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Pickling, broadly defined, is the use of brine, vinegar or a spicy solution to preserve and give a unique flavour to a food adaptable to the process. Numerous vegetables and fruits can be pickled not only to preserve them but also to modify their flavour. The categories of pickled products are many, the most common being those of cucumbers and other vegetables; fruits; nuts; relishes of all kinds; cured meats, fish and poultry; and such special products as pickled mushrooms and pickled cherries.
The pickling processes of particular interest in this monograph are the traditional methods used in some parts of China and Japan where elevated risks for oesophageal and gastric cancer have been observed. For example, an unusual variety of pickled vegetables is made in Linxian, China, by fermenting turnips, sweet potato leaves and other vegetables in water without salt or vinegar. Several special processes, with and without salt, are used in preparing certain types of Japanese and Korean vegetable products.
Traditionally, pickled vegetables are popular in some areas of China where there are high incidence rates of oesophageal cancer. Among the vegetables commonly prepared in this way are Chinese cabbage, turnip, soya bean, sweet potato, sesame, potherb mustard and others. They are prepared each autumn by chopping, washing and dipping briefly in boiling water the roots, stems and/or leaves, as appropriate, and cooling and packing the vegetables tightly in a large earthenware (ceramic) jar. The vegetables are covered with water, a heavy stone is placed on them and they are allowed to ferment for several weeks or months.
The leaves of takana (Brassica juncea L.), a popular cruciferous vegetable in Japan, are mainly processed by salting. The salted products are divided into two types. One is called shinzuke-takana, processed to contain 3 or 4% (w/w) salt in the final product. It has a pungent flavour owing to the presence of isothiocyanates, which are formed enzymatically from the corresponding glucosinolates during the salting process. In recent years, the product has been stored under refrigeration or frozen to retain the pungent flavour and its green appearance. The other product, furuzuke-takana, contains about 10% (w/w) salt. It is stored for over six months after the salting process, and during this time the salted materials undergo changes in volatile constituents and pigments; the final product has a characteristic flavour and amber colour. Other popular pickled products in Japan are nozawana-zuke and hiroshimana-zuke, produced by salting the fresh leaves of nozawana (Brassica campestris L var. rapa) and hiroshimana (B. campestris L. var.pekinensis) to achieve a salt concentration of 3–4% in the final products, similar to shinzuke-takana. The products are fermented at 3–12° C for five days .
Sunki, a pickle produced in Kiso district, Nagano Prefecture, from the leaves of green vegetables, is prepared without salt owing to lactic acid fermentation by lactobacilli contained in the ‘pickling seeds’. The pickling seeds generally used are dried sunki pickles produced in the previous year which contain several species of lactobacillus. The pickles are subsequently dried and preserved throughout the year. Some farmers make sunki from cooked leaves of otaki turnip, not only by adding dried sunki as the source of lactobacillus but also by adding wild fruits or berries.
Kimchi, spiced, lactic acid-fermented vegetables, are one of the commonest traditional side dishes in the daily meals of Koreans. They are prepared by salting Chinese cabbages and radishes, washing the salted vegetables in fresh water, adding spices and seasonings and then leaving the spiced vegetables to undergo a process of natural lactic acid fermentation The amount of salt used in the preparation of kimchi corresponds to about 10% of the weight of the fresh vegetables, and salting time usually ranges between 8 and 15 hours before washing The seasoning mixture used includes cayenne pepper, garlic, ginger and pickled seafood. Many kinds of microorganisms are involved in kimchi fermentation, the principal ones being Lactobacillus plantarum and L. brevis. Kimchi is usually prepared in the home; however, it is also now produced and distributed on a commercial basis in Japan and the USA.
In the USA and northern Europe, the manufacture of cucumber pickles consists of a cure measure of a 10% salt solution, during which fermentation by halophilic (salt-tolerant) bacteria takes place. The curing process takes from 28 to 42 days, and the salt prevents growth of spoilage organisms. When the curing process is completed, the product is placed in a more concentrated salt solution and stored until final processing, which includes immersion in water to remove the salt, the addition of vinegar and a final bath in water that contains calcium chloride, a firming agent and turmeric, a colour enhancer. To make sweet pickles a spiced sweet vinegar is added to the final soak. For dill pickles, the dill plant or its seeds are used as flavouring. The shelf-life of cucumber pickles is dependent upon the presence of preservatives and, when used, on pasteurization. Vinegar is the most commonly used preservative. Pickled vegetables are packed, for the most part, in sealed glass jars, usually under vacuum.
In China, pickled vegetables and juice are eaten either as such or cooked in a gruel During the summer, some of the juice is also consumed as a drink. In some families pickled vegetables are eaten daily for as many as 9–12 months in a year and are an important part of the diet.
In a survey in Japan in 1962–63, consumption of pickled vegetables more than 60 times a month was reported by 60 and 81% of the adult farm populations and 43 and 70% of the abult non-farm populations of Hiroshima and Miyagi prefectures, respectively . In a later survey, the dietary habits of Chinese residing in Japan were compared with those of native Japanese. Consumption of pickled vegetables three or more times a week was reported by 35% of 346 Chinese men and by 41% of 288 Chinese women interviewed and by 75% of 8071 Japanese men
and 78% of 9932 Japanese women The average daily per-caput ingestion of various salt-fermented vegetables in Japan was estimated to be about 37 g.