165 in. and 6.0 g of 0.0117 in.), monosodium glutamate (0.2 g), sodium caseinate (0.2 g), tricalcium phosphate (0.4 g), 50% reduced-sodium salt (2.0 g), corn starch (4.0 g), and MLO (4.5 g).

The ingredients were homogenized with 200 mL of water. The mixture was boiled for 15 min, stirring constantly. The consistency and saltiness of the preparation were evaluated by a sensory panel in order to establish the levels of incorporation and to obtain the optimal mixture.

Optimization of the soup formulation

To optimize the soup formulation, the RSM was used with a factorial central composite design 21, considering two control factors (X1: starch and X2: salt), three working levels each, and two axial points (−α and α). Coded working levels were: minimum level (−1), maximum level (+1), and central level (0), where the central point was repeated three times, obtaining 11 experimental runs. The working levels were determined through preliminary assays. The sensory quality (SQ) response was submitted to regression and variance analysis, the first to generate a fitted polynomial equation (Eq. 1), and the second to determine the degree of influence of the independent variables using the software Design 6.0.

The polynomial equation (Eq. 1) for the RSM analysis was as follows:

  • equation image((1))

where β0, β1, β2, and β12 represent the regression coefficients for the constant, linear, quadratic, and interaction terms respectively, and X1 and X2 represent the independent variables.

Sensorial analysis of soup

The SQ of the optimized soup was defined as the sum of the characteristics consistency and saltiness. In open panel sessions, the percentages of the relative influence of features were determined to obtain SQ using the following equation (Eq. 2):

  • equation image((2))

where Y is the sensorial quality, Y1 the sensorial quality of consistency, and Y2 is the sensorial quality of saltiness.

For determining the SQ of the optimized product, a panel of 8 trained judges was composed using the sensory test of the composite score 22 and a continuous descriptive analytical scale with five ranges of responses and extremes of SQ defined as very bad and very good. Eleven samples of soup (coded A–K) and two scorecards (one for evaluating the consistency and a second to evaluate the saltiness) were provided to panelists. The SQ obtained by means of this evaluation was called experimental sensorial quality (SQE) and the theoretical sensorial quality (SQT) was obtained by Software Design Expert 6.0.

Acceptability test

To determine the acceptability of the optimized product, the hedonic test was applied 22 using a sensorial scale with five sensorial points. For this purpose, 71 people ranging in age from 10 to 50+ were selected. Basic instructions were provided to consumers for a clear response.

Chemical characterization of corn soup
Proximal analyses

The chemical characterization (moisture, ash, protein, ether extract, crude fiber, and nitrogen-free extract) was performed on the optimized product and analyzed according to AOAC standard procedures 18. In order to determine the caloric intake, the percentage of proteins, carbohydrates, and ether extract of the soup, Atwater coefficients of 4.0 kcal/g for proteins, 4.0 kcal/g for carbohydrates, and 9.0 kcal for lipids were used 23.

Determination of oxidative stability of extracted oil from optimized soup

For these analyses, the extraction of oil from the optimized soup was carried out as described by Bligh and Dyer 19, with some modifications. Ten grams of homogeneous paste was extracted with 10 mL of chloroform and 20 mL of methanol, stirring for 2 min and 30 s, respectively. A second extraction was performed where 20 mL of chloroform were added to the mixture and homogenized for 30 s. Then, the solution was diluted with water and homogenized during 30 s. The mixture was centrifuged at 8872 × g for 10 min at 4°C to separate the phases. The solvent was evaporated in a rotary evaporator at 40°C and afterward with a N2 flow. The remaining residue was weighed and the oil content was determined.

The Rancimat was used to estimate the stability time at 20°C (OSI20) of optimized soup. The stability time of samples at five temperatures (80, 90, 100, 110, and 120°C) were determined and plotted to the log OSI 24. The estimation OSI20 (Eq. 3) was expressed in hours.

  • equation image((3))

Results and discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgements
  7. References

Microencapsulation efficiency of linseed oil

The ME of linseed oil for the points of the experimental design is shown in Table 1. The ME values of linseed oil were found to be between 54.6% (value for design point 2) and 90.7% (the value for design point 3). The results showed that higher ME values were obtained with a high concentration of encapsulating wall (30% wall material concentration, 14% oil concentration, and MD/GA wall type). According to Young et al. 25, ME can rise by increasing the concentration of solids in the wall solution. According to Jafari et al. 26, the most important factor determining the retention of food oils during spray drying is the dissolved solids content in the feed. A high solid content of the prepared emulsion increases retention principally by reducing the time required to form a semi-permeable membrane at the surface of the drying particle. Moreover, higher total solids lead to the increase of emulsion viscosity, preventing circulation inside the droplets, and, thereby, resulting in a rapid skin formation. With respect to the oil content, several reports have observed that higher oil loads generally result in poorer retention or lower encapsulation efficiency and higher surface oil content of the powder 15, 27–30.

Different biomolecules have been microencapsulated by spray drying using GA as a microencapsulation agent due to the efficient protection offered by this wall material 31. Researchers have tried to use a blend of GA with other wall materials and/or to replace GA completely 32. They have shown that MD can successfully replace a part of GA as the wall material, and they have determined the best ratios between them. Turchiuli et al. 16 studied the microencapsulation of vegetable oil in a solution of MD/GA (2:3) by spray drying and observed that the amount of free or non-encapsulated oil on the surface of solid microcapsules was low (<2% of total oil). Krishnan et al. 33 reported the microencapsulation of cardamom oleoresin by dryer spraying using GA, MD, and a modified starch as wall materials. The microcapsules were evaluated by organic solvent extraction of the non-volatile for 6 wk and the stability of volatile and non-volatile compounds was determined. The results showed that GA presented higher protection for the oleoresin than MD and modified starch. Krishnan et al. 34 reported the microencapsulation of cardamom oleoresin by spray drying using binary and ternary mixtures of GA, MD, and modified starch as the wall materials. The results obtained indicated that the mixture 4:1:1 of GA/MD/modified starch showed a higher protection from oxidation than the GA used alone.

The selection of the proper carrier is one of the most important factors in the microencapsulation of oils, since it can affect the viscosity of in-feed emulsion 35, 36. Although, MD shows low viscosity, is a poor emulsifier, and does not promote good retention of compounds during the spray drying process, it does protect encapsulated ingredients from oxidation 31, 37. On the other hand, GA is an excellent carrier for microencapsulation providing good retention of oils upon drying 38. The use of GA and MD mixtures for the microencapsulation of oils is a good compromise between cost and effectiveness as wall materials.

Table 2 shows results concerning the magnitude of average difference by control factors and working levels. The greater the difference, the higher the influence of the control factors on the ME, and it is possible to identify the working level that produces the best result. The concentration of encapsulating wall (Factor A) showed a higher influence on the ME of linseed oil with a difference of 19.6 units between the response of working level 2 and working level 1, followed by the oil concentration (Factor B) with a difference of 16.49 units between the two working levels. Factor C (type of wall material) did not generate an important impact on the response, with a difference of 5.09 units.

Table 2. Levels selected as greater is better in the results obtained for the microencapsulation efficiency response of linseed oil by spray drying
LevelControl factors
ABC
  1. Factor A, encapsulating wall; B, oil concentration; C, type of encapsulating wall.

N160.2678.367.51
N279.8661.8172.6
Difference ΔN(2 − 1)19.616.495.09

Figure 1 shows the degree of incline of the slope as response. The greater the difference between level 1 and level 2 for a variable, the higher the change magnitude of the response. Therefore, the concentration of wall material (variable A) presented the highest slope compared to the oil concentration (variable B). Consequently, the higher the wall material concentration and the lower the oil concentration, the higher the ME.

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Figure 1. Analysis of main effects of factors on the ME of linseed oil.

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It should be taken into account that increasing the solids concentration in the emulsion is favorable for an optimal viscosity, which leads to a suppression of the internal circulations and oscillations of droplets, thereby, improving retention 26. However, should the optimal limit of viscosity be increased, the retention will decrease due to a greater exposure during atomization, the slow formation of discrete droplets during atomization, and difficulties in droplet formation 26. As mentioned before, lower oil loads result in higher retention 15, 27–30, as shown in this study.

Regarding the type of wall material, this variable did not produce any significant change in the response since the values were close to the average, restricting the effect of control factors on the response. Furthermore, the combination (30% Factor A, 14% Factor B, and MD/GA Factor C) ensures optimal conditions for obtaining a higher ME of linseed oil. In addition, the Taguchi method made it possible to determine which factors of the process optimization most affect product quality with the minimum amount of assays.

The results of the ME were subject to an ANOVA with the aim of determining the degree of influence of the control factors on the response. The Fexp values were 19.83, 14.03, and 1.34 for Factors A, B, and C, respectively. The ANOVA demonstrated that the determination coefficients (R2) for the independent variables concentration of wall material (A), oil concentration (B), and type of wall material (C) were 51.0, 36.0, and 3.4% respectively, to which A and B contributed with 87% of the response. The analysis showed that the most significant factor (p ≤ 0.05) was the concentration of wall material with a contribution (R2) of 51% to the ME. However, the type of wall material did not significantly affect (p ≥ 0.05) the ME.

The determination coefficient for these three variables was significant (p ≤ 0.05), with R2 = 90.4%, indicating a high affinity or association of independent variables with the ME of linseed oil.

The OTE for ME was determined by means of Eq. (4), considering factors A and B together, which contributed 87% of the response.

  • equation image((4))

where T = 70.1 is the total average of responses of experimental runs, A and B are the control factors, and sub-indices 1 and 2 corresponding to working levels 1 and 2.

The OTE obtained (88.2%) represents the contribution per working level of the two control factors.

As reported by Imagi et al. 17, a lower percentage of free or non-encapsulated oil would indicate an efficient microencapsulation process, thereby, improving the quality of the microencapsulated product.

Determination of the oxidative stability of oil from microcapsules

The IT and the stability time (OSI) of the MLO by spray drying was evaluated on total oil extracted from microcapsule as an initial control of the optimized product (design point 3). The IT represents the time elapsed since the start of measurement until the beginning of the production of compounds due to oxidation 39. Therefore, a high IT value indicates that the oil has greater oxidation stability. The results of the Rancimat test for samples of MLO under optimal conditions showed the value for IT of 2.83 ± 0.62 h, and for OSI of 3.78 ± 0.01 h.

Drusch 12 reported that lipid oxidation during the spray drying depends on the drying temperature and on non-microencapsulated oil, since this fraction is mainly what deteriorates during drying. Velasco et al. 40 reported that detection of lipid oxidation in microencapsulated oils is critical because this oxidation produces a loss of nutritional value and adverse reactions in a wide range of foods on the market.

Microcapsule morphology

The samples of design points 1 and 3 obtained from spray drying were analyzed by SEM.

Figure 2a shows the microcapsules obtained by design point 3, which reached the highest ME. The particle surface is smooth and free of pores, which is essential for the stability of the microcapsule as the pores facilitate the entry of oxygen and the exit of the encapsulated material and, therefore, a decrease in the oxidation of compounds such as fatty acids. In recent studies, Fuchs et al. 41 encapsulated a vegetable oil by spray drying using MD and GA as the carriers, leading to the formation of small particles (<50 µm). The results showed that the encapsulated oil was protected against oxidation, contrary to the case of non-encapsulated oil.

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Figure 2. Morphology of micropasules by SEM obtained for (a) design point 3 and (b) design point 1. The particle surface of the microcapsules obtained by design point 3 is smooth and free of pores. The microcapsules of design point 1 produced with GA showed collapsed or shrunken particles with rough surfaces.

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Microcapsules with lower ME (design point 1) produced with GA showed morphological differences. Figure 2b shows collapsed or shrunken particles with rough surfaces.

According to Sheu and Rosenberg 42, microcapsules obtained by spray drying using polysaccharides as the wall material show remarkable surface cracks and the formation of dents or collapsed particles, which have been attributed to the effects of the composition of encapsulating material, atomization, and the drying parameters, among others. It has also been reported that microcapsules with GA mixed with MD and modified starch as wall materials showed improved morphology, obtaining a more spherical shape 34.

Figure 3 clearly shows the presence of oil globules in the microcapsules detected by the emitted fluorescence using confocal microscopy.

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Figure 3. Confocal micrographies of MLO staining with nile red. The presence of oil globules was detected in the microcapsules by the fluorescence emitted using confocal microscopy.

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Particle size distributions for microcapsules obtained from design points 1 and 3 were measured by laser diffraction. For design point 1, the 10% of volume of particles were distributed less to 5.8 µm, whereas, 90% of volume of particles were distributed less to 46.6 µm. The distribution mean was 17.6 µm. For design point 3, the 10% of volume of particles were distributed less to 7.3 µm, whereas, 90% of volume of particles were distributed less to 67.4 µm. The distribution mean was 23.1 µm showing a homogeneous distribution of microcapsules.

Fatty acid composition

To determine the fatty acid profile in this study (Table 3), the sample with the highest ME yield of linseed oil by spray drying (point design 3) was analyzed. Pure linseed oil was used as control in order to evaluate the effect of the microencapsulation treatment by spray drying on the fatty acid profile of linseed oil.

Table 3. Fatty acid profile of linseed oil and microencapsulated linseed oil
Fatty acidLinseed oilMicroencapsulated linseed oil
Fatty acid (%)
C14:0 Miristic0.100.09
C15:0 Pentadecanoic0.050.04
C16:0 Palmitic1.891.22
C16:1 Palmitoleic0.110.07
C17:0 Heptadecanoic0.040.01
C17:1 Heptadecenoic0.000.00
C18:0 Estearic3.191.57
C18:1n9c Oleic10.555.46
C18:2n6c Linoleic14.958.45
C20:0 Eicosanoic0.230.13
C18:3n3 α-Linolenic40.3534.97
C20:3n3 Eicosatrienoic0.180.09
C20:4n6 Eicosatetraenoic0.030.04
C22:2 Docosadienoic0.110.06
C22:6n3 Docosahexaneoic0.420.25

Fifteen fatty acids in extracted linseed oil were identified and quantified (Table 3). ALA was found in non-encapsulated linseed oil (40.35%) and in MLO (34.97%). Linoleic and oleic acids were also identified in non-encapsulated oil (14.95 and 10.55%, respectively), and MLO (8.45 and 5.46%, respectively).

The results in Table 3 showed that the homogenization of the emulsion and/or the microencapsulation process by spray drying affected the fatty acid composition of linseed oil. When comparing the percentage of microencapsulated oil with the untreated oil (control), a decrease in the percentage of fatty acids was observed, probably due to the physical process of encapsulation and chemical reactions that might change the nature of the original linseed oil. The amount of linolenic acid decreased slightly; however, the amounts of oleic and linoleic acid decreased by almost 50%.

Development of a soup powder enriched with microencapsulated linseed oil

Soup formulation optimization

The soup was prepared containing a fixed quantity of 14% of MLO that provides approximately 40–80% of the RDI. The European Academy of Nutritional Sciences EANS and the Health Council of the Netherlands suggest an average intake of 2 g of ALA per day, and the International Society for the Study of Fatty Acids and Lipids ISSFAL recommend 1.0 g of ALA per day.

The sensorial quality, expressed as the consistency and saltiness of soup, was evaluated by panelists for establishing the limits of the incorporation before optimization. Consistency is a parameter related to texture, and saltiness is one of the basic tastes and plays an important role for humans. Saltiness, which is caused mainly by ionic materials, is a good indicator of electrolyte balance in foods 43.

The optimization of the soup formulation was reached by the RSM, using the central composite design, two control factors (salty taste and consistence), and 11 design points. The central points of the response of control factors showed the best results with a description ranging between regular and very good according to the sensorial scale used, qualifying consistency as acceptable to suitable, and the salty taste as identifiable to suitable. Regarding the SQE, the central points presented the best and highest score, placing the response on the sensory scale between fair to good which according to the sensory scale used corresponds to still fair to good. In addition, no difference was found between the SQE versus SQT values.

In order to determine the dependence degree of the response with the independent variables, the experimental data were submitted to regression analysis. A second-order polynomial equation (Eq. 5) was obtained for the SQ (SQE) of corn and basil soup.

  • equation image((5))

The Fexp value = 6.20 indicates that the model is significant, with a 3.34% probability that this F value is due to noise. The control factors, consistency and saltiness, in their non-linear form showed a significant contribution of approximately 84% of the response variation. These control factors generate a greater impact on the SQ compared with linear forms that only contribute about 5%.

It was also demonstrated that the model has tight cause/effect dependence between control factors and QS considering parameters such as R2 (88.61%), variation coefficient (10.10%), and the signal/noise ratio 5.97 determining that the reponse is robust and consistent. In addition, considering that Fexp was significant (p < 0.05), it is possible to infer that the equation has predictive capacity.

By analyzing the response surface for the soup, the best combination obtained was corn starch 4.1 g and salt 2.3 g (Fig. 4). Then, the soup was formulated based on the best combination of corn starch and sodium-reduced salt to obtain the best SQ (Table 4).

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Figure 4. Response surface of sensorial quality for the soup.

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Table 4. Ingredients used in formulating soup for a portion of 32.3 g powdered soup re-constituted in 200 mL water
IngredientAmount (g) per size
Microencapsulated linseed oil4.50
Dehydrated corn14.00
Wheat flour3.00
Dehydrated basil powder0.08
Dehydrated onion powder0.30
Dehydrated pepper powder0.20
Skim milk 0% fat3.00
50% Reduced-sodium salt2.30
Corn starch4.10
Monosodium glutamate0.20
Sodium caseinate0.20
Tricalcium phosphate0.40
Sensorial analysis of optimized product

For the purposes of product validation, the optimized formulation was evaluated by a new panel session. The QS responses of panelists qualified the product according to the sensorial scale between 3.41 and 5.00 with an average of 4.40, indicating an acceptable, suitable, and good consistency and an accepatble and good salty taste. Therefore, the optimized product was validated by the panelist session.

Acceptability test

According to the age range, the consumers qualified the product with an average value of 4.6 from 10 to 19 years old, 4.7 from 20 to 29 years old, 4.7 from 30 to 39 years old, 4.5 from 40 to 49 years old, and 4.7 for panelists over 50. Furthermore, the product was qualified as a product that the consumers like a lot with an average value of 4.6. Regarding the product qualification, 66% of consumers like the soup a lot and 34% of them like it. According to the salty taste, 55% of consumers like the soup a lot, 37% of them like it, and 8% of consumers showed a neutral response I do not like it and I do not dislike it. With respect to the consistency, 54% of consumers like the soup a lot, 42% of them like it, and 4% of consumers showed a neutral response.

Soup characterization

A proximal analysis was performed to determine the chemical composition of the soup (Table 5a) and to elaborate a nutrition label 44 (Table 5b). These results were compared with the composition of soups currently on the market (Table 5c).

Table 5. (a) Chemical composition of the soup per 100 g of product, (b) nutritional information of soup and (c) Nutritional composition of commercial soups per 100 g of product
ParameterOptimized formulation
(a)
 Moisture (%)7.66
 Proteins (%)9.99
 Total fat (%)11.51
 Ash (%)10.94
 Crude fiber (%)1.5
 Carbohydrate (%)58.4
 Sodium (mg)1536
 Calories (kcal)377.15
Nutritional information
Portion: 32.3 g of powdered soup and 200 mL water
Servings per container: 5
 100 g1 portion
(b)
 Energy (kcal)377.15127.5
 Protein (g)9.993.38
 Fat (g)11.513.9
 Omega-3 fatty acid (mg)979316
 Carbohydrates (g)58.419.7
 Crude fiber (g)1.50.51
 Sodium (mg)1536519.17
ParameterRange
(c)
 Energy (kcal)296–388
 Protein (g)7.3–8.0
 Total fat (g)2.7–9.2
 Carbohydrate (g)58.0–69.3
 Sodium (mg)2700–5800

Compared with soups currently on the market, the soup formulated in this study presented similar energy and carbohydrate values, an increased protein content (between 24 and 36% more) and 25% greater total fat content. However, it is noted that the oil in the soup is unsaturated with a high omega-3 content. The oxidative stability and the shelf-life of oil extracted from the optimized soup were determined by Rancimat test. The average IT was 14.85 h and the stability time was 15.61 h. The determined shelf-life was 8.78 months (Table 6), which is less than the soups on the market (12 months). The MLO and soup formulated in this study contained no antioxidants so as to prevent the lipid peroxidation. Then, with the addition of antioxidants, the soup formulated in this study could present a longer shelf-life.

Table 6. Determination of shelf-life of soup using lineal regression of Log10(OSI) versus temperature (°C)
Temperature (°C)OSILog OSI
  1. OSI20 = 10Log(−0.0322 × 20 + 4.4449).

  2. OSI20 = 6322.66 h.

8074.491.87
9036.821.57
10015.611.19
1108.340.92
1203.860.59

In conclusion, by means of Taguchi methodology, the combination of variables that yielded the highest ME of oil (90.7%) was obtained from design point 3 using a wall material concentration of 30%, oil concentration of 14%, and a mixture of MD/GA as a type of wall material. The results of this study demonstrated that both the wall material concentration and the oil concentration significantly affect (p < 0.05) the efficiency of microencapsulation of linseed oil by spray drying. These variables together explained 87% of the variation of ME. Using SEM and laser diffraction, the microcapsules obtained under these conditions presented a spherical shape, with a smooth surface, and homogenous distribution. All characteristics provided stability of the product.

The incorporation of MLO in an optimized formulation of soup made it possible to provide a source of omega-3 for a high-consumption food (soup) with health benefits, obtaining a product with added value highly acceptable to consumers.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgements
  7. References

This research was supported by funding from Conicyt through Fondecyt project 1090516 and partially by the Research Office at the Universidad de La Frontera through GAP technical support.

The authors have declared no conflict of interest.

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  1. Top of page
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  3. Introduction
  4. Materials and methods
  5. Results and discussion
  6. Acknowledgements
  7. References
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