Methods for Reducing Acidity in Citrus Fruit

PRO-GEN® (arsanilic acid or P-G) has been shown to reduce acidity of Florida grapefruit as effectively as lead arsenate. A series of experiments in the 1987-88 citrus fruit sea son reconfirmed that P-G was effective for this use with con centrations of 600-1500 ppm. P-G is water soluble. However, deliberate attempts to wash it off immediately following spray application reduced its effectiveness significantly, but did not completely eliminate the effect of P-G. Reduction of acidity of 'Hamlin' and 'Valencia' oranges occurred within 2-3 weeks following spraying with CITRUS 10 and triacontanol (TRIA). Both compounds effectively reduced acidity in oranges, but results were inconsistent. The advent of colder winter temperatures greatly reduced the effective ness of both chemicals. Chemical application by standard airblast sprayers and fixed-wing aircraft was effective. Neither compound was effective in reducing acidity of 'Marsh' grapefruit. Both are biological materials with no known to xicology problems. Both compounds were effective at very low concentrations, but CITRUS TEN (20 ml/100 gal or 52.8 ppm) required 3-4 sprays 2-4 days apart, while TRIA (1-5 ppb) required a single spray. Sales of grapefruit (Citrus paradisi MacFadyen) have long been aided by the use of the plant growth regulator (PGR) lead arsenate (LA) to reduce total fruit acids, thus improving fruit flavor as well as beneficially lengthening Florida Agricultural Experiment Stations Journal Series No. 9412. The authors acknowledge the technical help of Mr. Charles Welch. •Research Scientist III (Adjunct Professor). 2Superintendant, Crop Research and Development. Proc. Fla. State Hort. Soc. 101: 1988. the shipping season. However, the safe use of LA, as well as the entire inorganic arsenic group, is under special re view by the U.S. Environmental Protection Agency (EPA). LA is no longer being manufactured and sold for use on Florida grapefruit. A summary of the biological effects of arsenic on the environment was made by Fowler (3). A recent review on the use of arsenic on Florida grapefruit was made by Wilson (9). Pro-Gen® (arsanilic acid or P-G) has been found to be an effective substitute for LA (9, 10). This compound is sold commercially as a growth stimulant in animal feed and a request has been made to the EPA for its use on Florida grapefruit. It has 0.5 ppm food tolerances in chic ken and hog meat and 2.0 ppm in livers. These values are far in excess of any residues found on grapefruit (G. F. Fleming, Jr. Unpublished data). The compound is a syn thetic organic arsenical, and this class of compounds is con sidered to have much lower toxicity than inorganic arsenics (7). Marine fish and invertebrates which contain arsenic in the organic form (2) may often have total arsenic contents 500-1000 times higher than that reported following P-G treatments on grapefruit (G. F. Fleming, Jr. Unpublished data). Sales of certain orange (C. sinensis [L.] Osbeck) cultivars could also benefit from PGR's which would reduce fruit acidity in a manner similar to that which occurs for grape fruit. However, until recently, no PGR with an EPA clear ance was available for this purpose. Although arsenicals reduce the acidity of oranges, they do so excessively and are, therefore, illegal for this purpose in Florida. Newly tested natural products are now available which show promise for acidity reduction for some citrus cultivars. The first of these, CITRUS 10 (C 10 or BRIX PLUS), is a prod uct of Bio-Organics, Inc., Longwood, FL and has demon strated the ability to increase the ratio, and to some extent, increase °Brix of some citrus cultivars (8). It is also re ported to have beneficial PGR effects on other fruits, veg etables and grains (8). It is a safe natural product (8), is used at a very low concentration (20 ml of manufactured product/acre), but usually requires 3-4 sprays. Its active ingredient(s) are unknown. The product is sold commer cially in Florida and in a number of agricultural areas.