Journal of Food Technology (1986) 21,517-519 Technical note: Kinetics of sorbic acid loss during storage of peaches preserved by combined factors L. N. GERSCHENSON, S. M. ALZAMORA AND J. CHIRIFE Summary It was found that the loss of sorbic acid in stored peaches preserved by combined factors (water activity, pH, additives) followed first order reaction kinetics. Rate constants and activation energy (14 kcal/mol) were almost identical to those previously reported for sorbic acid loss in concentrated glucose solutions of identical water activity and pH. Introduction Recently, Sajur (1985) developed a simple process to achieve microbial stability of peaches stored at ambient temperature. This process was based on a combination of reducing water activity (a,) through glucose incorporation, adjusting pH and addition of potassium sorbate and sodium bisulphite. The stabilized peaches were stored up to 4 months at 30°C without microbial deterioration. Sajur (1985) showed that sorbic acid was a key factor in achieving the microbial stability of peaches preserved as above. It is known that sorbic acid may be destroyed to a considerable extent during storage of foods (Bolin, King & Stafford, 1980; Vidyasagar & Arya, 1984). For this reason, present work was directed to studying the stability of sorbic acid in peaches stabilized against microbial deterioration by a combination of factors which included a, lowering, pH reduction and antimicrobials addition. Materials and methods Fresh yellow peaches were obtained from a local supermarket. They were pulped and thoroughly mixed with glucose and water (60.17% w/w peaches; 30.69% w/w glucose; 9.03% w/w water) using a high speed mixer. Potassium sorbate (0.10% w/w) and sodium thiosulphate (150 ppm) were also added. The pH was adjusted to 3.5 with 50% w/w aqueous citric acid solution. The resultant a, was 0.94 (Sajur, 1985). All chemicals used were reagent grade. Aliquots of 10 ml of peach suspension were placed in 100 ml stoppered polypropylene flasks which were stored, in the dark, at 20, 30 and 45°C (50.5"C) in forced convection constant temperature ovens. The flasks were hermeti- cally sealed to prevent evaporation. Headspace in each flask was 90% of total volume. Sorbic acid was determined according to the AOAC (1980) method. It has been previously shown that this technique produces reliable results when used for sorbic acid determination in concentrated sugar (glucose) systems (Gerschenson, Alzamora, & Chirife, 1986). The same procedure was used to check the reliability of the method Authors' address: PROIPA (CONICET-FCEyN), Departamento de Industrias,Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428 Buenos Aires, Republica Argentina.