Origin and general characterisation of the byproducts 1621 Fruit and vegetable juices

Juice production concerns a large variety of fruits and vegetables and generates annually around 5.5 million tonnes of solid waste and between 0.5 and 6 m3 of wastewater per tonne of raw material. The amount of solid waste depends strongly on the vegetable or fruit (from 5% for tomato to 75% for passion fruit) (Schieber et al., 2001) but represents an average of 30-50% of the raw material. Using enzymatic liquefaction can reduce the quantity of waste; however the degradation of cell wall material by enzymes decreases the added value of the by-product, by reducing the fibre content of the pulp.

The major solid waste is obtained by pressing of fruits or vegetables and solid-liquid separation. This 'pomace' can contain pulp, peels, seeds and stones. The further utilisation of pomace depends on the fruit or vegetable type. Pomace is generally used for extraction of valuable compounds and for production of foodstuffs. For instance, pectin can be found to a greater or lesser extent in most fruits and is, after extraction and purification (see Section 16.4.1), added as gelling agent in numerous food products (including jams, fillings, sweets, etc.). Pomace can also provide other food additives - such as dietary fibres (see Section 16.3.1), lactic acid, pigments, vinegar, natural sweeteners and cellulose (see Section 16.4.2) (Nawirska and Kwasniewska, 2005). Some tropical fruits contain protein-degrading enzymes (papain in papaya, or bromelain in pineapple) which are used as meat tenderisers or washing powders or used in beer brewing. Pharmaceuticals and phytochemicals are also produced, depending on the nature of the fruit or vegetable: essential oils and antioxidants (see Section 16.5.2) like fla-vanones are extracted from orange or citrus peels (Tomas-Barberan et al., 2004); the antioxidant lycopene, a bioactive terpenoid pigment, is extracted from tomato pomace (Al-Wandawi et al., 1985; Tomas-Barberan et al., 2004); polyphenols are extracted from apple pomace (Schieber et al., 2001). Some studies now deal with the combined recovery of dietary fibres and antioxidant compounds, to obtain antioxidant dietary fibres (Saura-Calixto,

1998; Schieber et al., 2003). Oil contained in the stones of some fruits (mango, apricot, peach) have culinary or cosmetics applications. The final solid waste is frequently used as animal feed, for composting or landfilling.

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