Development of natural rubber with low allergenic proteins by saponification process

Abstract

Protein allergens in natural rubber latex (NRL) and NRL products may cause life threatening allergenic hypersensitivity type 1 in hypersensitive users. The development of natural rubber with low allergenic proteins is thus the purpose of this study. Saponification is the method selected for deproteinization. Physical properties of saponified NR were studied at the level of raw rubber and vulcanized rubber by comparing with STR5L. Nitrogen content characteristics of protein allergens and allergenic response were compared between control and saponified rubber. The optimal conditions for saponification of field latex at 30%DRC resulted from using 5% KOH at 70 ํC for 3 h, then diluted to 15% DRC and coagulated by formic acid. The saponified rubber obtained has decreased nitrogen content 23% from control, but the ash content is higher than STR5L specification. Thus, saponification by using coagulated crumb rubber (C-NR) has been developed by soaking C-NR in 5% KOH at 70 ํC for 3 h. This new method can reduce KOH and wastewater during the process by recycling of alkali solution 7 cycles for ammoniated crumb rubber and 5 cycles for skim crumb rubber. Saponified skim rubber (SAP-SK), has better quality than saponified ammoniated crumb rubber (SAP-AL) and STR5L in lower nitrogen content, and more or less similar physical properties to STR5L except slightly high content of ash, volatile matter and too lower initial plasticity. Vulcanized SAP-NR shows a small decrease in 300% modulus comparing to its control NR. Nitrogen content and water extractable protein content in SAP-AL and SAP-SK are slightly decrease after saponification. Protein allergens pattern of SAP-NR is dominated by protein molecular weight of 45 kD when comparing to non-saponified rubber that have molecular weight in the range of 45-14.2 kD and lower. Enzyme allergosorbent test (EAST) was used to study the prevalence of latex allergy in 100 blood donors where 5% positive EAST was observed. Four out of six (4/6) health care workers with allergic history showed positive EAST to water extractable protein from normal skim rubber. There is no protein allergenic response of SAP-AL and SAP-SK determined by EAST in 5 persons with latex allergy and confirmed in one person by skin prick test. In conclusion, saponification can reduce the amount of and variety of protein allergens in SAP-AL and SAP-SK to the level, which are safe for high-risk allergic Thai people and healthy people.