QUALITY IS VITAL FOR LEAFY GREENS
With the demand for fresh, convenient and healthy food growing among consumers, leafy greens are the order of the day. From fresh cut to pre-washed and pre-packaged products, this is a rapidly growing market with significant potential.
However, with the market becoming increasingly competitive, and consumers ever more discerning, the pressure is on leafy green producers to deliver superior quality because, among retailers and consumers, there is zero tolerance towards foreign bodies and other quality-compromising defects.
Undoubtedly, optical sorting presents a unique opportunity for key players in the food industry to improve quality, increase yield and reduce waste – but what can this innovative technology do for leafy greens?
Foreign material: A significant threat to leafy greens
Quality remains a key priority for leafy green producers who are acutely aware of the widespread impact undetected foreign material and other contaminants can have on public health and safety.
In response to several E. coli outbreaks attributed to the consumption of leafy greens in 2018, five major U.S. food companies joined forces to encourage efforts on improving prevention and traceability. An integrated food safety approach like this highlights the importance of implementing best practices to ensure safe produce.
Not only does sub-quality produce pose a risk to public health, it also presents a significant threat to a brand and its reputation. Indeed, leafy green producers are particularly at risk when it comes to customer claims and product recalls.
Looking towards the future of food with optical sorting
While large rodents are easier to spot, smaller insects and frogs are more difficult to detect; indeed, they can unfortunately make their way into the finished product making headlines that can irreparably tarnish a brand – incidents like these are bad for business and the market has certainly become less forgiving. Thankfully, optical sorting provides the most efficient means of safeguarding your produce against such scenarios:
Stable, double-sided inspection ensures no foreign material can hide from a sorter’s sensors i.e. a snail that could be hidden behind a leaf
Efficient foreign material detection and removal of various poisonous weeds without compromising good product
Gentle handling ensures optimum quality is maintained by preventing bruising
With the increased performances of optical sorting it also becomes possible to exclude de-coring from the line and sort the cut product for core defects
How can leafy green producers benefit from partnering with TOMRA Food?
Not only does optical sorting maintain superior quality, it opens up new possibilities to increase yield and reduce waste. With multiple streams, product typically sent to the waste bin can be reworked to increase output, while sorting before and after washing also opens up additional possibilities.
The growing demand for traceability also strengthens the case for producers to invest in future-focused technology that is equipped to respond to the changing landscape of food safety. The ability to be able to track statistics, quality and data will become increasingly important as traceability becomes a greater focus across the food supply chain.
The bottom line is that, for leafy greens, the spectrum of quality control is vast. From foreign material, to secondary (and subtle) quality defects like leaf discolorations and insect damage, right through to microbial contamination – optical sorting responds to harvest demands by ensuring produce meets quality specifications and is safe to consume.
Postharvest Quality of Leafy Greens Growing in a Plant Factory
Quality at harvest and quality loss during postharvest storage were monitored. The main quality attributes of importance in leafy greens vegetables are the coloration (mainly for appearance), taste, shelf life, and nutrient content of the final product. Red coloration (anthocyanin) of lettuce was achieved most efficiently using preharvest dynamic light recipes with a high fraction of blue light to avoid yield loss during lettuce production. In addition, taste was also found to change as a function of light spectrum with arugula and various basil cultivars, but the magnitude of this change is shown to be strongly cultivar-dependent. We observed that light quality (high blue versus low blue with far red) affects shelf life of arugula by several days. The best light recipe identified for shelf life has a high blue content (35%), while the worst was with a high far red content (25%). In addition, the contents of vitamin C, K, chlorophyll, and anthocyanin were changing significantly under various light quality on lettuce and arugula. The nutrient content of wild arugula was strongly affected by preharvest continuous light, offering a way to improve the antioxidant level of the final product.
Green Leafy Vegetables: A Health Promoting Source
Green leafy vegetables (GLVs) are a blessing for a safe and healthier life and have been in use for centuries. They are considered as an essential part of the diet to meet the daily nutrient requirements. GLVs can be used fresh as a salad or can be cooked/processed as per the interest of the consumer. These are becoming more popular for the masses day by day due to the increased awareness of consumers about natural and organic foods. These possess a high place in the food pyramid and are an essential part of a balanced diet. The low caloric value of leafy vegetables makes them ideal for weight management. GLVs are a rich source of nutrients, high in dietary fiber, low in lipids, and rich in folate, ascorbic acid, vitamin K, Mg, and K. They also carry plenty of phytochemicals such as β-carotene flavonoids. The good nutrition profile of GLV is beneficial in lowering the risk of cardiovascular diseases and cancer. GLVs are also valued for individuals with type 2 diabetes due to their high Mg content, high fiber content, and low glycemic index. These contain a good blend of polyphenols and antioxidants, which render them unique for therapeutic values. They also possess antimicrobial activity and can be used in different food products to extend storage life. The burden over synthetic chemicals can be reduced by encouraging the use of GLVs in food and food products.
FACTORS DETERMINING POSTHARVEST QUALITY OF LEAFY VEGETABLES
Vegetable quality is a combination of characteristics, attributes and properties that give value to the commodity for human food. Many preharvest and postharvest factors such as genetic material, agroecological conditions, production technology, physiological stage at harvest, postharvest technology and the interaction among them affect vegetable composition and general quality of the product. Information about the influence of preharvest and postharvest factors on vegetable quality is an important issue for improving crop management and packaging techniques for fresh products. The aim of this research was: i) to study different crop management factors affecting lettuce quality and ii) to evaluate postharvest strategies to preserve minimally processed leafy vegetable quality along the marketing chain. Preharvest conditions such as plant population and nitrogen availability in soil of a leafy lettuce crop grown in Spring, and the effect of radiation and its interaction with N fertilization on growth patterns, yield and nitrate accumulation in upper biomass of a leafy lettuce crop grown in Winter were studied. Enzymatic browning on the lettuce-butts is one of the main changes in lettuce during postharvest due to the cutting practised to plants at harvest. Controlled atmosphere and chemical treatments were used to prevent enzymatic browning on crisphead and butterhead lettuce butts. The effect of processing degree and ascorbic acid concentration changes on the quality of different lettuce types during storage were studied. Minimally processed lettuce quality was related to the processing technique and the lettuce type. Enzymatic browning is one of the main causes of organoleptic quality loss during processing and storage of minimally processed lettuce. The effect of selected organic acids solutions as chemical inhibitors for enzymatic browning and the evaluation of the suitability of a range of polymeric films for modified atmosphere packaging on different lettuce types minimally processed during the storage period were studied.
Taking the Quality of Leafy Greens Beyond Organic
Leafy green vegetables such as lettuce, spinach and herbs travel long distances before they reach local retailers and eventually our plates. These journeys can sometimes be thousands of kilometers and result in plants with depleted nutritional value and flavor. Furthermore, for plants to survive these long journeys and retain some degree of freshness they are supplemented with harmful chemicals. Growing locally could be a solution but demands great efficiency in production.
Farmers Cut Vertical Farm Valoya LED Grow Lights
Picture 1 – Farmers Cut
The Hamburg based vertical farm ‘Farmers Cut’ brings together a network of agriculture experts to solve this problem and bring fresh, tasty and nutritious leafy greens to consumers’ tables. They have developed a fully automated vertical farm which, compared to traditional farming is 100 times more productive, produces year round using 90% less water, 60% less fertilizer and no pesticides whatsoever. Other contributing factors to their success are a proprietary, patented growth medium and propagation solution as well as research grade LED grow lights from Valoya. The final product is an organic plant but more than that – it is packed with more flavor and nutrients than when grown under weather dependent conditions and Hamburg locals get it to their plates freshly harvested.
Valoya LED Grow Lights Tube T8 Vertical Farming and Research
Picture 2 – Valoya’s AP673L spectrum in the L28 model.
Valoya’s team of plant biologists consulted Farmers Cut to determine the optimal light spectrum and growth protocols. The decision is based on more than 400 large scale trials Valoya conducted thus far with most commonly grown plant varieties worldwide. Combined with a comprehensive light plan, this ensures the smartest way to grow a plant is employed. The AP673L spectrum was chosen as it ensures rapid growth cycles and flavor intensity that ordinary LED grow lights or sunlight cannot achieve. It has been designed to stimulate vegetative growth and delay flowering which for vertical farmers means plants with great fresh weight and subsequently profits. Research conducted by Wageningen University (The Netherlands) and Democritus University of Thrace (Greece) has found that spectrum AP673L significantly boosts the Total Phenolic Content (TPC) in plants1. Phenolic compounds such as rosmarinic, caffeic and chicoric acids among others are responsible for flavor and fragrance intensity. Additionally, they contribute to the nutritional value of plants. This is why the AP673L spectrum is favored by vertical farmers worldwide.
Hamburg locals will as of soon have a steady supply of locally grown, fresh leafy greens. The farm will produce over 80 varieties of greens on the growth area of 1200m2 in the city of Hamburg. The mission for the future is to deploy these fully automated vertical farms in cities around the world bringing highest quality greens to urban populations all year round, no matter where.
Best Practices When Harvesting Leafy Greens for Market and Home
The harvesting of leafy greens to maintain quality and safety focuses on the key risk factors from the time harvest begins to selling at market. The food safety risk factors involve temperature, time, water, worker hygienic practices, and food contact surfaces. Growers need to address these factors when harvesting for their family as well as their market.
As always, the water used on the leafy greens must meet drinking water standards. Water should be used to maintain the quality and safety of produce, not be the source of contamination. The standards set by the South Dakota Department of Health (SD DOH) are consistent with federal standards set by the Environmental Protection Agency. If using a public water supply assume it has been tested and meets safe drinking water standards. If using a private water source, such as a well, periodic testing is required to demonstrate that water has met safe standards for drinking water. Well water should be tested at least twice a year, before growing season and just before harvest. Proposed federal standards would initially require testing every three months, with reduced frequency allowed if no coliform bacteria are found in 5 successive tests. To have private well water tested, contact one of the SDSU Extension Regional Centers for a test kit. Some county Extension offices also have water-testing kits for your convenience. Obtain the water for testing from the source that is closest to what is being used in the post harvest operation. Flooding can contribute to contaminated wells, so have well water tested if at risk from contamination by flood waters.
Save all test results as documentation that you are addressing the risk of contamination by water that is often associated food borne illness outbreaks related to leafy greens and other produce.
To maintain quality, leafy greens may be sprayed with a light mist when harvesting to reduce the loss of water. This must be an approved water source (having no E. coli) and the method used for spraying must not introduce additional contaminants. If the water is from a container, be certain the container and spraying equipment have been clean and sanitized. When possible, harvest early in the morning as the produce will be both cooler and better hydrated.
Growers may choose to use an antimicrobial agent such as a chlorine- or peroxide-type disinfectant in the water. The primary purpose of this is to keep the water from being a source of contamination. Water with an active disinfectant can decrease microbes on the surface of the product, however, the efficacy will depend on the concentration, wash time, temperature, and completeness of physical contact. The disinfectant must also be approved for the intended use and all label directions adhered to. It is very important the grower understand the chemistry of the disinfectant they may be using, as its effectiveness can be affected by the pH of the water as well as dirt or debris in the water. Growers using a disinfectant in the water should also test the concentration of the disinfectant, using indicator test-strips. The pH of the water may need to be tested as well. If using a water disinfectant, monitor routinely to maintain proper concentration levels.and document all use and tests.
COOLING AND WASHING
The temperature of the water is also critical to food safety. When greens and other crops are harvested they are warm, and the crop needs to be cooled quickly to maintain quality and safety. However, using water that is greater than 10F colder than the recently harvested produce can create a phenomenon of infiltration of water into the plant. This is concern if using dirty water that may be contaminated with pathogens (particularly if washing in a container that is used to wash and cool fruits and vegetables), or if the outside of the produce has been exposed to contaminated soil or other surfaces. Therefore, it is suggested to use several washings using water that starts out slightly cooler than the produce and progressively becomes colder.
One option for smaller-scale growers is to use a pass-thru system, where the greens are spread on clean mesh trays that allow quick drainage, and they are sprayed with fresh clean water rather than submerged in a water bath. It may be necessary to stir the greens several times so that all surfaces are cleaned.
Equipment and Storage Safety
After cooling with water, place leafy greens in a refrigerator to maintain a temperature of 32 to 36 F. The refrigeration unit should be kept clean. Do not store leafy greens in a closed container with other fruits or vegetables that produce ethylene gas as they ripen, such as apples, tomatoes, bananas, mangoes, onions and pears. High humidity (90 to 95%) needs to be maintained to minimize wilting, but avoid direct contact with standing water, which can serve as a source of cross-contamination. Clean moist (not soggy) paper towels can provide sufficient moisture if coolers are not equipped with humidifiers.
Harvesting equipment should be inspected daily during use. Make certain all knives, scythes, harvesting containers, etc. are properly cleaned and sanitized before use. That means washing in hot soapy water, rinsing thoroughly and dipping in a bleach solution of 100 ppm (1 tablespoon of bleach per two gallons of water) for 10 seconds and air-dried. Or, use a dishwasher to adequately clean and sanitize. Larger containers must be cleaned with hot soapy water, thoroughly rinsed then sprayed with a sanitizing solution and air-dried. All containers and harvesting equipment must be stored in a manner that will not contaminate the equipment. Have a system in place to maintain and monitor harvesting equipment. Consider the equipment used in harvesting fruits and vegetables to meet the same sanitation standards to safely prepare food in the home or restaurant.
Containers used in harvesting leafy greens and other produce should be labeled clearly for their purpose. This will not only reduce the risk for contamination by pathogens but chemicals as well. If you have several people working on your farm, communicating the risk factors and how to address these through best practices will improve morale in your growing operation as well as establish a culture of food safety.
Those harvesting the produce need to be certain they are not wearing clothing and shoes that contribute to cross contamination. For example, shoes and boots should be dedicated to working in the garden, not in areas where livestock are located. Workers need to always wash their hands before harvesting. Clothing should be clean. And if workers are sick, particularly with diarrhea and/or vomiting they should not be handling produce, or clean containers and utensils. The risks of contaminated food by workers with a foodborne illness is critical at every step of the food delivery system from growing, harvesting, marketing, and preparing and serving.
AT THE MARKET
At the market, use tongs or disposable gloves if bagging leafy greens for customers and avoid setups that allow customers’ hands to touch raw produce. Vendors also need to develop systems so they don’t directly touch produce after handling credit cards or money, which are often contaminated with potential pathogens.
When harvesting, continually survey your growing operation to make certain you are implementing good agricultural practices from the field to the market.