TEA SEED OIL Tea seeds are used as a source of supplementary protein and edible oil for human consumption, apart from many other industrial applications. The prospects of tea seed oil are immense. It can be a substitute for any edible oil; it can also be used as a cheaper alternative to olive oil which is mostly imported. The cosmetic industry may use it for manufacturing hair lotion, soap etc. The thiosaponin has some medicinal value. It acts as an adjuvant, anti-inflammatory agent. Tea oil cake and waste are used as fodder and bio-manuring.

OTHER PRODUCTS FROM TEA

INSTANT TEA People are accustomed to seeing and using different kinds of instant coffee, but the development of instant teas has lagged far behind that of instant coffee market. In the case of instant tea, the liquor (tea brew) itself is further concentrated and dried to form a powdered or granular product. Hot water soluble and cold water soluble instant teas, are found in the market. The process of the production of instant tea consists of the following operations, selection of raw materials, extraction, aroma stripping, cream processing, concentration and drying.

Criteria for the selection of the raw material include processing requirements of the market for which the tea is intended and the commercial restrictions placed upon manufacture. Instant tea can be made from black tea leaf, (partially) fermented, undried leaf, oolong or green tea. Manufacturers in tea producing countries use fermented undried leaf as a basis for instant black tea production, as this does not have to pass through the auctions and is therefore cheaper.

As per the final user of the instant tea the demand for the type of instant tea varies as hot water soluble, cold water soluble and green instant teas.

EXTRACTION Commercial extraction techniques are designed to optimize two parameters; yield of the solids extracted from the leaf and concentration of extract solution. Counter - current extraction is commonly used as a suitable technique to achieve these targets and is used in both batch and continuous forms. In a typical continuous counter - current extraction process tea leaves are fed into the lower end of the extractor and are conveyed upwards by the rotation of the screw while the extracting water flows in the reverse direction. The screws are perforated to allow water to flow more easily through the body of the tea and temperature of the extractor is controlled by the series of heaters on the body of the unit. Particle size of the leaf has to be carefully controlled to avoid too many fine particles which may pack together causing channeling or overflow of the water.

Yield of solids from the extraction system is commonly between 25 and 35% use of hydrogen peroxide, ammonia or ammonium carbonate, extraction at reduced pH 2.0 - 3.0. Use of enzymes such as tannase have been found to increase the yields up to 42% solids.

AROMA STRIPPING As tea aroma is an important criteria for the acceptability of tea, considerable efforts have been made to preserve the aroma in the instant tea product. Most process deal with the problem by stripping the aroma of the extract before concentrating and treating it separately.

The aroma is removed by either passing the stripping gas through extract or spraying extract into a moving stream of gas. The aroma is not condensed but is immediately added back to material which has already been concentrated. The use of inert gas is considered advantageous as it prevents the oxidation and hence deterioration of the aroma.

TEA CREAM PROCESSING When a solution of tea cools down it becomes opaque and changes color to pale brown due to a phenomenon known as 'creaming'. The cream essentially consists of caffeine, theaflavins and thearubigins and teas can be characterized by the amount of cream formed on cooling.

In the manufacture of instant tea, tea cream is processed either by maintaining the temperature above 65° C or by removal by cooling and precipitation or centrifugation. Since tea cream contains many flavor compounds removal by precipitation decreases the quality of the tea and incidentally, decreases the yield of solids from the leaf, so solubilisation by maintaining the temperature is a preferred method.

Cold soluble tea, is required to be clear and bright when reconstituted and the cream causes an unacceptable haze, hence solubilisation of the cream is crucial. The cream is separated from tea extract and is oxidized at 70° C at a pH of 9 - 10 with molecular oxygen. Use of enzyme tannase has also been documented in dissolving the tea cream. Cold soluble teas are produced by allowing the tannins in the cream to react with an aqueous solution of natural plant catechins extracted from other plants such as green tea.

CONCENTRATION The liquor from the extraction process is too dilute to pass directly to a drier. It is uneconomic to dry from such low solids but the powder produced by both spray and freeze drying is of such low density. The liquor has to be concentrated to 20 - 40 % solids before drying.

Historically concentration was carried out by evaporation under reduced pressure. Tea extract is easily damaged by exposure to high temperatures during concentration and drying. Most manufacturers supply units which separate the volatiles and condense them prior to addition back into concentrate before drying.

Techniques such as reverse osmosis and freeze concentration have also been documented.

DRYING Drum spray and freeze drying have all been proposed for instant tea, but spray drying is most commonly employed because it is cheaper in terms of both capital and running costs. Spray dried tea is rarely agglomerated and the most important criteria for the product are; taste, color, bulk density and moisture content.

The bulk density is controlled by changing the solids concentration of the feed stock and by careful choice of atomizing system.

Developments in the drying technologies have allowed the ratio of inlet to outlet temperature to change from 185° C / 95° C to 240° C / 70° C. This still allows the powder to experience no more than 70 C (decreasing the risk of flavor loss) and yet be dried within a few seconds to a moisture content of less than 5%. Moisture content of spray dried tea is generally between 3 and 5%.