Food is made up of many parts, including water, protein, carbs, fats, vitamins, and minerals. These parts are affected in different ways when food is frozen, and this affects the quality of the food. Below, we’ll talk about how each part can be damaged during frozen storage.
Water Migration
When food is frozen, the water in it can move around and cause problems. This is called water migration and it can happen in a few ways, like losing water through sublimation, or when ice crystals change shape.
Moisture loss is a big issue because it can make the food dry and change the way it looks and tastes. When frozen food loses too much moisture, it can get freezer burn, which is when it looks grayish-brown and leathery. Moisture loss can also affect the weight of the food, which can be bad for the company selling it.
Frozen dough can lose water and form frost inside the package bags, which can make the bread harder and change its quality.
When ice crystals change shape and become bigger, it can also affect the way the food looks and feels. This is called recrystallization and it can happen to ice cream, frozen desserts, and delicate plants like broccoli and strawberries. It can also affect food made with dough or starch.
Finally, when frozen food is thawed, water can drip out and cause nutrient loss. This is especially important for meat, vegetables, and fruits.
Protein Denaturation
Proteins in frozen food can become denatured due to freezing, which limits the shelf-life of frozen foods.
This is a well-known issue with gluten proteins in frozen dough. The degradation of glutenin macropolymers through interchain disulfide bond breakage is the cause of the problem, leading to reduced viscoelasticity.
Frozen storage also leads to conformational changes in glutenin and gliadin, which further weakens the water-holding capability, promotes ice recrystallization, and disrupts the glutenin network.
Additionally, frozen storage degrades the foaming properties of gliadin due to reduced molecular chain flexibility, surface hydrophobicity, and absorption ability at the air-water interfaces of g-gliadin.
In marine fish, formaldehyde from trimethylamine oxide can modify myofibrillar proteins and collagen by crosslinking adjacent polypeptides.
Finally, oxidative reactions, such as lipid peroxidation, are also involved in denaturation and deterioration in functional attributes of muscle proteins during frozen storage.
Starch Deterioration
Starch is the main component in most staple foods and freezing can change its properties. When starch-based frozen food undergoes freezing, it can result in textural changes that make the product undesirable to consumers.
For frozen precooked foods like rich starch paste and bread, the starch is gelatinized before being frozen. Freezing can disrupt the microstructure of the starch network, causing a high degree of syneresis in gelatinized starches and enhancing starch retrogradation, which makes frozen food products harder.
In frozen uncooked foods like frozen dough, the ungelatinized starch can deteriorate in several ways. Starch is the largest volume fraction of solids in dough, and the freezing treatment can alter its structural and functional properties. Freezing pressure induces irreversible changes in amylose and amylopectin, and frozen storage time is negatively correlated with the amylose/amylopectin ratio.
A new technique has been developed to study changes occurring during frozen dough storage, based on the absorption bands of the crystalline and amorphous zones of starch. It was found that a rapid retrogradation occurs in frozen dough by decreasing the amorphous material with an increase in crystallinity.
A series of studies were conducted to elucidate the comprehensive deterioration mechanism of starch in frozen dough. Wheat starch accelerated bread staling by altering the integrity of starch granules and leaching starch-associated materials after multiple freeze/thaw treatments. Frozen bread quality can be improved by increasing the content of A-granules.