Effect of freezing/thawing conditions and long-term frozen storage on the quality of mashed potatoes

The effects of freezing temperature (-80, -40 or -24 degrees C) and thawing mode (microwave or overnight at 4 degrees C) on quality parameters of mashed potatoes made from tubers (cv Kennebec) and from potato flakes were examined, as was the effect of long-term frozen storage on the quality of mashed potatoes. Mashed potatoes were tested for texture profile analysis (TPA) and cone penetration, oscillatory and steady rheometry, colour, dry matter, Brix and sensory analyses. In natural mashed potatoes, TPA hardness and oscillatory parameters showed that processing resulted in a softer product than the fresh control. The parameters were lower in the samples thawed at 4 degrees C than in those thawed by microwave at all the freezing temperatures used, which may be ascribed to gelatinisation of the starch released from damaged cells. Differences from the freshly prepared product decreased when the samples were frozen at -80 degrees C and thawed by microwave. No difference was found in sensory acceptability between samples frozen at - 80 and - 40 degrees C, which probably reflects the panellists' mixed preferences for air-thawed versus microwave-thawed samples. Increasing the time in frozen storage led to a natural mash with a firmer texture, higher L*lb* value and Brix; nonetheless, panellists found the samples at 0, 3 and 12 months of frozen storage equally acceptable. In commercial mash, penetration and oscillatory parameters showed that processing made for a firmer product than the fresh control, probably owing to retrogradation of gelatinised starch. Thawing mode had a significant effect on parameters, which were lower in the samples thawed at 4 degrees C. The structure and quality of commercial mash was more detrimentally affected by freezing and, therefore, we would not recommend either freezing or frozen storage of this mashed potato in the used conditions. Natural mash made from Kennebec potatoes should be frozen quickly and thawed by microwave in the conditions described to obtain a product more similar to that freshly made. If the samples are frozen by air blasting at -40 degrees C, the product can withstand frozen storage for one year. (c) 2005 Society of Chemical Industry.