EXPERIMENTAL PROCEDURES
Chicken fat. Rendered chicken fat was procured from a regional poultry renderer (Simmons Foods®, Silom Springs, AR). The experiment was begun within one week of the fat rendering.
Treatment of fat with antimicrobials . An aliquot of chicken fat was transferred into 90 clean and grease-free plastic cups and treated with two of the acidulants, 0.5% SBS, 0.5% LA or left untreated (control). The control consisted of distilled water only. The treatments were added to attain a 3% added moisture level in fat. All the sample cups were incubated at 40°C for up to 6 weeks. All subsamples for oxidative measurements were from the middle of sample cups and were only chicken fat (not added water) at the various pre-determined time intervals.
Shelf life study of rendered chicken fat. For the determination of free fatty acids, (American Oil Chemists’ Society (AOCS) official method Ca 51-40 was used) 75 ml of hot neutralized alcohol was added to 7.05 gm of well mixed sample in an Erlenmeyer flask followed by 2 ml of phenolphthalein indicator. Shaking vigorously, the content was titrated using 0.1% potassium hydroxide (KOH) until the appearance of first permanent pink color of the same intensity as that of the hot neutralized alcohol which persisted for at least 30 seconds.
The peroxide value of the fat was determined (AOAC official method 965.33) by adding 30 ml of acetic acid: chloroform (3:2, v/v) to 3 gm of sample in an Erlenmeyer flask with a glass stopper. After swirling to dissolve, 1 ml of saturated potassium iodide solution was added and mixed well. Then, after 1 min, 100 ml of distilled water was added to stop the reaction. After the addition of 1 ml of starch indicator, the mixture was titrated with 0.01N sodium thiosulfate under constant shaking until the blue color disappeared. A blank sample with 30mL of acetic acid: chloroform and 1.0mL of starch solution was also prepared.
The p-anisidine value (AV) was determined (AOCS official method Cd 18-90) with 0.75 gm of the fat sample transferred into a 25 mL volumetric flask and dissolved with 25 ml of isooctane. After dissolving for approximately 4-5 minutes, 5ml of the sample was transferred into an aluminum foil wrapped test tube followed by the addition of 1ml of p-anisidine. After 10 minutes reaction time, the sample was measured on a spectrophotometer at 350 nm. Both the sample (without p-anisidine) and reactions (with p-anisidine) were read separately.
Statistical analysis . The study was conducted as a completely randomized design with time interval as the block. A total of 3 replications for each treatment was performed. At each of the10-time points a duplicate sample was tested. Statistical software (SAS; version 9.2) was used to analyze the data for the effects of treatments and within the time interval. Means were separated with a pairwise comparison and considered different at a P of 0.05.