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Explore This IssueApril/May 2014
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As much as “food integrity” has been part of nearly every discussion related to the food supply chain, the term is in itself unclear to many stakeholders in this arena. On one hand, food integrity implies a global perspective that includes food production, distribution, and everything in between (procurement, processing, packaging, testing, etc.); on the other hand, it could simply mean the absence of any fraudulent, unknown ingredient in the food supply chain that would impact food safety and public health.
At U.S. Pharmacopeial Convention (USP), we try to confine food integrity to the food ingredient level, and that means we develop tools to help manufacturers, formulators, regulators, and other parties to assert food ingredient quality (identity, purity, strength, as well as absence of contaminants). The analogy is that our Food Chemicals Codex (FCC) can be seen as a dictionary for food trade. The FCC is not a specialty dictionary, but it aims to establish a common language and to facilitate communication among the many players in this field. Just as an example, even though a manufacturer of potato chips may have a very nuanced understanding of what “salt” means and how important granularity and crystal flow are from a technological production perspective, his/her understanding of the identity and purity of this ingredient should not differ from how “salt” is described in the FCC. The logic seems simple, when applied to describe ingredients such as those consisting of well-defined simple salts or single molecules, but the more complex the chemical composition of a food ingredient, the more difficult it is to determine its integrity.
Food integrity is intrinsic to food safety in the FCC context. Being able to determine the safety of food and its ingredients at the basic level depends on the knowledge of its composition. One can only make a safety assessment of those components that are known. Hence, if and when an unknown ingredient is introduced in the food supply chain, it is impossible to establish whether the ingredient and any food produced with it is safe or not, until the presence of such an unknown ingredient becomes transparent. Unfortunately, in some cases this happens only when consumers experience a negative health impact.
The development and application of identity and purity standards for food ingredients is no easy task. Vitamin A is an example that illustrates what goes into deciding which test methods to use. It is an ingredient used both as a dietary supplement and in food formulations. Often, the term “vitamin A” is used to refer to a group of different compounds (including retinol, retinoic acid, and several carotenoids, of which beta-carotene is arguably the best known). All these various compounds have their own features regarding stability, bioavailability, isomerism, and other important parameters. An analyst will have to tailor his/her analytical methods to the specific compound (e.g., provitamin A or beta-carotene to adequately assess its purity and identity). Right there, the definition of what compound exactly is meant by “vitamin A” will trigger a decision about the types of tests necessary to accurately establish authenticity. Questions that feed into the very definition of the somewhat loose term “vitamin A” are: Which are the criteria we want to capture with vitamin A? For which purpose are we testing? The analyst would measure vitamin A by international units if the purpose was related to biological activity and bioavailability rather than a milligram/milliliter concentration, which is how food ingredients are usually measured.
Moisture, or water content, as simple as it sounds, is an important residue to consider and a good example to demonstrate the challenges of setting standards. Moisture is important because it often impacts the chemical stability of an ingredient (e.g. too much water and your ingredient may disintegrate); and, more importantly, it determines the risk of microbiological spoilage. If only very little water is available to microorganisms, this can be measured through determining water activity, which will predict microbiological growth and spoilage. Keeping water activity low is a control mechanism to minimize risks from potentially harmful microorganisms.
But how do you measure water? It seems relatively trivial at first sight (water is water, it is H2O, right?), but measuring it in food ingredients may be complex. There are many methods for measuring water, but the way we use them can vary depending if we want to measure water activity or water content. Due to a variety of technical reasons, it is not easy to measure water activity in a reproducible and robust manner and test results depend even on the kind of equipment used.
Water content can be measured by a simple method called loss on drying, which is performed as simply as it sounds. An amount of the given sample is weighed, put in an oven at a certain temperature (typically slightly above the boiling point of water) for several hours, weighed again, and the process is repeated until two subsequent weightings do not indicate further weight loss. The assumption is that all evaporated material is water. This method is not specific because any weight loss is counted as water, even if it is due to flavors, fragrances, and other volatile substances that evaporate. In this specific method, all weight losses are counted as water. The challenge with certain heat-sensitive ingredients, such as milk powder, is that a chemical reaction takes place during the heating process and volatile substances are liberated, of which one is actually water, but not water that has been freely available in the sample, and, therefore, available for microbiological growth. It is water that became available after a chemical reaction took place. These types of heat-sensitive samples may actually continue to lose weight as the process continues and the measurement needs to be terminated after a fixed amount of time that is set by convention (e.g. after two hours in the oven).
Another method is a chemical reaction based on a Karl Fischer titration, which determines all water content that is present in a sample. While this method is capable of measuring all water in certain ingredients, the method requires complete dissolution of the sample, and that is not always possible to achieve. Besides, just as with the loss on drying method, there is a question of availability of water for microbiological growth, which may not be adequately addressed with this method (e.g. certain salt crystals have crystallization water that is not freely available, but part of the crystal structure, which would not be liberated using the loss on drying method, but it would be liberated and measured as water in the Karl Fischer titration).
So which water do we want to measure?
All these methods are valid and widely used, but they may return different results if applied to the same sample. So, it is important to agree upfront on what is the most scientifically-sound way to measure this one residue. Which method is considered the most appropriate often involves a discussion of regulatory requirements, scientific considerations, ease of use, cost, speed of analysis, and availability of instruments.
The examples above illustrate how complex it is to choose even one type of test to help establish food ingredient integrity. When complex ingredients come into play, especially those derived from biological sources, a multicomponent system needs to be considered. A food ingredient monograph many times suffices to establish the integrity of a particular ingredient and the FCC contains more than 1,200 of them. However, different approaches may be necessary for ingredients that are closer to raw agricultural products, such as pomegranate juice and other fruit juice concentrates.
Some of the components of pomegranate juice include sugars, polyphenols, acids, minerals, and water that present natural variability that is influenced by the species of pomegranate as well as environmental conditions (region where the fruit is grown, climate, harvest, and processing conditions, etc.).
Recognizing the exhaustive challenge in developing monographs for complex food ingredients, USP last year proposed the creation of FCC Identity Standards, which will, more than other FCC Monographs, not only establish ingredient identity, but also include tests for substances that should not be present in certain complex ingredients (in the case of pomegranate juice, artificial sugars or compounds that are not usually found in pomegranate, but may be found in other fruit juices with which pomegranate juice has historically been adulterated).
FCC Identity Standards are intended as a trigger to perform additional tests to make sure users are not unknowingly purchasing an adulterated product. If an ingredient fails the specifications in an FCC Identity Standard, it could as well be due to natural variability of that particular ingredient. However, results that show a particular material is compositionally very different from the majority of the products in that category should raise concerns, or at least questions.
It is important to emphasize that the FCC is limited to providing a routine measure to aid in the establishment of food integrity for ingredients that are commercially available. It’s not the goal of an FCC Identity Standard for pomegranate juice, for example, to represent the composition of pomegranate juice that is obtained from non-commercial processes or sources of the fruits themselves that are not intended for the production of pomegranate juice as a commercial food ingredient.
The intent is to reflect products that are used for commercial formulations, and not all pomegranate juice is commercially viable. Part of the challenge for USP is that our standards are not meant to exclude legitimate products. However, the specifications cannot be so broad that an unreasonable number of illegitimate ingredients suddenly become FCC-compliant.
Previous test methods to measure the protein content of skim milk powder have proved not sufficient to keep adulterators at bay.
Sometimes, asserting food integrity requires sound judgment paired with appropriate tests and reference materials. Skim milk powder is a widely used complex food ingredient that consists of variable compounds (proteins as a group, which in itself can be divided in numerous fractions, sugars, non-protein nitrogen, fats and lipid-like substances, water, etc.) and could also present natural variability dependent on the species, animal’s lactation period, animal’s nutrition, as well as processing conditions—heat treatment for instance.
Food analysis is an intrinsic and essential part of helping to ensure the integrity of food ingredients, but it is not sufficient by itself. It is impossible to test an ingredient to safety, and good supply chain management practices are essential components complementing testing. Yet, better tools to help establishing integrity for skim milk powder, for example, and therefore asserting that it is as safe an ingredient as possible is crucial, as instances of adulteration, such as the one in China in 2008, have put public health at risk.
For ingredients such as skim milk powder, USP, in conjunction with industry and academy experts that comprise the Skim Milk Powder Expert Panel, is developing a risk-based testing structure, which is designed to provide guidance to analysts to decide under which conditions more tests might be necessary to gain confidence in the ingredient’s integrity and under which conditions the load of testing may be reduced.
An aspect of risk-based assessment for skim milk powder, for example, takes into account that nitrogen-rich adulterants other than melamine may present a new risk. Previous test methods to measure the protein content of skim milk powder have proved not sufficient to keep adulterators at bay. To help offset the limitations of this test method, USP is coordinating the development of additional tests that are less vulnerable to the presence of adulterants, as well as methods for the non-targeted detection of adulterants and the development of reference materials, or physical samples, adulterated with melamine.
Establishing food integrity should be a task undertaken by all players in an increasingly global food supply chain. Therefore, USP is taking steps to bring together representatives from industry, regulatory agencies, consumer groups, and other standard-setting bodies to discuss proposed FCC standards and encourage collaboration.
One of these steps is access to the FCC Forum (www.usp.org/fcc/fccForum.html), where FCC monographs and identity standards are open for stakeholder feedback. In-person workshops on selected topics of interest are also available (www.usp.org/meetings-courses/workshops). In November 2013, USP held a workshop on food and dietary supplements adulteration and in November 2014, USP is scheduled to hold a workshop focused on food contamination.
Dr. Lipp is the senior director for food ingredients at USP. Reach him at firstname.lastname@example.org.