Updating Use of Glazing in the Frozen Seafood Industry

Seafood products are made from an important natural resource with a steadily growing consumption over the last several decades. According to a 2014 Food and Agriculture Organization report, the supply of fish food increased in the last five decades at an average annual rate of 3.2 percent, even outpacing population growth worldwide (1.6 percent). Since the 1990s this growth has been supported mainly by aquaculture production, which had a 6.2 percent annual growth rate between 2000 and 2012. Another recent trend has been the increasing demand for processed products, particularly frozen seafood products. In 2012, frozen seafood products accounted for 54 percent of the total processed fish for human consumption and for 29 percent of the total seafood market for edible purposes.

According to the Code of Practice for Fish and Fishery Products, glazing is the application of a protective layer of ice formed at the surface of a frozen product by spraying it with, or dipping it into, clean seawater, potable water, or potable water with approved additives, as appropriate. When frozen fish are to be stored, depending on packaging, they are exposed more or less to the cold air of the freezing chamber. Without glazing, the oxygen of the air will react with the fats (turning them rancid) and drying and dehydration of the product will not be prevented (which may lead to freezer burn). In addition, glazing is a physical barrier that protects the product from damage during production, packaging, transport, and retail.

The most common method of glazing is dipping, where frozen seafood products are immersed in a tank filled with cold water for a period of time, creating an ice coat that completely surrounds the product. Glazing carried out by spraying uses proper equipment to spray glazing solution over the product. Although dipping is a relatively simple and cheaper method, with more production capacity than spraying, it is more difficult to control the amount and uniformity of glaze. The amount of glaze formed is dependent on factors such as: a) product and glazing solution temperature; b) size, shape, and surface area of the product; and c) glazing time.

Glazing solution is commonly used at a temperature close to the freezing point. The amount of glazing added to the product should be considered wisely by manufactures in order to effectively guarantee the protection of the product, without being perceived by consumers as a method of deceiving and/or improving manufacturers’ profits.

Glaze Lost During Storage

Until now glaze has been viewed as a substance with the main function of acting as a barrier to protect the product surface from exposure to the (cold) environment. With that in mind, the amount of glaze should be defined according to the time it takes for it to be reduced during storage until the product’s surface is exposed to the cold temperatures. However, that is not the case since there is no information available regarding the amount of glaze needed to guarantee that. To address this goal a paradigm of the frozen seafood industry must be broken, but first let’s discuss how industry currently measures glazing.

It is common to read expressions like over glazing or excessive glazing. Unless a threshold is defined between client and manufacturer, these terms only reflect a subjective judgment since there is no threshold defined for the amount of glaze that is necessary to protect the product. On the other hand, when organizations intentionally mislabel the product weight in the pursuit of financial profit, it should be addressed as fraudulent behavior and not as excessive glazing.

Chart 1: Coating/glazing thickness variation along dipping time for salmon at -25° C/-13° F glazed with water at 2.5° C/36.5° F ( ) and coated with chitosan at 2.5° C/36.5° F ( ). Each point represents the mean ± standard deviation of 15 replications.