No abstract

By choosing an appropriate adsorbent, the bitter principles (naringin and limonin) and titratable acids could be removed from grapefruit juice in varying combinations.For example, Amberlite XAD-7 removed about 63 : < naringin, 85 % limonin and 3 % titratable acids and Deacidite-FFIP removed about 20% naringin, 8 % limonin and 23 0 , ; titratable acids when contacted for 1 h with grapefruit juice at the rate of 20 g (dry wt) of adsorbent per litre of juice. Such treatments, applied consecutively, would eliminate excessive bitterness and acidity from juices containing up to 2 g naringin and 36 mg limonin litre-1 and with a total soluble so1ids:titratable acid ratio of > 6 . The adsorbents are readily available, may be used as supplied and can be reactivated simply and economically; some of them have already been approved for use with foods, and such approval seems possible for the others.

Cellulose acetate as flake or powder is an efficient and selective sorbent for removing the bitter principle limonin from orange juice. Treatment of orange juice serum with powder (10 g,'litre) removed 4 4 7 0 % of the limonin content in less than an hour, at the same time removing relatively negligible amounts of hesperidin and ascorbic acid. Similar amounts of limonin could be removed by agitating the whole juice with cellulose acetate flakes held in open mesh bags which allowed contact between the enclosed flakes and the juice. Other materials, including related carbohydrate derivatives and polymers, were tested but only cellulose acetate butyrate shared the unusual sorptive properties of cellulose acetate.

A method is presented for the determination of limonin, the bitter principle of oranges, based upon selective extraction and conversion to the dinitrophenylhydrazone, which is separated by thin‐layer chromatography for estimation by spectrophotometry. The method can be used as a routine procedure for the study of variations in the limonin content of oranges and processed juices. Some examples are given of its application to the study of the problem of bitterness in orange juice.

Polyamides are shown to be effective adsorbents for removal of the bitter principle, limonin, from pasteurised Washington Navel orange juice. The extent of limonin removal varies with different juices, but sufficient can be removed by one or two treatments to bring the concentration below the organoleptically detectable level. The commercial use of polyamides to prepare non‐bitter juices from Navel oranges is discussed.