Following pre-treatment and freezing of mushrooms, there were significant decreases in lightness (L*) and hue parameter
of 7e35% and 2e30% respectively, while increases were noted in the a* parameter (0.5e0.9-fold), b* parameter (8e26%) and chroma (8e33%) (Table 1). Brennan et al. (1999)found a decrease in the L* parameter of approximately 27% inA. bisporusslices soaked in a sodium metabisulphite solution and stored for 20 days at 4 C. After 8 months of frozen storage, there were further decreases in lightness (3e9%) and generally in the a* parameter (10e20%); in mushrooms soaked in the sodium metabisulphite solution and organic acid solution there was an increase of 6e8% in the b* parameter. At all stages of the analysis, the highest values for lightness, lowest values for red colour (a*) and lowest activity of oxidoreductive enzymes were found in mushrooms soaked in the sodium metabisulphite solution (Tables 1 and 2). The product soaked in the organic acid solution had the lowest values for L* and b* parameters but the highest values for the a* parameter; in this case, however, the lowest value for lightness did not translate to the lowest activity of oxidoreductive enzymes. The use of onion extract in frozen products had a beneficial effect on mushroom colour; compared with the other vacuum soaked products, the hue plane was more shifted towards yellow (b*). The browning index (BI) was used to measure the degree of mushroom browning: the higher the BI, the greater the degree
of browning. Freezing resulted in a significant increase in BI values compared with the raw material (Table 1). The greatest changes occurred in mushrooms without any pre-treatment (NO), while the smallest were in those soaked in the sodium metabisulphite solution (SM). Further browning occurred during frozen storage was significant, except of product not soaked. Pre-treatment in sodium metabisulphite solution proved to be the most effective in retarding the browning
process; aqueous extract of onion was slightly (although statistically non-significantly) more effective than the organic
acid solution in this respect.
Following pre-treatment and freezing of mushrooms, there were significant decreases in lightness (L*) and hue parameterof 7e35% and 2e30% respectively, while increases were noted in the a* parameter (0.5e0.9-fold), b* parameter (8e26%) and chroma (8e33%) (Table 1). Brennan et al. (1999)found a decrease in the L* parameter of approximately 27% inA. bisporusslices soaked in a sodium metabisulphite solution and stored for 20 days at 4 C. After 8 months of frozen storage, there were further decreases in lightness (3e9%) and generally in the a* parameter (10e20%); in mushrooms soaked in the sodium metabisulphite solution and organic acid solution there was an increase of 6e8% in the b* parameter. At all stages of the analysis, the highest values for lightness, lowest values for red colour (a*) and lowest activity of oxidoreductive enzymes were found in mushrooms soaked in the sodium metabisulphite solution (Tables 1 and 2). The product soaked in the organic acid solution had the lowest values for L* and b* parameters but the highest values for the a* parameter; in this case, however, the lowest value for lightness did not translate to the lowest activity of oxidoreductive enzymes. The use of onion extract in frozen products had a beneficial effect on mushroom colour; compared with the other vacuum soaked products, the hue plane was more shifted towards yellow (b*). The browning index (BI) was used to measure the degree of mushroom browning: the higher the BI, the greater the degreeof browning. Freezing resulted in a significant increase in BI values compared with the raw material (Table 1). The greatest changes occurred in mushrooms without any pre-treatment (NO), while the smallest were in those soaked in the sodium metabisulphite solution (SM). Further browning occurred during frozen storage was significant, except of product not soaked. Pre-treatment in sodium metabisulphite solution proved to be the most effective in retarding the browningprocess; aqueous extract of onion was slightly (although statistically non-significantly) more effective than the organicacid solution in this respect.
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