The use of pulsed magnetic field-assisted freezing to minimize the freezing losses in strawberries

Conventional freezing of perishable fruits results in the loss of bioactive compounds and antioxidants, having a bad impact on their nutritional quality. Preserving the natural attributes of perishable food commodities is an emerging trend these days. Strawberries are perishable fruits that are very sensitive to high temperatures and humidity, so their preservation in frozen form requires some efficient and advanced techniques. The use of pulsed magnetic field (PMF)-assisted freezing is an effective way to preserve the natural nutritional characteristics of strawberries. In this research, strawberries were subjected to four PMF-assisted freezing treatments: for T1 (control), the strawberries were frozen at −35 °C without the application of a PMF, while all the samples under the other treatments, from T2 to T4, were placed in a 3D-printed acrylonitrile butadiene styrene container inside an electromagnet with varied frequencies (T2 = 44.7 mT/60Hz, T3 = 44.7 mT/90Hz, and T4 = 44.7 mT/120Hz) and subjected to freezing at −35 °C ± 1 °C. PMF-assisted freezing (from T2 to T4) was evaluated according to the different parameters of phase change time, nucleation time, temperature, and degree of supercooling. The parameters for T3 exhibited better results because smaller crystals were formed and the cellular structures were well preserved. T3 also promoted the highest antioxidant capacity (4.8 mg TE/g), and the amounts of polyphenols (3.25 mg GAE/g) and anthocyanins (2.5 mg C3G/g) were greater as compared to those in the other treatment samples, as T1 had a 3.4 mg TE/g antioxidant capacity, a 2.36 mg GAE/g phenolic content, and a 1.17 mg C3G/g anthocyanin content. T2 had a 3.9 mg TE/g antioxidant capacity, a 2.62 mg GAE/g phenolic content, and a 2.11 mg C3G/g anthocyanin content. Similarly, T4 had a 4.4 mg TE/g antioxidant capacity, a 3.08 mg GAE/g phenolic content, and a 2.39 mg C3G/g anthocyanin content.