Thermal, oxidative and hydrolytic stability of selected frying shortenings evaluated by new and conventional methods

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Virginia Polytechnic Institute and State University

The thermal, oxidative, and hydrolytic stability of several frying shortenings were studied via chemical, physical and sensory analyses. Corn, cottonseed and peanut oils, and cottonseed and soybean liquid shortenings were tested under static heating conditions, while peanut oil, and cottonseed and soybean oil liquid shortenings were evaluated under commercial frying conditions.

The research had two objectives: to evaluate the relative stability of the various shortenings under both heating condition; and to evaluate new or modified quality assessment methods which would provide early prediction of heat abuse for the fast-food industry.

Six of the conducted analyses were conventional or modified: free fatty acids; polar components; gas chromatograph volatile profiles; viscosity; FoodOil-Sensor; and sensory. Three were new: contact angle; high temperature; and high-temperature gas chromatographic analysis of triglyceride; and polar component % as determined by high-performance thin-layer chromatography (HPTLC).

Under static heating conditions, varying heating periods or shortening types had significant (P<0.000l) effects on the resulting data of the following tests: free fatty acids; polar component; total volatiles; dielectric constant; viscosity; polar component % measured by HPTLC; contact angle; and sensory analysis; but heating time had no significant effect on triglyceride profiles

Under commercial frying conditions of chicken nuggets and filets, heating time had significant effects on changes in the dielectric constant; free fatty acid %; viscosity; contact angle; and sensory rating; also it had a significant effect on the polar component % under chicken nugget frying conditions only. Furthermore, heating time had no significant effect on polar component % under chicken filet frying conditions and on polar component % by HPTLC under both frying conditions

Cottonseed oil liquid shortening had sensory scores equal to peanut oil under static and commercial frying conditions even though peanut oil exhibited a greater chemical and physical stability. Soybean oil liquid shortening had an objective quality identical to peanut oil, however, its subjective quality was lower. Cottonseed oil liquid shortening had better flavor but less objective stability than soybean oil liquid shortening

The cut-off quality level for the shortenings was not reached, because all the shortenings were discarded after seven days of use which was before the onset of significant-quality deterioration.

The best on-site index of shortening stability was the FoodOil-Sensor reading (dielectric constant) which was followed by the free fatty acid test.