Location: Food Science Research
Project Number: 6070-41420-008-02-T
Project Type: Trust Fund Cooperative Agreement
Start Date: May 1, 2017
End Date: Aug 31, 2019
To determine whether the application of a brief blanching step (e.g. 176°C, 15 sec) will improve the safety of non-pasteurized pickled vegetable products (including refrigerated pickles) without having adverse impact on the texture and quality during the shelf life of the product.
Microbiological and heat transfer modeling approaches were previously used to determine how brief (15 seconds or longer) blanching treatments at temperatures around 176°F (80°C) could reduce the numbers of bacteria naturally present on pickling cucumbers. However, little or no work has been done to determine how this technique may impact product quality, or specifically how the process will reduce the numbers of vegetative bacterial pathogens (Escherichia coli, Salmonella, and Listeria). Cursory examination of cucumbers blanched by this process showed little or no apparent change in the quality of the fruit. The goals of this project include: 1) determining the die-off of bacterial pathogens that can be expected, and 2) if the blanching process reduces the shelf of products that are not further heat treated, such as refrigerated pickles. Pathogen die-off will be modeled using existing heat transfer and bacterial killing kinetics data adapted for E. coli, Salmonella and Listeria. The kinetics of pathogen die-off will be experimentally validated by blanching cucumbers inoculated with 5- strain cocktails of the pathogens, and plating on non-selective media to determine log reduction values. The effect of blanching on texture and quality (cure, color, etc.) will be determined by evaluating refrigerated pickles product made with blanched cucumbers with 1 or more time-temperature treatments, focusing on the established treatment (176°C, 15 sec). Fresh-cut cucumbers from multiple lots will be divided into two treatment groups - no treatment and brief blanching. Cucumber pieces (slices or spears) will be brined in a cover liquor that is typical of refrigerated pickles and stored at 4°C for 4 months. Samples will be analyzed immediately after processing and after 1, 2, 3, and 4 months storage. Raw cucumbers and cucumbers post-blanching will be subjected to microbiological analysis to confirm the reduction in microbial load due to the blanching procedure. A puncture test that has shown high correlation to texture quality attributes of crispness and crunchiness will be used to measure the firmness of cucumber mesocarp for at least 15 cucumber pieces per treatment per replicate at each timepoint during storage. Color and cured appearance will also be evaluated using the Hunterlab colorimeter and visual scales, respectively. Data will be analyzed using an analysis of variance to determine whether the blanching step influences the firmness, color, and cured appearance of refrigerated cucumber pickles during storage.