Osmotic concentration of potato in corn syrup solutions prior to freezing

The feasibility of osmotic concentration of potato strips in corn syrup solutions, and the use of osmotic concentration as an intermediate step in producing frozen, French fried potato, were demonstrated. Potato strips were contacted with 26 DE and 43 DE com syrup solutions at three solute concentrations (40, 50 and 60%, w/w) and three temperatures (20, 30 and 40°C) for six time intervals (0, 1, 2, 3, 4 and 5 h). Moisture loss from, and solids gain by, potato were monitored. In general, moisture loss for 43 DE com syrup solutions was higher than that for 26 DE solutions. For each DE, moisture loss increased with increase in temperature and solute concentration. Moisture loss was very rapid at the beginning and decreased gradually with time of osmosis. Up to 70% of the original moisture content was removed, with a maximum solids gain of 0.43 kg/kg of original solids and a net weight reduction of about 50%.

Moisture loss was modeled using an exponential equation, assuming that the resistance to moisture movement remained in the potato tissue. Parameters of the model were estimated using non-linear regression with high R²-like values (0.95 and 0.96 for 26 and 43 DE, respectively). Solids gain varied inconsistently with solute concentration, temperature and time of contacting. Leaching of soluble solids from potato tissue was also observed.

Potato strips, concentrated with 26 DE com syrup solutions of 60% (w/w) solute concentration at 21°C for 3 h, were blanched in steam (atmospheric pressure), air-cooled, frozen in a CO₂ freezer and stored for 2 months. The "control" was similarly processed and stored as above but without osmotic concentration. At 0 and 2 mo, the control and osmotically treated frozen potato strips were deep fried in oil at 195°C for 4.5 and 1 min, respectively, and evaluated for moisture content, oil content, color, texture and sensory acceptability.

Initial moisture contents of fresh and osmotically concentrated potatoes were 80% and 65% (w.b.), respectively, with their respective final moisture contents of 47% and 53% (w.b.) after frying. Oil content of osmotically treated potato after frying was one third of that of the control. Color of the osmotically treated potato was slightly darker than that of the control, although the color of both potatoes was within the acceptability range. Osmotically treated potato exhibited softer texture than the control. Sensory evaluation of fried potatoes by a 50-member panel, using an eight-point hedonic scale and a five-point purchase intent scale, indicated that the panelists preferred the control over the osmotically treated potatoes. They would more likely purchase the control than the osmotically treated potato. "Softer texture" and "inadequate frying" were identified to be reasons for lower acceptability of the osmotically treated potato. The acceptability of the osmotically treated French fried potato might be improved by taking into account "doneness" of potato during frying, instead of just the color acceptability.