Flavor Encapsulation - American Chemical Society

Chapter 9

Encapsulated

Orange O i l

Influence of Spray-Dryer Air Temperatures on Retention and Shelf Life M . H . Anker and Gary A. Reineccius

Downloaded by COLUMBIA UNIV on May 30, 2014 | http://pubs.acs.org Publication Date: May 31, 1988 | doi: 10.1021/bk-1988-0370.ch009

Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108

Single fold orange oil was encapsulated with gum arabic via spray drying using inlet and exit air temperatures ranging from 160 to 280 C and 80 to 130 C respectively. The resultant powders were analyzed for moisture content (toluene distillation), surface oil (Soxhlet extraction), and total oil (Clevenger distillation) prior to shelf-life testing. The powders were then adjusted to a water activity (a ) of ca. 0.54 over Mg(NO ) for shelf-life testing. A preliminary drying run was done at 200 C inlet and 100 C exit air temperatures. The a of the resultant powder was adjusted from ca. 0.03 to ca. 0.54. Maximum shelf-life was observed at the highest a tested. Shelf-life testing was done at 37 C monitoring for the formation of limonene oxidation products (limonene oxide). The powder dried at the highest operating temperature (280 C inlet air) was found to have the maximum shelf-life. w

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In 1985 worldwide sales of flavors and fragrances were 5.26 b i l l i o n d o l l a r s (1 ). In the United States, which accounts for ca. 28% of t o t a l worldwide sales, the sale of dry flavors i s estimated to be nearly 50% of the total flavor sales (2). Dried f l a v o r s , and s p e c i f i c a l l y spray dried flavors, are an important segment of the flavor industry and their s t a b i l i t y i s c r i t i c a l to this industry. The s t a b i l i t y of encapsulated orange peel o i l has been investigated with attention directed to the oxidation of limonene, one of i t s major constitutuents. The formation of limonene oxide has been shown to be a good indicator of the s h e l f - l i f e of encapsulated orange peel o i l (3). Various parameters (encapsulating agent, solids concentration, feed temperature and a i r i n l e t temperatures) have been studied with respect to their e f f e c t on v o l a t i l e retention (4, _5> · ^ purpose of this study was to determine the e f f e c t of spray dryer n e

0097-6156/88/0370-0078$06.00/0 * 1988 American Chemical Society

In Flavor Encapsulation; Risch, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

9. A N K E R & REINECCIUS

79

Encapsulated Orange Oil

operating temperatures on s h e l f - l i f e , while eliminating the e f f e c t of other variables (such as encapsulating agent, solids concentration, and powder moisture content) on s h e l f - l i f e . Materials and Methods


Materials. Gum arabic was obtained from Colloïdes Naturels Inc. (Far H i l l s , NJ) and Meer Corp. (Bergen, NJ). Single strength cold pressed orange o i l was obtained from Sunkist Growers Inc. (Ontario, CA) The inorganic and organic chemicals used i n the analyses were ACS c e r t i f i e d grade. Water A c t i v i t y Study. A 30% (w/w) solids gum arabic solution was heated to and held at 82 C with constant s t i r r i n g for 45 minutes. The solution was covered and l e f t to stand overnight at room temperature. Single fold orange peel o i l (25% w/w of gum solids) was added to the hydrated gum arabic solution and homogenized using a Greerco Corp. laboratory high shear mixer. The emulsion was fed into a Niro U t i l i t y Dryer equipped with a centrifugal atomizer. Inside chamber dimensions of this spray d r i e r are 150 cm. height and 120 cm. diameter. The i n l e t a i r temperature was 200+5 C and exit a i r temperature was 100+3 C. Following drying, 40g samples were placed i n each of s i x desiccators containing either D r i e r i t e or saturated s a l t solutions of L i C l , KC2H3O2, MgCl , K C0 , or Mg(N0 ) . At 25 C the water a c t i v i t i e s (a 's) of these desiccants are 0.001, 0.115, 0.234, 0.329, 0.443, and 0.536 respectively. A vacuum was pulled on each desiccator and the a of the powder samples equilibrated at room temperature for 72 hours. The resulting powders were placed i n a 37 C walk-in incubator and samples were removed every two days for gas chromatographic analysis to determine the amount of oxidation products. 2

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Dryer Temperature Study. An orange peel oil/gum arabic emulsion was prepared and spray dried as previously described. Six runs were made varying both the i n l e t and e x i t a i r temperatures (Table I). Table I.

Spray Dryer Operating Inlet Τ ( C) 200 + 5 200 200 160 240 280

Temperatures Exit Τ ( C) 80 + 3 105 130 105 105 105

A 100g sample of each powder was placed i n a desiccator over a saturated solution of Mg(N03)2- A vacuum was pulled and the a of the powders was allowed to equilibrate at room temperature for 72 hours. The desiccator was then placed i n a 37 C walk-in incu bator where the temperature was allowed to equilibrate for 24 hours before s h e l f - l i f e sampling began. At a storage time of w


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ENCAPSULATION

zero, excess sample was removed and a i r was admitted to the desiccator. The remainder of each powder was placed i n glass containers and stored at 4 C f o r further analyses. Moisture Determination. Sample moisture was determined by using a modified A.O.A.C. toluene d i s t i l l a t i o n method (7) for both the powders stored at 37 C ( a adjusted over Mg(N03)o7 and the powders stored at 4 C ( a unadjusted). Toluene (175mL) was added to 40g of unadjusted powder or 20g of adjusted powder i n a 500 mL f l a t bottomed flask f i t t e d with a Bidwell-Sterling trap and water cooled condenser. Samples d i s t i l l e d for 3 hours and then the volume of water collected was recorded. w


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Surface O i l Determination. Surface o i l was extracted from a 12-15g sample of each powder using a Soxhlet apparatus (7). The sample was placed i n a Whatman cellulose extraction thimble (33mm χ 80mm) and covered with glass wool. The thimble was placed i n the Soxhlet extraction chamber, f i t t e d with a water cooled con denser, and attached to a 250 mL f l a t bottomed flask containing 125mL of petane. After re fluxing over steam for 4 hours, lmL of pentane containing 2.04mg/mL of 2-octanone as internal standard was added to the flask. The volume was reduced to ca. 2mL under N . The amount of surface o i l present was determined by the i n t e r n a l standard method a f t e r gas chromatographic analysis. The gas chromatographic conditions were as follows: 2

Column: 0.25mm i . d . χ 30m WCOT fused s i l i c a Stationary phase: DB-5 (J & W S c i e n t i f i c , Rancho Cordova, CA) Carrier gas: Hydrogen S p l i t r a t i o : 1:40 Column temperature: 50 C to 200 C programmed at 10 C/minute Detector temperature: 200 C Sample size: 2uL Total O i l Determination. Total o i l was determined by Clevenger h y d r o d i s t i l l a t i o n (8). A 20g sample of powder was mixed with 150mL of deionized water i n a 250mL f l a t bottomed f l a s k . B o i l i n g stones and antifoam ( s i l i c o n e o i l , A l d r i c h Chemical Company) were added. A Clevenger o i l trap and water cooled condenser were attached. The sample was d i s t i l l e d for three hours. The volume of o i l collected was multiplied by the o i l density (0.833g/mL) to give the weight of o i l present i n the sample. Storage S t a b i l i t y . Samples were prepared for gas chromatographic analysis by dissolving 0.15g powder i n 0.85g d i s t i l l e d water i n a 3-dram screw cap v i a l and mixing well using a vortex mixer ( S c i e n t i f i c Products deluxe mixer). Acetone (4mL) containing 0.25mg/mL of 2-octanone as internal standard was added slowly while mixing. Anhydrous MgS04 (0.10g) was added to the v i a l con tents. The r e s u l t i n g supernatant was injected without further preparation into a Hewlett-Packard Model 5840 gas chromatograph


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81


(flame ionization detector). The amount of limonene oxide present was determined by the internal standard method (7). The gas chromatographic conditions were as follows:


Column: 0.25mm i . d . χ 25m WCOT fused s i l i c a Stationary phase: OV-1 (J & W S c i e n t i f i c , Rancho Cordova, CA) Carrier Gas: Helium (18psig) S p l i t r a t i o : 1:40 Column temperature: 50 C to 250 C programmed at 10 C/minute Detector temperature: 275 C Injection port: 200 C Sample size: 2uL Results and Discussion E f f e c t of Water A c t i v i t y . A preliminary study was done to deter mine the a at which encapsulated orange peel o i l was the most stable to oxidation. Figure 1 summarizes the results of this study. The formation of the limonene oxidation product, limonene oxide, was the slowest for the powder adjusted over Mg(N03) ( a = 0.536). While the levels of oxidation product do not follow i n exact order of a , i t i s evident that better storage s t a b i l i t y correlates with a higher a of the powder. This r e l a tionship was not anticipated. Literature on l i p i d oxidation (]_, 8, 9) indicates that there i s an optimum a for product s h e l f - l i f e which corresponds to the monolayer region. For t y p i cal dry products, the monolayer region corresponds to an a ranging from ca. 0.2 to 0.35. Our higher a s are definately above the monolayer region and we would have expected the rate of oxidation to have increased. While i t i s possible that the rate of oxidation would have increased had we gone to higher a s , the moisture content was already well over what i s common for commer c i a l products. Therefore, the study of higher a 's i s imprac t i c a l since the products of commerce would never be manufactured at a 's higher than used i n our study. Once we had determined the optimum p r a c t i c a l a for the storage of encapsulated orange peel o i l , we i n i t i a t e d a study on the influence of spray dryer i n l e t and e x i t a i r temperature on product s h e l f - l i f e . w

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Moisture. As anticipated, moisture contents of the powder samples decreased with decreasing temperature d i f f e r e n t i a l s bet ween i n l e t and exit a i r temperatures when either i n l e t or exit a i r temperature was held constant (Figure 2). The sample with the highest temperature d i f f e r e n t i a l ( T=120 C) and lowest exit a i r temperature (T=80 C) had the highest moisture content (7.8%) of a l l the powder samples. The role of temperature d i f f e r e n t i a l on product moisture content i s apparent from either data series in Figure 2. While the sample dried at 280 C i n l e t and 105 C exit a i r temperatures had the greatest temperature d i f f e r e n t i a l , the


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dryer a i r at 105 C could hold substantially more water than the 80 C e x i t a i r on the 200/80 C product. This resulted in a lower moisture content despite a greater temperature d i f f e r e n t i a l . The unadjusted powder samples had a sample standard deviation of 1.62% moisture compared to 0.69% moisture for the powder samples adjusted over Mg(N03)2 (Figure 3). The moisture content of the samples adjusted of Mg(N03>2 ranged from 7.59% to 9.20%. Surface O i l . Surface o i l increased with decreasing i n l e t and e x i t a i r temperature d i f f e r e n t i a l for samples dried at an i n l e t a i r temperature of 200 C (Figure 4). This was also observed for the samples dried at a constant exit a i r temperature of 105 C, with the exception of the sample dried at an i n l e t a i r temperature of 160 C which may have been i n error since we would not expect a deviation i n the relationship between surface o i l and temperature d i f f e r e n t i a l . This sample should be reproduced and analyzed again. One might expect the drying droplet to balloon with increasing i n l e t a i r temperature creating a greater surface area and, therefore, a greater surface o i l content. We did not observe this in our study. The higher moisture of the powders with greater temperature d i f f e r e n t i a l s could have interfered with the surface o i l extraction procedure y i e l d i n g erroneous values. Further studies should be done i n this are to determine i f indeed the surface o i l content of spray dried orange peel o i l does decrease with increasing temperature d i f f e r e n t i a l . Total O i l . The results of the t o t a l o i l analysis are summarized i n Figure 5. Total o i l varied by less than one standard deviation for a l l samples ( i . e . , 0.86%). Therefore, i t appears that i n l e t and e x i t a i r operating temperatures did not have a s i g n i f i c a n t e f f e c t on the t o t a l o i l content of the powder samples. Previous work has shown that flavor retention increases with increasing i n l e t a i r temperature u n t i l internal steam i s formed in the drying droplet (12). The higher i n l e t a i r temperatures produce a more rapid drying which thereby results i n a shorter time u n t i l the formation of a high solids "skin" around the drying droplet. This " s k i n " acts as a semipermeable membrane which retains the larger ( r e l a t i v e to water) flavor molecules. At some i n l e t a i r temperature, however, internal steam formation w i l l cause "ballooning" of the drying droplet. Ballooning results i n a very high surface to volume ratio for the powder and, therefore, greater flavor losses. Apparently 280 C i s not adequate to produce ballooning. Previous work (12) has also demonstrated that higher exit a i r temperatures result i n improved flavor retention. It has been postulated that higher exit a i r temperatures result i n more rapid drying, thereby providing better retention of v o l a t i l e s . We do not observe this relationship i n this study. In this study, we have not observed a relationship between dryer operating temperatures and the retention of orange peel o i l . The e f f e c t of dryer operating temperatures on o i l retention may be p a r t i a l l y negated due to the inherently small losses of flavor


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3· 2.5 2 1.5 1 0.5 0

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STORAGE TIME (DAYS)

Figure 1. Effect of water a c t i v i t y on shelf l i f e of encapsulated orange peel o i l .

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INLET AIR Τ = 200 C

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105

130

EXIT AIR T, C

Figure 2. Influence of i the moisture content of s

EXIT AIR Τ = 105 C

160

200

240 280

INLET AIR T, C

and exit a i r temperatures on dried orange peel o i l .

160/105 200/80 200/105 200/130 240/105 280/105 DRYER OPERATING TEMPERATURES (INLET/EXIT, C)

Figure 3. Moisture contents of spray dried orange peel o i l which had been adjusted i n water a c t i v i t y over Mg(N0^)2.


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during drying. Flavor losses, at most, were only 15%. Previous studies have looked at the losses of more v o l a t i l e substances (e.g., d i a c e t y l , butanol, acetone) which were present from parts per m i l l i o n up to 1-2% ( 1_3). V o l a t i l e losses in these studies have often been up to 70-80%. When losses are greater, smaller e f f e c t s may more readily be ascertained. Storage S t a b i l i t y . The formation of limonene oxide at 37 C was measured as a function of time to determine s h e l f - l i f e of the encapsulated orange peel o i l samples. Figure 6 shows the s h e l f l i f e r e s u l t s . A value of 2mg limonene oxide/g limonene was used as the end of s h e l f - l i f e for oxidized encapsulated o i l samples (_3). The sample dried at 160 C and 105 C i n l e t and exit a i r temperatures respectively and the smallest temperature d i f f e r e n t i a l (55 C). This sample formed limonene oxide much faster than the other five samples. By 23 days, this powder had reached a value of 2mg limonene oxide/g limonene. The sample dried at 280 C and 105 C i n l e t and e x i t temperatures respectively did not reach 2 mg limonene oxide/g limonene u n t i l a f t e r 34 days of storage at 37 C. This sample also had the largest i n l e t and exit a i r temperature d i f f e r e n t i a l (175 C). The remaining four samples had reached 2mg limonene oxide/g limonene a f t e r about 30 days of storage at 37 C. Previous work has theorized that storage s t a b i l i t y i s enhanced when the surface o i l i s lower (_2, _7). For this study the opposite e f f e c t was observed: the sample with the lowest surface o i l (107mg surface oil/100g powder; drying conditions of 160 C i n l e t and 105 C exit a i r temperatures) had the shortest s h e l f l i f e . However, the sample with the longest s h e l f - l i f e (drying condition of 280 C i n l e t and 105 C exit a i r temperatures) had a surface o i l content nearly the same (llOmg surface oil/100g powder). It appears that surface o i l i s not an important determinant of s h e l f - l i f e . This i s supported by the recent work of Anandaraman and Reineccius (4) where an encapsulated orange peel o i l was washed with organic solvent to remove surface o i l prior to s h e l f - l i f e testing. The product with no surface o i l exhibited a s h e l f - l i f e very similar to the product with surface o i l . Other factors such as matrix porosity (to oxygen), absolute density, trace mineral level (copper and iron) and presence of a n t i o x i dants are most l i k e l y more s i g n i f i c a n t i n determining the rate of oxidation of encapsulated orange peel o i l . In summary, we have found that the optimum (within the l i m i t s of this study) a for s h e l f - l i f e i s 0.54. In addition, the dryer i n l e t and e x i t a i r temperatures had no e f f e c t upon o i l retention and perhaps only a minor e f f e c t upon s h e l f - l i f e . I f there i s a s i g n i f i c a n t e f f e c t i t i s that the higher i n l e t a i r temperature actually yielded a better s h e l f - l i f e . A higher temperature d i f f e r e n t i a l means that dryer throughput also i s increased and operating costs are cut. The more product that can be produced per hour, the lower the production costs. A larger temperature d i f f e r e n t i a l also results i n a higher f i n a l product moisture. This i s good for s h e l f - l i f e since a higher a means a longer s h e l f - l i f e . I f we had not adjusted the a 's of a l l our products to be the same a , we would have seen even greater effects of operating temperature on s h e l f - l i f e . w

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ANKER & REINECCIUS


EXIT AIR Τ = 105 C

INLET AIR Τ = 200 C

80

105 130

225200· 175150125· 100· 755025 0


EXIT AIR T, C

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200 240

280

INLET AIR T, C

F i g u r e 4. I n f l u e n c e o f d r y e r i n l e t and e x i t a i r t e m p e r a t u r e s on t h e s u r f a c e o i l c o n t e n t o f s p r a y d r i e d orange p e e l o i l . 20 18 16 14 12 10 8 6 4 2 0

160/105 200/130 200/105 200/80 240/105 280/105 DRYER OPERATING TEMPERATURES (INLET/EXIT, C)

F i g u r e 5. I n f l u e n c e o f i n l e t and e x i t a i r t e m p e r a t u r e s on t h e r e t e n t i o n o f orange p e e l o i l d u r i n g spray d r y i n g .

• 160/105 σ> 4

• 200/80

Û

• 200/105

Lu χ ο

3

ο 200/130 x 240/105

ο 1 1 Ε 0

- 280/105 10 20 30 STORAGE TIME (DAYS)

40

F i g u r e 6. I n f l u e n c e o f d r y e r i n l e t and e x i t a i r t e m p e r a t u r e s on t h e s h e l f l i f e (37 C) o f spray d r i e d orange p e e l o i l .


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ENCAPSULATION

Literature Cited 1.

Layman, P.L. C & EN. 1987, 65(29), 35-38.

2.

Brenner, J . Perfumer & Flavorist. 1983,

3.

Anandaraman, S. Ph.D. Thesis, University of Minnesota, 1984. Anandaraman, S.; Reineccius, G.A. Food Technology. 1986, 40(11), 88-93.


4.

40-44.

5.

Rulkens, W.H.; Thijssen, H.A.C. 7, 95-105.

6.

Leahy, M.M.; Anandaraman, S.; Bangs, W.E.; Reineccius, G.A. Perfumer & Flavorist. 1983, 8, 49-56.

7.

Anandaraman, S.; Reineccius, G.A. Perfumer & Flavorist. 1987, 12, 33-39.

8.

Essential Oil Association of U.S.A. Food of Standards and Specifications; New York, NY, 1975; pp.7,9.

9.

Labuza, T.P.; Silver, M.; Cohn, M.; Heidelbaugh, N.D.; Karel, M. J. American Oil Chemists' Society. 1971, 48(10), 527-531.

10.

J . Food Technology. 1972,

Chou, H.; Acott, Κ.; Labuza, T.P. J . Food Sci. 1973, 38, 316-319.

11.

Labuza, T.P. Food Technology. 1980, 34(4), 36-41, 59.

12. Reineccius, G.A.; Anandaraman, S.; Bangs, W.E. Perfumer & Flavorist. 1982, 7, 1-6. 13. Reineccius, G.A.; Coulter, S.T. J . Dairy Sci. 1969, 52, 1219-1223. RECEIVED December 29, 1987


Flavor Encapsulation - American Chemical Society

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