Effect of gamma radiation on water extractable protein content and physical properties of concentrated latex and vulcanized rubber film

Abstract

To study the effect of gamma radiation on water extractable proteins (WEP) in natural rubber latex and physical properties of concentrated latex and radiation vulcanized rubber film. The fresh field latex (FFL) used is free from of tetramethyl thiuram disulphide and zinc oxide and collected from Rayong province during 2001-2003. WEP content in FFL shows seasonal variation 70-20 mg/g rubber parallel to %DRC, which starts at 40% at the beginning of tapping season (May-October) and decreases to 30% towards the end of tapping season (November-January). The WEP can be reduced about 90% by centrifugation, and the concentrated latex (CL) 60% obtained shows seasonal variation in similar pattern as FFL starting about 5 mg/g rubber at the beginning of tapping season, and 1-2 mg/g at the end of tapping season. Irradiation of FFL at low dose of 1-10 kGy resulted in disintegration of water-soluble latex proteins, increased small peptides and easy for removal by leaching of rubber film, whereas high doses 40- 120 kGy resulted in disintegration of insoluble protein and consequently increasing amount of WEP greater than in non-irradiated FFL. Hence, deproteinized CL (DPCL) by Alcalase enzyme which had WEP 82 ± 28 µg/g rubber, nitrogen content < 0.09% and MST lower than 200 sec was therefore used for irradiated at 10 kGy. It was found that WEP still increased to 373 ± 72 µg/g rubber and MST could not be increased. The better approach was alginate addition to interact with protein and creaming of latex to improve recovery yield of concentrated latex 60%. WEP of alginate added CL (AGCL) was lower than 300 µg/g rubber and physical properties meets with ISO 2004 specification except magnesium content and nitrogen content was < 0.20%. Irradiation of AGCL at 10 kGy on days 17-150 after centrifugation could slightly increase MST, but not higher than 1200 sec. WEP extracted from radiation vulcanized rubber film (RVRF) was lower than 300 ug/g rubber. After leaching RVRF with distilled water at the ratio 1 g rubber to 10 ml at 70°c for 30 minutes, WEP was lower than 50 µg/g rubber and free from major allergen proteins molecular weight (MW) range 14-45 kDa. It was confirmed by skin prick test that shows the negative results in 2 volunteers who shows positive test with commercial standard allergen. The radiation vulcanized rubber film from CCL, DPCL and AGCL at thickness 0.2-0.3 mm had all physical properties comparable to commercial dental rubber dam.