Effects of water blanching on pea seeds.

Abstract

SummaryLaboratory scale experiments were conducted to elucidate the main mechanisms responsible for changes in the proportions of ascorbic acid (AA) and dehydroascorbic acid(DHA) in peas during water blanching. Studies utilized hand‐harvested peas from specially grown Dark Skinned Perfection (DSP), Swan and Swift cultivars. The influence of pea size/maturity, blanch time and damage to the pea were studied over the temperature range 35–97°C.With increasing DSP pea size/maturity, the proportion of AA oxidized increased, and the proportion of AA leached into the water decreased when blanching between 45 and 65°C. Maximum AA oxidation occurred at 60°C and leaching became the prime mode of loss above 70°C. Leaching of AA from DSP peas increased almost linearly from 40 to 97°C.Damaging peas by bruising and slitting the testa, induced enhanced AA oxidation below 60°C and allowed immediate leaching of vitamin C largely as DHA even at the lowest blanch temperatures. Results suggested that the oxygen content of the tissues was a factor limiting the amount of AA oxidation. Cultivars Swift and Swan contained higher proportions of DHA particularly in the testa tissues, and calculations indicated that greater proportions of vitamin C were leached as DHA. A negligible proportion of AA was oxidized and some 28% of the initial AA was leached into the water when undamaged DSP peas were blanched at 97°C for 1 min. Bruised plus slit peas lost significantly more AA than undamaged peas when blanched at 97°C. Further evidence indicated that the micropyle serves as a major pathway for leaching losses.