Different frozen foods have varying vulnerabilities during storage time depending on how fast the food develops discolorations, irregular flavors, and spoilage indicators like mold. Other factors that can influence the vulnerabilities include the quality and state of the initial raw product, processing method, ingredients, handling techniques, and packaging materials.
The underlying principle is that the colder the storage temperature, the longer the storage life, with zero degrees Fahrenheit as the benchmark temperature for food storage over six months. For food industry producers, predicting the shelf life is thus essential and depends on temperature tolerance time (TTT) and practical storage life (PSL).
Unlike dry foods, which have a wider tolerance for shelf life, time and temperature dramatically affect frozen foods’ quality in terms of texture, color, and flavor. TTT refers to the food’s resistance to the loss of quality. Regulations by the United States Department of Agriculture (USDA), other food regulators, and the pre-packed and frozen foods company standards aim to ensure that the time and temperatures of stored food remain within the tolerances.
Though maintaining the tolerances is costly for large volumes along the food chain, noncompliance can lead to customer dissatisfaction and risk of food loss or contamination. With all foods, there is quality loss along the chain, and the TTT can be estimated at different stages, divided into different isothermal episodes along the chain. Known as the TTT theory, with a known initial refrigeration temperature, the characteristics of the frozen food can be determined at different stages along the chain, and the remaining time is designated as the PSL or shelf life.
PSL, also known as the shelf life, directly affects the consumer acceptability of the frozen product and consumption safety. It indicates the duration the consumer can eat the food before spoilage and the period the food remains fresh and safe for consumption. The determining factors for PSL include the product, processing, and packaging (PPP).
The frozen product is the actual food, whether a fruit or meat, and the type of food significantly determines the PSL. Fish filet has a shorter PSL than frozen lean meat, even when frozen. Lean meat has approximately double the PSL of fatty meat, as the fat is prone to oxidation over time, which increases the chances of spoilage. Frozen food with perishables like tomatoes also exhibits shorter shelf lives than food with nuts.
The processing refers to the preliminary treatment that the food is exposed to and the freezing operation. The process should be suitable for food and hygiene all along the processing chain, from preparing the raw materials, cooking, and handling to packaging.
Lastly, the packaging aims to prevent contamination by microbes, dehydration, and loss of nutritional value. The packaging material varies and can range from tray sealing to cans. The material should be safe for food, stable, and without flavor or odor.
For ready-to-oven frozen foods, the packaging material should be stable at low and high temperatures, be tear-resistant and offer protection against UV light. The most common materials for packaging frozen foods are plastic film, cardboard lined with plastic film, and trays sealed with plastic film, among others.
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