Shelf Survival:
The Latest Technology in Preserving Product Quality

By Bob Durst


For thousands of years humans have tried to find ways to extend the life of fresh food. It started out as a means of survival, or making it through the winter. These days, however, it’s mainly about convenience, and thanks to the conventional food industry’s mass use of preservatives, consumers now expect foods that would normally degrade in days or weeks to last months, if not years. Organic processors also have the added challenges of minimal processing requirements, as well as supply limitations that often result in produce being shipped across country or internationally, thus losing days of freshness.

While organic processors have a few more challenges and may not have an arsenal of chemicals to work with, the good news is that today there are many exciting new technologies and advancements that both comply with organic standards and provide the customer the high quality and convenience they desire.

Processing for Product Preservation
The highest quality of most foodstuffs is when they are still on the plant at their peak of maturity. As soon as they are harvested the quality starts to diminish. Exposure to elements such as light, heat and oxygen has negative effects on everything from nutrient levels to color, texture and flavor. In addition, the natural population of microbial organisms starts to increase which can lead to food safety issues and/or product degradation. One of the main functions of processing is to stop this degradation and maintain the qual-ity of food. There are numerous ways to reach this goal depending on the desired level of quality and how much processors can budget into the bottom line.

On the formulating side, some ingredients have been shown to extend shelf life including antioxidants like rosemary and tocopherols (e.g., vitamin E) as well as polyphenols. While these can make a significant difference, it’s often the processing stage that determines the overall quality of a product.

There are four basic processing methods used to give a product shelf stability: heat, reducing water activity, freezing/chilling and fermentation. Cooking, baking and pasteurization use heat to kill microbes, alter protein structure and enhance flavor production. On the negative side, heating can destroy vitamins and enzymes, degrade colors and, in excess, result in unfavorable texture changes.

Pasteurization and Cutting Edge Alternatives
Out of these processes, pasteurization is one of the most popular methods used to reduce microbes, however the negative side effects of nutrient loss and overall quality degradation have led industry experts to search for ways to improve the process and develop alternatives. With standard pasteurization, or high-temperature, short-time processing (HTST), the product is heated to 75°C for 20 to 40 seconds and then quickly cooled down to minimize the negative effects of heat. Improved science has led to flash pasteurization, which heats and cools even faster and improves quality while still meeting federal requirements for a 5-log reduction in pathogens (the reduction of microbe count by 100,000 times). These methods are used for refrigerated items. A process called ultrapasteurization uses higher heat and/or longer heating times (142°C for 4 to 30 seconds) to give nonrefrigerated items shelf stability, but with these harsher conditions comes increased loss of quality.

One of the new technologies that has been developed to help better preserve quality is ultra high pressure processing (HPP or UHP). More widely used in Europe and Japan, this organic compliant method offers the microbial kill advantages of pasteurization without heat. In addition, it inactivates some enzymes that lead to product degradation and offers post-packaging microbial kill for certain products.

All of this is great stuff, but the equipment cost is unfortunately very high. There are also cases where enzymes are activated by the application of pressure, so testing of each product is necessary. Lastly, some microbes and spores are resistant to HPP. In spite of these shortfalls, HPP is a promising emerging technology and is one of most commercially advanced processes available.

HPP is applicable to a wide range of products, but only those that are liquid or semi-solid. A number of products from Fresherized Foods such as guacamole and juices use this process, resulting in a flavor profile nearly identical to that of a fresh product but with the added benefit of extended shelf life.

Another application of HPP is the post-packaging processing of sliced meat products. Cooked meats are a clean, safe product after they finish the cook step, but during the subsequent handling there is the risk of recontamination. The application of HPP to the finished package leads to a safe packaged product with minimal processing.

HPP is also being used with shellfish to reduce microbes while keeping the “raw” quality. In an unexpected turn, it also relaxes the abductor muscle so that the shells can be easily opened. In addition, HPP is currently undergoing testing on milk products to see if the microbial kill can be effected without the associated changes in flavor, vitamins and enzymes associated with thermal pasteurization.

Another new process, pulsed electric field (PEF), achieves microbial inactivation without the effects of heat by applying a short burst of electrical energy through the product. One of the first commercial installations of this is Genesis Juice in Eugene, Ore., and their products have been getting rave reviews. This process is only applicable for clear juices. The shelf life of PEF treated foods is comparable to HTST processed products.

A third new technique is ohmic heating, which uses a strong electric field and the inherent electrical resistance of a product to rapidly heat the entire volume of product in a way that is somewhat similar to microwave heating. Unlike typical heating, this process doesn’t denature proteins or gelatinize starches, which leads to unique textural characteristics. It’s also being investigated as an alternative to lye or steam peeling of fruits. This process is still under review by the USDA and FDA, but a number of foreign producers use the technique. Shelf life of these products is comparable to thermally canned products.

One last novel method is a process for orange juice that involves extensive washing of the fruit prior to juicing. This is then followed by careful extraction of juice without contact with the outside surface of the orange. Using carefully sanitized equipment, the product is then packed in sterile, or “aseptic,” cartons or bottles. Products using this process can be sold without the safety warning of unpasteurized juices and don’t undergo the thermal degradation of typically processed juices. This technique is currently only applicable to citrus juices and the shelf life is comparable to that of a fresh product.

A Look at Aseptic Packaging
As in the juicing process above, improved packaging techniques are very important in maintaining product quality. A process called aseptic packaging was recently named “the most significant food science innovation of the last 50 years” by the Institute of Food Technologists (IFT). This process can literally give new life to products, extending shelf life from weeks to months.

With the aseptic process, the product is treated using one of the methods listed above and then poured into a sterile container in a sterile environment so that the microbial integrity of the product is maintained. Aseptic packaging, the rectangular paper or plastic cartons juice and soup often comes in, is formed inside a machine that is completely sterilized by hydrogen peroxide. This multilayer packaging also creates a barrier impervious to light and oxygen, thus providing greater shelf stability.

Another type of aseptic package is the “bag in a box” cartons of wine or juice that have a spigot to dispense product. These bags are sterilized by irradiation and then filled in a machine that is sterilized by steam and/or UV light prior to the filling operations. There are many different variations on aseptic packaging. For more information more go to www.aseptic.org.

More Advancements and Areas of Research
The use of biological agents or their derivatives to improve food quality and safety is another emerging field. Some of the kinds of things that are being worked on here include coating of products with a thin, edible transparent film to minimize oxygen interaction and keep microbes from contacting the food, the addition of non-pathogenic organisms that out-compete spoilage organisms and botanically derived preservatives.

Coating food, in particular fresh fruits and vegetables, with an edible film such as wax helps to minimize the transpiration and evaporative water losses from the fruit, thereby extending shelf life. Recent research in coatings has been done using whey protein isolates, chitosan and carboxymethyl cellulose, some of which may be used in organic processing in the future.

Coatings are also being used as carriers for nutraceuticals, vitamins or antimicrobials, which can add functionality and/or improve the nutritional status of the product. One of the possible antimicrobials is lysozyme, a protein extracted from egg whites. It was added to the national list as an approved ingredient in organic products in September of 2006. However, it requires testing with each and every product as many of the bacteria that lysozyme is effective against are not pathogenic, so by killing them, there is less competition with pathogenic organisms, which can then grow faster. These techniques have limited acceptance at present but are very active areas of research. Stay tuned.

Bob Durst is a principal in Simple Organic Solutions LLC, a consulting group that assists industry with meeting the USDA organic regulations. He is also a senior faculty research assistant in the Department of Food Science and Technology at Oregon State University, where he works with a wide variety of fruit and juice processors regarding product quality issues. In addition, Durst is a processing plant inspector, a board member of the Independent Organic Inspectors Association (IOIA) and a member of the Organic Materials Review Institute (OMRI) Processing Review Panel. Durst can be reached at BobD@SimpleOrganicSolutions.com