Location: Dairy and Functional Foods Research
2018 Annual Report
Objectives
1: Integrate non-thermal milk processing technologies with replacing sodium with potassium during cheesemaking to determine the effects on quality traits, shelf-life, and bioactives of fresh high moisture cheeses, Queso Fresco and dry cottage cheese.
1.a: Characterize the effects of NTP, with and without heat, on the chemical, microbiological, and physical properties of milk.
1.b: Optimize cheesemaking protocols using NTP-modified milk.
1.c: Characterize the effects of NTP of cheesemilk and altering the Na-K levels on the chemical, microbiological, sensorial, functional, textural, rheological, and structural properties of aging low-sodium cheese.
2: Enable non-thermal milk processing technologies that alter protein-fat interactions on milk enriched with long-chained polyunsaturated fatty acids (PUFA) during cheesemaking to assess their impact on quality traits, shelf-life, and bioactives of fresh high-moisture cheeses, Queso Fresco and dry cottage cheese.
2.a: Characterize the chemical and physical properties of PUFA-enhanced fractions.
2.b: Characterize the effects of NTP, with and without heat, on the chemical, microbiological, and physical properties of PUFA-enhanced milk.
2.c: Characterize the effects of NTP of PUFA-enhanced cheesemilk on the chemical, microbiological, sensorial, functional, textural, rheological, and structural properties of aging cheese.
3: Integrate the impact of non-thermal milk processing on cheeses made in Objectives 1 and 2,with bioactive peptide formation during aging and in vitro digestion.
3.a: Characterize the effects of NTP on proteins and peptides in milk.
3.b: Characterize the effects of NTP on the formation of bioactive peptides in aging cheese and during in vitro digestion.
Approach
This study focuses on the incorporation of non-thermal processes (NTP) that use high pressure homogenization (microfluidization) or ultra-high frequencies (ultrasonication) in the manufacture of high-moisture cheeses with unique textures, such as Queso Fresco (QF) and dry curd cottage cheese (CC). A combination of treatments, including NTP with and without heat and homogenization will be used to modify cheesemilk for the manufacture of low sodium cheese in which different NaCl-KCl treatments will be applied to the curds before molding (QF) or packaging (CC). Modified milk fat fractions will be created and incorporated into the cheesemilk using the combination of treatments above and used to make QF and CC. All cheeses will be evaluated for compositional, physical, microbiological, functional, rheological, microstructural, and sensorial properties and profiles generated for lipid, proteins, and volatile compounds at intervals throughout aging. The effects of NTP on the release of bioactive peptides, such as casein phosphopeptides and peptides with antihypertensive or antimicrobial activities, from the proteins within the cheese matrix will be evaluated.
Progress Report
Research is progressing on all objectives, which are part of National Program 306– Quality and Utilization of Agricultural Products, Component I, Food. Progress on this project focuses on Problem Statement B - New Bioactive Ingredients and Health Promoting Foods and C - New and Improved Food Processing and Packaging Technologies.
The last phase of the microfluidization study was completed (Objective 1a), which examined the effects of microfluidization on ultra-high temperature (UHT) milk. Milk underwent UHT processing (137C for 2 seconds) before being microfluidized at the 4 treatments used in earlier phases (42C at 75 or 125 MPa and 54C at 125 or 170 MPa), and then characterized for key traits (microbial counts, fat droplet size, enzyme coagulation time/curd firmness, and milk/gel microstructure). Although the reduction in microbial counts and fat droplet size were similar to results from earlier phases, UHT milk failed to coagulate, even at 4X enzyme concentrations and 60 min holding times. The inability to form a gel removes UHT milk from future consideration in this project.
Optimization of operating parameters for the ultra-sonication system, the second of the two non-thermal processes to be explored in this project, was completed (Objective 1a). This is a novel continuous system with a configuration unlike anything reported in prior dairy research. Different pumping/heating systems were used to test flow rates from 0.04 to 30 gal/min. Models were generated to determine residence time and flow velocities through the ultrasonic processing cell. Flows greater that 0.2 gal/min resulted in very long processing times and were dropped from the study. A cumulative exposure time of 2 min was selected as it resulted in reductions in fat droplet size and fit processing time constraints. The characterization study was conducted using raw milk entering the ultrasonic cell at 42 or 54C at flow rates of 0.04, 0.08, or 0.12 gal/min; multiple passes were needed to obtain total exposures of 2 min (Objective 1a). Characterization results indicated that ultra-sonication did not alter milk composition, did not inactivate alkaline phosphatase, and did not reduce bacterial counts. Coagulation properties were altered based on cumulative exposure and inlet temperature. A lower inlet temperature (42C) resulted in gels up to 20% stronger when compared to controls, with little variation based on cumulative exposure. A higher inlet temperature (54C) affected gel strength based on total exposure time. Shorter exposure times resulted in gels up to 10% stronger, but longer exposure times resulted in decreases up to 50% of gel strength. Particle size data showed a continuous and controlled reduction in fat droplet sizes beginning with the largest particles. Correlating the curd firmness to particle size and exposure time will enhance the understanding of how specific fat droplet size affects milk gel matrix formation, which will help fine tune the cheesemaking process. The only drawback to ultra-sonication is a distinct off-aroma, the source of which is being investigated and may be possible to remove once identified.
Preliminary cheese trials using our standard cheesemaking protocol for Queso Fresco and NTP-modified milk (maximum exposure from microfluidizer and ultra-sonication) are currently underway (Objective 1b). This will identify cheese making parameters that are most affected when using NTP-modified milk. All results collected to date will then be evaluated to identify which milk samples will move forward to the next phase, 3-month aging of Queso Fresco. (Objective 1.c)
Development of a PUFA-enriched fraction is progressing (Objective 2a).
Development of a dairy-based PUFA-enriched fraction with concentrated levels of polyunsaturated fats (PUFAs), such as omega-3 and conjugated linoleic acid (CLAs), that are considered to be beneficial to human health, is progressing (Objective 2a). A modified, more efficient cold fractionation protocol using multi-stage centrifugation was developed that significantly shorten the time required to separate cream into different fractions of milk fat and can be used with fresh or frozen cream. One fraction contained nearly twice the amount of PUFA found in heavy cream; 0.17 g PUFA/100 g fat in cream compared to 0.31 g PUFA/100 g fat in fraction. Unfortunately, this PUFA-enhanced fraction is only 5% of the total sample rendering it impractical for large scale use in cheesemaking. However, this approach and the PUFA-enhanced fraction may have use in other small-batch, high-value applications, such as production of dietary supplements. As stated in our contingency plan for Objective 2b, we are currently confirming PUFA content in different commercial plant oils. When added to milk, the oils will increase the concentration of the omega-3 fatty acids and conjugated linoleic acids (CLAs) except for rumenic acid, which is the most biologically active of the CLAs and found only in animal fat. We also are evaluating different methodologies, including microfluidization and ultra-sonication, to stabilize the oils in milk (Objective 2.b).
Active participation in the ARS Grand Challenge - Dairy Production project, which objective is to “Develop genetic and management practices in the dairy industry for delivery of products that are nutrient dense and positively impact public health, but with a lower environmental impact.” Team members contributed their processing expertise to the development of the project and provided key input in designing the first working collaboration of the project. In this first study, six shipments of 154 milk samples were sent to Wyndmoor, Pennsylvania, for analyses; including proximate analysis on fresh samples and direct lactose analysis on frozen samples. One team member is on the database subcommittee and provided the proximate analysis data set (first to be completed) to help develop how meta data will be coded/organized and made available to users. Results from this project will enhance our understanding of the relationship between the environment (soil, plant, energy usage), farm (feed, animals, management), processing, and nutrition/wellness of dairy products in human health.
Accomplishments
1. Increased consumption of cheese and dairy products is driven by consumer demand for products that provide enhanced nutrition with new textures and flavors. ARS scientists at Wyndmoor, Pennsylvania, used the microfluidization technology that uses high pressures and shear to create nanoparticles and nanoemulsions, to homogenize milk. Milk fat droplet sizes were reduced 10-20 fold to ranges of 0.50 - 0.39 microns and the fat-protein interactions were altered to different degrees as pressure and temperature were varied. Conversion of the microfluidized milk samples to cheese curd indicated that at higher temperatures and pressure, the gels that formed ranged from those that were relatively weak, suitable as base ingredients for spreadable dairy foods or snacks, to firmer gels at lower temperatures and pressures, which would influence texture and mouthfeel. Implementation of microfluidization in milk processing will expand the number of textured dairy foods available to the consumer.
Review Publications
Tunick, M.H., Van Hekken, D.L. 2017. Fatty acid profiles of in vitro digested processed milk. Foods. 6:99.
Bucci, A.J., Van Hekken, D.L., Tunick, M.H., Renye Jr, J.A., Tomasula, P.M. 2018. The effects of microfluidization on the physical, microbial, chemical, and coagulation properties of milk. Journal of Dairy Science. 101:1-12.
Van Hekken, D.L., Tunick, M.H., Ren, D.X., Tomasula, P.M. 2017. Comparing the impact of homogenization and heat processing on the properties and in vitro digestion of milk from organic and conventional dairy herds. Journal of Dairy Science. 100:6042-6052.
