Abstract
Commercial food processing has had a significant impact on reducing food spoilage and increasing accessibility to nutrient-dense vegetables. The commercial freezing process, in particular, has given producers the ability to store vegetables with minimized risk of microbial and enzymatic spoilage. Despite the effectiveness of freezing as a preservation method, there is evidence that pre-freezing procedures and prolonged storage can reduce the concentration of vitamins present within certain vegetables. Spinach, one of the most widely produced and consumed vegetables, is particularly susceptible to nutrient loss during the commercial freezing process due to its large surface area and high mineral content. This review summarizes the known effects of the freezing process on hydrophilic and lipophilic vitamins including vitamin C, thiamin, riboflavin, β-carotene, and α-tocopherol. There are two key mechanisms that lead to decreased vitamin concentrations, with the first being attributed to pre-freezing processes including washing and blanching which favours the leaching of hydrophilic vitamins. The second mechanism of vitamin loss is attributed to residual enzymatic activity during storage, where the degree of residual activity can be partially attributed to differences in blanching protocols and freezing practices. Understanding the mechanisms and extent of vitamin loss that the commercial freezing process imparts on leafy green vegetables can help inform future research on improved food processing methods that minimize nutrient loss. Implementing procedures that maintain nutrient retention in frozen vegetables has the potential to assist individuals in achieving their recommended daily intakes of micronutrients.
Highlights
The commercial freezing process has allowed consumers to store foods for extended periods of time with minimal food spoilage[1]
Research suggests that pre-freezing processes and prolonged storage of spinach can result in considerable losses of vitamin C, thiamin, riboflavin, and β-carotene, and minor losses of α-tocopherol[4,5,6,7,8]
The kinetic modelling from this study suggests that enzyme-mediated degradation varies with temperature in a logarithmic fashion, indicating that in industrial and retail environments, where temperatures are often below -18°C, further decreases in residual enzymatic activity may be observed
Summary
The commercial freezing process has allowed consumers to store foods for extended periods of time with minimal food spoilage[1]. The observed large losses of water-soluble vitamins are mostly attributed to pre-freezing processes, namely blanching, which results in the leaching of vitamins and other soluble components of the food[4,6] In this context, leaching can be defined as the loss or extraction of nutrients from the food by way of a fluid medium, namely water or condensed steam, that acts as a solvent. Prolonged storage at sub-zero temperatures has been shown to augment vitamin loss, with the proposed mechanism being residual activity of enzymes involved in vitamin degradation[9] This residual enzymatic activity can be increased by the process of freeze concentration, where enzymes and their substrates are concentrated within a fluid medium present between intracellular ice crystal formations[10]. This review will evaluate evidence related to the effects of the commercial freezing process on vitamin availability in spinach
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