ROBERT A. BAKER and ROBERT D. HAGENMAIER
Fresh whole peeled grapefruit or segments produced by vacuum infusion with pectinases are considered minimally processed products. When dry packed, segments from mature late season fruit had ﬂuid losses 15% during 4 wk storage. Edible wax microemulsion coatingsreduced leakage of dry-packed segments by 80% after 2 wk, and 64% after 4 wk storage, and were optimally effective in reducing leakage when diluted to 12% solids. Coatings could be made with polyethylene, candelilla or carnauba wax, and with lauric, stearic, palmitic, oleic or myristic acids. Coatings with carnauba wax were most effective. Whether made with morpholine or ammonia as the base,coatings were not detected by informal taste panels before or after storage. Key Words: citrus, grapefruit, edible coating, minimal processing, ﬂuid loss
age from grapefruit segments, without compromising appearance or general acceptability. With low pH and high leakage rates, grapefruit segments represent an extreme example, and products capable of limiting leakage from this product should be ofvalue in coating other minimally processed fruits and vegetables with lower leakage rates and/or higher pH.
MATERIALS & METHODS
THE COMMERCIAL PECTINASE used for peeling and segmenting of fruit was Pectinex Ultra SP-L (Novo Enzymes, Danbury, CT). Reﬁned candelilla wax and carnauba wax grades 1 and 3 were obtained from Strahl and Pitsch (West Babylon, NY). Polyethylene waxes AC316, AC329 and AC680were from Allied Signal (Morristown, NJ), and polyethylene waxes E10 and E20 were from Eastman Chemicals (Kingsport, TN). Petroleum wax Parvan 6550 was from Exxon Corp. (Houston, TX). Various preparations of stearic, oleic, palmitic, myristic and lauric acids were from Sigma Chemical Co. (St. Louis, MO), Mallinkrodt Specialty Chemicals (Paris, KY) and Witco Corp. (Memphis, TN). Morpholine was 99% pure (Aldrich Chemical Co., Milwaukee, WI). Ammonium hydroxide was from Mallinkrodt, Inc. (Paris, KY).
COMMERCIAL FACILITIES are producing minimally processed citrus, either as whole fruit or segments, using vacuum infusion of pectinases to remove peel (Baker and Bruemmer, 1989; Baker and Grohmann, 1994, 1995; Baldwin and Baker, 1992; Bruemmer, 1981; Bruemmer et al., 1978).Peeled fruit, devoid of adhering albedo, is usually marketed fresh and unpreserved. The shelf-life of such products is 17–21 days, providing it is kept properly refrigerated and packaged (Baker and Bruemmer, 1989). In addition to off-ﬂavor generation and microbial deterioration, another factor which may limit acceptable shelf-life of dry packaged grapefruit segments is ﬂuid leakage. Separatedsegments, and to a lesser extent whole fruit, may undergo excessive loss of ﬂuid from mature late season fruit. In excess amounts such ﬂuid would detract from product appearance and consumer acceptability. If leakage is extreme, segments may lose turgor and appear ﬂaccid, further detracting from consumer acceptance. A potential means to control such leakage is through the use of edible coatings (Baldwinet al., 1995a, b). Attempts have been made to control leakage from grapefruit segments with edible coatings of calcium alginate, with varying levels of calcium hardener. The coatings effectively enhanced ﬁrmness of segments, but effects on ﬂuid loss were negligible. An 89% increase in tissue ﬁrmness was accompanied by only 16% decrease in ﬂuid loss (Baker and Bruemmer, 1989). Cross-linking ofstructural pectins with calcium was apparently insufﬁcient to impede migration of juice vesicle liquids, and the hydrophilic alginate coating did not provide an adequate barrier to ﬂuid movement. Many conventional edible coatings contain shellac, but preliminary experiments indicated they did not adhere adequately to segment surfaces, or developed chalkiness from exposure to moisture. However, wax...