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Milk Component Analysis: A Comparison of Instrumental Methods
Milk components are measured in native milk and nearly all derivative milk-based products. This includes raw milk, processed milk, homogenized milk, cream, whey, cheese milk, yogurt and ice cream mix. Components can be measured when the product is in liquid form and, in some cases, when it is in a finished semi-soft condition like cheese and yogurt. This paper focuses primarily on the liquid analysis of dairy products. Typical components measured include fat, protein, lactose and solids.
Milk used for drinking is referred to as fluid milk in the dairy industry. Fluid milk is legally required to have specific levels of butterfat. Non-fat milk (skim) is typically less than 0.10% butterfat. Low fat milks include 1% and 2%. Whole milk is 3.25% (3.5% in California). Producers must test their milk to ensure that they are meeting the fat requirements for the product that they are making. The state of California adds an additional requirement for fluid milk solids non-fat of 9.0% for skim milk, 11.0% for 1% milk, 10.0% for 2% milk and 8.7% for whole milk.
Cheese manufacturers measure protein and fat. Most of the protein is casein, about 78% in bovine milk. In the production of cheese, the ratio of casein to fat is a critical indicator of cheese yield and quality. Different types of cheeses have different casein to fat (C/F) ratios. Cheddar has a C/F ratio of 0.70 while Swiss has a 0.85, Parmesan a 1.10, Havarti a 0.60 and Low Moisture Part Skim Mozzarella has a 1.10 C/F ratio. Measurement of the fat and protein in every cheese vat is a key requirement for most cheese producers.
Ice Cream and Yogurt Production
Ice cream and yogurt manufacturers need to know their fat and total solids values on a per batch basis. Ice cream typically has between 10% to 16% butterfat. Many producers also require knowledge of the fat and solids values in their cream. Cream is typically targeted at 40% butterfat.
Primary and Secondary Analysis Methods
Milk component measurement can be completed by wet chemistry or instrumental methods. In general, wet chemistry methods are more labor intensive per test. These methods include Mojonnier, Gerber, and Babcock testing for fat determination. For protein determination, a Kjeldahl test method is typically used. These types of measurements are considered reference or primary methods of milk component determination.
Most dairy producers utilize an instrumental method of milk component determination. These methods require the use of calibration standards that have known fat, protein, lactose and solids values determined by testing performed by a primary method. External testing labs provide calibration samples or testing of customer samples on a periodic basis.
Instrumental methods have the benefit of a very low cost per test. In addition, operator training and skill required is significantly lower for instrumental testing. Reference methods require detailed lab technician training and facilities while instrumental methods can be employed by reasonably trained system operators. Instrument calibration is generally maintained by a lab technician or lab manager.
Various instrumental method technologies have been developed for the benefit of producers seeking to implement milk component testing as a quality assurance and production efficiency improvement investment.
Mid-infrared spectroscopy is the industry standard and preferred choice for most milk and cheese manufacturers. This method is well defined in third party industry publications for measurement of fat, protein, lactose and solids. It is approved as a farmer payment method for fat and protein. No other instrumental method is approved or used to any significant degree other than the mid-infrared method. Instruments that use this method include an onboard homogenizer prior to analysis. Worldwide there are four known companies that manufacture these instruments specifically for dairy product analysis. Metron Instruments, Inc. is one of those companies as the manufacturer of the York Dairy Analyzer. The typical investment for a mid-infrared instrument is between $35,000 to $70,000 USD. The York is a full featured instrument that is priced mid-range. Mid-infrared spectroscopy provides producers with the industry accepted method for all of their fluid dairy product analysis. Providing flexibility in analysis, excellent accuracy, and comprehensive results, mid-infrared is the technology of choice for most dairy producers.
Ultrasonic technology has found its place in the farmer and artisan cheese producer environment. This technology does not provide the flexibility or breadth of product capability like mid-infrared, but does offer a very attractive price. Ultrasonic units are more portable and less accurate than mid-infrared systems. Measurement variability on key components can be up to four times greater on ultrasonic devices versus their mid-infrared counterparts. This is one of the reasons why this technology is not used or approved for farmer payment. Prices for these devices range from $3,500 to $7,500 USD. In choosing this technology, it is important that producers understand and accept the limitations on what products can be tested.
Near Infrared Spectroscopy
Near infrared spectroscopy is a technology that is best used for semi-solid or high solids content products. Some efforts have been made to provide this technology into the liquid dairy product analysis. These systems are priced similarly to the mid-infrared instruments as they also require an onboard homogenizer. There are significant overlaps in the wavelengths of interest for measurement of fat, protein and lactose to a greater degree than other methods. As a result, more reference samples are required to calibrate a near infrared instrument. Because of practical reasons, very few near infrared systems are used to measure fluid dairy products components.
These are the typical instrumental method options available to producers: mid-infrared, ultrasonic and near infrared. Mid-infrared is higher in price but is by far the method of choice for most producers. Ultrasonic is well suited to artisan cheese makers and farmers because of its price point. Near infrared is accepted for semi-solid product analysis but is not accepted by the industry for lab analysis of fluid dairy products. Producers should be knowledgeable on the core technology employed by a particular instrument prior to making an investment decision.
Metron Instruments, Inc.
December 15, 2011