Abstract
One cause of destabilization of fresh natural rubber latex is growth of microorganisms. This is commonly controlled by use of ammonia (NH3) as a preservative. However, NH3 is highly volatile and exposure to its fume can lead to health hazards. Moreover, the evaporation of NH3 means that more NH3 must be added to maintain the concentration level needed for the preservation. Hence, this research aimed to explore use of pasteurization to control microbial growth in rubber latex before it is spun to be viscid latex. To prevent heat destabilization of rubber latex, the latex was adjusted to pH 10 using 20% by weight of potassium hydroxide (KOH) solution. Pasteurization (10-105 times) was done by immersing a plastic bottle containing 60 ml rubber latex in a hot water bath at (60˚C) for 15 minutes. Control of microbial growth was observed by measuring Volatile Fatty Acid (VFA) at different storage times (up to 13 hours) and comparing this result to the number of colonies using plate count method. It was found that pasteurization could decrease the number of microorganisms presenting in the latex initially. However, the number of microorganisms in the pasteurized latex increased with storage time. VFA was also observed to increase with time. The Dry Rubber Content (DRC) of rubber latex before pasteurization (DRC of 22.20-34.10) had no effect on efficiency pasteurization. However, the number of microorganism presenting in the rubber latex before pasteurization affected efficiency of pasteurization significantly. For instance, when the number of microorganism in rubber latex was so large that its VFA was above 0.08 (the VFA number accepted by Thai Industrial Standards Institute 506), the efficiency of pasteurization was poor. On the other hand, if the number of microorganism was small and VFA was below 0.08, pasteurization could efficiently preserve the latex at room temperature up to 13 hours.
