Fruit waste utilisation
Practical Action
Oils
The stones of some fruits (eg. mango, apricot, peach) contain appreciable quantities of oil or fat,
some of which have specialised markets for culinary or perfumery/toiletry applications. Palm
kernel oil is well established as both a cooking and industrial oil. In addition, some seeds (eg.
grape, papaya and passion fruit) contain oil which has a very specialised market. The main
problems are to identify the import/export agents who would buy such products, producing the oil
in sufficient quantities for them, meeting their very stringent quality standards and finally,
obtaining the equipment needed to produce the oils at low cost.
The process in summary involves grinding the seeds/nuts to release the oil without a significant
rise in temperature which (with the exception of palm kernel oil) would spoil their delicate
flavours. Generally, a powered hammer mill is needed for nut/kernels. A press is needed to
extract the oil but, to our knowledge, the existing manual presses have not been tried in this
application and a certain amount of experimentation is needed to establish oil yields and
suitability of the equipment. Solvent extraction is not recommended for small-scale applications.
However, steam distillation of citrus peel oils is well established at a small-scale.
The crude oil may be sold for refining elsewhere, but it is likely that at least preliminary (or part)
refining would need to be carried out by the producer. At present, we know of no detailed
publications on the special refining requirements for these oils. It would seem necessary to
contact the end-user to determine the quality required.
It is also possible that the sale of seeds or stones to larger oil processors could generate additional
income for small-scale fruit processors. This should be explored.
Pectin
This is a gelling-agent used in jams and some sweets found to a greater or lesser extent in most
fruits. Commercially, pectin is extracted from citrus peel and apple pomace (the residue left after
apple juice has been removed). Some other tropical fruits contain high levels of pectin, passion
fruit being a notable example. The utilisation of the 'shells' remaining after pulp removal offers
possibilities for pectin extraction.
In most developing countries, pectin is imported from Europe or USA and superficially at least
there would seem to be a good market for supplying local fruit processors with pectin to substitute
for imports. However, there are major problems:
• In countries where this has been tried, it has not been possible to produce pectin at a cost
which is lower than the imported products.
• It is difficult to produce pectin powder on a small-scale although liquid pectin is possible.
• There is not one type of pectin but many types - each of which has specific properties that
make it suitable for its intended application (eg jam that is to be used in baked goods
requires a different type of pectin to normal jam sold in jars).
A detailed knowledge of pectin and its properties is needed to ensure that a producer is supplying
the right product.
However, in essence the process of pectin extraction is not too complex. The shredded fruit peel
or de-juiced pulp is soaked in hot water (60-70°C), or the hot water is re-circulated through the
material, and the pectin is extracted into the water (along with sugars and other fruit
components). This is continued, often passing the same water through several batches of
material, until the pectin concentration increases to around 5% (in larger industries the
concentration may be increased by vacuum evaporation).
The pectin is then precipitated as a gel from solution by adding one of a number of chemicals.
The most common are hexane or spirit alcohol which are then recovered by distillation and reused
(the % recovery and cost of this step are often the most critical in determining profitability). It is
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