Thermal Inactivation of Clostridium sporogenes PA 3679 in Low Acid Foods: Case Study of Maple Sap Concentrates

Abstract

Maple sap is a sterile liquid extracted from maple trees in early spring. However, it is rapidly contaminated during handling and processing. Typically, raw sap undergoes a reverse osmosis process for concentration; meanwhile, this operation also concentrates the microorganisms present in the sap. The enrichment of microorganisms affects the quality of the sap and its derived products remarkably. Consumption of concentrated maple sap as a novel natural soft drink has increased considerably in recent years, mainly in North America but also worldwide. Adequate processing is required in order to eliminate the microorganisms and stabilize the quality of the concentrated maple sap for further consumption. Thermal processing is a safe preservation technique; however, severe thermal processing may affect negatively the quality of the product for consumer acceptance. Therefore, it is important to evaluate the right thermal processing parameters such as D- and Z-values for a given product. Spores of Clostridium sporogenes PA 3679 strain were used as a surrogate to evaluate the thermal destruction kinetic parameters of spores in concentrated maple sap (10°Brix–30°Brix) over a range of temperatures (90°C–105°C). Obtained D-values varied from 6.57 to 0.35 min depending on the sap concentration and temperature with an average Z-value of 7.84 ± 0.42°C. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses indicate that the spore cortex and core break down first during conventional thermal treatment as a result of heat transfer from the external media to the spore interior. The results of this study can be used by maple sap industries to design and perform a safe thermal process for pasteurization and/or sterilization of concentrated sap. It could also serve as a benchmark in the development of advanced green technologies such as ohmic heating.