Blueberries (Vaccinium corymbosum) have become a leading berry crop in the United States (U.S.); however, blueberries are very perishable postharvest (Sun et al). The U.S. is the world’s largest producer of blueberries (FAOSTAT, 2016). In 2019, the National Agricultural Statistics Service (NASS) reported a 21% increase in production of blueberries in the United States (NASS, 2019). With blueberries being small in size, blueberries are manually harvested and directly picked into baskets before being transported from fields to a packing house. Many small production operations use reusable plastic containers (RPC), for instance, polypropylene material. Polypropylene is a material that has low density, heat retardation properties, and chemical resistance (Calhoun, 2016). On the contrary, the RPC does not completely protect the fruit from injury during harvesting due to their thin skin and juicy pulp. As a result, fresh and frozen berries microbial safety are becoming more of a concern, with any probable recall or outbreak having a detrimental impact on the entire industry (Krasniewsk et al).
Blueberries are susceptible to contamination by various foodborne pathogens, such as Salmonella, Escherichia coli O157:H7, human norovirus, and hepatitis A virus, and have been implicated in several outbreaks (Oliveira et al). There are many sources of contamination for fresh fruit, for example, irrigation, injury, animal feces, cross-contamination, and equipment. In many cases, the source has been unknown. For instance, it has been stated Salmonella is prevalent in horticulture fruit production as it was detected Salmonella was positive on 4.9% of fruit and 7.1% of equipment used in packhouses. However, no Salmonella was present during pre-harvest operations (Gomba et al). In addition, six people were infected with Salmonella Newport in Minnesota, which was traced back to fresh blueberries (Miller et al). Approximately 15% of all Salmonella enterica- related salmonellosis infections are thought to be linked to the eating of fruits, seeds, and sprouts. (Deblais et al).
Cross-contamination, the transfer of pathogens from one surface to another, has been identified as a major risk factor in a number of food processing and handling environment. The transfer of pathogens between food and surfaces is dependent on the type of bacteria, surface, moisture level, and incubation dose (Brar et al). The primary causes of fruit spoilage and reduced stability are respiration and transpiration, as well as growth of fungal and bacterial species (Krasniewsk et al). Not only are there issues with pathogenic organisms, fresh fruit and vegetables are the most frequently wasted foods (Kelly et al). At a retail level, improper display conditions, limited shelf-life, and aesthetic standards have been linked to waste. Consumers typically store fruits and vegetables improperly which leads to food waste. (FAO; Porat et al). Hence, the utilization of chitosan as an edible coating and proper storage methods, food waste and spoilage could be decreased at a retail and consumer level.
Chitosan is a polysaccharide deacetylated form of chitin. Chitosan, which has attracted attention as a potential food preservative of natural origin, has been approved by the United States Food and Drug Administration (USFDA) as a Generally Recognized as Safe (GRAS) food additive (USFDA). Edible coatings can help preserve perishable food products by decreasing dehydration, respiration, microbial growth while providing a selective barrier to moisture. This also aids in retaining volatile flavor compounds and improving texture quality (Hussain et al). With the implementation of essential oils, the antimicrobial activity may increase and assist in preserving and extending shelf-life of produce. EOs are excellent sources of biologically active compounds, like terpenoids and phenolic acids; among them, carvacrol and thymol are present in oregano EO (Jahani et al). Carvacrol has proven its antimicrobial activity against several pathogens, including Salmonella (Dhumal et al). Therefore, for this study, the objectives were:
1) Evaluate the efficacy of chitosan-based coatings to extend shelf of blueberries in standard grocery store packing materials up to 5 days of storage
2) Evaluate the effectiveness of the chitosan-based coatings to inhibit growth or survival of Salmonella spp. on reusable plastic containers (RPCs)
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Highbush blueberry breeding began in the early twentieth century in the United States (Nishiyama, et al). In the 1800s, the commercial industry for blueberries began and continued to expand to the 1950s. Since the late 1970s, the consumption of blueberries in the United States has been increasing. (Kaiser,2020) Over time, the crop increased from less than one million pounds in 1896 to the bumper crop of over 110 million pounds produced in 2000 (Yarborough, 2018.) In 2018, per capita consumption was 46.5 ounces, which represents a 575% increase since 1970. (Kaiser, 2020) Blueberries were hand-picked, raked, and canned in contrast to now mostly all harvesting are done mechanically. A total of 99% of the crop is frozen and is used principally as an ingredient in processed foods (Yarborough, 2018). Blueberry production in Mississippi has increased over the years; however, the acreage and total yields does not compare with top-producing states (Collart, 2015.)
Blueberry Economic Impact
Blueberries are the second-most produced berries in the United States. In 2010, New Jersey, Georgia, and Michigan were the biggest U.S. producers of fresh-market blueberries (Kramer, 2020.) The American consumption of blueberries has increased fivefold. By 2019, California, Georgia, and Oregon emerged as the largest suppliers, each accounting for about 17% of U.S. production (Kamer, 2020.) Mississippi has one of the greatest percent of small operations averaging to 44% respectively. (USDA, 2017) It is indicated that small operations sell the blueberries at fresh market. The largest percent of producers report their fruit being retailed on the fresh market were 58% in Mississippi in 2014. (USDA, 2017) At postharvest, loss in terms of value and consumption can occur between harvest and consumption (Giuggioli et al.) Although blueberries have increased in production, the economic loss is caused by moisture loss (Bai et al.)
Chart, bar chart Description automatically generated
Figure 1: Blueberry Production in the Pacific Northwest and Southeast States from January to November
Preservation of Blueberries
Whole blueberries are usually preserved using techniques such as low-temperature preservation, ultraviolet radiation, modified atmosphere, high-oxygen concentration treatment preservation, packaging preservation, chemical preservation, and controlled atmosphere preservation. (Kong et al) Processing plants use vast materials to store fresh fruit. One of many materials used is polypropylene [recycle #5] plastic for manual harvesting. This material has low density, heat retardation properties, and chemical resistance. Blueberries are manually harvest and directly placed into baskets before being transported to packing house. The use of flexible films to wrap and pack blueberries with or without modified atmosphere may be more advantageous in terms of handling than the common packaging, for example, clamshells.
Shelf-life of Blueberries
The shelf-life of fresh blueberries typically range of 10-40 days depending on the different factors such as fruit maturity, cultivar, harvest method, and storage conditions (Abugoch et al., 2016.)
The transfer of pathogens from one surface to another has been identified as a risk factor in a number of food processing and handling environment. Cross contamination of pathogens between food and surfaces is dependent on the type of bacteria, type of surface, moisture level, and incubation dose (Brar et al.) There is potential for cross-contamination virulent pathogens such as Salmonella, toxigenic Shinga Toxin-producing Escherichia coli and Listeria monocytogenes, throughout supply chains because of reusable plastic containers (Anon, 2016.) It has not been proven that harvest containers are the source of pathogenic transfer; however, there was an outbreak of Salmonella linked to cucumbers sourced from Mexico which caused confirmed cases across 40 states. According to U.S. FDA, there was no specific sources of Salmonella, but a reference to the possibility of reusable plastic containers transfer Salmonella between batches of cucumbers. (U.S. FDA, 2016).
Salmonella is one of the major foodborne pathogens that occurs in food related recalls. Although, foodborne disease outbreaks are commonly associated with foods of animal origin, fresh produced has been linked to 46% of annual foodborne illnesses, 38% hospitalizations and 23% deaths in the United States (Painter et al.) With the increase of fresh fruit consumption, the increased risk of foodborne diseases outbreaks of which Salmonella has been identified as the most important pathogen in European Union and United States (Callejon et al.)
Dole Diversified North America, Inc.
Whole cantaloupe, select cut cantaloupe, fruit trays and bowl
Cut or sliced apples, grapes, pineapples, and cantaloupe
Potential to be contaminated with Listeria monocytogenes
Potential Salmonella contamination
Fresh cut cantaloupe, honeydew, melons, watermelon, more
Package products containing apple slices
Stuffed mushrooms, fruit and cheese
Ron’s Home Style Foods, Inc.
Fruit salads: tropical, pineapple nut, pistachio créme
Table 1. Small fruit recalls in the United States from 2016-2021
Function of Chitosan and its Structure
Chitosan, (1,4)-linked-2-amino-deoxy-b-d-glucan, is a polysaccharide deacetylated form of chitin (USFDA.) In the food industry, different forms of chitosan are used. Applications of chitosan aids in texture, flavor, appearance, and preservation. Chitosan can preserve food by decreasing microbial deterioration, acting as an antifungal, antibacterial, and antioxidants (Morin-Crini.) The utilization of edible coating that aid in preservation of perishable food products by decreasing dehydration, respiration, microbial growth while providing a selective barrier to maintain moisture (Hussain et al.) Likewise, the coating can provide a substate for the incorporation of other functional food additives, such as minerals, vitamins, or other drugs that can enhance fresh commodities (Romanazzi et al.) In the blueberry industry, chitosan can be used as a barrier, restricting water transfer and protecting the blueberry’s skin from mechanical injuries.
Diagram Description automatically generated Diagram Description automatically generatedFigure. Chitin and chitosan structure
Antimicrobial Properties of Chitosan
Chitosan and its derivatives have been shown to possess diverse biological activities, including antioxidant, antihypertensive, anticoagulant, antidiabetic, anti-obesity, antiallergic, anti-inflammatory, antimicrobial, anticancer, neuroprotective and matrix metalloproteinases inhibitory effects (Ngo et al.) Due to its versatility, chitosan has been widely used as an antimicrobial agent to improve food quality and extend shelf-life (Ahmed & Ikram.)
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