With the advent of the Food Safety Modernization Act, manufacturers of extruded and baked petfood and pet treats feel like they have their necks under a knife’s edge. To some, that may seem overly dramatic, especially given the blade at their neck is held by the smallest of creatures: Salmonella.
Yet despite “kill steps” and a multitude of processing safeguards, a connection of Salmonella from home to petfood to manufacturing plant can spell near financial disaster to a petfood company. So, it shouldn’t come as any surprise that there is an urgent search under way for a petfood additive that can provide a safety net well after all the other food safety steps have been completed.
Why an additive? For starters, no process is perfect. The food may be sterile at some point in the manufacturing process, but after it leaves the plant, store shelf or bag, any number of opportunities exists for (re)contamination.
Ideally, an additive with a residual effect would be beneficial. For example, compounds like formaldehyde would work for this purpose, but it has some serious side effects and certainly wouldn’t be looked upon favorably by pet owners. Something natural and label friendly that is already accepted for use in petfoods would be ideal. Lactic acid may be just that ingredient.
Lactic acid has been a part of food preservation and flavoring for years. We encounter lactic acid mostly in fermented foods like sauerkraut, yogurt, buttermilk and sourdough bread. Lactic acid was first refined from sour milk in 1780 by the German-Swedish chemist Carl Scheele; its production by lactic acid bacteria was first described by Louis Pasteur in 1856. The first commercial production dates back to 1895 by the German company Boehringer Ingelheim. Today, lactic acid is used in the food, confection, cosmetic, pharmaceutical, plastic-polymer and textile industries around the globe.
Lactic acid (2-hydroxypropanoic acid; C3H6O3) is considered a carboxyilic acid. Because the hydroxyl group is adjacent to the caroboxyl group, it may also be referred to as an alpha hydroxy acid. In the food industry, lactic acid is commonly described as an “organic acid” along with others such as acetic acid (vinegar) or propionic acid. Lactic acid has a mild sour-acid taste and is used in foods as an acidulant and pH buffer. It can also be used as a dough conditioner, leavening agent and emulsifier. It is soluble in water and ethanol and has wide application for inhibiting microbial spoilage.
It is this latter function that provides the most utility to petfood. Early examples of its use occurred in semi-moist/soft-moist petfoods nearly 50 years ago. It was promoted in early patents for its flavor, water binding and acidification properties—necessary attributes to keep these higher moisture products from molding.
Whether it actually imparted any benefit to flavoring is not completely described in the literature. It may be more folklore than hard fact, but the lore suggests that dogs and cats have a slight preference for the sour acidic taste of lactic acid in foods when compared to untreated foods.
The bigger factor is lactic acid’s preservation activity. It supposedly does this through disruption of the microbial cell membrane, which weakens the bacteria to the point of death. For these purposes, lactic acid in a petfood may be included at rates from under 1% to nearly 3% depending on ingredients and process. This matches with most of the literature in human foods, especially meat products, where microbial control (including Salmonella) has been achieved with application rates around 1% to 2%.
Lactic acid can be produced by synthetic means; however, the viable commercial production method today is fermentation. On an industrial scale, lactic acid is produced from carbohydrate fermentation with lactic acid bacteria such as Lactobacillus delbrueckii, L. amylophilus, L. bulgaricus, L. leichmanii and a whole host of others. The carbohydrate starting materials are corn steep liquor, corn syrup, molasses and other inexpensive carbonaceous compounds. Fermentation is fairly rapid, going to completion within two to three days.
During fermentation, the pH in the fermenter is maintained with calcium hydroxide or calcium carbonate, so the resulting end product is actually calcium lactate. This calcium lactate-rich broth is filtered to remove microbial cells and debris and then purified. By one process, acid is added to dissociate the calcium and create a technical grade lactic acid. For food and pharmaceutical-grade material, it is further distilled, then hydrolyzed with water. The process is under continuous revision by producers to improve yield, reduce input energy and costs and decrease environmentally unfriendly residues.
Commercially, lactic acid is available in liquid and dry forms at concentrations of 80%–90%. There are also mineral salts of the acid available for various applications. These include calcium lactate, sodium lactate and potassium lactate. They are more dilute powders (concentrations at about 50%) that are added to the flour or batter fraction of extruded or baked petfoods. From a regulatory perspective, lactic acid is approved for use in petfoods in most countries around the world.
Lactic acid is relatively easy to incorporate into dog and cat diets for the control of microbial growth; specifically, it may provide some residual Salmonella control after the food has left the manufacturing environment. Since lactic acid is naturally found in the gastrointestinal tract and systemic circulation and universally recognized as beneficial, there should be minimal push-back by pet owners. There are long-term rat studies showing the safety of its chronic consumption, but direct evidence in dogs and cats is lacking. We also lack meaningful descriptions regarding how this compound impacts petfood production or equipment wear.
Despite these minor shortcomings—and given that lactic acid is natural, is well liked by dogs and cats and plays a significant role in microbial control—it would seem to be a near ideal safety net for safe petfood production. Confirmation of this role and acceptance by consumers seems to be the only hurdles remaining to its wider use.
Find more columns by Dr. Aldrich at www.petfoodindustry.com/ingredientissues.aspx.
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