Vol. 68, Nr. 3, 2003—JOURNAL OF FOOD SCIENCE 879 © 2003 Institute of Food Technologists Further reproduction prohibited without permission Food Chemistry and Toxicology JFS: Food Chemistry and Toxicology Effect of Hydroxypropyl Methylcellulose– Lipid Edible Composite Coatings on Plum ( cv. Autumn giant ) Quality During Storage M.B. PEREZ-GAGO, C. ROJAS, AND M.A. DEL RÍO ABSTRACT: ‘Autumn Giant’ plums were coated with edible hydroxypropyl methylcellulose-lipid composite coat- ings. The coatings consisted of beeswax or shellac, at 2 lipid content levels (20% and 60% dry basis). Weight loss of coated plums decreased as lipid content increased. No differences on weight loss were observed between uncoated and 20% lipid-coated plums, indicating that the natural waxes of plums are as effective as coatings having 20% lipid. Water-dipped plums experienced the highest weight loss. Fruit texture was not affected by coating after short-term storage at 20 °C. However, for prolonged storage at 20 °C, the coatings significantly reduced texture loss and internal breakdown compared to uncoated and water-dipped plums. Keywords: autumn giant plums, edible composite coatings, beeswax, shellac, hydroxypropyl methylcellulose Introduction P LUMS ARE CLIMACTERIC FRUITS, WHICH ARE SUITABLE FOR COLD storage for a short period depending on the susceptibility to in- ternal breakdown and loss in texture. The market life varies among cultivars from 1 to 8 wk and is affected by temperature manage- ment. Maximum market life is obtained when fruits are stored at ap- proximately 0 °C and the minimum postharvest life occurs when stored around 5 °C (Crisosto and others 1999). Some cultivars have observed an improvement in postharvest life by the use of modified atmosphere (MA) or controlled atmosphere (CA) in combination with temperatures close to 0 °C. The major benefits of CA during storage are retention of fruit firmness and ground color. Conditions of 6% O 2 and 17% CO 2 are suggested for reduction of internal break- down, but its effectiveness depends on cultivar, preharvest factors, market life, and storage time (Crisosto and others 2002). Edible films and coatings can extend the shelf life and improve the quality of fruits and vegetables by creating a modified atmo- sphere inside the fruit due to the barrier to O 2 and CO 2. In addition, edible coatings can reduce weight loss, carry food ingredients, and/ or improve the mechanical integrity or handling characteristics of the product (Krochta 1997). The principal disadvantage, however, is the development of off-flavors if the inhibition to O 2 and CO 2 exchange results in anaerobic respiration. The barrier properties depend on the chemical composition and structure of the film- forming polymer and the conditions of storage. Many studies have focused on elucidating how composition, preparation, and storage conditions affect the properties of standing-alone films and re- views can be found (Guilbert 1986; Kester and Fennema 1986; Kro- chta and others 1994; Krochta and De Mulder-Johnston 1997; De- beaufort and others 1998). This knowledge is required to better understand the transfer mechanisms of gases and solutes through these edible materials. Currently, there are several polysaccharide- based coatings commercially available for postharvest use. Howev- er, the lack of knowledge about composition on many commercially available coatings makes it difficult to predict their performance on fruit quality. Therefore, there is a need to study the effect of coat- ing composition on postharvest quality of specific commodities. A few papers have been found in the literature where coatings have been applied to plums, showing some improvement in stor- age life and fruit quality (Dinamarca and others 1989; Basiouny and Baldwin 1997). The effect of edible coatings, creating a modified atmosphere inside the fruit due to the barrier to gases O 2 and CO 2 , is to extend the market life and improve quality by reducing the internal breakdown and loss in texture. This investigation aims to characterize the effect of lipid type and amount of hydroxypropyl methylcellulose (HPMC)–lipid composite coatings on postharvest quality of plums cv. Autumn Giant. Materials and Methods Materials Hydroxypropyl methylcellulose (HPMC) (Methocel E15) was supplied by Dow Chemical Co. (Midland, Mich., U.S.A.). Refined beeswax (BW) (grade 1) and dewaxed-decolourised flake shellac (acid nr 69.7) were purchased from Brillocera, S.A (Valencia, Spain). Stearic acid, glycerol, and ammonium hydroxide (30%) were from Panreac Química, S.A. (Barcelona, Spain). Coating formulation Emulsion coatings consisted of HPMC and beeswax (BW), or shellac, as the hydrophilic and lipidic phase, respectively, suspend- ed in water. To make the emulsion coatings, 5% HPMC was dis- persed in hot water at 80 °C. Next, stearic acid and glycerol were added as emulsifier and plasticizer, respectively. The HPMC-plas- ticizer phase consisted of 2 parts HPMC to 1 part glycerol (dry ba- sis), and this ratio was kept constant throughout the study. Lipid (BW or shellac)-stearic acid ratio was also kept constant and consist- ed of 5 parts lipid to 1 part fatty acid (dry basis). Either the BW or shellac were added to the HPMC-stearic acid-glycerol mixture at 2 different levels (20% and 60% dry basis). To help melting of the BW and shellac, solutions were previously heated to 10-to-20 °C above the melting point of the lipids, so they melted immediately. Since shellac is an alkali-soluble resin, the pH was increased by adding 1% NH 3 . Once the lipids were melted, samples were homogenized with a high-shear probe mixer (PolyTron, Model PT 2100; Kinemat- ica AG Inc., Lucerne, Switzerland) for 4 min at 30000 rpm. After ho-