Kinetic and Stability Studies of Pectin Methylesterase From Hot Peppers, (Capsicum frutescens L.)

A major concern of pepper sauce manufacturers is separation of sediments and layering of sauce after bottling. Separation is an undesirable production condition because consumers view this as a defect. Pectins play an important role in sauce processing since it influences the final consistency of the sauce, especially those having no additional stabilizers. Failures in pectin stability can sometimes be related to the presence of enzymes. Understanding how the pectin enzymes function during lactic acid fermentation of salted pepper mash is a necessary step in controlling the enzymatic activity, and thereby reducing production cost and the risk of having poor quality food product. In most cases, complete enzyme inactivation is the target. In the case of pepper products, there is very little information available in the literature on the effects of active enzymes on fermenting pepper mash quality or the characteristics of pectin methylesterase (PME) from hot pepper in terms of varied pectin substrate solutions, salt concentration, pH, and temperature optima. Tabasco peppers (Capsicum frutescens L.) plants were used in this study and were placed in a polyethylene covered greenhouse on the Louisiana State University Hill Farm Teaching Facility. The experiment included a micro-irrigation system with watering based on the seasonal temperatures. PME was extracted from mature red-ripe peppers and partially purified by weak anion-exchange and affinity chromatography. PME activity was spectrophotometrically assessed, absorbance read at 620 nm by measurement of methanol release through a colorimetric assay based on the condensation of aldehyde with MBTH under neutral conditions using citrus pectin as the substrate. Based on our SDS-PAGE results, two major bands were present at 22 kDa and 36 kDa. Our research revealed hot pepper PME K_M value was 0.23 ±0.05 mg/mL and the maximum rate (V_Max) was 48.1 ±3.1 nmoles methanol/min. The enzyme appears to be inactivated at concentrations of 8% (1.4 M) and above and lost most of its activity above pH 8.5. It exhibited 85% activity at 30°C and decline in activity at 50°C (65% activity) and higher. Our study of PME extracted from hot pepper will help characterize the enzyme further, to aid in addressing issues of the enzyme activity in the food industry.