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THE EFFECT OF PRE-FRYING TREATMENTS AND FRYING METHODS ON TEXTURAL AND SENSORY PROPERTIES OF CRISPY FRIED DEHUSKED MUNG

Although fried dehusked mung bean (DM) is a well known nutritious crispy snack in Thailand and other Asian countries, there is rare information regarding its quality and the influence of processing conditions. The objective of this study was therefore to investigate the effect of pre-frying treatments and frying methods on the quality attributes of crispy DM. Expansion ratio, hardness and sensory acceptance (9-point hedonic scale) were quality attributes evaluated for fried DM. Boiling of DM at temperature of 100 ̊C was performed at varied periods of 1, 3 and 5 minutes respectively. The results indicated that boiling periods did not significantly influence on expansion ratio and hardness (p > 0.05) of final product but that for 3 minutes gave the highest overall liking score (p < 0.05). Subsequently, the boiled DM samples with moisture content of 56%w.b. were dried at temperature of 60 ̊C to obtain varied moisture contents of 30, 40 and 50%w.b., respectively. It was found that as the moisture content of pre-fried DM decreased, it’s expansion ratio significantly decreased and hardness significantly increased (p < 0.05). Then pre-fried DM aged at various conditions including atmospheric temperature (approx. 35 ̊C), cooling at 4 ̊C and freezing at -20 ̊C for 12 hours were compared. It was found that ageing of cooked DM at -20 ̊C before frying gave significant increase in expansion ratio, textural liking score and significant decrease in hardness of fried DM (p < 0.05). Nevertheless, the ageing conditions did not significantly effect on liking scores for appearance, colour and overall liking score (p > 0.05). Then the vacuum frying was performed under varied vacuum pressures (23-43 cmHg) and frying temperatures (130-145 ̊C) under equivalent thermal driving force (ETDF) of 60 ̊C and compared with atmospheric condition (76 cmHg, 160 ̊C). The experimental results suggested that frying DM under vacuum pressures of 43 cmHg and temperatures of 145 ̊C gave the highest expansion ratio, the lowest hardness and the lowest water activity (a w ) of the fried DM. Sensory evaluation along with SEM structural analysis indicated dramatically improved textural attributes with significantly higher overall liking score of fried DM under vacuum pressure over atmospheric counterpart and local commercial product (p < 0.05).