Strawberries and Frozen Strawberries 

Summary information of Nirmal K. Sinha, Strawberries and Raspberries, Food science

Strawberry is a member of Rosaceae (Rose) family and Fragaria (F) genus. Fruits grow on stems in groups of three and are hand harvested at full ripeness. The flesh of strawberry is an enlarged receptacle and unlike other berries, seeds (achenes) are attached to the skin surface.

Strawberry is a popular dessert fruit (extensively used in ice cream and other desserts). It is also used in fruit fillings, jellies and jams, energy bars, breakfast cereals. About 75% of strawberries produced in the United States are utilized for fresh market, whereas the remaining 25% are frozen or processed into other products (USDA, 2003).

Strawberries are a good source of potassium and vitamin C. Fresh and frozen strawberries and strawberry juices are low calorie products. Even the sugar-infused and dried strawberries, which are used as snacks and as ingredients in various foods, on an ounce (28 g) serving size basis, contribute less than 100 calories. These products are also a good source of dietary fiber.

Frozen Strawberries

Strawberries are generally frozen either block or individually quick frozen (IQF) after the removal of stems and cap at the point of production. The preparatory steps after harvesting consist of strawberries vacuum precooling (about 0 - 2 C) the harvested fruit to maintain color, texture, and flavor and to remove field heat; air classifying to remove leaves, field debris, etc.; removing berry caps, leaves, etc.; quick rinsing or washing, preferably with about 20 ppm chlorinated water; inspecting and grading for size and defects; quick freezing the fruit individually (at about -40 C) in a blast air freeze tunnel; and packaging and storing under frozen temperatures. Quick freezing helps in minimizing large ice crystal formation, which is believed to cause drip losses on thawing. The IQF strawberries are free flowing, and hold their color and shape better. Thus, they are preferred as raw materials for manufacturing value-added products like freeze dried or infused dried strawberries.

Stabilized Frozen Strawberries

Processed frozen products such as stabilized frozen (strawberry fruit pieces are combined with a syrup matrix containing sweeteners, pectin, starch, and carrageenan or other gums, and heat processed) or infused frozen strawberries for use in ice cream, sorbets, yogurts, and bakery products are made by infusing and pasteurizing whole or sliced strawberries (Sinha, 1998) in sugar syrup or other types of sweeteners. These products typically are about 35 Brix, so that they do not become hard at freezer temperatures. The products are pasteurized and can be added directly to the formulations.