Limonin bitterness

More recently Maier et al. (3) published a comprehensive review of the limonoid constituents of Citrus and the impact of limonin bitterness on juice quality. This paper summarizes the chemical, biochemical and juice quality aspects of limonoids in Citrus (and related genera) and presents relevant advances since previous reviews. 

Influence of Sweeteners on Bitterness. In model system studies, natural fruit juice sugars were observed to raise the limonin threshold (24). An expanded study of natural and artificial sweeteners (26) demonstrated that sucrose, neohesperidin dihydro-chalcone (NHD), hesperetin dihydrochalcone glucoside (HDG) and aspartylphenylalanine methyl ester (AP) all raise the limonin threshold. At low sweetness levels HDG was the most effective followed by AP and NHD. Sucrose was without effect up to the 2% level. At sweetness levels equivalent to 1% sucrose, HDG, AP and NHD raised the limonin threshold in water from 1.0 ppm to 3.2, 2.5 and 1.3 ppm, respectively. Because of its high sweetness intensity, the concentration of NHD (16 ppm) was considerably lower than HDG (80 ppm) and AP (90 ppm). At 3-10% sucrose sweetness equivalency, the effectiveness of NHD increased substantially, sucrose moderately and HDG slightly, while that of AP decreased. Therefore, the sweeteners HDG, AP and NHD can effectively suppress limonin bitterness at low concentrations. 

Hasegawa, S. Brewster, L. C. Maier, V. P. Use of limonoate dehydrogenase of Arthrobacter globiformis for the prevention or removal of limonin bitterness in citrus products. J. Food Sci., 1973, 38, 1153-1155. 

The intact fruits do not contain bitter limonin, but rather a nonbitter precursor, limonoate A-ring lactone (8). When juice is extracted, this nonbitter precursor is gradually converted to limonin under acidic conditions and the conversion is accelerated by the action of limonin D-ring lactone hydrolase, which has been isolated from citrus (9). The bitterness due to nomilin in juices most likely develops in a manner similar to that of limonin bitterness, but this has not yet been directly proven. However, the contribution of nomilin to juices is minor. It occurs mainly In grapefruit juices (4). 

Physical Removal During the past several years, significant progress has been made in the development of selective adsorption processes for removal of two bitter principles, limonin and naringin, from citrus juices. Adsorbents such as cellulose esters (43), cross-linked polystyrenes (44) and 6-cyclodextrins (45, 46) have been shown to reduce effectively the limonin bitterness in the juice. 

Creation of Transgenic Citms Free from Limonin Bitterness... 

Limonoid UDP-D>glucose transferase Limonin bitterness is a problem in juices extracted from early-season to mid-season winter fruit, but not a problem in juice extracted from the late season fruit. As the fruit ripens, the concentration of limonoate A-ring lactone (2) decreases (23,24). This natural limonin debittering process has been known for over a century, but the mechanism of this metabolism was not understood until the recent discovery that limonoid glucosides are present in mature fruit tissues and seeds. We observed that in navel orange the initial... 

Hasegawa, S., M. N. Patel, and R. C. Snyder, Reduction of limonin bitterness in navel orange juice serum with bacterial cells immobilized in acrylamide gel, J. Agric. Food Chem., 30, 509-511 (1982). 

Limonin bitterness is especially acute in juice obtained from short maturation time fruits such as navel oranges. Juices obtained from most of the other citrus crops, such as Valencia oranges, usually do not have the limonin bitterness problem, as the concentration of limonin has decreased sufficiently by the time the processing season starts. Juices from navel oranges, particularly early- to mid-season fruits, can contain over 30 ppm of limonin, which is well above the bitterness detection threshold of 6 ppm. Grapefruit also has significant levels of limonin, which vary from 10 ppm in the early season to 1 ppm or less in the late season. 

Hasegawa S., Maier V.P. Solutions to the limonin bitterness problem of citrus juices. Food Technology, 73-75 (1983). 

Amur corktree bark contains alkaloids composed mainly of berberine (0.6-2.5%), phellodendrine, magnoflorine, jatrorrhizine, candicine, andpalmatine limonin (bitter principle) obakunone, dictamnolide, y-sitosterol, P-sitosterol, 7-dehydrostigmasterol, stigmas-terol, and mncilage, and so on. 

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