Wax Microemulsion Formulations Used As Fruit Coatings
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Proc. Fla. State Hart. Soc. 111:251-255. 1998. WAX MICROEMULSION FORMULATIONS USED AS FRUIT COATINGS Robert D. Hagenmaier Materials and Methods U.S. Citrus and Subtropical Products Laboratory USDA, ARS, SAA Polyethylene waxes E10 and E20 were from Eastman P.O. Box 1909 Chemical (Kingsport, TN); AC629, AC680, AC673 and AC316 Winter Haven, FL 33883-1909 were from Allied Signal Inc. (Morristown, NJ); and PED121 e-mail: [email protected] was from Clariant Corp. (Charlotte, NC). FDA approval for polyethylene wax (oxidized polyethylene) is given in 21 CFR Additional index words. Edible coatings, 'Hamlin' oranges, 172.260 (FDA, 1995). The candelilla wax (21 CFR 184.1976) 'Sunburst' tangerines. was bleached (No. 75 from Strahl & Pitsch Inc., W. Babylon, NY, type cbw2 from Berial, S. A., Mexico D. F., or No. 7808 Abstract. Wax microemulsions were made with three emulsifi- from Botanical Wax, Arlington Heights, IL) or unbleached cation techniques. Formulations are presented for making an- 'filtrada' from Berial, S. A. The beeswax (21 CFR 184.1973) ionic microemulsions with carnauba wax, candelilla wax, was from Koster Keunen Inc. (Sayville, NY). The rice bran oxidized polyethylene, beeswax, paraffin, montan wax and var wax (21 CFR 172.890) was from Strahl & Pitsch or Koster Ke ious hydrocarbon waxes, and also for making nonionic micro unen Inc. Yellow No. 3 and No. 1 carnauba wax (21 CFR emulsions with squalene, hydrocarbon waxes and rice bran 184.1978) were from Strahl & Pitsch Inc. The petroleum wax wax. Citrus fruit were coated with various mixtures of a wax (21 CFR 172.88 and 178.3710) with 61°C m.p., was Parvan emulsion and rosin. Those coatings with higher percentage wax had lower internal CO2 and higher O2. 4450 from Exxon (Houston, TX). The paraffin wax (CFR 178.3710) type 126, also with 61°C m.p., was from Koster Ke unen Inc. Rosin modified maleic wood resin (21 CFR In recent years we have evaluated the performance of var 172.210) was type 807Afrom Resinall Corp. (Stamford, CT). ious wax microemulsions as food and fruit coatings (Hagen Hydrogenated wood rosin (21 CFR 172.210) was Foral AX maier and Baker, 1993, 1994a, 194b, 1996, 1997). In the from Hercules Inc., (Wilmington, DE). The montan wax (21 course of those studies, more than 600 microemulsions were CFR 172.210) was type KPS from Clariant Corp. Hydrocarbon made in our laboratory, in attempts to develop better coat waxes Polywax 500 (21 CFR 172.888) and Be Squarel95 (21 ings. In our published studies <10% of the microemulsions CFR 172.886) were from Petrolite Corp. (Tulsa, OK). The were used, as there was insufficient time to thoroughly evalu oleic acid (21 CFR 172.860) was Emersol 6321, from Henkel ate all of those made. Here now is a summary of all formula Corp. (Cincinnati, OH). The myristic acid was Hystrene 9014 tions, not just the 10% included in our publications. from Witco Corp. (Memphis, TN) and Emery 655 from Hen Why were so many different formulations made? First, in kel Corp. Mineral oil (21 CFR 172.878z) was from Squibb 8c the course of work on coatings it became evident that the per Sons (Princeton, NJ) and petrolatum jelly (21 CFR 172.880) formance of any particular wax as a coating depended consid was from Albertson's (Boise, ID). The surfactants were sorbi- erably on the quality of the emulsions and also the presence tan monostearate (21 CFR 172.842), Capmul S from Abitec of minor ingredients in the formula. Thus, a conclusion Corp. (Janesville, WI) or Durtan 60 from Durkee Industrial about the potential as edible coating of any given wax would Foods (Cleveland, OH). Glycerol mono/di-oleate (21 seem to require the testing of a number of different formula CFR182.4505,GRAS) was GMO-Kfrom Abitec Corp. Polysor- tions. Secondly, in order to make progress in developing wax bate 60 (21 CFR 172.836) was Capmul POE-S from Abitec coatings, it was considered necessary to know the composi Corp. or Tween 60Kfrom ICI Surfactants (Wilmington, DE) tion of any coatings used. In early work, the wax microemul Microemulsions were made by three methods. For the wa sions evaluated in our laboratory were samples received from ter-to-wax method, the wax and other ingredients (less the suppliers whose formulations were proprietary information. water) were heated 10-20°C above the melting point of the We found that much trial and error was involved in arriving wax, hot water (95-100°) slowly added with stirring, and the at suitable formulations, which resulted in many trials. In gen mixture cooled to 50°C in a water bath, with stirring. For the eral, little information on wax microemulsion formulations was found in the literature (Bennett, 1975), especially formu wax-to-water method the same molten wax mixture was poured into the vortex of hot water being rapidly stirred in a lations whose ingredients were restricted to those approved beaker, and the mixture cooled in the same manner. For the for use in foods. pressure method, which is similar to the water-to-wax method, The purpose here is to make available the techniques and the unmelted wax, together with part of water (the initial wa ingredients used in our laboratory to make wax microemul ter) was placed in a 2-liter pressure cell (Parr Instrument Co., sions, in order to make it easier for others to make and test Moline, IL), heated to approximately 10-30°C above the melt these, particularly for use as food and fruit coatings. ing point of the wax, hot water forced into the cell with a pump (Haskel Inc., Burbank, CA) and the emulsion cooled South Atlantic Area, Agricultural Research Service, U.S. Department of to 50°C. For all three methods the total amount of water in Agriculture. Mention of a trademark or proprietary product is for identifica corporated was that required to make an emulsion contain tion only and does not imply a guarantee or warranty of the product by the ing 60-80% water. U.S. Department of Agriculture. The U.S. Department of Agriculture prohib The quality of the emulsions was evaluated by appearance its discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual ori and performance. Appearance was primarily evaluated by entation, and marital or family status. measurement of turbidity with the Ratio/XR turbidimeter Proc. Fla. StateHort. Soc. Ill: 1998. 251 (Hach Co., Loveland, CO). This measures turbidity over the acceptable by the Code of Federal Regulations for use in food range 0-2000 nephelometric turbidity units (NTU). In addi and/or fruit coatings. The ingredients for all of these coat tion, the amount of cream that separated by gravity was ob ings consist only of water, wax, fatty acids and a base (morpho served after storage at about 25°C for at least one week. line or ammonia, sometimes supplemented with KOH). For measurement of gloss, the emulsions were dried on The ranges indicated for various ingredients in Table 1 polystyrene weigh boats (0.5 g on an area of 25 cm2) or ap mean only that good emulsions were made in our laboratory plied to apples or citrus (0.3 ml per fruit). Gloss was evaluated within that range. Sometimes our only attempts were within by panel or by measurement of gloss units (G.U.) with a re that range, and sometimes poor emulsions were made with in flectance meter (micro-TRI-gloss, BYK Gardner Inc., Silver gredients outside that range. Table 1 shows only the successes Spring, MD). Tendency of coatings to 'fracture' was deter and not the many failures. mined subjectively after hitting and rubbing together two Carnauba wax emulsions. The type of carnauba wax used pieces of fruit, then wiping the contact surfaces with a black was Yellow No. 3 for most of our carnauba wax formulations. cloth, and rating the amount of coating found on the cloth Those made in the pressure cell generally had lower turbidity (1.0 = none; 2.0 = minimal; 3.0 = significant but acceptable; and cream than those made in beakers by water-to-wax or 4.0 = heavy and unacceptable; and 5.0 = virtually all coating wax-to-water methods, and the same was true for other waxes removed). as well. This is generally well known (Burns and Straus, 1965). The coatings applied to citrus fruit consisted of mixtures However, pressure vessels are expensive and not always avail of a wax microemulsion made of various mixtures of a wax able. The water-to-wax method was used extensively for mor- emulsion and a wood rosin solution. The wax microemulsion pholine-based carnauba wax emulsions, and these were contained 7.6% carnauba No. 3, 8.2% E20, 0.8% Foral AX generally very easy to make. As a demonstration, a good qual and 4.5% morpholine and the balance water. The rosin solu ity carnauba wax microemulsion (turbidity = 530 NTU) was tion contained 16.4% Resinall 807A, 4.6% oleic acid, 8.8% made with a stirring rod being the only mixing equipment morpholine and the balance water. The five coatings used (data not shown). Carnauba emulsions made by the wax-to- consisted of 0, 5, 15, 30 and 100% of the rosin solution and water method, by contrast, generally were quite turbid, ex the balance wax microemulsion. The coated fruit were stored cept when Foral AX was added before emulsification (5% was 7 days at 21°C. Internal gases and air flux were measured (10 sufficient, data not shown).