Press liquor from the dewatering of orange peel was used as a substrate for citric acid production. Of the three strains of Aspergillus niger examined, strain NRRL 599 produced the greatest amount of citric acid. The conditions favouring citric acid production were pH 5.0-6.2 in the presence of 40 ml kg-' methanol. Under these conditions 30 g of citric acid per kg of press liquor were produced, representing a yield of 630 g kg-' based on sugars consumed. The yield was further increased to 730 g kg-' by thermal pretreatment of the press liquor.

No abstract

Carotenoids were extracted from fresh orange peel with various solvents. Acetone was the most efficient of the solvents tested. Two successive extractions with acetone after an initial washing with either acetone or methanol were adequate to remove 89% of the total carotenoids. The extracts were concentrated, the carotenoids transferred to hexane and a crude pigment concentrate was obtained by hexane evaporation. Water washings prior to acetone extraction eliminated the solvent-solvent transfer to hexane. The extraction residue was used for pectin recovery. Carotenoid removal from the peel did not affect the yield and quality of the pectin.

Pectin was extracted from dry orange waste with nitric acid. A factorial experimental design was used and the effects of temperature, time and pH of extraction on pectin yield and 'jelly units', ie pectin yieldxviscosity of pectin solution were determined. Optimum conditions for pectin extraction are also discussed. According to ash and methoxyl content determinations the product can be classified as low ash and high methoxyl pectin. Its purity expressed as anhydrogalacturonic acid content varied from 68.5 to 75.0 YO.