How does time or season of the harvest affect the chemistry and nutritional contents of food?

Answer 1

I was recently asked this great question: Is there a nutritional difference in foods when they are in season vs. out of season? The short answer is yes --- foods are more nutritional when in season. More foods need to be tested until we have exact details on which foods differ in what kind of nutrients and to what extent. However, I believe that in this case the details do not matter that much. The important question is: "Should I eat seasonally because of this?" Let's look at some things that we do know and figure out the answer to this question.

Looking at the facts

The nutritional difference between seasonal and non-seasonal produce is due to two factors, both of which we will now examine in detail.

1. Out of season food is often not local

Eating in season means eating what is in season around you ---it is always "summer" somewhere! Therefore eating seasonally generally means eating (more) locally. Produce starts to lose nutrients and flavor as soon as it is harvested, so when food has to travel hundreds of miles before arriving at the supermarket, a lot of nutrients and flavor are lost.

Furthermore, since manufacturers want the food to look fresh and ripe when it hits the shelves, produce is often harvested too early and then later sprayed with plant hormones to speed up ripening. Since the ripening occurs so quickly and often in some crowded box, the plant cannot accumulate as many nutrients and as much flavor as it would if it slowly ripened on its own. This explains why a strawberry can have a beautiful deep red color but taste like nothing.

Weather differences can affect nutrients directlyPlants create phytonutrients in order to protect themselves from damaging UV-rays (sun), pests, and pollution. Since our own biochemistry is not all that different from a plant's, many phytonutrients can protect us as well.

In many cases, radiation from sunlight acts as the trigger that puts the biochemical processes in motion which ultimately create these phytonutrients, similar to when your skin produces more melanin (brown pigment) in response to sunlight in order to protect itself. Chilling is another possible environmental trigger thatpositively affects phytonutrient content in plants.

Since the amount of sunlight (and other possible triggers) is tightly linked to different seasons, phytonutrient content is too. A lot of phytonutrients are responsible for the color and flavor of a food, so it follows that they get compromised as well.

If taste is affected, nutrition most likely is tooEven without any direct evidence, we could have arrived at a similar conclusion. You only have to compare the flavor of a fresh vs. seasonal tomato and you know they are different. As stated above, both flavor and nutritional content comes down to a plant's biochemistry. Biological systems are so complex and interconnected that when a chemical difference causes a change in flavor, it likely also changes the nutritional value. The benefits of eating more seasonallyThere are definitely many benefits to eating more seasonally beyond nutritional differences. First of all, produce is often cheaper when in season. Also, there is absolutely no doubt that seasonal and fresh food tastes much better than what you usually find in supermarkets out of season. This can definitely help some people to eat more produce. A friend of mine converted from a complete tomato hater to a tomato lover when he tried a ripe fresh tomato for the first time.

Focusing on the food that is available during each season also helps you to eat a wider variety of foods. Every food has its very own nutrient composition (different phytonutrients) and eating different types of foods helps you reap a wide variety of health benefits. A lot of people have their standard fruits and vegetables that they consume all year round. While this is certainly good, eating different types of vegetables and fruits is almost as important as eating them in the first place.

Impact of Cultivar, Harvesting Time, and Seasonal Variation on the Content of Biophenols in Olive Mill Waste

Olive mill waste (OMW) contains substantial amounts of valuable antioxidant biophenols that can be recovered for possible applications in food, pharmaceutical, and cosmetic industries. However, the impact of cultivar, harvesting time, and seasonal variation on the phenolic composition of OMW has not yet been assessed. Total phenols, antioxidant activity, and phenol profiles of OMW extracts from five different Australian-grown cultivars (Barnea, Correggiola, Manzanillo, Mission, and Paragon) were studied at four different harvesting times in the 2004 season. The impact of seasonal variation was assessed by comparing total phenol content, antioxidant activity, and phenol profile of two cultivars (Correggiola and Mission) harvested in the 2004 and 2005 seasons. The phenol content and antioxidant activity at different harvesting times were mainly a function of the olive cultivar. Harvesting time had a quantitative effect rather than a qualitative effect on the phenol profile. Intercultivar and harvesting time variation accounted for a 2−5-fold change in the total phenol and antioxidant capacity, while levels of individual biophenols experienced up to 50-fold change. The phenol content and antioxidant capacity of OMW significantly changed between seasons with different variation patterns for different cultivars. EVANGEL FARAZ EMMANUEL BASHIR of class 8-A ST.Patricks high school CAMBRIDGE section