Waste Volume Solid Waste
Product (m3/U) BOD (kg/U) (kg/t product)
Apricots 29.0 15.0
Apples 90
All products 3.7 5.0
All except juice 5.4 6.4
Juice 2.9 2.0 Cranberries 5.8 2.8 10 Citrus 10.0 3.2 Sweet cherries 7.8 9.6 Sour cherries 12.0 17.0 Bing cherries 20.0 22.0 Dried fruit 13.0 12.0 Grapefruit Canned 72.0 11.0 Pressed 1.6 1.9 Olives 38.0 44.0 20 Peaches 180 Canned 13.0 14.0 Frozen 5.4 12.0 200 Pears 12.0 21.0 Pineapples 13.0 10.0 Plums 5.0 4.1 Raisins 2.8 6.0 Strawberries 13.0 5.3 60 Source: Anon, 1998.
economic and environmental benefits. The target loads per unit of production are shown in Table 10.2 (Anon, 1998). The data refer to the waste loads aris- ing from the production processes before the imple- mentation of pollution control measures. These levels are derived from the average loads recorded in a major study of the industry and should be used as maximum levels of unit pollution in the design of new plants.
By-product Treatment and
Utilization in the Case of Certain
Fruit-based Products
The processing of fruits produces two types of waste: solid waste [e.g., peel/skin (Larrauri et al., 1997; Negi et al., 2003; Fern´andez et al., 2004), seeds (Noguchi and Tanaka, 2004), and stones (Lussier et al., 1994)] and liquid waste [juice (Gil et al., 2000) and wash water]. A serious waste disposal problem can attract flies and rats in the processing room, if not corrected properly. If there is no plan to use the waste products, they should be buried or fed to animals in distant locations.
Solid Fruit Wastes
There are possible ways to use some solid fruit wastes, which are discussed below. However, it is stressed that a full financial evaluation should be done before the implementation of any of the suggestions. One major goal in using fruit wastes is to ensure a reasonable microbiological quality in them. This means that one should process waste products on the same day that they become available. It is not ad- visable to store wastes until the end of the week’s production before processing them. Even with this precaution, the wastes being used will most likely contain moldy fruit (discarded during processing), insects, leaves, stems, soils, etc. This will contami- nate any products derived from such wastes.
Therefore, some preliminary separation is needed during processing, such as
r peel and waste pulp in one bin
r moldy parts, leaves, soil, etc in a second bin, which may be discarded
10 Fruit Processing Waste Management 177 Possible Products
The six main products from wastes include r candied peel
r oils r pectin
r re-formed fruit pieces r enzymes
r wine/vinegar
Each is discussed below.
Candied Peel. Peel from citrus fruits (orange, lemon, and grapefruit) can be candied for use in, for example, baked goods and snack food. In addition, shreds of peel are used in marmalades, similar to the process of candying. That is, boil the slices or shreds of peel in a 20%-sugar syrup for 15–21 min and progressively increase the sugar concentration in the syrup to 65–70 Brix (percentage of sugar moni- tored by a refractometer) during soaking of the food for 4–5 days. It is then removed, rinsed, and given a final drying in the sun or in the hot air drier. This can serve as a secondary product for a fruit juice or jam processor. This assumes that a large food company is interested in buying the candied peel as an ingredient for their products. In one application, candied melon skin has been used to substitute for sultanas in baked goods and, in another, candied root vegetables have found a similar market.
Oils. The stones of some fruits (e.g., mango, apri- cot, and peach) contain appreciable quantities of oil or fat, some of which have specialized markets for culinary or perfumery/toiletry applications. Palm ker- nel oil is well known as a cooking and industrial oil. In addition, some seeds (e.g., grape, papaya, and pas- sion fruit) contain oil with a specialized market. Of course, for any commercial product in any country, the goal is to identify the import/export agents in- terested in such products. After that, the processor’s responsibility is to produce the oil to satisfy the cus- tomer in terms of sufficient quantity and stringent quality standards. Obviously, the manufacturer has to secure proper equipment to produce the oils at a reasonable cost.
The process involves grinding the seeds and nuts to release the oil without a significant rise in temper- ature, which would spoil their delicate flavors, with the exception of palm kernel oil. Generally, a powered hammer mill is needed for nut and kernels. A press is needed to extract the oil. Since the existing manual presses have not been tried for this application, a cer-
tain amount of experimentation is needed to establish oil yields and suitability of the equipment. Solvent extraction is not recommended for small-scale appli- cations. However, steam distillation of citrus peel oils is well established for small-scale operations.
The crude oil may be sold to be refined elsewhere, but it is likely that the producer is responsible for the initial refining.
Pectin. This is a gelling agent used in jams and some sweets and occurs in most fruits, ranging from a low to a high level. Commercially, pectin is extracted from citrus peel and apple pomace, the residue left af- ter apple juice has been removed. Other tropical fruits may contain high levels of pectin, passion fruit be- ing a notable example. The utilization of the “shells” remaining after pulp removal may permit pectin ex- traction.
In most developing countries, pectin is imported from Europe or United States. This may look like a good market or opportunity for processors in these countries to provide pectin locally to substitute for imports. However, there are major problems:
r In countries where this has been tried, it has not been possible to produce pectin at a cost lower than that for imported products.
r It is difficult to produce pectin powder on a small scale, although liquid pectin is possible.
r There are many types of pectin, each with specific properties suitable for a particular application. For example, pectin for jams as a preserve differs from that used in jam as an ingredient in baked goods.
Re-formed Fruit Pieces. Fruit pulp can be recov- ered and formed into fruit pieces. Although the pro- cess is relatively simple, the demand for this product is low. Therefore, a thorough evaluation of the poten- tial market is recommended before investing in the enterprise (Kilham, 1997).
The process involves preparing a concentrate by boiling the fruit pulp, followed by sterilization. Sugar may also be added. A gelling agent, sodium alginate, is then combined with the cooled pulp and then mixed with a strong solution of calcium chloride. All ingre- dients are safe for human consumption, being legal food additives in most countries. The calcium and the alginate combine to form a solid gel structure and the pulp can therefore be re-formed into fruit pieces. The most common way is to pour the mixture into fruit-shaped moulds and allow it to set.
It is also possible to allow drops of the fruit/alginate mixture to fall into a bath of calcium chloride solu- tion where they form small grains of re-formed fruit, which can be used in baked goods. Commercially, the most common product of this type is glaced cherries.
Enzymes. Commercially, the three most important enzymes from fruit are papain (from papaya), brome- lain (from pineapple), and ficin (from figs). Each is a protein-degrading enzyme used in such applications as meat tenderizers, and washing powders and is also used in leather tanning and beer brewing. However, it is unlikely to be economical to harvest these en- zymes from fruit processing waste. Currently, even the more efficient process of collecting enzymes from fresh whole fruit is no longer economical. Changes in both large-scale production with higher quality standards and use of biotechnology to produce “syn- thetic” enzymes mean that small-scale producers will be unlikely to compete effectively. In addition, there are proposals to phase out the use of these enzymes in food products in Europe and United States. Their market is therefore declining. Consequently, it is not cost effective to harvest enzymes from fruits process- ing waste.
Wine/Vinegar. Although products such as wine or vinegar should be produced from fresh, high-quality fruit juices in order to obtain high-quality products, it is technically feasible to produce them from both solid and liquid fruit wastes. Solid wastes should be shredded and then boiled for 20–30 min to extract the sugars from the fruit and to sterilize the liquid. Several batches of waste may be boiled in the same liquid to increase the sugar concentration. This is then filtered through boiled cloth to remove the solids and cooled in preparation for inoculation with yeast. Liq- uid wastes should be separated during production to ensure that fruit juice is kept separate from wash wa- ter. For example, the juice could be drained from a peeling/slicing table into a separate drum. The juice is then boiled for 10–15 min and treated as above.
The liquid is then inoculated with “wine” yeast and not bread or beer yeast and fermented in the normal way for wine production. This can then undergo the standard second fermentation to produce fruit vinegar.
In summary, each of the above uses of fruit waste requires
r a good knowledge of the potential market for the products and the quality standards required
r an assessment of the economics of production r a basic familiarity with the production technique r a reasonable capital investment in equipment r a fairly large amount of waste available to make
utilization or harvesting worthwhile
For small-scale operations, where reducing pollu- tion or increasing waste disposal is more important than process economics, the most likely solution is to use wastes as animal feeds.