Commodities / Zucchini
The quality of zucchini and yellow summer squash is often judged largely by appearance and size. The genetic background of a variety influences traits such as color that are directly associated with quality, and also controls how well a variety performs under pressure of insects, diseases, and stresses which can reduce quality. Harvest and postharvest practices have a particularly important role in maintaining quality of these commodities from the field to the consumer.
Zucchini and summer squash are usually slightly sweet. Flavor is not a major quality concern. Very rarely a squash fruit will be so bitter it is not edible and might cause medical problems. The bitter compounds are tetracyclic triterpenes called cucurbitacins. Although the reason for this occasional bitter squash is not definitely known, it has been proposed that it is due to rare cross-pollination with a bitter-fruited cucurbit during seed production, and subsequent planting and growth of a seed with the genes for bitterness. Contrary to what is sometimes thought, cross pollination of a zucchini or squash plant with a gourd plant will not cause the harvested zucchini or squash to be bitter.
Zucchini and summer squash for commercial market are harvested as immature fruit, while the skin and seeds are tender and the flesh is firm. Overmature squash with tough skin or seeds and pithy flesh is unacceptable
Zucchini squash varieties vary in color from light to very dark green. In the Eastern U.S. the market prefers light to medium green while the western market prefers medium to dark green. Yellow types of zucchini form a niche market. Yellow summer squash is usually a pale yellow that darkens as the squash fruit develops. Glossy skin indicates that the squash is not overmature.
Zucchinis will yellow more quickly if exposed to low levels of ethylene during storage.
The most desirable size for zucchini and summer squash will vary depending on the market, and may be specified to the nearest 1/4 inch. Whatever the desired dimension, uniform size is important for a high quality pack.
Squash fruit will grow more quickly when moisture is adequate and there are few fruit developing on the plant. Dry conditions and a heavy fruit load will slow the rate of growth.
Squash grows very quickly so harvest intervals should be timed to maximize the number of fruit of the desired size.
Zucchini should be straight and cylindrical with a slight taper towards the stem end. Yellow summer squash may be straight or curved, depending on the variety, with a larger blossom end. The crook-necked (curved) types are sold primarily in the Southeastern U.S. Misshapen squash may develop if pollination is inadequate. When pollination is incomplete the fruit develops unevenly because the ovary wall enlarges more adjacent to fertilized seed. One honey bee hive per one or two acres will help insure good pollination as long as male flowers are present. Sometimes female (pistillate) flowers open before male (staminate) flowers and there is little or no pollen available early in the season, resulting in poor pollination. This is more likely to occur with cool growing conditions.
Damage to Skin
Because squash is harvested as immature fruit the skin is very tender and easily scratched, detracting from quality. This is especially true for yellow squash. Very careful handling is critical in maintaining quality during harvest and packing. Varieties without spines and with an open growth habit make it easier to avoid scratches and abrasions on the fruit during harvest. Pickers can wear lightweight gloves to avoid scratching squash with their fingernails.
Several virus diseases can make summer squash fruit unmarketable. Watermelon mosaic and zucchini yellow mosaic viruses are the most common in the Midwest, but cucumber mosaic virus can also be a problem. Yellow squash with even mild infections will show green mottling while mild infections in zucchini may go un-noticed. Some varieties have tolerance or resistance to these viruses. Later plantings are more likely to become infected because aphids, which transmit the diseases, are present in greater numbers after midsummer. Using insecticides to control aphids does not prevent virus infection
Phytophthora capsici is a fungus that can devastate a field of squash. The fruit may not show symptoms when harvested but the disease will develop in transit after being packed. The fruit will quickly become water soaked and mushy and be covered with a growth of white mycelium. It may be necessary to abandon a field once the disease is present. The fungus can also attack the roots and crown of the plant.
Wet soils promote development of this soil borne disease. Recent research suggests that disease spores may be found in surface waters used for irrigation and distributed along drip irrigation lines.
Managing this fruit rot requires a multi-faceted approach. Growers use a combination of crop rotation, water management, and fungicide application. Specific recommendations may be found in the Midwest Vegetable Production Guide or through your local Cooperative Extension Service.
Summer squash and zucchini can be stored 1 to 2 weeks under optimum conditions.
Bruising the stem or fruit, or scraping the skin during harvest will promote decay and water loss and reduce shelf life. Squash stems should be cut cleanly from the vine.
Squash should be cooled rapidly after harvest to the proper storage temperature of 41˚F to 50˚F, and stored at 95% relative humidity. Waxes or oils applied to the squash can reduce water loss and help to maintain quality during storage. Temperatures below 41˚F cause chilling injury that reduces shelf life. Symptoms of chilling injury include water-soaked pitting and decay.
|Squash, Summer, Cooked and drained, 1 cup|
|Weight of Household Measure||% Water||Food Energy
|Protein||Fat||Saturated Fatty Acid||Mono - unsaturated Fatty Acid||Poly - unsaturated Fatty Acid|
|Cholesterol||Carbohydrate||Calcium||Phosphorus||Iron||Potassium||Sodium||Vitamin A (IU)|
|Vitamin A (RE)||Thiamin||Riboflavin||Niacin||Ascorbic Acid|
|(Source: USDA. Nutritive Value of Foods (HG-72), Release 3.2. 1990.)|
Content authors: E. Maynard and J. Neibauer, 2002. Links updated January 2012.