Effect of isochoric freezing on quality aspects of minimally processed potatoes

Abstract

The enhanced interest in greater convenience foods has recently led to the expansion of minimally processed potato products. This study investigated the effects of isochoric freezing on pre‐peeled potato cubes, including quality attributes (microstructure, texture, and color), nutritional value (ascorbic acid (AA) content, total phenolic content, and antioxidant capacity), and polyphenol oxidase activity. Isochoric freezing (−3 °C/30 MPa) was compared with isobaric freezing (−3 °C/0.1 MPa) and individual quick freezing followed by frozen storage at −20 °C for 4 weeks. The isochoric sample had lower drip loss and volume shrinkage as well as better preserved texture and microstructure than the other samples. All freezing methods caused an increase in total phenolic content and antioxidant capacity, but a decrease in AA content. Also, all freezing methods caused browning of the thawed potatoes, but isochoric freezing delayed its onset for more than 1 week. Practical Application Results showed that isochoric freezing of pre‐peeled and cut potatoes caused less freeze damage than isobaric and individual quick freezing, which might find application in the commercial preservation of minimally processed food products.

Effects of Isochoric Freezing Conditions on Cut Potato Quality

“…However, the increase in mass was significantly lower for these samples (2.3%) than for water-immersed potatoes (13.6%), since potato samples were in osmotic equilibrium with the AA solution. A previous study found no changes in the cellular tissue of potatoes frozen at −3 °C under isochoric conditions, suggesting that the slight increase in mass was probably due to the pressure-induced impregnation of the intercellular spaces in the potato tissue with the external solution [ 15 ]. This effect highlights isochoric freezing as an interesting tool for nutrient diffusion into the intercellular spaces and pores of solid foods.…”

“…For vacuum-packed samples and those immersed in water, BI values increased with a decrease in temperature. Previous authors have also found that isochoric freezing substantially reduced browning in potatoes but does not prevent it [ 15 , 16 ]. This might be due to the destruction of potato tissues and loss of cell compartmentalization at higher pressures and the subsequent increased interactions between polyphenolic substrates and PPO.…”

“…The increase in BI could also be due to an increase in enzyme activity with pressure. Previous authors had reported an increase in PPO activity with pressure in cut potatoes [ 15 , 25 ]. The vacuum-packed samples also had higher BI values (on average, 41% higher than fresh samples) than for samples immersed in water (on average, 10% higher than fresh samples).…”

“…A Texture Analyzer (Stable Microsystems Ltd., TA-XT2i, UK) with a 50 mm diameter circular flat plate (TA-25 probe) was used to determine the mechanical properties of the potato samples following the procedure described in Luscher et al [ 18 ], with minor modifications as described in Bilbao-Sainz et al [ 15 ]. The samples were compressed to 50% deformation in a single compression-decompression cycle at a speed of 0.1 mm/s.…”

“…In comparison, a potato has a shelf-life of 3–5 weeks at room temperature and 3–4 months in the refrigerator. The effects of isochoric freezing on quality aspects of minimally processed potatoes had been previously investigated [ 15 , 16 ]. The authors reported that cut potatoes frozen in an isochoric system showed better quality properties in terms of drip loss, volume shrinkage and texture than cut potatoes frozen at atmospheric pressure or individually quick-frozen potatoes.…”