Flavor Technology - American Chemical Society

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Chapter 10

A Novel Membrane Process for Folding Essential Oils M. H. Auerbach

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Food Science Research and Development, Pfizer Central Research, Eastern Point Road, Groton, CT 06340-5196

Raw (cold-pressed) citrus peel oils contain 89-98% terpene hydrocarbons, which are often undesirable as they oxidize easily and cause cloudiness in aqueous systems. Folded oils are enriched in the more desirable oxygenated components (aldehydes, alcohols, esters). Commercial folding is done primarily by vacuum distillation; lesser amounts are also folded by solvent extraction. Such folded products may be thermally stressed, contain solvent residues or undesirable component ratios, or are too costly. A novel continuous membrane process has been developed that yields undegraded folded oils free of solvent residues. Three process configurations were investigated using combinations of ultrafiltration, reverse osmosis, dialysis and pervaporation operations. A 100 g/day pilot unit was constructed to demonstrate feasibility. Membrane product component ratios differ from those of conventionally folded oils, giving the flavorist a new set of natural raw materials. The processes can also be used to recover valuable components from aqueous waste streams from oil processing plants. Although this work was done entirely with cold-pressed orange and lemon peel oils, the processes should also be applicable to other high-terpene essential oils. Based on published data and information from consultants, worldwide sales of citrus oils were estimated to be 15-20 MM kg/yr worth $100-150 MM in 1988. The leading use for these flavor raw materials is in beverages. Citrus peel oils are produced primarily by aqueous emulsion centrifugation during mechanical juice extraction (1). These oils cost $2.50-25/kg and contain 89-98% terpene hydrocarbons (2,3), which are often undesirable as they are easily oxidized and cause cloudiness in aqueous systems. Non-citrus essential oils are also produced by steam distillation (4). Citrus oils contain over a hundred individual components; the leading ones are given in Table I.

0097-6156/95/0610-0127$12.00/0 © 1995 American Chemical Society In Flavor Technology; Ho, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

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FLAVOR TECHNOLOGY

Table I - CITRUS OIL COMPONENTS - Hydrocarbons

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d-limonene oc-thujene myrcene p-cymene y-terpinene tr-P-ocimene oc/y-selinene

Monoterpenes a/p-pinene sabinene a-phellandrene terpinolene A -carene camphene ct/p-ylangene 3

Oxygenates Aldehydes octanal decanal citronellal neral geranial nonanal a/p-sinensal undecanal dodecanal perillaldehyde 2,4-decadienal hexanal

Alcohols linalool cc-terpineol octanol nerol geraniol terpinen-4-ol isopulegol borneol fenchol pinol p-cymen-8-ol tr-carveol thymol elemol citronellol

Sesquiterpenes P-caryophyllene oc/p-copaene a/p-famesene valencene 8-cadinene P-bisabolene tr-a-bergamotene sesquicitronellene P-cubebbene p-elemene a-humulene longifolene Esters octyl acetate neryl acetate decyl acetate geranyl acetate citronellyl acetate N-Me,Me-anthranilate Ketones nootkatone carvone Others limonene oxides thymyl Me ether linalool oxide

"Folding" is an imprecise term used in theflavorindustry to describe the volume reduction of an essential oil. Folded citrus oils are enriched in the desirable oxygenated components (aldehydes, alcohols, esters). They contain 5-95% oxygenates and sell for $22-990/kg. If a distillate is one-fifth the original volume of the raw feed oil, it is said to be five-fold, even though the oxygenate content of the product may not be five times that of the feed. Folding is done commercially primarily by vacuum distillation (5); smaller volumes are also folded by solvent/countercurrent extraction (6) [ethanol or C 0 (7)]. Other non-conventional processes for removing 2

In Flavor Technology; Ho, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

10. AUERBACH

Novel Membrane Process for Folding Essential Oils 129

terpenes from essential oils involve adsorption of oxygenates onto a polar particulate solid followed by recovery with supercritical C 0 (8), or extraction with P-cyclodextrin (9). These processes are not continuous and have limited terpene removal potential. There is generally no industry-wide consensus or accepted specification for what constitutes a five-fold orange oil. Many unique products are offered by, for example, combining a vacuum-distilled cold-pressed peel oil with an essence oil [organic phase of condensate from juice concentration (evaporation) process] or aroma (aqueous phase of condensate from juice concentration process). Typical compositions of some vacuum distilled orange oils are given in Table II. Such folded materials may be thermally stressed, contain solvent residues or undesirable component ratios, or be prohibitively costly. Membrane processes offer the potential advantages of low-temperature, organic solvent-free operation, reduced oxidative degradation, and controllable selectivity for certain components. They have been used to a certain extent in juice processing and oil recovery (10-13), but until the present work, a continuous hybrid process for folding essential oils had not been developed. The objective of this work was to investigate possible membrane systems that would yield useful citrus oil flavor materials with improved organoleptic properties vs conventionally folded oils.

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2

Experimental Three basic process scenarios were investigated for the concentration of oxygenated components from cold-pressed citrus oils (14). 1. DA/PV: Raw citrus oil was recirculated through a dialysis module against water and oxygenated components of the oil were selectively extracted into the water. These components were then removed from the water by pervaporation and condensed, yielding an oil product greatly enriched in oxygenated components. 2. UF/RO/DA: An aqueous suspension of raw citrus oil was prepared and recirculated through an ultrafiltration module, giving a dilute aqueous permeate greatly enriched in oxygenated components. The oil content of the UF permeate was concentrated 15-20x by recirculation through a reverse osmosis module. The oil phase of the more concentrated RO reject was extracted into fresh raw oil by recirculation through a dialysis module, enriching the oxygenate content of the oil. 3. RO/DA: As much as 20% of the peel oil is lost in commercial processing plants in aqueous emulsion clarification centrifuge waste discharges (10). In an attempt to recover a significant portion of this oil, the aqueous waste stream from a commercial processing plant was obtained and concentrated by recirculating through a reverse osmosis module. The oil phase of the RO reject stream was extracted into fresh raw oil by dialysis as in process 2 above.

In Flavor Technology; Ho, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

In Flavor Technology; Ho, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

0.02 0.07 0.08 0.56 93.4 0.12 2.0 0.33 0.16 2.0 0.63 0.56 ND ND

0.56 0.51 0.14 1.7 95.7 0.17 0.42 0.04 0.06 0.42 0.14 0.19

ND ND

other terpenes other oxygenate --

0.04 0.1 0.6 0.33 0.97 0.71 4.8 8 3 4.8 4.5 2.9

4.4

C/F

0.16 0.22

0.42 0.24 NR 1.86 95.2 NR 0.25 0.05 0.03 0.28 0.07 0.10

1.0%

CPVal

b

1.42 2.44

0.23 0.14 NR 1.05 79.9 NR 0.52 0.14 0.17 1.48 0.41 0.68

5.8%

b

10x

8.9 11

2.1 3 6 5.3 6 7

--

0.56 0.84

—

0.55 0.58

5.8

C/F

0.14 0.18

0.43 0.34 NR 1.81 95.4 NR 0.17 0.04 0.03 0.18 0.05 0.08

0.73%

CPMS

b

0.78 1.33

0.26 0.23 NR 1.31 82.8 NR 0.37 0.12 0.14 0.96 0.30 0.52

3.74%

b

10x

5.6 7.4

2.2 3 5 5.3 6 6

—

0.72 0.87

—

0.60 0.68

5.1

C/F

C/F = concentration factoR.; ND = not determined; NR = not reported a. Raw and 5-fold vacuum distilled oil from commercial source F, 1994 b. Cold-pressed Valencia (Val) and mid-season (MS) raw and 10-fold vacuum distilled oils from Vora et al 1984 (reference 5) c. Oxygenate and component percent by weight from GC analyses (see text)

c

Component % a-pinene sabinene p-pinene myrcene/octanal d-limonene y-terpinene linalool citronellal a-terpineol decanal neral geranial

5.7%

1.3%

VDF1"

Oxygenates

a

RawFl

Sample

Table H - VACUUM DISTILLED ORANGE OIL ANALYSES

Downloaded by PRINCETON UNIV on June 21, 2013 | http://pubs.acs.org Publication Date: May 5, 1997 | doi: 10.1021/bk-1995-0610.ch010

Downloaded by PRINCETON UNIV on June 21, 2013 | http://pubs.acs.org Publication Date: May 5, 1997 | doi: 10.1021/bk-1995-0610.ch010

10. AUERBACH

Novel Membrane Process for Folding Essential Oils 131

The chemical compositions of essential oils are generally determined by capillary column gas chromatography (15-17). The raw citrus oils, intermediate process streams and resulting products were analysed using GC conditions similar to those of Anandaraman and Reineccius (17). In some cases a DB-Wax column (J&W Scientific, Folsom, CA) was used instead of OV-101 or SE-30 silicone to resolve P-myrcene from octanal. Oil samples were prepared for analysis by dilution 1:50 in hexane containing 1000 ppm n-octane as an internal standard. Aqueous samples (10 mL) were vigorously shaken with 1 mL hexane (w/1000 ppm n-octane internal standard) for 1 minute followed by 2 minutes high-speed centrifugation. The hexane phase was then injected into the GC. The method was validated and response factors determined using authentic standards. A representative chromatogram with GC conditions is given in Figure 3. Results Results of the investigation of various membrane folding processes are given below. Process 1: DA/PV - A diagram of this process is given in Figure 1 and compositions of products from cold-pressed orange peel oil in this process are given in Table III. The oil content of the aqueous dialysate was about 30 ppm. Several types of pervaporation membranes were tested; certain types were more selective but gave lower flux than others. Compared to the vacuum distilled folded oils in Table I, the products from this process were generally richer in linalool, octanal, neral, geranial and a-terpineol, and less rich in decanal. Although the product composition was interesting, process development was discontinued in favor of the systems below because of uneconomically low membrane flux rates and the lack of a commercial source for larger scale pervaporation modules. Process 2: UF/RO/DA - A diagram of this process is given in Figure 2; compositions of products from cold-pressed orange and lemon oils in this process are given in Table IV. Several types of membranes were tested; some had a tendency to leak oil within a few hours, while for others selectivity for oxygenates declined rapidly. For the pilot scale membrane unit run on orange oil, the aqueous feed emulsion was prepared to contain 8-10% oil and the UF permeate contained 10-16 ppm oil (70-80% oxygenates). The UF reject stream contained 1.2-1.3% oxygenates, confirming membrane selectivity for oxygenates. Recycle of the permeate through the RO module concentrated the RO reject to 150-350 ppm oil (90-96% oxygenates), while the RO permeate contained 0.5-2.0 ppm oil. Although the proportion of oxygenates in the UF permeate/RO reject recycle stream was quite high, the total oil content was relatively low because the RO unit had to be operated below about 1000 ppm oil content. Above this value a separate oil phase would separate out and foul the membrane, reducing water flux and oil rejection dramatically. Thus direct recovery of oxygenates from the dilute aqueous

In Flavor Technology; Ho, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

132

FLAVOR TECHNOLOGY

Pervaporation

Oxygenate-Enriched Oil Vapor

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y

Dialysis

Vacuum Pump Cold Trap OxygenateEnriched Aqueous Dialysate

Raw Orange Oil

Figure 1 - Combined dialysis/pervaporation system Dialysis

UF Bleed UF Permeate Raw Orange OH"

LJ

Water-

Orange Oil Product RO Permeate

Figure 2 - Combined ultrafiltration/reverse osmosis/dialysis system

In Flavor Technology; Ho, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

Downloaded by PRINCETON UNIV on June 21, 2013 | http://pubs.acs.org Publication Date: May 5, 1997 | doi: 10.1021/bk-1995-0610.ch010

10. AUERBACH

Novel Membrane Process for Folding Essential Oils 133

c