Agriculture Reference
In-Depth Information
then allowed to ferment in 10% brine for 24-96 h. During fermentation,
sugars in the bulbs are converted to lactic acid plus small amounts of acetic
acid and alcohol. The fermentation is controlled by adding small quantities of
lactic acid. A decrease in pH to < 4.6 in the bulbs within a few days prevents the
growth of botulism bacteria. The pickled bulbs are bottled in vinegar, possibly
darkened with caramel and pasteurized at 80°C. In Japan, bulbs of rakkyo are
similarly pickled in brine and then bottled in vinegar plus sugar to make sweet
pickle, or vinegar plus salt to make a sour pickle (Toyama and Wakamiya,
1990).
Onion waste processing
In Europe, 450,000 t of onion waste consisting of brown skins and outer fleshy
scales are produced annually from the industrial processing of onions. This
material is not suitable for animal fodder because of its strong taste and it also
carries the risk of spreading crop disease - for example, white rot (see Chapter
5). The waste may be transformable into a valuable source of pectic substances
and dietary fibre-rich, food-grade products (see Chapter 7, 'The Skin of Onion
Bulbs') using appropriate extraction and cooking techniques - for example,
extrusion cooking (Ng
et al.
, 1999).
