Starch gelatinization and physical quality of pea flakes in canine dinners as affected by soaking, steam treatment and infrared radiation

Cleaned, whole smooth green peas (Pisum sativum L.) were reconstituted by soaking in tap water of 40¿°C (15, 20 or 25¿min) and subsequently either toasted (100¿°C during 1.5¿min) and infrared (IR) radiated or just IR radiated. For IR radiation, a small-scale, propane-fired IR radiation plant was used with average residence times of 58 and 92¿s respectively. After exiting the conveyor belt, peas were held for a pre-determined period (holding: 0, 15 or 30¿min respectively) in a well-insulated container. Finally, all radiated peas were flaked (roll distance 0.75¿mm) in a flaking mill located posterior to the IR plant and analysed for chemical and physical properties. Initial pea starch gelatinization degree (SGD) was 10.1% at a total starch content of 410.1¿g/kg. Infrared processing during 92¿s significantly improved the SGD (from 10.1% to 32.8%) of pea flakes compared to treatment during 58¿s (SGD of 18.6%). The SGD was further improved with steam treatment of peas, prior to IR. For all determined parameters, no effect of holding time could be observed. Starch gelatinization degree can be improved by soaking, toasting and IR processing. The substantial improvement of SGD, however can be only obtained by a longer IR residence time as well as through toasting, prior to the IR processing. The improvements in SGD, however are paralleled by a lower durability of flakes (range 34.9% to 87.4%).