Fluid milk processing

Vitamin addition is required in the low-fat milks, therefore all reduced fat, low-fat and skim varieties have Vitamin A palmitate as an added ingredient. In the case of whole milks it is optional for the dairy to add vitamins. The consumer usually has the option to purchase the milk he or she prefers. 

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The goals of most LCA have been limited to determination of the impact of the fluid milk process on GHG emissions and energy due to the availability of relevant data and guidelines from the IPCC and other government agencies. Data for conducting LCA of the other impact factors such as water use, aquatic toxicity, human health, and land use are scarce, but new initiatives to reduce the impact of dairy production in... 

Figure 2.4 compares the GHG emissions in different sectors of the fluid milk process from three LCA analyses performed for U.S. dairy farms. The Cashman et al. (2009) study was conducted using primary data from farmers and processors for organic operations. The Thoma et al. (2010) study utilized... 

Energy information data for the fluid milk process as reported by Xu and Flapper (2009) or obtained by energy audit is very useful for establishing benchmark performance of dairy processing plants. However, since the fluid milk process consists of several steps, energy information on each step in the fluid milk process is needed as well to lower the energy costs and GHG emissions associated with pasteurization. 

In a preliminary study, Tomasula et al. (2009) simulated the fluid milk process to identify energy usage and GHGs associated with HTST pasteurization and the related unit operations, such as homogenization. Physical property data for milk and cream were provided to the simulator. Packaging was not included as part of the simulation. GHGs were... 

The dairy industry is committed to reducing GHG emissions across the fluid milk processing chain by 25% by the year 2020, and this can only be accomplished in the fluid milk process plant through use of alternative... 

Xu, T. and Flapper, J. (2009). Energy use and implications for efficiency strategies in global fluid-milk processing industry. Energy Policy 37(12), 5334-5341. doi 10.1016/j.enpol.2009.07.056. 

The basic constituents of milk - protein, lipid, carbohydrate - can serve as precursor substrates for the formation of a wide variety of flavor compounds. Nearly two hundred volatiles have reportedly been found in fresh and processed milk (4). Numerous research efforts have focused on the conditions and mechanisms of off-flavor development in milk. The chemical compounds responsible for these off-flavors have been characterized (3,5-7). Most fluid milk processing is carefiiUy controlled so that the appearance of caramelized and scorched flavor notes rarely occurs. The rich flavor associated with the thermal formation of diacetyl and various lactones is not objectionable to most consumers and, therefore, not a serious concern. Conversely, the sulfurous off-flavor in cooked milk is of concern and is especially prevalent in freshly processed UHT milk. 

Milk has been a source for food for humans since the beginning of recorded history. Although the use of fresh milk has increased with economic development, the majority of consumption occurs after milk has been heated, processed, or made into butter. The milk industry became a commercial enterprise when methods for preservation of fluid milk were introduced. The successful evolution of the dairy industry from small to large units of production, ie, the farm to the dairy plant, depended on sanitation of animals, products, and equipment cooling faciUties health standards for animals and workers transportation systems constmction materials for process machinery and product containers pasteurization and sterilization methods containers for distribution and refrigeration for products in stores and homes. 

Pasteurization may be carried out by batch- or continuous-flow processes. In the batch process, each particle of milk must be heated to at least 63°C and held continuously at this temperature for at least 30 min. In the continuous process, milk is heated to at least 72°C for at least 15 s ia what is known as high temperature—short time (HTST) pasteurization, the primary method used for fluid milk. For milk products having a fat content above that of milk or that contain added sweeteners, 66°C is requited for the batch process and 75°C for the HTST process. For either method, foUowiag pasteurization the product should be cooled quickly to <7.2° C. Time—temperature relationships have been estabHshed for other products including ice cream mix, which is heated to 78°C for 15 s, and eggnog, which must be pasteurized at 69°C for 30 min or 80°C for 25 s. 

FIGURE 2.2 Percentage contributed by each unit process toward the total U.S. fluid milk emissions (Thoma et al., 2010). 

The goal of the LCA is to understand the impact of the existing fluid milk supply chain on energy usage and GHG emissions, as well as the other impact categories provided that data are available, and to use the information as a roadmap for improvements to the process. The LCA also provides an environmental benchmark to identify points where improvements to the fluid milk supply chain may be made. 

GHG emissions for milk packaging are mainly CO2 and arise from the energy used to process and produce the raw materials, container formation which is done on site in fluid milk plants and from transportation of the raw material (Irmovation Center for U.S. Dairy, 2008 Keoleian and Spitzley, 1999 Spitzley et ah, 1997). 

The milk production stage is the largest source of GHG emissions over the entire life cycle of fluid milk production. CH4 is generafed primarily through enteric fermentation of dairy cows and also through the microbial, anaerobic decomposition of manure. Manure deposifed on soil or handled as a solid, an aerobic process, emits little CH4. However, manure generates CH4 when stored under the aerobic conditions of a lagoon. 

Nicol et al. (2005) performed one of the few case studies for determination of the influence of the regeneration step in pasteurization and partial or total homogenization processes on the total energy and specific energy of the whole pasteurization process in an operating fluid milk pasteurization plant. The plant handled 24,000 L/h of milk with a plant... 

A discussion of redox reactions and photooxidation is presented in the text by Walstra and Jenness (1984). This topic is especially important in view of the long light exposures given to fluid milk in transparent packages during the marketing process. 

Clarification is normally one of the initial steps in processing fluid milk and is important for removing somatic cells, bacteria, and other foreign particles. It is accomplished by passing milk through a rapidly rotating clarifier bowl to sediment suspended particles. 

Fluid milk is commonly subjected to a combination steam injection/in-fusion and vacuum flash evaporation process to remove volatile off-flavor compounds. The process is designed to remove the same amount of water by the flash treatment as is added during steam injection/infu-sion, so that the composition of the milk remains unchanged. This treatment is most effective for removing volatile, water-soluble flavor compounds, such as those from weeds and feed consumed by the cow. The additional heat from this process usually provides further improvement in product shelf life. 

Jones, V. A. and Harper, W. J. 1976. General processes for fluid milks. In Dairy Technology and Engineering. W. J. Harper and C. W. Hall (Editors). AVI Publishing Co., Westport, Conn., pp. 141-184. 

The fat-soluble vitamins comprise vitamins A, D, E, and K, whose biological activities are attributed to a number of structurally related compounds known as vitamers. Also included are those carotenoids that are precursors of vitamin A. Recommended dietary allowances (RDAs) based on human epidemiological and experimental animal studies have been published in the United States for vitamins A, D, E, and K (1). Other countries and international bodies have compiled similar recommendations. In the United States and Canada, fluid milk is supplemented by law with vitamin D to a level of 400 international units per quart (10 /zg/0.95 L) to meet the RDA of 10 p%. Other commodities, such as margarine, milk products, ready-to-eat breakfast cereals, and dietetic foods, are commonly supplemented with vitamins A, D, and E. Except for infant formulas, vitamin K is not added to foods. The addition of vitamins to a particular processed food is intended to provide a specific proportion of the RDA. 

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