The consequences of varying degrees of blanching on the quality of frozen green beans
1984
Katsaboxakis, Z.K. | Papanicolaou, N.D. (Ministry of Agriculture, Lykovrissi-Athens (Greece). Food Technology Inst.)
The effect of the degree of blanching (0-3 min and every 30 secs) in boiling water (98 +/- 2 deg C), on the quality of green beans during frozen storage at -18 deg C, was studied. Quality was evaluated by organoleptic tests (for colour, odour and taste) and determination of total Chlorophyll, L-ascorbic acid, Peroxide index, Colour (Hunterlab) and Peroxidase activity. Samples which were frozen without previous blanching showed a 75% loss of L-ascorbic acid during the first 6 months of frozen storage and an almost complete loss 6 months later. The same samples showed an over 50% loss of total chlorophyll after 12 months of frozen storage and a gradual loss of total Pheophytin in the same period. The Peroxidase test showed an almost complete enzyme inactivation (96%) in samples blanched for 30 secs. Peroxide index was rapidly increased in unblanced samples. An increased Peroxide index was also found in samples blanched for 30 and 180 secs after the 9th month of frozen storage. Samples blanched from 0.5 to 3 min had a good total chlorophyll retention with no significant differences among them for the first 6 months of frozen storage. However after that period an increased loss rate was found in samples blanched from 2 to 3 min. The organoleptic evaluation of odour and taste gave no significant differences for samples which had undergone blanching. The odour and taste of unblanched samples was rapidly deteriorated during frozen storage. Their odour was considered unacceptable after 3 months of frozen storage. Finally a significant green colour difference was noted among samples with different degree of blanching. Samples blanched from 30 to 90 secs were scored higher colourwise than samples which received more severe heat treatment
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