Local Food, Issues, 3: Freshness and Nutritional Quality / Vegetables and Fruits

One often stated reason that consumers should prefer local foods over factory foods is that local foods are fresher and have higher nutritional quality. This claim is sometimes coupled with the qualifier, "organic"; hence, it's local, organic foods that have the highest nutritional quality. The belief behind the claim is that foods begin to lose nutrients at the moment of harvest or slaughter. The sooner they are consumed, the more nutrients will remain in them. Fruits and vegetables that travel interstate or international distances will have lost many nutrients by the time they are eaten.

Certainly, this belief in the superior quality of fresh, local produce meets with casual experience. The best restaurants grow their own produce and herbs or purchase them locally. The food we have eaten, harvested that day from the garden, bursts with flavor, moisture, and presumably nutritional quality. At the same time, we have all seen how a week's storage of fresh produce in the home refrigerator's produce draw leaves wilted, dehydrated fruits and vegetables diminished in flavor and color.

Farmers Market, Manhattan, 2007

Unfortunately, it is difficult to find publicly available evidence, on the Internet, to settle the question about freshness in a detailed scientific way. Scientific evidence surely there is in scientific journals and industry journals; but such evidence is hidden behind password gates. Within the limitations of Internet publication, we shall try to determine the truth of the claim, fresher is better.

Because of the differences in defining freshness for vegetables and fruits, on the one hand, and meats, on the other hand, we shall treat these foods separately.

We also distinguish between nutritional quality and food quality. Nutritional quality refers to the chemical and biological components of a food that benefit its consumer's health and growth. Food quality ("palatability") refers to the aesthetic qualities that induce a consumer to eat a food, such as lack of blemishes or spoilage, brightness of color, sweetness, tenderness, and so on, depending upon what vegetable, fruit, or meat is being discussed. We will be discussing only nutritional quality.

Picked This Morning, Strawberries, Farmers Market, Riverside, California, 2007

What causes nutritional quality?

The amount of time after harvest that a food lays around, losing nutrients, is, as it turns out, just one of the causes of nutritional quality. To determine the greatest source of differences in nutritional quality, we need to sort out the many factors in determining nutritional quality of the food at harvest and the food at time of consumption. Here we go:

Table 1. Factors in nutritional quality of vegetables and fruits

1. Soil quality
2. Water quality
3. Sunlight
4. Cultivation practices--
   1. conventional
   2. natural
   3. organic
5. Harvest time
6. Harvest methods
   1. Manual
   2. Mechanical
   3. Careful handling
   4. Commodity handling
7. Post-harvest storage, prior to any processing
   1. Temperature
   2. Humidity
   3. Sunlight
   4. Packing
8. Processing--
   1. None (consumer's garden, farm gate)/raw at time of sale
   2. Cleaned of dirt, washed, trimmed (farm gate, farmers' markets)/raw at time of sale
   3. Fresh-cut packed (cleaned, washed, packed into bags[e.g., salad greens])/raw at time of sale
   4. Fresh packed-preserved (microfilm waxes and/or preservatives to retard spoilage [e.g., apples, oranges])/raw at time of sale
   5. Canning
   6. Freezing
   7. Freeze-drying
   8. Drying
   9. Curing
   10. Pickling
   11. Pasteurizing
   12. Processing into prepared foods and meals
   13. Other/otherwise
9. Time between harvest and consumption
10. Cooking preparation of food by consumer, if not eaten raw

Looking over this list of ten factors, we can easily see that within each category, many sub-factors must be measured to determine their relative role in contributing to nutritional quality. Under cultivation practices, for instance, we would need to examine fertilizers--type (chemical, compost, composite), and when and how often fertilizers are applied. We might also, under the category of cultivation practices, examine weeding techniques and pest control.

To examine cooking preparation by the consumer, we would have to sort out the different effects of boiling, steaming, baking, frying, grilling, and so on, on the nutrient content of the products (frying appears to remove more nutrients from produce than other cooking techniques). We would also have to look at the effect of herbs, spices, sugars, and other flavorings added to the produce by the consumer in cooking, on the produce's nutritional quality at the time it is consumed.

Such factors as soil quality and cooking preparation are not irrelevant in evaluating the net nutritional quality of produce available to the consumer at the time of eating. We shall return to this point later.

What research shows

The single largest determinant of the nutritional quality of a vegetable or fruit at time of harvest is the soil quality, including its conditions, in which the plant grew (table 1, 1-4).

Whether a soil is rich in minerals and micro-organisms, is properly drained and aerated with necessary luff, and has the right amount of moisture and sunlight, determines the nutritional quality of the vegetable or fruit.

Soil conditions are more important than whether the vegetable or fruit is organic or conventional in culture in determining the nutritional quality of fruit or vegetable at time of harvest (Tina Finesilver, "Comparison of Food Quality of Organically Versus Conventionally Grown Plant Foods"; 'Google' Tina Finesilver for other scientific studies). Most investigators have been unable to find major differences in nutritional quality of vegetables and fruits between organic and commodity samples (see, however, Organic Trade Association, "Nutritional Consideration [of organically grown produce]".).

On the issue of organic versus conventional farming cultivation of produce, there is an important caveat. Vegetables and fruits contain many more minerals, vitamins, enzymes, and other components than are normally measured in making such comparisons. Tests usually relate to the few important elements in the fruit or vegetable that appear in the USDA food pyramid,  which are the consumer's main guide to nutritional quality. There is some indirect evidence that organic produce retains its nutritional quality longer than conventionally cultivated produce (Tina Finesilver, "Comparison of Food Quality of Organically Versus Conventionally Grown Plant Foods"; 'Google' Tina Finesilver for other scientific studies); but it is difficult to know the implications of this knowledge. Scientists don't know, as far as I can tell, how all these elements chemically relate to one another, to their activity in the human digestive tract, how well they cross the intestinal cells into the blood, and to health and illness and growth in the people eating them. It is difficult, therefore, to evaluate the practical importance of consuming fresh organic produce versus fresh conventionally farmed produce ("A Summary of the Safety and Nutritional Quality of Organic Food", prepared for CropLife Canada by Safefood Consulting, 2007.).

The single greatest determinant of the nutritional quality of a vegetable or fruit at time of consumption, if it is consumed raw, is (other things being equal) the amount of time between harvest and consumption.

The bare claim of nutritional superiority of the freshest foods is verified.

Why? When a fruit or vegetable is harvested, it continues to "live." By live, we mean that the fruit or vegetable continues to undergo metabolic and chemical changes. Some fruits, for instance, ripen--make sugars--off the plant.

After a vegetable is harvested and after the fruit has ripened, it begins to decompose (or spoil or deteriorate). Decomposition involves several processes. Oxygen in the atmosphere enters the produce and burns (oxidizes) its cells. Micro-organisms enter the produce and consume it. Enzymes released by the fruit or vegetable and by micro-organisms breakdown the components of fruit and vegetables, such as pectin and sugar, making them inedible. Water in the fruit evaporates out of the fruit or vegetable and is not replaced. (Dehydration occurs rapidly in households refrigerators, as homemakers observe.)

Decomposition is speeded, and can begin before harvest, if the fruit or vegetable surface has punctures to admit oxygen and micro-organisms. Regarding fruits, the casing of the fruit, if unpunctured, will protect the fruit against oxygen and micro-organisms until it is fully ripened. Heat also affects the fruit or vegetable. High heat breaks down enzymes in them. Punctures releases vitamins.

Decomposition increases in intensity as time of storage lengthens; nonetheless, it can be significantly delayed by careful handling, avoidance of contact of the fruit or vegetable with human and animal pathogens (such as found in manure used to fertilize), and storage in cool, dark environment. It is to prevent spoilage that preservation of produce is done by canning and freezing, for instance (see factor #8 above).

Studies have been conducted comparing the rate of nutrient loss in storage of fresh-cut vegetables (e.g., cleaned, cut, chlorine-washed raw salad greens in closed packs) and raw vegetables and fruits. In general, these studies show little difference in nutrient quality loss between the two, fresh-cut and raw (International Fresh-Cut Produce Association, "The Convenience, Nutritional Value and Safety of Fresh-cut Produce"). so the following results are also a good indicator of the storage life and nutrient quality of local, fresh fruits and vegetables (d := degrees f := Fahrenheit).

• Broccoli. Stored 21 days at 39d f. vitamin C level stable.
• Carrots. Stored 10 days at 39d-45d f. No loss of vitamin A precursors.
• Kiwifruit. Stored 6 days at 32d f. No loss of vitamin C.
• Orange slices. Stored 12 days at 39d f. No loss of vitamin C.
• Potatoes. Stored 2-4 days at 38d f. Increased vitamin C due to continued synthesis in the fresh-cut pack.
• Watermelon. Stored 7 days at 36d f. Insignificant loss of lycopene.

As we can see from this list of representative produce, how long a particular fruit or vegetable will store without great loss of nutrient content or spoilage is unique to each particular product.

Evaluation of practical importance of freshest local foods

The superior nutritional content of freshest local foods at time of harvest is unimportant by itself. What is important is the nutritional content of foods when they are eaten. The issue of foods when eaten (looking only at nutritional quality) is affected by so many factors that the significance of fresher and local becomes less important.

Consider how much time a food is actually stored before consumed. Few consumers eat fresh foods the day they purchase them; rather, they store them for a few days. If a farmer sells produce at a farmer's market to the consumer one day after harvesting, and the consumer stores the food for three days before eating it, then the food has been stored for four days, losing nutrients. In this case, why is local, fresh food better in nutrient quality than food shipped a thousand miles by refrigerated truck and placed in markets on the third day after harvest, then to be consumed several days after purchase? The evidence is, the local food is not significantly superior.

Consider the issue of preparation and cooking methods. Except for salads and fruit, most produce is consumed cooked. Choice of cooking method has a greater impact on net nutritional content of the food when consumed than a few days more or less of storage in the refrigerator.

The issue of food quality in fruits and vegetables is, in practical terms, as important as nutritional quality. The beginning signs of food spoilage will inhibit many consumers from eating the produce, even it its nutritional quality remains great. Growers and grocers testify that most consumers will not even purchase blemished, but highly nutritious, fruit and vegetables. Palatability, as marketers know well, is important. In this case, the retention of nutritional quality is of no value whatsoever, because it is not being consumed!

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Contents

Local Food

1. Definitions and Contexts
2. The Case for Global Food
3. Freshness and Nutritional Quality / Vegetables and Fruits
4. Freshness and Nutritional Quality / Meats
5. Food Safety
6. Pesticides
7. National Security