S: Sensory & Nutritive Qualities of Food JFS S: Sensory and Nutritive Qualities of Food Optimization of trans-Resveratrol Concentration and Sensory Properties of Peanut Kernels by Slicing and Ultrasound Treatment, Using Response Surface Methodology J.L. RUDOLF AND A.V.A. RESURRECCION ABSTRACT: Effect of postharvest stress application by slicing at 0.2, 0.4, and 0.6 cm, exposure to ultrasound (power density of 39.2 mW/cm 3 ) for 4 min at 25 ◦ C and subsequent incubation for 24, 36, 42, and 48 h on trans-resveratrol concentrations, and sensory attributes were evaluated using response surface methodology. Peanuts sliced 0.4 and 0.6 cm, exposed to ultrasound, and incubated for 42 h had trans-resveratrol concentrations above 1.0 μg/g, as did all samples incubated for 48 h. The optimized area was bound by peanut size of 0.89, 0.72, and 0.64 and incubation time of 48, 41.5, and 48 h, respectively. Combinations of treatments that fall within the optimized area were predicted to result in a peanut with a trans-resveratrol ≥1.0 μg/g; slightly lower roasted peanut aroma (>24) and flavor (>43); peanut butter aroma (>14), and flavor (>31) compared to controls with attribute ratings of 33, 78, 38, and 51, respectively; and slightly higher oxidized aroma (<6), and painty (<0.5), fishy (<6), and cardboard flavor (>4) compared to controls rated 0 for all attributes. Keywords: optimization, peanut, response surface methodology, resveratrol, ultrasound Introduction T he peanut, Arachis hypogaea L., is a versatile crop, mainly due to its pleasing aromas and flavor; crunchy texture; high en- ergy value; high protein, minerals, and niacin; ability to be stored or shipped to any point in the world; and suitability for being made into the various products for all occasions (McWatters 1983). Peanuts are grown primarily for vegetable oil in most parts of the world (Carley 1983). However, about one-half of the peanuts used in the United States are manufactured into peanut butter, candy, salted, and roasted in shell (Carley 1983). Resveratrol (trans-3, 5, 4 ′ -trihydroxystilbene) is a stilbene phy- toalexin produced in plant materials, particularly grape and peanuts. Resveratrol is an antioxidant compound shown to reduce the risk of coronary heart disease (Frankel and others 1993), provide cancer chemopreventive activity (Jang and others 1997), and exhibit variable degrees of estrogen receptor agonist activity as described by Gehm and others (1997). The concentration of resveratrol in com- mercial peanut and peanut products is 0.055 ± 0.023 μg/g in roasted peanuts, 0.324 ± 0.129 μg/g in peanut butter, and 5.138 ± 2.849 μg/g in boiled peanuts (Sobolev and Cole 1999). Red wine is the most com- mon food source containing the highest amount of resveratrol, 0.99 to 5.01 mg/L (μg/g) according to McMurtrey and others (1994) who note that the concentration in wine varies dramatically between the geographical area where the grapes are grown, year of harvest, and species of Vitaceae. Pinot Noir grapes were reported as having the highest intrinsic ability to synthesize resveratrol (McMurtrey and others 1994). MS 20060613 Submitted 11/10/2006, Accepted 6/16/2007. Authors are with Dept. of Food Science and Technology, Univ. of Georgia, 1109 Experiment Street, Griffin, GA 30223-1797, U.S.A. Direct inquiries to author Resurreccion (E-mail: aresurr@uga.edu). Resveratrol is produced in plants in response to exterior stress such as microbial exposure as reported by Aguamah and others (1981), to Helminthosporium carbonum (Ingham 1976), and to Botrytis cinerea as shown by Langcake and Pryce (1976). Abiotic stress such as injury by slicing peanut kernels up to 2-mm thick (Aguamah and others 1981; Wotton and Strange 1985; Cooksey and others 1988; Arora and Strange 1991) or ultraviolet (UV) light expo- sure at 254 nm (Langcake and Pryce 1976; Creasy and Coffee 1988; Cantos and others 2000, 2001) and 340 nm as described by Cantos and others (2000) results in increased synthesis of resveratrol in plant material. Rudolf and Resurreccion (2005) previously studied appli- cation of size reduction, by grinding, chopping, and slicing, along with exposure to UV light (254 nm) and ultrasound (power density of 39.2 mW/cm 3 , 260 W, 50/60 Hz, 2.2 A) to increase trans-resveratrol concentration in peanut kernels. Their findings demonstrated that peanut kernels sliced into 2-mm pieces, exposed to ultrasound for 4 min, and incubated at 23 ◦ C for 36 h were the most effective elic- itor, increasing trans-resveratrol concentration from 0.20 μg/g in untreated peanuts to 3.96 μg/g in treated peanuts (dry weight). Pro- ducing peanut-based products such as peanut butter from resver- atrol enhanced peanuts (REPs) would allow consumers to avail of the functional component and the health benefits associated with trans-resveratrol. However, to be accepted by consumers, REP prod- ucts need to have similar sensory characteristics as their traditional counterparts. Response surface methodology (RSM) is a set of statistical proce- dures used to predict the value of a response variable, or dependent variable, based on observed responses (experimental data) to the ex- perimental factors, or independent variables (Meilgaard and others 1991). RSM is frequently used as a tool for optimization of process- ing variables, by allowing simultaneous determination of the effects of multiple factors on multiple response variables while minimizing S450 JOURNAL OF FOOD SCIENCE—Vol. 72, Nr. 7, 2007 C  2007 Institute of Food Technologists doi: 10.1111/j.1750-3841.2007.00467.x Further reproduction without permission is prohibited