Symptoms Of Maturity

• Tobacco is grown for the production of quality leaves which largely depends upon the stage of the leaf at which they are harvested.
• The sign of maturity and method of harvesting differ from type to type of tobacco.

However, the sign of maturity, in general, may be mentioned as

• Change in colour of leaves from normal green to yellowish,
• Thickening of leaves due to more starch accumulation in them,
• Accumulation of gummy substances on them
• Flowering of plants
• Brittleness of the leaves in flue-cured Virginia tobacco, nitrogenous constituents except alkaloids and water soluble acidity decreased and total sugars increased with reduction of chlorophyll content of leaves at maturity.
• Bulging of the interveinal portions of the leaf and appearance of the brown spot on the leaves are the signs of maturity.
• The harvesting based on visible symptoms may be erroneous. Therefore, an objective test paper (a modified starch iodide paper) has been developed by Sastry et al., in 1969 to determine the correct stage of maturity.
• When a drop of the leaf juice is placed on the strip of the moistened test paper, the paper turns green, colourless or retains its original blue colour depending upon stage as immature, mature or over mature respectively.
• Thus the leaves possessing all above signs are the matured ones which may be harvested but all of them do not mature at one time because of which the method of harvesting differs from type to type according to their prerequisite for quality.

• In general, there are two methods of harvesting in tobacco
• Priming
• Stalk cut method

• In case of priming the leaves are harvested as and when they are fully developed and matured.
• Priming is supposed to be the best method of harvesting as every leaf gets sufficient time and nutrients for its full development. If the plants are cut, the younger leaves get lesser time to grow and as a result they remain underdeveloped and immatured which ultimately affect the quality.
• Thus for the production of quality leaves priming is more appropriate method of harvesting, though it is more time consuming and expensive.

• In case of stalk cut, the plants consisting of all the leaves intact are cut from close to the ground.
• It is essential to see that the maximum number of leaves are matured so that the quality is assured.
• The leaves are not separated until 3-4 days.

• Leaf wise method : Only matured leaves showing full spangle development are picked and placed on the ground face down.
• Whole plant harvest : Whole plant is cut at bottom when almost all the leaves are matured and kept inverted at the same place for drying.
• Gugro method : Normally harvesting is done 3-4 weeks after topping but it again depends upon the type of finished products.

• Tobacco seed when stored at room temperature which often touches 40° C during summer, looses its viability in 2-3 years.
• But if properly stored in air tight containers at a temperature not exceeding 20° C, it keeps its viability for a fairly long time.

• During the fermentation and ageing which improves the odour and aroma of cured tobacco, several molds develop which not only deteriorate the quality of the tobacco but is often accompanied by undesirable aroma.
• It was also found that certain storage molds may produce harmful toxins.
• The most important storage disease is the black rot caused by Aspergillus niger although A. flavus, A. terreus and Penicillium brevicaule are also associated with it.
• In general, black rot does not occur in leaves that are regularly redried before packing. Infected leaves become rotted and dark coloured in contrast to orange-brown or yellow colour of the normal leaf.
• Entire leaf may not be affected. Often the decay occurs only on the tip end of the leaves, which overlap in packing.
• Affected leaves emit bad odour. Occurrence of black rot is influenced by excessive moisture content during fermentation.
• In addition to black rot, minor storage diseases such as white mold or mustiness (Streptomyces sp.), stock mold (Oospora nicotianae) and other molds like Mucor sp., Cladosporium sp., Aspergillus sp., were reported on air-cured and flue-cured tobacco.
• Recently propionic acid added at the rate of 0.4 or 0.8% w/v to cured tobacco stored at 25° C prevented mold growth for 166 days at 23% moisture content and 120 days at 32% moisture content.

• Tobacco waste is a rich source of industrially and pharmaceutically important by-products like nicotine sulphate, solanesol and organic acids.
• Viable process technologies are developed for isolating these useful chemicals.
• Nicotine sulphate can be used as an effective insecticide for the control of the two major tobacco pests S. litura and Heliothis and is being exported to several countries like Japan and UK. It is reported that solanesol is an important basic material for manufacturing cardiac drugs.
• Tobacco seedlings left over in the nursery are found to be a source of edible proteins of high purity (80%) and nutritive value. The yield per hectare of proteins is 182 kg. The protein was found virtually devoid of many tobacco constituents.