And against zombie food
When I was in the first year of my food science and technology programme, one of my lecturers told us that food is such a biochemically active material that it behaves more like a living organism than an inert material.
Years later, I still find myself wondering how many people, including professionals working in the food industry, truly understand the implications of that statement.
Food lasts longer than at any other point in human history. It survives months in warehouses, weeks on supermarket shelves, and days in our refrigerators before eventually reaching our plates. Supply chains now span continents. A strawberry picked in one hemisphere can be eaten in another weeks later, while tomatoes harvested green complete their ripening inside shipping containers rather than under the sun.
Consumers increasingly expect fresh food to remain fresh for what would once have been considered ridiculous lengths of time. Retailers demand ever longer shelf-lives, while manufacturers are expected to deliver products that look, taste and behave as though they had only just been harvested or produced.
Of course, there is a separate category of foods designed for long-term preservation. Preserves, dried products, fermented foods and cured products have existed for centuries. Their stability is part of their identity.
Fresh food is different, however.
The food industry has made enormous advances in preservation over the last century. Refrigeration, freezing, dehydration, modified-atmosphere packaging, barrier technologies and a growing number of novel preservation techniques have dramatically extended the shelf-life of fresh products by slowing biochemical reactions and microbiological spoilage.
But slowing biological processes does not mean stopping them as food continues to change after harvest. Cells continue to respire, enzymes remain active, oxidation continues,vitamins degrade, pigments slowly break down, while many bioactive compounds become less abundant over time. Preservation protects food from microbial spoilage, but it does not actively preserve every nutrient.
The peasants in the village where I grew up never fully trusted fruit or vegetables that remained untouched by spoilage for unusually long periods of time. At the time, I dismissed this as another example of traditional scepticism towards modern technology.
Now I wonder whether they intuitively understood something that we have gradually forgotten.
We optimise what we measure (and we do not measure everything)
One of the most persistent weaknesses of modern food systems is that they optimise for variables that are easy to quantify: shelf-life, yield, uniformity, transportability, processing efficiency, economic return, contaminants, etc… These are all easily measurable.
Quality, however, is considerably more difficult to measure.
Not because quality is subjective, but because it emerges from the interaction of dozens, sometimes hundreds, of characteristics. Paradoxically, many of these characteristics are implied as stable, unchanging and eternal that aren’t even properly agreed in contracts or on product specs.
Flavour, texture, aroma, micronutrient composition, phytochemical diversity, consumer experience, cultural significance – many of these are either poorly understood or economically invisible.
Consequently, they receive far less attention and the result is predictable. We have designed a food system that excels at preserving products while gradually eroding many of the properties that made those products worth preserving in the first place.
Deep dive into the rabbit hole: food continues to live after harvest and processing – risk of boredom disclaimer, proceed with caution!
One of the most common misconceptions about fresh food is that harvesting marks the end of its biological activity.
It does not.
Harvest simply marks the moment when the plant is separated from its source of nutrients. The cells remain metabolically active, enzymes continue to function, oxidation continues, and the product slowly begins to consume its own reserves. In many respects, fruit and vegetables continue to behave more like living tissues than inert materials.
This is precisely why preservation technologies exist.
Refrigeration, freezing, dehydration, modified-atmosphere packaging and other modern preservation techniques are remarkably effective at slowing biochemical reactions and microbiological spoilage. They slow down biological time, but they do not stop it.
The stability of many nutrients and biologically active ingredients depends on numerous factors, including the chemical composition of the food matrix, the raw material itself, the presence of pro-oxidants, the processing technology employed and the storage conditions (Macari, 2003).
As an example, many antioxidants are continuously involved in oxidation-reduction (REDOX) reactions after harvest, during processing and throughout storage. In performing their protective role against oxidation, they are gradually consumed themselves. Their reducing capacity decreases, and with it their ability to neutralise free radicals (Sandulachi, 2007).
In other words, antioxidants sacrifice themselves in order to protect the food.
Vitamin C – the first casualty
Perhaps no micronutrient illustrates this better than vitamin C.
Ascorbic acid is inherently unstable in the presence of oxygen. Its degradation is influenced by pH, dissolved oxygen, temperature, light and heavy metals, particularly copper, whose catalytic activity is especially pronounced (Banu et al., 2003). In fruits and vegetables, oxidation often occurs indirectly through interactions with polyphenols such as catechins.
Sugars, starch and anthocyanins provide a certain degree of protection, but the losses remain considerable under many technological treatments.
Table 1 summarises typical losses reported by Banu et al. (2003).
| Technological treatment | Vitamin C losses (%) |
| Thermal sterilisation | 26–79 |
| Freezing | 10–50 |
| Lactic fermentation of cabbage | 10 |
| Lactic fermentation of cucumbers | 30 |
| Cutting cabbage | 3–9 |
| Boiling in water | ~50 |
| Cooking in oil (up to 20 min) | 55–80 |
| Peeled potatoes stored in water (28 h) | 14 |
| Apples stored in water | 8–20 |
These figures should not be interpreted as an argument against cooking or food preservation. Rather, they illustrate an important principle.
Every preservation method involves trade-offs.
There is no technology capable of perfectly preserving every desirable characteristic of fresh food.
Storage tells a similar story.
The concentration of vitamin C declines gradually during refrigeration, although the rate varies considerably between products. Green peas are among the most sensitive examples, with approximately 70% of their ascorbic acid destroyed after only one week of storage (Howard et al., 1999).
Other fruits behave differently. During 135 days of storage at 0°C, quinces lose around 45% of their vitamin C. Cherries preserve it less successfully than grapes, while refrigerated blackcurrants treated with sugar retain approximately 75% of their initial vitamin C content. Even blackcurrant jam retains around 66%, demonstrating that processing does not inevitably eliminate nutritional value (Петрушевский et al., 1985).
Interestingly, blanching vegetables before refrigeration inactivates many of the enzymes responsible for oxidation, substantially reducing subsequent vitamin C losses during storage (Howard et al., 1999).
Once again, preservation proves to be more nuanced than a simple opposition between “fresh” and “processed”.
Not every nutrient behaves the same
This complexity becomes even more apparent when considering carotenoids. Unlike vitamin C, certain carotenoids actually become more bioavailable after cooking.
For example, it is well known that lycopene, the pigment responsible for the characteristic red colour of tomatoes, is released from plant cell structures during heating. Consequently, cooked tomato products such as tomato sauce may contain up to four times more bioavailable lycopene than fresh tomatoes.
This observation is frequently presented as evidence that processing improves nutrition. And it certainly can, but this should not be confused with the broader conclusion that processing universally enhances nutritional quality.
Carotenoids themselves remain vulnerable to oxygen, light and prolonged heat exposure. Vitamin A and its precursors are partially destroyed during thermal processing, with oxygen and temperature acting as the principal drivers of degradation. After only four days of exposure to light, approximately 75% of the original α- and β-carotene content may be lost, whereas lycopene proves somewhat more stable under identical conditions (Pesek et al., 2001).
The extent of these losses can be substantial. Banu et al. (2003) report vitamin A losses of approximately 97% during the thermal sterilisation of canned maize and 87% in canned green beans, whereas freezing vegetables results in much smaller losses of around 12%.
Again, optimisation inevitably involves compromise.
Polyphenols: protectors that are consumed
Polyphenols present another interesting paradox.
These compounds, including flavonoids, catechins, anthocyanins and related phenolic substances, are among the most important natural antioxidants found in plants. Their biological role is not passive. They actively intercept reactive oxygen species and, in doing so, are themselves transformed into inactive compounds (Macari, 2003).
Their degradation depends on several interacting factors, including pH, temperature, oxygen availability and the activity of oxidative enzymes such as polyphenol oxidase and peroxidase.
At acidic pH values (2–3), degradation proceeds relatively slowly. Between pH 3 and 4, almost half of the polyphenols may already be destroyed. By pH 6, oxidation can become almost complete (Macari, 2003).
This is one of the central paradoxes of food preservation. The very compounds that protect food against oxidation are gradually sacrificed during that protection. The better they perform their biological role, the less of them remain.
Deep Dive into the rabbit hole: the antioxidant paradox as a marker of biological activity
If the previous section appears to suggest that processing inevitably destroys most nutritional quality, the scientific evidence tells a more complicated story. The relationship between food processing and antioxidant activity is far from linear.
Consumer perception often assumes that processing invariably reduces the nutritional value of fruits and vegetables. This assumption is understandable given the above-illustrated vitamin C example. Many bioactive compounds are indeed unstable and may be lost during harvesting, processing and storage. Nevertheless, the scientific literature presents a far more nuanced picture when it comes to measured total antioxidant potential.
As modern lifestyles increasingly favour convenience, the demand for ready-to-use (RTU) and ready-to-eat products continues to grow. Food manufacturers have responded by developing products that minimise preparation time while maintaining safety and acceptable quality. At the same time, concerns remain that processed food may possess a lower nutritional value than their fresh counterparts due to losses of bioactive compounds during processing (Klimczak, Malecka, Szlachta, & Gliszczynska-Swiglo, 2007).
This concern has become an important area of research over the last two decades. Food processing encompasses an extraordinary range of technologies, including thermal treatments, high-pressure processing, microwave heating, osmotic dehydration, freeze-drying and numerous other preservation techniques. Each modifies the biochemical environment differently, meaning that antioxidant activity cannot be predicted simply from whether a product is “fresh” or “processed”…Or, to use the current hated buzzword…”Ultra-processed”.
Rather than asking whether processing is beneficial or harmful, a more meaningful question is:
What happens to a particular compound under a particular treatment?
The answer, unsurprisingly, depends on the chemistry and the physics.
Storage: a slow form of processing
Storage itself should be regarded as a technological treatment. Even when food appears unchanged, chemical reactions continue throughout its shelf-life.
Klimczak and colleagues (2007) investigated orange juice stored for two, four and six months at 18°C, 28°C and 38°C. Vitamin C and hydroxycinnamic acids proved particularly susceptible to degradation, resulting in a measurable decline in overall antioxidant activity. In this case, storage temperature played a decisive role. After four months, total polyphenol content had declined by approximately 7% at 18°C, 11% at 28°C and almost 20% at 38°C (Klimczak, Malecka, Szlachta, & Gliszczynska-Swiglo, 2007).
The lesson is straightforward. Even when microbiological spoilage is successfully prevented, nutritional deterioration quietly continues.
Shelf-life and nutritional stability are not synonymous.
Heat: destructive or transformative?
Heat is often portrayed as the principal enemy of nutritional quality. Even I did it in the text above.
Frequently, this is true, yet not always.
The effects of thermal processing depend not only on the compound itself but also on the surrounding food matrix. Some compounds are destroyed while others become considerably more accessible, as seen in the lycopene case.
Tomatoes provide perhaps the best-known example. Heating disrupts plant cell walls and releases lycopene from intracellular structures, increasing its bioavailability. Similar observations have been reported for thermally processed tomatoes, where increases in antioxidant activity have been attributed to greater lycopene availability (Dewanto, Wu, Adom, & Liu, 2002).
Shiitake mushrooms provide another interesting example. Choi and colleagues (2006) demonstrated that increasing both heating temperature and duration significantly increased total antioxidant activity as measured by ABTS and DPPH assays. Total phenolic content also increased with thermal treatment (Choi, Lee, Chun, Lee, & Lee, 2006).
These findings remind us that antioxidant activity cannot be reduced to the concentration of a single molecule.
Food chemistry is considerably more dynamic and complex than that…
When processing causes losses
Other technologies, however, produce substantial reductions.
Stojanovic and Silva (2007) examined osmotic dehydration of Rabbiteye blueberries followed by hot-air drying. After twelve hours of osmotic concentration, approximately 60% of anthocyanins and polyphenols had already been lost. Subsequent drying caused even greater reductions, particularly in anthocyanins, while high-frequency ultrasound treatment (a novel processing technique that should (and will) gain popularity in the future) further accelerated these losses.
The combination of elevated temperature, high sugar concentration and oxygen availability produced the greatest decline in antioxidant properties as well as significant colour changes (Stojanovic & Silva, 2007).
Similarly, drying grape pomace above 100°C significantly reduced both extractable polyphenols and antioxidant activity while simultaneously altering colour (Laurrari, Ruperez, & Saura-Calixto, 1997).
These studies illustrate that preservation is rarely governed by a single variable.
Temperature, oxygen, water activity and processing duration often interact, amplifying each other’s effects.
New technologies are changing the picture
The encouraging news is that not all modern processing technologies rely on heat.
High-pressure processing (HPP), for example, has emerged as one of the most promising alternatives for preserving both safety and nutritional quality.
When Gonzalez-Cebrino and colleagues (2016) compared HPP-treated green asparagus juice with conventionally heat-treated samples, the high-pressure process retained significantly more vitamin C, rutin, total polyphenols and overall antioxidant activity than thermal processing.
Likewise, Pataro and colleagues (2011) found that ohmic heating caused only a slight reduction in ascorbic acid during the production of apricot syrup.
These technologies illustrate an important point.
Innovation in food preservation is not merely about extending shelf-life.
Increasingly, it is about preserving nutritional integrity as well.
Sometimes antioxidant activity increases
Perhaps the most surprising finding in this field is that antioxidant activity can occasionally increase while concentrations of certain antioxidants decrease. At first glance, this appears contradictory, but in reality, several mechanisms may explain the phenomenon.
Thermal treatments may alter the oxidation state of polyphenols, producing compounds with greater antioxidant activity. Heat also promotes Maillard reactions, generating new compounds that themselves possess antioxidant properties (Mendas, Medic, Bojic, Irena, & Vinkovic, 2011).
Similarly, digestion within the gastrointestinal tract may further enhance antioxidant activity in vivo despite reductions in measurable polyphenol concentrations, as demonstrated by Liyana-Pathirana and Shahidi (2005).
Consequently, antioxidant capacity should not be viewed as a simple function of the concentration of individual molecules, but as an emergent property of an extraordinarily complex chemical system.
The real enemy is oxygen
Across almost every preservation technology, one factor appears repeatedly: oxygen.
Whether introduced during mixing, pumping, filling or simply trapped in the headspace of a package, oxygen remains one of the principal drivers of oxidative deterioration.
Light adds to the problem.
Carotenoids are particularly susceptible to photo-oxidation, meaning that both sunlight and artificial lighting during storage or retail display may contribute to degradation. Even the mineral composition of processing water may destabilise certain natural antioxidants and colourants (Chapman, 2011).
In many respects, food preservation is less a battle against microorganisms than against oxygen itself.
What the evidence really shows
Taken together, these studies reveal something that is often lost in public discussions.
There is no universal hierarchy in which fresh food is always superior and processed food is always inferior. This is why the term ultra-processed food has become both useful and misleading. Useful because it draws attention to genuine problems in modern food systems. Misleading because it can tempt us to judge foods by the complexity of their processing rather than by the quality of the final product, its nutritional value, and its place within the wider diet.
Processing is not a moral (and even legal) category, but a technological intervention. Like any technology, its value depends on what problem it solves, what compromises it demands, and whether those compromises are justified.
Perhaps this is why the concept of ultra-processed food has become such an attractive, yet ultimately incomplete, explanation for the deterioration of modern diets. The real question is not whether food has been processed, but what has been optimised. Shelf-life? Convenience? Cost? Uniformity? Or nutritional integrity? Processing is merely the tool. Optimisation is the philosophy behind it.
Nor is the opposite true.
The effect of processing depends on the food, the compound of interest, the technology employed, the storage conditions and, ultimately, how we define quality.
What the literature does consistently demonstrate is that every intervention carries consequences: some improve bioavailability, some reduce it, and some preserve it remarkably well. Some achieve all three simultaneously, depending on how nutritional quality is defined.
The question, therefore, is not whether we should process food.
It is whether we have become so preoccupied with maximising shelf-life that we sometimes optimise one characteristic at the expense of many others.
Conclusion
We have reached a point where a clean label is no longer enough. Consumers increasingly expect those claims to be verified, supported by evidence and independently validated.
At the same time, the industry continues to pursue ever longer shelf-lives for products that were never meant to last indefinitely, or even as long as the current supply chain actors desire.
Perhaps we should ask whether these increasingly ambitious shelf-life targets are becoming an objective in themselves rather than a genuine benefit to consumers.
Decay is the proof of life…And that life existed in the first place. Trying to stop apparent degradation post a certain point simply leads to vacuous shelf-life…And to some extent vacuous food.
Every additional day comes at a cost. Sometimes that cost is negligible. Sometimes it affects flavour, taste, texture or nutritional quality. Sometimes it simply reflects a level of optimisation that no longer serves a meaningful purpose, but just ends up producing „zombie food” – rich in caloric value, devoid of any biological (and often hedonic) activity.
Would it make more sense to invest in better logistics, improved forecasting and more efficient warehouse management instead?
For decades, the industry has spoken about just-in-time supply chains. Yet increasingly, “just in time” feels more like a slogan than an operating principle. Rather than bringing food to consumers while it is still at its best, we have often chosen to make food survive the inefficiencies of the system.
And perhaps that is the real question this essay asks:
Have we become so good at preserving food that we have forgotten what fresh good food is supposed to be?
References
Banu, C., Nour, V., Iordan, M., & Musteaţă, G. (2003). Procesarea materiilor prime alimentare şi pierderile de substanţe biologic active (pp. 80–82, 91–94, 137). Editura Tehnica.
Chapman, S. (2011). Guidelines on approaches to the replacement of Tartrazine, Allura Red, Ponceau 4R, Quinoline Yellow, Sunset Yellow and Carmoisine in food and beverages. Food Standards Agency in Scotland.
Choi, Y., Lee, S., Chun, J., Lee, H., & Lee, J. (2006). Influence of heat treatment on the antioxidant activities and polyphenolic compounds of Shiitake (Lentinus edodes) mushroom. Food Chemistry, 99(2), 381–387.
Cilla, A., Perales, S., Lagarda, M., Barbera, R., Clemente, G., & Farré, R. (2011). Influence of storage and in vitro gastrointestinal digestion on total antioxidant capacity of fruit beverages. Journal of Food Composition and Analysis, 24(1), 87–94.
Connor, A., Luby, J., Hancock, J., Berkheimer, S., & Hanson, E. (2002). Changes in fruit antioxidant activity among blueberry cultivars during cold-temperature storage. Journal of Agricultural and Food Chemistry, 50(4), 893–898.
Cordenunsi, B. R., Genovese, M. I., Oliveira do Nascimento, J. R., Hassimotto, N. M., José dos Santos, R., & Lajolo, F. M. (2005). Effects of temperature on the chemical composition and antioxidant activity of three strawberry cultivars. Food Chemistry, 91, 113–121.
Dewanto, V., Wu, X., Adom, K., & Liu, R. (2002). Thermal processing enhances the nutritional value of tomatoes by increasing total antioxidant activity. Journal of Agricultural and Food Chemistry, 50(10), 3010–3014.
Gazzani, G., Papetti, A., Daglia, M., Berte, F., & Gregotti, C. (1998). Protective activity of water-soluble components of some common diet vegetables on rat liver microsomes and the effect of thermal treatment. Journal of Agricultural and Food Chemistry, 46, 4123–4127.
Gonzalez-Cebrino, F., Duran, R., Delgado-Adámez, J., Contador, R., & Barnabé, P. (2016). Impact of high pressure processing on colour, bioactive compounds, polyphenol oxidase activity, and microbiological attributes of pumpkin purée. Food Science and Technology International, 22(3), 235–245.
Howard, L. A., Wong, A. D., Perry, A. K., & Klein, B. P. (1999). Beta-carotene and ascorbic acid retention in fresh and processed vegetables. Journal of Food Science, 64(5).
Klimczak, I., Malecka, M., Szlachta, M., & Gliszczynska-Swiglo, A. (2007). Effect of storage on the content of polyphenols, vitamin C and the antioxidant activity of orange juices. Journal of Food Composition and Analysis, 20(3–4), 313–322.
Laurrari, J. A., Ruperez, P., & Saura-Calixto, F. (1997). Effect of drying temperature on the stability of polyphenols and antioxidant activity of red grape pomace peels. Journal of Agricultural and Food Chemistry, 45(4), 1390–1393.
Liyana-Pathirana, C., & Shahidi, F. (2005). Antioxidant activity of commercial soft and hard wheat (Triticum aestivum L.) as affected by gastric pH conditions. Journal of Agricultural and Food Chemistry, 53(7), 2433–2440.
Macari, A. (2003). Influenţa proprietăţilor oxidoreducătoare ale sucului şi pulpei de fructe şi pomuşoare asupra evoluţiei bioantioxidanţilor. Chişinău.
Mendaš, G., Medić, M., Bojić, M., Vinković, I., & colleagues. (2011). Phenol content, antioxidant activity and metal composition of Croatian wines deriving from organically and conventionally grown grapes. Food Chemistry, 124, 354–361.
Pataro, G., Donsì, G., & Ferrari, G. (2011). Aseptic processing of apricots in syrup by means of a continuous pilot-scale ohmic unit. LWT – Food Science and Technology, 44(6), 1546–1554.
Pesek, C. A., & Warthessen, J. J. (2001). Photodegradation of carotenoids in a vegetable juice system. Food Chemistry.
Sandulachi, E. (2007). Impactul tratamentului tehnologic asupra proprietăţilor oxido-reducătoare ale produselor din fructe conservate (Doctoral dissertation). Chişinău.
Shin, Y., Liu, R., Nock, J., Holliday, D., & Watkins, C. (2007). Temperature and relative humidity effects on quality, total ascorbic acid, phenolics and flavonoid concentrations, and antioxidant activity of strawberry. Postharvest Biology and Technology, 45(3), 349–357.
Spigno, G., Tramelli, L., & De Faveri, D. (2007). Effects of extraction time, temperature and solvent on concentration and antioxidant activity of grape marc phenolics. Journal of Food Engineering, 81(1), 200–208.
Stojanovic, J., & Silva, J. L. (2007). Influence of osmotic concentration, continuous high-frequency ultrasound and dehydration on antioxidants, colour and chemical properties of rabbiteye blueberries. Food Chemistry, 101(3), 898–906.
Wikipedia contributors. (n.d.). Lycopene. Wikipedia. https://www.wikipedia.org
Петрушевский, В. В., Казанов, А. Л., & Бандюкова, В. А. (1985). Биологически активные вещества пищевых продуктов. Техника.
Скорикова, Ю. Г. (1959). Полифенольный состав плодов и овощей и его изменения в процессе консервирования. Краснодар.