Papain production
Practical Action
After two or three months the fruits are ripe and should be removed from the tree. The ripe fruits
are edible but have little sale value due to their scarred appearance. However, ripe green papaya
skin does contain about 10% pectin (dry weight): the fruits could be processed to extract this.
Drying papaya latex
The method of drying is the main factor that determines the final quality of papain. Various
grades have been used since the enzyme has become an international commodity. Up until the
mid-1950s, Sri Lankan papain dominated the market, three grades were known:
1 - fine white powder;
2 - white oven-dried crumb, and
3 - dark sun-dried crumb.
Until the 1970s there were two grades:
1 - first or high grade oven-dried papain in powder or crumb form (usually creamy white in
colour);
2 - second or low grade sun dried brown papain in crumb form.
As a result of new processing techniques, papain has been reclassified into three groups since
1970:
1 - crude papain - ranging from first grade white down to second-grade brown.
2 - crude papain in flake or powder form - sometimes referred to as semi refined.
3 - spray-dried crude papain - in powder form, referred to as refined papain.
Sun-drying
Sun-drying gives the lowest quality of product, as there is considerable loss of enzyme activity
and the papain can easily turn brown. In many countries, however, sun-drying is still the most
common processing technique. The latex is simply spread on trays and left in the sun to dry.
Oven-drying
Papain driers can be of simple construction. In Sri Lanka they are generally simple outdoor
stoves. They are typically about one metre high and made of mud or clay bricks. Drying times
vary, but an approximate guide is 4-5 hours at a temperature of 35-40°C. Drying is complete
when the latex is crumbly and no longer sticky. A better quality product is obtained if the latex is
sieved before drying. The dried product should be kept in air-tight, light-proof containers (eg.
sealed clay pots or metal cans) and stored in a cool place. Metal containers should be lined with
polythene.
Spray-drying
Not possible at small-scale because considerable investment in equipment is required. However,
it is feasible to buy spray-dried papain for the small-scale processing of foods. Spray-dried
papain has a higher level of enzyme activity than other types of papain and is totally soluble in
water. Extreme care must be taken when handling this form of papain: it can cause allergies and
emphysema if inhaled. For this reason, spray-dried papain is often encapsulated in a gelatine
coat.
Enzyme activity
Whether papain is to be exploited commercially for an export market or for local food industry
use, it is important to be able to determine the level of enzyme activity, a process known as
assaying.
This can be carried out by, say, the National Standards office. Papain is used to hydrolyse (or
break down) proteins. Therefore, assays to measure papain activity are based on measuring a
product of the hydrolysis. There are two main methods of carrying out assays:
Method 1
This method relies on the ability of papain to clot milk. It is a low-cost method but is time
consuming. Furthermore, the absence of a standardised method of finding the clotting point,
combined with variations in the milk powder used, can introduce errors.
3