AN OPTIMIZATION STUDY ON THE ULTRASONIC TREATMENTS FOR SACCHAROMYCES CEREVISIAE INACTIVATION IN RED GRAPE JUICE WITH MAINTAINING CRITICAL QUALITY ATTRIBUTES MARYAM NAFAR 2 , ZAHRA EMAM-DJOMEH 1,3 , SHIMA YOUSEFI 1 and MAHNAZ HASHEMI RAVAN 2 1 Transfer Phenomena Lab (TPL), Department of Food Science and Technology, Faculty of Agricultural Engineering and Technology, University of Tehran, 31587-11167 Karaj, Iran 2 Department of Food Science and Technology, Islamic Azad University, Varamin-Pishva Branch, Varamin, Iran 3 Corresponding author. TEL: +98-26-32248804; FAX: +98-26-32248804; EMAIL: emamj@ut.ac.ir Received for Publication December 2, 2012Accepted for Publication April 3, 2013 10.1111/jfq.12032 ABSTRACT This study was conducted to decrease Saccharomyces cerevisiae cell count and to maximize levels of quality characteristics in red grape juice during ultrasound process using response surface methodology (RSM). The effects of three process parameters (considered as independent variables), namely temperature (25–50C), time (20–40 min) and frequency (0–135 Hz), on the yeast inactivation, total anthocyanin content (TAC), total color difference (TCD), antioxidant activity (AA), polymeric color content (PCC), pH, total titratable acidity (TTA) and total soluble solids (TSS) (considered as dependent variables) were studied based on RSM. The optimum operating conditions for the maximum yeast inactivation and the optimal juice quality characteristics were found to be frequency of 135.0 kHz, temperature of 30.9C and time of 40.0 min. In these conditions, the yeast inactiva- tion, TAC, PCC, AA, TCD, pH, TTA and TSS were 1 cfu/mL, 808.0 mg/g, 67.85%, 0.94 mmol/L, 1.64, 3.47, 977.4 mg citric acid/100 mL and 20.04, respectively. PRACTICAL APPLICATIONS In recent years, emerging nonthermal methods, such as ultrasound (US), for inac- tivating microorganisms have been developed in food industries to manufacture natural products. Red grape juice, due to the presence of anthocyanins and fla- vonoids, has many health-promoting effects. As the nutritive and organoleptic characteristics of grapes decrease during storage and ripening periods because of their high susceptibility to pathogenic infection and physiological deterioration, the use of US method as a potential technology can inactive foodborne spoilage or pathogenic microorganisms and produce juices with organoleptic and nutritional qualities. Moreover, the optimization of US conditions enabled us to shorten the process duration and to reduce the production costs while maintaining the quality at a relatively high level. INTRODUCTION Red grape juice largely contains water, sugars (glucose and fructose) and potassium. This juice, due to the presence of tartaric, malic and citric acids, has an elevated acidity, and thus its low pH value is a guarantee for equilibrium between acidic and sweet tastes. Generally, grape juices, because of their rich constitution, are considered a differentiated bever- age with positive energetic, nutritional and bioactive effects (Mazarotto 2005). Fruits and vegetable products such as red grape juice are usually spoiled by the presence and growth of yeasts. This led to the decrease of the nutritive and organoleptic characteristics of these products. The tradi- tional and most common procedure is thermal pasteuri- zation, which prevents microbial spoilage of acidic juices (Gunes et al. 2005). Pulsed electric field (PEF) processing Journal of Food Quality ISSN 1745-4557 1 Journal of Food Quality •• (2013) ••–•• © 2013 Wiley Periodicals, Inc.