Limonin orange

Poncirus trifoliata Rafin Gou Gi (Trifoliate orange) (fruit) Poncirin, limonin, imperatorin, bergapten, neohesperidin, citrifoliol, myrcene, camphene, gamma-terpinene.33 Treat gastric pain, constipation, and prolapse of the uterus or rectum. 

A number of other processes have become commonplace in the manufacture of fruit juices. For example, if oranges of the varieties Navel or Navellina are processed the juice becomes unpleasantly bitter because of the biochemical development of a glycoside, limonin. This substance can be partially or totally removed by the use of appropriate ion-exchange resins to yield a juice of acceptable taste. 

Fruit juices can be deacidified with a weak base anion-exchange resin. Removal of compounds which cause a bitter taste is a more popular application (26,27). It is accomplished with resins that have no ion-exchange fimctionality. In essence, they are similar to the copolymer intermediates used by resin manufacturers in the production of macroporous cation and anion exchangers. These products are called polymeric adsorbents. They are excellent for removal of limonin [1180-71-8] and naringin [1023647-2], the principal compounds responsible for bitterness in orange, lemon, and grapefruit juices. The adsorbents are regenerated with steam or alcohol. Decaffeination of coffee (qv) and tea (qv) is practiced with the same polymeric adsorbents (28). 

Table VIII. Limonin Content of Commercial Orange and Grapefruit Juices Throughout the Harvesting Season...

While most of the limonoids of Citrus have been isolated from seeds, several occur in detectable amounts in other parts of the fruit. Minor amounts of deacetylnomilin, nomilin, obacunone, de-acetylnomilinic acid and nomilinic acid were identified in extracts of navel orange peel (37). 17-Dehydrolimonoate A-ring lactone was isolated from peel and juice of navel oranges (38) and nomilin has been reported to occur in grapefruit juice and juice vesicles (39). The only Citrus limonoids known to be bitter are limonin, VI, XII, obacunoic acid and IX (3). 

The inverse relationship between limonin content and taste preference was confirmed in another study (41) using a stepwise multiple regression analysis of data from 60 samples of commercial frozen-concentrated orange juice (FCOJ) packed during two seasons. This and a latter report (42) concluded that limonin content was highly correlated with the flavor quality of the juice. 

Recently, a nonspecific enzyme capable of degrading the precursor was extracted from Navel orange albedo (63). Nicol and Chandler (63) used a proximate assay for the degrading enzyme that is, the substrate was not identified except as a limonin precursor. The crude extracts from albedo contained degradation activity that was concentrated by 40 to 60% saturation with (NH J SO. Instability of the enzyme prevented further purification. 

Pectinesterase and limonin D-ring lactonase are the only enzymes known to catalyze reactions that adversely affect the quality of citrus juices. Bruemmer et al. (64) listed other enzymes that have been detected in citrus juices and described some of the reactions that can occur in the juices. None of the reactions appear to noticeably affect the quality of commercial juices. Freshly extracted citrus juices contain esterase (EC 3.1.1.1) (65, 66) and phosphatase (EC 3.1.32) (66, 67) activities. Native substrates in orange juice for peroxidase... 

Several postharvest treatments to citrus fruits have been tested in an effort to improve the quality of the extracted juice. Bruemmer and Roe subjected citrus fruits to anaerobic conditions for periods of 20 to 32 hours at 32.2 to 43°C (228, 229). This treatment reduced the titratable acidity and increased the Brix-acid ratio by about 10%. The decrease in acidity was accompanied, however, by a 20-fold increase in ethanol (229). Since the soluble solids-acid ratio is a major criterion of citrus juice quality, this procedure, if perfected, could allow earlier harvesting of fruit and a more consistent supply of fruit during the processing season. Bitterness of products from navel oranges, lemons, and grapefruit is related to limonin content. A 3-hour treatment of fruit with 20 ul ethylene/1 of air lowered the limonin content, reduced bitterness, and the juice was judged more palatable than juice from untreated fruit (230). 

As previously discussed by Maier and co-workers (Chapter 4), in Navel, Shamouti and certain other orange cultivars, the presence of limonin, a bitter triterpenoid, causes many economic and organoleptic problems and greatly affects the taste quality of processed fruit. Limonin is also prevalent in the grapefruit but the intrinsic quality of this fruit is further complicated by the presence of naringin, a bitter flavanone neohesperidoside (Chapter 5). 

While our work on the RIA and EIA for limonin was in progress, a research group in Israel (35) reported on an immunoassay for estimating the orange juice content of commercial soft drinks and reconstituted juice. This is of great importance to the citrus industry since adulterated or improperly reconstituted products greatly affect the quality of the product and thus ultimately reflect upon citrus quality control credibility. 

Limonin and nomilin are two bitter limonoids present in citrus juices. Systematic organoleptic tests showed that the bitterness threshold is 6 ppm (5) for limonin, and 6 ppm (6) or 3 ppm (7) for nomilin. The bitterness due to limonin develops gradually in juices after extraction from certain varieties of oranges, grapefruit, lemon, Natsudaidai, mandarin and some other minor citrus such as Iyokan and Ponkan. This phenomenon is generally referred to as "delayed bitterness". 

Cellulose acetate jels and beads were used to effectively remove limonin below the bitterness threshold from citrus juies (43). The resins can be regenerated readily by washing with a small volume of warm water. The process has been used commercially in Australia in debittering bitter orange juices (47). 

Polystyrene-divinylbenzene cross-linked copolymer adsorbent resins removed effectively both limonin and naringin from citrus juices (44). Over 85% of limonin was adsorbed from about 50 bed volume juices of grapefruit, navel orange, lemon and tangerine. Up to 70% of naringin was also removed from grapefruit juice. 

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... 

Chandler, B.V. and Robertson, G.L. 1983. Effect of pectic enzymes on cloud stability and soluble limonin concentration in stored orange juice. J. Sci Food Agric. 34, 599-611. 

Limonoids (Tetranortriterpenoids) Quassinoids (Decanortriterpenoids) Pentanortriterpenoids Chemosystematic Studies Biological Activity Antifeedant Activity Medicinal and Antitumor Properties Limonin in Orange Juice References... 

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). 

Bitterness in navel orange juice (ef. Marsh, 1953) is due to the presence of limonin, which is not a flavonoid compound. 

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