Comparative studies of different heat treatments on quality of fried shallots and their frying oils

The objectives of this study were to compare the quality of shallot-flavour ed frying oil from microwave heat treatment with that from gas heat treatme nt. Frying of shallot pieces by the microwave treatment required shorter he ating time to obtain the same colour quality as through gas treatment. The amount of total volatile compounds of shallot-flavoured frying oil obtained from microwave treatment was greater than that from gas treatment. Oil-fry ing of shallots by microwave heating showed better oil quality, with lower acid and peroxide values than after frying by gas heating. In storage tests these two differently treated oils at 25 degreesC, the acid value (AV) sho wed no significant increase during storage for 80 days. However, the peroxi de value (PV) of these two oils increased in parallel as storage time incre ased. The effect of moisture content, of the shallots, on the quality of re sultant shallot-flavoured frying oil was studied. Slight moisture reduction of shallot pieces from 72 to 63%, by a toasting pretreatment gave the high est amount of total volatile compounds of the shallot-flavoured frying oil. However, this total volatile compounds decreased if the moisture content o f shallot pieces was less than 63%. (C) 2001 Elsevier Science Ltd. All righ ts reserved.