Location: Food Science and Market Quality and Handling Research Unit
2023 Annual Report
Objectives
1. Determine how food components influence pathogen die-off in acidic food products. Modeling pH and acid effects on pathogen reduction in ready-to-eat vegetable fermentations.
2. Determine how processing conditions influence survival of fungal spores, toxins and vegetative cells in fermented or acidified vegetables. Supporting research to reduce food waste by fermentation.
Approach
Objective 1: Determine how food components influence pathogen die-off in acidic food products.
Goal/hypothesis 1: Our hypothesis is that buffer capacity (BC) models can be used to link pH with acid accumulation and therefore log reduction times for bacterial pathogens in a binary (lactic and acetic) acid RTE vegetable fermentations. The goal is to develop methods for determining the safety of a variety of different RTE fermentations based on pH.
Experimental design overview:
1. BC modeling of pH and lactic and acetic acid concentrations in a brined vegetable medium. BC models for pH and acid concentration will be developed using the combined buffering of CJ (or other vegetable brines) with the buffering of added acids.
2. What are the typical acid mixtures produced by heterolactic LAB? It is important to know the ratio of lactic and acetic acids typical of low salt fermentations because the acids have different antimicrobial effects.
3. How do acid mixtures affect pathogen (STEC) die-off in vegetable brines? Determination of log reduction times based on protonated lactic acid and acetic acid mixtures in ACJ.
4. Can the BC of unfermented brines be used to accurately model pH changes in fermentations? BC models will be used to assess pH changes resulting from acid production by LAB in CJ brine and cucumber and cabbage fermentations.
5. Validation of BC models for estimating pathogen die-off in fermentation based on pH. Reduction of bacterial pathogens will be estimated based on pH of cucumber and cabbage fermentation brines and data compared to CJ and cabbage or cucumber fermentations.
0bjective 2: Determine how processing conditions influence survival of fungal spores, toxins and vegetative cells in fermented or acidified vegetables.
Goal/hypotheses: Discovery: Identify fungi that are present on spoiling cucumbers. Hypothesis 1: In addition to inhibition of bacterial pathogens (Objective 1) organic acids and pH will prevent growth or persistence of fungal cells and/or toxins in RTE vegetable fermentation brines. Hypothesis 2: LAB may produce acids and antifungal compounds active against fungal cells, and persistence of fungal toxins in fermentation brines may be reduced by LAB due to degradation or LAB binding. The goal is to develop recommendations for safe preservation of surplus vegetables by fermentation.
Experimental design overview:
1. What fungi are present on spoiling cucumbers? Identification of the fungi typically present on spoiling cucumbers.
2. Do LAB present in cucumber fermentation produce antifungal compounds? LAB strains will be screened for antifungal compounds
3. Do fungal cells and/or toxins persist during fermentation of CJ by LAB? Fungi and/or toxins will be inoculated into ACJ brines or cucumber fermentations to measure die-off during fermentation due to acid accumulation and possibly antifungal compounds produced by LAB.
Progress Report
Controlling pH is a critical factor in acid and acidified food safety. The goal of Objective 1 of the project plan is to develop methods for determining the safety of a variety of different acidic foods, including fermented vegetable products. Many fermented vegetable products are sold without thermal or other processing, relying on low pH (pH < 4.6) and acids produced by lactic acid bacteria to meet United States Food and Drug Administration standards, as specified in the Food Safety Modernization Act. Food ingredients can affect the ability of acids to lower the pH to varying degrees based on each ingredient’s buffer capacity. Therefore, a database containing quantitative data on the buffer capacity of food ingredients was developed along with database software.
Buffer models for over 50 ingredients have been generated and the data are available online for public use. Two software programs were developed. BufferCapacity3 is a user-friendly graphical windows program that can be used to generate buffer models for the database from ingredient titration curves. A second software program, IngredientDB, allows users to mix selected combinations of ingredients from the ingredient database and combine the ingredients with one or more acids commonly used in acidified foods or present in food fermentations. Together these software programs enable users to formulate acid and acidified food products in silico and predict the resulting pH. By changing ingredient or acid concentrations, users can determine the influence of individual ingredients on the product pH (and therefore safety), as well as determine the pH stability if changes in the ingredient concentrations occur. The results also include predictions of total buffering and the percentage of buffering contributed by each of the ingredients. Published validation studies have shown that most pH predictions in fermentations, the water phase of salad dressings formulations, and acidified food products with multiple added acids were within 0.1 pH units of measured values.
Predictions of pH changes that occur during vegetable fermentations or by addition of one or more acids to low acid fermentation brines were compared using the IngredientDB program. The results showed that the software can be used to link pH and multiple protonated acid concentrations (the antimicrobial form of fermentation acids), and therefore fermentation safety. Previously, only fermentations with a single acid such as cucumber pickle fermentations were able to link pH with safety. Buffer modeling enabled food safety predictions based on easily obtained pH measurements for mixed acid fermentations such as sauerkraut or kimchi. The data from these studies are currently being used internationally by researchers at the World Institute of Kimchi (Gwangju, South Korea) for research to help develop safety standards for kimchi, which is growing in popularity in the United States.
Manufacturers of acid and acidified foods, including member companies of the Association for Dressings and Sauces, as well as Pickle Packers International, have supported the development of buffer models and accompanying software to aid in product development, as well as meet federal safety standards. The United States Food and Drug Administration has expressed interest in using buffer modeling software to help develop science-based regulations for differentiating acid and acidified foods. The definition of these foods is important because acid and acidified foods are regulated differently (Code of Federal Regulations, 21 CFR, Part 114), and the current regulations lack clarity as to how ingredients may influence pH changes and regulatory decisions. Buffer modeling software may be useful for developing more precise standards by defining how ingredient concentrations affect pH.
Accomplishments
1. Software for pH prediction in acidic food products. ARS scientists in Raleigh, North Carolina, developed two user-friendly Microsoft Windows software programs and a database of food ingredient buffering to aid in the assurance of safety for acid and acidified foods. The pH of acidic food products is critical to food safety and regulated by the Food and Drug Administration (FDA). The software programs can be used to estimate pH from food ingredient mixtures prior to manufacture or measurements of the finished product pH. The first software program, BufferCapacity3, was used to generate a database with the buffering from over 50 ingredients common to salad dressings and pickled or fermented vegetable products to aid the pH predictions. The second program, IngredientDB, allows users to combine ingredients from the database and predict pH and pH stability of the final product ingredient mixtures. Published validation studies showed that pH predictions by IngredientDB were accurate. The software has had more than 50 downloads on the USDA download website, including downloads by university researchers and major United States and international food companies. These software programs can reduce product development costs and help select formulations that will likely meet FDA safety standards, reducing the amount of product testing that is needed to formulate products that will meet safety standards. The software and data from these studies benefits manufacturers of acid and acidified foods, including member companies of the Association for Dressings and Sauces, Pickle Packers International as well as FDA. Consumers ultimately benefit by the assurance of safety for a variety of acidic food products.
Review Publications
Breidt, F. 2023. BufferCapacity3 an interactive GUI program for modelling food ingredient buffering and pH. SoftwareX. 22:101351. https://doi.org/10.1016/j.softx.2023.101351.
Breidt, F., Skinner, C.R. 2022. Buffer models for pH and acid changes occurring in cucumber juice fermented with Lactiplantibacillus pentosus and Leuconostoc mesenteroides. Journal of Food Protection. 85(9):1273-1281. https://doi.org/10.4315/JFP-22-068.
Fragedakis, N., Skinner, C.R., Shriner, M., Ruinsky, M., Yang, S., Wine, R.P., Johnston, L., Breidt, F. 2023. Modeling the formulation pH of elderberry syrup with multiple weak acids. Journal of Food Science. 88:3373-3383. https://doi.org/10.1111/1750-3841.16664.
