Project Description
Every year, 1.3 billion tons of food are discarded worldwide, accounting for more than one-third of all food produced globally. This food waste causes various problems. Carbon dioxide generated through the disposal of food waste accounts for 8 to 10 percent of global greenhouse gas emissions, causing significant environmental damage. And the economic loss from food waste amounts to one trillion dollars annually. Furthermore, while such vast quantities of food are being discarded, a social contradiction exists where hundreds of millions of people suffer from food shortages. (1)
As a local issue in Japan, domestic food loss reached approximately 4.64 million tons in fiscal year 2023. (1) In Japan, it is not uncommon for fruits and vegetables that are perfectly safe and tasty to be removed early from store shelves and discarded while still edible, simply because of minor imperfections like slight bruises or color variations. In addition, strict retail sales and delivery standards create pressure to remove products from store shelves before they reach their actual peak edibility, driving up waste. Our project, PreserVEG, aims to reduce food waste by improving produce safety and enabling the visualization of deterioration.
Over half of food loss occurs in households, where fruit and vegetables account for approximately 45% of total food loss by category. (2) Some of the reasons why produce is discarded include the following factors:
Despite often being consumed uncooked, microbial contamination in fruits and vegetables cannot be detected by appearance alone. Consequently, freshness is often regarded as an indicator of safety, with the assumption that “fresh = safe.” If safety seems uncertain, disposal is frequently chosen. Particularly in Japan, where the emphasis on freshness is strong (3), households tend to adopt the behavior of “discarding if there is even slight concern.” This preventive disposal directly contributes to increased food loss.
Fruit and vegetables can be categorized as climacteric or non-climacteric. Climacteric produce releases ethylene during ripening, increasing respiration rates. This ethylene diffuses into the surrounding environment, triggering a chain reaction of ripening. Consequently, overripening of a single item can accelerate deterioration across an entire box or shelf, significantly shortening the shelf life of all produce.
One factor contributing to increased food loss in fresh produce is the lack of clear, easy-to-use criteria for judging deterioration, such as best-before dates or use-by dates. Consequently, we rely on subjective cues like appearance, smell, and texture based on experience to assess deterioration at stores and in homes. On the other hand, objective evaluation methods exist, such as measuring components that fluctuate after harvest, using hardness meters, and analyzing gases like ethylene (6). However, the reality is that these methods are difficult to apply in households, and many distribution settings are due to equipment, cost, and time constraints. As a result, both premature disposal—where produce is discarded prematurely despite still being edible—and late disposal—where signs of deterioration are overlooked—occur, leading to increased food loss of fresh produce. Despite often being consumed raw, microbial contamination in fresh produce cannot be detected by appearance alone.
To solve above problem, we have developed PreserVEG, which is a Cre/loxP-based three-in-one system for climacteric fruits and vegetables. The three key functions are as follows:
Produce sold at supermarkets and other stores is handled by many people during the distribution process. Various bacteria that can cause spoilage, deterioration, and food borne illness adhere to the surface of that produce. Our system produces the antibacterial peptide Nisin Q, which prevents harmful bacteria from proliferating on the surface of produce while also contributing to maintaining quality. This enables a longer preservation of freshness, quality, and safety at high levels.
Various bacteria adhering to fresh produce are likely to be attached not only during the distribution process but also during the storage period at home. In addition to exposure to hands, the risk of contamination by foodborne illness-causing bacteria can increase depending on storage conditions and locations. For example, S. aureus, one of the most common causes of foodborne illness outbreaks in many countries, is found in refrigerators. (7)
Apples are one of the primary fruits and vegetables we focus on. Research on bacteria adhering to apple surfaces has identified E. coli, S. aureus, and B. cereus present on apple surfaces. Among these, S. aureus and B.cereus have proven difficult to remove from apple surfaces through washing. Preventing the proliferation of these bacteria on fruit and vegetable surfaces could significantly contribute to preventing food borne illness. (8) (9)
The antimicrobial substance we focus on is Nisin Q. Nisin Q exhibits broad antibacterial activity and a wide antibacterial spectrum against Gram-positive bacteria. S. aureus and B. cereus, mentioned above, are types of Gram-negative bacteria. E. coli is a Gram-negative bacterium, and while it is not affected by Nisin Q, more of it can be removed from the surface of produce through washing (8). Furthermore, Nisin Q inhibits the deterioration of produce and contributes to maintaining its quality (10).
Briefly speaking, Nisin Q is a superior version of Nisin A, which is what we commonly refer to as “Nisin.”. Nisin Q possesses the same biochemical characteristics as Nisin A and exhibits a similar antibacterial spectrum. However, Nisin Q demonstrates higher stability than Nisin A under oxidative conditions. This enables it to maintain its antibacterial activity for a longer period. (11)
Climacteric fruits and vegetables such as bananas, apples, and tomatoes emit ethylene gas and increased ethylene concentration (Climacteric rise) occurs due to ripening. During ripening, which accelerates their own deterioration as well as that of surrounding produce. (12)
We focused on this climacteric rise. By incorporating ethylene-metabolizing bacterial proteins into this system, it becomes possible to detect ethylene gas released at high concentrations. This makes it possible to monitor the degree of deterioration and prevent further spoilage.
How to sense ethylene ??
Many ethylene metabolism-related proteins are induced not by ethylene itself, but by its epoxide, epoxyethane. Therefore, detecting fruit and vegetable deterioration requires a process that converts released ethylene into epoxyethane. We engineered a mutant based on the toluene/o-xylene monooxygenase (TOM) from Burkholderia cepacia G4, designed to efficiently convert ethylene into epoxyethane. This enables the detection of ethylene emitted by fruit and vegetable as epoxyethane, allowing for the sensing of deterioration. (13) (14)
When some produce is deteriorating, the system expresses GFP protein to visibly indicate the detected level of deterioration. This provides clear labeling indicating whether fruit and vegetables are still edible or should be discarded.
Furthermore, by judging deterioration visually and removing degraded specimens, ethylene diffusion can be prevented. In other words, this prevents the accelerated deterioration of surrounding produce. Based on Human Practice, we selected the method of GFP protein expression to prevent discoloration of the produce itself. GFP protein expression can be easily detected by black light irradiation.
The three key functions described above operate as follows through Cre/loxP system:
This system functions in phases through two plasmids: Cre plasmid and loxP plasmid. Under normal conditions, antibacterial peptide Nisin Q is constantly expressed from Cre plasmid. When ethylene is released from produce, Cre plasmid detects ethylene and expresses Cre recombinase, which cuts and removes the Nisin Q sequence from loxP plasmid. Simultaneously, the terminator upstream of the GFP on the loxP sequence is also cut, causing the GFP downstream of the loxP sequence to be expressed and fluorescent.
For more detail about Our system, click here
PreserVEG is a simple tool designed to simultaneously provide deterioration visualization and antimicrobial functionality by simply spraying it onto fruit and vegetable. Visualization enables the suppression of early disposal of still-edible produce and the isolation of sources causing chain reactions of overripening. Furthermore, its antimicrobial properties help ensure the safety of produce at retail locations and in households.
The spray format requires no specialized equipment, lowering barriers to implementation. As an easily deployable solution usable at distribution, retail, and household stages, it is expected to contribute to reducing food loss.
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