According to the agriculture census 2010-11, approximately three million tons of vegetables were grown on an area of 252,000 hectares.
This sounds impressive, but based on the population, current vegetable production is far less per person than that needed for a balanced diet; it is certainly not enough to meet the five-servings-a-day quota advocated by nutritionists. Unavailability of good quality seeds and inadequate market facilities are the main limitations hindering vegetable production and this is something we need to address urgently.
One group of vegetables that should be given priority status is the brassica which includes turnip, broccoli, swede, Indian mustard, radish, cabbage, cauliflower and black mustard. Brassicas are the oldest cultivated plants on this planet and are thought to have been grown for consumption at least 10,000 years ago. Generally they are temperate weather crops, growing at temperatures between four to 30°C, although they prefer a range of 14 to 21°C. Since Pakistan hosts temperate, tropical and sub-tropical areas, several regions are suited for vegetable, and in particular, for brassica production.
Brassica vegetables were used as herbal remedies for centuries before scientists identified the active compounds that give these vegetables their distinctive bitter taste and healing properties; these are nitrogen and sulphur containing compounds naturally present in brassica, called glucosinolates (GS). In the past few decades the importance of GS has increased due to their potential uses as crop protection and bio-fumigants in agriculture (GS is a natural mechanism for preventing insects from eating valuable leaves due to bitter taste) and most importantly as cancer prevention agents.
Though most brassica species contain a limited number of GS (generally fewer than 12) when these vegetables are chopped or chewed, the plant produces (or induces) them in greater concentrations. Distribution of GS varies between plant organs, with both quantitative and qualitative differences between roots, leaves, stems and seeds. For example, one gram of fresh broccoli sprouts may contain between 70-100 mmol GS which decreases gradually as the plant ages.
Plant age is therefore a major determinant of the quantitative or qualitative GS composition of plants. Several environmental factors such as soil fertility can affect GS levels and distribution among plant organs. Apart from GS, brassicas also contain other compounds beneficial for human health including vitamins, fibre and minerals.
Isothiocyanates, a by-product of GS are considered to be the most effective compounds against cancer. Among the isothiocyanates, a compound called sulforaphane, which is present in high concentrations in broccoli sprouts, is believed to contain curative properties against colon tumours, breast and prostate cancers and to some extent it may also inhibit stomach cancer.
Many research studies in the last 20 years have indicated that eating raw brassicas can be beneficial in the case of several types of cancers, including colon, bladder, breast, prostate and lung cancer. It is a well established fact that consumption of just two servings of brassica vegetables a day may result in a 50pc reduction in the relative risk of developing cancer. Fresh and uncooked vegetables have higher amounts of these anti-cancer compounds. When chewed, complex biochemical reactions involving the GS take place in the plant and result in formation of nitriles or isothiocyanates. Nitriles are mostly produced when brassicas are eaten raw, whilst isothiocyanates result when vegetables are gently cooked. However, extensive cooking, prolonged storage and freezing of brassicas may result in the complete deterioration of GS and loss of possible health benefits.
The results of all these biomedical and epidemiological research studies are compelling. Therefore, farmers should be encouraged to allocate a greater area to vegetable production and initiatives by the government to subsidise seed production should be developed.