Preparation and Properties of Encapsulated Fat Powders Containing Speciality Fat and ω/Pufa-Rich Oils

Abstract

Fat powders with high fat content using three types of fats/oils, namely semi-solid fats like vanaspati, trans free speciality fat, and liquid oils like safflower or flax seed, were prepared by spray drying. The effect of type and quantity of wall materials and additives on total fat and quality of powders were studied and found that casein was effective as wall material to encapsulate maximum fat of up to 75%. Sugar and tricalcium phosphate were found to improve flowability of the powders. The quantity of fat encapsulated depends on type of fat or oil and found that semi-solid fats could be encapsulated at a higher percentage compared to liquid oils. The moisture of powders was 1–2 g/100 g, bulk density 0.3–0.4 g/cc, surface fat 15–19% and angle of repose 50–55°. The powders with bakery fat or speciality fat were lighter (creamish) in appearance compared to those with safflower or flax seed oils, which were light yellow due to the colour of the parent oil. Scanning electron microscopy of fat powders revealed that those prepared with bakery fat or speciality fat and with casein and sugar showed distinct spheres indicating effective encapsulation. Scanning electron microscopy of powders with skim milk powder and also those without added sugar showed aggregation of particles. The powders with PUFA-rich oils had a high proportion of ω-3 and PUFA. Equilibrium relative humidity and storage stability of powders were determined.

Keywords:

• Fat powder
• PUFA-rich powders
• Encapsulation
• Casein

INTRODUCTION

Microencapsulation is a sort of packaging technology where in small droplets of liquid or solid particles were packed into continuous individual shells. The shells (walls) were designed to protect the inside material from factors which might cause deterioration due to oxygen, water and/or light. In another approach, the wall was designed to enable controlled release of encapsulated material under desired conditions.[1–3 Successful microencapsulation could be achieved by the use of right choice of wall material and encapsulation technique for a specific core material and also on understanding of how the core material is organized and protected within the microcapsules.[4] Use of microencapsulation to incorporate sensitive ingredients, such as omega-3 fatty acids into foods; conjugated linoleic acid (CLA); improving the oxidative stability of fish oils; and micro encapsulation techniques were reported.[5,6] Preparation of butter powder with 80% fat using casein & /or skim milk powder was reported.[7]

Sodium caseinate was reported to be the most effective emulsion stabilizer to get small fat globules in the emulsion.[8] Stickiness and lumpiness of powder were found to be directly related to emulsion stability; the more stable the emulsion the more free flowing was the powder.[9] Effects of emulsifiers, wall, carbohydrates and processing conditions on physical properties of encapsulated milk fat were studied and found that surface fat decreased with increasing DE (dextrose equivalent) of carbohydrates and unaffected by outlet temperature of drying.[10] For several decades, microencapsulation by spray drying has been applied in the food industry and is still the preferred technology as it was rather inexpensive and simple.[11,12] It has been reported that the use of modified cellulose as a coating material for the preparation of spray-dried fish oil improved the stability of the microcapsules and the concentration of fish oil in the powder.[13]

Encapsulating different oils and fats including PUFA, ω-3 rich, using casein, sugars and other additives have been patented.[14–17 Singh and Mathur[18] described encapsulation of milk fat and vegetable oils in a matrix comprising whey proteins and mixtures of caseins and whey proteins. Due to the water insoluble nature of caseins, these proteins were used in various mixtures with water soluble whey proteins in order to obtain a water dispersible dry product. It has been concluded that encapsulation of fat globules with whey protein rather than casein improved the physical performance of the product. The purpose of the present paper was to prepare powders with high fat or oil content containing both solid fats like vanaspati (bakery shortening) or low trans speciality fat and liquid PUFA/ω-3 fatty acid rich oils like safflower, flaxseed and study their properties and storage behaviour. These fat rich powders find applications in various food formulations as well as in nutritional supplements and pharmaceutical applications, in addition to extending the stability.

MATERIALS AND METHODS

Materials

Vanaspati (Marvo brand), refined safflower oil, sugar, skim milk powder were procured from local market. Flax seed oil was extracted from flax seeds purchased from local market, and the oil was refined and used in the study. Casein from Himedia Lab P Ltd, Mumbai, India, GMS (glyceryl monostearate) from Enzyme India P Ltd, Chennai, TCP (tricalcium phosphate) from SD fine chemicals Ltd., Mumbai, India were procured. Lecithin was procured from Shakti Soya, Coimbatore, India. Whey powder was procured from Mahaan Proteins Ltd, New Delhi, India. Palm oil was procured from Palmtech India Ltd., Mysore, India.

Preparation of Low Trans Speciality Fat

Refined palm oil was heated to about 60°C to destroy all crystal nuclei, cooled gradually to 20°C and kept at this temperature for 3–4 h. The partially crystallized mass was filtered to separate stearin (55% yield), which was used in the study.

Process for Preparation of Fat Powders

The process flow sheet is shown in Fig. 1. Aqueous phase was prepared by dispersing casein in water, adjusting pH to 7.0 with 2.5 N NaOH, sugar and TCP were added and dissolved by heating to about 50°C and the total soluble solids were adjusted to 18–22°B (Hand refractometer, Erma, Japan). The total soluble solids (TSS) content was also found to influence the process and quality of the end product and the desirable TSS were found to be 18–22°B. Less than 18% TSS took longer time for completion of spray drying but above 25% there was a problem of clogging the orifice. Fat phase was prepared by melting the fat by heating to about 50°C, adding emulsifiers and dissolving. Aqueous and fat phases were mixed and homogenized using a lab homogenizer (Ultraturax TK 25, IKA Labortechnik, Staufen, Germany) for 15–20 min. Immediately it was taken for spray drying, operating at inlet temperature of 140°C and outlet temperature of 80°C. Fats used include: commercial bakery fat, specialilty fat, and PUFA-rich oils like safflower and flax seed oils. Skim milk powder (SKMP) and whey powder also were used as wall material for comparison. The standardized formulations of powders are shown in Table 1.

Table 1 Standardized formulation of fat powder

Ingredient	Wt (g)
Casein	100
Sugar	50–100
Tricalcium phosphate	10
Fat	500–600
Emulsifiers (GMS + Lecithin)	10
Water	750–800 ml

Figure 1 Process flow sheet for preparation of fat rich powders.

PUFA-Rich Oil Powders

To improve the nutritional quality, fat powders using ω-3 and PUFA rich oils were also prepared, as they will have various health benefits, such as for healthy heart, brain development, improving memory, etc. In powdery form, they are advantageous for usage in health food formulations and also to improve their stability. Safflower oil and flaxseed oils were chosen for the purpose.

Analysis of Surface (Free) and Total Fat

The encapsulation efficiency was determined from the amount of surface fat (easily extractable fat) measured after hexane extraction. Hexane or petroleum ether (60–80°C) (15 ml) was added to 2–3 g of powder, mixed for 2 min and centrifuged. The supernatant was filtered and filtrate was dried and percent of extractable (surface) fat was expressed as percent by wt of powder.[10] The total fat/oil in powder was determined by Soxhlet extraction using petroleum ether (60–80°C) as solvent as per AOCS (2000) procedure.[19]

Measurement of Moisture, Colour, and Bulk Density

Moisture content of fat powders was determined by keeping the sample in hot air oven at 110°C for 3 h. The colour of the powders was measured using CIELAB colour meter (Labscan XE, Hunter Assoc. Lab Inc. Reston, VA, USA). Colour was represented by L*, a*, b*, where L* indicates lightness or brightness, values range from black (0) to white (100), a* values range from green (-) to red (+) and b* values range from blue (-) to yellow (+). Bulk density of fat powders was determined by weighing 20 g of powder and then filling it into a 50 ml measuring cylinder. Bulk density was calculated by dividing mass (wt) of the powder by the volume occupied in the cylinder.[20]

Angle of Repose

The static angle of repose is defined as the angle at which a material will rest on a stationary heap; it is the angle formed by the heap slope and the horizontal when the powder is dropped on a platform when a given wt of powder flows through a funnel of known dimensions to form a pile. The angle was measured by allowing the known amount of powder (80 g) to fall from a funnel having a wide bore stem onto a plat form and measuring the angle of heap. The angle of repose was calculated using the formula,[21] Tan α = h/(r - 1/2a), where: α = angle of repose, h = height of stem above base, r = radius of the base of the heap, a = diameter of the funnel stem. It has been reported that powders with angles of repose <35° should be considered as free flowing, those with angles 35–45° as some cohesiveness, while powders with 45–55° as cohesive and 55° and above having little or no flow.[21,22] Also, it has been mentioned that depending on the conditions and procedures, different angles could be obtained and hence literature values can not be always comparable.[22]

ERH of Powders

All three types of powders, viz., with bakery fat, safflower, and flax seed oils were subjected to ERH. Powders (20 g) were accurately weighed in glass petri dishes and kept in dessicators containing saturated salt solutions of different relative humidities (RHs) ranging from 11 to 92%. The samples were weighed periodically till the product showed constant weight for three consecutive readings or mold growth observed. The equilibrium moisture content (EMC) of each sample at different RHs were calculated by adding or subtracting the weights due to gain or loss of moisture compared to the initial moisture content (IMC). Sorption isotherms were drawn by plotting EMC vs. RHs.

Storage Stability of Fat Powders

The storage stability of three types of fat powders was determined by keeping at ambient (27°C) and at accelerated, 38°C conditions. The samples were periodically drawn and oil/fat was extracted from powders with chloroform and peroxide value was determined after solvent removal, according to the AOCS (2000) procedure.[19]

Fatty Acid Composition of Fat Powders

The fatty acid compositions of powders prepared with different types of fats/oils were determined by gas chromatograph (GC). The fat/oil from powders was extracted with chloroform and converted to fatty acid methyl esters (FAME) using KOH/Methanol (AOCS, 2000)[19] and were analysed by GC (Fisons, 8000 series, CE Instruments, Rodano, Italy) with FID and using Supelco, SP-2340 (Supelco, Bellefonte, PA, USA) (0.25 mm × 30 m) capillary column, operating at column temperature 50 to 200°C at 5°C/min and maintaining at 200°C for 10 min; injection temperature 230°C, detector temperature 240°C, nitrogen flow, 0.9 mL/min. The fatty acids were identified by using authentic standards and presented as relative percentage.

Differential Scanning Calorimetry (DSC)

A Mettler (Zurich, Switzerland) differential scanning calorimeter (DSC-30) was used to determine thermal properties of the samples. The heat flow of the instrument was calibrated using indium. The PT-100 sensor was calibrated using indium, zinc, and lead. About 15 mg of fat powder was accurately weighed into a standard aluminum crucible and the cover crimped in place. An empty aluminum crucible with a pierced lid was used as a reference. Thermograms were recorded by heating at the rate of 10.0°C/min from −20 to 300°C. The peak temperatures and heat of fusion (ΔH) were recorded directly using a TC-10A data processor and STARe program (Mettler Tolecto, Zurich, Switzerland).

Particle Morphology

Surface morphology of fat powders was evaluated by scanning electron microscopy (SEM). Samples were mounted on SEM stubs secured by double sided adhesive tape and samples were covered by gold using a sputter and examined with SEM (Leo 435 VP; Leo Electronics System, Cambridge, UK), operating at 15 kV and magnification of 500×.

RESULTS AND DISCUSSION

The effect of ingredients, wall materials (type and proportion), additives like TCP, and sugar on total fat encapsulation and quality of powders were studied to standardize the formulation to prepare powder with maximum fat content.

Effect of Wall Material

Casein and whey powders were found to be desirable encapsulating agents and spray drying was the preferred process. Skim milk powder (SKMP) was found to be less effective as an encapsulating agent compared to casein to accommodate high fat content in powder. It can be seen from Table 2 that SKMP was used at high proportions (above 25%) to get fat powder with a maximum of 70% fat, whereas only 13–18% casein was sufficient to obtain powder with more than 75% fat. It can be seen from Table 2 that even at low levels, casein can accommodate a large quantity of fat (at 6.5% level, 78% total fat). Hence, further studies were conducted using only casein as an encapsulating agent. The proportion of casein had marginal influence on total fat encapsulated. It was reported that encapsulating efficiency increased with increasing solids concentration of wall solution and was adversely affected by milk fat load and improved by addition of lactose along with whey protein.[3]

Table 2 Formulations (g/100 g) and properties of fat powders obtained by spray drying

Encapsulating agent		Sugar	Total fat* g/100 g	Free fat g/100 g	Angle of repose (°)
Casein
1.	17.9	—	80.6	23	50
2.	19.55	—	78.2	18	53
3.	17.6	—	79.0	28	50
4.	14.6	—	82.0	26	50
5.	13.9	—	83.0	27	49
6.	16.2	8.0	73.0	24	49
7.	13.0	6.5	78.0	24	54
8.	13.4	8.3	75.4	24	50
9.	18.3	6.1	73.0	24	53
10.	6.5	13.0	78.0	20	46
11.	12.2	12.2	70.0 ^a	15	48
12.	12.2	12.2	65.0 ^b	19	55
SKMP
13.	36.7	—	61.0	17	54
14.	27.9	—	70.0	22	—
15.	26.0	6.5	65.0	15	51
*Bakery fat; ^aSafflower oil; ^bFlax seed oil; SKMP = Skim milk powder; Emulsifiers (GMS + lecithin) = 5 g + 5 g; TCP = 10 g per batch as shown in Table 2. Moisture of fat powders = 1–2%.

Effect of Sugar

It was reported that the addition of simple carbohydrates like sugar improved the stability of the emulsions and, thus, powder with good flowability could be obtained.[23] Hence, sucrose at 50 and 100 g/batch (6.5–13%) levels was used in the formulations. Powders with no added sugar had slightly higher surface fat and increasing sugar content had beneficial effect on quality of encapsulated powder. Increasing sugar and decreasing casein had the same effect on total fat (Table 2). Also, casein and sugar were found to have a complementary effect on total fat encapsulated and quality. Low casein and high sugar contents have a similar effect on total fat content and quality of fat powders. Maltodextrin (MD) has the same effect as sugar.

Properties of Fat Powders

The powders had bulk density of 0.3–0.4 g/cc, free or surface fat 15–19%, and total fat 65–80%. Encapsulating agents did not show much influence on bulk density and powders with liquid oils also showed similar bulk density compared to that of solid fats (0.3–0.36 g/cc). Surface fat did not significantly alter though total fat content varied (Table 2), unlike those reported in the literature that surface fat in milk powder increased with increasing the fat content of the emulsion.[24] The moisture content of the fat powders ranged between 1.8–3.0%. Pasty powders had moisture above 3.2%. The free or surface fat, which indicates the efficiency of encapsulation, was about 20–22% (Table 2) and that with casein was found to have the least free fat and the total fat content was about 75%. The angle of repose (indicator of flowability) for different powders ranged 50–55°, showing some cohesiveness. The addition of 2% starch marginally improved flowability of these powders as shown by lower angle of repose 45° as against 50–55° with no starch. It has been reported that milk powders with 26 and 73% fat were found to be cohesive and that with low fat showed easy flow properties.[25] It was reported that lowest free fat content (<10%) was found in powder with 40% fat, encapsulated in sucrose with angles of repose 37–46° and bulk density was reported to be dependent on the encapsulant and declined with increasing fat content.[9,23] It has been reported that increasing the fat content of the emulsion from 20.2 to 50.2% increased surface fat content in the milk fat powder microencapsulated using whey proteins.[24]

The total fat that could be incorporated was 65–70% in case of oils like safflower or flax seed as compared to about 80% using plastic fat like bakery fat. The flowability of powders with oils was also less than that with bakery fat. The fat powder was off-white or creamish in appearance, especially that with commercial bakery fat, with lightness (L*) 83–87 (standard 90.41) and whiteness index 77–86. The wall materials had no significant influence on appearance of powders (Table 3). The powders prepared with liquid oils like safflower or flax seed oil showed slightly different colour values compared to those of commercial bakery fat (Table 4), which were mainly due to differences in appearance of parent fats/oils. The powder with flax seed oil had a slight yellowish tint due to the dark yellow colour of the parent oil, which has been reflected in instrumental colour values (Table 3). Accordingly, the whiteness index of 85.8 and 76.9% were observed for powders with safflower and flaxseed oils, respectively (Table 3).

Table 3 Colour measurement of fat powders

	L*	a*	b*	ΔE*	Whiteness index
Standard	90.41	−0.96	1.07
Safflower oil powder ^a	87.15	−0.36	5.59	5.61	85.86
Flax seed oil powder ^a	83.00	−3.13	15.31	16.20	76.90
Bakery fat ^a	89.00	−1.5	11.1	11.0
Casein + SKMP ^b	85	−1.8	12.9	14.4
Casein + MD ^b	90	−1.5	12.2	11.8
Whey powder ^b	88	−1.6	13.0	13.2
SKMP = Skim milk powder; MD = Maltodextrin; ^aCasein used; ^bBakery fat used.

Table 4 Fatty acid composition of fat powders

	16:0	18:0	18:1c	18:1t	18:2	18:3
Bakery fat	40	4.7	32.4	14.3	3.9	—
Speciality fat	35.4	4.0	40.0	—	30.0	—
Flax seed oil	7.3	8.0	25.5	—	12.2	47.0
Safflower oil	7.4	3.3	17.0	—	72.0	—
c = cis; t = trans.

Fatty Acid Composition

Commercial bakery fat consisted of major palmitic and oleic acids, including trans isomer. The low trans specialty fat was rich in PUFA with no trans fatty acids. The powders prepared with safflower and flax seed oils are rich in ω-3 and PUFA (Table 4) and, hence, could be used in nutritional supplements in addition to application in speciality foods.

Thermal Properties of Fat Powders

Thermal properties of different fat powders determined by DSC showed four endotherms for all fat powders for moisture, phase transition of fat, fusion of encapsulating agent, and sugar (Fig. 2). The powders without added sugar did not show a peak corresponding to sugar.

Figure 2 DSC endotherms of fat powders (1 = Skim milk powder and bakery fat and added sugar; 2 = Casein; 3 = Casein, bakery fat with no sugar; 4 = Casein, bakery fat and sugar; 5 = Casein, safflower oil and sugar).

Storage Studies of Fat Powders

ERH (equilibrium relative humidity) studies, which determine the type of packaging material required for better storage stability revealed that all powders absorbed moisture progressively at all RHs and it was very low for all fat powders (Fig. 3) and, hence, require protective packaging material to extend the shelf life. It was reported that moisture sorption isotherms of powders with sucrose showed characteristic breaks caused by sugar crystallization followed by moisture desorption, whereas powders with modified starch or all purpose flour continuously absorbed moisture with increasing RH.[26] Similarly, critical aw for dehydrated acerola juice powder encapsulated with maltodextrin, gum or mixtures of these two, was found to be 0.3–0.43 depending on storage temperature and stickiness was observed at temperature close to glass transition temperature.[27] The moisture absorption by powders with lower fat content was higher than those with higher fat (Fig. 3), which may be due to a higher proportion of non-fat ingredients in powders with lower fat.

Figure 3 ERH of fat powders prepared with different fat/oils at various proportions.

Storage studies revealed that the oxidative deterioration of fat powder with flax seed oil was higher than that of safflower oil, which in turn was higher than that of bakery fat. This was due to differences in fatty acid composition of the three parent oils/fats. The results showed that PV increased initially up to 3 weeks both at ambient and at 38°C, and thereafter decreased in both flax seed and safflower oils containing powders (Fig. 4). This indicated breakdown of peroxides to secondary oxidation products. Fat powder with bakery fat was more stable against oxidative rancidity compared to other powders containing oils. In native oils, a gradual increase in PV was observed, while in powders, PV increased initially up to 2–3 weeks and thereafter it was decreased. Though oils/fats were encapsulated, the oxidative deterioration may be due to the presence of free surface fat. It has been reported that total oxidation of powders was strongly influenced by the extent of oxidation in the encapsulated fraction although the surface fat fraction was oxidized more rapidly.[28]

Figure 4 Storage stability of different fat powders at ambient (25°C) and accelerated (38°C) temperatures.

Microstructure of Fat Powders by Scanning Electron Microscopy (SEM)

The microstructure of fat powders prepared using different types of fats/oils and additives were examined with SEM to find out the reasons for different properties of fat powders prepared using different ingredients. SEM of fat powders prepared with casein along with sugar using bakery fat showed clear distinct spheres (Fig. 5a), indicating perfect encapsulation as there were no dents or cracks.[4] Fat powders prepared with SKMP showed aggregation and fused particles (Fig. 6c). This may be due to surface oil released due to structural changes in the inner part of the powder as observed by Stephen et al. (2006).[29] This may be one of the reasons for poor flowability and less fat encapsulating ability of SKMP compared to casein.

Figure 5 Scanning electron microscopy of fat powder particles containing bakery fat; A: (Total fat, 73%), casein (16%), and sugar (6.5%); B: casein (13–13.4%), (Fat, 65%), and sugar (6.5%); C: Same as A and no sugar; Magnification 500×. For formulation details see Table 2.

Figure 6 Scanning electron microscopy of fat powder particles containing: A = Safflower oil; B = Flax seed oil; C = Bakery fat with Skim milk powder; Magnification 500×. For formulation details see Table 2.

SEM of fat powders using safflower and flax seed oils prepared with casein along with sugar showed some aggregates (Figs. 6a and 6b) and were similar to that of bakery fat with less casein (Fig. 5b). Effect of additives like sugar could be clearly seen in SEM of fat powders (Fig. 5). SEM of fat powder without any added sugar showed aggregate clusters (Fig. 5c) similar to that with SKMP (Fig. 6c) unlike those with added sugar (Figs. 5a and 5b), indicating the beneficial effect of the sugar. It was reported that sugar improves the emulsion stability and thereby improves encapsulation. Sucrose encapsulated particles were found to enclose fat droplets without central voids and were structurally stable, suggesting a good resistance to air diffusion during storage.[25] Milk fat powders with casein and carbohydrates showed spherical morphology with some wrinkles or scars on the surface and some large internal voids.[10]

Agglomeration of particles was also due to moisture absorption or surface oil swelling as observed by Onwulata and Holsinger (1995)[26] Also, it has been observed that on storage, the particles were highly agglomerated, especially those with soya oil, storage in humid atmosphere led to release of fat onto the surface.[30] In the present study, as there was no difference in moisture content, the observed effects were due to ingredients like wall materials and sugars. In general, SEM studies revealed that powders prepared with solid fats like vanaspati or speciality fat at a high percent showed distinct spheres showing efficient encapsulation, whereas powders with liquid oils like safflower or flax seed could be encapsulated at a lower percentage to get similar quality powders.

CONCLUSIONS

The formulations and process parameters to prepare powders with high fat content were standardized by spray drying. Casein was found to be an effective and efficient wall material. Small proportions of sugar and TCP had a beneficial effect on flowability of powders. Powders with solid fats like vanaspati or speciality fat could be encapsulated at a high percentage up to 75%, whereas liquid oils like safflower or flax seed could be effectively encapsulated up to 65%. The powders had low ERH and require a protective packaging material to protect from moisture absorption. The powders with oils were rich in ω-3 and PUFA and application in nutrition supplements and health foods and those with fats could be used in a bakery and traditional sweets and in various instant food formulations.

ACKNOWLEDGMENTS

The authors wish to thank Dr. B. R. Lokesh, Head of the Department and Dr. V. Prakash, Director of the Institute for their keen interest in the work. The authors also thank the Ministry of Consumer Affairs, Food & Public Distribution, Directorate of Vanaspati, Vegetable Oils & Fats, New Delhi for financial support.