About

Nicole Martin is an Assistant Research Professor in Dairy Foods Microbiology and the Director of the Milk Quality Improvement Program (MQIP) in the Department of Food Science at Cornell University. She also serves as the Director of the Cornell Dairy Foods Center (CDFC). Nicole grew up in the Southern Tier of New York State, where she developed a lifelong interest in dairy farming through work on a local dairy farm. She earned her BS, MS, and PhD degrees in Food Science from Cornell University, with minors in microbiology and animal science. In her professional role, Nicole oversees farm-to-consumer dairy microbiology research conducted through MQIP and collaborates closely with dairy industry stakeholders, including producers and processors. Her research focuses on the holistic approach to dairy product quality and safety, emphasizing that high-quality dairy products must start at the farm and be maintained throughout processing, distribution, and retail. She is particularly interested in the transmission of dairy-associated spoilage organisms from environmental niches into raw and processed dairy products, strategies to reduce or eliminate this transmission, the implications of spoilage organisms on finished products, and methods of detection. Nicole is actively involved in professional organizations such as the American Dairy Science Association (ADSA), where she was awarded the ADSA Foundation Scholar Award in Dairy Foods in 2019, and she currently serves as the chair of the ADSA Dairy Foods Division. She is also a section editor for the Journal of Dairy Science and a member of the International Association of Food Protection (IAFP) and the New York State Association of Food Protection (NYSAFP). Additionally, she contributes to Cornell Dairy Foods Extension programs by teaching courses related to fluid milk processing, yogurt and fermented dairy products, and membrane and evaporation technology.

Research topics

• Biology
• Environmental science
• Food science
• Machine Learning
• Computer Science
• Genetics
• Ecology
• Biotechnology
• Engineering
• Mathematics
• Operations management
• Environmental economics
• Statistics

Selected publications

• Preventive maintenance has limited effect on decreasing incidence of post pasteurization contamination in single-serve milk cartons

  Journal of Dairy Science · 2026-05-01

  articleOpen accessSenior author

  The microbial quality of fluid milk is improved via processing steps, such as pasteurization which reduces the overall microbial population of milk and in particular is effective against Gram-negative, heat sensitive bacteria. Therefore, the presence of Gram-negative bacteria, such as Pseudomonas, in properly pasteurized fluid milk is indicative of post pasteurization contamination (PPC). While several proposed routes of contamination have been suggested, one likely source is the filling equipment. Preventive maintenance (PM) is the routine upkeep of equipment, such of fillers, which includes the replacement of wearable rubber components (e.g gaskets, seal rings). If not regularly replaced, these components may form cracks and allow the establishment of bacterial niches that may not be addressed by regular cleaning and sanitation procedures. To understand the role of PM in reducing rates of PPC we conducted 3 total visits to 2 dairy processing facilities. At the facilities we collected all wearable rubber components replaced during PM as well as milk cartons produced pre-PM and post-PM. Milk cartons were stored at 6°C for 14 d to simulate mild temperature abuse, while components were enriched with brain heart infusion broth at 32°C for 24 h. All samples were streaked on standard methods agar and crystal violet tetrazolium agar for the assessment of PPC. Our results indicate that even when milk was free of PPC before entering the filler, PPC was still present in 26% - 64% of tested finished cartons. Additionally, we found that Gram-negative bacteria were present in 0% - 99% of wearable components from each of the 3 visits. Bacterial isolates taken from milk were most frequently identified as Pseudomonas and Microbacterium, while those taken from components were primarily Staphylococcus. Overall, we observed that PM did not reduce the rates of PPC, and the effectiveness of PM may have been influenced by employee behavior and standard practices at the processing facilities. Future studies should further investigate areas within filling equipment that may serve as bacterial niches for Gram-negative spoilage microorganisms.

  PublisherOA PDFDOI

• From sporeformers to sensory: Measures of bulk tank raw milk quality are affected by dairy farm characteristics and management practices

  Journal of Dairy Science · 2026-02-04

  articleOpen accessSenior author

  The microbial, chemical, and sensory quality of bulk tank raw milk affects the shelf life and quality of finished dairy products. Traditionally, raw milk quality is determined using total bacteria count (TBC) and SCC. Here, a longitudinal study was conducted over a 15-mo period with 100 conventional dairy farms enrolled, each sampled 6 times. The farms represented a variety of sizes, milking systems, and other farming practices. Samples were evaluated for 24 different quality parameters, covering both traditional (e.g., TBC, SCC, and chemical composition) and novel measures of quality (e.g., sensory defect evaluation, mesophilic spore counts [MSC], thermophilic spore counts [TSC], psychrotolerant spore counts [PSC], and butyric acid bacteria [BAB]). Overall, we collected 593 bulk tank raw milk samples and conducted microbial, physicochemical, and sensory analyses. Our results showed that New York State raw milk is of exceptional quality, with a mean and SD for total bacteria count of 3.52 ± 0.70 log cfu/mL and geometric mean for SCC of 133,000 cells/mL. Overall sensory scores were also high, with a mean and SD of 8.6 ± 1.4 on a 0.0 to 10.0 scale. The most common attribute was oxidized. For sporeformer levels, mean and SD were 0.61 ± 0.60 log cfu/mL, 0.32 ± 0.60 log cfu/mL, 1.70 ± 0.60 log MPN/L, and 2.22 ± 0.60 log MPN/L for MSC, TSC, PSC, and BAB, respectively. Alongside sample collection, a survey was administered to farm owners and herd managers to capture comprehensive data, including but not limited to farm characteristics, milking characteristics, and parlor practices. Random forest models were developed to identify factors that may be influential in affecting milk quality, specifically through sporeformers and sensory characteristics (overall sensory scores and presence of oxidative defects). For sporeformer levels, the models most commonly identified herd size along with factors associated with udder health and hygiene (predip usage, frequency of udder clipping or flaming, and the vacuum of the milking system) as variables of importance. For sensory parameters, herd size, time spent on pasture, and measures of milk composition, including overall butterfat, percentage of preformed fatty acids, and percentage of de novo fatty acids, were identified as variables of importance. Given the financial and time burden associated with quality testing, parameters must be carefully selected to maximize utility of data. Thus, correlation analysis between test results was performed to identify quality parameters that could signal issues in other parameters. Relationships of note included log TBC and log preliminary incubation count (r = 0.79), log MSC and log TSC (r = 0.71), as well as overall sensory score and proportion of oxidized samples (r = -0.77). Overall, our study provides information that establishes a baseline dataset that can be used by the dairy industry to evaluate incremental improvements in raw milk quality, to identify farming practices that have potential to impact finished products, and to support the selection of parameters that may be used for quality monitoring.

  PublisherDOI

• Assessment of drivers of Listeria environmental monitoring programs in small- and medium-sized dairy processing plants

  JDS Communications · 2025-03-18 · 2 citations

  articleOpen access

  <h2>Abstract</h2> Small- and medium-sized dairy processing plants (SMDPP) may face unique challenges, such as limited financial resources, when implementing <i>Listeria</i> environmental monitoring programs (EMP). To better understand what drives investment in <i>Listeria</i> EMP, 9 SMDPP, which had previously participated in an ∼1-yr longitudinal study focused on implementing <i>Listeria</i> EMP, completed a questionnaire regarding their EMP-associated costs. This questionnaire was used to obtain each plant's (1) self-reported product value (i.e., estimated total value of finished product [ETVFP] in a plant at any given time) and other EMP-associated costs (e.g., corrective action costs), as well as (2) perceived ability to control pathogens in their processing environment. Additionally, we used a predefined rubric to assess each SMDPP's commitment to their <i>Listeria</i> EMP; these data were used to obtain a "food safety culture score" out of 225 possible points. Overall, a wide range of total EMP investments ($1,186.96–$55,530.58) and food safety culture scores (56 out of 225 to 222 out of 225) were reported across plants. Linear regression analysis identified that predictor variables of plant size, overall environmental <i>Listeria</i> prevalence during the EMP implementation period, ETVFP, and food safety culture score were not significantly associated with the outcome of the total amount of money that plants spent on their <i>Listeria</i> EMP (i.e., their total EMP investment). Although small, our study suggests that SMDPP's financial investments in <i>Listeria</i> EMP may be influenced by other external factors or factors not related to food safety, such as owners' gut feelings, beliefs, and attitudes. To address this, we recommend that food safety training and educational programs for small and medium food businesses include coverage of food safety–related business risks.

  PublisherOA PDFDOI

• Variability of temperature exposure of dairy products during refrigerated e-commerce distribution and its impact on dairy quality

  Journal of Dairy Science · 2025-09-12 · 2 citations

  articleOpen accessSenior author

  E-commerce food distribution has grown drastically in recent years, a trend that was accelerated by the COVID-19 pandemic. The range of perishable products purchased through e-commerce as well as the distance over which these products travel to consumers has also increased considerably. Perishable goods are commonly available through various e-commerce channels (e.g., third-party grocery shopping and delivery, direct processor-to-consumer delivery, and overnight shipment via centralized distribution centers). These e-commerce distribution methods have grown to accommodate the increasing demand for grocery delivery, which can introduce the potential for temperature abuse of these perishable goods, possibly leading to premature spoilage and quality deterioration. To determine the effect of e-commerce distribution on the shelf life of dairy products, we assessed the variability of simulated and real e-commerce time-temperature profiles of fluid milk and Greek yogurt in 3 transportation channels: (1) direct-to-consumer, (2) distributor or business-to-consumer, and (3) business-to-business-to-consumer. To further identify how real dairy products ordered through business-to-business-to-consumer (e.g., grocery delivery to consumers from retail stores through a third party) channels, containers of 1.89 L (1/2 gal) of milk and 157 mL (5.3 oz) of Greek yogurt were delivered to customers from local retail chains, and temperatures were measured upon delivery. Finally, the temperature profiles measured during 1.89 L milk transportation were used to conduct microbial and sensory shelf-life testing on commercial containers of milk and were also incorporated into a previously developed computational model that predicts milk spoilage based on the initial concentration of primary groups of bacterial contaminants and other relevant conditions (e.g., storage temperature). Our time-temperature profile results showed that product temperature at the time of delivery ranged from 0.2°C to 10.1°C for the direct-to-consumer pathway, -0.9°C to 19.2°C for the business-to-consumer pathway, and 3.1°C to 18.3°C during the simulated business-to-business-to-consumer pathway. Average milk and yogurt arrival temperatures from real business-to-business-to-consumer deliveries were 7.2°C and 7.3°C, respectively, and ranged from 3.1 to 10.5°C and 3.4 to 12.7°C, respectively. Results from fluid milk shelf-life microbial testing and end of shelf-life sensory testing showed limited effect following simulated short-term temperature exposure from e-commerce conditions, although more data are needed. This is supported by our model, which also indicates that there are minimal changes to expected microbial spoilage of fluid milk at the end of shelf life. However, our models only predict microbial growth and not sensory quality, which has a larger effect on consumer acceptance and should be assessed in future studies. Overall, our study provides important information on the exposure of dairy products to temperature variability during e-commerce distribution, which can be used to further develop strategies for controlling and monitoring the cold chain.

  PublisherDOI

• Raw milk from individual teats with an optimal teat-end score has lower spore levels compared with teats with a suboptimal teat-end score

  JDS Communications · 2025-09-17

  articleOpen accessSenior author

  Udder health in dairy cows is routinely monitored (for example, through determination of SCC) to help identify and control mastitis and other infectious diseases. Another parameter used to both assess udder health and milking machine performance is the teat-end condition, typically assessed at the herd level using a 4-point scoring system. Recently, the teat-end score has been suggested as a factor associated with the levels of bacterial spores in raw milk. Spores of cold-tolerant sporeforming bacteria present in raw milk can survive pasteurization and contribute to the spoilage of fluid milk. Therefore, the objective of this study was to determine whether the condition of individual teat-ends (specifically, optimal versus suboptimal teat-end scores) affects the spore levels in raw milk obtained from these teats. A total of 102 raw milk samples were collected from 102 individual teats from cows on a single dairy farm, and tested for mesophilic spores, with 51 samples each from teats scored as either 1 (optimal) or 4 (suboptimal). A significantly lower mesophilic spore count was found in the raw milk samples collected from teats with a teat-end score of 1 compared with samples collected from teats with score of 4. The observed difference in mesophilic spore counts suggests that maintaining optimal teat-end condition through good udder health and milking machine management may help reduce spore levels in raw milk. Although the observed difference in mesophilic spore counts is expected to result in minimal improvement of fluid milk shelf-life and other quality parameters, interventions targeting teat-end status or farm management practices that aim to improve the same can still be an important incremental contributor to the overall improvement of these parameters as part of a comprehensive, multipronged approach to raw milk quality management.

  PublisherOA PDFDOI

• Non-spore-forming thermoduric bacteria vary considerably in thermal resistance in milk media between strains from the same genus

  Journal of Dairy Science · 2025-01-30 · 1 citations

  articleOpen accessSenior author

  Thermoduric bacteria, defined as those that survive temperatures considerably above their maximum growth temperature, are enumerated in milk using the laboratory pasteurization count (LPC) test. This test selects for bacteria that show limited cell count reductions under vat pasteurization conditions (i.e., 63°C for 30 min); however, this test has limitations. One limitation of the LPC is that the test selects for a broad group of thermoduric bacteria, many of which are not reported to survive HTST pasteurization, the most commonly used pasteurization method in the United States. There are 2 distinct groups of thermoduric bacteria that can affect milk quality if implicated in finished product: spore-forming and non-spore-forming. Contemporary studies have primarily focused on spore-forming bacteria, leaving a gap in research regarding non-spore-forming thermoduric bacteria. Therefore, the goals of this study were to (1) assemble a set of non-spore-forming thermoduric bacteria previously isolated from heat-treated dairy matrices and (2) use that set to identify one or more laboratory enumeration method(s) that select for thermoduric bacteria relevant to contemporary HTST-treated dairy products. To that end, a set of 38 isolates of non-spore-forming thermoduric bacteria were inoculated into skim milk broth and independently subjected to 4 different heat treatments (A: 63°C for 30 min, B: 65°C for 15 min, C: 68°C for 7 min, and D: 70°C for 5 min), followed by plating using 2 different media types (standard methods agar [SMA] and aerobic count Petrifilms [AC Petrifilms; Neogen, Lansing, MI]), each of which were incubated at 32°C and enumerated after 3 different incubation periods (24, 48, and 72 h). Results from each unique method were compared with the standard method (i.e., LPC test). Results indicate that AC Petrifilms overestimate cell count reductions for some genera, suggesting that AC Petrifilm may not be an appropriate medium for enumerating these genera. Heat treatment D (i.e., 70°C for 5 min) showed a trend for higher reduction in cell counts compared with heat treatment A (i.e., standard method) and 48 h incubation allowed enough time for bacterial recovery. Therefore, we propose the evaluation of heat treatment D (i.e., 70°C for 5 min), followed by plating with SMA and incubation of 48h at 32°C in future studies of naturally contaminated milk. Our results also suggest that there is considerable variability in thermal resistance among isolates of the same genus. These phenotypic differences may be driven by yet unknown genotypic features that should be further examined. Ultimately, this study provides an update to the existing knowledge of non-spore-forming thermoduric bacteria and future studies should focus on evaluating non-spore-forming thermoduric bacteria in naturally contaminated dairy products.

  PublisherDOI

• A fluid milk spoilage simulation framework reveals the need for spoilage intervention strategies that account for frequency of bacterial postpasteurization contamination

  Journal of Dairy Science · 2025-07-15 · 2 citations

  articleOpen access

  <h2>ABSTRACT</h2> Postpasteurization contamination (PPC) with gram-negative bacteria and the growth of spore-forming bacteria are major causes of fluid milk spoilage, typically leading to sensory defects when bacterial concentrations exceed 6 log₁₀ cfu/mL. Existing models focus on individual spoilage pathways, limiting their ability to capture the complexity of milk spoilage. To address this, we developed a simulation framework that simultaneously models the growth of both types of bacteria in high-temperature short-time pasteurized milk along a supply chain. Dairy processing plants were categorized into 3 groups based on shelf life of historical fluid milk: long, medium, and short shelf-life plants. We assumed varying initial PPC frequencies for each category, with ranges of 0% to 33% for long, 34% to 66% for medium, and 67% to 100% for short shelf-life plants. Shelf life, defined as when 25% of milk containers exceeded 6 log₁₀ cfu/mL, was predicted as 25, 12, and 8 d for long, medium, and short shelf-life plants, respectively. Our predictions aligned with observed bacterial growth in commercial milk stored at 6°C, with the percentage of milk containers exceeding 6 log₁₀ cfu/mL on d 14 falling within the fifth to 95th percentiles of simulated values. Sensitivity analysis identified key parameters influencing bacterial concentrations at shelf life d 7, 14, and 21 for long, medium, and short shelf-life plants, respectively, guiding intervention strategies. What-if scenario analysis revealed that effective intervention strategies to extend shelf life vary by plant categories. While interventions targeting spore-forming bacteria, such as microfiltration, bactofugation, and improved home storage conditions, extended the shelf life for long shelf-life milk by 3 to 5 d, PPC reduction extended shelf life by 5 and 4 d in medium and short shelf-life plants, respectively. This simulation framework provides a comprehensive spoilage prediction tool to support data-driven decision making for fluid milk processors.

  PublisherOA PDFDOI

• Diverse spore-forming bacterial populations in US organic raw milk are driven by climate region

  Journal of Dairy Science · 2025-03-03 · 1 citations

  articleOpen accessSenior author

  Spore-forming bacteria pose significant challenges to the dairy industry, as they are present at high levels in the natural environment and can cause finished product spoilage. To improve organic raw milk quality and minimize spoilage caused by spore-forming bacteria, we used a farm-to-table approach, by assessing the levels and diversity of various spore types through longitudinal studies of United States (US) organic dairy supplies, including (1) raw milk from 100 organic dairy farms, (2) raw milk intended for organic cheese production from 5 processing plants, (3) pasteurized milk from 5 processing plants, and (iv) dairy powders from 2 processing plants. Based on a total of 4,194 isolates characterized by either rpoB or 16S rRNA gene sequencing, Bacillus spp. dominated the aerobic spore-formers isolated from farm raw milk, pasteurized milk, and powders. Nonmetric multidimensional scaling revealed that aerobic spore-former populations in organic farm raw milk differ significantly between climate zones at genus, species, and allelic type levels. The anaerobic/facultative anaerobic spore-formers isolated from farm and cheese raw milk samples represented the orders Clostridiales and Bacillales. Evaluation of the gas produced by anaerobic/facultative anaerobic spore-forming bacteria isolates showed that gas production varied significantly between Clostridiales clades, and 1 Bacillales clade produced gas amounts that were not significantly different from most Clostridiales clades. Overall, our data indicate (1) a substantial diversity of aerobic and anaerobic spore-formers in US organic dairy supplies with predominant genera and species similar between organic and conventional dairy supplies as previously described; (2) both anaerobic and facultative anaerobic spore-formers found in organic raw milk produce gas; and (3) climate may affect aerobic spore-former diversity in farm raw milk.

  PublisherOA PDFDOI

• A Machine–Learning Approach Reveals That Bacterial Spore Levels in Organic Bulk Tank Milk are Dependent on Farm Characteristics and Meteorological Factors

  Journal of Food Protection · 2025-03-07 · 1 citations

  articleOpen accessSenior authorCorresponding

  • Spore levels and farm characteristics vary considerably by organic farms. • Cow number, certification year, and udder clipping show importance for spore levels. • The model represents an individualized approach to inform contamination risk. Bacterial spores in raw milk can lead to quality issues in milk and milk derived products. As these spores originate from farm environments, it is important to understand contributions of farm-level factors to spore levels. This study aimed to investigate the impact of farm management practices and meteorological factors on levels of different spore types in organic raw milk using machine learning models. Raw milk from certified organic dairy farms (n = 102) located across 11 states was collected 6 times over a year and tested for standard plate count, psychrotolerant spore count, mesophilic spore count, thermophilic spore count, and butyric acid bacteria. At each sampling date, a survey about farm management practices was collected and meteorological factors were obtained on the date of sampling as well as 1, 2, and 3 days prior. The dataset was stratified separately based on the use of a parlor for milking, number of years since organic certification, and pasture time into sub-datasets to address confounders. We constructed random forest regression models to predict log 10 mesophilic spore count, log 10 thermophilic spore count, and log 10 butyric acid bacteria most probable number as well as a random forest classification model to classify the presence of psychrotolerant spores in each raw milk sample. The summary statistics showed that spore levels vary considerably between certified organic farms but were only slightly higher than those from conventional farms in previous longitudinal studies. The variable importance plots from the models suggest that herd size, certification year, employee-related variables, clipping and flaming udders are important for the spore levels in organic raw milk. The small effects of these variables as shown in partial dependence plots suggest a need for individualized risk-based approach to manage spore levels. Incorporating novel data streams has the potential to enhance the performance of the model as a real-time monitoring tool.

  PublisherDOI

• Spore levels in bulk tank organic raw milk and whole milk powder are reduced by udder hair singeing

  JDS Communications · 2025-03-18 · 2 citations

  articleOpen accessSenior author

  <h2>Abstract</h2> Routine removal of udder hair through singeing or clipping is a farm management practice that is often used with the intention of reducing SCC and mastitis caused by environmental pathogens. Udder hair removal was also recently identified as a factor of importance for the level of bacterial spores in certified organic bulk tank raw milk. Sporeforming bacteria form resistant endospores, or spores, that allow the organisms to survive harsh environmental conditions, including high temperatures, low moisture, exposure to chemicals, and other conditions that would otherwise be lethal to the vegetative cell. Due to this resistance, spores that are present in raw milk can survive processing hurdles used in dairy product manufacturing, germinate into vegetative cells, and ultimately cause spoilage and quality deterioration in dairy products including fluid milk, cheese, and products using dairy powders as ingredients. Therefore, the aim of this study was to determine if udder hair removal through singeing reduces the concentration of bacterial spores in certified organic bulk tank raw milk. Four organic dairy farms that had not routinely removed udder hair were recruited, and bulk tank samples were collected before and after a singeing intervention on all lactating dairy cows contributing to the bulk tank. Raw milk samples, as well as whole milk powder manufactured from the raw milk collected before and after the intervention, were assessed for different groups of dairy relevant bacterial spores. A numerical reduction from before to after intervention was observed in the mean raw milk mesophilic spore count, thermophilic spore count, and butyric acid bacteria most probable number, whereas a numerical increase was observed in the mean raw milk total bacteria count and psychrotolerant spore most probable number, although none of these changes were significant. The mean mesophilic spore count and thermophilic spore count in whole milk powder manufactured from pre- and post-intervention raw milk was, however, significantly reduced from 2.46 to 1.58 log₁₀ cfu/g and 1.44 to 1.22 log₁₀ cfu/g, respectively. The results of our study indicate that udder hair removal may aid in reducing key populations of spores found in organic raw milk and resulting dairy powders manufactured from that raw milk, although the small sample size in our study likely affected the significance of our results. Future studies should further investigate the role of udder hair removal on a larger set of organic farms, as well as the downstream impact on spore levels in other manufactured dairy products.

  PublisherOA PDFDOI

Frequent coauthors

• Martin Wiedmann

  Cornell University

  66 shared

• Kathryn J. Boor

  33 shared

• David Kent

  18 shared

• Aljoša Trmčić

  Cornell University

  13 shared

• Dieter Stiers

  KU Leuven

  12 shared

• Rachel L. Evanowski

  Cornell University

  11 shared

• Sarah I. Murphy

  Cornell University

  11 shared

• Giacomo Vagni

  University of Essex

  9 shared

Education

• B.S., Food Science

  Cornell University

  2006

• M.S., Food Science

  Cornell University

  2011

• Ph.D., Food Science

  Cornell University

  2018

Awards & honors

• ADSA Foundation Scholar Award in Dairy Foods (2019)