Citrus Juice Waste as a Potential Source of Dietary Fiber

In recent years, the annual production of citrus fruits has been about 4 million tons. Supply of these fruits is in excess of demand on the fresh fruit market, so about 750 thousand tons are used for canning and for juice processing. After juice extraction is completed, the amounts of peel and pulp refuse are almost equal to that of juice. Although this refuse can be used for live-stock, and provides the raw materials for vinegar, molases, orange flour and feed yeast, these are only limited uses. This study was carried out to obtain fundamental data with respect to development of new uses for pulp refuse. A summary of the results is shown below.1. Chemical analyses of the main composition of pulp refuse showed that crude protein, crude fat, crude fiber, ash and nitrogen free extract contents ranged from 8.0 to 19.8%, 4.6 to 12.3%, 9.4 to 16.0%, 2.5 to 5.3% and 48.1 to 71.5% by dry weight, respectively. More detailed fiber analyses showed that the refuse included 7.2-14.7% pectic substances, 6.5-10.0% cellulose and 1.3-2.8% hemicellulose, with their total content amounting to 15.9-26.0% by dry weight.2. Under the microscope the segment wall of Hassaku was found to have a honeycomb like structure. Such organization would serve to hold much water or oil.3. A soft white powder of washed, dried pulp refuse was made by copious washing with warm water and exposure to sunlight for 8hrs. at 35-40°C, and humidity above 80%. For each species tested, the pulp refuse yielded about 5% soft white powder.4. Washed, dried pulp refuse was composed of 6.3-12.3% crude protein, 1.5-8.7% crude fat, 25.2-30.9% crude fiber, 2.0-4.2% ash and 49.8-63.2% nitrogen free extract. It contained 12.3-37.5% pectic substances, 10.6-29.6% cellulose and 4.1-18.8% hemicellulose and the sum of these components accounted for 39.5-68.4% on the dry matter basis.5. Water or oil holding capacities were 9.7-15.1g/g or 5.8-9.3g/g, respectively. The settling volume of washed, dried pulp refuse prepared from Wase satsuma mandarin and from satsuma mandarin were 10.4ml/g and 10.3ml/g, respectively. When washed, dried pulp refuse was treated with cellulase, the water or oil holding capacities were increased.From these results, it was concluded that pulp refuse may be used as a source of dietary fiber.