Manufacturing - Milk Powder - 1999


Effects of Standardization With Milk Powder on Yield and Quality of Full-Fat and Low-Fat Cheddar Cheese - Nana Y. Farkye, Cal Poly San Luis Obispo
Effect of Storage on Properties of Whole and Skim Milk Powders - Nana Y Farkye, Cal Poly San Luis Obispo
Properties of Milk Protein Concentrate for Cheesemaking - Nana Y. Farkye, Cal Poly San Luis Obispo
Evaluation of Concentrated and Dry Milk Ingredients—Dairy Ingredient Application Guide - Phillip S. Tong, Cal Poly San Luis Obispo
Survey of Sources of Spore Contamination in Milk Powder - Rafael Jiménez-Flores, Cal Poly San Luis Obispo
Development and Standardization of a PCR-Based Rapid Assay For Spore Count Determination in Powder Milk - Rafael Jiménez-Flores, Cal Poly San Luis Obispo
Reduction of Spore Loads in Milk Powder by Controlling Processing Parameters - Rafael Jiménez-Flores, Cal Poly San Luis Obispo
Developing a Highly Functional Long Shelf-Life Whole Milk Powder - Moshe Rosenberg, UC Davis
Dairy Powder and Concentrate Application Support Program - Phillip S. Tong, Cal Poly San Luis Obispo


Effects of Standardization With Milk Powder on Yield and Quality of Full-Fat and Low-Fat Cheddar Cheese


Nana Y. Farkye, Cal Poly San Luis Obispo


Standardization of cheese milk is important to produce cheese that meets the minimum legal standards of identity. Standardization also helps produce cheese of uniform composition and quality. Methods of standardization involve addition or removal of fat from milk as cream, addition of casein in the form of nonfat dry milk (NDM), skimmilk and condensed skimmilk. The method of standardization is economically driven—depending on the value of fat and casein in cheese or as dairy ingredients. Currently, it is economically advantageous to the cheesemaker and dairy producer to sell fat in cheese for use as cream or butter. Use of NDM in standardization is advantageous because it is readily available. Therefore, cheese plants that do not have a separator for cream removal or evaporators to condense milk can readily standardize cheese milk. Also, addition of NDM increases the total solids in the vat, thereby resulting in the production of more cheese per vat of standardized milk. However, a drawback for using NDM is its relatively high lactose content, which may lead to undesirable fermentations during storage and aging.

The purpose of this study is to compare the yield and manufacturing procedure of light Cheddar cheese produced from milk standardized by the addition of NDM or skim milk. A second objective of the study is to determine the maximum amount of NDM that can be used to standardize whole milk containing more than 4 percent fat and standardizing whole milk (containing ~ 3.5 percent fat) with nonfat dry milk (NDM) for lower-fat Cheddar cheese manufacture. For comparison, lower-fat Cheddar cheese was made from milk standardized with skim milk. The advantages of standardizing whole milk with NDM are high yields, increased plant efficiency and reduced manufacturing costs per unit weight of cheese manufactured. Our second objective is to compare the proteolysis of the cheeses obtained by both methods of standardization.

Results of this project show the following:
- That, standardization of cheese milk by addition of NDM is beneficial to cheesemaking. This is because milkfat can be sold in cheese instead of cream or butter when cheese prices are high.
- Standardization by NDM addition results in higher total solids in milk and enhanced yields. Therefore, more cheese is produced using the same amount of labor thereby increasing profitability of cheesemaking.
- Use of NDM increases the buffering capacity of cheese due to the high total solids and high casein content of the cheesemilk.
- Ripening of cheese made from milk standardized with NDM lagged behind that made from milk standardized with skimmilk.
- Drawback for using NDM is its high lactose content, thereby leaving large amounts of residual lactose in the cheese, which may lead to undesirable fermentation if ripening is not controlled.
- Good quality low-fat, reduced-fat or full-fat Cheddar cheese can be manufactured from whole milk standardized with NDM.


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Effect of Storage on Properties of Whole and Skim Milk Powders


Nana Y Farkye, Cal Poly San Luis Obispo


The objectives of this project were:
- To determine the effects of package type and storage on some physical and chemical properties of milk powder
- To measure the durability of milk powder bags

The bag durability study was conducted at the School of Packaging, Michigan State University. The storage study was conducted at Cal Poly San Luis Obispo’s Dairy Products Technology Center.

Bag Durability Study
This portion of the study was conducted at the Michigan State University (MSU), School of Packaging. Milk powder producers who participated in the study shipped several bags of milk powder to MSU for the bag durability test (butt-drop and side-drop tests). Bag styles tested were cap-sac (bag-in-bag) versus inner-ply (non bag-in-bag), liner types ranged from 1- to 4-mil polythene liners. Cap-sac bags performed better than inner-ply bags in both side-drop and butt-drop tests. Average failure height of cap-sac bags was about 29 inches for side-drop test and 36 inches for butt-drop tests. Average failure height for inner-ply bags was about 18 inches for both butt- and side-drop tests.

The performance level of the bag-in-bag (cap-sac) style was about 14 inches for the side-drop and 20 inches for the butt-drop. Performance level for inner-ply style bags was 12.5 and 13.5 inches, respectively, for side- and butt-drop tests.

Side-drops test a bag’s end closures and liner seal. Bags containing 3-mil liners performed better than those with 4-mil liners in the side-drop test, suggesting faulty top sealing of the bags after filling. Most of the failures in the side-drop test occurred at the end closed by the dairy. Such seal variation is commonly related to the seal temperature, pressure and well time. Contrarily, in the butt-drop test, which shows the strength of the side walls, the bags with 4-mil liners had a higher failure height (approx. 38 inches) than failure height of 34 inches for bags with 3-mil liners.

The Cap-sac (bag-within-a-bag) style performed best in both the butt- and side-drop tests because when the outer paper plies failed at a lower drop height, the plastic liner carried the product without damage through several higher drops. All of the Cap-sac bags performed above the USDA’s butt-drop test performance level (18 inches on the shock machine) specified for all government purchases. Bags with thicker, 4-mil, low-density polyethylene (LDPE) and 4-mil high-impact LDPE performed slightly better than the 3-mil high-impact LDPE.

Storage Study
Statistical analyses of data showed significant increase in moisture content, water activity (Aw), tritable acidity (TA) and solubility index of milk powder, while pH decreased during storage. Overall, whole milk powder (WMP) samples had higher Aw value and significantly higher solubility index during storage than skim milk powder (SMP). Onset of browning reaction (Aw of 0.3 - 0.45) coincided with the increase in Aw and noticeable browning with caking (especially SMP). Caking occurred as early as three and definitely by four months in most SMP samples. Lipid oxidation, as measured by peroxide value and free-fat content, increased in whole milk powder during storage. Changes that occurred in New Zealand milk powder samples purchased from different countries were similar to changes that occurred in domestic powder samples under similar storage conditions.

General linear models showed significant changes over time in moisture, pH, and T.A. values as influenced by sample source, package type (including liner) and storage time. The least changes occurred in samples stored in cans. Also, chemical changes in samples packaged in 4-mil liners were slightly lower than those packaged in 3-mil liners. Changes that occurred in powder samples stored at ambient temperature for 12 months were equivalent to storage for two to three months at 37oC and 90 percent relative humidity. Bonferroni Simulation Test and Kolmogorov-Smirnov Test for variability of package type showed that, in general, package-time interactions were more significantly correlated than sample-time interaction.


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Properties of Milk Protein Concentrate for Cheesemaking


Nana Y. Farkye, Cal Poly San Luis Obispo


The objective of this project is to characterize and determine properties of milk protein concentrate 65 (MPC65) and to standardize whole milk with MPC65 for lower fat Cheddar cheese manufacture.

MPC is a relatively new dairy ingredient. It is produced by membrane filtration of skimmilk followed by subsequent drying. Generally, MPC contains high levels of protein and calcium and low lactose content. Leading dairy countries such as New Zealand produce and market MPC. While many U.S. processors produce in-house and use liquid MPC, availability of dried MPC would be beneficial especially for manufacturing operations that do not have membrane filtration equipment. Currently only one U.S. manufacturer produces dried MPC. Characterization of the domestic MPC65 showed it contains 65 percent protein, 53.4 percent casein, 1.3 percent fat, 0.22 percent sodium and 1.91 percent calcium. It is similar in composition to New Zealand’s ALAPRO 4700, which contains 70 percent protein, 55.6 percent casein, 1.4 percent fat, 0.3 percent sodium and 2.2 percent calcium. We found the approximate ratios of alpha(s1 + s2), beta- and kappa-casein in MPC 65 to be 5.5:3.5:1.0 whereas that for ALAPRO 4700 was found to be 4.7:4.3:1.0.

Both proteins exhibited identical solubility, between pH 2.0 – 12.0 at 20°C. Minimal solubility (~20 percent) occurred at pH 5.0 with solubility increasing above or below pH 5.0 and reaching a maximum (~80 percent) at pH <3.0 or >9.0. When a 2 percent colloidal suspension of MPC was allowed to stand, some sedimentation occurred at the bottom of the container. Characterization of proteins in the insoluble sediment and those in solution revealed that the insoluble component was rich in as-casein, which is attributable to the high calcium content of MPC.

The chemical composition of MPC65 shows that it contains high protein, low lactose and high calcium. The casein-to-whey protein ratio in MPC is 80:20. The high calcium content of MPC causes the formation of sediments when a colloidal suspension of MPC is left to stand. The sediment is rich in as1-casein because of its sensitivity to calcium.


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Evaluation of Concentrated and Dry Milk Ingredients—Dairy Ingredient Application Guide


Phillip S. Tong, Cal Poly San Luis Obispo


The purpose of the Dairy Ingredient Application Guide is to provide product developers with a working knowledge of the various functional and sensory attributes of dairy ingredients and to assist product developers in formulating high-quality, wholesome foods using dairy ingredients. The formulas in the Application Guide were evaluated for quality and relevancy to the market.

Our research objectives were to:
- Evaluate the formulas in the Concentrated and Dry Milk Ingredients in the Dairy Ingredient Application Guide for flavor, appearance and texture to determine quality of the finished product.
- Identify the formulas in the Concentrated and Dry Milk Ingredients in the Dairy Ingredient Application Guide that should be improved or updated.

A total of 58 formulas were prepared and evaluated for flavor, appearance and texture. Following formula evaluations, recommendations were made that should increase the benefits of using this guide by product development personnel. Increased use of the guide will create more opportunities for dairy ingredients in new products.


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Survey of Sources of Spore Contamination in Milk Powder


Rafael Jiménez-Flores, Cal Poly San Luis Obispo


Bacillus spp. are commonly found in dehydrated foods, and have been isolated from milk powder. This bacteria has the particular characteristic of forming spores, which allow them to survive adverse environmental affects such as hot and dry conditions, extreme pH and disinfectants. Therefore, the bacteria can be found in the final stages of the processing of milk powder. Milk powder is used as an ingredient in the production of many foods, such as infant formulas, desserts and breads. Endospore-formers present in milk powder can survive processing conditions in many formulated foods, and thus, after germinating and growing they can be hazardous if ingested. Spores in milk powder pose concern in the dairy industry because they lower the quality of products. By the year 2000 the government will no longer purchase excess milk powder, therefore milk powder manufacturers will need to compete in the international market with Australia, New Zealand and Canada, which are recognized milk powder producers and exporters. Spores are present in silage fed to the cows, therefore their presence cannot be prevented in milk produced from silage-fed cows. Good manufacturing practices are not enough to guarantee low spore counts in milk powder, and more detailed data are necessary to establish procedures that would eventually minimize their presence in the end product.

The aim of this work was to find the main source of endospore-formers during milk powder processing, to characterize them, and to correlate their presence in milk with the plant and farm environment. An additional goal of this study was to establish the effect of seasonal change on the endospore-forming microorganism population.

To pursue these objectives a survey was conducted in three processing plants in the San Joaquin Valley, during summer 1997 and winter 1998. Raw, condensed and powdered milk samples were taken at the beginning, middle and end of each run, which varied from 24 to 36 hours, taking care that the samples represented the same lot of milk processed along the line. Air samples were taken with a portable air sampler every 12 hours at specific points in the processing areas. Mesophilic and thermophilic spore-formers were found in all stages of the milk powder manufacturing and in all of the air samples. Thermophiles predominated over mesophiles during the summer months, and mesophiles were greater during winter months. In some cases, the number of spores decreased during the evaporation process; however, spore counts increased again in the finished product. This increase in numbers occurred presumably after the condensed milk left the evaporator and the powder was collected at the packaging room. Counts are significant in powder manufacturing, since all the data is normalized to report spore counts per gram of solid. This suggests either a change in the physiology of spores as they change from the condensed milk environment to powder, or a point of contamination between the evaporator and the point of powder collection that was the filling room.

Activation of spores during processing and its presence in the samples may be due to long runs or deficiencies during sanitation of the equipment, such as the pump before the nozzle, or the filters in the air intake of the burners. In the environmental survey, air intakes of the dryers resulted in greater spore numbers compared to the rest of the analyzed rooms in the plant. This suggests that improper filtration of air into the dryer, may contribute to the spore load during processing. The spore-former species found in both air and milk samples corresponded to the genera Bacillus.

In conjunction with another project that uses biochemical, microbiological and molecular techniques for the identification and characterization of the microorganisms contributing spores to the milk powder, it was found that the abundance of microorganisms in our samples are in the range described in Table 1.

Relative abundance of spore-forming microorganism in milk powder produced in California

This work represents a baseline data for the California dairy industry. It presents results of monitoring random production days with samples from raw milk to finished powder on the same run. The study allows an analysis of operations and indicates areas of concern to the processor and identifies the microorganisms that play a major role in different contaminations, which is useful information for quality control and processing managers.

Solutions to spore contamination may vary, and this serves as a measuring tool to evaluate different strategies that may be implemented in the different processing plants.

Conclusions:
- A thorough survey of the skim milk powder produced throughout two years was monitored. In this survey endospore, or simply spore-forming bacteria, was closely monitored, and several tests were developed to better understand the bacterial population of powders.
- Microbiological differentiation of spore-forming bacteria was achieved by careful development and selection of procedures and techniques that were sensitive to the different population of aerobic spore-forming bacteria present in the powders and in the processing environment.
- Environmental monitoring of sources of spore-former bacteria throughout the processing plants was completed.
- Fluctuation in the population of spore-forming bacteria was characterized.
- Particular sites during processing were identified as possible problem sources for the overall quality of the skim milk powder produced. These sites are being monitored more closely to assess their impact in spore-forming contamination.

Results of our investigation were presented to the plants that requested particular attention to their operation, and the average of the results were presented at the annual meeting of the ADSA.
This project addressed the need to gather reliable data on the microbial quality of milk powder produced in California. Establishment of reliable techniques that yield significant and reliable number of spore-forming bacteria present in the milk, concentrate and powder as well as in the environment along the production line of dairy products is of great industrial and scientific importance. The developments of these procedures have made possible the consistent monitoring of different populations of spores that naturally present differences in their ability to germinate and be counted in any sample.


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Development and Standardization of a PCR-Based Rapid Assay For Spore Count Determination in Powder Milk


Rafael Jiménez-Flores, Cal Poly San Luis Obispo


The unique resistive properties of bacterial endospores make pasteurization, evaporation and spray drying ineffective for eliminating spores from milk powder. Consequently, under the proper conditions following pasteurization, spores have the ability to germinate, grow and initiate proteolysis and lipolysis of milk protein and fat. The detection of these sporeformers is integral for the production of a safe and marketable product. Current methods for testing and quantifying spores are labor intensive, time consuming (up to five days) and have poor detection limits.

The Polymerase Chain Reaction (PCR) offers a rapid and sensitive method for detection over "traditional" biochemical methods. Direct PCR tests have previously been created for the detection of B. sporothermodurans and Clostridium tyrobutyricum in raw milk. However, in order to be the most beneficial for producers and food processors, the detection of a broad species range of commonly identified sporeformers would be ideal.

By amplifying a conserved region of the germination gene gerC3, we have developed a direct PCR assay in order to detect the most commonly identified Bacilli identified in milk powder produced in California. Of the 75 sporeformer isolates obtained from Cal Poly Dairy Products Technology Center’s (DPTC) spore library, we were able to achieve positive PCR results on 39 samples (52 percent) including three of six isolates that were able to hydrolyze casein, starch and fat. BLAST (Basic Alignment Search Tool) alignments and unsuccessful amplification of non-spore forming bacteria commonly isolated from milk powder proved the specificity of the primers.

Detection limits for the five most commonly identified sporeformers B. licheniformis, B. subtilis, B. pumilus, B. megaterium and B. amyloliquefacens were four (Colony Forming Units) CFU’s/10 ml, 117 CFU’s/10ml, seven CFU’s/10ml and 22CFU’s/10ml and 15 CFU’s/10ml, respectively. The entire assay from start to finish (raw milk to PCR signal) is approximately 13-15 hours.

Sequencing results of a 460-base pair amplified product of B. licheniformis ATCC# 14580 showed 85 percent homology to B. firmus and 83 percent homology to B. subtilis (DNAstar). This result was significant in that it showed that the gerC3 gene is conserved within three species of Bacilli and therefore may be highly conserved within other species of Bacilus and potentially Clostridia.

In order to determine phenotypically what types of sporeformers we were able to detect via PCR of the gerC3, an enzymatic survey of 75 sporeforming isolates (60 isolates plus 15 ATCC strains) obtained from three Central California milk powder facilities was performed. Casein, starch, fat hydrolysis and beta-galactosidase activity was identified in all the above samples. Of the 75 isolates (60 isolates from dairies and 15 ATCC samples) 48 hydrolyzed lipase, 27 hydrolyzed casein, 22 hydrolyzed starch and 38 fermented lactose. Six of the 75 isolates were positive for all four enzymes. Four of those isolates were from low-heat powder. However, no statistical differences were noted between the low, medium and high-heat milk powder with respect to total and individual enzymatic activity. We were able to get positive PCR results for three of the six Bacilli isolates that were positive for all four enzymes.

The final part of our work focused on investigating the microbial ecology of milk powder production. The complex microbial communities present during milk powder production are difficult to characterize. While Fatty Acid Methyl Ester (FAME), Randomly Amplified Polymorphic DNA (RAPD), and biochemical analysis are ideal for species identification of cultured isolates, they have limitations in representing the diversity of microbial communities present during milk powder production. Therefore, we investigated the efficacy of Terminal Restriction Fragment Patterns (TRFP) for bacterial community analysis, in order to observe the temporal and spatial differences in the microbial ecology of milk powder production.

Our results showed a clear reduction in the microbial diversity between raw, condensed and pasteurized milk samples. Specifically, peaks corresponding to B. pseudomega-terium, B. subtilis (Ribosomal Database) showed the highest relative areas (i.e. concentration) in condensed milk and powdered milk samples.

In conclusion we have developed a 15-hour direct PCR assay for the detection of the five most common Bacilli sporeformers in milk powder. Enzymatically the sporeformers we were able to detect had 45.3 percent enzymatic activity (100 percent enzymatic activity was defined as an isolate that hydrolyzed casein, starch, fat and fermented lactose) versus 35 percent enzymatic activity for non-gerC3 PCR samples. This shows that we were able to detect not only the most common Bacilli sporeformers but also the sporeformers that induce the most hydrolysis of milk components. However, with respect to activation rates under condenser conditions, PCR-negative samples had significantly higher activation rates (-0.400) than PCR-positive samples (-0.232). Consequently, while we are able to detect sporeformers that are the most damaging enzymatically we may not be detecting the sporeformers which are growing the fastest.


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Reduction of Spore Loads in Milk Powder by Controlling Processing Parameters


Rafael Jiménez-Flores, Cal Poly San Luis Obispo


The objectives of this project are to:
- Evaluate the use of bio-silicates in a pre-coat filtration procedure and optimize the filtration parameters (flux rate and the type of bio-silicate) to achieve a maximum endospore
reduction.
- Study the effect of two heat treatments on Bacillus spore growth rates.
- Study the evolution of the ecology during milk powder processing by terminal restriction fragment patterns technique.

California’s milk powder maintains high standards of quality and is widely used as an ingredient in the manufacture of other dairy products and processed food. Yet, seasonal variations in composition and quality have been detected. A survey of California’s milk reported variable spore concentration at different times of the year. The spores present in raw milk are resistant to the heat treatments applied during processing and are present in milk powder. Therefore, the spores in the milk powder reflect the initial contamination in the raw milk as well as any further contamination during the drying process. Spores become a concern in specific applications in which milk powder with spore counts lower than the current averages are required.

The goal of this research is to find a method that would allow the dairy industry to always maintain very low spore-counts. We developed a filtration procedure that uses bio-silicate as a filtering media in a pre-coat filtration process. The objective is to optimize the flux rate and the types of bio-silicate used during the filtration in order to achieve a maximum endospore reduction. In addition, we studied the effect of two heat treatments on spore growth rates as well as the evolution of the ecology during milk powder processing using a terminal restriction fragment pattern technique.

Filtration
The filtration process we developed uses bio-silicate as filtering media. We worked in collaboration with scientists at World Minerals Inc. to elaborate a pre-coat filtration procedure applicable to milk. We found that the flux rate during the filtration is directly related to the efficiency of removal. Using the filtering media Celite 1032, a removal of at least 97 percent can be achieved at a flux rate of 1.5 L/m2min. If the flux rate is increased to 15.8 L/m2min the removal drops to 85 percent, and at 103 L/m2min the filtration removes only 12 percent of the spores present. When comparing several bio-silicates at a flux rate of 15.8 L/m2min, Celite 1032 and Hyflo Super-Cel retained more than 85 percent of an initial spore load of 2 x 104 cfu/ml. Our work showed that the flux rate and the type of bio-silicate determines the efficiency of spore removal. To obtain a significant reduction, the flux rate should not exceed 15.8 L/m2min. Likewise, only two types of bio-silicates significantly retained Bacillus spp. spores.

We determined that no affinity binding occurred between the filtering media and the spores. Therefore, we concluded that the filtering cake, according to a size exclusion mechanism, physically removed the spores. Moreover, we determined that the average spore diameter for a Bacillus is 1mm.

This result confirms the hypothesis of a physical sieving of the spores since the pore sizes formed by the filtering material are smaller than the spore diameter. We will scale-up the process to our pilot plant plate and frame filtration unit. By simple mathematical calculation, we will be able to adjust the flow in order to have equivalent flux rates to those in the lab. The pre-coat filtration method is simple and inexpensive. The industry should rapidly benefit from this new application that allows them to offer a superior quality of milk powder. The procedure could also be used with other existing methods such as bactofugation.

Heat treatments
Heat is commonly used to assure the microbial quality of several products. However, the heat treatments involved in milk powder processing are not sufficient to destroy the spore. Heat treatment only kills vegetative cells, so we used a sequence of heat treatment to first trigger the germination of the spore, allow time for the spore to become a vegetative cell, and then used a final heat treatment to kill the bacteria. For this experiment, seven strains of Bacillus common to California milk powder were selected. The strains studied were: B. amyloliquefaciens ATCC 23853, B. subtilis ATCC 6051, B. subtilis ATCC 23059, B. pumilus ATCC 72, B. megaterium ATCC 14581, B. licheniformis ATCC 12759 and, B. licheniformis ATCC 14580. The experimental procedure involved three steps: 1) Heat shock at 60oC, 70oC, 80oC, 90oC and 100oC for 12 minutes; 2) Incubation at 35oC for 30 minutes; 3) Second heat shock (repetition of step 1). The results indicate that the temperature of the second heat-shock variably affects the growth rate between the Bacilli. Overall, a net reduction occurred in the growth rate of all the strains studied. Two heat treatments at 100oC have the greatest effect. The survival from the initial counts is reduced by more than 5 log units for B. amyloliquifaciens, B. subtilis 23059, B. pumilus, B. licheniformis 12759, B. megaterium; and by more than 3 log units for B. subtilis 6051, B. licheniformis 14580.

Our results demonstrate variable heat sensitivity among the Bacillus species and between the different strains. Nevertheless, a reduction of the spore load is achieved. This method could be applied in the industry to reduce the amount of spores present in the milk.

Terminal restriction fragment patterns
Our work also focused on investigating the evolution of the microbial ecology during milk powder processing. Using a terminal restriction fragment patterns (TRFP) technique, we tried to identify the organisms present in raw, condensed and powdered milk at the beginning and end of a run. Our results showed that the microbial diversity is greatly diminished by the heat treatments. Also, peaks corresponding to the Bacillus spp. show a higher concentration in condensed and powdered milk.

Our work indicates that the pre-coat filtration process can reduce spores from milk. The final product should have at least one order of magnitude less spores. This process is economical. The only limitation of the process is the large filtration area needed if large volumes of milk are used. However, in a commercial practice, this method should be very suitable for volumes up to 500,000 litters per day, and is a good complement to high volume commercial procedures such as bactofugation.


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Developing a Highly Functional Long Shelf-Life Whole Milk Powder


Moshe Rosenberg, UC Davis


Milk powders containing high fat load are prone to oxidation that limits the product shelf life and adversely affects quality and consumer acceptability. Milk powders containing fat are currently being used as an ingredient in dairy and non-dairy products. In many cases, such products are subjected to environmental conditions that favor lipid oxidation (exposure to air and/or light). In order to enhance utilization of milk powder with high fat content as a food ingredient, its oxidative stability has to be enhanced. Previous research in our lab has indicated that microencapsulation of milkfat in whey proteins provided a means to effectively protect the lipids against oxidation, even under conditions that favor oxidation. This protection has been attributed to the whey protein-based films adsorbed at the surface of the milkfat droplets. The present project makes use of the aforementioned findings and is focused on developing a highly functional, long shelf-life milk powder with high fat content. Our main objective and approach is to investigate and develop milk powder consisting of whey protein-coated milkfat droplets embedded in a nonfat milk solid-based matrix. A process for preparing an emulsion consisting of whey protein-coated milkfat droplets dispersed in a solution of nonfat milk solids has been developed.

Conditions to maximize the proportion of whey proteins at the oil/water interfaces in the presence of caseins have been identified. Emulsions in which milkfat droplets are coated with protein films consisting of up to 9:1 ratio of whey proteins-to-caseins were developed. Using these emulsions, spray-dried powders containing 43 percent fat were developed, and their oxidative stability investigated at conditions that favor oxidation (accelerated test at 50ºC). Long-term oxidative stability of the developed powder were investigated for up to 400 days at 20 and 30°C, and the study continues. Results of oxidative stability tests conducted indicate that the stability of the developed model powders are significantly higher than that of control powders consisting of milkfat and nonfat milk solids (mainly caseins). The model powders exhibited outstanding stability and accumulation of only 0.1-0.4 ppm hexanal/g fat was detected during storage. Control powders, stored at the same conditions, developed hexanal levels 20-40 times higher than those in the model powders.

Preparing milk powders in which milkfat droplets coated with whey proteins are embedded in dry matrix consisting of nonfat milk solids provides a means to effectively protect milkfat against oxidation. Results of our study indicate that the developed powders have oxidative stability significantly better than that of common commercially available whole milk powders. This information will provide the industry with the know-how and technology for manufacturing milk powders with high fat content to be used as a food ingredient. The unique oxidative stability of the powder will allow its incorporation in a variety of products that can be stored at conditions known to favor oxidation.


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Dairy Powder and Concentrate Application Support Program


Phillip S. Tong, Cal Poly San Luis Obispo


A Dairy Ingredients Applications Program has been initiated with the hiring of a Dairy Ingredients Applications Specialist. Immediate project work included trouble shooting end-user difficulties in using skim milk powder in a yogurt application, and reassessment of formulations in the Milk Powder and Concentrate Applications Guide. Several California manufacturers have met with the project team and provided input as an ad-hoc steering committee.

Additional equipment has been purchased to improve our capabilities to conduct physical and chemical characterization of milk powders and concentrates. In addition, support provided by Dairy America has allowed us to obtain needed pilot scale processing equipment (spray dryer and membrane system). These systems were received, installed and are now operational.

As anticipated, several activities have spun off from initiation of the applications program. Several outreach activities have been completed, including a two-day symposium on value-added dairy ingredients, presentations at a major food company that utilizes dairy concentrates and powders, two winning entries into the DMI Dry Dairy Ingredients Product Development Contest, participation in a scientific exchange on the dairy industry in China, an invitation to present U.S. perspectives on milk powder for an international conference on recombined milk (Malaysia), a short course on whey ingredients in frozen desserts for the Latin American dairy industry and a training session on milk powder for a major food company.

Despite being a relatively new endeavor, the strong interest demonstrated to date in the services of the powder applications lab indicates that it will continue to grow as more people become aware of it through the various publications that have been produced as well as other communications.

The frequent inquiries we have received from powder processors and end-users indicate that the powder applications program is meeting a need. Our 1999 activities accomplished key basic parts of infrastructure needed to establish a strong and credible dairy ingredients applications program. Dairy processor support and interest reaffirm the program is on target.


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